Investigating the Influence of Spatial Constraints on Ultimate Receive Coil Performance for Monkey Brain MRI at 7 T

Gao, Yang; Chen, Weidao; Zhang, Xiaolin

doi:10.1109/tmi.2018.2812151

Cited by 11 publications

(4 citation statements)

References 45 publications

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“…An important property of the macaque coil is its improved ability to provide parallel imaging due to a higher loop density and shorter loop-to-subject distance [28]. Fig.…”

Section: Resultsmentioning

confidence: 99%

A 16-channel loop array for in vivo macaque whole-brain imaging at 3 T

Quan

Gao

et al. 2020

Magnetic Resonance Imaging

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Non-human primates (NHPs) are vital models for neuroscience research. These animals have been widely used in behavioral, electrophysiological, molecular, and more recently, multimodal neuroimaging and neuro-engineering studies. Several RF coil arrays have been designed for functional, high-resolution brain magnetic resonance imaging (MRI), but few have been designed to accommodate multimodal devices. In the present study, a 16-channel array coil was constructed for brain imaging of macaques at 3 Tesla (3T). To construct this coil, a close-fitting helmet-shaped form was designed to host 16 coil loops for whole-brain coverage. This assembly is mountable onto stereotaxic head frame bars, and the coil functions while the monkey is in the sphinx position with a clear line of vision of stimuli presented from outside of the MRI system. In addition, 4 openings were allocated in the coil housing, allowing multimodal devices to directly access visual cortical regions such as V1-V4 and MT. Coil performance was evaluated in an anesthetized macaque by quantifying and comparing signal-to-noise ratios (SNRs), noise correlations, and gfactor maps to a vendor-supplied human pediatric coil frequently used for NHP MRI. The result from in vivo experiments showed that the NHP coil was well-decoupled, had higher SNRs in *

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“…An important property of the macaque coil is its improved ability to provide parallel imaging due to a higher loop density and shorter loop-to-subject distance [28]. Fig.…”

Section: Resultsmentioning

confidence: 99%

A 16-channel loop array for in vivo macaque whole-brain imaging at 3 T

Quan

Gao

et al. 2020

Magnetic Resonance Imaging

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“…It has been shown that theoretical performance limits could be used as absolute references against which to evaluate RF coil performance and to derive guidelines for optimal coil design 1,17–25 . For example, the ultimate intrinsic signal‐to‐noise ratio (UISNR) could be used to assess receive arrays, 26–29 while the associated ideal current patterns could be employed to guide coil design 30–33 . Ultimate performance bounds were also used to investigate transmit array performance, in terms of SAR and excitation homogeneity, as a function of the number of coil elements in RF shimming and parallel transmission 1,34 .…”

Section: Introductionmentioning

confidence: 99%

A formalism to investigate the optimal transmit efficiency in radiofrequency shimming

2020

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Transmit efficiency specifies the amplitude of the magnetic resonance excitation field produced over a region of interest with respect to the radiofrequency (RF) power deposited in the sample. This metric is highly important at ultra-high field magnetic resonance imaging (≥7 T), where excitation inhomogeneities and electric field interference effects could prevent achieving the desired flip angle distribution while satisfying the power safety limits. The aim of this work was to introduce an approach to calculate a theoretical upper bound on the transmit efficiency (OPTXE) for RF shimming, independent from any particular coil design. We computed the OPTXE for head-mimicking uniform spherical samples and a realistic heterogeneous head model by maximizing the square of the net transmit field per unit power deposition. The corresponding RF shimming weights were used to combine the analytical surface current modes into ideal current patterns. OPTXE grew monotonically as the target excitation voxel approached the surface of the object, and overall decreased at higher field strengths, presenting similar trends in both the uniform sphere and heterogeneous head model. Arrays with an increasing number of loops could closely approach OPTXE in the central region of the object, but performance decreased closer to the surface and at higher magnetic field strengths. The performance of 32 loops for a two-dimensional excitation region at 7 T increased from 34% to 93% when they were arranged based on the shape of the ideal current patterns. OPTXE provides an absolute reference to evaluate coil designs and RF shimming algorithms, whereas ideal current patterns could serve as guidelines for novel coil designs at ultra-high field. The uniform sphere model enables rapid analytic simulations and provides a good approximation of the OPTXE distribution in a realistic heterogeneous head model with comparable dimensions.

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“…Gao et al 2018)-all coil were positioned at 1 cm above each model. Each coil was tuned, matched (<−15 dB) and excited with a 50 Ω port at 297.2 MHz which is the operating frequency of 7T proton MRI.EM field and SAR distributions were calculated by using the FIT (Finite Integration Technique) solver in the CST software and exported into MATLAB (Mathworks, Natick, Massachusetts, USA) for analysis.…”

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confidence: 99%

The design and evaluation of single-channel loopole coils at 7T MRI

Zheng¹,

Gao²,

Quan³

et al. 2022

Phys. Med. Biol.

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Objective: Improving the local uniformity of B_1^+ field for awake monkey brain MRI at ultra-high fields while facilitating convenient placement and fixation of MRI-compatible multimodal devices for neuroscience study, can eventually advance our understanding of the primate’s brain organization. Approach: A group of single-channel RF coils including conventional loop coils and loopole coils sharing the same size and shape were designed for comparison; their performance as the transmit coil was quantitatively evaluated through a series of numerical electromagnetic (EM) simulations, and further verified by using 7T MRI over a saline phantom and a monkey in vivo. Main results. Compared to conventional loop coils, the optimized loopole coil brought up to 23.5% B_1^+ uniformity improvement for monkey brain imaging in EM simulations, and this performance was further verified over monkey brain imaging at 7T in vivo. Importantly, we have systematically explored the underlying mechanism regarding the relationship between loopole coils' current density distribution and B_1^+ uniformity, observing that it can be approximated as a sinusoidal curve. Significance: The proposed loopole coil design can improve the imaging quality in awake and behaving monkeys, thus benefiting advanced brain research at UHF.

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Investigating the Influence of Spatial Constraints on Ultimate Receive Coil Performance for Monkey Brain MRI at 7 T

Cited by 11 publications

References 45 publications

A 16-channel loop array for in vivo macaque whole-brain imaging at 3 T

A 16-channel loop array for in vivo macaque whole-brain imaging at 3 T

A formalism to investigate the optimal transmit efficiency in radiofrequency shimming

The design and evaluation of single-channel loopole coils at 7T MRI

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