scholarly journals Effect of radiofrequency shield diameter on signal‐to‐noise ratio at ultra‐high field MRI

2021 ◽  
Vol 85 (6) ◽  
pp. 3522-3530
Author(s):  
Bei Zhang ◽  
Gregor Adriany ◽  
Lance Delabarre ◽  
Jerahmie Radder ◽  
Russell Lagore ◽  
...  
Keyword(s):  
High Field ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Ultra High Field ◽  
High Field Mri ◽  
Ultra High Field Mri ◽  
Noise Ratio

scholarly journals The “Loopole” Antenna: A Hybrid Coil Combining Loop and Electric Dipole Properties for Ultra-High-Field MRI

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Karthik Lakshmanan ◽  
Martijn Cloos ◽  
Ryan Brown ◽  
Riccardo Lattanzi ◽  
Daniel K. Sodickson ◽  
...  
Keyword(s):  
Current Distribution ◽  
Electric Dipole ◽  
High Field ◽  
High Performance ◽  
Signal To Noise Ratio ◽  
Ultra High Field ◽  
High Field Mri ◽  
Electric Dipoles ◽  
Ultra High Field Mri ◽  
Free Current

Purpose. To revisit the “loopole,” an unusual coil topology whose unbalanced current distribution captures both loop and electric dipole properties, which can be advantageous in ultra-high-field MRI. Methods. Loopole coils were built by deliberately breaking the capacitor symmetry of traditional loop coils. The corresponding current distribution, transmit efficiency, and signal-to-noise ratio (SNR) were evaluated in simulation and experiments in comparison to those of loops and electric dipoles at 7 T (297 MHz). Results. The loopole coil exhibited a hybrid current pattern, comprising features of both loops and electric dipole current patterns. Depending on the orientation relative to B0, the loopole demonstrated significant performance boost in either the transmit efficiency or SNR at the center of a dielectric sample when compared to a traditional loop. Modest improvements were observed when compared to an electric dipole. Conclusion. The loopole can achieve high performance by supporting both divergence-free and curl-free current patterns, which are both significant contributors to the ultimate intrinsic performance at ultra-high field. While electric dipoles exhibit similar hybrid properties, loopoles maintain the engineering advantages of loops, such as geometric decoupling and reduced resonance frequency dependence on sample loading.

scholarly journals Improving Signal to Noise Ratio in Ultra High Field Magnetic Resonance Imaging

2021 ◽  
Author(s):  
Nader Tavaf
Keyword(s):  
Human Brain ◽  
High Field ◽  
Signal To Noise Ratio ◽  
Noise Correlation ◽  
Resonance Imaging ◽  
Mr Images ◽  
Signal To Noise ◽  
Ultra High Field ◽  
Noise Ratio ◽  
Receive Array

Ultra-High Field (UHF) Magnetic Resonance Imaging (MRI) advantages, including higher image resolution, reduced acquisition time via parallel imaging, and better signal-to-noise ratio (SNR) have opened new opportunities for various clinical and research projects, including functional MRI, brain connectivity mapping, and anatomical imaging. The advancement of these UHF MRI performance metrics, especially SNR, was the primary motivation of this thesis. Unaccelerated SNR depends on receive array sensitivity profile, receiver noise correlation and static magnetic field strength. Various receive array decoupling technologies, including overlap/inductive and preamplifier decoupling, were previously utilized to mitigate noise correlation. In this dissertation, I developed a novel self-decoupling principle to isolate elements of a loop-based receive array and demonstrated, via full-wave electromagnetic/circuit co-simulations validated by bench measurements, that the self-decoupling technique provides inter-element isolation on par with overlap decoupling while self-decoupling improves SNR. I then designed and constructed the first self-decoupled 32 and 64 channel receiver arrays for human brain MR imaging at 10.5T / 447MHz. Experimental comparisons of these receive arrays with the industry’s gold-standard 7T 32 channel receiver resulted in 1.81 times and 3.53 times more average SNR using the 10.5T 32 and 64 channel receivers I built, respectively. To further improve the SNR of accelerated MR images, I developed a novel data-driven model using a customized conditional generative adversarial network (GAN) architecture for parallel MR image reconstruction and demonstrated that, when applied to human brain images subsampled with rate of 4, the GAN model results in a peak signal-to-noise ratio (PSNR) of 37.65 compared to GeneRalized Autocalibrating Partial Parallel Acquisition (GRAPPA)’s PSNR of 33.88.In summary, the works presented in this dissertation improved the SNR available for human brain imaging and provided the experimental realization of the advantages anticipated at 10.5T MRI. The insights from this thesis inform future efforts to build self-decoupled transmit arrays and high density, 128 channel loop-based receive arrays for human brain MRI especially at ultra-high field as well as future studies to utilize deep learning techniques for reconstruction and post-processing of parallel MR images.

An Electrically Long Ultra-High Field MRI Volume Body Coil Design

2021 ◽  
Author(s):  
Sayim Gokyar ◽  
Henning U. Voss ◽  
Fraser Robb ◽  
Douglas J. Ballon ◽  
Simone Angela Winkler
Keyword(s):  
High Field ◽  
Coil Design ◽  
Ultra High Field ◽  
High Field Mri ◽  
Body Coil ◽  
Ultra High Field Mri

scholarly journals Ultra high field MRI (150 micron) assessment of the structural elements of the knee entheses in healthy subjects

Bone Reports ◽  
2020 ◽  
Vol 13 ◽  
pp. 100525
Author(s):  
Damien Roche ◽  
Constance Michel ◽  
Pierre Daudé ◽  
Arnaud Le Troter ◽  
Christophe Chagnaud ◽  
...  
Keyword(s):  
Healthy Subjects ◽  
High Field ◽  
Structural Elements ◽  
Ultra High Field ◽  
High Field Mri ◽  
Ultra High Field Mri
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