Design of a High Selectivity Filter for MRI Guided RF Hyperthermia Therapy

Hyperthermia devices have been integrated with MR scanners to exploit MR thermometry. Integrating two RF systems require the filtering of high-power RF heating signal from MR system for simultaneous heating and imaging. Currently, a filter that suppresses 100MHz and its harmonics is in use. Development of a MR-compatible hyperthermia applicator for head and neck requires a filter that can suppress also the 433.92MHz signal. A unique new filter which has high power handling, extremely high suppression, and selectivity has been designed that attenuates 100MHz and 433.92MHz signals with low insertion loss (<0.25dB) at 63.89MHz. 0.14dB insertion loss at 63.89MHz, 112dB, 88dB and 93dB signal attenuation were achieved at 100MHz, 200MHz and 433.92MHz, respectively, with the new filter design using model of LM-500 cable. A proof of concept filter was constructed to validate the design. Our investigation shows that filter requirements can be satisfied, but high-power low-loss coaxial cables are necessary.