Electromagnetic simulation of RF burn injuries occurring at skin-skin and skin-bore wall contact points in an MRI scanner with a birdcage coil.

Abstract

To simulate radiofrequency (RF) burns that frequently occur at skin-skin and skin-bore wall contact points. RF burn injuries (thumb-thigh and elbow-bore wall contacts) that typically occur on the lateral side of the body during 1.5T magnetic resonance imaging (MRI) scans were simulated using a computational human model. The model was shifted to investigate the influence of the position of the patient in an MRI scanner. The specific absorption rate (SAR), electric field, and temperature were mapped. Regarding the contact points located near the edge of the birdcage transmission coil, under the allowable maximum RF power exposure i.e., the average whole-body SAR at the safety limit value (2W/kg), the 10-g-tissue-averaged SAR (SAR10g) at those points significantly increased for both the thumb-thigh (180W/kg) and elbow-bore wall (48W/kg) cases. Both values significantly exceeded the highest safety limit of the partial-body SAR (10W/kg). The electric field, the square of which is proportional to SAR, was remarkably high near the edge of the birdcage transmission coil. The peak SAR10g for each injury case was associated with contact-point peak temperatures that reached 52°C at approximately 1min following RF exposure onset; a 1-min period of exposure to this temperature causes a first-degree burn. We demonstrated high heat generation in RF burn injury cases in silico. The RF heating occurring on the lateral side of the body was strongly dependent on the electric field distribution, which is dominantly determined by an RF transmission coil.