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  • 1
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    Online Resource
    Suppression of lipid artifacts in amide proton transfer imaging
    Wiley ; 2005
    In:  Magnetic Resonance in Medicine Vol. 54, No. 1 ( 2005-07), p. 222-225
    Details
    In: Magnetic Resonance in Medicine, Wiley, Vol. 54, No. 1 ( 2005-07), p. 222-225
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    URL: Journal
    URL: Article
    DOI: 10.1002/mrm.v54:1
    DOI: 10.1002/(ISSN)1522-2594
    DOI: 10.1002/mrm.20530
    Language: English
    Publisher: Wiley
    Publication Date: 2005
    detail.hit.zdb_id: 1493786-4
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  • 2
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    Tissue perfusion of the kurtosis/diffusion mismatch differs from the central core and peripheral regions in acute cerebral infarction patients
    SAGE Publications ; 2023
    In:  Acta Radiologica Vol. 64, No. 3 ( 2023-03), p. 1155-1165
    Details
    In: Acta Radiologica, SAGE Publications, Vol. 64, No. 3 ( 2023-03), p. 1155-1165
    Abstract: Despite its wide adoption in stroke imaging, the diffusion-weighted imaging (DWI) lesion is heterogeneous. The emerging diffusion kurtosis imaging (DKI) has been postulated to resolve the graded DWI lesion. Purpose To determine the perfusion characteristics of the central infarction core, kurtosis/diffusion mismatch, and peripheral regions. Material and Methods Patients with acute ischemic stroke underwent DWI, DKI, and perfusion-weighted imaging (PWI) scans. The patients were divided into mean kurtosis (MK)/mean diffusivity (MD) match and mismatch groups. Perfusion parameters were measured in the MK/MD lesion and peripheral areas in the MK/MD match group. We also analyzed perfusion status in the MK/MD lesion mismatch area for the mismatch group. Results A total of 40 eligible patients (24 MK/MD match and 16 MK/MD mismatch) were enrolled in the final data analysis. The MTT and TTP progressively decreased, while the cerebral blood flow (CBF) and cerebral blood volume (CBV) increased from the central to peripheral areas. In addition, CBF in the MK/MD mismatch region was significantly higher than that in the central region ( P  〈  0.05), but similar to the peripheral region. Furthermore, CBV in the MK/MD mismatch region did not differ significantly from that of the central region, but both were significantly lower than that of the peripheral area ( P  〈  0.05). Conclusion The MK/MD mismatch region had blood flow similar to the peripheral region but with a reduced blood volume, indicating that it was less ischemic from the infarction core, albeit insufficient collateral circulation.
    Type of Medium: Online Resource
    ISSN: 0284-1851 , 1600-0455
    URL: Article
    DOI: 10.1177/02841851221109678
    RVK:
    XA 10000
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2023
    detail.hit.zdb_id: 2024579-8
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  • 3
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    Detection of the Ischemic Penumbra Using pH-Weighted MRI
    SAGE Publications ; 2007
    In:  Journal of Cerebral Blood Flow & Metabolism Vol. 27, No. 6 ( 2007-06), p. 1129-1136
    Details
    In: Journal of Cerebral Blood Flow & Metabolism, SAGE Publications, Vol. 27, No. 6 ( 2007-06), p. 1129-1136
    Abstract: The classic definition of the ischemic penumbra is a hypoperfused region in which metabolism is impaired, but still sufficient to maintain cellular polarization. Perfusion- and diffusion-weighted MRI (PWI, DWI) can identify regions of reduced perfusion and cellular depolarization, respectively, but it often remains unclear whether a PWI—DWI mismatch corresponds to benign oligemia or a true penumbra. We hypothesized that pH-weighted MRI (pHWI) can subdivide the PWI—DWI mismatch into these regions. Twenty-one rats underwent permanent middle cerebral artery occlusion and ischemic evolution over the first 3.5 h post-occlusion was studied using multiparametric MRI. End point was the stroke area defined by T 2 -hyperintensity at 24 h. In the acute phase, areas of reduced pH were always larger than or equal to DWI deficits and smaller than or equal to PWI deficits. Group analysis showed that pHWI deficits during this phase coincided with the resulting infarct area at endpoint. Final infarcts were smaller than PWI deficits (range 65% to 90%, depending on the severity of the occlusion) and much larger than acute DWI deficits. These data suggest that the outer boundary of the hypoperfused area showing a decrease in pH without DWI abnormality may correspond to the outer boundary of the ischemic penumbra, while the hypoperfused region at normal pH may correspond to benign oligemia. These first results show that pHWI can provide information complementary to PWI and DWI in the delineation of ischemic tissue.
    Type of Medium: Online Resource
    ISSN: 0271-678X , 1559-7016
    URL: Article
    DOI: 10.1038/sj.jcbfm.9600424
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2007
    detail.hit.zdb_id: 2039456-1
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  • 4
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    Diffusion Kurtosis Imaging of Acute Infarction: Comparison with Routine Diffusion and Follow-up MR Imaging
    Radiological Society of North America (RSNA) ; 2018
    In:  Radiology Vol. 287, No. 2 ( 2018-05), p. 651-657
    Details
    In: Radiology, Radiological Society of North America (RSNA), Vol. 287, No. 2 ( 2018-05), p. 651-657
    Type of Medium: Online Resource
    ISSN: 0033-8419 , 1527-1315
    URL: Article
    DOI: 10.1148/radiol.2017170553
    RVK:
    XA 10000
    Language: English
    Publisher: Radiological Society of North America (RSNA)
    Publication Date: 2018
    detail.hit.zdb_id: 80324-8
    detail.hit.zdb_id: 2010588-5
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  • 5
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    Stratification of Heterogeneous Diffusion MRI Ischemic Lesion With Kurtosis Imaging : Evaluation of Mean Diffusion and Kurtosis MRI Mismatch in an Animal Model of Transient Focal Ischemia
    Ovid Technologies (Wolters Kluwer Health) ; 2012
    In:  Stroke Vol. 43, No. 8 ( 2012-08), p. 2252-2254
    Details
    In: Stroke, Ovid Technologies (Wolters Kluwer Health), Vol. 43, No. 8 ( 2012-08), p. 2252-2254
    Abstract: Ischemic tissue damage is heterogeneous, resulting in complex patterns in the widely used diffusion-weighted MRI. Our study examined the spatiotemporal characteristics of diffusion kurtosis imaging in an animal model of transient middle cerebral artery occlusion. Methods— Adult male Wistar rats (N=18) were subjected to 90 minutes middle cerebral artery occlusion. Multiparametric MR images were obtained during middle cerebral artery occlusion and 20 minutes after reperfusion with diffusion-weighted MRI obtained using 8 b-values from 250 to 3000 s/mm 2 in 6 diffusion gradient directions. Diffusion and kurtosis lesions were outlined in shuffled images by 2 investigators independently. T 2 MRI was obtained 24 hours after middle cerebral artery occlusion to evaluate stroke outcome. Results— Mean diffusion lesion (23.5%±8.1%, percentage of the brain slice) was significantly larger than mean kurtosis lesion (13.2%±2.0%) during middle cerebral artery occlusion. Mean diffusion lesion decreased significantly after reperfusion (13.8%±4.3%), whereas mean kurtosis lesion showed little change (13.0%±2.5%) with their lesion size difference being insignificant. Conclusions— We demonstrated that mean diffusion/mean kurtosis mismatch recovered reasonably well on reperfusion, whereas regions with concurrent mean diffusion and mean kurtosis deficits showed poor recovery. Diffusion kurtosis imaging may help stratify heterogeneous diffusion-weighted MRI lesions for enhanced characterization of ischemic tissue injury.
    Type of Medium: Online Resource
    ISSN: 0039-2499 , 1524-4628
    URL: Article
    DOI: 10.1161/STROKEAHA.112.661926
    RVK:
    XA 10000
    Language: English
    Publisher: Ovid Technologies (Wolters Kluwer Health)
    Publication Date: 2012
    detail.hit.zdb_id: 1467823-8
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  • 6
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    Development of intravoxel inhomogeneity correction for chemical exchange saturation transfer spectral imaging: a high‐resolution field map‐based deconvolution algorithm for magnetic field inhomogeneity correction
    Wiley ; 2020
    In:  Magnetic Resonance in Medicine Vol. 83, No. 4 ( 2020-04), p. 1348-1355
    Details
    In: Magnetic Resonance in Medicine, Wiley, Vol. 83, No. 4 ( 2020-04), p. 1348-1355
    Abstract: CEST MRI is sensitive to dilute proteins/peptides and microenvironmental properties yet susceptible to magnetic field inhomogeneity. We aimed to develop a high‐resolution field map‐based CEST intravoxel inhomogeneity correction (CIVIC) algorithm for CEST Z‐spectral imaging. Methods The proposed CIVIC approach treats the intravoxel inhomogeneity as a point spread function and applies the deconvolution algorithm to reconstruct the original Z‐spectrum. We simulated the effect of B 0 field inhomogeneity on CEST measurement and tested the efficacy of the proposed CIVIC algorithm. We also performed CEST MRI on a dual‐pH Creatine‐gel phantom under varied field homogeneity conditions and compared the CEST MRI contrast‐to‐noise ratio from the raw Z‐spectrum, water saturation shift referencing, and the proposed CIVIC methods. Results The numerical simulation showed that the CIVIC algorithm remains effective even in the case of symmetric field dispersion with a 0 mean shift. The experimental results confirmed that the proposed CIVIC method substantially improves the CEST MRI contrast‐to‐noise ratio under different field homogeneity conditions. Conclusion Our study established a new intravoxel B 0 inhomogeneity correction algorithm, promising to facilitate CEST spectral imaging in challenging experimental conditions.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    URL: Article
    DOI: 10.1002/mrm.v83.4
    DOI: 10.1002/mrm.28015
    Language: English
    Publisher: Wiley
    Publication Date: 2020
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  • 7
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    Improved MR fingerprinting for relaxation measurement in the presence of semisolid magnetization transfer
    Wiley ; 2020
    In:  Magnetic Resonance in Medicine Vol. 84, No. 2 ( 2020-08), p. 727-737
    Details
    In: Magnetic Resonance in Medicine, Wiley, Vol. 84, No. 2 ( 2020-08), p. 727-737
    Abstract: To characterize and minimize the magnetization transfer (MT) effect in MR fingerprinting (MRF) relaxation measurements with a 2‐pool (2P) MT model of multiple tissue types. Theory and Methods Semisolid MT effect in MRF was modeled using 2P Bloch‐McConnell equations. The combinations of MT parameters of multiple tissues (white [WM] and gray matter [GM] ) were used to build the MRF dictionary. Both 1‐pool (1P) and 2P models were simulated to characterize the dependence on MT. Relaxations measured using MRF with spin‐echo saturation‐recovery (SR) or inversion‐recovery preparations were compared with conventional SR‐prepared T 1 and multiple spin‐echo T 2 measurements. The simulations results were validated with phantoms and brain tissue samples. Results The MRF signal was different from the 1P and 2P models. 1P MRF produced significantly ( P 〈 .05) underestimated T 1 in WM (20‐30%) and GM (7‐10%), while 2P MRF measured consistent T 1 and T 2 in both WM and GM with conventional measurements (pairwise test P 〉 .1; correlated P 〈 .05). Simulations showed that SR‐prepared MRF measuring T 1 had much less errors against the variation of the macromolecular fraction. Compared with inversion‐recovery preparation, SR‐prepared MRF produced higher relaxation correlations (R 〉 0.9) with conventional measurements in both WM and GM across samples, suggesting that SR‐prepared MRF was less sensitive to the compositive effect of multiple MT parameters variations. Conclusions 2P MRF using a combination of MT parameters for multiple tissue types can measure consistent relaxations with conventional methods. With the 2P models, SR‐prepared MRF would provide an option for robust relaxation measurement under heterogeneous MT.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    URL: Article
    DOI: 10.1002/mrm.v84.2
    DOI: 10.1002/mrm.28159
    Language: English
    Publisher: Wiley
    Publication Date: 2020
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  • 8
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    Comparison of model‐free Lorentzian and spinlock model‐based fittings in quantitative CEST imaging of acute stroke
    Wiley ; 2023
    In:  Magnetic Resonance in Medicine Vol. 90, No. 5 ( 2023-11), p. 1958-1968
    Details
    In: Magnetic Resonance in Medicine, Wiley, Vol. 90, No. 5 ( 2023-11), p. 1958-1968
    Abstract: CEST MRI detects complex tissue changes following acute stroke. Our study aimed to test if spinlock model‐based fitting of the quasi‐steady‐state (QUASS)‐reconstructed equilibrium CEST MRI improves the determination of multi‐pool signal changes over the commonly‐used model‐free Lorentzian fitting in acute stroke. Theory and Methods Multiple three‐pool CEST Z ‐spectra were simulated using Bloch‐McConnell equations for a range of T 1 , relaxation delay, and saturation times. The multi‐pool CEST signals were solved from the simulated Z ‐spectra to test the accuracy of routine Lorentzian (model‐free) and spinlock (model‐based) fittings without and with QUASS reconstruction. In addition, multiparametric MRI scans were obtained in rat models of acute stroke, including relaxation, diffusion, and CEST Z ‐spectrum. Finally, we compared model‐free and model‐based per‐pixel CEST quantification in vivo. Results The spinlock model‐based fitting of QUASS CEST MRI provided a nearly T 1 ‐independent determination of multi‐pool CEST signals, advantageous over the fittings of apparent CEST MRI (model‐free and model‐based). In vivo data also demonstrated that the spinlock model‐based QUASS fitting captured significantly different changes in semisolid magnetization transfer (−0.9 ± 0.8 vs. 0.3 ± 0.8%), amide (−1.1 ± 0.4 vs. −0.5 ± 0.2%), and guanidyl (1.0 ± 0.4 vs. 0.7 ± 0.3%) signals over the model‐free Lorentzian analysis. Conclusion Our study demonstrated that spinlock model‐based fitting of QUASS CEST MRI improved the determination of the underlying tissue changes following acute stroke, promising further clinical translation of quantitative CEST imaging.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    URL: Article
    DOI: 10.1002/mrm.v90.5
    DOI: 10.1002/mrm.29772
    Language: English
    Publisher: Wiley
    Publication Date: 2023
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  • 9
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    Fast multislice pH‐weighted chemical exchange saturation transfer (CEST) MRI with Unevenly segmented RF irradiation
    Wiley ; 2011
    In:  Magnetic Resonance in Medicine Vol. 65, No. 2 ( 2011-02), p. 588-594
    Details
    In: Magnetic Resonance in Medicine, Wiley, Vol. 65, No. 2 ( 2011-02), p. 588-594
    Abstract: Chemical exchange saturation transfer (CEST) MRI is a versatile imaging technique for measuring microenvironment properties via dilute CEST labile groups. Conventionally, CEST MRI is implemented with a long radiofrequency irradiation module, followed by fast image acquisition to obtain the steady state CEST contrast. Nevertheless, the sensitivity, scan time, and spatial coverage of the conventional CEST MRI method may not be optimal. Our study proposed a segmented radiofrequency labeling scheme that includes a long primary radiofrequency irradiation module to generate the steady state CEST contrast and repetitive short secondary radiofrequency irradiation module immediately after the image acquisition so as to maintain the steady state CEST contrast for multislice acquisition and signal averaging. The proposed CEST MRI method was validated experimentally with a tissue‐like pH phantom and optimized for the maximal contrast‐to‐noise ratio. In addition, the proposed sequence was evaluated for imaging ischemic acidosis via pH‐weighted endogenous amide proton transfer MRI, which showed similar contrast as conventional amide proton transfer MRI. In sum, a fast multislice relaxation self‐compensated CEST MRI sequence was developed, with significantly improved sensitivity and suitable for in vivo applications. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    URL: Article
    DOI: 10.1002/mrm.v65.2
    DOI: 10.1002/mrm.22628
    Language: English
    Publisher: Wiley
    Publication Date: 2011
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  • 10
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    Relaxation-compensated fast multislice amide proton transfer (APT) imaging of acute ischemic stroke
    Wiley ; 2008
    In:  Magnetic Resonance in Medicine Vol. 59, No. 5 ( 2008-05), p. 1175-1182
    Details
    In: Magnetic Resonance in Medicine, Wiley, Vol. 59, No. 5 ( 2008-05), p. 1175-1182
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    URL: Journal
    URL: Article
    DOI: 10.1002/mrm.v59:5
    DOI: 10.1002/(ISSN)1522-2594
    DOI: 10.1002/mrm.21591
    Language: English
    Publisher: Wiley
    Publication Date: 2008
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