COMPARISON OF TRANSCOLONIC ¹²³I‐IODOAMPHETAMINE AND PORTAL VEIN INJECTION OF ^99mTc‐MACROAGGREGATED ALBUMIN SHUNT FRACTION CALCU‐LATIONS IN EXPERIMENTAL DOGS WITH ACQUIRED POR‐TOSYSTEMIC SHUNTS

Abstract

Shunt fraction was determined using transcolonic 123I‐iodoamphetamine (IMP) and portal vein injection of 99mTc‐macroaggregated albumin (MAA) in a group of eight dogs with chronic cirrhosis and acquired portosystemic shunts subsequent to total common bile duct ligation. Hepatic parenchymal damage was confirmed by alterations in liver function tests and liver histology. Seven of the eight dogs developed portal hypertension and had angiographic evidence of hepatofugal portal blood flow with multiple peripheral portosystemic anastomoses. Shunt fractions determined in the seven dogs with shunts varied from 39 to 100 using IMP and 45 to 93 using MAA. The remaining dog had normal portal pressure, a normal portal angiogram, and normal IMP and MAA scintigraphic studies. There was an excellent correlation between the two methods of shunt fraction calculation (R2= 0.98) and the line of regression was not significantly different from unity (IMP = 1.09 × MAA ‐ 0.03).

Evaluation ofIn VivoBehavior of Ameroid Ring Constrictors in Dogs with Congenital Extrahepatic Portosystemic Shunts Using Computed Tomography

“…There is normally a very large difference between dogs with portosystemic shunting (>80% SF) and those without (<15 ± 5% error). Because of the known limitations of calculating shunt fraction, and as most dogs in our study weighed <5 kg, shunt fractions of up to 20% in dogs with complete CPS occlusion were considered to be normal. Presence of blood in the heart before the liver was used as a discrimination of shunt fraction, rather than the numerical value, to account for these variances .…”

Evaluation of interoperator variance in shunt fraction calculation after transcolonic scintigraphy for diagnosis of portosystemic shunts in dogs and cats

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The current imaging agent of choice for portoscintigraphy is sodium pertechnetate Tc 99m (Na 99m TcO 4 ). Several radiopharmaceuticals and methods of administration have been investigated.…”

“…Shunting is diagnosed if radiopharmaceutical activity is identified in the heart prior to the liver or if simultaneous activity in both organs is detected. 8 It has been postulated that the disparity in shunt fraction values between Na 99m TcO 4 and IMP is a reflection of the inherent inability to appropriately model the complex kinetics of Na 99m TcO 4 tracer uptake and distribution, and that differences in determination of organ ROI and time-zero selection among individuals are not substantial. 14 Shunt fractions are calculated in an empirical attempt to quantify the percentage of total portal blood flow that is diverted through 1 or more shunt vessels.…”

“…When radiopharmaceutical activity is detected in the liver a minimum of 2 seconds before it is detected in the heart, shunting is ruled out. 8 Approximately 100 portoscintigraphic studies are performed at our institution yearly. Regions of interest (ROI) for the heart and liver are typically hand-drawn from a composite image that comprises multiple still frames acquired during the initial pass of radiopharmaceutical through the portal vein to the heart.…”