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  • 1
    In: Medical Physics, Wiley, Vol. 44, No. 3 ( 2017-03), p. 1063-1070
    Abstract: Since Diffusion Weighted Imaging ( DWI ) data acquisition and processing are not standardized, substantial differences in DWI derived measures such as Apparent Diffusion Coefficient ( ADC ) may arise which are related to the acquisition or MRI processing method, but not to the sample under study. Quality assurance using a standardized test object, or phantom, is a key factor in standardizing DWI across scanners. Methods Current diffusion phantoms are either complex to use, not available in larger quantities, contain substances unwanted in a clinical environment, or are expensive. A diffusion phantom based on a polyvinylpyrrolidone ( PVP ) solution, together with a phantom holder, is presented and compared to existing diffusion phantoms for use in clinical DWI scans. An ADC vs. temperature calibration curve was obtained. Results ADC of the phantom (808 to 857 ± 0.2 mm 2 /s) is in the same range as ADC values found in brain tissue. ADC measurements are highly reproducible across time with an intra‐class correlation coefficient of 〉 0.8. ADC as function of temperature (in Kelvin) can be estimated as with a total uncertainty (95% confidence limit) of ± 1.7%. Conclusion We present an isotropic diffusion MRI phantom, together with its temperature calibration curve, that is easy‐to‐use in a clinical environment, cost‐effective, reproducible to produce, and that contains no harmful substances.
    Type of Medium: Online Resource
    ISSN: 0094-2405 , 2473-4209
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2017
    detail.hit.zdb_id: 1466421-5
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  • 2
    Online Resource
    Online Resource
    Wiley ; 2010
    In:  Journal of Magnetic Resonance Imaging Vol. 32, No. 2 ( 2010-07-22), p. 482-488
    In: Journal of Magnetic Resonance Imaging, Wiley, Vol. 32, No. 2 ( 2010-07-22), p. 482-488
    Type of Medium: Online Resource
    ISSN: 1053-1807 , 1522-2586
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2010
    detail.hit.zdb_id: 1497154-9
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  • 3
    Online Resource
    Online Resource
    Wiley ; 2023
    In:  Journal of Magnetic Resonance Imaging
    In: Journal of Magnetic Resonance Imaging, Wiley
    Type of Medium: Online Resource
    ISSN: 1053-1807 , 1522-2586
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 1497154-9
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  • 4
    In: Magnetic Resonance in Medicine, Wiley, Vol. 80, No. 2 ( 2018-08), p. 802-813
    Abstract: Diffusion kurtosis imaging (DKI) is an advanced magnetic resonance imaging modality that is known to be sensitive to changes in the underlying microstructure of the brain. Image voxels in diffusion weighted images, however, are typically relatively large making them susceptible to partial volume effects, especially when part of the voxel contains cerebrospinal fluid. In this work, we introduce the “Diffusion Kurtosis Imaging with Free Water Elimination” (DKI‐FWE) model that separates the signal contributions of free water and tissue, where the latter is modeled using DKI. Theory and Methods A theoretical study of the DKI‐FWE model, including an optimal experiment design and an evaluation of the relative goodness of fit, is carried out. To stabilize the ill‐conditioned estimation process, a Bayesian approach with a shrinkage prior (BSP) is proposed. In subsequent steps, the DKI‐FWE model and the BSP estimation approach are evaluated in terms of estimation error, both in simulation and real data experiments. Results Although it is shown that the DKI‐FWE model parameter estimation problem is ill‐conditioned, DKI‐FWE was found to describe the data significantly better compared to the standard DKI model for a large range of free water fractions. The acquisition protocol was optimized in terms of the maximally attainable precision of the DKI‐FWE model parameters. The BSP estimator is shown to provide reliable DKI‐FWE model parameter estimates. Conclusion The combination of the DKI‐FWE model with BSP is shown to be a feasible approach to estimate DKI parameters, while simultaneously eliminating free water partial volume effects. Magn Reson Med 80:802–813, 2018. © 2018 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 1493786-4
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  • 5
    In: Magnetic Resonance in Medicine, Wiley, Vol. 54, No. 6 ( 2005-12), p. 1465-1472
    Abstract: The blood oxygen level dependent (BOLD) response, as measured with fMRI, offers good spatial resolution compared to other non‐invasive neuroimaging methods. The use of a spin echo technique rather than the conventional gradient echo technique may further improve the resolution by refocusing static dephasing effects around the larger vessels, so sensitizing the signal to the microvasculature. In this work the width of the point spread function (PSF) of the BOLD response at a field strength of 3 Tesla is compared for these two approaches. A double echo EPI pulse sequence with simultaneous collection of gradient echo and spin echo signal allows a direct comparison of the techniques. Rotating multiple‐wedge stimuli of different spatial frequencies are used to estimate the width of the BOLD response. Waves of activation are created on the surface of the visual cortex, which begin to overlap as the wedge separation decreases. The modulation of the BOLD response decreases with increasing spatial frequency in a manner dependent on its width. The spin echo response shows a 13% reduction in the width of the PSF, but at a cost of at least 3‐fold reduction in contrast to noise ratio. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2005
    detail.hit.zdb_id: 1493786-4
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  • 6
    Online Resource
    Online Resource
    Wiley ; 2017
    In:  Journal of Magnetic Resonance Imaging Vol. 46, No. 5 ( 2017-11), p. 1423-1432
    In: Journal of Magnetic Resonance Imaging, Wiley, Vol. 46, No. 5 ( 2017-11), p. 1423-1432
    Abstract: A great need exists for objective biomarkers to assess graft healing following ACL reconstruction to guide the time of return to sports. The purpose of this study was to evaluate the feasibility and reliability of diffusion tensor imaging (DTI) to delineate the anterior cruciate ligament (ACL) graft and to investigate its diffusion properties using a clinical 3T scanner. Materials and Methods DTI of the knee (b = 0, 400, and 800 s/mm 2 , 10 diffusion directions, repeated 16 times for a total of 336 diffusion‐weighted volumes) was performed at 3T in 17 patients between 3 and 7 months (mean, 4 months) following ACL reconstruction. Tractography was performed by two independent observers to delineate the ACL graft. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated within the graft. Interrater reliability was assessed using the intraclass correlation coefficient (ICC) and the scan–rescan reproducibility was evaluated based on the percentage coefficient of variance (%CV) across 20 repetition bootknife samples. Results In all subjects, tractography of the ACL graft was feasible. Quantitative evaluation of the diffusion properties of the ACL graft yielded the following mean ± SD values: FA = 0.23 ± 0.04; MD = 1.30 ± 0.11 × 10 −3 mm 2 /s; AD = 1.61 ± 0.12 × 10 −3 mm 2 /s, and RD = 1.15 ± 0.11 × 10 −3 mm 2 /s. Interrater reliability for the DTI parameters was excellent (ICC = 0.91–0.98). Mean %CVs for FA, MD, AD, and RD were 4.6%, 3.5%, 3.7%, and 4.4%, respectively. Conclusion We demonstrated the feasibility and reliability of DTI for the visualization and quantitative evaluation of the ACL graft at 3T. Level of Evidence: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1423–1432.
    Type of Medium: Online Resource
    ISSN: 1053-1807 , 1522-2586
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2017
    detail.hit.zdb_id: 1497154-9
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  • 7
    Online Resource
    Online Resource
    Wiley ; 2021
    In:  Journal of Magnetic Resonance Imaging Vol. 53, No. 4 ( 2021-04), p. 1188-1189
    In: Journal of Magnetic Resonance Imaging, Wiley, Vol. 53, No. 4 ( 2021-04), p. 1188-1189
    Type of Medium: Online Resource
    ISSN: 1053-1807 , 1522-2586
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 1497154-9
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