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Portasystemic Shunt Fraction Quantification with Colonic Iodine-123 Iodoamphetamine

Departments of Nuclear Medicine and Surgery, San Francisco General Hospital Medical Center and University of California, San Francisco
Department of Nuclear Medicine, Presbyterian Hospital of San Francisco
Medi-Physics, Inc., Richmond, California

Correspondence: For reprints contact: Chi-Kwan Yen, MD, Dept. of Nuclear Medicine, Bldg. 100, San Francisco General Hospital Medical Center, 1001 Potrero Ave., San Francisco, CA 94110.

ABSTRACT

Portasystemic shunting was quantified in dogs with [¹²³I]iodoamphetamine (IMP) administered transrectally into the colon and monitored externally with a gamma camera. IMP was absorbed rapidly and unchanged from the colon. After direct injection into the portal vein, IMP was almost completely extracted by the liver on the first pass, and the washout half-life was 60 min. Based on these kinetic data, computer simulation of this biologic system was carried out. Errors associated with simplified models are calculated. The simplest model with insignificant error, which assumed that the tracer behaved like microspheres, was used to quantitate portasystemic shunt fraction in animals with surgically created shunts. Results were compared with the standard of ^99mTc-labeled macroaggregated albumin infused into a branch of inferior mesenteric vein. For shunt fractions ranging from 0 to 100%, an excellent correlation was seen, indicating that this approach is potentially a simple, noninvasive method of portasystemic shunt fraction quantification.