ORCID Profile
0000-0002-9167-8778
Current Organisation
Mayo Clinic
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Wiley
Date: 17-10-2018
DOI: 10.1002/JMRI.26516
Abstract: Using lower refocusing flip angles in multi-echo turbo spin echo (ME-TSE) sequences at ultra-high magnetic field leads to non-monoexponential signal decay and overestimation of T To investigate the feasibility of a fast and accurate reconstruction of quantitative T Prospective. Phantom measurements with relaxation phantom, four healthy volunteers. 7 Tesla MRI, multi-echo turbo spin echo (ME-TSE), spin echo (SE), and B Based on Bloch simulations and the extended phase graph model, signal decay curves were calculated to account for nonrectangular slice profile, B Welch's t-test was used to compare T T The proposed dictionary-based ME-TSE approach provided accurate T 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019 :1253-1262.
Publisher: Springer Science and Business Media LLC
Date: 04-07-2014
Publisher: Wiley
Date: 30-06-2015
DOI: 10.1002/MRM.25812
Abstract: The effects of microstructure on susceptibility mapping have recently received increasing attention. In this work, the capability of p-space imaging to resolve subvoxel structure and susceptibility is assessed. In a simulation study, the p-space contrast of axon bundles comprised of hollow cylinders is investigated. Various axon and susceptibility distributions are considered and compared with the corresponding case of a voxel with homogeneous substructure of the order of the voxel size. MR signal behavior for p-space imaging of a voxel containing axon bundles and a voxel containing homogeneous substructure are nearly identical. p-Space imaging resolves subvoxel structure of the order of the voxel size. Due to dephasing effects, strong susceptibility variations alter p-space contrast. However, p-space contrast is not directly linked to the susceptibility of the axon compartment. Magn Reson Med 75:2526-2533, 2016. © 2015 Wiley Periodicals, Inc.
Publisher: Frontiers Media SA
Date: 21-06-2021
DOI: 10.3389/FNINS.2021.661504
Abstract: Objectives To characterize subcortical nuclei by multi-parametric quantitative magnetic resonance imaging. Materials and Methods: The following quantitative multiparametric MR data of five healthy volunteers were acquired on a 7T MRI system: 3D gradient echo (GRE) data for the calculation of quantitative susceptibility maps (QSM), GRE sequences with and without off-resonant magnetic transfer pulse for magnetization transfer ratio (MTR) calculation, a magnetization−prepared 2 rapid acquisition gradient echo sequence for T 1 mapping, and (after a coil change) a density-adapted 3D radial pulse sequence for 23 Na imaging. First, all data were co-registered to the GRE data, volumes of interest (VOIs) for 21 subcortical structures were drawn manually for each volunteer, and a combined voxel-wise analysis of the four MR contrasts (QSM, MTR, T 1 , 23 Na) in each structure was conducted to assess the quantitative, MR value-based differentiability of structures. Second, a machine learning algorithm based on random forests was trained to automatically classify the groups of multi-parametric voxel values from each VOI according to their association to one of the 21 subcortical structures. Results The analysis of the integrated multimodal visualization of quantitative MR values in each structure yielded a successful classification among nuclei of the ascending reticular activation system (ARAS), the limbic system and the extrapyramidal system, while classification among (epi-)thalamic nuclei was less successful. The machine learning-based approach facilitated quantitative MR value-based structure classification especially in the group of extrapyramidal nuclei and reached an overall accuracy of 85% regarding all selected nuclei. Conclusion Multimodal quantitative MR enabled excellent differentiation of a wide spectrum of subcortical nuclei with reasonable accuracy and may thus enable sensitive detection of disease and nucleus-specific MR-based contrast alterations in the future.
Publisher: Wiley
Date: 14-11-2022
DOI: 10.1002/NBM.4847
Abstract: Substantial cortical gray matter tissue damage, which correlates with clinical disease severity, has been revealed in multiple sclerosis (MS) using advanced magnetic resonance imaging (MRI) methods at 3 T and the use of ultra‐high field, as well as in histopathology studies. While clinical assessment mainly focuses on lesions using ‐ and ‐weighted MRI, quantitative MRI (qMRI) methods are capable of uncovering subtle microstructural changes. The aim of this ultra‐high field study is to extract possible future MR biomarkers for the quantitative evaluation of regional cortical pathology. Because of their sensitivity to iron, myelin, and in part specifically to cortical demyelination, , , , and susceptibility mapping were performed including two novel susceptibility markers in addition, cortical thickness as well as the volumes of 34 cortical regions were computed. Data were acquired in 20 patients and 16 age‐ and sex‐matched healthy controls. In 18 cortical regions, large to very large effect sizes (Cohen's d ≥ 1) and statistically significant differences in qMRI values between patients and controls were revealed compared with only four regions when using more standard MR measures, namely, volume and cortical thickness. Moreover, a decrease in all susceptibility contrasts ( , , and values indicates that the role of cortical demyelination might outweigh inflammatory processes in the form of iron accumulation in cortical MS pathology, and might also indicate iron loss. A significant association between susceptibility contrasts as well as of the caudal middle frontal gyrus and disease duration was found (adjusted R 2 : 0.602, p = 0.0011). Quantitative MRI parameters might be more sensitive towards regional cortical pathology compared with the use of conventional markers only and therefore may play a role in early detection of tissue damage in MS in the future.
Publisher: Wiley
Date: 06-03-2018
DOI: 10.1002/MP.12785
Abstract: To investigate the extent of MR image distortions in the pelvis caused by susceptibility‐induced field inhomogeneities in MR images in the context of a study on MR ‐guided radiotherapy. Using a high‐bandwidth double‐echo gradient echo sequence, field maps and distortion maps of the pelvis were calculated and evaluated for 219 exams (92 of female and 127 of male patients) to investigate patient‐related image distortions caused by susceptibility differences in an ongoing study on MR ‐guided radiotherapy. The evaluation of distortions in the regions “rectum”, “prostate”, “cervix”, and in a reference region in the gluteus maximus was based on masks drawn by two readers. Distortions in the prostate and cervix were smaller than 0.03 px (0.1 mm) for 99% of voxels, and reached a maximum value of 0.09 px (0.3 mm). In the reference region, maximum distortions were smaller than in the prostate and cervix. Using a geometric uncertainty of 0.2 px (0.6 mm) in margin definition for organs that are close to the rectum like the prostate and the cervix would be a cautious choice to account for susceptibility‐induced distortions that can arise during MR ‐based treatment guidance for the imaging setting used in this study. Since distortions are inversely proportional to the readout bandwidth of the sequence, safety margins need to be adapted adequately. Additional sources of image distortions like gradient nonlinearities are not included in our margin recommendations and should be considered separately.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 25-06-2020
Publisher: Springer Berlin Heidelberg
Date: 2022
Publisher: Elsevier BV
Date: 09-2021
DOI: 10.1016/J.JMR.2021.107033
Abstract: In biological tissue, phase contrast is determined by multiple substances such as iron, myelin or calcifications. Often, these substances occur co-located within the same measurement volume. However, quantitative susceptibility mapping can solely measure the average susceptibility per voxel. To provide new insight in disease progression and mechanisms in neurological diseases, where multiple processes such as demyelination and iron accumulation occur simultaneously in the same location, a separation of susceptibility sources is desirable to disentangle the underlying susceptibility proportions. The basic concept of separating the susceptibility effects from sources with different sign within one voxel is to include information on relaxation rate ΔR In numerical simulations, the feasibility of disentangling susceptibility sources within the same voxel was confirmed provided the critera of the static dephasing regime were fulfilled. In phantom experiments, the magnitude decay kernel, which is an essential reconstruction parameter of the algorithm, was determined to be D In conclusion, in this study a detailed description of the implementation of an algorithm for the separation of positive and negative susceptibility sources within the same volume element as well as its limitations is presented and validated quantitatively in both simulation and phantom experiments for the first time. An application to multiple sclerosis lesions shows promising results for in vivo usability.
Publisher: Elsevier BV
Date: 08-2021
Publisher: Elsevier BV
Date: 05-2021
Publisher: Wiley
Date: 16-02-2017
DOI: 10.1002/JMRI.25674
Publisher: Elsevier BV
Date: 07-2020
Publisher: Wiley
Date: 16-08-2016
DOI: 10.1002/MRM.26369
Abstract: Since quantitative susceptibility mapping (QSM) quantifies magnetic susceptibility relative to a reference value, a suitable reference tissue has to be available to compare different subjects and stages of disease. To find such a suitable reference tissue for QSM of the brain, melanoma patients with and without brain metastases were measured. Twelve reference regions were chosen and assessed for stability of susceptibility values with respect to multiple intra-in idual and inter-in idual measurements, age, and stage of disease. Cerebrospinal fluid (CSF), the internal capsule and one region in the splenium of the corpus callosum are the regions with the smallest standard deviations of the mean susceptibility value. The mean susceptibility is 0.010 ± 0.014 ppm for CSF in the atrium of the lateral ventricles (csf The internal capsule and CSF appear to be the most suitable reference regions for QSM of the brain in the melanoma patients studied. Both showed virtually no dependence on age or disease and small variations among patients. Magn Reson Med 78:204-214, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Publisher: Wiley
Date: 07-02-2023
DOI: 10.1002/JMRI.28624
Abstract: Magnetic materials in tissue, such as iron, calcium, or collagen, can be studied using quantitative susceptibility mapping (QSM). To date, QSM has been overwhelmingly applied in the brain, but is increasingly utilized outside the brain. QSM relies on the effect of tissue magnetic susceptibility sources on the MR signal phase obtained with gradient echo sequence. However, in the body, the chemical shift of fat present within the region of interest contributes to the MR signal phase as well. Therefore, correcting for the chemical shift effect by means of water‐fat separation is essential for body QSM. By employing techniques to compensate for cardiac and respiratory motion artifacts, body QSM has been applied to study liver iron and fibrosis, heart chamber blood and placenta oxygenation, myocardial hemorrhage, atherosclerotic plaque, cartilage, bone, prostate, breast calcification, and kidney stone.
Publisher: Springer Science and Business Media LLC
Date: 08-08-2019
DOI: 10.1007/S00062-019-00816-X
Abstract: To quantify the influence of melanin content on magnetic susceptibility of cerebral melanoma metastases. Patients with non-hemorrhagic metastases were included based on the absence of susceptibility blooming artifacts. Susceptibility maps were calculated from 3D gradient echo data, using Laplacian-based phase unwrapping, sophisticated harmonic artefact reduction for phase data (V-SHARP) with varying spherical kernel sizes for background field removal and the iLSQR algorithm for the inversion of phase data. Susceptibility maps were referenced to cerebrospinal fluid. Non-hemorrhagic metastases were identified on contrast-enhanced T1-weighted images and susceptibility weighted images. Metastases masks were drawn on T1-weighted post-contrast images and used to compute mean susceptibility values of each metastasis. A total of 33 non-hemorrhagic melanoma brain metastases in 20 patients were quantitatively evaluated. Metastases without and with hyperintense signal on T1-weighted images, which corresponds to the melanin content, showed median susceptibility values of -0.028 ppm and -0.020 ppm, respectively. The susceptibility differences between metastases without and with T1-weighted hyperintense signal was not statistically significant (p ≥ 0.05). Non-hemorrhagic cerebral melanoma metastases showed weak diamagnetic susceptibility values and susceptibility did not significantly correlate to T1-weighted signals. Therefore, melanin does not seem to be a major contributor to susceptibility in cerebral melanoma metastases.
Publisher: Elsevier BV
Date: 08-2021
Publisher: Wiley
Date: 30-07-2020
DOI: 10.1002/JNR.24701
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2017
Publisher: Wiley
Date: 09-07-2019
DOI: 10.1002/NBM.4118
Abstract: Structural high-resolution imaging of the brainstem can be of high importance in clinical practice. However, ultra-high field magnetic resonance imaging (MRI) is still restricted in use due to limited availability. Therefore, quantitative MRI techniques (quantitative susceptibility mapping [QSM], relaxation measurements [
Publisher: MDPI AG
Date: 06-2017
DOI: 10.18383/J.TOM.2017.00005
Abstract: We propose an alternative processing method for quantitative susceptibility mapping of the prostate that reduces artifacts and enables better visibility and quantification of calcifications and other lesions. Three-dimensional gradient-echo magnetic resonance data were obtained from 26 patients at 3 T who previously received a planning computed tomography of the prostate. Phase images were unwrapped using Laplacian-based phase unwrapping. The background field was removed with the V-SHARP method using tissue masks for the entire abdomen (Method 1) and masks that excluded bone and the rectum (Method 2). Susceptibility maps were calculated with the iLSQR method. The quality of susceptibility maps was assessed by one radiologist and two physicists who rated the data for visibility of lesions and data quality on a scale from 1 (poor) to 4 (good). The readers rated susceptibility maps computed with Method 2 to be, on average, better for visibility of lesions with a score of 2.9 ± 1.1 and image quality with a score of 2.8 ± 0.8 compared with maps computed with Method 1 (2.4 ± 1.2/2.3 ± 1.0). Regarding strong artifacts, these could be removed using adapted masks, and the susceptibility values seemed less biased by the artifacts. Thus, using an adapted mask for background field removal when calculating susceptibility maps of the prostate from phase data reduces artifacts and improves visibility of lesions.
Publisher: Wiley
Date: 25-04-2018
DOI: 10.1002/NBM.3926
Abstract: Blood clotting is a fundamental biochemical process in post-hemorrhagic hemostasis. Although the varying appearance of coagulating blood in T
Publisher: Elsevier BV
Date: 12-2018
DOI: 10.1016/J.PNMRS.2018.06.001
Abstract: Magnetic resonance imaging and spectroscopic techniques are widely used in humans both for clinical diagnostic applications and in basic research areas such as cognitive neuroimaging. In recent years, new human MR systems have become available operating at static magnetic fields of 7 T or higher (≥300 MHz proton frequency). Imaging human-sized objects at such high frequencies presents several challenges including non-uniform radiofrequency fields, enhanced susceptibility artifacts, and higher radiofrequency energy deposition in the tissue. On the other side of the scale are gains in signal-to-noise or contrast-to-noise ratio that allow finer structures to be visualized and smaller physiological effects to be detected. This review presents an overview of some of the latest methodological developments in human ultra-high field MRI/MRS as well as associated clinical and scientific applications. Emphasis is given to techniques that particularly benefit from the changing physical characteristics at high magnetic fields, including susceptibility-weighted imaging and phase-contrast techniques, imaging with X-nuclei, MR spectroscopy, CEST imaging, as well as functional MRI. In addition, more general methodological developments such as parallel transmission and motion correction will be discussed that are required to leverage the full potential of higher magnetic fields, and an overview of relevant physiological considerations of human high magnetic field exposure is provided.
Publisher: Wiley
Date: 15-07-2016
DOI: 10.1002/JMRI.25385
Abstract: To evaluate whether quantitative susceptibility (QSM) may be used as an alternative to computed tomography (CT) to detect calcification in prostate cancer patients. Susceptibility map calculation was performed using 3D gradient echo magnetic resonance imaging (MRI) data from 26 patients measured at 3T who previously received a planning CT of the prostate. Phase images were unwrapped using Laplacian-based phase unwrapping, the background field was removed with the V-SHARP method, and susceptibility maps were calculated with the iLSQR method. Two blinded readers were asked to identify peri- and intraprostatic calcifications. Average mean and minimum susceptibility values (referenced to iliopsoas muscle) of calcifications were -0.249 ± 0.179 ppm and -0.551 ± 0.323 ppm, and average mean and maximum intensities in CT images were 319 ± 164 HU and 679 ± 392 HU. Twenty-one and 17 out of 22 prostatic calcifications were identified using susceptibility maps and magnitude images, respectively, as well as more than half of periprostatic phleboliths depicted by CT. Calcifications in the prostate and its periphery were quantitatively differentiable from noncalcified prostate tissue in CT (mean values for calcifications / for noncalcified tissue: 71 to 649 / -1 to 83 HU) and in QSM (mean values for calcifications / for noncalcified tissue: -0.641 to 0.063 / -0.046 to 0.181 ppm). Moreover, there was a significant correlation between susceptibility values and CT image intensities for calcifications (P < 0.004). Prostatic calcifications could be well identified with QSM. Susceptibility maps can be easily obtained from clinical prostate MR protocols that include a 3D gradient echo sequence, rendering it a promising technique for detection and quantification of intraprostatic calcifications. 1 J. Magn. Reson. Imaging 2017 :889-898.
Publisher: Wiley
Date: 31-07-2019
Publisher: Elsevier BV
Date: 09-2020
Publisher: Elsevier BV
Date: 04-2022
DOI: 10.1016/J.NEUROIMAGE.2022.118931
Abstract: Accurate segmentation of cerebral venous vasculature from gradient echo data is of central importance in several areas of neuroimaging such as for the susceptibility-based assessment of brain oxygenation or planning of electrode placement in deep brain stimulation. In this study, a vein segmentation algorithm for single- and multi-echo gradient echo data is proposed. First, susceptibility maps, true susceptibility-weighted images, and, in the multi-echo case, R
Location: Germany
Start Date: 2017
End Date: End date not available
Funder: German Research Foundation
View Funded Activity