Implant hyperthermia resonant circuit produces heat in response to MRI unit radiofrequency pulses

Abstract

A small resonant circuit was investigated for its potential for producing hyperthermia to treat cancer. Implant hyperthermia has been performed using tiny elements implanted inside the body that are heated by an external energy source. We assessed the effect on heat generation of a resonant circuit used as an implant hyperthermia device by MRI unit radiofrequency (RF) pulses with different imaging sequences. The resonant circuit used as a heating device consisted of a closed connection between a coil and a capacitor. The resonant frequency was set to 63.9 MHz so that the circuit would react and generate heat in response to the RF pulses of a 1.5 T MRI unit. The resonant circuit was placed in the MRI unit with an optical thermometer enclosed by insulating material, and the temperature rise was monitored during imaging sequences. Standard imaging MRI sequences--fast low angle shot gradient echo (FLASH), T1 weighted spin echo image (T1WI) and rapid acquisition with refocused echoes (RARE)--were used to produce RF pulses that affected the resonant circuit. This circuit was gradually heated during all MRI sequences. The temperature rise ranged from 7.2 degrees C to 12.6 degrees C. The highest temperature rise was obtained with RARE, followed by FLASH and T1WI. Thus, this apparatus may have potential for implant hyperthermia, which could provide minimally invasive anticancer therapy.