The potential of MR thermometry (MRT) fostered the development of MRI compatible radiofrequency (RF) hyperthermia devices. Such device integration creates major technological challenges and a crucial point for image quality is the water bolus (WB). The WB is located between the patient body and external sources to both couple electromagnetic energy and to cool the patient skin. However, the WB causes MRT errors and unnecessarily large field of view. In this work, we studied making the WB MRI transparent by an optimal concentration of compounds capable of modifying T2 * relaxation without an impact on the efficiency of RF heating. Three different T2 * reducing compounds were investigated, namely CuSO4, MnCl2, and Fe3 O4. First, electromagnetic properties and T2 * relaxation rates at 1.5 T were measured. Next, through multi-physics simulations, the predicted effect on the RF-power deposition pattern was evaluated and MRT precision was experimentally assessed. Our results identified 5 mM Fe3 O4 solution as optimal since it does not alter the RF-power level needed and improved MRT precision from 0.39◦ C to 0.09◦ C. MnCl2 showed a similar MRT improvement, but caused unacceptable RF-power losses. We conclude that adding Fe3 O4 has significant potential to improve RF hyperthermia treatment monitoring under MR guidance.

Dielectric properties, Hyperthermia, MR thermometry, MRI guided interventions, MRI properties, Water bolus,
Sensors (Basel, Switzerland)
Department of Radiation Oncology

Sumser, K. (Kemal), Bellizzi, G.G, van Rhoon, G.C, & Paulides, M.M. (2020). The potential of adjusting water bolus liquid properties for economic and precise MR thermometry guided radiofrequency hyperthermia. Sensors (Basel, Switzerland), 20(10). doi:10.3390/s20102946