Abstract
Thermal Magnetic Resonance (ThermalMR) leverages radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. To advance RF heating with multi-channel RF antenna arrays and overcome the shortcomings of current RF signal sources, this work reports on a 32-channel modular signal generator (SGPLL). The SGPLL was designed around phase-locked loop (PLL) chips and a field-programmable gate array chip. To examine the system properties, switching/settling times, accuracy of RF power level and phase shifting were characterized. Electric field manipulation was successfully demonstrated in deionized water. RF heating was conducted in a phantom setup using self-grounded bow-tie RF antennae driven by the SGPLL. Commercial signal generators limited to a lower number of RF channels were used for comparison. RF heating was evaluated with numerical temperature simulations and experimentally validated with MR thermometry. Numerical temperature simulations and heating experiments controlled by the SGPLL revealed the same RF interference patterns. Upon RF heating similar temperature changes across the phantom were observed for the SGPLL and for the commercial devices. To conclude, this work presents the first 32-channel modular signal source for RF heating. The large number of coherent RF channels, wide frequency range and accurate phase shift provided by the SGPLL form a technological basis for ThermalMR controlled hyperthermia anti-cancer treatment.
Highlights
Temperature is a critical parameter of life with diverse biological implications and intense clinical interest
In a ThermalMR setting, the radio frequency (RF) signal could potentially come from the MR scanner; the current maximum number of independent transmission RF channels in a state-of-the-art MR scanner is constrained to a single TX channel for the combined mode transmission regime and eight or sixteen for the parallel transmission mode with RF signals being constrained to a small transmitter bandwidth covering a fixed center frequency (Larmor frequency)
The compact modular phase-locked loop (PLL) based design implemented in this study provides a theoretically unlimited number of coherent, independent RF channels and a wide frequency range, facilitating future
Summary
Temperature is a critical parameter of life with diverse biological implications and intense clinical interest. The aberrant thermal properties of pathological tissue have led to a strong interest in temperature as a clinical parameter. Mild regional hyperthermia (HT, T = 40–44 ◦ C) is a potent sensitizer for chemotherapy (CH) and radiotherapy (RT), and a clinically proven adjuvant anti-cancer treatment in conjunction with RT and/or CH that significantly improves survival [1,2,3,4,5,6,7]. HT devices are increasingly capable of the personalized radio frequency (RF)-induced heating of target tissue volumes guided by sophisticated treatment planning procedures and thermal dose control [10,11,12,13,14,15,16,17]. Thermal Magnetic Resonance (ThermalMR) is an HT variant that accommodates
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