Noise problem in MR images and its solution during MR-guided microwave surgery

For the image guidance in the interventional microwave surgery, ultrasonography has mainly been utilized. Recently, MR-guided thermotherapy has developed, because MRI can be used not only for image guidance, but also for temperature monitoring. It was reported that noises in MRI during microwave thermocoagulation are negligible under various magnetic fields. We started MR-guided microwave thermocoagulation therapy of liver tumors using a 0.5T GE SIGNA SP/i system. Real time MRIs were useful for image guidance during puncture. However, considerable noise interfered with MRI during microwave irradiation. Microtaze was fixed in a shielded box and a notch filter was inserted in the output line. Afterwards, the noise was reduced to a negligible level. Fluoroscopic monitoring and temperature mapping of MRI during microwave irradiation could be successfully carried out.