Experimental Validation of the MRcollar: An MR Compatible Applicator for Deep Heating in the Head and Neck Region

SIMPLE SUMMARY: Hyperthermia treatments where tumor tissue is heated to 40–44 °C for 60–90 min can be hampered by a lack of accurate temperature monitoring. To solve this need, we have designed an MR compatible head and neck hyperthermia applicator: the MRcollar. In this work, we experimentally validated the design, heating capabilities and the MR compatibility of the MRcollar. The MRcollar antennas efficiently transfer the power and have low interaction between the antenna elements. The heating and focusing capabilities satisfy the requirements. The MRcollar can operate in an MR scanner and it can acquire higher quality MR images due to the built in receiver elements. The MRcollar has great potential to improve hyperthermia treatment in the head and neck region and it is now ready for in vivo studies. ABSTRACT: Clinical effectiveness of hyperthermia treatments, in which tumor tissue is artificially heated to 40–44 °C for 60–90 min, can be hampered by a lack of accurate temperature monitoring. The need for noninvasive temperature monitoring in the head and neck region (H&N) and the potential of MR thermometry prompt us to design an MR compatible hyperthermia applicator: the MRcollar. In this work, we validate the design, numerical model, and MR performance of the MRcollar. The MRcollar antennas have low reflection coefficients (<−15 dB) and the intended low interaction between the individual antenna modules (<−32 dB). A 10 °C increase in 3 min was reached in a muscle-equivalent phantom, such that the specifications from the European Society for Hyperthermic Oncology were easily reached. The MRcollar had a minimal effect on MR image quality and a five-fold improvement in SNR was achieved using the integrated coils of the MRcollar, compared to the body coil. The feasibility of using the MRcollar in an MR environment was shown by a synchronous heating experiment. The match between the predicted SAR and measured SAR using MR thermometry satisfied the gamma criteria [distance-to-agreement = 5 mm, dose-difference = 7%]. All experiments combined show that the MRcollar delivers on the needs for MR—hyperthermia in the H&N and is ready for in vivo investigation.