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 Cardiac imaging at 7 tesla: Single- and two-spoke radiofrequency pulse design with 16-channel parallel excitation

2013 ◽  
Vol 70 (5) ◽  
pp. 1210-1219 ◽  
Author(s):  
Sebastian Schmitter ◽  
Lance DelaBarre ◽  
Xiaoping Wu ◽  
Andreas Greiser ◽  
Dingxin Wang ◽  
...  
Keyword(s):  
Cardiac Imaging ◽  
7 Tesla ◽  
Pulse Design ◽  
Parallel Excitation ◽  
Radiofrequency Pulse

scholarly journals A Statistical Robust Approach to Design Parallel Transmit Radiofrequency Excitations in MRI

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Vincent Gras ◽  
Franck Mauconduit ◽  
Nicolas Boulant
Keyword(s):  
Performance Metrics ◽  
Magnetic Field Gradient ◽  
Population Sample ◽  
Computation Time ◽  
7 Tesla ◽  
Spin Excitation ◽  
Pulse Design ◽  
Pulse Technique ◽  
Parallel Transmit ◽  
Design Database

In MRI, at ultrahigh field, the use of parallel transmit radiofrequency (RF) arrays is very beneficial to better control spin excitation spatially. In that framework, the so-called “universal pulse” technique, proposed recently for head imaging at 7 tesla, gives access to “plug-and-play” nonadiabatic solutions exhibiting good robustness against intersubject variations in the resonant transmit fields. This new type of solution has been defined so far as the result of numerical pulse optimizations performed across a collection of RF field maps acquired on a small population sample (pulse design database). In this work, we investigate an alternative universal pulse design approach in the linear small tip angle regime whereby the database of RF field maps is first transformed into a second-order statistical model and which then exploits a statistical robust design formalism for the optimization of the RF and magnetic field gradient waveforms. Experimental validation with an eightfold transmit RF coil for 7 tesla brain imaging shows that this new approach brings some benefit in terms of computational efficiency. Hence, for a design database composed of 35 maps, the computation time initially of 50 min could be reduced down to 3 min. The proposed statistical approach thus enables integration of large databases, presumably necessary to ensure robust solutions. Finally, it provides means to compute flip angle statistics and, along with it, simple performance metrics for quality assurance (RF pulse performance) or guidance in the optimization of TX array architectures.

scholarly journals Local specific absorption rate (SAR), global SAR, transmitter power, and excitation accuracy trade-offs in low flip-angle parallel transmit pulse design

2013 ◽  
Vol 71 (4) ◽  
pp. 1446-1457 ◽  
Author(s):  
Bastien Guérin ◽  
Matthias Gebhardt ◽  
Steven Cauley ◽  
Elfar Adalsteinsson ◽  
Lawrence L. Wald
Keyword(s):  
Absorption Rate ◽  
Specific Absorption Rate ◽  
Flip Angle ◽  
Pulse Design ◽  
Specific Absorption ◽  
Transmitter Power ◽  
Parallel Transmit ◽  
Trade Offs

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 T1-weighted in vivo human whole brain MRI dataset with an ultrahigh isotropic resolution of 250 μm

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Falk Lüsebrink ◽  
Alessandro Sciarra ◽  
Hendrik Mattern ◽  
Renat Yakupov ◽  
Oliver Speck
Keyword(s):  
Brain Mri ◽  
Brain Magnetic Resonance Imaging ◽  
Brain Atlas ◽  
7 Tesla ◽  
Ultrahigh Resolution ◽  
Raw Data ◽  
Whole Brain ◽  
Isotropic Resolution ◽  
High Magnetic Field Strength

Abstract We present an ultrahigh resolution in vivo human brain magnetic resonance imaging (MRI) dataset. It consists of T1-weighted whole brain anatomical data acquired at 7 Tesla with a nominal isotropic resolution of 250 μm of a single young healthy Caucasian subject and was recorded using prospective motion correction. The raw data amounts to approximately 1.2 TB and was acquired in eight hours total scan time. The resolution of this dataset is far beyond any previously published in vivo structural whole brain dataset. Its potential use is to build an in vivo MR brain atlas. Methods for image reconstruction and image restoration can be improved as the raw data is made available. Pre-processing and segmentation procedures can possibly be enhanced for high magnetic field strength and ultrahigh resolution data. Furthermore, potential resolution induced changes in quantitative data analysis can be assessed, e.g., cortical thickness or volumetric measures, as high quality images with an isotropic resolution of 1 and 0.5 mm of the same subject are included in the repository as well.

scholarly journals Seven-Tesla Time-of-Flight Angiography Using a 16-Channel Parallel Transmit System With Power-Constrained 3-dimensional Spoke Radiofrequency Pulse Design

2014 ◽  
Vol 49 (5) ◽  
pp. 314-325 ◽  
Author(s):  
Sebastian Schmitter ◽  
Xiaoping Wu ◽  
Edward J. Auerbach ◽  
Gregor Adriany ◽  
Josef Pfeuffer ◽  
...  
Keyword(s):  
Time Of Flight ◽  
Pulse Design ◽  
3 Dimensional ◽  
Parallel Transmit ◽  
Radiofrequency Pulse

scholarly journals Whole-brain 3D MR fingerprinting brain imaging: clinical validation and feasibility to patients with meningioma

2021 ◽  
Author(s):  
Thomaz R. Mostardeiro ◽  
Ananya Panda ◽  
Robert J. Witte ◽  
Norbert G. Campeau ◽  
Kiaran P. McGee ◽  
...  
Keyword(s):  
White Matter ◽  
Statistical Significance ◽  
Relaxation Times ◽  
Brain Structures ◽  
Centrum Semiovale ◽  
In Vivo Evaluation ◽  
Whole Brain ◽  
Mean Values ◽  
Caudate Head

Abstract Purpose MR fingerprinting (MRF) is a MR technique that allows assessment of tissue relaxation times. The purpose of this study is to evaluate the clinical application of this technique in patients with meningioma. Materials and methods A whole-brain 3D isotropic 1mm3 acquisition under a 3.0T field strength was used to obtain MRF T1 and T2-based relaxometry values in 4:38 s. The accuracy of values was quantified by scanning a quantitative MR relaxometry phantom. In vivo evaluation was performed by applying the sequence to 20 subjects with 25 meningiomas. Regions of interest included the meningioma, caudate head, centrum semiovale, contralateral white matter and thalamus. For both phantom and subjects, mean values of both T1 and T2 estimates were obtained. Statistical significance of differences in mean values between the meningioma and other brain structures was tested using a Friedman’s ANOVA test. Results MR fingerprinting phantom data demonstrated a linear relationship between measured and reference relaxometry estimates for both T1 (r2 = 0.99) and T2 (r2 = 0.97). MRF T1 relaxation times were longer in meningioma (mean ± SD 1429 ± 202 ms) compared to thalamus (mean ± SD 1054 ± 58 ms; p = 0.004), centrum semiovale (mean ± SD 825 ± 42 ms; p < 0.001) and contralateral white matter (mean ± SD 799 ± 40 ms; p < 0.001). MRF T2 relaxation times were longer for meningioma (mean ± SD 69 ± 27 ms) as compared to thalamus (mean ± SD 27 ± 3 ms; p < 0.001), caudate head (mean ± SD 39 ± 5 ms; p < 0.001) and contralateral white matter (mean ± SD 35 ± 4 ms; p < 0.001) Conclusions Phantom measurements indicate that the proposed 3D-MRF sequence relaxometry estimations are valid and reproducible. For in vivo, entire brain coverage was obtained in clinically feasible time and allows quantitative assessment of meningioma in clinical practice.

scholarly journals High resolution structural and functional MRI of the hippocampus in young adults with Down syndrome

2021 ◽  
Author(s):  
Katherine A Koenig ◽  
Se-Hong Oh ◽  
Melissa R Stasko ◽  
Elizabeth C Roth ◽  
H Gerry Taylor ◽  
...  
Keyword(s):  
Down Syndrome ◽  
Functional Connectivity ◽  
Cortical Thickness ◽  
Right Hemisphere ◽  
Gray Matter Volume ◽  
Drug Efficacy ◽  
Structure And Function ◽  
7 Tesla ◽  
Whole Brain ◽  
And Function

Abstract Down syndrome is the phenotypic consequence of trisomy 21, with clinical presentation including both neurodevelopmental and neurodegenerative components. Although the intellectual disability typically displayed by individuals with Down syndrome is generally global, it also involves disproportionate deficits in hippocampally-mediated cognitive processes. Hippocampal dysfunction may also relate to Alzheimer’s disease-type pathology, which can appear in as early as the first decade of life and becomes universal by age 40. Using 7-tesla MRI of the brain, we present an assessment of the structure and function of the hippocampus in 34 individuals with Down syndrome (mean age 24.5 years ± 6.5) and 27 age- and sex-matched typically developing healthy controls. In addition to increased whole-brain mean cortical thickness and lateral ventricle volumes (p &lt; 1.0 × 10−4), individuals with Down syndrome showed selective volume reductions in bilateral hippocampal subfields CA1, dentate gyrus, and tail (p &lt; 0.005). In the group with Down syndrome, bilateral hippocampi showed widespread reductions in the strength of functional connectivity, predominately to frontal regions (p &lt; 0.02). Age was not related to hippocampal volumes or functional connectivity measures in either group, but both groups showed similar relationships of age to whole-brain volume measures (p &lt; 0.05). Finally, we performed an exploratory analysis of a subgroup of individuals with Down syndrome with both imaging and neuropsychological assessments. This analysis indicated that measures of spatial memory were related to mean cortical thickness, total gray matter volume, and right hemisphere hippocampal subfield volumes (p &lt; 0.02). This work provides a first demonstration of the usefulness of high-field MRI to detect subtle differences in structure and function of the hippocampus in individuals with Down syndrome, and suggests the potential for development of MRI-derived measures as surrogate markers of drug efficacy in pharmacological studies designed to investigate enhancement of cognitive function.

scholarly journals Alteration within the Hippocampal Volume in Patients with LHON Disease—7 Tesla MRI Study

2020 ◽  
Vol 10 (1) ◽  
pp. 14
Author(s):  
Cezary Grochowski ◽  
Kamil Jonak ◽  
Marcin Maciejewski ◽  
Andrzej Stępniewski ◽  
Mansur Rahnama-Hezavah
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Molecular Layer ◽  
Three Dimensional ◽  
Hippocampal Volume ◽  
7 Tesla ◽  
Diagnostic Process ◽  
Resonance Imaging ◽  
The Right

Purpose: The aim of this study was to assess the volumetry of the hippocampus in the Leber’s hereditary optic neuropathy (LHON) of blind patients. Methods: A total of 25 patients with LHON were randomly included into the study from the national health database. A total of 15 patients were selected according to the inclusion criteria. The submillimeter segmentation of the hippocampus was based on three-dimensional spoiled gradient recalled acquisition in steady state (3D-SPGR) BRAVO 7T magnetic resonance imaging (MRI) protocol. Results: Statistical analysis revealed that compared to healthy controls (HC), LHON subjects had multiple significant differences only in the right hippocampus, including a significantly higher volume of hippocampal tail (p = 0.009), subiculum body (p = 0.018), CA1 body (p = 0.002), hippocampal fissure (p = 0.046), molecular layer hippocampus (HP) body (p = 0.014), CA3 body (p = 0.006), Granule Cell (GC) and Molecular Layer (ML) of the Dentate Gyrus (DG)–GC ML DG body (p = 0.003), CA4 body (p = 0.001), whole hippocampal body (p = 0.018), and the whole hippocampus volume (p = 0.023). Discussion: The ultra-high-field magnetic resonance imaging allowed hippocampus quality visualization and analysis, serving as a powerful in vivo diagnostic tool in the diagnostic process and LHON disease course assessment. The study confirmed previous reports regarding volumetry of hippocampus in blind individuals.

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