In vivo human head MRI at 10.5T: A radiofrequency safety study and preliminary imaging results

Sadeghi‐Tarakameh, Alireza; DelaBarre, Lance; Lagore, Russell; Torrado‐Carvajal, Angel; Wu, Xiaoping; Grant, Andrea; Adriany, Gregor; Metzger, Gregory J.; Moortele, Pierre-François Van de; Uğurbil, Kâmil; Atalar, Ergin; Eryaman, Yiğitcan

doi:10.1002/mrm.28093

Cited by 63 publications

(87 citation statements)

References 38 publications

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“…This limitation is a major impediment to expanding the spatiotemporal scale of fMRI applications as well as the utility, interpretation, and ultimate impact of fMRI data. One strategy to alleviate this limitation is to pursue even higher magnetic fields [11][12][13] . Another simple and commonly used approach is the implementation of longer scan sessions, though this approach is not always optimal, since cognitive responses are modulated by attention and internal mental states, which likely change over long scan sessions.…”

Section: Introductionmentioning

confidence: 99%

Lowering the Thermal Noise Barrier in Functional Brain Mapping with Magnetic Resonance Imaging

Vizioli

Moeller

Dowdle

et al. 2020

Preprint

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Functional magnetic resonance imaging (fMRI) has become one of the most powerful tools for investigating the human brain. However, virtually all fMRI studies have relatively poor signal-to-noise ratio (SNR). We introduce a novel fMRI denoising technique, which removes noise that is indistinguishable from zero-mean Gaussian-distributed noise. Thermal noise, falling in this category, is a major noise source in fMRI, particularly, but not exclusively, at high spatial and/or temporal resolutions. Using 7-Tesla high-resolution data, we demonstrate remarkable improvements in temporal-SNR, the detection of stimulus-induced signal changes, and functional maps, while leaving stimulus-induced signal change amplitudes, image spatial resolution, and functional point-spread-function unaltered. We also provide supplementary data demonstrating that the method is equally applicable to supra-millimeter resolution 3- and 7-Tesla fMRI data, different cortical regions, stimulation/task paradigms, and acquisition strategies. The proposed denoising approach is expected to have a transformative impact on the scope and applications of fMRI to study the brain.

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Section: Introductionmentioning

confidence: 99%

Lowering the Thermal Noise Barrier in Functional Brain Mapping with Magnetic Resonance Imaging

Vizioli

Moeller

Dowdle

et al. 2020

Preprint

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“…The SAR efficiency of the 16-channel LD antenna array in the ROI of the phantom is ~7 % higher than the 8-channel dipole antenna and 8-channel loop arrays. Our 16 channel LD array may benefit from the increased distance of the array elements from the sample, which can improve SAR efficiency, as was recently demonstrated by Sadeghi-Tarakameh, et al [15]. Further supporting material is demonstrated in the supplementary Fig.…”

Section: Resultsmentioning

confidence: 64%

“…However, the short wavelength in the human body at such frequencies contributes to a significantly non-uniform field distribution [10][11][12]. Upon expanding the highest MR field strength from 4 tesla (T) [13] to 7 T [5], [12] then to 10.5 T [14], [15], it became apparent that more control over the transmit field was required to achieve acceptable imaging uniformity in the human body. Considering an average relative permittivity (εr) of 50 for water dominated tissue types at UHF for 10.5 T proton based imaging, the resulting shortened wavelength (~95 mm) leads to the type of non-uniform field distribution in the head at 10.5 T previously experienced in the torso at 7 T [16], [17].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a 16-Channel Transceiver Loop + Dipole Antenna Array for Human Head Imaging at 10.5 Tesla

et al. 2020

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We evaluated a 16-channel loop + dipole (LD) transceiver antenna array with improved specific absorption rate (SAR) efficiency for 10.5 Tesla (T) human head imaging applications. Three different array designs with equal inner dimensions were considered: an 8-channel dipole antenna, an 8channel loop, and a 16-channel LD antenna arrays. Signal-to-noise ratio (SNR) and B1 + efficiency (in units of µT per √W) were simulated and measured in 10.5 T magnetic resonance imaging (MRI) experiments. For the safety validation, 10 g SAR and SAR efficiency (defined as the B1 + over √ (peak 10 g SAR)) were calculated through simulation. Finally, high resolution porcine brain images were acquired with the 16channel LD antenna array, including a fast turbo-spin echo (TSE) sequence incorporating B1 shimming techniques. Both the simulation and experiments demonstrated that the combined 16-channel LD antenna array showed similar B1 + efficiency compared to the 8-channel dipole antenna and the 8-channel loop arrays in a circular polarized (CP) mode. In a central 2 mm × 2 mm region of the phantom, however, the 16-channel LD antenna array showed an improvement in peak 10 g SAR of 27.5 % and 32.5 % over the 8channel dipole antenna and the 8-channel loop arrays, respectively. We conclude that the proposed 16channel head LD antenna array design is capable of achieving ~7% higher SAR efficiency at 10.5 T compared to either the 8-channel loop-only or the 8-channel dipole-only antenna arrays of the same dimensions. INDEX TERMS dipole antenna array, human head array, loop array, magnetic resonance imaging, RF coil, ultra-high field

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“…This approach works especially well when the target of interest is relatively far away from the coil (i.e., prostate imaging). A similar advantage may also be present for head imaging studies at UHF, 33,34 especially for spectroscopy studies that aim to maximize B + 1 -power efficiency at a single voxel near the middle of the brain. 35 We demonstrated the advantage of adding bumps for SAR reduction using three transmit elements; loop coils and snake antennas at 7T, and fractionated dipoles at 10.5T.…”

Section: Discussionmentioning

confidence: 99%

Improving radiofrequency power and specific absorption rate management with bumped transmit elements in ultra‐high field MRI

Sadeghi‐Tarakameh

Adriany

Metzger

et al. 2020

Magnetic Resonance in Med

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Purpose In this study, we investigate a strategy to reduce the local specific absorption rate (SAR) while keeping B1+ constant inside the region of interest (ROI) at the ultra‐high field (B0 ≥ 7T) MRI. Methods Locally raising the resonance structure under the discontinuity (i.e., creating a bump) increases the distance between the accumulated charges and the tissue. As a result, it reduces the electric field and local SAR generated by these charges inside the tissue. The B1+ at a point that is sufficiently far from the coil, however, is not affected by this modification. In this study, three different resonant elements (i.e., loop coil, snake antenna, and fractionated dipole [FD]) are investigated. For experimental validation, a bumped FD is further investigated at 10.5T. After the validation, the transmit performances of eight‐channel arrays of each element are compared through electromagnetic (EM) simulations. Results Introducing a bump reduced the peak 10g‐averaged SAR by 21, 26, 23% for the loop and snake antenna at 7T, and FD at 10.5T, respectively. In addition, eight‐channel bumped FD array at 10.5T had a 27% lower peak 10g‐averaged SAR in a realistic human body simulation (i.e., prostate imaging) compared to an eight‐channel FD array. Conclusion In this study, we investigated a simple design strategy based on adding bumps to a resonant element to reduce the local SAR while maintaining B1+ inside an ROI. As an example, we modified an FD and performed EM simulations and phantom experiments with a 10.5T scanner. Results show that the peak 10g‐averaged SAR can be reduced more than 25%.

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In vivo human head MRI at 10.5T: A radiofrequency safety study and preliminary imaging results

Cited by 63 publications

References 38 publications

Lowering the Thermal Noise Barrier in Functional Brain Mapping with Magnetic Resonance Imaging

Lowering the Thermal Noise Barrier in Functional Brain Mapping with Magnetic Resonance Imaging

Evaluation of a 16-Channel Transceiver Loop + Dipole Antenna Array for Human Head Imaging at 10.5 Tesla

Improving radiofrequency power and specific absorption rate management with bumped transmit elements in ultra‐high field MRI

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