Ultrasound can be very useful in investigating various disease processes, but especially those of the abdomen. It is likely that you pet will be given some sedation and their hair clipped over the abdomen in order that high quality ultrasound images can be achieved which will help advance their diagnosis.
Image guided biopsies
Very commonly ultrasound can be used to guide needle biopsy of areas of disease within the patient. Under sedation or general anaesthesia the ultrasound image allows the careful placement of the biopsy tool (often just a hypodermic needle) into the area of interest without damaging surrounding areas. Then samples can be retrieved for examination at the external lab.