On the heating of linear conductive structures as guide wires and catheters in interventional MRI

Abstract

The interest in performing vascular interventions under magnetic resonance (MR) guidance has initiated the evaluation of the potential hazard of long conductive wires and catheters. The objective of this work is to present a simple analytical approach to address this concern and to demonstrate the agreement with experimental results. The first hypothesis is that a long conductive structure couples with the electric field of the radio frequency (RF) transmit coil. The second hypothesis is that this coupling induces high voltages near the wire ends. These voltages can cause tissue heating due to induced currents. The experimental results show an increase in coupling when moving a guide wire toward the wall of an RF transmit coil, documented with a temperature increase of a saline solution in close proximity to the tip of the guide wire. The coupling of the wire not only presents a potential hazard to the patient, but also interferes with the visualization of the wire. A safe alternative would be the use of nonconducting guide wires. J. Magn. Reson. Imaging 2001;13:105–114. © 2001 Wiley‐Liss, Inc.

B1 field-insensitive transformers for RF-safe transmission lines

“…Here, the segmented cable heated up by 3.5 K, whereas the unsegmented cable showed a temperature increase of up to 30 K. It was confirmed that RF-induced heating is highly dependent on the position of the active tracking device within the transmitting body resonator [13,14]. Close to the magnet bore and to the end rings of the bird-cage body resonator high electric field components are present which lead to the strongest temperature increases.…”

“…In combination with fast projection measurements interventional devices can thus be localized in a few milliseconds [7][8][9][10]. Unfortunately, potentially dangerous resonant heating can occur with active devices [11][12][13][14], which arises from resonant coupling of the RF transmit field with conducting structures that are in contact with dissipative materials.…”

Whole-body MRI at high field: technical limits and clinical potential

“…Especially metallic parts surrounded by aqueous media tend to show resonance effects even for smaller extensions owing to shorter wavelengths [49][50][51]. The conditions for RF resonance circuits and for RF antennas are more easily obtained by implants and metallic instruments, e.g., aspiration needles.…”

An overview on the advances in cardiovascular interventional MR imaging

“…Commercially available endovascular devices are in most cases not appropriate for MR imaging because (1) ferromagnetic components receive strong attractive forces from the magnet; (2) conductive materials could distort the radiofrequency (RF) field; and (3) long electrical conductors could cause significant heating effects in the MR environment [48]. It has been confirmed that long conductive instruments cause heating during the RF excitation (especially when using real-time sequences with high flip angles and short repetition times) [49]. Ladd and Quick placed resonant structures (chokes) into the conducting miniaturized cables to prevent the onset of RF-induced resonant waves on the cables [50].…”