NUMERICAL AND EXPERIMENTAL STUDY OF MRI RF SIGNAL INTERACTIONS WITH VARIOUS MEDICAL DEVICES

This dissertation consists of three topics related to the RF-induced heating on medical devices in the magnetic resonance imaging (MRI) system. The first topic is the RF heating for passive medical devices. Electromagnetic simulation using the Finite Difference Time Domain (FDTD) method and thermal simulation are applied to understand the potential temperature increase inside the human body when the patient with an implantable device undergoes the MR scanner. Measurements are performed to validate simulation results. For devices with multiple components and complex structures, e.g., the external fixation devices, the RF heating mechanism is discussed extensively by investigating various parameters that can contribute to the device’s RF heating effect. The second topic is the RF heating for active implantable medical devices (AIMDs). It is studied using alternative approaches due to the fine features inside leads attached to AIMDs. The Tier 2 approach proposed by the International Electrotechnical Commission (IEC) is used to study the RF effect on leads tip under different configurations such as coil dimension, patient loading location in MRI, tissue properties as well as leads winding pattern. Due to the overestimation of the Tier 2 approach, another method based on the reciprocity theorem is used to establish the relationship between incident fields and field intensity at leads tip to estimate the temperature rise. This method is proven to be a powerful method to estimate the RF heating for leads structure on AIMDs. The third topic covers the measurement uncertainty of using fiber optic thermal probes in the RF heating assessment. The fiber optic probes which are used to measure temperature rise around the medical device can lead to significant temperature variation from the original temperature without probes. Three medical devices have been investigated to quantify the effect on the change of temperature rise due to the existence of thermal probes. It is found that thermal probes have more influence on the temperature rise around small and tiny structures such as screws and leads.