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  • 1
    In: Journal of Magnetic Resonance Imaging, Wiley, Vol. 50, No. 4 ( 2019-10), p. 1133-1143
    Abstract: The 3D breast magnetic resonance fingerprinting (MRF) technique enables T 1 and T 2 mapping in breast tissues. Combined repeatability and reproducibility studies on breast T 1 and T 2 relaxometry are lacking. Purpose To assess test–retest and two‐visit repeatability and interscanner reproducibility of the 3D breast MRF technique in a single‐institution setting. Study Type Prospective. Subjects Eighteen women (median age 29 years, range, 22–33 years) underwent Visit 1 scans on scanner 1. Ten of these women underwent test–retest scan repositioning after a 10‐minute interval. Thirteen women had Visit 2 scans within 7–15 days in same menstrual cycle. The remaining five women had Visit 2 scans in the same menstrual phase in next menstrual cycle. Five women were also scanned on scanner 2 at both visits for interscanner reproducibility. Field Strength/Sequence Two 3T MR scanners with the 3D breast MRF technique. Assessment T 1 and T 2 MRF maps of both breasts. Statistical Tests Mean T 1 and T 2 values for normal fibroglandular tissues were quantified at all scans. For variability, between and within‐subjects coefficients of variation (bCV and wCV, respectively) were assessed. Repeatability was assessed with Bland–Altman analysis and coefficient of repeatability (CR). Reproducibility was assessed with interscanner coefficient of variation (CoV) and Wilcoxon signed‐rank test. Results The bCV at test–retest scans was 9–12% for T 1 , 7–17% for T 2 , wCV was 〈 4% for T 1 , and 〈 7% for T 2 . For two visits in same menstrual cycle, bCV was 10–15% for T 1 , 13–17% for T 2 , wCV was 〈 7% for T 1 and 〈 5% for T 2 . For two visits in the same menstrual phase, bCV was 6–14% for T 1 , 15–18% for T 2 , wCV was 〈 7% for T 1 , and 〈 9% for T 2 . For test–retest scans, CR for T 1 and T 2 were 130 msec and 11 msec. For two visit scans, CR was 〈 290 msec for T 1 and 10–14 msec for T 2 . Interscanner CoV was 3.3–3.6% for T 1 and 5.1–6.6% for T 2 , with no differences between interscanner measurements ( P  = 1.00 for T 1 , P  = 0.344 for T 2 ). Data Conclusion 3D breast MRF measurements are repeatable across scan timings and scanners and may be useful in clinical applications in breast imaging. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:1133–1143.
    Type of Medium: Online Resource
    ISSN: 1053-1807 , 1522-2586
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 1497154-9
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  • 2
    In: Magnetic Resonance in Medicine, Wiley, Vol. 77, No. 1 ( 2017-01), p. 250-264
    Abstract: Real‐time free‐breathing cardiac imaging with highly undersampled radial trajectories has previously been successfully demonstrated using calibrated radial generalized autocalibrating partially parallel acquisition (rGRAPPA). A self‐calibrated approach for rGRAPPA is proposed that removes the need for the calibration prescan. Methods To investigate the effect of various parameters on image quality, a comprehensive imaging study on one normal swine was performed. Root mean squared errors (RMSEs) were computed with respect to gold standard acquisitions, and several acquisition/reconstruction strategies were compared. Additionally, the method was tested on 13 human subjects, and RMSEs relative to standard through‐time radial GRAPPA were computed. Results Real‐time images with high spatiotemporal resolution were obtained. Image quality was comparable to calibrated through‐time rGRAPPA with endocardial and epicardial borders clearly delineated. In the swine, the average RMSE between self‐calibrated and gold‐standard calibrated images was 5.18 ± 0.84%. In normal human subjects, the average RMSE between self‐calibrated and calibrated through‐time rGRAPPA was 3.79 ± 0.64%. For lower accelerations rates (R = 6‐8) image quality was similar to comparable calibrated scans though RMSE increased for higher degrees of undersampling (R = 12–16). Conclusion Highly accelerated real‐time imaging with undersampled radial trajectories without additional calibration data is feasible. Image quality was acceptable for real‐time cardiac MRI applications demanding high speed. Magn Reson Med 77:250–264, 2017. © 2016 Wiley Periodicals, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2017
    detail.hit.zdb_id: 1493786-4
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  • 3
    Online Resource
    Online Resource
    Wiley ; 2021
    In:  Magnetic Resonance in Medicine Vol. 85, No. 4 ( 2021-04), p. 2127-2135
    In: Magnetic Resonance in Medicine, Wiley, Vol. 85, No. 4 ( 2021-04), p. 2127-2135
    Abstract: To develop a deep learning method for rapidly reconstructing T 1 and T 2 maps from undersampled electrocardiogram (ECG) triggered cardiac magnetic resonance fingerprinting (cMRF) images. Methods A neural network was developed that outputs T 1 and T 2 values when given a measured cMRF signal time course and cardiac RR interval times recorded by an ECG. Over 8 million cMRF signals, corresponding to 4000 random cardiac rhythms, were simulated for training. The training signals were corrupted by simulated k‐space undersampling artifacts and random phase shifts to promote robust learning. The deep learning reconstruction was evaluated in Monte Carlo simulations for a variety of cardiac rhythms and compared with dictionary‐based pattern matching in 58 healthy subjects at 1.5T. Results In simulations, the normalized root‐mean‐square error (nRMSE) for T 1 was below 1% in myocardium, blood, and liver for all tested heart rates. For T 2 , the nRMSE was below 4% for myocardium and liver and below 6% for blood for all heart rates. The difference in the mean myocardial T 1 or T 2 observed in vivo between dictionary matching and deep learning was 3.6 ms for T 1 and −0.2 ms for T 2 . Whereas dictionary generation and pattern matching required more than 4 min per slice, the deep learning reconstruction only required 336 ms. Conclusion A neural network is introduced for reconstructing cMRF T 1 and T 2 maps directly from undersampled spiral images in under 400 ms and is robust to arbitrary cardiac rhythms, which paves the way for rapid online display of cMRF maps.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 1493786-4
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  • 4
    Online Resource
    Online Resource
    Wiley ; 2011
    In:  Magnetic Resonance in Medicine Vol. 66, No. 6 ( 2011-12), p. 1682-1688
    In: Magnetic Resonance in Medicine, Wiley, Vol. 66, No. 6 ( 2011-12), p. 1682-1688
    Abstract: Previous work has shown that the use of radial GRAPPA for the reconstruction of undersampled real‐time free‐breathing cardiac data allows for frame rates of up to 30 images/s. It is well known that the spiral trajectory offers a higher scan efficiency compared to radial trajectories. For this reason, we have developed a novel through‐time spiral GRAPPA method and demonstrate its application to real‐time cardiac imaging. By moving from the radial trajectory to the spiral trajectory, the temporal resolution can be further improved at lower acceleration factors compared to radial GRAPPA. In addition, the image quality is improved compared to those generated using the radial trajectory due to the lower acceleration factor. Here, we show that 2D frame rates of up to 56 images/s can be achieved using this parallel imaging method with the spiral trajectory. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2011
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  • 5
    Online Resource
    Online Resource
    Wiley ; 2006
    In:  Magnetic Resonance in Medicine Vol. 56, No. 6 ( 2006-12), p. 1359-1364
    In: Magnetic Resonance in Medicine, Wiley, Vol. 56, No. 6 ( 2006-12), p. 1359-1364
    Abstract: When using parallel MRI (pMRI) methods in combination with three‐dimensional (3D) imaging, it is beneficial to subsample the k ‐space along both phase‐encoding directions because one can then take advantage of coil sensitivity variations along two spatial dimensions. This results in an improved reconstruction quality and therefore allows greater scan time reductions as compared to subsampling along one dimension. In this work we present a new approach based on the generalized autocalibrating partially parallel acquisitions (GRAPPA) technique that allows Fourier‐domain reconstructions of data sets that are subsampled along two dimensions. The method works by splitting the 2D reconstruction process into two separate 1D reconstructions. This approach is compared with an extension of the conventional GRAPPA method that directly regenerates missing data points of a 2D subsampled k ‐space by performing a linear combination of acquired data points. In this paper we describe the theoretical background and present computer simulations and in vivo experiments. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2006
    detail.hit.zdb_id: 1493786-4
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  • 6
    Online Resource
    Online Resource
    Wiley ; 2008
    In:  Magnetic Resonance in Medicine Vol. 60, No. 2 ( 2008-08), p. 474-478
    In: Magnetic Resonance in Medicine, Wiley, Vol. 60, No. 2 ( 2008-08), p. 474-478
    Abstract: Conventional Cartesian parallel MRI methods are limited to the sensitivity variations provided by the underlying receiver coil array in the dimension in which the data reduction is carried out, namely, the phase‐encoding directions. However, in this work an acquisition strategy is presented that takes advantage of sensitivity variations in the readout direction, thus improving the parallel imaging reconstruction process. This is achieved by employing rapidly oscillating phase‐encoding gradients during the actual readout. The benefit of this approach is demonstrated in vivo using various zigzag‐shaped gradient trajectory designs. It is shown that zigzag type sampling, in analogy to CAIPIRINHA, modifies the appearance of aliasing in 2D and 3D imaging, thereby utilizing additional sensitivity variations in the readout direction directly resulting in improved parallel imaging reconstruction performance. Magn Reson Med 60:474–478, 2008. © 2008 Wiley‐Liss, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2008
    detail.hit.zdb_id: 1493786-4
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  • 7
    Online Resource
    Online Resource
    Wiley ; 2007
    In:  Magnetic Resonance in Medicine Vol. 57, No. 6 ( 2007-06), p. 1037-1046
    In: Magnetic Resonance in Medicine, Wiley, Vol. 57, No. 6 ( 2007-06), p. 1037-1046
    Abstract: MRI with non‐Cartesian sampling schemes can offer inherent advantages. Radial acquisitions are known to be very robust, even in the case of vast undersampling. This is also true for 1D non‐Cartesian MRI, in which the center of k ‐space is oversampled or at least sampled at the Nyquist rate. There are two main reasons for the more relaxed foldover artifact behavior: First, due to the oversampling of the center, high‐energy foldover artifacts originating from the center of k ‐space are avoided. Second, due to the non‐equidistant sampling of k ‐space, the corresponding field of view (FOV) is no longer well defined. As a result, foldover artifacts are blurred over a broad range and appear less severe. The more relaxed foldover artifact behavior and the densely sampled central k ‐space make trajectories of this type an ideal complement to autocalibrated parallel MRI (pMRI) techniques, such as generalized autocalibrating partially parallel acquisitions (GRAPPA). Although pMRI can benefit from non‐Cartesian trajectories, this combination has not yet entered routine clinical use. One of the main reasons for this is the need for long reconstruction times due to the complex calculations necessary for non‐Cartesian pMRI. In this work it is shown that one can significantly reduce the complexity of the calculations by exploiting a few specific properties of k ‐space‐based pMRI. Magn Reson Med 57:1037–1046, 2007. © 2007 Wiley‐Liss, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2007
    detail.hit.zdb_id: 1493786-4
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  • 8
    In: Magnetic Resonance in Medicine, Wiley, Vol. 75, No. 2 ( 2016-02), p. 883-896
    Abstract: In radial imaging, projections may become “miscentered” due to gradient errors such as delays and eddy currents. These errors may result in image artifacts and can disrupt the reliability of direct current (DC) navigation. The proposed parallel imaging–based technique retrospectively estimates trajectory error from miscentered radial data without extra acquisitions, hardware, or sequence modification. Theory and Methods After phase correction, self‐calibrated GRAPPA operator gridding (GROG) weights are iteratively applied to shift‐miscentered projections toward the center of k‐space. A search algorithm identifies the shift that aligns the peak k‐space signals by maximizing the sum‐of‐squares DC signal estimate of each projection. The algorithm returns a trajectory estimate and a corrected radial k‐space signal. Results Data from a spherical phantom, the head, and the heart demonstrate that image reconstruction with the estimated trajectory restores image quality and reduces artifacts such as streaks and signal voids. The DC signal level is increased and variability is reduced. Conclusion Retrospective phase correction and iterative application of GROG can be used to successfully estimate the trajectory error in two‐dimensional radial acquisitions for improved image reconstruction without requiring extra data acquisition or sequence modification. Magn Reson Med 75:883–896, 2016. © 2015 Wiley Periodicals, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 1493786-4
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  • 9
    In: Magnetic Resonance in Medicine, Wiley, Vol. 75, No. 4 ( 2016-04), p. 1457-1465
    Abstract: To develop an ultrafast T 1 mapping method for high‐resolution, volumetric T 1 measurements in the abdomen. Methods The Look‐Locker method was combined with a stack‐of‐spirals acquisition accelerated using three‐dimensional (3D) through‐time spiral GRAPPA reconstruction for fast data acquisition. A segmented k‐space acquisition scheme was proposed and the time delay between segments for the recovery of longitudinal magnetization was optimized using Bloch equation simulations. The accuracy of this method was validated in a phantom experiment and in vivo T 1 measurements were performed with 35 asymptomatic subjects on both 1.5 Tesla (T) and 3T MRI systems. Results Phantom experiments yielded close agreement between the proposed method and gold standard measurements for a large range of T 1 values (200 to 1600 ms). The in vivo results further demonstrate that high‐resolution T 1 maps (2 × 2 × 4 mm 3 ) for 32 slices can be achieved in a single clinically feasible breath‐hold of approximately 20 s. The T 1 values for multiple organs and tissues in the abdomen are in agreement with the published literature. Conclusion A high‐resolution 3D abdominal T 1 mapping technique was developed, which allows fast and accurate T 1 mapping of multiple abdominal organs and tissues in a single breath‐hold. Magn Reson Med 75:1457–1465, 2016. © 2015 Wiley Periodicals, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 1493786-4
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  • 10
    In: NMR in Biomedicine, Wiley
    Abstract: The purpose of this study was to assess the quality of clinical brain imaging in healthy subjects and patients on an FDA‐approved commercial 0.55 T MRI scanner, and to provide information about the feasibility of using this scanner in a clinical workflow. In this IRB‐approved study, brain examinations on the scanner were prospectively performed in 10 healthy subjects (February–April 2022) and retrospectively derived from 44 patients (February–July 2022). Images collected using the following pulse sequences were available for assessment: axial DWI (diffusion‐weighted imaging), apparent diffusion coefficient maps, 2D axial fluid‐attenuated inversion recovery images, axial susceptibility‐weighted images (both magnitude and phase), sagittal T 1 ‐weighted (T1w) Sampling Perfection with Application Optimized Contrast images, sagittal T1w MPRAGE (magnetization prepared rapid gradient echo) with contrast enhancement, axial T1w turbo spin echo (TSE) with and without contrast enhancement, and axial T 2 ‐weighted TSE. Two readers retrospectively and independently evaluated image quality and specific anatomical features in a blinded fashion on a four‐point Likert scale, with a score of 1 being unacceptable and 4 being excellent, and determined the ability to answer the clinical question in patients. For each category of image sequences, the mean, standard deviation, and percentage of unacceptable quality images ( 〈 2) were calculated. Acceptable (rating ≥ 2) image quality was achieved at 0.55 T in all sequences for patients and 85% of the sequences for healthy subjects. Radiologists were able to answer the clinical question in all patients scanned. In total, 50% of the sequences used in patients and about 60% of the sequences used in healthy subjects exhibited good (rating ≥ 3) image quality. Based on these findings, we conclude that diagnostic quality clinical brain images can be successfully collected on this commercial 0.55 T scanner, indicating that the routine brain imaging protocol may be deployed on this system in the clinical workflow.
    Type of Medium: Online Resource
    ISSN: 0952-3480 , 1099-1492
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 2002003-X
    detail.hit.zdb_id: 1000976-0
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