Radiographic Anatomy
Owing to the large number of tissues all of much the same density, there is a lack of radiological contrast between the organs of the abdomen. Air in the lungs promotes a contrast effect and greater definition in thoracic radiographs.
However, the presence of fat in the abdomen provides better contrast in older or obese animals, thereby emphasising the outline of the kidneys, spleen, liver and the urinary bladder, for example. Other contrasting materials are gas and radiopaque substances within the lumen of the intestines. Large masses within the intestine may hide other organs and may necessitate emptying of the alimentary tract before radiographic study.Since movement of the animal may cause blurring of the radiograph, sedation or anaesthesia may be necessary. Correct positioning of the abdominal organs is only obtained with the animal standing, particularly when lateral views are required. However, the usual positioning will be in lateral, sternal or dorsal recumbency.
The poor contrast between abdominal tissues may make it difficult to define a specific organ clearly. In these circumstances it may be necessary to administer a contrast medium. This is a radiopaque agent such as barium sulphate or a water-soluble iodine preparation. Barium is given by mouth as a colloidal suspension and is used to investigate the alimentary tract. The iodine compounds are given intravenously and are used especially to identify vascular lesions and for excretion urography.
Whereas in small animals good radiography will demonstrate the liver, spleen, kidneys, urinary bladder, stomach and intestines, other organs, e.g. pancreas, uterus, ovaries and lymph nodes, will not be visible unless they are grossly abnormal.
18.2