RF-induced heating of interventional devices at 23.66 MHz.

OBJECTIVE: Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.66 MHz) with a focus on the effect of patient size, target organ, and device position on maximum temperature rise. MATERIALS AND METHODS: To assess RF-induced heating, high-resolution measurements of the electric field, temperature, and transfer function were combined. Realistic device trajectories were derived from vascular models to evaluate the variation of the temperature increase as a function of the device trajectory. At a low-field RF test bench, the effects of patient size and positioning, target organ (liver and heart) and body coil type were measured for six commonly used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle). RESULTS: Electric field mapping shows that the hotspots are not necessarily localized at the device tip. Of all procedures, the liver catheterizations showed the lowest heating, and a modification of the transmit body coil could further reduce the temperature increase. For common commercial needles no significant heating was measured at the needle tip. Comparable local SAR values were found in the temperature measurements and the TF-based calculations. CONCLUSION: At low fields, interventions with shorter insertion lengths such as hepatic catheterizations result in less RF-induced heating than coronary interventions. The maximum temperature increase depends on body coil design.

Transauricular arterial access for hepatic artery embolization in rabbit VX2 liver tumor.

PURPOSE: The purpose of this study is to evaluate the feasibility of percutaneous transauricular artery access for hepatic artery catheterization using a peripherally inserted central catheter (PICC) device and hepatic artery catheterization through auricular approach. METHODS: Ten New Zealand White rabbits were used to establish a VX2 liver tumor model. Hepatic artery angiography and embolization were performed 3 weeks after inoculation. The rabbits were restrained in supine position under anesthesia. Intra-arterial access was accomplished with percutaneous Seldinger technique through the auricular artery using a PICC device. The hepatic artery catheterization was performed with a microcatheter and guide wire. The rate of technical success and procedure time was investigated. RESULTS: Two rabbits failed initial percutaneous transauricular arterial access, with success in a contralateral attempt. Thus, percutaneous transauricular arterial access was achieved in 10 of 12 auricular arteries, with a technical success rate of 83.3%. The time needed to obtain intra-auricular access was 7.2 ± 3.1 min. Hepatic artery catheterization, angiography, and embolization were accomplished through the auricular approach in all 10 rabbits. CONCLUSION: Arterial access in rabbits can be achieved through the auricular artery. Hepatic artery catheterization, angiography, and embolization can be performed through auricular arterial access.