Abstract
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 T* relaxation without an impact on the efficiency of RF heating. Three different T* reducing compounds were investigated, namely CuSO, MnCl, and FeO. First, electromagnetic properties and T* 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 FeO 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. MnCl showed a similar MRT improvement, but caused unacceptable RF-power losses. We conclude that adding FeO has significant potential to improve RF hyperthermia treatment monitoring under MR guidance.
Highlights
Clinical trials have shown that the clinical outcome and local control of chemotherapy and radiotherapy treatments can be enhanced with the addition of hyperthermia treatments [1,2,3,4,5]
We focused on MR guided RF hyperthermia treatments but our findings can be applied for MR guided high intensity focused ultrasound (HIFU) applications
Removal of water bolus (WB) signal will result in similar improvements in MR thermometry (MRT) precision as we have shown in this study as shown in [22]
Summary
Advances in hyperthermia technologies improved the delivery of the treatment [6,7,8]. Electromagnetic radiofrequency systems consists of multiple antennas organized in an annular array configuration and using constructive interference provides focused energy deposition at depth, whereby the location of the focus can be dynamical adapted using phase and amplitude control per antenna [9,10]. The frequency range is 70–120 MHz, for deep heating of head and neck tumors the frequency range is 400–600 MHz. A multi-functional water bolus is used to reduce the antenna size, cool the skin and obtain a preferential energy transfer to the tissue. A multi-functional water bolus is used to reduce the antenna size, cool the skin and obtain a preferential energy transfer to the tissue
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