A Steerable Stylet for the Transjugular Intrahepatic Portosystemic Shunt Procedure

Abstract

In recent years, more and more medical operations are done minimally invasive. Intervention radiology is a medical specialty which uses minimally invasive techniques to diagnose, or treat diseases. Instruments like needles and catheters are used by radiologists to enter the network of veins and arteries guided by image modalities. A complex treatment in the interventional radiology is the Transjugular Intrahepatic Portosystemic Shunt (TIPS) procedure. This treatment is developed for people who suffer from liver cirrhosis which are not eligible for liver transplantation. The problem which arise with a liver affected by cirrhosis is that it can not transmit enough blood. Without transplantation or a treatment this will eventually lead to death. During the TIPS procedure a connection is made between the right hepatic and the portal vein by a shunt. As a result, blood pressure reduction in the portal system since the blood can flow back to the right atrium of the heart, bypassing the liver.

The hardest part in a TIPS procedure is the intrahepatic puncture between the hepatic and portal vein. The interventional radiologist tries to enter the portal vein by puncturing a small stylet from the hepatic vein through the liver tissue. Due to cirrhosis the liver tissue is very stiff and stylet deflection will occur. To reduce the uncertainty of entering the portal vein, this thesis is focused on designing a stylet that is more stiff and able to steer. It is expected that the complexity of the procedure will be reduced and a higher hit rate to enter the portal vein will be achieved.\
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The prototype of the steerable stylet has been evaluated through various experiments, a visibility test and with procedures in a test liver model. During these experiments the steering characteristics, the stiffness of the stylet, the maximum lateral forces exerted by the tip while steering, the influence of the stylet orientation and the visibility are obtained. Afterwards, an evaluation was done in a liver model, made of PVA, to determine whether the stylet is capable to reduce the complexity of the intrahepatic puncture step in the TIPS procedure.

With the prototype made in this graduation project, based on a steerable ablation needle, the complexity of the TIPS procedure is not reduced yet. The steerable stylet was not able to enter the portal vein. It was already hard to enter the right hepatic vein since the pre-bent stiffening cannula was adapted with a smaller angle which was necessary since the steerable stylet was too stiff to push through the pre-bent angle. According to this prototype, possibilities are shown to use a mechanical steering mechanism in instruments with a long thin shaft. The transmission in combination with the joint mechanisms fits within 1.3mm diameter, was able to bridge 60cm from distal end to proximal end and had only 4 components, the stylet, the rigid cannula, the key to fix the stylet to the rigid cannula and the transmission. By translating the stylet in a push or pull direction relative to the rigid cannula, steering angles could be achieved. With further research and development this steering mechanism must be able to steer the required amount of degrees without any extra components, is well visible with ultrasound, and is good resistant against lateral forces.