Heat equation inversion framework for average SAR calculation from magnetic resonance thermal imaging

Alon, Leeor; Sodickson, Daniel K.; Deniz, Cem M.

doi:10.1002/bem.21996

Cited by 15 publications

(16 citation statements)

References 27 publications

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“…The SAR varies spatially and temporally in the tissue and it often requires averaging over a prescribed mass or volume. The measurement of SAR by thermal methods is also complicated and it requires the determination of thermal transport parameters [47,[50][51][52] to assess SAR accurately.…”

Section: Introduction To This Studymentioning

confidence: 99%

Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time

Gültekin

Siegel

2020

IEEE Access

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The rapid release of 5G wireless communications networks has spurred renewed concerns regarding the interactions of higher radiofrequency (RF) radiation with living species. We examine RF exposure and absorption in ex vivo bovine brain tissue and a brain simulating gel at three frequencies: 1.9 GHz, 4 GHz and 39 GHz that are relevant to current (4G), and upcoming (5G) spectra. We introduce a highly sensitive thermal method for the assessment of radiation exposure, and derive experimentally, accurate relations between the temperature rise (ΔT), specific absorption rate (SAR) and the incident power density (F), and tabulate the coefficients, ΔT/ΔF and Δ(SAR)/ΔF, as a function of frequency, depth and time. This new method provides both ΔT and SAR applicable to the frequency range below and above 6 GHz as shown at 1.9, 4 and 39 GHz, and demonstrates the most sensitive experimental assessment of brain tissue exposure to millimeter-wave radiation to date, with a detection limit of 1 mW. We examine the beam penetration, absorption and thermal diffusion at representative 4G and 5G frequencies and show that the RF heating increases rapidly with frequency due to decreasing RF source wavelength and increasing power density with the same incident power and exposure time. We also show the temperature effects of continuous wave, rapid pulse sequences and single pulses with varying pulse duration, and we employ electromagnetic modeling to map the field distributions in the tissue. Finally, using this new methodology, we measure the thermal diffusivity of ex vivo bovine brain tissue experimentally.

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Section: Introduction To This Studymentioning

confidence: 99%

Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time

Gültekin

Siegel

2020

IEEE Access

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“…For all 4 studies, the proposed complex difference‐based L+S CS reconstruction method was compared to a previously published complex difference‐based L 1 +TV CS reconstruction method, and the conventional L+S CS reconstruction method . Studies were first performed on the 4 data sets with all available 12 time frames as input (denoted as “All”) to demonstrate the feasibility of the proposed method for retrospective applications such as evaluating MRgFUS treatment outcome and quantification of tissue thermal properties, Bioheat equation coefficients, and biological response to temperature elevations . Then, the reconstructions were repeated with input data from the first time frame up to each reconstructed time frame (denoted as “Up‐to”), for the simulated 8 channel beef RF heating data and the experimental 8 channel in vivo MRgFUS data, to demonstrate the feasibility of the proposed method for prospective applications such as real‐time RF heating evaluation and FUS guidance.…”

Section: Methodsmentioning

confidence: 99%

Low‐rank plus sparse compressed sensing for accelerated proton resonance frequency shift MR temperature imaging

Cao

Gore

Grissom

2019

Magnetic Resonance in Med

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Purpose To improve multichannel compressed sensing (CS) reconstruction for MR proton resonance frequency (PRF) shift thermography, with application to MRI‐induced RF heating evaluation and MR guided high intensity focused ultrasound (MRgFUS) temperature monitoring. Methods A new compressed sensing reconstruction is proposed that enforces joint low rank and sparsity of complex difference domain PRF data between post heating and baseline images. Validations were performed on 4 retrospectively undersampled dynamic data sets in PRF applications, by comparing the proposed method to a previously described L1 and total variation‐ (TV‐) based CS approach that also operates on complex difference domain data, and to a conventional low rank plus sparse (L+S) separation‐based CS reconstruction applied to the original domain data. Results In all 4 retrospective validations, the proposed reconstruction method outperformed the conventional L+S and L1+TV CS reconstruction methods with a 3.6× acceleration ratio in terms of temperature accuracy with respect to fully sampled data. For RF heating evaluation, the proposed method achieved RMS error of 12%, compared to 19% for the L+S method and 17% for the L1+TV method. For in vivo MRgFUS thalamotomy, the peak temperature reconstruction errors were 19%, 31%, and 35%, respectively. Conclusion The complex difference‐based low rank and sparse model enhances compressibility for dynamic PRF temperature imaging applications. The proposed multichannel CS reconstruction method enables high acceleration factors for PRF applications including RF heating evaluation and MRgFUS sonication.

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“…Conventional SAR measurement systems are based on the electrical and magnetic field measurements and temperature distribution on the tissues [29][30][31]. In the literature, SAR values have been calculated accurately by using magnetic resonance thermal images and phantom thermal properties [32]. Varshini and Rama Rao proposed that the thermal distribution measurement using infrared thermography is a simple and effective technique that can be parallel to SAR or power density measurements to determine the suitability of wearable devices for various wireless applications or biocompatibility [17].…”

Section: Our Studymentioning

confidence: 99%

Experimental and Computational Analysis of the Effects of Tri-Band Antennas of Wearable Smart Glasses

Geyikoğlu¹,

Kaburcuk²,

Çavuşoğlu³

2019

PIER C

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The goal of this study is to analyze the effect of tri-band antennas in 2.45, 3.6, 3.8, 4.56, and 6 GHz frequencies, which cover Wi-Fi and some of the future 5G frequencies for wearable smart glasses applications. The latter 4 frequencies are studied for the first time for smart glasses. In order to provide a thorough analysis, first a simulation study for the head model with the proposed antennas is performed, then a realistic experiment by using a semi-liquid gel phantom head model with the infrared thermography method is conducted, and also 4 male subjects are included to analyze temperature rise effects on the skin. The phantom prepared for this study is also validated for its robustness and matching parameters. The SAR values and temperature rise due to the usage of smart glasses calculated by simulation modeling, bio-heat analytical solution, and infrared thermography technique are in good agreement. The temperature rise of the skin regions gets monotonically increased in the duration of usage. The simulations for all indicated frequencies are performed. Also, to provide comparable and practical results, the phantom study is compared with simulations for 2.45 GHz. According to the quantitative data obtained on the liquid-gel head phantom and on the subjects, the temperature increase is below 1 • C, and its compliance with safety standards is determined. The results show that tri-band antennas for these frequencies can be safely used; however, a limiting behavior for the power is necessary for lower frequencies due to the increasing SAR values and temperature rise.

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Heat equation inversion framework for average SAR calculation from magnetic resonance thermal imaging

Cited by 15 publications

References 27 publications

Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time

Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time

Low‐rank plus sparse compressed sensing for accelerated proton resonance frequency shift MR temperature imaging

Experimental and Computational Analysis of the Effects of Tri-Band Antennas of Wearable Smart Glasses

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