[Investigation of the local heating caused by a closed conducting loop at clinical MR imaging: Phantom study]

Several reports have suggested that unusual thermal injuries in magnetic resonance (MR) imaging have occurred due to a closed conducting loop formed accidentally in a part of the patient's body. In this study, we investigated the relationship between the increases in temperature and several parameter settings for MR imaging by use of a human body-equivalent phantom.

A standard clinical 1.5T MR system (SIGNA HORIZON; GE) and a pelvic phased-array coil were used. The human body-equivalent phantom (agar, 0.9% saline, antiseptic) simulated a part of the pelvis and both femurs in a patient. A closed conducting loop could be reproduced when two ends of femurs contacted each other at a point, so that we could measure the temperature changes without and with a closed conducting loop. The temperature of the phantom was measured at the contact point of a closed conducting loop and the center of phantom by use of an optical fiber thermometer which was immune to the influences of radiofrequency (RF) and magnetic and electronic fields. We tested two imaging sequences of spin echo (SE) and fast spin echo (FSE) with 60 minutes of scanning time. In addition to the standard imaging sequences we measured temperature changes without the RF irradiation or gradient magnetic fields. The average temperature changes were recorded from five measurements which were repeated at intervals of more than one day.

When the closed conducting loop was reproduced, the temperatures at the contact point significantly increased (p<0.001) compared with the temperatures at the center of phantom. The temperature changes at 60 minutes of scanning time were 7.0 and 8.1 degrees C by use of the SE and FSE, respectively. There were no significant temperature changes when the imaging was performed without the RF irradiation.

Our result obtained by use of a human body-equivalent phantom demonstrated that local heating, which can lead to thermal injuries accidentally, could occur when a closed conducting loop was formed in part of the patient body. CLINICAL RELEVANCE/APPLICATION: Radiologists should be more careful about local heating which can occur in patients during clinical MR imaging by a closed conducting loop.