Radiography: abdomen

• 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 gastro-intestinal tract, urinary tract or reproductive tract.
• 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.
  • Some films 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 artifacts.
• 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 gastro-intestinal obstruction (gas patterns).
• Demonstration of radio-opaque or linear gastro-intestinal foreign bodies Intestine: foreign body - linear.
• Detection of peritonitis Peritonitis  or free abdominal fluid  .
• Detection of pregnancy  .
• Detection of radio-opaque urinary calculi Urolithiasis             .

Advantages

• Non-invasive.
• Relatively simple procedure.

Disadvantages

• 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 more often used in conjunction with radiography.

Preparation

• Dependent upon the method of chemical restraint. (General anesthetic or sedation.)

Procedure

• 10 - 15 mins, 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?

Choosing the right projections

• Lateral recumbency:
  • Right lateral recumbency - first standard projection. Gives information on size, shape and position of most abdominal organs.
  • The second lateral recumbency projection is of limited use in plain radiography of the abdomen. It may allow a gas bubble (eg in the stomach), to rise and fill the opposite side of the structure, thus optimizing visibility of that structure's lumen, or clarifying its position.
• Ventrodorsal:
  • Ventrodorsal - 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.
• Dorsovental:
  • Dorsoventral - useful when ventrodorsal positioning is not possible, or to cause gas to rise to a different position within a structure.

Other involvement

• Radiographer / Technician carrying out radiographic examination.

Minimum equipment

• X-ray machine.
• Cassettes of sufficient size.
• Processing facilities.
• Immobilization and positioning aids: sandbags, foam wedges.
• Protective clothing (lead-rubber aprons).

Ideal equipment

• High output X-ray machine (500mA plus).
• Rare Earth screens.
• Automatic processing facilities.
• Positioning trough  Radiography: positioning aids .

Minimum consumables

• X-ray film.
• Pharmaceuticals for chemical restraint.

• One to two competent people.
• Sandbags   .
• Foam wedges.
• Positioning trough.

• Remove any radio-opaque objects which may be in the field.
  Consider enema 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.
• There will also be many occasions when it is not necessary to include the whole abdomen, particularly on follow-up films and the centering point can be chosen to suit the purpose.
• The dorsoventral centering 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 position with no rotation to either side.
• Center the beam in the midline at a level ranging from caudal ribs to iliac crest, depending on particular area of interest and size of patient.
• Collimate to include lateral skin surfaces and lengthwise area of interest
  Take into account the long slope of the diaphragm and be careful not to cut off the cranioventral abdomen inadvertently.
• Expose on expiration.

Step 3 - Dorsoventral

• Place the patient in ventral recumbency.
• Immobilize.
• 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 iliac crest.
• Collimate to include lateral skin surfaces, and the length of the field of interest.
• Expose on expiration.

• Inadequate sedation.
• Poor technique: exposure factors, positioning, etc.
• Poor processing.
• Equipment failure.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Shiroma J T, Gabriel J K, Carter R L et al (1999) Effect of reproductive state on feline renal size. Vet Radiol Ultrasound 40 (3), 242-245 PubMed.
• Miles K (1997) Imaging abdominal masses. Vet Clin North Am Small Anim Pract 27 (6), 1403-1431 PubMed.
• Fucci V, Pechman R D, Hedlund C S et al (1995) Large bowel transit times using radiopaque markers in normal cats. JAAHA 31 (6), 473-477 PubMed.
• Wolvekamp W T (1994) Basic principles of abdominal radiography. Vet Q 16 (Suppl 1), 40S-42S PubMed.
• Tiemessen I, Wolvekamp W T (1991) Diagnostic imaging in small animals - ultrasonographic and radiographic examination of thorax and abdomen - a comparison. Tijdschr Diergeneeskd 116 (Suppl 1), 54S-55S PubMed.