The quality of your radiographs reflects a level of excellence in your practice. Proper patient preparation, restraint, and positioning are essential for making good quality radiographs. Patients in distress must be stabilized prior to radiography. Radiation safety protocols should always be in effect (see ALARA in the Radiation Safety section of the previous chapter).
The patient’s hair coat should be clean and dry. Examine the patient’s body for any cutaneous or subcutaneous nodules, masses, or other structures which may mimic lesions in the radiograph. Remove collars, harnesses, leashes, clothing, etc., before making radiographs. Move any medical monitoring equipment and positioning devices out of the field of view.
Whenever practical, empty the GI tract and urinary bladder prior to abdominal radiography. Remove known large volumes of pleural or peritoneal fluid prior to thoracic or abdominal radiography.
Patient movement is a major cause of poor‐quality radiographs in veterinary medicine. Motion artifacts often require repeat radiographs, which wastes time, money, and exposes both the patient and nearby personnel to more radiation. Adequate patient restraint is crucial to minimize stress to both the patient and the radiographer.
Non‐manual restraint is recommended whenever possible. This means avoid holding the patient with your hands. Instead, use positioning devices such as foam wedges, towels, sandbags, V‐troughs, and tie‐downs (e.g., rope, tape, gauze) to help maintain the proper alignment of the body part being imaged (Figures 2.1 and 2.2). When sedation/anesthesia is used, note the agents in the radiography file for future reference and good medical record keeping. Patient sedation frequently is less stressful than struggling with the animal and often yields superior radiographs.
Figure 2.1Positioning devices. Whenever feasible, use non‐manual animal restraint during radiography. Common positioning devices include sandbags, ties (e.g., rope, gauze, tape), and foam wedges or towels.
Figure 2.2V‐trough. A padded V‐shaped positioning device can be used to help maintain the alignment of the patient’s spine and sternum and keep the pelvis straight during radiography.
Orthogonal views
Radiographs are two‐dimensional pictures of three‐dimensional objects. With rare exceptions, at least two orthogonal views are necessary for accurate evaluation of a body part. The term “orthogonal” means perpendicular or 90° to each other (e.g., lateral and VD radiographic views). When an orthogonal view is not possible, try to make a second view at an alternative angle to the first view or from the opposite side. This often is more beneficial than no second view at all.
At least two views are important because a structure can appear normal in one view and abnormal in the other (Figure 2.3). Two views also help us understand the positions of structures in relation to each other, such as a foreign object relative to an organ.
Figure 2.3The importance of two views. A body part can appear one way from one perspective and quite different in the orthogonal view.
Standard radiographic views are those that are essential to a complete radiographic study. Typically, this means a lateral view and either a ventrodorsal/dorsoventral view or a dorsopalmar/dorsoplantar view of the body part of interest. Supplemental views frequently are added to further evaluate a specific structure or to help clarify a radiographic finding.
Radiographic views are named according to the direction in which the x‐ray beam passes through the body. For example, in a ventrodorsal view, the x‐rays enter the ventral surface and exit the dorsal surface. In a dorsopalmar view, the x‐rays enter the dorsal side and exit the palmar side. In a right‐to‐left lateral view, the x‐rays enter the right side and exit the left side. In many cases, the name of a lateral view has been shortened and it is simply called either a right lateral view or a left lateral view. In these cases, the name is based on the side that is closest to the image receptor. For example, a lateral view made with the patient lying on its right side (right side is close to the image receptor) is called a right lateral view.
When imaging the extremities, the lateral side of the limb usually is closest to the image receptor and the x‐ray beam passes from the medial side to the lateral side. Commonly, this is simply called a lateral view of the limb being imaged.
Procedure for making radiographs
Plan for success. As much as practical, prepare the radiography room, equipment, and the patient prior to performing the procedure. Select the appropriate technique chart to use for the body part of interest (e.g., thorax, abdomen, skeleton).
Create the ID for the radiographs. Make a label for film radiography or enter the information into the digital system. The radiograph ID should include the following information:
Patient name and owner name.
Date the radiograph is being made.
Hospital name or name of veterinarian.
Initials of technicians making the radiograph.
Select the appropriate body markers to indicate the patient’s right or left side and which view was made (e.g., VD, DV). Calibration markers may be needed to provide a reference for making measurements from the radiograph. Position markers are used to indicate the direction of gravity, which is helpful to determine whether the patient was standing or recumbent at the time of radiography. All markers should be placed in the field‐of‐view (FOV) so they will be visible in the radiograph, but away from the area of interest.
Make sure nothing is superimposed on the body part being imaged (e.g., positioning devices, IV lines, ECG leads).
Measure the thickest portion of the body part. Measurements tend to be most accurate when made while the patient is in position for radiography because the thickness of some parts will vary between standing and lying down. Use a grid when body part thickness exceeds 10 cm (12 cm for thorax).
Set the technique on the x‐ray machine prior to final patient positioning to minimize the length of time the animal must remain in position and lessen its stress. Use the small focal spot whenever feasible to maximize radiographic detail. Make the exposure time as short as practical to minimize motion artifact.
Center the x‐ray beam on the body part of interest. Collimate the FOV as small as practical to include the entire body part. The smaller the FOV, the less scatter radiation, and the higher the quality of the radiograph. Commonly, the FOV is made too large for the thorax and too small for the abdomen. Pay attention to the landmarks for the body part of interest, as described in the positioning guide in this chapter.
When the body part is too large to fit in one view, divide the anatomy over two overlapping images. The FOV for the first radiograph should extend from the cranial landmark caudally (for abdomen, this would be from the diaphragm caudally, as shown in Figures 2.4 and 2.5). The FOV for the second radiograph should extend from the caudal landmark cranially (for abdomen, this would be from the pelvic inlet cranially). The two radiographs will overlap in the middle.
Figure 2.4Lateral views of a large dog abdomen. The abdomen is too large to be imaged in its entirety in one radiograph, so the anatomy is divided over two overlapping views as shown in (A) and (B).
Figure 2.5Ventrodorsal views of a large dog abdomen. The abdomen is too large to be imaged in its entirety in one radiograph, so the anatomy is divided over two overlapping views as shown in (A) and (B).
With many patients it may be useful to make the lateral radiograph first because positioning an animal in lateral recumbency tends to be less stressful than dorsal recumbency and may improve compliance with subsequent radiographs.
Nomenclature
It is important to use correct veterinary terminology when communicating your radiographic findings (Figure 2.6; Table 2.1). This includes accurately describing the radiographic views and the locations of the radiographic abnormalities. For descriptive purposes, the body may be divided into three imaginary anatomical planes: sagittal, dorsal, and transverse (Figure 2.7).
Figure 2.6Anatomical nomenclature. This illustration depicts the correct veterinary terms used to describe the direction of the x‐ray beam and the locations of radiographic findings.
Table 2.1Veterinary nomenclature and their meanings
Term
Meaning and anatomical direction
Cranial
Toward the head
Caudal
Toward the tail
Dorsal
Toward the back or spine
Ventral
Toward the front or sternum
Lateral
Away from midline of the body
Medial
Toward midline of the body
Median
On the midline of the body
Rostral
Toward the nose
Proximal
Toward the point of origin or nearer the center of the body
Distal
Toward the point of insertion or away from the center of the body
Superficial
Toward the surface of the body
Deep
Away from the body surface or below the body surface
Ipsilateral
On the same side of the body
Contralateral
On the opposite side of the body
Palmar
Bottom or caudal part of the manus (front paw with carpus)
Plantar
Bottom, sole, or caudal part of the pes (rear paw with tarsus)
Recumbency
Lying down
Anatomical planes
Transverse planes
Divide body into cranial and caudal sections and divide limbs into proximal and distal sections.
Dorsal planes
Divide body into dorsal and ventral sections
Sagittal planes
Divide body into right and left sections
Median plane
Sagittal plane on midline (divides body into equal right and left halves)
Anatomical movements
Flexion
Decrease the angle of the joint
Extension
Increase the angle of the joint
Abduction
Move limb away from midline
Adduction
Move limb toward midline
Supination
Rotate palmar side to face up or cranial
Pronation
Rotate palmar side to face down or caudal
Radiographic views
Ventrodorsal (VD)
X‐rays pass from ventral to dorsal
Dorsoventral (DV)
X‐rays pass from dorsal to ventral
Lateral (L)
X‐rays pass from one side of the body to the other through the axial plane
Right lateral (RL)
Patient lying on right side, right side is closest to image receptor
Left lateral (LL)
Patient lying on left side, left side is closest to image receptor
Craniocaudal (CrCa)
X‐rays pass from cranial to caudal
Caudocranial (CaCr)
X‐rays pass from caudal to cranial
Dorsopalmar or dorsoplantar (DP)
X‐rays pass from dorsal to palmar/plantar
Oblique (O)
X‐ray beam enters the body at an angle other than 90°.
20° CrM‐CaLO
20° craniomedial to caudolateral oblique, which means the central ray enters cranially and medially at 20° off perpendicular and exits the caudal, lateral side.
Figure 2.7Anatomical planes. This illustration depicts the three imaginary planes used to describe anatomy. The sagittal plane divides the body into right and left. The dorsal plane divides the body into dorsal and ventral. The transverse plane divides the body into cranial and caudal.
The sagittal plane divides the body into right and left sections. The mid‐sagittal or median plane divides the body into equal right and left halves. The dorsal plane (also called frontal or coronal plane) divides the body into dorsal and ventral sections. The transverse plane (also called axial or cross‐sectional plane) divides the body into cranial and caudal sections. The transverse plane divides the limbs into proximal and distal parts.
Patient is in lateral recumbency; both right and left lateral views are recommended for a complete study.
Thoracic limbs are pulled cranially; avoid overstretching the patient.
Sternum and spine are aligned in the same horizontal plane, parallel with the image receptor. Place a foam wedge (pictured) or a towel under the sternum to correct rotation.
Measure the thickest part of the thorax, usually over the liver.
X‐ray beam is centered on the heart or caudal edge of the scapula (+).
Field‐of‐view (FOV) is collimated to include the entire bony thorax from thoracic inlet to last ribs.
Elbows and stifles are slightly abducted and pelvic limbs are in a crouching position for the patient’s comfort.
Sternum and spine are superimposed in the same vertical plane, perpendicular to the image receptor.
Head and neck are in‐line with the spine.
Measure the thickest part of the thorax, usually over the liver.
X‐ray beam is centered on the heart or at the caudal edge of the scapula (+); NOTE: A common error is centering the x‐ray beam too far caudally and missing the cranial thorax.
Collimate the FOV to include the entire boney thorax from the thoracic inlet to the last ribs.
This is a supplemental radiograph of the thorax made in addition to the standard lateral and VD/DV views. Positioning
Patient is positioned for VD view of the thorax as described in Figure 2.9.
Thoracic limbs are pulled caudally instead of cranially.
Radiograph VD view of the thorax with the limbs pulled caudally to eliminate superimposition of the scapula and associated musculature on the cranial thorax.
This is a supplemental radiograph of the thorax made in addition to the standard lateral and VD/DV views. Positioning
Patient is positioned for a VD thorax view as described in Figure 2.9.
Sternum is rotated to the right or left to better visualize the area of interest by eliminating superimposition of the heart, spine, and sternum.
X‐ray beam is centered on the area of interest (+).
Collimate the FOV as for the VD view.
Make exposure at peak inspiration.
Radiograph
VD oblique view of the thorax (B), the sternum is rotated to the right, which enhances visualization of the left lung (the heart follows the sternum); notice the thoracic dorsal spinous processes project to the left in this view.
To name an oblique view, we describe the path of the x‐rays. For example, a D15R‐VLO view means the x‐rays passed through the thorax from Dorsal 15° Right to Ventral Left Obliquely. In simple terms, the patient was in sternal recumbency (DV view) and rotated 15° to the left.
This is a supplemental radiograph of the thorax made in addition to the standard lateral and VD/DV views. A.Positioning
Patient is positioned for a VD thorax view as described in Figure 2.9.
Sternum is rotated to the right or left, whichever makes the area of interest perpendicular to the x‐ray beam.
X‐ray beam is centered on the area of interest (+).
Collimate the FOV as small as feasible to the size of the area of interest. This view is not made to image the entire thorax, rather it is intended to focus on a specific site or lesion.
B.RadiographVD tangential view of the thorax (white arrows point to rib fractures).
Patient is standing, held erect, or recumbent, depending on the purpose of the study.
A: the dog is in right lateral recumbency with the image receptor along its dorsum for a horizontal beam VD view.
C: the dog is in dorsal recumbency with the image receptor alongside its body for a horizontal beam lateral view.
X‐ray beam is directed across the table, perpendicular to the image receptor, and centered on the area of interest.
Set the source‐to‐image distance (SID) to the standard SID for your practice, typically 100 cm or 40 in.
Measure the thickest part of the body part being imaged.
Collimate the FOV to the size of the area of interest.
BandD.Radiographs
B: horizontal beam VD view of the thorax. The dependent (down) lung is partially collapsed and increased in opacity and the heart “falls” toward the dependent side due to the effects of gravity and the collapsed lung.
D: horizontal beam lateral view of the thorax. A small volume of abnormal pleural gas is visible between the cardiac silhouette and the sternum (arrow). Gas rises to the uppermost part of the thoracic cavity. The dorsal lungs are dependent, partially collapsed, and increased in opacity.
Elbows and stifles are slightly abducted and the pelvic limbs are in a crouching position for the patient’s comfort.
Sternum and spine are superimposed in the same vertical plane, perpendicular to the image receptor.
Measure the thickest part of abdomen, usually over the liver.
X‐ray beam is centered near the last rib, midway between the diaphragm and the pelvic canal (+).
Collimate the FOV to include the diaphragm, greater trochanters, and lateral body walls.
Make the exposure at the end of expiration.
B.Radiograph
Dorsoventral (DV) view of the abdomen. This view is not routinely made because it leads to visceral crowding and less distinct intra‐abdominal margins.
This is a supplemental radiograph of the abdomen made in addition to the standard lateral and VD views. A.Positioning
Patient may be in position for either a lateral or VD view (Figure 2.16 or 2.17).
A low‐opacity paddle, such as a plastic or wooden spoon, is used to gently compress the abdomen and displace the moveable viscera (e.g., intestines) away from structures that are more fixed in position (e.g., urinary bladder, kidney).
Decrease the x‐ray exposure to compensate for the reduced abdominal thickness. In most cases, cut the exposure time in half.
X‐ray beam is centered on the structure being investigated.
Collimate the FOV to include the structure; this FOV will be smaller than the one used for the standard view.
BandC.Radiographs
B: lateral view of the abdomen without compression. The margins of the urinary bladder and uterus are not identified.
C: lateral view of the same dog abdomen with compression; the intestines are displaced cranially and dorsally away from the uterus (u) and urinary bladder (b). Notice that the x‐ray exposure was decreased for compression radiography.
This is a supplemental radiograph of the abdomen made in addition to the standard lateral and VD views. It is used to evaluate the penile urethra in male dogs. A.Positioning
Patient is in right or left lateral recumbency.
Pelvic limbs are pulled cranially to eliminate superimposition.
X‐ray beam is centered on the mid‐portion of the urethra (+).
Collimate the FOV to include the urinary bladder and the entire urethra.
B.Radiograph
Lateral view of the urethra. Mineral opacity calculi are visible in the urethra just proximal to the os penis (arrow).
Patient is in lateral recumbency with the limb of interest down (closest to the image receptor) and fully extended.
The head and neck are extended to eliminate superimposition of the cervical spine on the scapulohumeral joint.
The opposite (up) limb is pulled caudally out of the FOV. Avoid pulling the limb too far caudally as this will superimpose the two shoulders.
Limb thickness is measured at the shoulder, between the dependent thoracic wall and about the level of the sternum.
X‐ray beam is centered on the scapulohumeral joint (+). Palpate the thoracic inlet and then move your fingers cranially until you feel the scapulohumeral joint.
Collimate the FOV to include the distal third of the scapula and the proximal third of the humerus.
As needed, the lateral view can be repeated with the limb pronated or supinated (green arrow) to view more of the humeral head. This is particularly useful when searching for osteochondrosis lesions on the humeral head.
Diagram B illustrates the correct alignment of the head, neck, spine, and thoracic limbs. The neck is angled about 135° in relation to the thoracic spine. The down limb is perpendicular (90°) to the line of the neck and the up limb is in a straight line with the neck.
Patient is in lateral recumbency with the limb of interest down (closest to the image receptor).
Head and neck are mildly flexed.
Push the down limb dorsally to move the scapula dorsal to the spine (arrow 1) and pull the up limb ventrally (arrow 2) to eliminate superimposition.
Limb thickness is measured laterally across the scapula.
X‐ray beam is centered on the scapula (+).
Collimate the FOV to the size of the scapula and adjacent soft tissues.
Alternatively, this view can be made with the limb of interest up and pushed dorsally while pulling the down limb ventrally; however, the up limb will be magnified.
B.Radiograph
Lateral view of the right scapula, which is visible dorsal to the thoracic spine.
Patient is in dorsal recumbency with the limb of interest fully extended.
Sternum is rotated about 30° toward the opposite limb.
Limb thickness is measured from ventral to dorsal across the scapula.
X‐ray beam is centered on the scapulohumeral joint (+) or on the scapula, depending on the purpose of the study. Palpate the scapular spine to help locate the center point.
Collimate the FOV for the scapulohumeral joint to include the distal third of the scapula and the proximal third of the humerus. For the scapula, collimated to include the entire scapula and any swelling in the adjacent soft tissues.Collimate the FOV to the area of interest. For the scapulohumeral joint, include the distal third of the scapula and the proximal third of the humerus. For the scapula, include the entire scapula and the adjacent soft tissues.
BandC.Radiographs
B: caudocranial view of the left scapulohumeral joint.
Patient is positioned for a lateral elbow view (Figure 2.25) with the elbow extremely flexed (dashed arrow). Flexion should be greater than 90° to eliminate superimposition of the humeral medial epicondyle on the ulna.
Patient is positioned for a craniocaudal elbow view (Figure 2.27).
The limb of interest is in a neutral, slightly pronated position. It is not fully extended. Allow the limb to relax so the elbow rotates slightly inward to eliminate superimposition of the olecranon on the medial coronoid process.
X‐ray beam is centered on the elbow (+).
B.Radiograph
Craniolateral‐caudomedial oblique view (CrLCaMO) of the right elbow. The x‐rays pass through the joint in a cranial‐lateral to caudal‐medial direction to produce a tangential view of the medial coronoid process (MCP).
Figure 2.29 Carpus and manus lateral and lateral oblique views.
A.Positioning
Patient is in lateral recumbency with the limb of interest down, closest to the image receptor, and extended. The carpus may be more easily extended by pushing on the elbow rather than pulling on the foot.
The “up” limb is pulled caudally to eliminate superimposition.
Limb thickness is measured at the level of the carpus.
X‐ray beam is centered on the carpus (+).
Collimate the FOV to include the distal third of the antebrachium and the proximal third of the metacarpus.
As needed, the lateral view can be repeated with the limb slightly supinated or pronated to visualize more of the bony margins in the carpus (green dashed arrow).
Band C.Radiographs
B: lateral view of the right carpus (medial‐to‐lateral view).
C: lateral oblique view of the right carpus. The limb was pronated (rotated inward) about 45° so the x‐ray beam passed through the carpus from the dorsal and lateral side to the palmar and medial side; a dorsopalmar‐to‐lateromedial oblique view (DPLMO).
Figure 2.30 Carpus and manus dorsopalmar (DP) view.
A.Positioning
Patient is in ventral (sternal) recumbency.
The limb of interest is extended. The carpus may be more easily positioned by pushing the elbow rather than pulling the foot.
Turn the patient’s head toward opposite limb.
Limb thickness is measured at the distal antebrachium.
X‐ray beam is centered on the carpus (+).
Collimate the FOV to include the distal third of the antebrachium and the proximal third of the metacarpus.
B.Radiograph
Dorsopalmar (DP) view of the right carpus.
C.Skyline view
To better visualize the dorsal aspects of the carpus, the limb can be flexed and the x‐ray beam directed perpendicular to the image receptor (1) or slightly angled from proximal to distal (2). A flexed dorsoproximal‐to‐dorsodistal view enhances visualization of the dorsal border of the distal radius or intercarpal bones or proximal metacarpus, depending on the degree of carpal flexion and the angle of the x‐ray beam (particularly useful when looking for chip fractures).
These supplemental views are used to assess joint laxity. They are made in addition to the standard orthogonal views. Aand B.Positioning
Patient may be in ventral, dorsal, or lateral recumbency with the joint of interest closest to the image receptor.
The bones proximal and distal to the joint are stabilized and a force is applied to the joint using something like a wooden or plastic stick.
A: a lateral‐to‐medial force is applied to the elbow while the carpus is stabilized using rope ties.
B: a medial‐to‐lateral force is applied to the carpus while the manus is stabilized with a rope tie.
X‐ray beam is centered on the joint of interest.
Collimate the FOV as small as feasible to include the adjacent one‐third of the long bones proximal and distal to the joint.
Make the x‐ray exposure while the force is being applied to the joint.
Cand D.Radiographs
C: craniocaudal view of the elbow without stress.
D: craniocaudal view of the same elbow made while a lateral‐to‐medial force was applied (black arrow). Widening of the medial aspect of the elbow joint (white arrow) and malalignment between the humerus and antebrachium indicate joint laxity.
Patient is positioned for a lateral view of the manus or pes (Figure 2.29 or 2.46).
Digits may be separated using either a compression technique or traction.
A: a low opacity paddle (e.g., plastic or wooden spoon) is used to gently compress the foot.
B: tape or gauze is wrapped around the digits and used to gently pull them apart.
X‐ray beam is centered on the digits.
Collimate the FOV to include the digits and the distal half of the metacarpus or metatarsus.
C.Radiograph
Close up lateral view of the left digits (mediolateral view). The foot was gently compressed with a wooden spoon to separate the digits and eliminate superimposition.
Figure 2.33 Digits dorsopalmar or dorsoplantar (DP) view.
A.Positioning
Patient is positioned for DP view of manus or pes (Figure 2.30 or 2.43).
A low opacity paddle (e.g., plastic or wooden spoon) is used to gently hold the paw in position and to softly compress and separate the digits. Wrapping a tie around the foot can distort the anatomy.
X‐ray beam is centered on the digits.
Collimate the FOV as small as feasible to include distal half of the metacarpus or metatarsus.
The pelvic limbs are in a neutral position with the down limb moved slightly cranial to the up limb.
The ilial wings are superimposed in the same vertical plane, perpendicular to the image receptor.
A foam wedge or towel between the stifles is used to correct pelvic rotation as shown in B and C.
B: viewing the dog from the caudal aspect, the dotted lines represent the dorsal and sagittal planes. The dorsal plane naturally rotates in lateral recumbency, making the pelvis oblique to the x‐ray beam.
C: a rolled towel between the stifles corrects the rotation of the pelvis and spine.
Pelvis thickness is measured at the iliac crests.
X‐ray beam is centered on the greater trochanters (+).
Collimate the FOV to include the iliac crests, ischiatic tuberosities and proximal half of each femur.
Dand E.Radiographs
D: lateral oblique view of the pelvis (due to patient rotation). Notice the ilial wings are not aligned. Note: sometimes an oblique view is desirable to view each hemipelvis with less summation.
E: true lateral view of the pelvis. The ilial wings are superimposed and the intervertebral disc spaces and coxofemoral joint space are more distinct.
Patient is in dorsal recumbency. A padded V‐trough can be used to simplify positioning and to make the patient more comfortable. Notice that the edge of the trough is cranial to the pelvis to avoid superimposition and magnification artifacts.
The pelvic limbs are extended and parallel. If extending the pelvic limbs is difficult, try temporarily binding the stifles together with a piece of gauze or tape (as shown in A) and then extend both limbs while bound together.
Rotate the stifles inward (toward each other) to center each patella in the middle of its femur.
Pelvic thickness is measured across the iliac crests.
X‐ray beam is centered at level of greater trochanters (+).
Collimate the FOV to include the ilial crests and both stifles.
This is a supplemental radiograph of the pelvis made in addition to the standard orthogonal views. It is used to assess hip laxity. Aand B.Positioning
Patient is in dorsal recumbency as described in Figure 2.35.
Pelvic limbs are parallel and in a neutral position.
A: a rolled towel is placed between the thighs, proximal to the stifles, to act as a fulcrum. When the tarsi are adducted (black arrows) the hips are distracted (red arrows). The tarsi can be temporarily bound together while making the radiograph.
B: the pelvic limbs are neither extended (E) nor flexed (F). The neutral position (N) results in less ‘twisting’ of the hip muscles and joint capsules than the extended VD view, making it easier for a “loose” hip to subluxate.
Pelvic thickness is measured at the iliac crests.
X‐ray beam is centered at the level of greater trochanters (+).
Collimate the FOV to include the iliac crests and the stifles.
Make the exposure while the tarsi are adducted.
Cand D.Radiographs
C: extended VD view of the pelvis (made without a fulcrum). The coxofemoral joints are highlighted and appear normal.
D: half‐axial VD view of the same pelvis. The rolled towel fulcrum is visible between the femurs. Distraction causes both coxofemoral joints to subluxate (each femoral head is displaced laterally and there is cranial wedging of the joint spaces), indicating excessive hip laxity.
This is a supplemental radiograph of the pelvis made in addition to the standard orthogonal views. It is used to evaluate coxofemoral fit and acetabular depth. A.Positioning (A)
Patient is in ventral (sternal) recumbency.
The pelvic limbs are moved cranially, flexing the hips.
The tarsi are elevated about 5 cm. In illustration A, the tarsus is resting on a sandbag.
X‐ray beam is centered at the level of the greater trochanters (red arrow). The x‐ray beam passes through the long axis of the pelvis, from cranial to caudal.
Collimate the FOV to include the ilial crests, proximal third of each femur, and the ischiatic tuberosities.
B.Radiograph
Dorsal acetabular rim view of pelvis. The black arrows point to the right dorsal acetabular rim. The white dashed circle indicates the left femoral head. The white arrow points to the left ischiatic tuberosity.
Limb of interest is down (closest to the image receptor) and in a neutral position. The angle of the stifle should be about 120°.
The opposite (up) pelvic limb is flexed and abducted to eliminate superimposition (up limb may be secured with tape, as shown).
To make a true lateral view, you may need to slightly rotate the patella toward the image receptor to superimpose the femoral condyles (arrow at tarsus).
Stifle thickness is measured at the distal femur.
X‐ray beam is centered on the stifle (+).
Collimate the FOV to include the distal third of the femur and the proximal third of the tibia.
For surgical planning the stifle may need to be flexed 90° instead of a neutral 120°.
Figure 2.41 Stifle flexed lateral view with tibial compression.
This is a supplemental radiograph of the stifle made in addition to the standard orthogonal views. A.Positioning
Patient is positioned for a lateral view of the stifle (Figure 2.39).
Stifle is flexed 90° and the tarsus is maximally flexed (curved arrow). Try to make the metatarsus parallel with the femur.
Stifle thickness is measured at the distal femur.
X‐ray beam is centered on the stifle (+).
Collimate the FOV to include the distal third of the femur and the proximal third of the tibia.
Make the x‐ray exposure while both the stifle and the tarsus are flexed.
Band C.Radiographs
B: lateral view of the stifle (without tibial compression). The proximal tibia and distal femur appear to be in normal alignment.
C: flexed lateral view made with the tarsus flexed. The proximal tibia is cranially displaced in relation to the distal femur. In many cases, this tibial compression view is as sensitive and specific for the diagnosis of cranial cruciate ligament injury as palpation for a cranial drawer sign.
Figure 2.42 Stifle cranioproximal–craniodistal view (skyline view of stifle).
This is a supplemental radiograph of the stifle made in addition to the standard orthogonal views. It is used to examine the patella and patellar groove. A.Positioning
Patient is in ventral (sternal) recumbency with both pelvic limbs extended caudally.
The stifle of interest is then flexed and pushed cranially, but the tarsus remains extended.
Angle the x‐ray beam about 10° off perpendicular (caudoproximal‐to‐craniodistal, as shown by the red arrow) to better visualize the patellar groove.
Stifle thickness is measured at the distal femur.
X‐ray beam is centered on the cranial aspect of the stifle.
Collimate the FOV to include the distal third of the femur and the patella.
Limb of interest is down (closest to the image receptor) with the tarsus in a neutral position. The tarsus may be more easily positioned by pushing the stifle rather than pulling the foot.
The opposite (up) limb is moved out of the FOV.
Tarsal thickness is measured at the distal crus.
X‐ray beam is centered on the tarsus (+).
Collimate the FOV to include the distal third of the tibia and the proximal third of the metatarsus.
Limb of interest is extended cranially and moved slightly laterally, away from the body. The tarsus may be more easily positioned by pushing the stifle rather than pulling the foot.
Tarsal thickness is measured at the distal crus.
X‐ray beam is centered on the tarsus (+).
Collimate the FOV to include the distal third of the tibia and the proximal third of the metatarsus.
As needed, the DP view can be repeated with the tarsus slightly rotated to the right or left to visualize more of the bony margins (arrow).
B–D. Radiographs
B: dorsoplantar view of the right tarsus.
C: dorsolateral‐to‐plantaromedial oblique (DLPMO) view of the tarsus (the limb was rotated outward about 45°).
D: dorsomedial‐to‐plantarolateral oblique (DMPLO) view of the tarsus (the limb was rotated inward about 45°).
Notice the “R” marker is positioned on the lateral side in each radiograph.
This is a supplemental radiograph of the tarsus made in addition to the standard orthogonal views. It is used to visualize the tibiotarsal joint without superimposition of the calcaneus. A.Positioning
Patient is in dorsal recumbency.
The tarsus of interest is elevated atop a small cardboard box or similar device. The tarsus is flexed with the toes pointing up toward the x‐ray tube.
If feasible, place the image receptor on top of the box and under the tarsus to minimize magnification distortion.
Adjust the source‐to‐image distance (SID) as needed.
Tarsal thickness is measured at the distal crus.
X‐ray beam (red arrow) is centered on the tibiotarsal joint.
Collimate the FOV to include the distal third of the tibia and the plantar border of the foot.
B.Radiograph
Flexed dorsoplantar view of the right tarsus.
Figure 2.46 Tarsus plantaroproximal–plantarodistal view of calcaneus (skyline view of calcaneus).
This is a supplemental radiograph of the tarsus made in addition to the standard orthogonal views. It is used to evaluate the calcaneus. A.Positioning
Patient is in ventral (sternal) recumbency.
Both pelvic limbs are in a crouching position under the animal.
Slide the limb of interest caudally until the calcaneus is caudal to the ischium (black dotted arrow) to eliminate superimposition.
X‐ray beam (red arrow) is centered on the calcaneus.
Collimate the FOV to include the calcaneus and adjacent soft tissues.
Patient is in lateral recumbency with the side of interest down, closest to the image receptor.
The head and neck are extended.
As needed, elevate the nose with a foam wedge or similar to make the median plane of the head parallel to the image receptor.
Align the patient’s eyes in a vertical plane perpendicular to the image receptor and do the same with the mandibles. If you can open the mouth and visualize the hard palate, this may help in positioning: if you align the hard palate, you align the skull.
Thickness of the head is measured mid‐way between the level of the eyes and the level of the ears.
X‐ray beam (red arrow) is centered at the level of the eyes (+).
Collimate the FOV to include the entire head, from the tip of the nose to the first cervical vertebra.
To better visualize the nasopharynx, open the mouth to rotate the mandibular rami away from the nasopharynx. This view is helpful when looking for evidence of a mass or foreign object in the nasopharynx. Increase the x‐ray exposure for this view by doubling the mAs (or increase the kVp 20%).
The head and neck are extended with the mandibles resting on the top table or on top of the image receptor.
The hard palate should be parallel with the table top.
The eyes should be level, aligned in the same horizontal plane. The same with the right and left zygomatic arches.
Thickness of the head is measured mid‐way between the level of the eyes and the level of the ears.
X‐ray beam is centered on midline at the level of the eyes (+).
Collimate the FOV to include the entire head, from the tip of the nose to the first cervical vertebra.
A ventrodorsal (VD) view of the head can be made with the patient in dorsal recumbency but may be more difficult to position with symmetry than a DV view.
This is a supplemental radiograph of the head made in addition to the standard lateral and DV views. It is used to better isolate and evaluate a part of the skull. A.Positioning
Patient is in lateral recumbency with the side of interest closest to the image receptor.
The head is propped up, resting obliquely on a foam wedge or similar (the side of interest is against the wedge).
Thickness of the head is measured mid‐way between the level of the eyes and the level of the ears.
Both “Right” and “Left” markers are recommended to avoid confusion. The side of interest will be projected dorsally in the radiograph.
X‐ray beam is centered on the area of interest (e.g., frontal sinus, mass on head).
Collimate the FOV to include the entire head, from the tip of the nose to the first cervical vertebra.
B.Radiograph
Lateral oblique view of head. The right frontal sinus and the right nasal passage are projected dorsal to the left. The left hemimandible is ventral to the right.
This is a supplemental radiograph of the head made in addition to the standard lateral and DV views. It is used to evaluate a mandible or maxilla. Aand B.Positioning
Patient is in lateral recumbency with the head resting obliquely against a foam wedge; the side of interest adjacent to the wedge and closest to the image receptor.
Open the mouth and move the tongue and endotracheal tube away from the area of interest. If needed, support the mouth open with an oral speculum or other device, but be careful not to superimpose the device on the area of interest.
A: positioning to evaluate the right hemimandible.
B: positioning to evaluate the left maxilla.
Thickness of the head is measured at the level of the eyes.
Both “Right” and “Left” markers are recommended to help avoid confusion.
X‐ray beam is centered on the area of interest (the mandible in illustration A and the maxilla in B).
Collimate the FOV as small as feasible to include the entire area of interest. Remember: the smaller the FOV, the better the radiographic detail.
Cand D.Radiographs
C: open‐mouth lateral oblique view of the mandible. The right mandibular dental arcade is projected dorsal to the left.
D: open‐mouth lateral oblique view of the maxilla. The left maxillary dental arcade is ventral to the right.
Figure 2.51 Head open mouth ventrodorsal (VD) view.
This is a supplemental radiograph of the head made in addition to the standard lateral and DV views. It is used to evaluate the maxilla and nasal cavities without superimposition of the mandible. A.Positioning
Patient is in dorsal recumbency.
Head is extended with the mouth fully open. The mouth may be held open using tape or gauze (as shown in A), an oral speculum, or another device. Be sure the positioning device is not in the area of interest.
Move the tongue and endotracheal tube away from the area of interest.
Thickness of the head is measured at the level of the eyes, between the hard palate and the medial canthus of the eye.
X‐ray beam is angled about 20° rostroventral to caudodorsal (red arrow) to make it parallel with the mandible. Center the beam in the middle of the hard palate.
Collimate the FOV as small as practical to include the tip of the nose, the tip of the mandible, and the lateral soft tissues.
This is a supplemental radiograph of the head made in addition to the standard lateral and DV views. It is used to evaluate the frontal sinuses. Aand B.Positioning
Patient is in dorsal recumbency.
The head is flexed with the nose pointing up, toward the x‐ray tube.
Thickness of the head is measured from the medial canthus of the eye to the caudal part of the head.
X‐ray beam is centered on midline, just dorsal to the eyes and between the frontal sinuses (red arrow in A).
Collimate the FOV as small as feasible to include the top of the head, the tip of the nose, and the width of skull.
When properly positioned, the collimator light will project a shadow of the frontal sinuses as two humps above the head (arrows point to the two humps in B). The nose may need to be tipped about 10° dorsally, depending on the patient conformation.
C.Radiograph
Rostrocaudal view of the head, tightly collimated to the frontal sinuses. This view sometimes called a “frog‐eye” view.
This is a supplemental radiograph of the head made in addition to the standard lateral and DV views. It is used to evaluate the foramen magnum. A.Positioning
Patient is in dorsal recumbency.
The head is flexed with nose tipped toward the sternum, about 20° past vertical.
Thickness of the head is measured from the medial canthus of the eye to the caudal part of the head.
X‐ray beam is centered between the eyes (red arrow).
Collimate the FOV as small as feasible to include the top of the head, the tip of the nose, and the width of the skull.
Increase the x‐ray exposure by doubling the mAs (or increase kVp 20%) to better penetrate the skull and visualize the foramen magnum.
B.Radiograph
Rostrocaudal flexed view of the head. The arrow points to the foramen magnum.
Figure 2.54 Feline head extended rostrocaudal view.
This is a supplemental radiograph of the feline head made in addition to the standard lateral and DV views. It is used to evaluate the tympanic bullae in cats. This view is also called a VD 10° dorsal oblique view of the head. A.Positioning
Cat is in dorsal recumbency with the mouth closed and the nose pointing up, toward the x‐ray tube. The nose is tilted dorsally about 10° off vertical (dotted arrow).
Thickness of the head is measured from the corner of the mouth to the caudal part of the head.
X‐ray beam is centered on midline at the level of the ears (red arrow) and directed so that it passes between the tympanic bullae.
Collimate the FOV as small as feasible to include the tip of the nose, the first cervical vertebra, and the width of the skull.
B.Radiograph
Extended rostrocaudal view of the feline head. The arrows point to the tympanic bullae. The endotracheal is visible between the bullae as a thin white line.
This supplemental radiograph of the head is made in addition to the standard lateral and DV views. It is used to evaluate the odontoid process and canine tympanic bullae. A, B, and C. Positioning
Patient is in dorsal recumbency with the nose pointed up, toward the x‐ray tube.
Open the mouth and move the tongue and endotracheal tube away from the area of interest. The mouth may be held open using gauze or tape (as shown in A and B) or an oral speculum or other device positioned away from the area of interest.
A: to image the odontoid process (dens), tilt the nose dorsally about 45° past vertical (curved arrow).
B: to image the tympanic bullae, tilt the nose about 20° past vertical.
C: when the head is in the correct position, the collimator light projects the shadows of the nose and the two frontal sinuses as 3 humps of equal height (sometimes described as the “sun setting between two mountains”).
Thickness of the head is measured from the medial canthus of the eye to the caudal part of the head.
X‐ray beam is centered in the middle of the mouth, directed at the uvula (red arrows in A and B).
Collimate the FOV as small as feasible to include the area of interest.
D and E. Radiographs
D: open‐mouth 45° rostrocaudal view of the head. The arrow points to the dens.
E: open‐mouth 20° rostrocaudal view, tightly collimated to the tympanic bullae (arrows).
This supplemental radiograph of the head is made in addition to the standard lateral and DV views. A. Positioning
Patient is in ventral (sternal) recumbency.
The image receptor is placed inside the patient’s mouth. Insert the receptor corner first to image the caudal part of the maxilla.
Thickness of the maxilla is measured from the medial canthus of the eye to the hard palate.
X‐ray beam is centered on midline, halfway between the eyes and the to reduce superimposition of the frontal bones and image the more caudal aspect of the maxilla, angle the beam 20° rostrodorsal‐to‐caudoventral (dashed arrow).
Collimate the FOV as small as feasible to include all of the maxilla that will fit on the image receptor.
B.Radiograph
Intraoral view of the rostral maxilla and nasal cavities.
This supplemental radiograph of the head is made in addition to the standard lateral and DV views. A.Positioning
Patient is in dorsal recumbency.
The image receptor is placed inside the patient’s mouth; insert the corner of the receptor first to image the more caudal mandible.
Measure the thickness of the mandible from the corner of the mouth to the ventral border of the mandible.
X‐ray beam is centered on midline, in the middle of the mandible. Angle the beam about 20° rostroventral‐to‐caudodorsal to better visualize the rostral mandible (red arrow).
Collimate the FOV as small as feasible to include as much of the mandible as will fit on the image receptor.
B.Radiograph
Intraoral view of the rostral mandible.
Figure 2.58 Head lateral oblique view for temporomandibular joint (TMJ).
This supplemental radiograph of the head is made in addition to the standard the lateral and DV views. A, B, and C.Positioning
Patient is in right or left lateral recumbency.
The patient’s head and neck are extended with the head resting on a foam block or towel and the nose tilted as needed.
A and B: to image a TMJ with minimal distortion, position it closest to the image receptor and tilt the patient’s nose up, toward the x‐ray tube. In dogs, tilt the nose up about 20°. In cats, tilt it up about 10°. As can be seen in B, the x‐ray beam (arrow) is well‐aligned with the “down” TMJ. The “up” TMJ will be less visible in the radiograph.
C: to magnify a TMJ, position it up, closest to the x‐ray tube, and tilt the patient’s nose downward. The x‐ray beam (arrow) will align with the “up” TMJ. Tilting the nose downward to image a TMJ is not recommended in cats because there will be too much distortion in the radiograph.
Thickness of the head is measured at the level of the eyes.
X‐ray beam is centered on the TMJ, about the middle of the masseter muscle (arrows in A, B, and C).
Collimate the FOV as small as feasible to include the TMJ (the smaller the FOV, the better the radiographic detail).
D.Radiograph
Lateral oblique view of the head. The white arrow points to the dependent (down) TMJ, which was well‐aligned with the x‐ray beam. The black arrow points to the “up” TMJ which was not aligned with the x‐ray beam and is indistinct in the radiograph. In cats, the down TMJ often is more ventral in position than in dogs.
This supplemental radiograph of the head is made in addition to the standard lateral and DV views. It is used when a parallel view of the tooth is not possible. A, B, and C.Positioning
Patient is in ventral (A) or dorsal (B) recumbency with its mouth open.
Place the image receptor (IR) inside the patient’s mouth, as close to the tooth as possible.
The bisecting line (B‐line) is an imaginary line that equally divides (bisects) the angle between the long axis of the tooth (white dashed line) and the plane of the image receptor.
Make the x‐ray beam (red arrow) perpendicular to the B‐line and center it on the tooth.
Collimate the FOV as small as feasible to include the entire tooth.
D.Radiograph
Bisecting angle view of a mandibular canine tooth, tightly collimated to maximize radiographic detail.
A: without support, the cervical and lumbar regions of the spinal column normally sag while the patient is in lateral recumbency. Poor positioning of the spine can easily mimic or mask vertebral and intervertebral abnormalities.
B: Small rolled towels (shown in the illustration), foam wedges, or similar low opacity materials placed under the patient’s nose, neck, and mid‐lumbar spine will help support the sagging areas and improve the alignment of the vertebrae.
Sternum and spine are aligned in the same horizontal plane and parallel with the image receptor. Place a foam wedge or towel under the sternum to correct rotation.
Slightly flex the pelvis to help straighten the thoracic spine.
Measure the thickest part of thorax, typically over the liver.
X‐ray beam is centered on T5–7 (+).
Collimate the FOV as narrow as feasible to include the width of the thoracic spine from the last 2–3 cervical vertebrae to the first 2–3 lumbar vertebrae.
Patient is in dorsal recumbency with the thoracic limbs extended.
Spine and sternum are straight and superimposed in the same vertical plane, perpendicular to the image receptor.
Measure the thickest part of the thorax, usually over the liver.
X‐ray beam is centered on T5–7 (+).
Collimate the FOV as narrow as feasible to include the width of the thoracic spine from the last 2–3 cervical vertebrae to the first 2–3 lumbar vertebrae.
Place foam wedges or towels between the stifles and under the sternum to correct rotation (Figures 2.35 and 2.59) and under the lumbar region to eliminate sagging of the spine (Figure 2.60).
Measure the thickest part of the abdomen, usually over the liver.
X‐ray beam is centered on L3–4 (+).
Collimate the FOV as narrow as practical to include the width of the lumbar spine from the last 2–3 thoracic vertebrae to the end of the sacrum.
Patient is in dorsal recumbency with the pelvic limbs extended.
Spine and sternum are straight and superimposed in the same vertical plane, perpendicular to the image receptor.
Both ilial wings should be equal distance from table top. The right and left vertebral transverse processes should be equal distance from the table top.
Measure the thickest part of the abdomen, usually over the liver.
X‐ray beam is centered on L3–4 (+).
Collimate the FOV as narrow as practical to include the width of the lumbar spine from the last 2–3 thoracic vertebrae to the end of the sacrum.
B.Radiograph
Ventrodorsal (VD) view of the lumbar spine.
Artifacts
An artifact is something seen in a radiograph that is not present in the patient. It is a variation between the image of the patient and the reality of the patient.
Artifacts can vary greatly in appearance, but they mostly cause abnormal darkening or lightening in part or all of the radiograph. Dark artifacts may be called plus density artifacts because they increase radiographic density. Light artifacts may be called minus density artifacts.
Artifacts can degrade radiograph quality and mimic or mask abnormalities. It is important to understand the conditions under which artifacts occur so you can take steps to prevent them and recognize their presence when interpreting radiographs.
Film radiography artifacts most often occur in the darkroom or in the cassette. They are more common with manual processing than with automatic processors. Most film artifacts are permanent and cannot be removed. If the artifact is severe enough, the radiograph must be repeated to correct the problem.
Dark or plus density film artifacts result from conditions that alter the silver halide crystals prior to finished processing. Essentially, they overexpose part or all of the radiograph. Light or minus density film artifacts result from conditions that prevent exposure, interfere with development, or remove emulsion from the film.
Digital radiography has reduced the occurrence of many film artifacts because digital systems are much more tolerant of errors in exposure. However, digital radiography has not eliminated artifacts. Technical errors still occur, including malpositioning, motion, double exposures, and various computer‐related problems. Many of these are discussed in the following pages.
Motion artifacts are a frequent and major cause of poor detail in both film and digital radiography. They usually result from voluntary or involuntary movements by the patient during x‐ray exposure. Sometimes they are due to movement of the x‐ray tube or image receptor caused by loose equipment or inadvertently bumping into the equipment.
Dark or plus density artifacts
Causes in both film and digital radiography:
Overexposure or double exposure.
Scatter fog.
Negative Mach band.
Causes limited to film radiography:
Overdevelopment.
Light fog (e.g., light leak in darkroom, cassette, film storage container; static electricity).
Pressure fog (e.g., rough handling of film, improper storage of film).
Chemical fog (e.g., processing solutions, cleaning agents).
Age fog (expired film).
Dirt or stain on the viewbox that causes uneven lighting behind the film.
Causes limited to digital radiography:
Processing error (LUT error).
Calibration error.
Halo artifact (überschwinger artifact).
Light or minus density artifacts
Causes in both film and digital radiography:
Underexposure.
Grid lines.
Superimposition of objects outside the patient:
Collar, harness
ID/vaccination tags.
Wet/dirty hair coat.
Skin nodules, masses, defects.
ECG leads.
Tissue drains.
Blanket/sweater.
Bandaging or casting material.
Stretcher.
Positioning devices (e.g., sandbags).
Objects inside the patient:
Microchip.
Foreign objects (e.g., metal projectiles).
Sutures.
Implants.
Debris in or on the cassette (e.g., dust, hair, contrast agent).
Damaged image receptor.
Positive Mach band.
Causes limited to film radiography:
Underdevelopment.
Film exposed to fixer before developer.
Film not in contact with developer (e.g., air bubbles on film, film stuck to side of tank).
Contaminated developer with fixer.
Causes limited to digital radiography:
Processing error (LUT error).
Calibration error.
Dead pixels.
Figure A1. Artifacts
Appearances:
Abnormal blackening or whitening in part or all of a radiograph.
Artifacts can present in a variety of shapes, sizes, patterns, and densities.
Artifacts may be focal, multifocal, or diffuse.
Figure A1 is an example of a good‐quality film radiograph that can be used for comparison with the various artifacts described and pictured below (Figures A2 through A38). NOTE: the radiographic images are enhanced to better illustrate the artifact being described.
Understand the conditions that produce artifacts and take steps to prevent their occurrence.
Be aware of how artifacts look in radiographs. When artifacts are present, take them into account when interpreting the radiographs.
Figure A1VD view of a dog pelvis. This is a good‐quality radiograph that can be used as a comparison with the artifacts presented below. The pelvis is slightly rotated to the right and the pelvic limbs are slightly shifted to the right. Radiograph identification is photo‐flashed into the upper left corner of the image.
Figure A2. Mottling (film and digital)
Other names:
Noise, quantum mottle, graininess.
Appearance:
Generalized grainy, sand‐like or speckled pattern throughout the radiograph (Figure A2).
Causes:
Insufficient x‐rays recorded by the film or digital image receptor due to either underexposure or low receptor sensitivity.
Film radiography: the larger the grain size (sizes of the silver crystals and phosphors), the more sensitive (faster speed) the film:screen system, and the more mottling in the images.
Digital radiography: low signal‐to‐noise ratio (low SNR).
Remedies:
Increase the x‐ray exposure (double the mAs or increase kVp 20%).
Switch to a film:screen system with smaller grains (lower sensitivity).
Computer software may be available to increase the SNR.
Figure A2Quantum mottle.
Figure A3. Overexposure (film and digital)
Appearance:
The entire image is too dark; radiographic density overall is too high (Figure A3).
Film radiograph: if a photo‐flash was used to label the radiograph, the area with the film ID will not be overexposed.
Digital radiography: clipping/saturation artifact usually is concurrent with overexposure (see Figure A23).
Causes:
Too many x‐rays recorded by the image receptor due to:
User input error (wrong exposure selected).
SID too short.
X‐ray machine malfunction (i.e., surge in power supply).
If a film radiograph is all black (no visible image), it is more likely the film was completely exposed to light rather than too many x‐rays.
Digital radiography: in addition to too many x‐rays, a digital image that is too dark may result from using the wrong LUT to display pixel values which may be due to:
User input error (i.e., wrong body part selected).
Field‐of‐view (FOV) too large.
Computer error.
Remedies:
Repeat the study with proper exposure and FOV as small as practical.
Film radiographs can be viewed with a high‐intensity light source (“hot light”) to enhance the image.
Digital radiographs: reprocess the raw data with the correct LUT.
Figure A3Overexposed film radiograph. Notice the identification label in the upper left corner is not overexposed because the ID was added via photo‐flash after the x‐ray exposure.
Figure A4. Overdevelopment (film)
Appearance:The entire
film is too dark; radiographic density overall is too high (Figure A4).
Area with photo‐flash ID labeling also is too dark because all exposures, either from x‐rays or photo‐flash light, have been overdeveloped.
Cause:
Developer was too warm or too concentrated.
Film was immersed in developer for too long a time.
Localized dark areas in the film (spots of increased radiographic density) may result from developer splashed on the film prior to processing.
Remedies:
Maintain proper temperature and concentration of developer.
Pay attention to immersion times and thoroughly rinse film after development.
Make sure the automatic processor is functioning properly.
Figure A4Overdeveloped film radiograph. The identification label in the upper left corner also is too dark because all exposed parts of the film are overdeveloped.
Figure A5. Underexposure (Film and Digital)
Appearance:
The entire image is too light; radiographic density overall is too low (Figure A5).
Film radiography: if photo‐flash was used to label the radiograph, the area with the film ID will not be underexposed.
Digital radiography: quantum mottling usually is concurrent with underexposure due to low SNR (see Figure A2).
Causes:
Too few x‐rays recorded by the film or digital image receptor due to:
User input error (wrong exposure selected).
Source‐to‐image distance (SID) too long.
X‐ray machine malfunction (e.g., drop in incoming line voltage).
Wrong film:screen combination (film type not matched to screen type). NOTE: If a film radiograph is completely clear (i.e., a transparent sheet with no visible image), it is likely the x‐ray machine malfunctioned (no exposure was made) or the film was placed in fixer before developer.
Digital radiography: in addition to too few x‐rays, a digital image that is too light may result from using the wrong LUT used to display pixel values, either due to user input error (wrong body part selected) or computer error.
Remedies:
Repeat the study with proper exposure.
Digital radiography: reprocess the raw data with the correct LUT.
Figure A5Underexposed film radiograph. Notice the area with the identification label is not underexposed because the ID was added via photo‐flash after x‐ray exposure.
Figure A6. Underdevelopment (film)
Appearance:
The entire film is too light; radiographic density overall is too low (Figure A6).
Area with photo‐flash ID labeling also is too light because all exposures, whether from x‐rays or photo‐flash light, have been underdeveloped.
Cause:
Developer was too cold or too weak (exhausted chemicals).
Film was immersed in developer for insufficient length of time.
Remedies:
Maintain proper temperature and concentration of developer.
Pay attention to immersion times.
Make sure automatic processor is functioning properly.
Figure A6Underdeveloped film radiograph. The area with the identification label also is too light.
Figure A7. Uneven development (film)
Appearance:
Non‐uniform, mottled streaking in part or all of the film radiograph (Figure A7).
Ill‐defined, patchy, lighter areas in the film (minus density artifacts).
Cause:
Uneven contact between the film and the developer chemicals due to insufficient mixing (stirring) of the developer solution.
Remedies:
Maintain proper temperatures and replenishment rates of processing chemicals.
Manual processing:
Thoroughly mix solutions prior to each use.
Agitate film for a few seconds after each immersion to evenly coat the film and remove air bubbles.
Thoroughly rinse and dry each film prior to viewing and storage.
Figure A7Uneven development. Film radiograph that was processed in developer that was insufficiently mixed.
Figure A8. Yellowish stains (film)
Appearance:
Cloudy, sticky residue on film with a sulfur smell.
Yellow‐brown discoloration of film that commonly appears dichroic or multi‐colored in reflected light (Figure A8).
Cause:
Dried fixer on the film due to insufficient rinsing.
Prolonged adherence of fixer will stain the film a yellowish‐brown.
Remedies:
Thoroughly rinse and dry each film radiograph prior to viewing and storage.
If the film is not yet stained yellow, try rinsing it again or running it through the automatic processor again.
Figure A8Yellow stains on film. Film radiograph stained by retained fixer.
Figures A9–10. Fog (film and digital)
Appearance:
Hazy darkening or graying in the radiograph that reduces contrast and visible detail.
Fog can be diffuse throughout the entire image (Figure A9) or localized (Figure A10).
Causes:
Scatter radiation is a common cause and increases with:
Thicker body part.
Larger field‐of‐view (FOV).
Higher kVp.
No grid.
Scatter fog also can result from a previous exposure (e.g., the film or CR cassette was near the x‐ray machine during an earlier radiographic study).
Causes unique to film radiography
Light fog: film was exposed to visible light prior to development:
Light leak in darkroom, cassette, or storage area.
Film not completely in processor before lights turned on.
Film was exposed to light prior to finished development (e.g., darkroom door was opened).
Safelight with wrong filter or too bright lightbulb.
Static electricity (localized light fog, see Figure A22).
Pressure fog: film was exposed to excessive pressure prior to development:
Rough handling of film (Figure A23).
Improper storage of film (laying boxes of unused film flat instead of on‐end results in the weight of the upper sheets, eventually fogging the lower sheets).
Heat fog: prolonged exposure of unused film to heat (temperature above 24 °C or 75 °F).
Chemical fog: exposure of unused film to chemicals (e.g., cleaning agents, hydrogen peroxide, formaldehyde).
Age fog: film is expired; over time, unused film will eventually undergo “self‐development” and become fogged.
Remedies:
Repeat the study with less scatter radiation:
Collimate the FOV as small as practical; this will have the greatest impact on reducing the amount of scatter fog.
Use a grid whenever body part thickness exceeds 10 cm.
Lower the kVp: decrease kVp 16% and double mAs; repeat as often as needed to achieve desired contrast.
Shield unused film and cassettes from scatter radiation.
Remedies unique to film radiography:
Correct any light leaks.
Perform a Safelight test (see Figure A11).
Ensure proper storage of unused x‐ray film:
Temperature: 10–24 °C (50–75 °F).
Humidity: 30%–60%.
Store boxes of unused film on‐end instead of flat.
No nearby chemicals.
Figure A9Diffuse scatter fog. Digital radiograph made without a grid. Figure A10Localized light fog. Film radiograph that was exposed to light along the bottom and left side of the film.
Figure A11. Safelight test (film)
Do this test to evaluate the amount of light fog caused by your safelight:
Darkroom should be completely dark with the safelight turned off.
Place a piece of unexposed film on the countertop.
Cover half of the film with a piece of cardboard.
Turn on the safelight.
Leave the film exposed for 2 min.
Process the film.
The two halves of the film should be equal in density; if not, there is safelight fog (Figure A11).
Figure A11Safelight test. A. Passed: safelight does not produce significant light fog. B. Failed: the part of the film that was exposed to the safelight is darker than the covered part due to light fog. Fog may be due to either a wrong safelight filter or the safelight bulb is too bright (wattage too high).
There are black areas in the digital radiograph where tissues should be visible (Figure A12); the black areas cannot be brightened enough to restore missing information.
Usually occurs in the thinner, less opaque, or peripheral parts of the patient (e.g., extremities, lungs); more opaque tissues such as bone often are visible, but the soft tissues are lost.
Causes:
Overexposure: pixels are overwhelmed by too many x‐rays and incapable of responding to windowing and leveling.
Computer processing error (e.g., LUT error, problem with contrast enhancement software).
Damaged or otherwise non‐functional pixels.
Remedy:
Repeat the study with proper exposure and correct LUT settings.
If clipping artifact remains, image receptor may need to be repaired or replaced.
Figure A12Clipping artifact in a digital radiograph.
Figures 13–14. LUT errors (digital)
Appearance:
Poor quality radiograph with incorrect levels of contrast, brightness, and/or detail (Figures A13 and A14).
Other artifacts may be concurrent (e.g., overexposure, underexposure, clipping).
Cause:
Computer used wrong look‐up table (LUT) to display pixel values due to:
User selected wrong body part, such as entering “thorax” for a pelvic radiograph (thorax typically is a low contrast study, so pelvic radiographs will be displayed with insufficient contrast, as depicted in Figure A13).
Computer malfunction.
Remedies:
Re‐process the raw data using appropriate LUT settings.
Repeat the study with correct LUT settings.
Figure A13LUT error. Digital radiograph of dog pelvis with too low contrast and density due to LUT error (user selected “thorax” instead of “pelvis”). Figure A14LUT error. Digital radiograph of dog thorax with too high contrast and density due to LUT error (user selected “pelvis” instead of “thorax”).
Figure A15. Pixelated image (digital)
Appearance:
Digital radiograph appears grainy with poor detail (Figure A15).
Causes:
Pixel size is too large due to:
Computer processing error.
Excessive magnification by user.
Low‐quality monitor with insufficient resolution.
Remedies:
Adjust image processing algorithm.
View image with higher quality monitor
Figure A15Pixelated. Digital radiograph displayed with large pixels, resulting in a grainy image with poor detail.
Figure A16. Planking artifact (digital)
Appearance:
Broad, dark bands across the entire radiograph (Figure A16).
Cause:
Overexposure; x‐ray saturation of the digital image receptor reveals the plank‐like arrangement of the receptor components.
Remedy:
Repeat the study with proper exposure.
Figure A16Planking artifact. Digital radiograph with dark bands due to overexposure.
Figures A17–18. Moiré pattern or Aliasing (digital)
Appearance:
A series of repeating dark and light lines that run across the entire digital radiograph (Figures A17 and A18); the thickness and orientation of the lines do not correspond to grid lines.
The term “moiré” describes a repeating wavy or rippled pattern in an image (it was originally used to describe the appearance of silk fabrics).
Causes:
Inadequate sampling of the x‐ray data by the computer leads to distortion of the grid lines; a moiré pattern is more prevalent with low‐frequency grids.
Faulty data cable (cable is damaged or loose).
Remedy:
If the artifact is severe enough, repeat the study.
Use a high‐frequency grid.
Make sure the Bucky mechanism is functioning properly.
Increase the computer sampling rate.
Inspect and tighten the data cables.
Figure A17Moiré pattern. Digital radiograph with numerous repeating lines running vertically across the entire image due to computer error and insufficient sampling of grid lines. Figure A18Moiré pattern. Digital radiograph with repeating lines due to a loose data cable.
Figure A19. Motion blur (film and digital)
Appearance:
Unsharp margins or a streak‐like appearance associated with the edges and outlines of structures in the film or digital radiograph (Figure A19).
Causes:
Voluntarily or involuntarily movements by the patient (e.g., struggling, tachypnea) during x‐ray exposure. Motion is a major cause of poor quality radiographs in veterinary radiology.
X‐ray tube movement during exposure (e.g., loose equipment; equipment bumped by personnel or patient, hand holding the x‐ray tube).
Remedies:
Repeat the study with proper patient restraint.
Use the shortest exposure time practical.
Secure all imaging equipment.
Figure A19Motion blur. Radiograph with reduced detail in the pelvic limbs due to movement during exposure.
Figure A20. Double exposure (film and digital)
Appearance:
Two images of the same body part in one radiograph (Figure A20).
Margins usually are blurry (may resemble motion artifact).
Film: the image will be too dark (overexposed).
Digital: radiographic density often is the same as it would be with a single exposure because the computer performs an automatic correction.
Causes:
Two exposures were made of the same body part, one immediately following the other.
Patient moved during a long exposure time.
Remedy:
Repeat the study using a shorter exposure time and proper patient restraint.
Figure A20Double exposure in a digital radiograph.
Figure A21. Ghost image (film and digital)
Other names:
Phantom image; image lag; ghosting artifact.
Appearance:
Two images are visible in the same film or digital radiograph. Often it is the orthogonal view of the same body part, but sometimes a different body part is visible (Figure A21).
Cause:
Persistence of a latent image from a previous study.
Film radiography: a piece of film that was previously exposed, but not processed, was inadvertently used again (i.e., user forgot to change to a new cassette).
Digital radiography: image receptor was not completely erased (e.g., failure of erasure mechanism in CR reader) or was reused too quickly (receptor had not lost all of its charge from the previous exposure).
Remedy:
Repeat the study with unused film or a “clean” digital imaging plate.
Figure A21Ghost image. A lateral view of a thorax is faintly visible in this VD view of a pelvis.
Figure A22. Static electricity (film)
Appearances:
Localized black areas (plus density artifacts) that can present in a variety of patterns in a film radiograph (Figure A22). They may appear as:
Irregular branching black lines that resemble “lightning” or “trees.”
Multiple, tiny black spots or smudges.
Linear dark areas that are somewhat mottled and inhomogeneous.
Cause:
Static electricity exposes undeveloped film to visible light (i.e., static electricity is a type of light fog).
Static electricity can be generated by rapidly opening a film packet or it can be directly transferred from the user to the film.
Remedies:
If the artifact is severe enough, repeat the study.
Maintain relative humidity at 30%–60% in the radiology department.
Handle film gently, avoid friction, slowly unwrap film from its packaging.
Ground yourself before handling film.
Use an antistatic cleaner with film cassettes.
Figure A22Static electricity artifacts. Film radiograph depicting light fog as a 1. Lightning pattern. 2. Multiple tiny spots and smudges. 3. Tree‐like branching. 4. Linear pattern.
Figure A23. Rough handling of film
Appearances:
Localized plus density artifacts; dark or black spots, lines, or regions in a film radiograph (Figure A23). These artifacts are a type of pressure fog.
Crimping marks are common and appear as thin, crescent‐shaped, dark lines in the radiograph (sometimes called “thumbnail” or “fingernail” marks).
Abrasion marks appear as fine black lines or dark hazy smudges.
Some of the dark patterns may resemble fingerprints.
Causes:
Bending, flexing, or creasing the film prior to development creates crimping marks due to pressure (Figure A23 B). Note that these artifacts are not made by “digging” a thumbnail into the film as the name “thumbnail artifact” might suggest.
Pushing or sliding undeveloped film across the darkroom table or countertop causes abrasion damage and pressure fog.
Touching undeveloped film with dirty or contaminated fingers (e.g., developer on fingers) can create a fingerprint pattern in the developed film. (Note: white fingerprints in a film radiograph may be caused by transferring fixer to the undeveloped film or by leaving skin oil on the film that blocks contact with the developer.)
Remedy:
If the artifact is severe enough, repeat the study.
Careful handling of x‐ray film.
Keep fingers clean and dry.
Figure A23Localized plus density artifacts. (A) Film radiograph depicting various types of pressure fog: 1. Abrasion marks. 2. Fingerprints. 3. Crimping mark. (B) The crimping mark seen in radiograph A is caused by bending the undeveloped piece of film as indicated by the arrow.
Figure A24. Local white areas in film
Appearance:
Localized minus density artifacts; lighter or whiter spots, lines, or regions in a film radiograph (Figure A24).
The edges of these artifacts tend to be sharp and well‐defined because their causes are located immediately adjacent to the film, which means there is little or no magnification distortion or edge blurring.
Causes: A high opacity material such as contrast medium or a metallic object is present on the surface of the cassette, table top, or patient.
Debris is present in the cassette (dust, hair, etc.). The debris blocks emitted light from reaching the film. NOTE: debris in a cassette is very close to the film so the artifact will be sharply‐defined with very distinct margins.
Debris on a roller in the automatic processor can produce white lines across the radiograph or can scratch and remove film emulsion. Artifacts generated by automatic processors usually repeat in multiple studies.
Water spot on the film.
Poor contact between the developer chemicals and the film due to:
Film stuck to the side of the dip tank or to another piece of film; latter sometimes is called a “kissing artifact” because both pieces of film will have the same lighter area where they were in contact with each other.
Air bubbles on the film during development.
Fixer splashed on film prior to development.
Physical scratches in film; wet film is especially vulnerable to loss of emulsion, which can result from rough handling.
Cracked or permanently stained intensifying screen (no light is emitted from the damaged part of the phosphorescent screen).
Remedies:
If artifact is severe, repeat the study (with a new cassette if needed).
In the darkroom, inspect the open cassette with a blacklight, looking for damage or debris on the intensifying screen; clean the cassette as needed.
Damaged screens will need to be replaced, but in the interim you should label any damaged cassettes and make note of the locations of any problem areas that produce artifacts.
Inspect and clean the automatic processor.
Be careful when handling and processing x‐ray film.
Figure A24Localized minus density artifacts. Film radiograph depicting various light area artifacts: 1. Fingerprint due to fixer on fingers. 2. Well‐defined round spots caused by air bubbles clinging to film during development or fixer splashed on film prior to development. 3. Well‐defined larger white area representing either a water spot on the film or a “kissing” artifact. 4. Scratch in the film emulsion. 5. Either debris in a cassette (located between the screen and the film) or pieces of metallic material on the table top or patient’s hair. Debris inside the cassette will produce an artifact with sharp margins. 6. A damaged intensifying screen (e.g., cracked screen) or a stain in the corner of a screen that prevents light emission from this area.
Localized minus density artifacts; brighter or whiter spots, lines, or regions in a digital radiograph (Figure A25).
Causes:
A high opacity material such as contrast medium or a metallic object is present on the table or on the surface of the image receptor.
Dust, dirt, hair, etc. in the CR cassette can block emitted light from reaching the imaging plate. NOTE: debris in a cassette is very close to the imaging plate so the artifact will be displayed with very sharp, well‐defined edges in the radiograph.
Dead pixels; the affected pixels cannot display any shade of gray due to a physically damaged image receptor or a calibration error.
Causes of parallel white lines across the entire digital image include:
Poor calibration.
Faulty or loose data cable.
Damaged imaging plate.
Defective laser scanner (CR system).
Dust or debris on the light guide (CR system).
Remedies:
If the artifact is severe, repeat the study after cleaning or repairing the image receptor (remove any debris).
Calibrate or re‐calibrate the image receptor.
Severely damaged digital receptors will need to be replaced.
Inspect and tighten all data cables.
Figure A25Localized minus density artifacts. Digital radiograph depicting: 1. White line caused by debris on a light guide in a CR reader. 2. Dead pixels.
Figure A26–27. Superimposition of objects outside the patient (film and digital)
Appearance:
Objects external to the patient can create superimposition artifacts that appear as lighter, brighter, or whiter lines, streaks, or distinct shapes in the radiograph (Figure A26).
Causes:
High opacity materials on the patient or next to the patient that are in the field‐of‐view, such as:
Patient’s collar, harness, leash, etc.
Medical devices (e.g., ECG leads, IV tubing).
Positioning aids (e.g., sandbags, lead gloves).
Wet or dirty patient hair coat.
Contrast agent or medication on the patient’s skin or hair coat.
Skin folds (Figure A27).
Cutaneous nodule or mass (e.g., nipple, lipoma, engorged tick).
Mineralization on or in the skin.
Remedy:
If the artifact is severe enough (and removable), repeat the radiograph after correcting the cause of the artifact (e.g., move it out of the field‐of‐view, clean it up).
Figure A26Superimposition artifacts. Radiograph of the thorax depicting superimposition of external structures: 1. Harness with dorsal and ventral metal D‐rings; 2. IV tubing; 3. ECG leads; 4. Wet or dirty haircoat along the patient’s ventrum. Figure A27Skin folds. VD radiograph of a Shar‐pei dog with visible skin folds superimposed on the pelvic limbs. Also present in this digital radiograph is clipping artifact. Notice that the peripheral soft tissues and the distal part of the tail are not visible.
Figure A28–29. Backscatter (film and digital)
Appearance:
Shapes of objects or structures located behind the film or digital image receptor are visible in the radiograph.
The support structures in the back of the cassette may appear as radiating white lines (Figure A28).
The electronics inside a wireless digital image receptor may be visible (Figure A29).
Causes:
Backscatter refers to x‐rays that pass through the patient and image receptor to interact with the floor, wall, table, or other structure and produce secondary x‐rays that travel back toward the x‐ray tube.
Backscatter adds an image of the structures located behind the receptor to the radiograph of the patient.
The back of a cassette may also be visible in the patient’s radiograph if the cassette was installed upside down.
Remedies:
If the artifact is severe enough, repeat the study with less kVp; lower energy x‐rays are less likely to result in backscatter.
Make sure the image receptor is properly installed and positioned.
Add shielding behind the film or digital image receptor:
For an immediate fix, place a lead apron behind the image receptor to provide temporary shielding.
Long‐term shielding usually requires the manufacturer to install additional shielding to the back of the cassette or behind the image receptor.
Figure A28Backscatter. Visible in this VD view of a pelvis are the support structures in the back of the cassette. They appear as multiple crossing white lines. The lines are due to backscatter but may also be caused by a cassette that was installed upside down. Figure A29Backscatter. In this VD view of a pelvis, the electronics inside the digital image receptor are visible due to backscatter.
Figure A30. Gridlines (film and digital)
Appearance:
Parallel, evenly‐spaced white lines that extend across the entire film or digital radiograph (Figure A30).
Cause:
Undesirable absorption of transmitted x‐rays by the grid due to:
Stationary grid.
Grid ratio too low.
Grid frequency too low.
Failure of the Bucky mechanism to move the grid.
Digital: failure of grid suppression software.
Remedies:
Change to a higher ratio grid.
Change to a higher frequency grid.
Ensure that the Bucky mechanism is functioning properly.
Digital: add or correct grid‐line removal software.
Figure A30Gridlines. (A) Grid is properly positioned in relation to the x‐ray beam. (B) Radiograph with visible parallel white lines.
Figure A31–A34. Grid cutoff (film and digital)
Off‐center grid cutoff Appearance:
Parallel white lines across one side of the film or digital radiograph; one side of the image is too light (underexposed) and the other side is too dark (overexposed) (Figure A31).
Cause:
Grid is laterally misaligned with the center of the x‐ray beam resulting in increased absorption of transmitted x‐rays along one side.
Cutoff is more severe with cross‐hatched grids, which must be perfectly aligned with the central ray.
Remedy:
Repeat the study after correcting the grid position.
Figure A31Grid cutoff. A. Grid is off‐center in relation to the x‐ray beam (grid is moved to the right). B. Radiograph with parallel white lines on one side of the image due to an off‐center grid.
Off‐level grid cutoff Appearance:
Parallel white lines across the entire film or digital radiograph; image is overall too light (underexposed) (Figure A32).
Causes:
Grid is tilted in relation to the center of the x‐ray beam resulting in increased absorption of transmitted x‐rays.
Cutoff also will occur when the x‐ray beam is angled in relation to the grid.
Remedy:
Repeat the study after correcting the alignment between the grid and the x‐ray beam.
Figure A32Grid cutoff. (A) Grid is tilted in relation to the x‐ray beam (right side is closer to the x‐ray tube). (B) Radiograph with parallel white lines across the entire image due to an off‐level grid.
Off‐focus grid cutoff Appearance:
Parallel white lines along both sides of the film or digital radiograph; the edges of the image are too light or underexposed (Figure A33).
Cause:
The distance between the grid and the focal spot is not within the recommended range, which means the lead strips are not properly aligned with the x‐ray beam and there is increased absorption of transmitted x‐rays at the periphery.
The distance at which cutoff occurs is determined by SID/grid ratio.
Remedy
Repeat the study after correcting the distance between the grid and the x‐ray tube or focal spot.
Figure A33Grid cutoff. (A) Grid is too close to the x‐ray tube (the source‐to‐grid distance is too short for this focused grid). (B) Radiograph with parallel white lines on either side of the image due to an off‐focus grid.
Upside‐down grid cutoff Appearance:
Parallel white lines that span the entire film or digital radiograph, especially at the edges of the image where there will be severe grid cutoff (Figure A34).
Radiograph is overall too light (underexposed).
Cause:
Grid is installed upside down, which greatly increases absorption of the transmitted x‐rays, especially peripherally.
Remedy:
Repeat the study after correcting the grid position.
Figure A34Grid cutoff. (A) Grid is upside down in relation to the x‐ray beam. (B) Radiograph with parallel white lines that are more numerous on either side of the image due to an upside down grid.
Figure A35. Halo effect (digital)
Other names:
Rebound artifact, überschwinger artifact.
Appearance:
A local plus density artifact in a digital radiograph.
A dark zone or black rim is seen adjacent to a high opacity structure such as metallic object (Figure A35).
Halo artifacts can mimic osteolysis and may be mistaken for loosening or infection near an implant.
Cause:
Computer edge‐enhancement error; edge‐sharpening algorithms commonly are used to enhance digital radiographic contrast and image detail, but frequently create this artifact near high opacity objects.
Remedies:
Repeat the study with corrected computer settings.
Turn off the edge‐enhancement algorithm and view the digital image as raw data.
Figure A35Halo artifact. (A) VD view of the pelvis and (B) a close‐up of the hip implant. The white arrow points to the dark “halo” adjacent to the metal implant.
Figure A36. Radiofrequency or “zipper” artifact (digital)
Appearance:
Multiple, repeating, dark lines in a digital radiograph (Figure A36).
The size and pattern of the lines vary with the severity of the cause and often occur only intermittently. Zipper artifacts seldom are seen in every radiographic study.
Causes:
Interference from a nearby radiofrequency (RF) source (e.g., computer equipment, cell phones, Bluetooth devices, microwaves, fluorescent lights, electric motors, others).
Loose or damaged data cable.
Patient making rapid, minor movements against the image receptor (i.e., patient is trembling or shaking).
Remedies:
If the artifact is severe enough, repeat the study.
Identify the source of the RF interference (sometimes difficult, especially when the artifact occurs intermittently).
Inspect and tighten data cables.
Move the patient slightly further away from the image receptor.
Add RF shielding to the radiology room.
Figure A36Radiofrequency artifact VD view of a pelvis depicting multiple, thin, black, repeating lines caused by interference from nearby electrical equipment.
Figure A37. Border detection error or Cropping artifact (digital)
Appearance:
Plus density artifact in a digital radiograph in which an edge of the field‐of‐view is seen in the area of interest (Figure A37).
Cause:
Computer error with automatic border detection software caused by:
Imaging receptor and field‐of‐view (FOV) not properly aligned.
User attempting to divide the digital image receptor for multiple x‐ray exposures (create more than one radiograph in the final image).
Area of interest is positioned off‐center.
Presence of a high opacity structure (e.g., bone, metal) which the computer mistakes for the edge of the field‐of‐view.
Remedies:
Turn off automatic border detection software and view the digital image as raw data.
Repeat the study after improving alignment between the field‐of‐view and the digital image receptor.
Figure A37Cropping artifact. Digital radiograph depicting darkening along the left side of the patient due to a border detection error.
Figure A38. Edge enhancement or Mach band/Mach line (film and digital)
Appearance:
The edges of objects appear darker or lighter in the radiograph than actual. For example, in the grayscale image below, the edge of a shade of gray appears lighter next to a darker shade (white arrow) and darker next to a lighter shade (black arrow) (Figure A38).
Mach bands can be mistaken for bone fractures, osteosclerosis, osteolysis, free gas, and other abnormal radiographic findings. A Mach line may be mistaken for a cavitary lung lesion.
Cause:
A Mach line is an optical illusion. It may be caused by an abrupt change from one shade of gray to the next or it may be caused by the curved edge of a structure. A curved structure such as a blood vessel, bronchus, rib, or costal cartilage can falsely increase or decrease the adjacent opacity.
Negative Mach bands are darker than actual and occur along convex edges and where a darker edge meets a lighter edge.
Positive Mach bands are lighter than actual and occur along concave edges and where a lighter edge meets a darker edge.
Remedies:
Mach lines are not real and seldom repeat in serial radiographs. When in doubt, make another radiograph with the subject at a slightly different angle to the x‐ray beam.
Knowledge of the edge enhancement artifact does not eliminate it. The illusion occurs inside the retina. But knowing about Mach bands helps prevent mistaking them for true abnormalities.
Figure A38Mach band. Close up VD views of a dog pelvis. A. The concave cranial aspect of the acetabulum appears sclerotic next to the darker joint space (arrow) due to a positive Mach band. B. When the joint space is made whiter, the Mach band and apparent sclerosis are less evident (arrow).
Contrast radiography
Radiographic contrast studies are performed to enhance visualization of a specific organ or structure of interest. A gas or metal opacity contrast medium is introduced into a lumen or potential space to create an opacity interface where none exists. The different types of contrast media frequently used in veterinary radiography, as well as their advantages and disadvantages, are discussed below. Detailed descriptions of numerous contrast procedures are provided on the subsequent pages. Representative normal radiographs are included with each study description. Abnormalities are discussed with each body part in Chapters 3–5.
Indications for contrast radiography
To obtain needed information that is not available in survey radiographs.
To better evaluate the size, shape, and position of an organ or structure that is not adequately seen in survey radiographs.
To examine the luminal contents, mucosal margin, or inner wall of a hollow viscus.
To provide some assessment of organ function.
To aid in determining appropriate therapy, such as whether surgery is indicated.
The ideal contrast medium
Sufficiently alters the opacity of the organ or structure of interest to make it visible in radiographs.
Persists long enough to make radiographs.
Carries a low risk of harm to the patient.
Is successfully eliminated from the body.
Types of contrast media
In veterinary radiography, we use both positive and negative contrast agents. Negative contrast agents are gases. The most commonly used gases are atmospheric air (room air), carbon dioxide, nitrous oxide, and oxygen. Room air, of course, is readily available, but it is less soluble than the other gases and therefore carries a greater risk of gas embolism.
Positive contrast media contain either barium or iodine. They may be administered enterally or parenterally to assess the position, size, shape, margination, and internal architecture of an organ. They also provide a non‐invasive means of detecting leakage from an organ. Positive contrast media are metal opacity and most opaque in radiographs when the kVp is close to 70 (see discussion about K‐edge in Chapter 2).
Both negative and positive contrast agents sometimes are used together to create a double contrast study. Typically, this is accomplished by filling the organ of interest with gas and then adding a small amount of positive contrast medium to coat the mucosal surface. Double contrast studies tend to provide better visualization of the mucosa than either a positive or negative contrast study alone.
Barium contrast media contain barium sulfate, a chalky‐white, crystalline powder that is micropulverized and placed in suspension. The barium sulfate usually is combined with carboxymethylcellulose to enable it to remain in suspension and more efficiently coat the mucosal surfaces. Barium sulfate powder is available by itself (e.g., USP BaSO4), but it is difficult to mix evenly and tends to quickly fall out of suspension. The commercially available premixed preparations generally are preferred because they tend to produce better contrast studies that are easier to interpret. Notice that a barium contrast medium is a suspension, not a solution. Barium never is injected intravenously.
Barium contrast agents (or simply “barium”) most often are used to study the alimentary tract. They may be administered orally or per‐rectum. Barium is not absorbed in the GI tract and is eliminated in the feces. A variety of concentrations of barium are available to provide a thin or thick suspension to fill or coat different parts of the GI tract. The concentration needed for a particular study is discussed with each specific procedure later in this chapter. Concentrations may be listed as a percentage weight‐to‐volume (w/v), a weight‐to‐weight (w/w) ratio, or as specific gravity. Many commercial barium preparations include additional ingredients to provide therapeutic benefits to the patient’s alimentary tract, including a protective coating action, additives to help reduce GI gas, and compounds that help bind irritating or harmful substances (e.g., bile acids, toxins, and bacteria).
Iodinated contrast media contain compounds that are composed of benzene rings with three iodine atoms plus various side chains. They are water‐soluble and either ionic or non‐ionic. Ionic compounds split into two ions when placed in solution. Non‐ionic agents do not disassociate in solution. The osmolality of most ionic contrast media is high, about 5–8 times that of serum. This is particularly true of the older or “first generation” ionic agents. High osmolar agents are hypertonic, and they are quickly diluted and absorbed in the body. Ionic agents are irritating and much more likely to cause an adverse reaction than non‐ionic agents. Non‐ionic agents are less than three times the osmolality of serum. Ionic agents should not be used in very young or debilitated patients due to their hypertonicity. They are occasionally used for alimentary and cystourethral studies in adult animals, but in general, ionic contrast agents are not recommended.
Non‐ionic contrast media are more available to veterinarians today than in the past, greatly reducing the need to use ionic agents. Non‐ionic agents may be administered intrathecally, intravenously, orally, or intra‐articular. They are used in numerous radiographic contrast studies, including angiography, myelography, urography, and to study the alimentary tract.
Iodinated contrast media are available in a variety of concentrations, expressed as milligrams of iodine per milliliter of solution or mgI/ml (Table 2.2). The higher the concentration, the greater the opacity. With some iodinated agents, a higher concentration makes them more viscous (thick and sticky) and resistant to flow. In these cases, the viscosity may be reduced by warming the contrast medium to body temperature. The mgI/ml needed for a particular contrast study is discussed with each specific procedure later in this chapter. When the concentration exceeds what is needed, the contrast medium can be diluted with sterile water or saline.
a In this table, the common trade names of various iodinated contrast agents are listed in order of decreasing osmolality. The key component of each agent is shown in parenthesis. A concentration in mgI/ml is given for each agent, but other concentrations frequently are available from the manufacturer. Some of the contrast media listed are discontinued in the United States.
About 98% of an iodinated contrast medium is eliminated from the body via the kidneys. The remainder is removed by the small intestine and the biliary system. Clearance from the central nervous system is slower than from the vascular system due to the blood–brain barrier. Iodinated compounds that are used to study the hepatobiliary system are designed to be preferentially excreted in the bile.
Contrast medium in the urine can inhibit bacterial growth, increase urine specific gravity, and affect the appearance of the urine sediment. These are not contraindications to a contrast study, but keep them in mind if laboratory testing is to follow radiography. Also, intravenous iodinated contrast agents will temporarily increase the level of iodine in the blood, which may inhibit the uptake of I‐131 by the thyroid gland. Decreased iodine uptake means radioisotope therapy may be less effective.
Adverse effects related to contrast media
Unwanted reactions to contrast media range from a mild inconvenience to a life‐threatening emergency situation. It is important to be aware of the risk factors and the signs of an adverse reaction before administering a contrast agent. A successful outcome depends on prevention and early treatment. A problem can arise during the contrast study or after the study is completed; some adverse effects may be delayed 30 minutes or longer after dosing.
Adverse effects of gas
A potentially serious complication from a negative contrast study is a gas embolism. Gas emboli are more likely to occur when the study involves an organ that is bleeding, such as pneumocystography in a patient with hematuria. The risk of gas embolism is less when using a soluble gas such as carbon dioxide, nitrous oxide, or oxygen. Symptoms of gas embolism often develop quickly and may include dyspnea, tachycardia, altered mentation, hypotension, and abnormal heart sounds (the latter has been described as a “rumbling” heart sound). The severity of the clinical signs depends on the size and extent of the embolism. Sudden death has been reported.
Treatment of a suspected gas embolism must begin immediately. The goal is to prevent embolization of the pulmonary outflow tract. Place the patient in left lateral recumbency and elevate its caudal body in an effort to trap the gas in the right ventricle. The patient may need to remain in this position for up to 60 minutes to allow the gas to be absorbed. Additional treatments such as fluid therapy and oxygen therapy may be needed.
Adverse effects of barium
Barium in the alimentary tract generally is safe because it is not irritating and not absorbed or metabolized. Barium in the esophagus, stomach, or intestines may physically obscure visualization of the mucosal surfaces during endoscopy or surgery. Barium also can block the propagation of ultrasound waves, which can complicate an ultrasonography examination. When practical, a barium contrast study should be avoided when one of these other procedures is planned.
Although a barium contrast study can be performed to investigate a possible rupture in the esophagus, stomach, or bowel, it should be performed with caution. Barium outside the alimentary tract is irritating and inflammatory. The severity of a reaction to barium depends on the amount and location. Reactions to small amounts of barium in the peritoneal cavity or mediastinum often are no more severe than reactions to equal amounts of ingesta without barium. A large amount of barium, however, can become life‐threatening. Patients that survive may develop extensive adhesions and chronic granulomas.
Keep in mind that a rupture along the alimentary tract is likely to leak gas as easily, if not easier, than liquids. When leakage is suspected, make plain radiographs (without contrast) to detect free gas. Use horizontal beam radiography if needed (Figure 2.15). If free gas is detected, the diagnosis is confirmed. If no free gas is seen, then the leakage most likely is absent or very small. At this point, the risk of using barium is as low as using an iodinated contrast agent, and barium is more likely to demonstrate a leak. Iodinated contrast media may be preferred when a GI contrast study is needed during the first few days after GI surgery because there is already free gas in the abdominal cavity.
Barium in the trachea or lungs may or may not cause problems. Again, it depends on the volume. Small amounts of barium usually are benign and mostly cleared by the bronchial cilia or alveolar macrophages. Some barium may localize in the tracheobronchial lymph nodes or in the alveoli where it can persist for long periods of time, but rarely is it clinically significant. A large volume of barium in the respiratory tract, however, can lead to airway obstruction, hypoxia, and respiratory distress. In these cases, as much barium as possible should be removed using endotracheal suction. Sometimes barium is aspirated during oral administration or secondary to vomiting or inadvertently deposited in the respiratory tract due to incorrect placement of an orogastric or nasogastric tube. Rarely, an esophageal fistula is the cause of in barium in the trachea, lungs, or mediastinum.
Adverse effects of iodinated compounds
Ionic contrast media are much more likely to induce an adverse reaction than non‐ionic agents. Adverse effects range from mild to severe (Table 2.3). Warming an ionic agent to body temperature and injecting it as slowly as possible reduces risk, but the increased availability and affordability of non‐ionic compounds has virtually eliminated the need to use ionic contrast media.
Table 2.3Adverse effects of IONIC contrast agentsa
Mild
Bitter taste; patient may be reluctant to accept oral dosing.
Nausea, brief retching or vomiting.
Peripheral vasodilation and skin erythema.
Osmotic diuresis or osmotic diarrhea.
Local irritation at the injection site.
General discomfort.
Moderate
Persistent vomiting.
Facial swelling.
Laryngeal edema.
Dehydration; due to osmotic diuresis or diarrhea.
Tachycardia or bradycardia.
Hypertension; due to osmotic hypervolemia.
Severe
Cardiac arrhythmias.
Hypotension; due to bradycardia, vasodilation, osmotic diarrhea.
Pulmonary edema; due to hypertonic contrast agent inadvertently deposited in lungs.
Vascular collapse; due to damaged capillaries and desiccated red blood cells caused by hypertonic agents; may lead to thromboemboli and hemorrhage.
Acute renal failure; due to direct tubular toxicity or renal vasoconstriction or hypotension.
Cerebral edema, seizures, syncope; due to increased permeability of the blood–brain barrier.
Death.
a This table lists the physiologic changes and clinical signs that may result from the administration of an ionic contrast agent. Adverse effects are more likely to occur with intravenous and intra‐thecal routes than with oral dosing.
Adverse reactions to non‐ionic agents are uncommon. Most are mild and transient, requiring no specific therapy (e.g., tachycardia, nausea, vomiting). Rarely, more severe reactions can occur (e.g., bronchospasm, hypotension). Fatal reactions are extremely rare (less than 0.001%). Unfortunately, the likelihood of an adverse reaction cannot be predicted, even by administering a small test dose to the patient. It is important to be prepared to treat any adverse effects. Keep emergency supplies readily available (e.g., IV fluids, oxygen, antihistamines, corticosteroids, epinephrine, atropine, valium). Patients at increased risk include those with a history of sensitivity to the contrast agent and those with a preexisting condition (e.g., renal disease, hypovolemia, diabetes mellitus).
Procedures in contrast radiography
Although many radiographic contrast studies are less frequently performed in modern veterinary medicine, they still are useful. Endoscopy and advanced imaging modalities such as ultrasonography, computed tomography, and magnetic resonance imaging often yield superior anatomic detail and frequently are less invasive. However, a contrast study can provide valuable diagnostic information, especially when the other modalities are unavailable due to cost, time constraints, travel distance, or other. In the following pages, you will find indications, contraindications, and step‐by‐step procedures for performing many different radiographic contrast studies. Some of the contraindications to performing contrast radiography are listed in Box 2.1.
When performing a contrast study, it is important to proceed in an accurate and systematic manner, paying special attention to the type and volume of contrast medium, the x‐ray exposure settings, patient positioning, and appropriate imaging intervals. Proper patient preparation is essential, including an empty GI tract and empty urinary bladder when required, adequate patient hydration, and a clean and dry hair coat. Patient sedation or anesthesia is recommended whenever practical. A plan of action should be in place for any medical emergencies that may arise.
Any procedure may need to be modified, depending on the specific reason for the study, the type of equipment available, and the status of the patient. The experience of the radiographer is important. During some contrast studies, a new or unexpected radiographic finding leads to a modification of the procedure.
The patient body conformation can alter the recommended dose of a contrast medium because dosage is based on ideal body weight. Patients that are overweight or have a large amount of fluid in a body cavity may require a lower dose.
Always make survey radiographs prior to beginning a contrast study, even if radiographs were made only a few days earlier. Things can change. Survey radiographs are valuable to:
Determine whether the contrast study is needed.
Confirm proper preparation of the patient.
Establish correct settings for kVp and mAs.
Detect abnormalities that may become masked by the contrast medium.
Provide a baseline from which to compare and interpret the contrast study.
The x‐ray exposure used to make survey radiographs usually needs to be adjusted for the contrast radiographs. In most cases, the exposure is doubled for a positive contrast study and cut it in half for a negative contrast study. Doubling the exposure may be accomplished by using twice the mAs or increasing the kVp by 20%. Try to keep the time as short as possible and the kVp as close to 70 as practical. Reducing the exposure usually is accomplished by decreasing the exposure time by half. Alternatively, the kVp can be reduced by 16%.
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