Radio frequency sensing-based in situ temperature measurements during magnetic resonance imaging interventional procedures

Abstract

Magnetic resonance imaging (MRI)-tuned radio-frequency (RF) sensors are used as a radiation-free alternative for tracking minimally invasive medical tool positions. However, in situ temperature sensing capabilities of the MRI-tuned RF sensors have not been thoroughly investigated yet. A self-resonating RF sensor capable of remote in situ temperature sensing during real-time interventional MRI is presented. The proposed RF sensor design relies on the temperature-dependent permittivity to tune or detune the resonant frequency. The sensor is tuned to match the resonant frequency of a 7 Tesla MRI (298 MHz) at body temperature, enabling a hyperintense signal in MR images. As temperature increases, the sensor detunes due to the change in the relative permittivity, and the hyperintense signal disappears in the MR image, serving as a direct visual indicator of the temperature change in real-time. In addition, the localized signal can be used for 3D position tracking of interventional medical devices. Using a 7 Tesla preclinical MRI, in vitro characterization and ex vivo feasibility of the proposed temperature sensing method are demonstrated in the clinically relevant temperature range of 36-42 degrees C with an accuracy of +/- 0.6 degrees C. Such RF sensors can provide safer operations in future MRI interventional procedures.