Tissue warming and regulatory responses induced by radio frequency energy deposition on a whole‐body 3‐Tesla magnetic resonance imager

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Abstract
Purpose To quantify the B1‐field induced tissue warming on a 3T‐whole‐body scanner, to test whether the patient is able to sense the temperature change, and to evaluate whether the imaging procedure constitutes a significant cardiovascular stress. Materials and Methods A total of 18 volunteers were divided into three equal groups for 3.0T MRI of the pelvis, the head, or the knee. An imaging protocol operating at first level mode was applied, allowing radio frequency (RF) irradiation up to the legal specific absorption rate (SAR) limits. An identical placebo protocol with active gradient switching but without RF transmission was used. Temperature changes were measured with a fiber‐optic thermometer (FO) and an infrared camera (IR). Results Temperature differences to the placebo were highest for imaging of the pelvis (FO: ΔT = 0.88 ± 0.13°C, IR: ΔT = 1.01 ± 0.15°C) as compared to the head (FO: ΔT = 0.46 ± 0.12°C, IR: ΔT = 0.47 ± 0.10°C) and the knee (FO: ΔT = 0.33 ± 0.11°C, IR: ΔT = 0.37 ± 0.09°C). The volunteers were able to discriminate between imaging and placebo for pelvic (P < 0.0001) and head (P = 0.0005) imaging but not for knee imaging (P = 0.209). No changes in heart rate or blood pressure were detected. Conclusion The 3.0T MRI in the first operational mode may lead to measurable and perceptible thermal energy deposition. However, it may be regarded as safe concerning the thermoregulatory cardiovascular stress. J. Magn. Reson. Imaging 2007;26:1334–1339.