Results for diffusion‐weighted imaging with a fourth‐channel gradient insert

Feldman, Rebecca E.; Scholl, Timothy J.; Alford, Jamu K.; Handler, William B.; Harris, Chad; Chronik, Blaine A.

doi:10.1002/mrm.22971

Cited by 6 publications

(6 citation statements)

References 28 publications

(27 reference statements)

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“…Furthermore, some single‐channel insert coils with nonorthogonal field profiles might be advantageous to mitigate the B 1 + inhomogeneity, field of view reduction, and diffusion encoding when simultaneously used with linear gradients. Mutual coupling between the insert coil and the system gradient coils can also significantly degrade the performance of the system depending on the application.…”

Section: Discussionmentioning

confidence: 99%

Driving mutually coupled gradient array coils in magnetic resonance imaging

Ertan

Taraghinia

Atalar

2019

Magnetic Resonance in Med

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Purpose:In contrast to conventional linear gradients, gradient coil arrays with arbitrary spatial dependency might experience strong mutual coupling. Although conventional gradient power amplifiers with feedback loop might compensate the effect of coupling, required voltages for the compensation are generally unknown and has to be considered beforehand to ensure that amplifier voltage limits are not exceeded. A first-order circuit model is proposed to be used as a feedforward model which enables analytical formulas of required voltages to drive the mutually coupled gradient coil arrays. Theory and Methods: A first-order circuit model including the mutual couplings is provided to analytically calculate the input voltages and minimum achievable rise times for a given set of gradient array currents and amplifier limitations. Previously designed 9-channel Z-gradient coil array and home-built gradient amplifiers (50 V and 20 A) are used in the experiments. Three sets of currents optimized for linear Z-gradient, second-order Z2, and third-order Z3 fields are used in the bench-top experiments. The current weightings for the linear Z-gradient are also used as the readout gradient in the 3T MRI experiments. Results: Current measurements for the example magnetic field profiles with minimum rise times are demonstrated for the simultaneous use of 9-channel gradient coils and amplifiers. MRI experiments verify that a linear Z-gradient field with a desired time waveform can be generated using a mutually coupled array coils. Conclusion: Bench-top and MRI experiments demonstrate the feasibility of the proposed circuit model and analytical formulas to drive the mutually coupled gradient coils. K E Y W O R D Sfeedforward model, gradient arrays, gradient power amplifiers, MRI, mutual coupling, mutual inductance, mutually coupled gradient array coils

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Section: Discussionmentioning

confidence: 99%

Driving mutually coupled gradient array coils in magnetic resonance imaging

Ertan

Taraghinia

Atalar

2019

Magnetic Resonance in Med

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“…Traumatic Brain Injury), and enable new approaches to structural and functional brain connectivity analysis. Recent advances in high-strength gradient system designs for clinical magnets, such as the Siemens “ConnectomeScanner” (Van Essen et al) and the growing acceptance of high gradient-strength head-insert coils (Feldman et al, 2011), herald innovative clinical applications of mPFG diffusion MRI leveraging increased SNR, shorter TEs, higher spatial resolution, and more flexibility in varying parameters (e.g., τ m , Δ, δ , gradient amplitude, number of mPFGs blocks). Higher gradient amplitude and/or larger number of PFG diffusion blocks for instance could maximize SNR in tissues with larger diffusivities, while increased spatial resolution could resolve partial volume effects and open up the possibility of applying mPFG MRI in convoluted gray matter to quantify small diameter features of randomly oriented dendrites (Komlosh et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

In vivo detection of microscopic anisotropy using quadruple pulsed-field gradient (qPFG) diffusion MRI on a clinical scanner

et al. 2013

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We report our design and implementation of a quadruple pulsed-field gradient (qPFG) diffusion MRI pulse sequence on a whole-body clinical scanner and demonstrate its ability to non-invasively detect restriction-induced microscopic anisotropy in human brain tissue. The microstructural information measured using qPFG diffusion MRI in white matter complements that provided by diffusion tensor imaging (DTI) and exclusively characterizes diffusion of water trapped in microscopic compartments with unique measures of average cell geometry. We describe the effect of white matter fiber orientation on the expected MR signal and highlight the importance of incorporating such information in the axon diameter measurement using a suitable mathematical framework. Integration of qPFG diffusion-weighted images (DWI) with fiber orientations measured using high-resolution DTI allows the estimation of average axon diameters in the corpus callosum of healthy human volunteers. Maps of inter-hemispheric average axon diameters reveal an anterior-posterior variation in good topographical agreement with anatomical measurements reported in previous post-mortem studies. With further technical refinements and additional clinical validation, qPFG diffusion MRI could provide a quantitative whole-brain histological assessment of white and gray matter, enabling a wide range of neuroimaging applications for improved diagnosis of neurodegenerative pathologies, monitoring neurodevelopmental processes, and mapping brain connectivity.

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“…Studies focusing on diffusion‐weighted imaging of the breast or the prostate are examples of this. To produce diffusion‐weighted images, diffusion‐tensor images, or conduct diffusion‐based tractography over these localized areas, the production of larger b ‐values using minimum possible echo times is desirable (1). At the same time, full field of view (FOV) images of the surrounding tissues must be obtained with minimal distortion.…”

Section: Introductionmentioning

confidence: 99%

“…One approach to this problem is the addition of “insert” gradient coils, powered by supplementary gradient amplifier channels, capable of achieving extremely high performance over localized regions of interest. Such coil inserts can be implemented to provide fourth, fifth, and sixth gradient channels (i.e., channels operated in addition to the three whole‐body gradient coil axes) exclusively for very high‐performance diffusion‐weighted imaging over a specified volume of tissue such as the breast, prostate, lungs, or posterior regions of the brain due to their possible open geometry (1, 6–8). Additionally, insert coils can be used for imaging alone (2, 9–13).…”

Section: Introductionmentioning

confidence: 99%

“…The size constraint imposed by the scanner bore, along with the necessity of maintaining access for the subject has required that the design of these coils stray from traditional cylindrical geometry (6, 9–13). Because of their open geometry and PNS advantages (14), planar gradient insert coils have been used as additional insert coils exclusively for high‐performance diffusion‐weighted imaging (1). Challenges in planar gradient coil design include relatively poor gradient homogeneity, torque issues, asymmetric eddy‐current profiles, and a drastic decrease in efficiency as the region of interest (ROI) moves away from the coil surface.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Design study to investigate the effect of curvature on gradient coil performance for localized regions of interest

Harris¹,

Handler²,

Chronik³

2012

Concepts Magn Reson

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In this study, a boundary element method has been implemented to design and analyze the performance of curved gradient coil geometries as a function of the degree of curvature over all three axes, with designs varying continuously from planar to full cylindrical. It was found that there is a monotonic increase in gradient performance with degree of curvature with little gain beyond half‐cylindrical coil geometries for a specific region of interest located 10 cm above the coil surface. The efficiencies of the half‐cylindrical geometry coils are 0.76 mT m−1 A−1, 0.71 mT m−1 A−1, and 0.76 mT m−1 A−1 for the x‐, y‐, and z‐gradient axes, respectively, when scaled to 800 μH inductance. The gradient coils presented in this study would serve as anatomically specific gradient channels to be used in conjunction with larger, whole‐body coils to comprise a 6‐channel hybrid system. The function of these channels could include the ability to provide very high performance diffusion tensor imaging in a specified volume of tissue such as the breast, prostate, or posterior regions of the brain. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 62–71, 2012

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Results for diffusion‐weighted imaging with a fourth‐channel gradient insert

Cited by 6 publications

References 28 publications

Driving mutually coupled gradient array coils in magnetic resonance imaging

Driving mutually coupled gradient array coils in magnetic resonance imaging

In vivo detection of microscopic anisotropy using quadruple pulsed-field gradient (qPFG) diffusion MRI on a clinical scanner

Design study to investigate the effect of curvature on gradient coil performance for localized regions of interest

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