Contributors: Justin Goggin, Patsy Whelehan
Species: Canine | Classification: Techniques
- A large amount of information can be obtained from a plain abdominal radiograph if it is produced to a high standard and interpretation skills are high.
- Plain abdominal radiography may need to be supplemented by contrast studies where further information is required about the gastrointestinal, urinary or reproductive tracts.
- Ultrasonography is often a valuable supplementary procedure.
- Image contrast must be maximized as the inherent subject contrast is low, particularly in thinner patients:
- Relatively low kV values.
- Use of a secondary radiation grid where the thickness exceeds about 10 cm.
- Some films and screens have higher inherent contrast than others.
- Breathing blur may occasionally be a problem, particularly when using lower output X-ray machines, but as the film is exposed on expiration, blur is less likely than in thoracic radiography.
Exposure on expiration facilitates better demonstration of abdominal contents, in addition to minimizing risk of breathing movement blur.
- Close collimation of the primary beam should be practised at all times.
- The objective is to produce a radiograph which includes the whole area of interest, is correctly exposed and developed, and is free from movement blur and artefacts.
- The film should be clearly marked with the anatomical marker, the patient's identification, the date and the name of the hospital or practice.
- Assessing size and shape of abdominal organs.
- Detection of gastrointestinal obstruction (gas patterns Intestine: obstruction ).
- Demonstration of radio-opaque or linear gastrointestinal foreign bodies Intestine: linear foreign bodies .
- Detection of peritonitis Peritonitis or free abdominal fluid .
- Detection of radio-opaque urinary calculi Urolithiasis.
- Relatively simple procedure.
- Supplementary procedures, eg ultrasonography or contrast studies are frequently required.
- Shortcomings in technique make interpretation particularly difficult, eg low contrast image may mimic pathology.
- Ultrasonography may be an alternative but is best used in conjunction with radiography.
- Dependent upon the method of chemical restraint (GA or sedation).
- 10-15 min or longer, dependent upon skill of radiographer.
Criteria for choosing test
Is the examination appropriate?
- Can you make the diagnosis without it?
- Can it tell you what you need to know?
- Will your management be affected by the radiological findings?
- Right lateral recumbency - first standard projection. Gives information on size, shape and position of most abdominal organs.
- The second lateral recumbency projection is of some use in plain radiography of the abdomen. It may allow gas in the stomach or intestine to rise and outline other portions of the structure, thus optimising visibility of that structure's lumen, or clarifying its position.
The left lateral may help to separate the kidneys better.
- Second standard projection.
- Gives additonal information on size, shape and position of abdominal organs.
Particularly useful for separating the two kidneys.
Do not attempt ventrodorsal position if pleural fluid is suspected.
- Useful when ventrodorsal positioning is not possible or to cause gas to rise to a different position within a structure.
- Radiographer, or veterinary nurse/technician to carry out radiographic examination.
- X-ray machine.
- Cassettes of sufficient size.
- Grid if thickness of patient >10 cm.
- Processing facilities.
- Immobilization and positioning aids: sandbags, foam wedges.
- Protective clothing (lead-rubber aprons, gloves, thyroid shields).
- High output X-ray machine (500 mA plus).
- Rare earth screens.
- Automatic processing facilities.
- Positioning trough.
- Film label system.
- Film ID camera.
- X-ray film.
- Pharmaceuticals for chemical restraint.
- One to two competent people.
- Foam wedges.
- Positioning trough.
- Remove any radio-opaque objects which may be in the field.
- Ideally, if the study is planned, the patient should be fasted for 24 h and an enema performed to increase visualization of abdominal organs.
- Take patient for walk prior to examination to give an opportunity for defecation. This may improve demonstration of some structures.
Consider enema if necessary.
Muzzle patient if necessary.
Step 1 - Right lateral recumbency
- Place patient in right lateral recumbency on the X-ray table.
- Immobilize with sandbags over the neck and legs .
- Ensure the hindlegs are drawn caudally and are parallel to each other.
- Ensure that the median sagittal plane of the abdomen is parallel to the film. This is likely to require the use of foam pads to raise the sternum and rotate the pelvis.
- The precise centering point can be varied according to the area of the abdomen which is of particular interest, and the size of the dog:
- For a large dog it will often be necessary to take two films to cover the whole abdomen.
- The first can be centered at or cranial to the last rib and the second at the level of the iliac crest.
- A complete study should include the entire diaphragm to the coxofemoral joints.
- There will also be some occasions when it is not necessary to include the whole abdomen, eg survey films for urinary calculi.
- The dorsoventral centring level is midway between the dorsal aspect of the spine and the ventral abdominal wall, including the skin surface.
- Collimate to include these two borders, and the selected area of interest in the craniocaudal direction.
- Expose on expiration.
Step 2 - Ventrodorsal
- Place the patient in dorsal recumbency, using a positioning trough except in cases of very broad, and compliant, patients.
- Immobilize using sandbags, with the hindlimbs in a 'frog-legged' position, weighted across the hocks.
- Ensure that both the thorax and the pelvis are in a true ventrodorsal postion with no rotation to either side.
- Center the beam in the midline at a level ranging from caudal ribs to the coxofemoral joint, depending on particular area of interest, and size of patient .
- Collimate to include lateral skin surfaces and lengthwise area of interest.
- Expose on expiration.
Step 3 - Dorsoventral.
- Place the patient in ventral recumbency.
- Ensure there is no rotation.
- Position hindlimbs away from caudal abdomen as far as is possible. In the anesthetized or very relaxed patient it is possible to extend the hindlimbs caudally in this situation.
This tends to increase the weight on the lungs to the extent that breathing can be restricted.
- Center in the midline at a level ranging from caudal ribs to the coxofemoral joints .
- Collimate to include lateral skin surfaces, and the length of the field of interest.
- Expose on expiration.
Reasons for Treatment Failure
- Inadequate sedation.
- Incomplete study (ventrodorsal and lateral views are required).
- Poor technique: exposure factors, positioning, etc.
- Poor processing.
- Equipment failure.
- Failure to label film properly.