Abstract. TIPS (Transjugular Intrahepatic Portosystemic Shunt) is an effective treatment for portal hypertension. However, during the procedure, respiration, needle pressure, and possibly other factors cause the liver to move. This complicates the procedure since the portal vein is not visible during needle insertion. We present the results of a study of intraoperative liver motion.

Transjugular intrahepatic portosystemic shunt formation (TIPS) is an effective treatment for portal hypertension [LaBerge 1995]. The procedure requires the insertion of a needle through the liver to connect the hepatic and portal veins. This operation is traditionally guided by fluoroscopic images that do not show the location of the target veins during needle insertion. We propose to provide the clinician an interactive, three-dimensional (3D), stereo display so that the position and orientation of the clinician's needle can be seen relative to the target vasculature intraoperatively. This paper describes the visualizations we are providing for intraoperative guidance.

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Creation of a Transjugular Intrahepatic Portosystemic Shunt (TIPS) requires passage of a needle toward a moving target that is only seen transiently by x-ray prior to needle passage. Intraoperative, 3D target localization would facilitate target access and improve the safety of the procedure. The clinical assumption is that patients undergoing the TIPS procedure possess rigid, cirrhotic livers that undergo only intraoperative translation without significant deformation or rotation. Based upon this assumption, we hypothesize that the position of any unseen, 3D target point within the liver can be determined intraoperatively by precalculation of the relative positions of the target point to a different 3D point that can be tracked intraoperatively. This paper examines this hypothesis using intraoperatively acquired, biplane, x-ray images of 7 patients. In 6, we tracked the effects of cardiac and respiratory motion, and in 3 the effects of needle pressure. Methods involved reconstruction of 3D vessel bifurcation and other trackable intrahepatic points from biplane angiograms, measurement of liver deformation by examining changing distances between these 3D points over time, and comparison of expected to actual displacements of these points with respect to a fixed reference point in the liver. We conclude that, for the rigid livers associated with patients undergoing TIPS, that there is less intraoperative deformation than previously reported by other groups addressing healthy liver deformation, and that the location of an unseen target can be predicted within 3 mm accuracy.

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