Consideration of physiological response in numerical models of temperature during MRI of the human head

Purpose: To examine the thermal effects of the physiological response to heating during exposure to radiofrequency (RF) electromagnetic fields in magnetic resonance imaging (MRI) with a head-specific volume coil. Materials and Methods: Numerical methods were used to calculate the temperature elevation in MRI of the human head within volume coils from 64-400 MHz at different power levels both with and without consideration of temperature-induced changes in rates of metabolism, perspiration, radiation, and perfusion. Results: At the highest power levels currently allowed in MRI for head volume coils, there is little effect from the physiological response as predicted with existing methods. This study does not rule out the possibility that at higher power levels or in different types of coils (such as extremity or whole-body coils) the physiological response may have more significant effects. Conclusion: In modeling temperature increase during MRI of the human head in a head-sized volume coil at up to 3.0 W/kg head-average specific energy absorption rates, it may not be necessary to consider thermally induced changes in rates of metabolism, perfusion, perspiration, and radiation.