Biology subjects

Lagore, R. L.

Publications and source records attributed to Lagore, R. L..

11 recordsLinked to original sources

bioRxiv2026

SNR Enhancement Considerations for Loop Receive Coils at Ultra-High Fields

PurposeTo quantify parasitic losses in ultra-high field (UHF) magnetic resonance imaging (MRI) receive coils and determine how they contribute to the mismatch between numerically predicted and experimentally realized signal-to-noise ratio (SNR), with the goal of guiding receive-array designs toward ultimate intrinsic SNR (uiSNR). MethodsSNR was measured across multiple field strengths (3T, 7T, 10.5T) using commercial and custom-built arrays. To quantify parasitic losses, unloaded-to-loaded quality factor ratio (QR) measurements were performed on representative loop resonators and practical RF coils. Measured losses were combined with single-loop electromagnetic simulations to separate conductor, radiation, and component losses. These bench-derived loss estimates were then incorporated into full-array electromagnetic simulations of a 128-channel receive array to evaluate their impact on predicted intrinsic SNR. ResultsMeasurements across field strengths supported the expected supralinear increase of SNR with B0. QR analysis showed that, at UHF, radiation loss must be excluded from unloaded-Q measurements to avoid overestimating electronic-noise penalties, and that multiple seemingly modest parasitic losses collectively impose substantial SNR degradation. In the 128-channel array, simulations including only conductor and radiation losses predicted 93% of central uiSNR, whereas inclusion of the full measured parasitic-loss budget reduced predicted performance to 78%, in close agreement with the experimentally measured 77%. ConclusionsThe gap between predicted and realized SNR performance of high-channel-count 10.5T loop arrays can be largely explained by parasitic losses that are not captured in conventional simulations. A bench-measurement-informed simulation framework enables more realistic prediction of coil performance and provides practical guidance for optimizing future UHF receive arrays.

bioengineering↗

bioRxiv2026

An 80-channel receive array for 10.5T neuroimaging: Key considerations for SNR optimization

PurposeHigh-density RF receive arrays are required to realize the inherently available SNR and parallel imaging advantages at ultrahigh field strengths, which are essential for high-resolution functional and anatomical brain MRI. This study aims to systematically assess the impacts of often-overlooked parasitic losses associated with various RF coil components, as these losses can degrade the realized SNR and cause significant deviation from the ultimate intrinsic SNR (uiSNR; the theoretical upper bound of available SNR). In addition, we seek to detail engineering solutions to each of these loss mechanisms in pursuit of achieving a higher fraction of the uiSNR limit. MethodsA 16-channel loop-folded dipole transceiver array was developed for 10.5T human head applications and paired with a fully-updated 64-channel receive-only loop array. The optimization of the receive array considered several factors, including (but not limited to) coil dimensions to accommodate a larger population, the size and number of loops to enhance SNR and parallel imaging performance, and circuit design strategies to minimize parasitic losses. The SNR and parallel imaging performance of the receive array were quantitatively assessed by comparison with the uiSNR, as well as existing high-channel-count receive arrays at 7T and 10.5T. Finally, the complete 16-channel transmit, 80-channel receive coil array was safety validated for human use and employed for high-resolution functional and anatomical MRI at 10.5T. ResultsInitial results show that the 80-channel array, featuring larger loops in an overlapped layout with optimized circuitry, significantly improves the SNR and approaches the uiSNR limit in a large fraction of the head, while maintaining or enhancing the parallel imaging performance compared to previously used non-overlap layout. ConclusionThis study suggests that, although the traditionally used high-channel-count loop receive array technology can approach the uiSNR limit in the >10T regime, meticulous design optimization--including systematic assessment and minimization of parasitic losses--has become increasingly critical for achieving this goal in this new field-strength territory.

neuroscience↗

bioRxiv2026

Distant Dipoles: A Multi-Parameter and Multi-Objective Analysis of RF Coil Performance For 7T Body MRI

PurposeTo address the limitations of single-distance, 1D performance metrics in RF coil design. This work introduces a multi-objective, volume-of-interest (VOI) based analysis to systematically characterize the trade-offs between power efficiency, pSAR efficiency, and homogeneity as a function of dipole length (l) and distance-to-load (d) for multiple dipole geometries and target anatomies. MethodsElectromagnetic simulations of straight and end-meandered dipole antennas were performed with varying lengths (100-500 mm) and distance-to-load (1-81 mm) over three anatomical targets (prostate, kidney, heart). Homogeneity, power efficiency, pSAR efficiency, and load sensitivity performance metrics were calculated within each anatomical VOI. Inter-element coupling at variable d was assessed in a 3-element array, and a subset of single-element simulations was experimentally validated using B1+ mapping. ResultsA fundamental trade-off was found between power efficiency and pSAR efficiency. Optimal power efficiency was achieved with shorter dipoles (150 mm < l < 300 mm) closer to the sample (d < 30 mm), while optimal pSAR efficiency and homogeneity were achieved with longer dipoles at further from the sample (d > 60 mm). Inter-element coupling increased with distance-to-load but could be managed by increasing element spacing. Experimental measurements were in good agreement with simulation trends. ConclusionIncreasing distance-to-load to 40-60 mm, compared with commonly used distances of 20-30 mm, offers a practical strategy for improving pSAR efficiency and homogeneity with a minimal decrease in power efficiency. This work provides a quantitative analysis that enables RF coil designers to make informed, data-driven decisions when developing next-generation body arrays and suggests that unshielded end-meandered dipoles could be an optimal transmit element geometry.

biophysics↗

bioRxiv2025

An RF coil array system for in vivo & ex vivo non-human primate brain studies at 10.5 Tesla

PurposeWe aimed to develop an innovative RF coil toolset for high resolution in vivo and ex vivo non-human primate neuroimaging applications at 10.5T MRI. The main goal was to improve our multimodal neural connectivity pipeline through the improved SNR, CNR, and spatial resolution that result from utilizing high-density RF coil arrays in combination with ultra-high field MRI. MethodsTwo RF coil arrays, both comprising 8 transmit and 40 receive channels, were designed and built for in vivo and ex vivo NHP imaging at 10.5 T. Experimental data was collected on multiple in vivo and ex vivo specimens, showing the utility UHF MRI for NHP neuroscience. ResultsExperimental results demonstrate uniform whole-brain coverage within both in vivo--which included the cerebellar, and spinal cord regions--and ex vivo specimens. High spatial resolutions (in vivo: 0.1x0.1x0.5 mm, ex vivo: 120 micron isotropic) were achieved, revealing detailed anatomical structures throughout. High temporal stability allowed for EPI and dMRI applications. ConclusionAn RF coil toolset comprising two 8ch transmit/40ch receive arrays was successfully designed for both in vivo and ex vivo NHP brain applications at 10.5 T. Both high-density RF coil arrays coupled with the SNR and CNR benefits available at UHF supported unmatched anatomical, functional, and diffusion applications at some of the highest spatial resolutions to date. Additionally, the combined capability of both in vivo and ex vivo MRI with the same brain specimen allows for tighter control for experimental-paradigm multistage studies examining translation between in vivo and ex vivo methodologies.

neuroscience↗

bioRxiv2025

A Numerical Alternative to MR Thermometry for Safety Validation of Multi-Channel RF Transmit Coils

PurposeThis study proposes an alternative approach to MR thermometry (MRT) for the safety validation of multi-channel RF transmit coils and demonstrates its use to enable human studies at 10.5T. MethodsTo ensure patient safety, specific absorption rate (SAR) limits established under international guidelines must not be exceeded. Predicting SAR on state-of-the-art parallel transmit systems relies on electromagnetic simulations, which require extensive experimental validation. Despite a well-established validation workflow, SAR prediction errors are unavoidable and must be quantified as a safety margin. While MRT tests are commonly used for this purpose, their technical challenges necessitate an alternative. The proposed technique propagates the error between experimentally and numerically acquired B+distributions to the uncertainty in simulated peak local SAR using Monte-Carlo simulations without the need for MRT. This method was validated using a 16-channel transceiver coil for imaging the human torso (henceforth referred to as a "body" coil) at 10.5T with two excitation scenarios, as well as an 8-channel 10.5T head coil with four excitation scenarios. ResultsThe proposed numerical technique proved more conservative than existing MRT-based SAR error quantification methods across all tested scenarios. Its application to validate three state-of-the-art head coils (16Tx/32Rx, 16Tx/80Rx, and 16Tx/128Rx) led to regulatory approval for human head imaging and high-quality functional as well as diffusion MRI results at 10.5T. ConclusionA numerical alternative to MRT requires only the experimental acquisition of B+ maps for comparison with simulations, enabling the quantification of uncertainty in SAR prediction. This technique was applied to three 16-channel transmit arrays, each used in conjunction with high-channel-count receive arrays for in vivo imaging.

neuroscience↗

bioRxiv2025

Mesoscopic whole-brain T2*-weighted and associated quantitative MRI in healthy humans at 10.5 T

PurposeTo demonstrate the feasibility and performance of mesoscopic whole brain T2*-weighted (T2*w) MRI at 10.5 T by combining a motion-robust multi-echo gradient-echo (GRE) method with high-density RF receive arrays. MethodsMulti-echo GRE data were collected in healthy adults at isotropic 0.5 mm resolution using a custom-built 16-channel transmit/80-channel receive (16Tx/80Rx) RF coil. Whole brain images were reconstructed with navigator-guided joint motion and field correction and were used for quantitative R2* and susceptibility ({chi}) mapping. Intrinsic signal-to-noise ratio (iSNR) and quantification precision for R2* and{chi} were also estimated. The results were compared with those obtained in the same subjects with matched resolution at 7 T using the commercial Nova 1Tx/32Rx coil, to demonstrate the iSNR and quantification precision gains at 10.5 T. G-factors were also calculated at each field strength to evaluate parallel imaging performances. To demonstrate the benefit of increased parallel imaging performances at 10.5 T, whole brain images with higher acceleration were also obtained using a custom-built 16Tx/128Rx coil. Resultsthe utilized motion robust GRE sequence and reconstruction effectively reduced artifacts from motion and field changes during scans, producing high-quality whole-brain T2*w images and multi-parametric maps at 10.5 T with delineation of fine-scale brain structures. Compared to 7 T, the 10.5 T approach led to gains in both iSNR and quantification precision of R2* and{chi} . Quantitatively, iSNR estimated in the peripheral cortical gray matter increased by 42%. Parallel imaging performances were also improved at 10.5 T owing to the utilized high-density coils compared to the commonly used commercially available coil at 7 T, allowing high-quality images with up to 12-fold combined acceleration when using the 128Rx coil. ConclusionIt is feasible to perform motion-robust whole-brain mesoscopic multi-echo gradient echo imaging of the human brain at 10.5 T. Intrinsic SNR and quantification precision of R2* and{chi} were estimated and compared with 7 T results. The results presented here may shed light on future optimal implementation of anatomic T2*w brain MRI at ultrahigh field beyond 7 T.

bioengineering↗

bioRxiv2025

Simultaneous zero echo time fMRI of rat brain and spinal cord

PurposeFunctional assessments of the central nervous system (CNS) are essential for many areas of research. Functional MRI (fMRI) typically targets either the brain or the spinal cord, but usually not both, due to the obstacles associated with simultaneous image acquisitions from distant fields of view (FOVs) with conventional MRI. In this work, we establish a novel MRI approach that enables artefact-free, quiet, simultaneous fMRI of both brain and spinal cord, avoiding the need for dynamic shimming procedures. MethodsWe utilized zero echo time (TE) Multi-Band-SWeep Imaging with Fourier Transformation (MB-SWIFT) technique at 9.4T in a simultaneous dual-FOV configuration and two separate radio frequency (RF) transmit-receive surface coils. The first coil covered the rat brain, while the second was positioned approximately at the T13-L1 level of the rat"s spinal cord with copper shielding to minimize the coupling between the RF coils. Eight Sprague-Dawley rats were used for hindlimb stimulation fMRI studies. ResultsRobust and specific activations were detected in both the brain and spinal cord during hind paw stimulation at individual and group levels. The results established the feasibility of the novel approach for simultaneous functional assessment of the lumbar spinal cord and brain in rats. ConclusionThis study demonstrated the feasibility of a novel dual-FOV fMRI approach based on zero-TE MB-SWIFT and set the stage for translation to humans. The methodology enables comprehensive functional CNS evaluations of great value in different conditions such as pain, spinal cord injury, neurodegenerative diseases, and aging.

neuroscience↗

bioRxiv2024

A 128-channel receive array with enhanced SNR performance for 10.5 tesla brain imaging

PurposeTo develop and characterize the performance of a 128-channel head array for brain imaging at 10.5 tesla and evaluate the potential of brain imaging at this unique, >10 tesla magnetic field. MethodsThe coil is composed of a 16-channel self-decoupled loop transmit/receive array with a 112-loop receive-only (Rx) insert. Interactions between the outer transmitter and the inner 112Rx insert were mitigated using coaxial cable traps placed every 1/16 of a wavelength on each feed cable, locating most preamplifier boards outside the transmitter field and miniaturizing those placed directly on individual coils. ResultsThe 128-channel array described herein achieved 77% of ultimate intrinsic SNR in the center of the brain. Transmit field maps obtained experimentally on a phantom with and without the receive array were similar and matched EM simulations, leading to FDA approval for human imaging. Anatomical and functional data, including with power demanding sequences, were acquired successfully on human volunteers. ConclusionsCounterintuitive to expectations based on magnetic fields [≤]7T, the higher channel counts provided SNR gains centrally, capturing [~]80% uiSNR. Fraction of uiSNR achieved centrally in 64Rx, 80Rx, and 128Rx arrays suggested that a plateau was being reached at 80%. At this plateau, linear to approximately quadratic B0 dependent SNR gains for the periphery and the center, respectively, were observed for 10.5T relative 7T.

neuroscience↗

bioRxiv2024

RF coil design strategies for improving SNR at theultrahigh magnetic field of 10.5 Tesla

PurposeTo develop multichannel transmit and receive arrays towards capturing the ultimate-intrinsic-SNR (uiSNR) at 10.5 Tesla (T) and to demonstrate the feasibility and potential of whole-brain, high-resolution human brain imaging at this high field strength. MethodsA dual row 16-channel self-decoupled transmit (Tx) array was converted to a 16Tx/Rx transceiver using custom transmit/receive switches. A 64-channel receive-only (64Rx) array was built to fit into the 16Tx/Rx array. Electromagnetic modeling and experiments were employed to define safe operation limits of the resulting 16Tx/80Rx array and obtain FDA approval for human use. ResultsThe 64Rx array alone captured approximately 50% of the central uiSNR at 10.5T while the identical 7T 64Rx array captured [~]76% of uiSNR at this lower field strength. The 16Tx/80Rx configuration brought the fraction of uiSNR captured at 10.5T to levels comparable to the performance of the 64Rx array at 7T. SNR data obtained at the two field strengths with these arrays displayed [Formula] dependent increases over a large central region. Whole-brain high resolution T2* and T1 weighted anatomical and gradient-recalled echo EPI BOLD fMRI images were obtained at 10.5T for the first time with such an advanced array, illustrating the promise of >10T fields in studying the human brain. ConclusionWe demonstrated the ability to approach the uiSNR at 10.5T over the human brain with a novel, high channel count array, achieving large SNR gains over 7T, currently the most commonly employed ultrahigh field platform, and demonstrate high resolution and high contrast anatomical and functional imaging at 10.5T.

neuroscience↗

bioRxiv2020

An 8 Dipole Transceive and 24 Loop Receive Array for Non-Human Primate Head Imaging at 10.5T

A 32-channel RF coil was developed for brain imaging of anesthetized non-human primates (Rhesus Macaque) at 10.5 tesla. The coil is composed of an 8-channel dipole transmit/receive array, close-fitting 16-channel loop receive array headcap, and 8-channel loop receive array lower insert. The transceiver dipole array is composed of eight end-loaded dipole elements self-resonant at the 10.5 tesla proton Larmor frequency. These dipole elements were arranged on a plastic cylindrical former which was split in two to allow for convenient animal positioning. Nested into the bottom of the dipole array former is located an 8-channel loop receive array which contains 5x10 cm2 square loops arranged in two rows of four loops. Arranged in a close-fitting plastic headcap is located a high-density 16-channel loop receive array. This array is composed of 14 round loops 37 mm in diameter and two partially detachable, irregularly shaped loops that encircle the ears. Imaging experiments were performed on anesthetized non-human primates on a 10.5 tesla MRI system equipped with body gradients with a 60 cm open bore. The coil enabled submillimeter (0.58 mm isotropic) high resolution anatomical and functional imaging as well as tractography of fasciculated axonal bundles. The combination of a close-fitting loop receive array and dipole transceiver array allowed for a higher channel count receiver and consequent higher SNR and parallel imaging gains. Parallel imaging performance supports high resolution fMRI and dMRI with a factor of three reduction in sampling. The transceive array elements during reception contributed approximately one quarter of SNR in the lower half of the brain which was farthest from the close-fitting headcap receive array.

bioengineering↗

bioRxiv2020

Ultra-high field (10.5 T) resting state fMRI in the macaque

Resting state functional connectivity refers to the temporal correlations between spontaneous hemodynamic signals obtained using functional magnetic resonance imaging. This technique has demonstrated that the structure and dynamics of identifiable networks are altered in psychiatric and neurological disease states. Thus, resting state network organizations can be used as a diagnostic, or prognostic recovery indicator. However, much about the physiological basis of this technique is unknown. Thus, providing a translational bridge to an optimal animal model, the macaque, in which invasive circuit manipulations are possible, is of utmost importance. Current approaches to resting state measurements in macaques face unique challenges associated with signal-to-noise, the need for invasive contrast agents, and within-subject designs. These limitations can, in principle, be overcome through ultra-high magnetic fields. However, ultra-high field imaging has yet to be adapted for fMRI in macaques. Here, we demonstrate that the combination of high channel count transmitter and receiver arrays, optimized pulse sequences, and careful anesthesia regimens, allows for detailed within-subject resting state analysis at ultra-high resolutions. In this study, we uncover thirty spatially detailed resting state components that are highly robust across individual macaques and closely resemble the quality and findings of connectomes from large human datasets. This detailed map of the rsfMRI macaque connectome will be the basis for future neurobiological circuit manipulation work, providing valuable biological insights into human connectomics.

neuroscience↗