Novel considerations in computed tomography for feline lung and hepatic imaging and cholangiography

Abstract

Cats with respiratory and hepatobiliary disease commonly present to veterinary hospitals with non-specific clinical signs, making a timely diagnosis difficult. Imaging plays an important role in the diagnosis of these diseases to accurately prognosticate and guide therapeutic options to improve the patient’s outcome. The aim of this thesis is to investigate some novel applications for CT using Gd-EOB-DTPA in hepatic imaging and cholangiography and body position in lung imaging. To evaluate contrast hepatobiliary imaging, three doses of Gd-EOB-DTPA were used for hepatic CT and cholangiography in healthy cats to determine the optimal timing for hepatobiliary image acquisition and to evaluate the contrast-enhanced hepatobiliary anatomy. It was proven that Gd-EOB-DTPA was safe to use in healthy cats at a dose of up to 0.3 mmol/kg with no adverse clinical signs. Using CT, each increase in dose of contrast medium resulted in a significant increase in attenuation measured by HU across the hepatobiliary system including the liver, gall bladder, cystic duct and common bile duct. There was a positive relationship in contrast enhancement with increasing dose of contrast medium.

In a separate study, thoracic CT was used to evaluate and quantify the effect of time and recumbency on CT measurements of lung volume and attenuation in healthy cats under general anaesthesia. A separate group of cats was anaesthetized and positioned in different recumbencies. It was determined that cats in lateral recumbency, have a significantly greater lung attenuation (HU) and lower volume on CT in the dependent lung than the non-dependent lung. Within the dependent lung, there was a significantly higher percentage of poorly aerated lung tissue (- 500 to -101 HU) compared to the non-dependent lung. These changes occurred immediately after positioning in lateral recumbency and remained static with no further significant time related change.