Thermal Effects Associated with RF Exposures in Diagnostic MRI: Overview of Existing and Emerging Concepts of Protection

Figure 3

(a) Estimated core temperature increase for a 70kg human using the simplified assessment proposed in [26], to demonstrate sensitivity on several model parameters. The lower (orange and red) lines show the significant dependence on room temperature (orange versus red lines), clothing (dotted versus solid lines), and thermoregulatory health of the patient. The upper (blue and green) lines show that room humidity is a less important parameter to control, even at high RF deposition (4 W/kg)

(b) Estimated core temperature increase for a 70kg human with normal thermoregulation [26], at different environmental conditions, and for three levels of Specific Absorption (80, 160, and 240 W.min/kg), up to a SAR level of 4 W/kg. Each graph represents an iso-SA line, and the corresponding SA value (e.g., 160 W.min/kg for the lowest dashed blue line) divided by the scan or examination duration provides the average whole-body SAR. For example, a duration of 80 min and SA = 160 W.min/kg correspond to an average SAR of 2 W/kg and a predicted core temperature rise of approx. 0.2°C. Similarly, a duration of 40 min on the same line corresponds to an average SAR 4 W/kg and a predicted temperature increase of 0.7°C. Notably, the predictions for SA of 80 W.min/kg correspond reasonably well with the data in Table 1 (estimated 1 clo, room temperature not specified but likely close to 23°C)

(c) Representative estimates of core temperature increase for a 70kg human with impaired thermoregulation, at different environmental conditions, and for three levels of Specific Absorption (80,160, and 240 W.min/kg), up to a SAR level of 2 W/kg