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  • 1
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    Magnetization transfer from inhomogeneously broadened lines (ihMT): Improved imaging strategy for spinal cord applications (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2016-03-10
    Description: Purpose Inhomogeneous magnetization transfer (ihMT) shows great promise for specific imaging of myelinated tissues. Whereas the ihMT technique has been previously applied in brain applications, the current report presents a strategy for cervical spinal cord (SC) imaging free of cerebrospinal fluid (CSF) pulsatility artifacts. Methods A pulsed ihMT preparation was combined with a single-shot HASTE readout. Electrocardiogram (ECG) synchronization was used to acquire all images during the quiescent phase of SC motion. However ihMT signal quantification errors may occur when a variable recovery delay is introduced in the sequence as a consequence of variable cardiac cycle. A semiautomatic retrospective correction algorithm, based on repetition time (TR) -matching, is proposed to correct for signal variations of long T 1 -components (e.g., CSF). Results The proposed strategy combining ECG synchronization and retrospective data pairing led to clean SC images free of CSF artifacts. Lower variability of the ihMT metrics were obtained with the correction algorithm, and allowed for shorter TR to be used, hence improving signal-to-noise ratio efficiency. Conclusion The proposed methodology enabled faster acquisitions, while offering robust ihMT quantification and exquisite SC image quality. This opens great perspectives for widening the in vivo characterization of SC physiopathology using MRI, such as studying white matter tracts microstructure or impairment in degenerative pathologies. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
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  • 2
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    In vivo free-breathing DTI and IVIM of the whole human heart using a real-time slice-followed SE-EPI navigator-based sequence: A reproducibility study in healthy volunteers (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2016-06-16
    Description: Purpose In this study, we proposed an efficient free-breathing strategy for rapid and improved cardiac diffusion-weighted imaging (DWI) acquisition using a single-shot spin-echo echo planar imaging (SE-EPI) sequence. Methods : A real-time slice-following technique during free-breathing was combined with a sliding acquisition-window strategy prior Principal Component Analysis temporal Maximum Intensity Projection (PCAtMIP) postprocessing of in-plane co-registered diffusion-weighted images. This methodology was applied to 10 volunteers to quantify the performance of the motion correction technique and the reproducibility of diffusion parameters. Results : The slice-following technique offers a powerful head–foot respiratory motion management solution for SE-EPI cDWI with the advantage of a 100% duty cycle scanning efficiency. The level of co-registration was further improved using nonrigid motion corrections and was evaluated with a co-registration index. Vascular fraction f and the diffusion coefficients D and D* were determined to be 0.122 ± 0.013, 1.41 ± 0.09 × 10 −3 mm 2 /s and 43.6 ± 9.2 × 10 −3 mm 2 /s, respectively. From the multidirectional dataset, the measured mean diffusivity was 1.72 ± 0.09 × 10 −3 mm 2 /s and the fractional anisotropy was 0.36 ± 0.02. Conclusion : The slice-following DWI SE-EPI sequence is a promising solution for clinical implementation, offering a robust improved workflow for further evaluation of DWI in cardiology. Magn Reson Med 76:1–2, 2016. © 2015 Wiley Periodicals, Inc.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
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  • 3
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    Parallel-transmission-enabled three-dimensional T2-weighted imaging of the human brain at 7 Tesla (2014)
    Wiley-Blackwell
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    Publication Date: 2014-07-09
    Description: Purpose: A promise of ultra high field MRI is to produce images of the human brain with higher spatial resolution due to an increased signal to noise ratio. Yet, the shorter radiofrequency wavelength induces an inhomogeneous distribution of the transmit magnetic field and thus challenges the applicability of MRI sequences which rely on the spin excitation homogeneity. In this work, the ability of parallel-transmission to obtain high-quality T 2 -weighted images of the human brain at 7 Tesla, using an original pulse design method is evaluated. Methods: Excitation and refocusing square pulses of a SPACE sequence were replaced with short nonselective transmit-SENSE pulses individually tailored with the gradient ascent pulse engineering algorithm, adopting a k T -point trajectory to simultaneously mitigate B 1 + and ΔB 0 nonuniformities. Results: In vivo experiments showed that exploiting parallel-transmission at 7T with the proposed methodology produces high quality T 2 -weighted whole brain images with uniform signal and contrast. Subsequent white and gray matter segmentation confirmed the expected improvements in image quality. Conclusion: This work demonstrates that the adopted formalism based on optimal control, combined with the k T -point method, successfully enables three-dimensional T 2 -weighted brain imaging at 7T devoid of artifacts resulting from B 1 + inhomogeneity. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
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  • 4
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    Myocardial perfusion assessment in humans using steady-pulsed arterial spin labeling (2014)
    Wiley-Blackwell
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    Publication Date: 2014-09-27
    Description: Purpose Although arterial spin labeling (ASL) has become a routinely performed method in the rodent heart, its application to the human heart remains challenged by low tissue blood flow and cardiac and respiratory motion. We hypothesized that an alternative steady-pulsed ASL (spASL) method would provide more efficient perfusion signal averaging by driving the tissue magnetization into a perfusion-dependent steady state. Methods We evaluated the feasibility of spASL in the human heart by combining pulsed labeling in the aortic root with a balanced steady state free precession sequence. The spASL scheme was applied to 13 subjects under free breathing. Breathing motion was addressed using retrospective image exclusion based on a contour-based cross-correlation algorithm. Results The measured signal with spASL was due to labeled blood. We found that the perfusion signal was larger than that obtained with the earlier flow-sensitive alternating inversion recovery (FAIR) method. Averaged myocardial blood flow (MBF) over four myocardial regions was 1.28 ± 0.36 mL·g −1 ·min −1 . Conclusion spASL was able to quantify MBF in healthy subjects under free breathing. Because quantification with ASL is more direct than with first-pass perfusion MRI, it appears particularly suited for pathologies with diffuse microvascular alterations, MBF reserve, and follow-up studies. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
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    PAPER CURRENT
  • 5
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    In vivo free-breathing DTI and IVIM of the whole human heart using a real-time slice-followed SE-EPI navigator-based sequence: A reproducibility study in healthy volunteers (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2015-08-25
    Description: Purpose In this study, we proposed an efficient free-breathing strategy for rapid and improved cardiac diffusion-weighted imaging (DWI) acquisition using a single-shot spin-echo echo planar imaging (SE-EPI) sequence. Methods : A real-time slice-following technique during free-breathing was combined with a sliding acquisition-window strategy prior Principal Component Analysis temporal Maximum Intensity Projection (PCAtMIP) postprocessing of in-plane co-registered diffusion-weighted images. This methodology was applied to 10 volunteers to quantify the performance of the motion correction technique and the reproducibility of diffusion parameters. Results : The slice-following technique offers a powerful head–foot respiratory motion management solution for SE-EPI cDWI with the advantage of a 100% duty cycle scanning efficiency. The level of co-registration was further improved using nonrigid motion corrections and was evaluated with a co-registration index. Vascular fraction f and the diffusion coefficients D and D* were determined to be 0.122 ± 0.013, 1.41 ± 0.09 × 10 −3 mm 2 /s and 43.6 ± 9.2 × 10 −3 mm 2 /s, respectively. From the multidirectional dataset, the measured mean diffusivity was 1.72 ± 0.09 × 10 −3 mm 2 /s and the fractional anisotropy was 0.36 ± 0.02. Conclusion : The slice-following DWI SE-EPI sequence is a promising solution for clinical implementation, offering a robust improved workflow for further evaluation of DWI in cardiology. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
    Print ISSN: 0740-3194
    Electronic ISSN: 1522-2594
    Topics: Medicine
    Published by Wiley-Blackwell
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
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