Diagnostic imaging



Diagnostic imaging


Suzanne Easton



INTRODUCTION


The term radiography covers all the procedures involved in the production and processing of a radiograph. The veterinary nurse is often given the responsibility for positioning the patient, setting up the X-ray machine ready for the exposure and then for processing the radiograph either in an automatic or in a manual processor. It is important that the quality of the resulting radiograph is such that it aids the diagnosis of the veterinary surgeon – if it does not, there is little point in the technique. To achieve a high standard of radiography the nurse must have a clear understanding of the steps involved in each procedure and how each step contributes to the final product. In addition, health and safety considerations are of particular importance when dealing with ionizing radiation and the veterinary nurses must always be aware of the danger to themselves and to others in the vicinity of the machine.


Nowadays, radiography is not the only diagnostic imaging technique available in a veterinary practice. Ultrasonography – the use of high-frequency sound waves to create an image – is becoming commonplace and the veterinary nurse is likely to be responsible for the preparation of the patient and for setting up and maintaining the machine. The advantage of diagnostic ultrasound is that there is little danger to the patient or to the personnel involved in its use.


This chapter describes the procedures involved in the use of both X-rays and ultrasound and in the care of the equipment associated with both diagnostic techniques.





Procedure: Setting up the X-ray machine



1. Action: Place the X-ray machine in the designated room or controlled area.


    Rationale: To ensure that the local rules are followed, the X-ray machine must be used in a specifically designated area as outlined in the rules.


2. Action: Make sure that the radiation warning signs are displayed and visible.


    Rationale: Warning signs must be displayed when X-rays are being used. The position of these warning signs will be specified in the local rules.


3. Action: Plug the machine into the mains.


    Rationale: Most machines rely on mains electricity to work.


4. Action: Switch the X-ray machine on at the console or the main body of the machine.


    Rationale: The machine must be plugged in prior to switching on the machine.


5. Action: Check that the mains voltage compensation is accurate.


    Rationale: Mains voltage compensation ensures that the voltage received by the machine remains constant despite fluctuations within the mains voltage.


6. Action: Adjust the mains voltage compensation if needed.


    Rationale: Without adjustment of the mains voltage, radiographic exposure factors will not be accurate.


7. Action: Set the X-ray tube to the correct height above the film.


    Rationale: The X-ray tube should always be at a standard distance from the film – the film focal distance. This depends on the height of the table and the length of the stand supporting the tube.


8. Action: Set the exposure factors suitable for the examination, patient type and the equipment being used.


    Rationale: Exposure factors depend on the type of machine, the film/screen combination, the size of the patient and the region being examined.



Procedure: Preparing the X-ray room for a radiographic examination



1. Action: Place the X-ray machine in the room and ensure that the correct exposure factors are set.


    Rationale: Setting the exposure factors prior to positioning the patient ensures that once positioned an exposure can be made immediately.


2. Action: Place the cassette on the table and centre it under the centre of the X-ray tube.


    Rationale: The cassette should be placed securely on the table to prevent it falling on to the floor and breaking.


3. Action: If a stationary grid is being used, place this in the correct position over the cassette.


    Rationale: Incorrect use of the grid will result in poor-quality/non-diagnostic images.


4. Action: Place sandbags, ties and foam pads so that they can be easily reached if needed to position the patient.


    Rationale: Sandbags, ties and foam pads are used to hold the patient in the required position.


5. Action: Remove unnecessary equipment from the room.


    Rationale: This includes any objects that may cause an accident or be needed at a later part of the examination.


6. Action: Remove any distractions from the room.


    Rationale: Anything that may prevent the animal cooperating or cause unnecessary distress.



Procedure: Preparing the patient for a radiographic examination



1. Action: Ensure that there is a valid clinical indication for the examination.


    Rationale: Under the Ionising Radiation Regulations 1999, all examinations must be clinically justified and all exposures must be kept to a minimum.


2. Action: Use some form of chemical restraint – either sedation or general anaesthesia – as appropriate to the patient.


    Rationale: Suitable chemical restraint should be used unless the patient is considered to be an anaesthetic risk. Manual restraint should be used only in extreme circumstances as it poses a risk to the health and safety of personnel.


3. Action: Remove any artefacts from the patient, e.g. leads, collars, clips, matted or wet hair.


    Rationale: Artefacts may distract the attention from and may overlie the main point of interest.


4. Action: If required for the procedure, ensure that any preparation of the patient, e.g. fasting, use of an enema or emptying the bladder, has taken place.


    Rationale: In some examinations, the presence of faeces or urine, or food in the stomach may restrict the view of the diagnostic points.


5. Action: Position the animal correctly for the radiograph.


    Rationale: If the animal is conscious and/or sedated, it may be necessary to calm the animal while it is positioned.



POSITIONING THE PATIENT (TABLES 10.1 AND 10.2, FIG. 10.1)


THORAX



Procedure: Lateral thorax (Fig. 10.2)







1. Action: Place the patient in right lateral recumbency.


    Rationale: This is the conventional position for a thoracic radiograph.


2. Action: Extend the forelegs and secure them using sandbags or ties.


    Rationale: Extending the forelegs prevents the soft-tissue mass of the shoulder girdle impeding the view of the thoracic contents.


3. Action: Place a pad under the sternum.


    Rationale: This prevents rotation of the chest and ensures that it is in the same horizontal plane as the spine. This prevents distortion of structures in the thorax.


4. Action: Place sandbags over the neck and hind legs to hold them in place.


    Rationale: The hind legs should be secure but should not be extended as this rotates the chest.


5. Action: Centre the beam (indicated by the cross of the light beam diaphragm) midway between the sternum and spine, level with the caudal border of the scapula.


    Rationale: This ensures that the centre of the primary beam coincides with the base of the heart.


6. Action: Collimate the beam to include the front of the shoulder and the edge of the sternum.


    Rationale: All regions of the lung field will be included.


7. Action: Expose on inspiration.


    Rationale: The lungs are fully inflated during inspiration, which provides better contrast between the air and the soft tissues.



Procedure: Dorsoventral thorax (Fig. 10.3)




1. Action: Place the patient in sternal recumbency.


    Rationale: This is particularly used for examination of the heart.


2. Action: Support the chin on a pad.


    Rationale: This keeps the head, neck and spine in a horizontal plane. The patient may also be more comfortable.


3. Action: Place a sandbag over the neck.


    Rationale: To prevent movement.


4. Action: Extend the forelegs and adduct them with the elbows out to the sides.


    Rationale: This prevents the muscle mass of the shoulder girdle overlying the thoracic cavity.


5. Action: Centre the beam (indicated by the cross of the light beam diaphragm) in the midline on the caudal border of the scapula.


    Rationale: This ensures that the heart base is in the centre of the image.


6. Action: Collimate the beam to include the skin surfaces laterally, the thoracic inlet and the diaphragm.


    Rationale: The image will include the cranial and caudal extent of the lung field.


7. Action: Expose on inspiration.


    Rationale: The lungs are fully inflated during inspiration, which provides better contrast between the air and the soft tissues.


N.B.: A ventrodorsal view of the thorax may be used to examine the lungs; however, if the animal is in respiratory distress, this position should be avoided as it may make respiration even more difficult.



ABDOMEN



Procedure: Lateral abdomen (Fig. 10.4)




1. Action: Place the patient in right lateral recumbency.


    Rationale: This is the conventional position for viewing the abdomen.


2. Action: Place a pad under the sternum.


    Rationale: A pad will support the sternum to keep the body in a horizontal plane.


3. Action: Extend the fore- and hindlimbs and secure them with sandbags or ties.


    Rationale: To prevent movement.


4. Action: Centre the beam (indicated by the cross of the light beam diaphragm) at the 11th/12th intercostal space, just cranial to the last rib.


    Rationale: This ensures that the entire abdomen is included.


5. Action: Collimate the beam to include the dorsal and lateral skin edges, the diaphragm and pubic symphysis. If the patient is large, then move the beam towards the diaphragm or pubic symphysis depending on the area of interest.


    Rationale: The top of the liver should be included in all radiographs of the complete abdomen.


6. Action: Expose on expiration.


    Rationale: During expiration the diaphragm relaxes into its characteristic dome shape and the lungs contract, providing the maximum amount of space for the abdominal contents.



Procedure: Ventrodorsal abdomen (Fig. 10.5)




1. Action: Place the patient in dorsal recumbency.


    Rationale: Care must be taken if the animal is only lightly anaesthetized.


2. Action: Extend each foreleg cranially and secure with a tie or sandbag placed over the carpus.


    Rationale: This prevents rotation of the body. Do not place sandbags over the axillae as this can be uncomfortable.


3. Action: Make sure that the body does not rotate so that the sternum and spine are in vertical alignment.


    Rationale: The use of a trough or sandbags placed on either side may help to support this position.


4. Action: Centre the beam (indicated by the cross of the light beam diaphragm) on the midline at the level of the umbilicus. This point may be adjusted towards the diaphragm or the pubic symphysis in larger breeds of dog.


    Rationale: This ensures that the whole abdominal area is included.


5. Action: Collimate the beam to include the lateral skin surfaces, the diaphragm and the pubic symphysis.


    Rationale: The cranial border of the liver must be shown in an abdominal radiograph.


6. Action: Expose on expiration.


    Rationale: During expiration the diaphragm relaxes into its characteristic dome shape and the lungs contract, providing the maximum amount of space for the abdominal contents.



PELVIS




Procedure: Ventrodorsal pelvis (extended hip position) (Fig. 10.7)

This is the position required by the British Veterinary Association/Kennel Club hip dysplasia scheme. It is important to make sure that the radiograph is correctly positioned as those that are not will be returned to the veterinary surgeon. The radiograph must also be labelled with the dog’s Kennel Club registration number, the date of radiography and left and/or right markers.




1. Action: Place the patient in dorsal recumbency ensuring that the body is straight.


    Rationale: This may be helped by the use of a trough or sandbags placed on either side of the upper abdomen. If the upper body is straight the pelvis should also be straight. If the pelvis rotates, a foam pad may be placed under the lower hip.


2. Action: Extend the hind legs caudally so that the hips and stifles are fully extended. Secure with ties at the hocks.


    Rationale: This will further ensure that the pelvis is straight.


3. Action: Rotate the hind legs medially so that the femurs lie parallel to each other and the patellae are centred over the distal femurs.


    Rationale: Rotation of the femur places the femoral head into the acetabulum, which gives an indication of the degree of hip dysplasia.


4. Action: Hold the femurs together by placing a tie around the level of the mid-femurs. Sticky tape may be a convenient way of doing this.


    Rationale: The use of ties will ensure that the patient remains in this position.


5. Action: Added security may be achieved by placing another tie around the legs at the level of the mid-tibia. Again sticky tape may be of use.


6. Action: Centre the beam (indicated by the cross on the light beam diaphragm) in the midline over the pubic symphysis.


    Rationale: This should provide equal detail on either side of the pelvic girdle.


7. Action: Collimate the beam to include the wings of the ilium and the proximal half of the femurs.


    Rationale: This should demonstrate the entire pelvic girdle and the hip joints. The obturator foramina should be of equal size. Any inequality may be due to tilting of the pelvis and poor positioning.



SKULL



Procedure: Ventrodorsal skull (Fig. 10.8)





Procedure: Open-mouth rostrocaudal view of the tympanic bullae (Fig. 10.9)




1. Action: Place the animal in dorsal recumbency, with the hard palate perpendicular to the cassette. Tip the nose slightly past the vertical.


    Rationale: This position ensures that the bullae are as close as possible to the cassette. By tilting the head, the skull bones do not obstruct the view of the tympanic bullae.


2. Action: Hold the mouth open to form a V-shape, using tapes around each jaw, or place an old needle case (with one end cut off to create a hole) between the teeth of the upper and lower jaws.


    Rationale: In this position, the mandible and the maxilla are removed from the area of interest.


3. Action: Orientate the primary beam parallel to the hard palate and centre it (indicated by the cross of the light beam diaphragm) on the base of the tongue.


    Rationale: The tympanic bullae are located directly behind the base of the tongue in this position.


4. Action: If the animal is intubated, remove the endotracheal tube before exposure.


    Rationale: The endotracheal tube will be superimposed on the tympanic bullae if not removed.



Procedure: Dorsoventral intraoral view of the nasal chambers (Fig. 10.10)




1. Action: The patient must be fully anaesthetized.


    Rationale: The cassette must be placed in the patient’s mouth and without anaesthesia the animal will chew on the film.


2. Action: Place the animal in sternal recumbency.


    Rationale: This position ensures that the maxilla does not overlie the nasal chambers and provides a comfortable supported position for the animal.


3. Action: Extend the neck.


    Rationale: The position of the head is straighter if the neck is extended.


4. Action: Place a sandbag over the neck.


    Rationale: This prevents the head from rotating.


5. Action: Place a non-screen film into the mouth, corner first, as far into the mouth as possible.


    Rationale: Non-screen film is used as it provides excellent definition.


6. Action: Centre the beam (indicated by the cross on the light beam diaphragm) on a line midway between the external nares and the interpupillary line.


    Rationale: This allows visualization of the entire area of the nasal chambers.


7. Action: Place a left/right marker on the relevant side.


    Rationale: This ensures that any lesion can be related to the relevant nasal chamber. Most non-screen film cannot be labelled after processing so this must be done prior to exposure.



Procedure: Nasopharynx (Fig. 10.11)




1. Action: Place the patient in lateral recumbency.


    Rationale: This will provide radiographic access to the nasopharynx.


2. Action: Place pads under the nose and under the neck.


    Rationale: These maintain the skull in a horizontal line and prevent rotation.


3. Action: Pull the forelegs caudally to lie against the wall of the thorax using ties.


    Rationale: This pulls the shoulders and associated soft-tissue structures away from the area of interest.


4. Action: Centre the beam (indicated by the cross on the light beam diaphragm) on the mid cervical area to include the pharynx and thoracic inlet.


    Rationale: The areas cranial and caudal to the pharynx must be included.


5. Action: If the animal is intubated, remove the endotracheal tube before exposure.


    Rationale: The endotracheal tube may mask a stricture or a mass.

Jan 8, 2017 | Posted by in NURSING & ANIMAL CARE | Comments Off on Diagnostic imaging
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