While standard radiographic and ultrasound imaging techniques are common diagnostic tools in exotic animal medicine, the use of more advanced imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) currently appear to be underutilized for exotic patients.
Let's begin with the upper urinary tract – the kidneys and ureters. Knowing normal anatomy is of course initially necessary to perform an adequate ultrasound examination. You should always scan in two planes (sagittal and transverse). The right kidney is harder to visualize as it is located at the level of T13 and is located in the caudate fossa of the liver.
Before pathology can be discussed, the normal appearance of the liver, biliary system, and pancreas will be reviewed. Determination of liver size via US is not accurate and is best done on radiographs. Ultrasound is best performed with the animal in dorsal recumbency (on their back) and the area must be clipped free of hair.
Indications for an esophagram include regurgitation, gagging or retching, dysphagia, cough associated with eating, as well as the presence of a mediastinal, cervical, or thoracic mass. The pertinent anatomy to remember is that in the cat the caudal 1/3 of the esophagus is smooth muscle.
Radiology is like standing on the outside of the building; it allows you to see the size, shape and contour of the building; ultrasound allows you to look into each room in the building i.e. the liver room, the gallbladder room, the pancreas room, the kidney room, the urinary bladder room etc.
Initially we have to review all the normal structures on a thoracic radiograph before we can begin to discuss pathology. So a review....There are three main normal structures in the lungs: the interstitium, airways, and vessels. The interstitium is the supporting structure of the lungs.
The survey ultrasound study is primarily used to assess soft tissue composition and in some cases function (echocardiogram) as well as guide you in biopsying "soft tissue" lesions. It has limited value in assessing bone-primarily restricted to the bone surface and it has no value in evaluating gas other than letting you know gas is present.