RF Exposure Analysis of an MRI System Based on Thermal Simulation

The increased magnetic field strength in MRI improves the spatial resolution and image quality of the metabolic activity of the human body by increasing the SNR. As the magnetic field increases, the level of RF exposure increases; therefore, extra care should be taken with high-field MRI scans. MRI regulated by IEC 60601-2-33 has been reported in several studies to be inefficient in MRI operation owing to overly conservative SAR-based regulations. The latest revisions to the IEC and ICNIRP show a dramatic increase in the use of temperature-based analytical descriptions. This is mainly because SAR does not consider the thermoregulatory mechanisms of the human body, which makes the SAR exposure levels conservative, whereas temperature-based analyses assume that the thermoregulatory mechanisms of the human body are inherently present. In this study, we synthesized the results of a primate numerical model and thermal simulation in a 1.5 T MRI to analyze the exposure to electromagnetic waves in the MRI and the resulting temperature increase. In addition, we analyzed the results of numerical observations of the impact on body temperature rise when blood flow, a major factor in thermoregulation, was decreased by 90 %, showing a temperature rise of 39.3°C and a CEM43 value of 0.07 min.