Purpose: Thermal intervention is a potent sensitizer of cells to chemo-and radiotherapy in cancer treatment. Glioblastoma multiforme (GBM) is a potential clinical target, given the cancer's aggressive nature and resistance to current treatment options. The annular phased array (APA) technique employing electromagnetic waves in the radiofrequency (RF) range allows for localized temperature increase in deep seated target volumes (TVs). Reports on clinical applications of the APA technique in the brain are still missing. Ultrahigh field magnetic resonance (MR) employs higher frequencies than conventional MR and has potential to provide focal temperature manipulation, high resolution imaging and noninvasive temperature monitoring using an integrated RF applicator (ThermalMR). This work examines the applicability of RF applicator concepts for ThermalMR of brain tumors at 297 MHz (7.0 Tesla). Methods: Electromagnetic field (EMF) simulations are performed for clinically realistic data based on GBM patients. Two algorithms are used for specific RF energy absorption rate based thermal intervention planning for small and large TVs in the brain, aiming at maximum RF power deposition or RF power uniformity in the TV for 10 RF applicator designs. Results: For both TVs, the power optimization outperformed the uniformity optimization. The best results for the small TV are obtained for the 16 element interleaved RF applicator using an elliptical antenna arrangement with water bolus. The two row elliptical RF applicator yielded the best result for the large TV. Discussion: This work investigates the capacity of ThermalMR to achieve targeted thermal interventions in model systems resembling human brain tissue and brain tumors.
Purpose Cardiorenal syndrome describes disorders of the heart and the kidneys in which a dysfunction of 1 organ induces a dysfunction in the other. This work describes the design, evaluation, and application of a 4/4‐channel hydrogen‐1/sodium (1H/23Na) RF array tailored for cardiorenal MRI at 7.0 Tesla (T) for a better physiometabolic understanding of cardiorenal syndrome. Methods The dual‐frequency RF array is composed of a planar posterior section and a modestly curved anterior section, each section consisting of 2 loop elements tailored for 23Na MR and 2 loopole‐type elements customized for 1H MR. Numerical electromagnetic field and specific absorption rate simulations were carried out. Transmission field (B1+) uniformity was optimized and benchmarked against electromagnetic field simulations. An in vivo feasibility study was performed. Results The proposed array exhibits sufficient RF characteristics, B1+ homogeneity, and penetration depth to perform 23Na MRI of the heart and kidney at 7.0 T. The mean B1+ field for sodium in the heart is 7.7 ± 0.8 µT/√kW and in the kidney is 6.9 ± 2.3 µT/√kW. The suitability of the RF array for 23Na MRI was demonstrated in healthy subjects (acquisition time for 23Na MRI: 18 min; nominal isotropic spatial resolution: 5 mm [kidney] and 6 mm [heart]). Conclusion This work provides encouragement for further explorations into densely packed multichannel transceiver arrays tailored for 23Na MRI of the heart and kidney. Equipped with this technology, the ability to probe sodium concentration in the heart and kidney in vivo using 23Na MRI stands to make a critical contribution to deciphering the complex interactions between both organs.
The objective of this study was the design, implementation, evaluation and application of a compact wideband self-grounded bow-tie (SGBT) radiofrequency (RF) antenna building block that supports anatomical proton ( 1 H) MRI, fluorine ( 19 F) MRI, MR thermometry and broadband thermal intervention integrated in a wholebody 7.0 T system. Design considerations and optimizations were conducted with numerical electromagnetic field (EMF) simulations to facilitate a broadband thermal intervention frequency of the RF antenna building block. RF transmission (B 1 + ) field efficiency and specific absorption rate (SAR) were obtained in a phantom, and the thigh of human voxel models (Ella, Duke) for 1 H and 19 F MRI at 7.0 T. B 1 + efficiency simulations were validated with actual flip-angle imaging measurements. The feasibility of thermal intervention was examined by temperature simulations (f = 300, 400 and 500 MHz) in a phantom. The RF heating intervention (P in = 100 W, t = 120 seconds) was validated experimentally using the proton resonance shift method and fiberoptic probes for temperature monitoring. The applicability of the SGBT RF antenna building block for in vivo 1 H and 19 F MRI was demonstrated for the thigh and forearm of a healthy volunteer. The SGBT RF antenna building block facilitated 19 F and 1 H MRI at 7.0 T as well as broadband thermal intervention (234-561 MHz). For the thigh of the human voxel models, a B 1 + efficiency ≥11.8 μT/√kW was achieved at a depth of 50 mm. Temperature simulations and heating experiments in a phantom demonstrated a temperature increase ΔT >7 K at a depth of 10 mm.The compact SGBT antenna building block provides technology for the design of integrated high-density RF applicators and for the study of the role of temperature in
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