2Radiographs
Introduction – plan for success
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 2.1 Positioning 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 2.2 V‐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 2.3 The importance of two views. A body part can appear one way from one perspective and quite different in the orthogonal view.
Source: (A) Reuters/Peter Nicholls. (B) Reuters/Hannah Mckay.
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 2.4 Lateral 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 2.5 Ventrodorsal 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 2.6 Anatomical 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 2.1 Veterinary 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 2.7 Anatomical 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.
Positioning guide |
Figure 2.8 Thorax lateral view. | |
A.Positioning
|
![]() |
Figure 2.9 Thorax ventrodorsal (VD) view. | |
Positioning
|
![]() |
Figure 2.10 Thorax dorsoventral (DV) view. | |
Positioning
|
![]() |
Figure 2.11 Thorax VD view with limbs pulled caudal (human view). | |
This is a supplemental radiograph of the thorax made in addition to the standard lateral and VD/DV views.Positioning
|
![]() |
Figure 2.12 Thorax VD oblique view. | |
This is a supplemental radiograph of the thorax made in addition to the standard lateral and VD/DV views.Positioning
|
![]() |
Figure 2.13 Thorax VD tangential view. | |
This is a supplemental radiograph of the thorax made in addition to the standard lateral and VD/DV views.A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.14 Thorax craniodorsal–caudoventral view (skyline view). | |
This supplemental radiograph of the thorax is made in addition to the standard lateral and VD/DV views.A. Positioning
|
![]() |
Figure 2.15 Horizontal beam radiography. |
||
AandC. Positioning
|
![]() ![]() |
Abdominal radiographs |
Figure 2.16 Abdomen lateral view. |
||
A. Positioning
|
![]() |
Figure 2.17 Abdomen ventrodorsal (VD) view. |
||
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.18 Abdomen dorsoventral (DV) view. |
||
A. Positioning
|
![]() |
Figure 2.19 Abdominal compression. |
||
This is a supplemental radiograph of the abdomen made in addition to the standard lateral and VD views.A. Positioning
|
![]() |
Figure 2.20 Abdomen lateral view of urethra. |
||
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
|
![]() |
Appendicular skeleton |
Figure 2.21 Shoulder lateral view (medial‐to‐lateral view). | |
AandB. Positioning
|
![]() |
Figure 2.22 Shoulder cranioproximal–craniodistal view (skyline view). | |
This supplemental radiograph of the shoulder is made in addition to the standard lateral and caudocranial views.A. Positioning
|
![]() |
Figure 2.23 Scapula lateral view. |
||
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.24 Shoulder (or scapula) caudocranial (CrCa) view. | |
A. Positioning
|
![]() |
Figure 2.25 Elbow lateral view (medial‐to‐lateral view). | |
A. Positioning
|
![]() |
Figure 2.26 Elbow flexed lateral view (flexed medial‐to‐lateral view). | |
A. Positioning
|
![]() |
Figure 2.27 Elbow craniocaudal (CrCa) view. | |
AandB. Positioning
|
![]() |
Figure 2.28 Elbow craniolateral–caudomedial oblique (CrLCaMO) view. | |
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.29 Carpus and manus lateral and lateral oblique views. |
||
A. Positioning
|
![]() |
Figure 2.30 Carpus and manus dorsopalmar (DP) view. | |
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.31 Stress radiography. | |
These supplemental views are used to assess joint laxity. They are made in addition to the standard orthogonal views.Aand B. Positioning
|
![]() |
Figure 2.32 Digits mediolateral view. | |
Aand B. Positioning
|
![]() |
Figure 2.33 Digits dorsopalmar or dorsoplantar (DP) view. | |
A. Positioning
|
![]() |
Figure 2.34 Pelvis lateral view. | |
A, B, and C. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.35 Pelvis extended ventrodorsal (VD) view. | |
A. Positioning
|
![]() |
Figure 2.36 Pelvis flexed ventrodorsal (VD) view (frog‐leg view). | |
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.37 Pelvis half‐axial VD view. | |
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
|
![]() |
Figure 2.38 Pelvis dorsal acetabular rim view. | |
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)
|
![]() |
Figure 2.39 Stifle lateral view. | |
A. Positioning
|
![]() |
Figure 2.40 Stifle caudocranial view. | |
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
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
|
![]() |
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
|
![]() |
Figure 2.43 Tarsus mediolateral view. | |
A. Positioning
|
![]() |
Figure 2.44 Tarsus dorsoplantar (DP) view. | |
A. Positioning
|
![]() |
Figure 2.45 Tarsus flexed dorsoplantar view. | |
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
|
![]() |
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
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
Axial skeleton |
Figure 2.47 Head lateral view. | |
Aand B. Positioning
|
![]() |
Figure 2.48 Head dorsoventral (DV) view. | |
Aand B. Positioning
|
![]() |
Figure 2.49 Head lateral oblique 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
|
![]() |
Figure 2.50 Head open‐mouth lateral oblique view. | |
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
|
![]() |
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
|
![]() |
Figure 2.52 Head rostrocaudal 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 frontal sinuses.Aand B. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.53 Head rostrocaudal flexed 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
|
![]() |
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
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.55 Head open‐mouth rostrocaudal view. | |
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
|
![]() |
Figure 2.56 Intra‐oral view of the maxilla. | |
This supplemental radiograph of the head is made in addition to the standard lateral and DV views.A. Positioning
|
![]() |
Figure 2.57 Intra‐oral view of the mandible. | |
This supplemental radiograph of the head is made in addition to the standard lateral and DV views.A. Positioning
|
![]() |
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
|
![]() |
Figure 2.59 Bisecting angle view of tooth. | |
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
|
![]() |
Figure 2.60 Spine positioning. | |
|
![]() |
Figure 2.61 Cervical spine lateral view. | |
A. Positioning
|
![]() |
Figure 2.62 Cervical spine ventrodorsal (VD) view. | |
A and B. Positioning
|
![]() |
Figure 2.63 Thoracic spine lateral view. | |
A. Positioning
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure 2.64 Thoracic spine ventrodorsal (VD) view. | |
A. Positioning
|
![]() |
Figure 2.65 Lumbar spine lateral view. | |
A. Positioning
|
![]() |
Figure 2.66 Lumbar spine ventrodorsal (VD) view. | |
A. Positioning
|
![]() |
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:
|
![]() |
Figure A2. Mottling (film and digital) | |
Other names:
|
![]() |
Figure A3. Overexposure (film and digital) | |
Appearance:
|
![]() |
Figure A4. Overdevelopment (film) | |
Appearance:The entire
|
![]() |
Figure A5. Underexposure (Film and Digital) | |
Appearance:
|
![]() |
Figure A6. Underdevelopment (film) | |
Appearance:
|
![]() |
Figure A7. Uneven development (film) | |
Appearance:
|
![]() |
Figure A8. Yellowish stains (film) | |
Appearance:
|
![]() |
Figures A9–10. Fog (film and digital) | |
Appearance:
|
![]() ![]() |
Figure A11. Safelight test (film) | |
Do this test to evaluate the amount of light fog caused by your safelight:
|
![]() |
Figure A12. Clipping artifact (digital) | |
Other names:
|
![]() |
Figures 13–14. LUT errors (digital) | |
Appearance:
|
![]() ![]() |
Figure A15. Pixelated image (digital) | |
Appearance:
|
![]() |
Figure A16. Planking artifact (digital) | |
Appearance:
|
![]() |
Figures A17–18. Moiré pattern or Aliasing (digital) | |
Appearance:
|
![]() ![]() |
Figure A19. Motion blur (film and digital) | |
Appearance:
|
![]() |
Figure A20. Double exposure (film and digital) | |
Appearance:
|
![]() |
Figure A21. Ghost image (film and digital) | |
Other names:
|
![]() |
Figure A22. Static electricity (film) | |
Appearances:
|
![]() |
Figure A23. Rough handling of film | |
Appearances:
|
![]() |
Figure A24. Local white areas in film | |
Appearance:
|
![]() |
NOTES:
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Figure A25. Local white areas in digital | |
Appearance:
|
![]() |
Figure A26–27. Superimposition of objects outside the patient (film and digital) | |
Appearance:
|
![]() ![]() |
Figure A28–29. Backscatter (film and digital) | |
Appearance:
|
![]() ![]() |
Figure A30. Gridlines (film and digital) | |
Appearance:
|
![]() ![]() |
Figure A31–A34. Grid cutoff (film and digital) | |
Off‐center grid cutoff Appearance:
|
![]() ![]() |
Off‐level grid cutoff Appearance:
|
![]() ![]() |
Off‐focus grid cutoff Appearance:
|
![]() ![]() |
Upside‐down grid cutoff Appearance:
|
![]() ![]() |
Figure A35. Halo effect (digital) | |
Other names:
|
![]() |
Figure A36. Radiofrequency or “zipper” artifact (digital) | |
Appearance:
|
![]() |
Figure A37. Border detection error or Cropping artifact (digital) | |
Appearance:
|
![]() |
Figure A38. Edge enhancement or Mach band/Mach line (film and digital) | |
Appearance:
![]() |
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.
Name | Type | Osmolality | mgI/ml | |
---|---|---|---|---|
Isopaque‐370 (metrizoate) | Ionic | 2100 | High | 370 |
Hypaque‐76, Gastrografin (diatrizoate) | Ionic | 2000 | High | 370 |
Conray‐60 (iothalamate) | Ionic | 1800 | High | 325 |
Hypaque‐50, Renografin‐60 (diatrizoate) | Ionic | 1550 | High | 300 |
Omnipaque‐350 (iohexol) | Non‐ionic | 884 | Low | 350 |
Isovue‐370 (iopamidol) | Non‐ionic | 796 | Low | 370 |
Ultravist‐370 (iopromide) | Non‐ionic | 774 | Low | 370 |
Oxilan‐350 (ioxilan) | Non‐ionic | 695 | Low | 350 |
Optiray‐300 (ioversal) | Non‐ionic | 651 | Low | 300 |
Iomeron‐350 (iomeprol) | Non‐ionic | 618 | Low | 350 |
Hexabrix (ioxaglate) | Ionic | 580 | Low | 320 |
Isovist (iotrolan) | Non‐ionic | 320 | Low | 300 |
Visipaque‐320 (iodixanol) | Non‐ionic | 290 | Low | 320 |
Serum | — | 300 | — | — |
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.
Mild
|
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%.

Full access? Get Clinical Tree

