Thallium scintigraphy in the evaluation of portal systemic shunting. The problem of rectal absorption.

Thallium-201 scintigraphy is an attractive method for studying the portal systemic shunting. However, the technique is sometimes hampered by a low rectal absorption. The present work shows that cirrhotic patients present a significantly lower activity in the regions of interest in relation to the low absorption of the tracer as compared with non-cirrhotic subjects (p less than 0.01). This study also demonstrates that the dilution of the tracer in a large volume cannot be envisaged in order to increase the surface contact and secondarily the absorption, because part of the tracer can reach the inferior vena cava via portal systemic communications in the lower part of the rectum. Oral administration of the thallium was also attempted but this route cannot be used in relation to its poor absorption and due to the difficulty in separating liver from intestinal activity. The study also shows that even in the case of low activity in the regions of interest, the interpretation of the test in cirrhotic patients is usually possible on the condition that the curves of radioactivity in the liver and cardiac areas are ascending. Using these criteria, only 6.7% of the tests were in fact not interpretable in this study.