scholarly journals A Nested Eight-Channel Transmit Array With Open-Face Concept for Human Brain Imaging at 7 Tesla

2021 ◽  
Vol 9 ◽  
Author(s):  
Sydney N. Williams ◽  
Sarah Allwood-Spiers ◽  
Paul McElhinney ◽  
Gavin Paterson ◽  
Jürgen Herrler ◽  
...  
Keyword(s):  
Human Brain ◽  
High Performance ◽  
Patient Monitoring ◽  
Single Channel ◽  
7 Tesla ◽  
Parallel Transmit ◽  
The Individual ◽  
Open Face ◽  
Head Coil

Purpose: Parallel transmit technology for MRI at 7 tesla will significantly benefit from high performance transmit arrays that offer high transmit efficiency and low mutual coupling between the individual array elements. A novel dual-mode transmit array with nested array elements has been developed to support imaging the human brain in both the single-channel (sTx) and parallel-transmit (pTx) excitation modes of a 7 tesla MRI scanner. In this work, the design, implementation, validation, specific absorption rate (SAR) management, and performance of the head coil is presented.Methods: The transmit array consisted of a nested arrangement to improve decoupling between the second-neighboring elements. Two large cut-outs were introduced in the RF shield for an open-face design to reduce claustrophobia and to allow patient monitoring. A hardware interface allows the coil to be used in both the sTx and pTx modes. SAR monitoring is done with virtual observation points (VOP) derived from human body models. The transmit efficiency and coverage is compared with the commercial single-channel and parallel-transmit head coils.Results: Decoupling inductors between the second-neighboring coil elements reduced the coupling to less than −20 dB. Local SAR estimates from the electromagnetic (EM) simulations were always less than the EM-based VOPs, which in turn were always less than scanner predictions and measurements for static and dynamic pTx waveforms. In sTx mode, we demonstrate improved coverage of the brain compared to the commercial sTx coil. The transmit efficiency is within 10% of the commercial pTx coil despite the two large cut-outs in the RF shield. In pTx mode, improved signal homogeneity was shown when the Universal Pulse was used for acquisition in vivo.Conclusion: A novel head coil which includes a nested eight-channel transmit array has been presented. The large cut-outs improve patient monitoring and reduce claustrophobia. For pTx mode, the EM simulation and VOP-based SAR management provided greater flexibility to apply pTx methods without the limitations of SAR constraints. For scanning in vivo, the coil was shown to provide an improved coverage in sTx mode compared to a standard commercial head coil.

scholarly journals Improved 7 Tesla Transmit Field Homogeneity with Reduced Electromagnetic Power Deposition Using Coupled Tic Tac Toe Antennas

2020 ◽  
Author(s):  
Tales Santini ◽  
Sossena Wood ◽  
Narayanan Krishnamurthy ◽  
Tiago Martins ◽  
Howard J. Aizenstein ◽  
...  
Keyword(s):  
Large Scale ◽  
Superposition Principle ◽  
Homogeneous Magnetic Field ◽  
7 Tesla ◽  
Full Potential ◽  
Power Deposition ◽  
Electromagnetic Power ◽  
Mri Scans ◽  
Head Coil

AbstractRecently cleared by the FDA, 7 Tesla (7T) MRI is a rapidly growing technology that can provide higher resolution and enhanced contrast in human MRI images. However, the increased operational frequency (~297 MHz) hinders its full potential since it causes inhomogeneities in the images and increases the power deposition in the tissues. This work describes the optimization of an innovative radiofrequency (RF) head coil coupled design, named Tic Tac Toe, currently used in large scale human MRI scanning at 7T; to date, this device was used in more than 1,300 patient/volunteer neuro 7T MRI scans. Electromagnetic simulations were performed for each of the coil’s antennas using the finite-difference time-domain method. Numerical optimizations were used to combine the calculated electromagnetic fields produced by these antennas, based on the superposition principle, and successfully produced homogeneous magnetic field distributions at low levels of power deposition in the tissues. The simulations were then successfully validated in-vivo using the Tic Tac Toe RF head coil system on a 7T MRI scanner.

scholarly journals High resolution atlas of the venous brain vasculature from 7 T quantitative susceptibility maps

2018 ◽  
Author(s):  
Julia Huck ◽  
Yvonne Wanner ◽  
Audrey P. Fan ◽  
Anna-Thekla Jäger ◽  
Sophia Grahl ◽  
...  
Keyword(s):  
Human Brain ◽  
Blood Oxygen Level Dependent ◽  
7 Tesla ◽  
Cerebral Vein ◽  
Registration Method ◽  
Isotropic Resolution ◽  
Common Location ◽  
Susceptibility Maps ◽  
Venous Vasculature

AbstractThe vascular organization of the human brain can determine neurological and neurophysiological functions, yet thus far it has not been comprehensively mapped. Aging and diseases such as dementia are known to be associated with changes to the vasculature and normative data could help detect these vascular changes in neuroimaging studies. Furthermore, given the well-known impact of venous vessels on the blood oxygen level dependent (BOLD) signal, information about the common location of veins could help detect biases in existing datasets. In this work, a quantitative atlas of the venous vasculature using quantitative susceptibility maps (QSM) acquired with a 0.6 mm isotropic resolution is presented. The Venous Neuroanatomy (VENAT) atlas was created from 5 repeated 7 Tesla MRI measurements in young and healthy volunteers (n = 20, 10 females, mean age = 25.1 ± 2.5 years) using a two-step registration method on 3D segmentations of the venous vasculature. This cerebral vein atlas includes the average vessel location, diameter (mean: 0.84 ± 0.33 mm) and curvature (0.11 ± 0.05 mm−1) from all participants and provides an in vivo measure of the angio-architectonic organization of the human brain and its variability. This atlas can be used as a basis to understand changes in the vasculature during aging and neurodegeneration, as well as vascular and physiological effects in neuroimaging.

scholarly journals In vivo 3D Reconstruction of the Human Pallidothalamic and Nigrothalamic Pathways With Super-Resolution 7T MR Track Density Imaging and Fiber Tractography

2021 ◽  
Vol 15 ◽  
Author(s):  
Dae-Hyuk Kwon ◽  
Sun Ha Paek ◽  
Young-Bo Kim ◽  
Haigun Lee ◽  
Zang-Hee Cho
Keyword(s):  
Basal Ganglia ◽  
3D Reconstruction ◽  
Human Brain ◽  
Super Resolution ◽  
Track Density ◽  
7 Tesla ◽  
Fiber Tractography ◽  
Resolution Limit ◽  
Magnetic Resonance Imaging Mri

The output network of the basal ganglia plays an important role in motor, associative, and limbic processing and is generally characterized by the pallidothalamic and nigrothalamic pathways. However, these connections in the human brain remain difficult to elucidate because of the resolution limit of current neuroimaging techniques. The present study aimed to investigate the mesoscopic nature of these connections between the thalamus, substantia nigra pars reticulata, and globus pallidus internal segment using 7 Tesla (7T) magnetic resonance imaging (MRI). In this study, track-density imaging (TDI) of the whole human brain was employed to overcome the limitations of observing the pallidothalamic and nigrothalamic tracts. Owing to the super-resolution of the TD images, the substructures of the SN, as well as the associated tracts, were identified. This study demonstrates that 7T MRI and MR tractography can be used to visualize anatomical details, as well as 3D reconstruction, of the output projections of the basal ganglia.

In vivo demonstration of whole-brain multislice multispoke parallel transmit radiofrequency pulse design in the small and large flip angle regimes at 7 Tesla

2016 ◽  
Vol 78 (3) ◽  
pp. 1009-1019 ◽  
Author(s):  
Vincent Gras ◽  
Alexandre Vignaud ◽  
Alexis Amadon ◽  
Franck Mauconduit ◽  
Denis Le Bihan ◽  
...  
Keyword(s):  
Flip Angle ◽  
7 Tesla ◽  
Whole Brain ◽  
Pulse Design ◽  
Parallel Transmit ◽  
Radiofrequency Pulse

scholarly journals PSVII-1 Effects of exogenous fibrolytic enzymes on the release of xylo-oligosaccharides from six varieties of wheat in-vitro

2019 ◽  
Vol 97 (Supplement_3) ◽  
pp. 360-361 ◽  
Author(s):  
Tom N Dale ◽  
Tim Parr ◽  
Julie King ◽  
John Brameld
Keyword(s):  
High Performance ◽  
Wheat Variety ◽  
Anion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Citrate Buffer ◽  
Wheat Varieties ◽  
Study Objective ◽  
The Individual

Abstract The study objective was to investigate the effects of in-vitro fibrolytic enzyme incubation on xylooligosaccharide (XOS) release from different wheat varieties. Six varieties of wheat were ground to a 300µm powder and subjected to total non-cellulosic hydrolysis with Trifluroacetic acid (TFA) and in-vitro incubations with one of three commercially available enzymes at their recommended doses: Econase XT (xylanase 160,000 BXU/g), Econase MP1000 (Mannase 100,000 MNU/g) or Econase BP700 (ß-glucanase 700,000 BU/g) or no added enzymes. Each wheat variety was suspended (at 5mg/ml) in 50mM sodium citrate buffer (pH 5.2) with or without the individual enzymes (n = 3), and incubated at 40.7°C in a shaking incubator. Samples were taken at 0 and 6hr. Concentrations of xylose, xylobiose and xylotriose were determined by High-Performance Anion-Exchange Chromatography coupled with Pulsed Electrochemical Detection fitted with a CarboPac PA20 (xylose) or CarboPac PA200 Column (Dionex, Thermo Scientific) and known xylose and XOS standards (Megazyme, Ltd). Data were analysed by one or two-way ANOVA (Genstat 19th Edition), with significance accepted at P < 0.05. After TFA hydrolysis, there were significant differences between varieties (P < .001, ANOVA) in total xylose contents (Huntsman > Paragon > Chinese spring > Sinuelo > Highbury = Pavon 74). In the in-vitro incubations, there was a significant effect of enzyme, but not wheat variety, on both xylose (P = 0.009) and xylotriose (P < .001) release at 6 hours, with Econase XT releasing more than the other two enzymes. There was a significant enzyme x wheat variety interaction (P < .001) for xylobiose release at 6 hours, with Econase MP1000 releasing the most from Huntsman. In conclusion, the 6 wheat varieties differed in their non-cellulosic xylose contents and there were clear differences in the amounts of XOS released by the 3 enzymes. Further trials are needed to investigate whether the in-vitro experiments are indicative of results observed in-vivo.

scholarly journals Kinetic Analysis of Glycogen Turnover: Relevance to Human Brain 13C-NMR Spectroscopy

2013 ◽  
Vol 33 (10) ◽  
pp. 1540-1548 ◽  
Author(s):  
Mauro DiNuzzo
Keyword(s):  
Human Brain ◽  
Simulated Data ◽  
13C Nmr Spectroscopy ◽  
Equilibrium Structure ◽  
Biophysical Model ◽  
Resonance Spectroscopy ◽  
Functional Roles ◽  
Set Up ◽  
The Individual

A biophysical model of the glycogen molecule is developed, which takes into account the points of attack of synthase and phosphorylase at the level of the individual glucose chain. Under the sole assumption of steric effects governing enzyme accessibility to glucosyl residues, the model reproduces the known equilibrium structure of cellular glycogen at steady state. In particular, experimental data are reproduced assuming that synthase (1) operates preferentially on inner chains of the molecule and (2) exhibits a faster mobility than phosphorylase in translocating from an attacked chain to another. The model is then used to examine the turnover of outer versus inner tiers during the labeling process of isotopic enrichment (IE) experiments. Simulated data are fitted to in vivo13C nuclear magnetic resonance spectroscopy measurements obtained in the human brain under resting conditions. Within this experimental set-up, analysis of simulated label incorporation and retention shows that 7% to 35% of labeled glucose is lost from the rapidly turning-over surface of the glycogen molecule when stimulation onset is delayed by 7 to 11.5 hours after the end of [1-13C]glucose infusion as done in actual procedures. The substantial label washout before stimulation suggests that much of the subsequent activation-induced glycogenolysis could remain undetected. Overall, these results show that the molecular structure significantly affects the patterns of synthesis and degradation of glycogen, which is relevant for appropriate design of labeling experiments aiming at investigating the functional roles of this glucose reserve.

scholarly journals Improved 7 Tesla transmit field homogeneity with reduced electromagnetic power deposition using coupled Tic Tac Toe antennas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tales Santini ◽  
Sossena Wood ◽  
Narayanan Krishnamurthy ◽  
Tiago Martins ◽  
Howard J. Aizenstein ◽  
...  
Keyword(s):  
Large Scale ◽  
Superposition Principle ◽  
Homogeneous Magnetic Field ◽  
7 Tesla ◽  
Full Potential ◽  
Power Deposition ◽  
Electromagnetic Power ◽  
Mri Scans ◽  
Head Coil

AbstractRecently cleared by the FDA, 7 Tesla (7 T) MRI is a rapidly growing technology that can provide higher resolution and enhanced contrast in human MRI images. However, the increased operational frequency (~ 297 MHz) hinders its full potential since it causes inhomogeneities in the images and increases the power deposition in the tissues. This work describes the optimization of an innovative radiofrequency (RF) head coil coupled design, named Tic Tac Toe, currently used in large scale human MRI scanning at 7 T; to date, this device was used in more than 1,300 neuro 7 T MRI scans. Electromagnetic simulations of the coil were performed using the finite-difference time-domain method. Numerical optimizations were used to combine the calculated electromagnetic fields produced by these antennas, based on the superposition principle, resulting in homogeneous magnetic field distributions at low levels of power deposition in the tissues. The simulations were validated in-vivo using the Tic Tac Toe RF head coil system on a 7 T MRI scanner.

scholarly journals Evaluation of Lactate Production and Clearance Kinetics by 1H NMR in a Model of Brief Repetitive Cerebral Ischemia

1994 ◽  
Vol 14 (4) ◽  
pp. 591-596 ◽  
Author(s):  
Hoby P. Hetherington ◽  
Min-Jie Tan ◽  
Kang-Li Luo ◽  
Gerald M. Pohost ◽  
James H. Halsey ◽  
...  
Keyword(s):  
Cerebral Ischemia ◽  
High Performance ◽  
Time Course ◽  
Lactate Production ◽  
Transient Cerebral Ischemia ◽  
Specific Level ◽  
Lactate Accumulation ◽  
Gravitational Stress ◽  
The Individual

Pilots of high-performance aircraft are subject to repeated transient cerebral ischemia during high-gravitational stress maneuvers. Previously we have demonstrated that repeated episodes of transient cerebral ischemia and reflow are cumulative and lactate accumulations appear to be exponential. To evaluate the metabolic events determining the kinetics of lactate accumulation, and therefore the rates of substrate utilization, we have used in vivo 1H nuclear magnetic resonance with a 5-s time resolution to measure lactate production and clearance. The individual rates for each animal were then used to predict the accumulation of lactate in the same animal during 30 episodes of ischemia and reflow. Lactate accumulation was modeled as the balance between a zero-order production process during the ischemic period and a first-order clearance process. The predicted lactate accumulation showed excellent agreement with the observed time course, validating the predictive power of the simple model used. The highly reproducible nature of this model and its accuracy in predicting lactate accumulation should enable more accurate studies of the deleterious effects of lactate accumulation in cerebral ischemia by providing a highly reproducible means for generating a specific level of lactate accumulation.

scholarly journals A 48-Channel Receive Array Coil for Mesoscopic Diffusion-Weighted MRI of Human ex vivo Brain Imaging on the 3T Connectome Scanner

2021 ◽  
Author(s):  
Alina Scholz ◽  
Robin Etzel ◽  
Markus W May ◽  
Mirsad Mahmutovic ◽  
Qiyuan Tian ◽  
...  
Keyword(s):  
High Resolution ◽  
Human Brain ◽  
Brain Imaging ◽  
Ex Vivo ◽  
Whole Brain ◽  
Diffusion Weighted ◽  
Noise Amplification ◽  
Head Coil ◽  
Array Coil

AbstractIn vivo diffusion-weighted magnetic resonance imaging is limited in signal-to-noise-ratio (SNR) and acquisition time, which constrains spatial resolution to the macroscale regime. Ex vivo imaging, which allows for arbitrarily long scan times, is critical for exploring human brain structure in the mesoscale regime without loss of SNR. Standard head array coils designed for patients are sub-optimal for imaging ex vivo whole brain specimens. The goal of this work was to design and construct a 48-channel ex vivo whole brain array coil for high-resolution and high b-value diffusion-weighted imaging on a 3T Connectome scanner. The coil was validated with bench measurements and characterized by imaging metrics on an agar brain phantom and an ex vivo human brain sample. The two-segment coil former was constructed for a close fit to a whole human brain, with small receive elements distributed over the entire brain. Imaging tests including SNR and G-factor maps were compared to a 64-channel head coil designed for in vivo use. There was a 2.9-fold increase in SNR in the peripheral cortex and a 1.3-fold gain in the center when compared to the 64-ch head coil. The 48-channel ex vivo whole brain coil also decreases noise amplification in highly parallel imaging, allowing acceleration factors of approximately one unit higher for a given noise amplification level. The acquired diffusion-weighted images in a whole ex vivo brain specimen demonstrate the applicability of the developed coil for high-resolution and high b-value diffusion-weighted ex vivo brain MRI studies.

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