The Potential of Adjusting Water Bolus Liquid Properties for Economic and Precise MR Thermometry Guided Radiofrequency Hyperthermia

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 2 * relaxation without an impact on the efficiency of RF heating. Three different T 2 * reducing compounds were investigated, namely CuSO 4 , MnCl 2 , and Fe 3 O 4 . First, electromagnetic properties and T 2 * 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 Fe 3 O 4 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 2 showed a similar MRT improvement, but caused unacceptable RF-power losses. We conclude that adding Fe 3 O 4 has significant potential to improve RF hyperthermia treatment monitoring under MR guidance.

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

“…In addition to the SNR benefits, the integrated coil-array also allows for the use of advanced MR techniques, such as parallel imaging, to enable faster acquisition times (from 8.7 s in this study to 2–4 s) for correction of the impact of respiratory motion. Earlier, we showed that a further increase in SNR and acquisition speed can be achieved by using iron oxide nanoparticles in the water bolus to enable reducing the imaging field of view [ 46 ]. All benefits combined can further help the adoption of MR-guided hyperthermia treatments and pave the way for wider acceptance in the clinic.…”

External Basic Hyperthermia Devices for Preclinical Studies in Small Animals

“…MR imaging and -thermometry on the other hand could benefit from presence of the water bolus by homogenizing the magnetic field, called “shimming”. Sumser et al observed that for hyperthermia purposes, the water bolus fluid should be spiked with Fe 3 O 4 nanoparticles in order to improve the signal-to-noise ratio [ 57 ]. This is in contrast to standard water baths, which frequently use demineralized water.…”

Microstrip coils for MR‐imaging with induced RF heating for hyperthermia

“…[2][3][4][5][6][7] Moreover, MRI is the most often used noninvasive way to estimate the temperature, whilst undergoing hyperthermia therapy. [8][9][10][11][12] With the use of high-field MRI, researchers have analysed the characteristics and diagnosis methods of cancerous organs using a human phantom model. 12,13 In case studies involving small animal experiments, where a heating and temperature monitoring system is used, it is vital to precisely measure the energy translation properties (excitation power, duration of temperature and simulation period) to establish a robust hyperthermia protocol in clinical trials.…”

“…This method is capable of diagnosing and differentiating between healthy and cancerous tissues 2–7 . Moreover, MRI is the most often used non‐invasive way to estimate the temperature, whilst undergoing hyperthermia therapy 8–12 . With the use of high‐field MRI, researchers have analysed the characteristics and diagnosis methods of cancerous organs using a human phantom model 12,13 .…”