| 1. |
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| 2. |
- Andersen, Oluf, 1941, et al.
(author)
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Diffusion tensor imaging in multiple sclerosis at different final outcomes
- 2018
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In: Acta Neurologica Scandinavica. - : Hindawi Limited. - 1600-0404 .- 0001-6314. ; 137:2, s. 165-173
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Journal article (peer-reviewed)abstract
- OBJECTIVES:Methods to evaluate the relative contributions of demyelination vs axonal degeneration over the long-term course of MS are urgently needed. We used magnetic resonance diffusion tensor imaging (DTI) to estimate degrees of demyelination and axonal degeneration in the corpus callosum (CC) in cases of MS with different final outcomes.MATERIALS AND METHODS:We determined DTI measures mean diffusivity (MD), fractional anisotropy (FA), and axial (AD) and radial (RD) diffusivities in the CC of 31 MS patients, of whom 13 presented a secondary progressive course, 11 a non-progressive course, and seven a monophasic course. The study participants were survivors from an incidence cohort of 254 attack-onset MS patients with 50 years of longitudinal follow-up. As reference, we included five healthy individuals without significant morbidity.RESULTS:In patients with secondary progression, compared to all other groups, the corpus callosum showed increased RD and reduced FA, but no change in AD. None of the parameters exhibited differences among non-progressive and monophasic course groups and controls.CONCLUSION:Increased RD was observed in secondary progressive MS, indicating significant myelin loss. Normal RD values observed in the clinically isolated syndrome and non-progressive groups confirm their benign nature. AD was not a characterizing parameter for long-term outcome. Demyelination revealed by increased RD is a distinguishing trait for secondary progression.
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| 3. |
- Fedorov, A., et al.
(author)
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Segmented diffusion-weighted imaging of the prostate: Application to transperineal in-bore 3 T MR image-guided targeted biopsy
- 2016
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In: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X. ; 34:8, s. 1146-1154
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Journal article (peer-reviewed)abstract
- Objective: This study aims to evaluate the applicability of using single-shot and multi-shot segmented diffusion-weighted imaging (DWI) techniques to support biopsy target localization in a cohort of targeted MRI-guided prostate biopsy patients. Materials and methods: Single-shot echo-planar diffusion-weighted imaging (SS-DWI) and multi-shot segmented (MS-DWI) were performed intra-procedurally on a 3 Tesla system in a total of 35 men, who underwent in-bore prostate biopsy inside the scanner bore. Comparisons between SS-DWI and MS-DWI were performed with (in 16 men) and without (in 19 men) parallel coil acceleration (iPAT) for SS-DWI. Overall image quality and artifacts were scored by a radiologist and scores were compared with the Wilcoxon-Mann-Whitney rank test. Correlation between the presence of air and image quality scores was evaluated with Spearman statistics. To quantify distortion, the anteroposterior prostate dimension was measured in SS and MS b = 0 diffusion- and T-2-weighted images. Signal-to-noise ratio was estimated in a phantom experiment. Agreement and accuracy of targeting based on retrospective localization of restricted diffusion areas in DWI was evaluated with respect to the targets identified using multi-parametric MRI (mpMRI). Results: Compared to SS-DWI without iPAT, the average image quality score in MS-DWI improved from 2.0 to 33 (p < 0.005) and the artifact score improved from 23 to 1.4 (p < 0.005). When iPAT was used in SS-DWI, the average image quality score in MS-DWI improved from 2.6 to 33 (p < 0.05) and the artifact score improved from 2.1 to 1.4 (p < 0.01). Image quality (rho = 0.74, p < 0.0005) and artifact scores (rho = 0.77, p < 0.0005) both showed strong correlation with the presence of air in the rectum for the SS-DWI sequence without iPAT. These correlations remained significant when iPAT was enabled (rho = 052, p < 0.05 and rho = 0.64, p < 0.01). For the comparison MS-DWI vs SS-DWI without iPAT, median differences between diffusion- and T2-weighted image gland measurements were 1.1 (0.03-10.4) mm and 4.4 (0.5-22.7) mm, respectively. In the SS-DWI-iPAT cohort, median gland dimension differences were 2.7 (0.4-5.9) mm and 42 (0.7-8.9) mm, respectively. Out of the total of 89 targets identified in mpMRI, 20 had corresponding restricted diffusion areas in SS-DWI and 28 in MS-DWI. No statistically significant difference was observed between the distances for the targets in the target-concordant SS- and MS-DWI restricted diffusion areas (5.5 mm in SS-DWI vs 45 mm in MS-DWI, p > 0.05). Conclusions: MS-DWI applied to prostate imaging leads to a significant reduction of image distortion in comparison with SS-DWI. There is no sufficient evidence however to suggest that intra-procedural DWI can serve as a replacement for tracking of the targets identified in mpMRI for the purposes of targeted MRI-guided prostate biopsy. (C) 2016 Elsevier Inc. All rights reserved.
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| 4. |
- Aksit Ciris, P., et al.
(author)
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Accelerated Segmented Diffusion-Weighted Prostate Imaging for Higher Resolution, Higher Geometric Fidelity, and Multi-b Perfusion Estimation
- 2019
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In: Investigative Radiology. - 0020-9996. ; 54:4, s. 238-246
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Journal article (peer-reviewed)abstract
- Purpose The aim of this study was to improve the geometric fidelity and spatial resolution of multi-b diffusion-weighted magnetic resonance imaging of the prostate. Materials and Methods An accelerated segmented diffusion imaging sequence was developed and evaluated in 25 patients undergoing multiparametric magnetic resonance imaging examinations of the prostate. A reduced field of view was acquired using an endorectal coil. The number of sampled diffusion weightings, or b-factors, was increased to allow estimation of tissue perfusion based on the intravoxel incoherent motion (IVIM) model. Apparent diffusion coefficients measured with the proposed segmented method were compared with those obtained with conventional single-shot echo-planar imaging (EPI). Results Compared with single-shot EPI, the segmented method resulted in faster acquisition with 2-fold improvement in spatial resolution and a greater than 3-fold improvement in geometric fidelity. Apparent diffusion coefficient values measured with the novel sequence demonstrated excellent agreement with those obtained from the conventional scan (R 2 = 0.91 for b max = 500 s/mm 2 and R 2 = 0.89 for b max = 1400 s/mm 2 ). The IVIM perfusion fraction was 4.0% ± 2.7% for normal peripheral zone, 6.6% ± 3.6% for normal transition zone, and 4.4% ± 2.9% for suspected tumor lesions. Conclusions The proposed accelerated segmented prostate diffusion imaging sequence achieved improvements in both spatial resolution and geometric fidelity, along with concurrent quantification of IVIM perfusion. © 2019 Wolters Kluwer Health, Inc. All rights reserved.
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| 5. |
- Alipoor, Mohammad, 1983, et al.
(author)
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Fourth order tensor-based diffusion MRI signal modeling
- 2015
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In: International symposium on biomedical imaging, White Matter Modeling Challenge. 16-19 April 2015, New York, USA..
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Conference paper (other academic/artistic)abstract
- This abstract describes forth order tensor-based diffusion signal modeling as proposed in [1].
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| 6. |
- Alipoor, Mohammad, 1983, et al.
(author)
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K-Optimal Gradient Encoding Scheme for Fourth-Order Tensor-Based Diffusion Profile Imaging
- 2015
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In: Biomed Research International. - : Hindawi Limited. - 2314-6133 .- 2314-6141.
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Journal article (peer-reviewed)abstract
- The design of an optimal gradient encoding scheme (GES) is a fundamental problem in diffusion MRI. It is well studied for the case of second-order tensor imaging (Gaussian diffusion). However, it has not been investigated for the wide range of non-Gaussian diffusion models. The optimal GES is the one that minimizes the variance of the estimated parameters. Such a GES can be realized by minimizing the condition number of the design matrix (K-optimal design). In this paper, we propose a new approach to solve the K-optimal GES design problem for fourth-order tensor-based diffusion profile imaging. The problem is a nonconvex experiment design problem. Using convex relaxation, we reformulate it as a tractable semidefinite programming problem. Solving this problem leads to several theoretical properties of K-optimal design: (i) the odd moments of the K-optimal design must be zero; (ii) the even moments of the K-optimal design are proportional to the total number of measurements; (iii) the K-optimal design is not unique, in general; and (iv) the proposed method can be used to compute the K-optimal design for an arbitrary number of measurements. Our Monte Carlo simulations support the theoretical results and show that, in comparison with existing designs, the K-optimal design leads to the minimum signal deviation.
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| 7. |
- Alipoor, Mohammad, 1983, et al.
(author)
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Optimal Experiment Design for Mono-Exponential Model Fitting: Application to Apparent Diffusion Coefficient Imaging
- 2015
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In: BioMed Research International. - : Hindawi Limited. - 2314-6133 .- 2314-6141. ; 2015
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Journal article (peer-reviewed)abstract
- The mono-exponential model is widely used in quantitative biomedical imaging. Notable applications include apparent diffusion coefficient (ADC) imaging and pharmacokinetics.The application of ADC imaging to the detection of malignant tissue has in turn prompted several studies concerning optimal experiment design for mono-exponential model fitting. In this paper, we propose a new experiment design method that is based on minimizing the determinant of the covariance matrix of the estimated parameters (?-optimal design). In contrast to previous methods, ?-optimal design is independent of the imaged quantities. Applying this method to ADC imaging, we demonstrate its steady performance for the whole range of input variables (imaged parameters, number of measurements, range of ?-values). Using Monte Carlo simulations we show that the ?-optimal design outperforms existing experiment design methods in terms of accuracy and precision of the estimated parameters.
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| 8. |
- Alipoor, Mohammad, 1983, et al.
(author)
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Optimal Gradient Encoding Schemes for Diffusion Tensor and Kurtosis Imaging
- 2016
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In: IEEE transactions on Computational Imaging. - 2333-9403. ; 2:3, s. 375-391
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Journal article (peer-reviewed)abstract
- Diffusion-derived parameters find application in characterizing pathological and developmental changes in living tissues. Robust estimation of these parameters is important because they are used for medical diagnosis. An optimal gradient encoding scheme (GES) is one that minimizes the variance of the estimated diffusion parameters. This paper proposes a method for optimal GES design for two diffusion models: high-order diffusion tensor (HODT) imaging and diffusion kurtosis imaging (DKI). In both cases, the optimal GES design problem is formulated as a D-optimal (minimum determinant) experiment design problem. Then, using convex relaxation, it is reformulated as a semidefinite programming problem. Solving these problems we show that: 1) there exists a D-optimal solution for DKI that is simultaneously D-optimal for second- and fourth-order diffusion tensor imaging (DTI); 2) the traditionally used icosahedral scheme is approximately D-optimal for DTI and DKI; 3) the proposed D-optimal design is rotation invariant; 4) the proposed method can be used to compute the optimal design ($b$ -values and directions) for an arbitrary number of measurements and shells; and 5) using the proposed method one can obtain uniform distribution of gradient encoding directions for a typical number of measurements. Importantly, these theoretical findings provide the first mathematical proof of the optimality of uniformly distributed GESs for DKI and HODT imaging. The utility of the proposed method is further supported by the evaluation results and comparisons with with existing methods.
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| 9. |
- Chao, Tzu-Cheng, et al.
(author)
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Fast diffusion imaging with high angular resolution.
- 2017
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In: Magnetic resonance in medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 77:2, s. 696-706
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Journal article (peer-reviewed)abstract
- High angular resolution diffusion imaging (HARDI) is a well-established method to help reveal the architecture of nerve bundles, but long scan times and geometric distortions inherent to echo planar imaging (EPI) have limited its integration into clinical protocols.A fast imaging method is proposed here that combines accelerated multishot diffusion imaging (AMDI), multiplexed sensitivity encoding (MUSE), and crossing fiber angular resolution of intravoxel structure (CFARI) to reduce spatial distortions and reduce total scan time. A multishot EPI sequence was used to improve geometrical fidelity as compared to a single-shot EPI acquisition, and acceleration in both k-space and diffusion sampling enabled reductions in scan time. The method is regularized and self-navigated for motion correction. Seven volunteers were scanned in this study, including four with volumetric whole brain acquisitions.The average similarity of microstructural orientations between undersampled datasets and their fully sampled counterparts was above 85%, with scan times below 5min for whole-brain acquisitions. Up to 2.7-fold scan time acceleration along with four-fold distortion reduction was achieved.The proposed imaging strategy can generate HARDI results with relatively good geometrical fidelity and low scan duration, which may help facilitate the transition of HARDI from a successful research tool to a practical clinical one. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
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| 10. |
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| 11. |
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| 12. |
- Fennessy, F. M., et al.
(author)
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Quantitative diffusion MRI in prostate cancer: Image quality, what we can measure and how it improves clinical assessment
- 2023
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In: European Journal of Radiology. - 0720-048X. ; 167
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Research review (peer-reviewed)abstract
- Diffusion-weighted imaging is a dependable method for detection of clinically significant prostate cancer. In prostate tissue, there are several compartments that can be distinguished from each other, based on different water diffusion decay signals observed. Alterations in cell architecture, such as a relative increase in tumor infiltration and decrease in stroma, will influence the observed diffusion signal in a voxel due to impeded random motion of water molecules. The amount of restricted diffusion can be assessed quantitatively by measuring the apparent diffusion coefficient (ADC) value. This is traditionally calculated using a monoexponential decay formula represented by the slope of a line produced between the logarithm of signal intensity decay plotted against selected b-values. However, the choice and number of b-values and their distribution, has a significant effect on the measured ADC values. There have been many models that attempt to use higher-order functions to better describe the observed diffusion signal decay, requiring an increased number and range of b-values. While ADC can probe heterogeneity on a macroscopic level, there is a need to optimize advanced diffusion techniques to better interrogate prostate tissue microstructure. This could be of benefit in clinical challenges such as identifying sparse tumors in normal prostate tissue or better defining tumor margins. This paper reviews the principles of diffusion MRI and novel higher order diffusion signal analysis techniques to improve the detection of prostate cancer.
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| 13. |
- Johansson, Jens, et al.
(author)
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Brain diffusion MRI with multiplexed sensitivity encoding for reduced distortion in a pediatric patient population
- 2022
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In: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X. ; 87, s. 97-103
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Journal article (peer-reviewed)abstract
- Background: Diffusion-weighted imaging (DWI) is a valuable tool for routine imaging of the pediatric brain. However, the commonly used single-shot (ss) echo-planar imaging (EPI) DWI sequence is prone to geometric distortions and T2*-blurring. This study aimed to investigate in a pediatric population the benefits of using multiplexed sensitivity-encoding (MUSE) without and with reversed polarity gradients (RPG) instead. Methods: This retrospective study compared image quality, geometric distortions, and diffusion values between three different approaches for DWI (ssEPI, MUSE, and RPG-MUSE) in 14 patients (median age = 4 (0.6–15) years, 11 males). Distortion levels were quantified and compared in two brain regions, i.e., the brain stem and the temporal lobes, using the Dice Coefficient and the Hausdorff Distance, with T2-weighted images as reference. Expected geometrical distortion was further evaluated by comparing the effective echo spacing between the DWI sequences. Apparent diffusion coefficient (ADC) values were determined in the genu of the corpus callosum and the optic nerves. Two raters graded overall image quality and image distortions on a Likert scale. Results: Distortion levels assessed with Dice coefficient and Hausdorff distance were significantly lower for MUSE (p < 0.05) and RPG-MUSE (p < 0.01) compared to ssEPI. No significant difference in ADC values was observed between methods. The RPG-MUSE method was graded by one rater as significantly higher in overall image quality than ssEPI (p < 0.05) and by both raters as significantly lower in levels of image distortions than both MUSE (p < 0.05) and ssEPI (p < 0.05). These results were in agreement with the reduced effective echo spacing was that was attained with MUSE and RPG-MUSE. Conclusion: For imaging of the pediatric brain, MUSE and even more so RPG-MUSE offers both improved geometric fidelity and image quality compared to ssEPI. © 2022 The Authors
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| 14. |
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| 15. |
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| 16. |
- Kuczera, Stefan, et al.
(author)
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Optimized bias and signal inference in diffusion-weighted image analysis (OBSIDIAN)
- 2021
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In: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 86:5, s. 2716-2732
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Journal article (peer-reviewed)abstract
- Purpose Correction of Rician signal bias in magnitude MR images. Methods A model-based, iterative fitting procedure is used to simultaneously estimate true signal and underlying Gaussian noise with standard deviation sigma g on a pixel-by-pixel basis in magnitude MR images. A precomputed function that relates absolute residuals between measured signals and model fit to sigma g is used to iteratively estimate sigma g. The feasibility of the method is evaluated and compared to maximum likelihood estimation (MLE) for diffusion signal decay simulations and diffusion-weighted images of the prostate considering 21 linearly spaced b-values from 0 to 3000 s/mm(2). A multidirectional analysis was performed with publically available brain data. Results Model simulations show that the Rician bias correction algorithm is fast, with an accuracy and precision that is on par to model-based MLE and direct fitting in the case of pure Gaussian noise. Increased accuracy in parameter prediction in a low signal-to-noise ratio (SNR) scenario is ideally achieved by using a composite of multiple signal decays from neighboring voxels as input for the algorithm. For patient data, good agreement with high SNR reference data of diffusion in prostate is achieved. Conclusions OBSIDIAN is a novel, alternative, simple to implement approach for rapid Rician bias correction applicable in any case where differences between true signal decay and underlying model function can be considered negligible in comparison to noise. The proposed composite fitting approach permits accurate parameter estimation even in typical clinical scenarios with low SNR, which significantly simplifies comparison of complex diffusion parameters among studies.
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| 17. |
- Kuczera, Stefan, et al.
(author)
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Truly reproducible uniform estimation of the ADC with multi-b diffusion data- Application in prostate diffusion imaging
- 2023
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In: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 89:4, s. 1586-1600
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Journal article (peer-reviewed)abstract
- Purpose: The ADC is a well-established parameter for clinical diagnostic applications, but lacks reproducibility because it is also influenced by the choice diffusion weighting level. A framework is evaluated that is based on multi-b measurement over a wider range of diffusion-weighting levels and higher order tissue diffusion modeling with retrospective, fully reproducible ADC calculation. Methods: Averaging effect from curve fitting for various model functions at 20 linearly spaced b-values was determined by means of simulations and theoretical calculations. Simulation and patient multi-b image data were used to compare the new approach for diffusion-weighted image and ADC map reconstruction with and without Rician bias correction to an active clinical trial protocol probing three non-zero b-values. Results: Averaging effect at a certain b-value varies for model function and maximum b-value used. Images and ADC maps from the novel procedure are on-par with the clinical protocol. Higher order modeling and Rician bias correction is feasible, but comes at the cost of longer computation times. Conclusions: Application of the new framework makes higher order modeling more feasible in a clinical setting while still providing patient images and reproducible ADC maps of adequate quality.
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| 18. |
- Langkilde, Fredrik, 1990, et al.
(author)
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Evaluation of fitting models for prostate tissue characterization using extended-range b-factor diffusion-weighted imaging.
- 2018
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In: Magnetic resonance in medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 79:4, s. 2346-2358
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Journal article (peer-reviewed)abstract
- To compare the fitting and tissue discrimination performance of biexponential, kurtosis, stretched exponential, and gamma distribution models for high b-factor diffusion-weighted images in prostate cancer.Diffusion-weighted images with 15 b-factors ranging from b=0 to 3500 s/mm(2) were obtained in 62 prostate cancer patients. Pixel-wise signal decay fits for each model were evaluated with the Akaike Information Criterion (AIC). Parameter values for each model were determined within normal prostate and the index lesion. Their potential to differentiate normal from cancerous tissue was investigated through receiver operating characteristic analysis and comparison with Gleason score.The biexponential slow diffusion fraction fslow , the apparent kurtosis diffusion coefficient ADCK , and the excess kurtosis factor K differ significantly among normal peripheral zone (PZ), normal transition zone (TZ), tumor PZ, and tumor TZ. Biexponential and gamma distribution models result in the lowest AIC, indicating a superior fit. Maximum areas under the curve (AUCs) of all models ranged from 0.93 to 0.96 for the PZ and from 0.95 to 0.97 for the TZ. Similar AUCs also result from the apparent diffusion coefficient (ADC) of a monoexponential fit to a b-factor sub-range up to 1250 s/mm(2) . For kurtosis and stretched exponential models, single parameters yield the highest AUCs, whereas for the biexponential and gamma distribution models, linear combinations of parameters produce the highest AUCs. Parameters with high AUC show a trend in differentiating low from high Gleason score, whereas parameters with low AUC show no such ability.All models, including a monoexponential fit to a lower-b sub-range, achieve similar AUCs for discrimination of normal and cancer tissue. The biexponential model, which is favored statistically, also appears to provide insight into disease-related microstructural changes. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
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| 19. |
- Langkilde, Fredrik, 1990, et al.
(author)
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Manual prostate MRI segmentation by readers with different experience: a study of the learning progress
- 2024
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In: European Radiology. - 0938-7994 .- 1432-1084.
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Journal article (peer-reviewed)abstract
- Objective: To evaluate the learning progress of less experienced readers in prostate MRI segmentation. Materials and methods: One hundred bi-parametric prostate MRI scans were retrospectively selected from the Göteborg Prostate Cancer Screening 2 Trial (single center). Nine readers with varying degrees of segmentation experience were involved: one expert radiologist, two experienced radiology residents, two inexperienced radiology residents, and four novices. The task was to segment the whole prostate gland. The expert’s segmentations were used as reference. For all other readers except three novices, the 100 MRI scans were divided into five rounds (cases 1–10, 11–25, 26–50, 51–76, 76–100). Three novices segmented only 50 cases (three rounds). After each round, a one-on-one feedback session between the expert and the reader was held, with feedback on systematic errors and potential improvements for the next round. Dice similarity coefficient (DSC) > 0.8 was considered accurate. Results: Using DSC > 0.8 as the threshold, the novices had a total of 194 accurate segmentations out of 250 (77.6%). The residents had a total of 397/400 (99.2%) accurate segmentations. In round 1, the novices had 19/40 (47.5%) accurate segmentations, in round 2 41/60 (68.3%), and in round 3 84/100 (84.0%) indicating learning progress. Conclusions: Radiology residents, regardless of prior experience, showed high segmentation accuracy. Novices showed larger interindividual variation and lower segmentation accuracy than radiology residents. To prepare datasets for artificial intelligence (AI) development, employing radiology residents seems safe and provides a good balance between cost-effectiveness and segmentation accuracy. Employing novices should only be considered on an individual basis. Clinical relevance statement: Employing radiology residents for prostate MRI segmentation seems safe and can potentially reduce the workload of expert radiologists. Employing novices should only be considered on an individual basis. Key Points: • Using less experienced readers for prostate MRI segmentation is cost-effective but may reduce quality. • Radiology residents provided high accuracy segmentations while novices showed large inter-reader variability. • To prepare datasets for AI development, employing radiology residents seems safe and might provide a good balance between cost-effectiveness and segmentation accuracy while novices should only be employed on an individual basis. Graphical abstract: [Figure not available: see fulltext.]
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| 20. |
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| 21. |
- Maier, Stephan E, 1959, et al.
(author)
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Prostate Cancer Diffusion-Weighted Magnetic Resonance Imaging: Does the Choice of Diffusion-Weighting Level Matter?
- 2022
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 55:3, s. 842-853
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Journal article (peer-reviewed)abstract
- Background Diffusion-weighted magnetic resonance imaging plays an important role in multiparametric assessment of prostate lesions. The derived apparent diffusion coefficient (ADC) could be a useful quantitative biomarker for malignant growth, but lacks acceptance because of low reproducibility. Purpose To investigate the impact of the choice of diffusion-weighting levels (b-values) on contrast-to-noise ratio and quantitative measures in prostate diffusion-weighted MRI. Study Type Retrospective and simulation based on published data. Subjects Patient cohort (21 men with Prostate Imaging-Reporting and Data System (PI-RADS) version 2 score >= 3) from a single-center study. Field Strength/Sequence 3 T/diffusion-weighted imaging with single-shot echo-planar imaging. Assessment Both clinical data and simulations based on previously acquired data were used to quantify the influence of b-value choice in normal peripheral zone (PZ) and PZ tumor lesions. For clinical data, ADC was determined for different combinations of b-values. Contrast-to-noise ratio and quantitative diffusion measures were simulated for a wide range of b-values. Statistical Tests Tissue ADC and the lesion-to-normal tissue ADC ratios of different b-value combinations were compared with paired two-tailed Student's t-tests. A P-value Findings about b-value dependence derived from clinical data and from simulations agreed with each other. Provided measurement was limited to two b-values, simulation-derived optimal b-value choices coincided with PI-RADSv2 recommendations. For two-point measurements, ADC decreased by 15% when the maximum b-value increased from 1000 to 1500 seconds/mm(2), but corresponding lesion-to-normal tissue ADC ratio showed no significant change (P = 0.86 for acquired data). Simulations with three or more measurement points produced ADCs that declined by only 8% over this range of maximum b-value. Corresponding ADC ratios declined between 2.6% (three points) and 3.8% (21 points). Simulations also revealed an ADC reduction of about 19% with the shorter echo and diffusion time evaluated. Data Conclusion The comprehensive assessment of b-value dependence permits better formulation of protocol and analysis recommendations for obtaining reproducible results in prostate cancer diffusion-weighted MRI. Level of Evidence 4 Technical Efficacy Stage 2
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| 22. |
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| 23. |
- Mitsouras, D., et al.
(author)
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Multicomponent T-2 relaxation studies of the avian egg
- 2016
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In: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194. ; 75:5, s. 2156-2164
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Journal article (peer-reviewed)abstract
- PurposeTo investigate the tissue-like multiexponential T-2 signal decays in avian eggs. MethodsTransverse relaxation studies of raw, soft-boiled and hard-boiled eggs were performed at 3 Tesla using a three-dimensional Carr-Purcell-Meiboom-Gill imaging sequence. Signal decays over a TE range of 11 to 354 ms were fitted assuming single- and multicomponent signal decays with up to three separately decaying components. Fat saturation was used to facilitate spectral assignment of observed decay components. ResultsEgg white, yolk and the centrally located latebra all demonstrate nonmonoexponential T-2 decays. Specifically, egg white exhibits two-component decays with intermediate and long T-2 times. Meanwhile, yolk and latebra are generally best characterized with triexponential decays, with short, intermediate and very long T-2 decay times. Fat saturation revealed that the intermediate component of yolk could be attributed to lipids. Cooking of the egg profoundly altered the decay curves. ConclusionAvian egg T-2 decay curves cover a wide range of decay times. Observed T-2 components in yolk and latebra as short as 10 ms, may prove valuable for testing clinical sequences designed to measure short T-2 components, such as myelin-associated water in the brain. Thus we propose that the egg can be a versatile and widely available MR transverse relaxation phantom. Magn Reson Med 75:2156-2164, 2016. (c) 2015 Wiley Periodicals, Inc.
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| 24. |
- Mitsouras, Dimitris, et al.
(author)
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Three-dimensional printing of MRI-visible phantoms and MR image-guided therapy simulation.
- 2017
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In: Magnetic resonance in medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 77:2, s. 613-622
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Journal article (peer-reviewed)abstract
- To demonstrate the use of anatomic MRI-visible three-dimensional (3D)-printed phantoms and to assess process accuracy and material MR signal properties.A cervical spine model was generated from computed tomography (CT) data and 3D-printed using an MR signal-generating material. Printed phantom accuracy and signal characteristics were assessed using 120 kVp CT and 3 Tesla (T) MR imaging. The MR relaxation rates and diffusion coefficient of the fabricated phantom were measured and (1) H spectra were acquired to provide insight into the nature of the proton signal. Finally, T2 -weighted imaging was performed during cryoablation of the model.The printed model produced a CT signal of 102±8 Hounsfield unit, and an MR signal roughly 1/3(rd) that of saline in short echo time/short repetition time GRE MRI (456±36 versus 1526±121 arbitrary signal units). Compared with the model designed from the in vivo CT scan, the printed model differed by 0.13±0.11mm in CT, and 0.62±0.28mm in MR. The printed material had T2 ∼32 ms, T2*∼7 ms, T1 ∼193 ms, and a very small diffusion coefficient less than olive oil. MRI monitoring of the cryoablation demonstrated iceball formation similar to an in vivo procedure.Current 3D printing technology can be used to print anatomically accurate phantoms that can be imaged by both CT and MRI. Such models can be used to simulate MRI-guided interventions such as cryosurgeries. Future development of the proposed technique can potentially lead to printed models that depict different tissues and anatomical structures with different MR signal characteristics. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
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| 25. |
- Molinder, Anna, et al.
(author)
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Validity and reliability of the medial temporal lobe atrophy scale in a memory clinic population
- 2021
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In: BMC Neurology. - : Springer Science and Business Media LLC. - 1471-2377. ; 21:1
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Journal article (peer-reviewed)abstract
- Background Visual rating of medial temporal lobe atrophy (MTA) is often performed in conjunction with dementia workup. Most prior studies involved patients with known or probable Alzheimer's disease (AD). This study investigated the validity and reliability of MTA in a memory clinic population. Methods MTA was rated in 752 MRI examinations, of which 105 were performed in cognitively healthy participants (CH), 184 in participants with subjective cognitive impairment, 249 in subjects with mild cognitive impairment, and 214 in patients with dementia, including AD, subcortical vascular dementia and mixed dementia. Hippocampal volumes, measured manually or using FreeSurfer, were available in the majority of cases. Intra- and interrater reliability was tested using Cohen's weighted kappa. Correlation between MTA and quantitative hippocampal measurements was ascertained with Spearman's rank correlation coefficient. Moreover, diagnostic ability of MTA was assessed with receiver operating characteristic (ROC) analysis and suitable, age-dependent MTA thresholds were determined. Results Rater agreement was moderate to substantial. MTA correlation with quantitative volumetric methods ranged from -0.20 (p< 0.05) to -0.68 (p < 0.001) depending on the quantitative method used. Both MTA and FreeSurfer are able to distinguish dementia subgroups from CH. Suggested age-dependent MTA thresholds are 1 for the age group below 75 years and 1.5 for the age group 75 years and older. Conclusions MTA can be considered a valid marker of medial temporal lobe atrophy and may thus be valuable in the assessment of patients with cognitive impairment, even in a heterogeneous patient population.
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| 26. |
- Wallström, Jonas, et al.
(author)
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Bi- or multiparametric MRI in a sequential screening program for prostate cancer with PSA followed by MRI? Results from the Goteborg prostate cancer screening 2 trial
- 2021
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In: European Radiology. - : Springer Science and Business Media LLC. - 0938-7994 .- 1432-1084. ; 31, s. 8692-8702
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Journal article (peer-reviewed)abstract
- Objectives The PIRADS Steering Committee has called for "higher quality data before making evidence-based recommendations on MRI without contrast enhancement as an initial diagnostic work up," however, recognizing biparametric (bp) MRI as a reasonable option in a low-risk setting such as screening. With bpMRI, more men can undergo MRI at a lower cost and they can be spared the invasiveness of intravenous access. The aim of this study was to assess cancer detection in bpMRI vs mpMRI in sequential screening for prostate cancer (PCa). Methods Within the ongoing Goteborg PCa screening 2 trial, we assessed cancer detection in 551 consecutive participants undergoing prostate MRI. In the same session, readers first assessed bpMRI and then mpMRI. Four targeted biopsies were performed for lesions scored PIRADS 3-5 with bpMRI and/or mpMRI. Results Cancer was detected in 84/551 cases (15.2%; 95% CI: 12.4-18.4) with mpMRI and in 83/551 cases (15.1%; 95% CI: 12.3-18.2%) with bpMRI. The relative risk (RR) for cancer detection with bpMRI compared to mpMRI was 0.99 (95% one-sided CI: > 94.8); bpMRI was non-inferior to mpMRI (10% non-inferiority margin). bpMRI resulted in fewer false positives, 45/128 (35.2%), compared to mpMRI, 52/136 (38.2%), RR = 0.92; 95% CI: 0.84-0.98. Of 8 lesions scored positive only with mpMRI, 7 were false positives. The PPV for MRI and targeted biopsy was 83/128 (64.8%) for bpMRI and 84/136 (61.8%) for mpMRI, RR = 1.05, 95% CI: 1.01-1.10. Conclusions In a PSA-screened population, bpMRI was non-inferior to mpMRI for cancer detection and resulted in fewer false positives.
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| 27. |
- Wallström, Jonas, et al.
(author)
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Prostate Cancer Screening with Magnetic Resonance Imaging: Results from the Second Round of the Göteborg Prostate Cancer Screening 2 Trial.
- 2022
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In: European urology oncology. - : Elsevier BV. - 2588-9311. ; 5:1, s. 54-60
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Journal article (peer-reviewed)abstract
- The Göteborg 2 prostate cancer (PC) screening (G2) trial evaluates screening with prostate-specific antigen (PSA) followed by magnetic resonance imaging (MRI) in case of elevated PSA levels.To assess the safety of using a 2-yr interval in men who were previously screened positive with PSA but had negative MRI or positive MRI with a negative biopsy.A total of 61 201 men aged 50-60 yr were randomized and 38 366 were invited for screening (years 2015-2020). Men with positive MRI (Prostate Imaging Reporting and Data System [PI-RADS] score ≥3) were scheduled for targeted biopsies. Men with negative MRI or negative biopsies were reinvited after 2yr. Round 1 and 2 MRI scans (PI-RADS ≥3) of men not diagnosed with PC in round 1 were re-read and classified according to Prostate Cancer Radiological Estimation of Change in Sequential Evaluation (PRECISE) by two radiologists. Interval PCs (detected outside the program before invitation to round 2) were identified by linking to the Regional PC Registry.Tabulation of overall detection of PC was done.Between October 2017 and June 2020, 474 men with round 1 elevated PSA and MRI underwent a second screening. Of those, 19% had nonelevated PSA in round 2 and were not examined further. Of the remaining 376 men, 89% had negative MRI. Targeted biopsies yielded 14 PCs: nine grade group (GG) 1 and five GG 2-3. In men with PI-RADS ≥3 and PC diagnosed in round 2, only two (GG 1) progressed according to the PRECISE criteria and the remainder were stable. Ten interval PCs were diagnosed: seven GG 1, one GG 2, and two GG 5. The two GG 5 PCs were PI-RADS 4 and 5 with negative round 1 biopsy.A 2-yr interval seems to be safe in men with negative MRI, while men with PI-RADS 4 and 5 lesions with negative biopsies should have a closer follow-up.In prostate cancer screening, a 2-yr follow-up seems to be safe if magnetic resonance imaging did not show highly suspicious findings.
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| 28. |
- Yamauchi, F. I., et al.
(author)
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Prostate cancer discrimination in the peripheral zone with a reduced field-of-view T-2-mapping MRI sequence
- 2015
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In: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X. ; 33:5, s. 525-530
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Journal article (peer-reviewed)abstract
- Objectives: To evaluate the performance of T-2 mapping in discriminating prostate cancer from normal prostate tissue in the peripheral zone using a practical reduced field-of-view MRI sequence requiring less than 3 minutes of scan time. Materials and methods: Thirty-six patients with biopsy-proven peripheral zone prostate cancer without prior treatment underwent routine multiparametric MRI at 3.0 T with an endorectal coil. An Inner-Volume Carr-Purcell-Meiboom-Gill imaging sequence that required 2.8 minutes to obtain data for quantitative T-2 mapping covering the entire prostate gland was added to the routine multiparametric protocol. Suspected cancer (SC) and suspected healthy (SH) tissue in the peripheral zone were identified in consensus by three radiologists and were correlated with available biopsy results. Differences in mean T-2 values in SC and SH regions-of-interest (ROIs) were tested for significance using unpaired Student's two-tailed t-test. The area under the receiver operating characteristic curve was used to assess the optimal threshold T-2 value for cancer discrimination. Results: ROI analyses revealed significantly (p < 0.0001) shorter T-2 values in SC (85.4 +/- 12.3 ms) compared to SH (169.6 +/- 38.7 ms). An estimated T-2 threshold of 99 ms yielded a sensitivity of 92% and a specificity of 97% for prostate cancer discrimination. Conclusions: Quantitative values derived from this clinically practical T-2-mapping sequence allow high precision discrimination between healthy and cancerous peripheral zone in the prostate. (C) 2015 Elsevier Inc. All rights reserved.
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| 29. |
- Zhang, S. H., et al.
(author)
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Improved spatial localization in magnetic resonance spectroscopic imaging with two-dimensional PSF-Choice encoding
- 2018
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In: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807. ; 290, s. 18-28
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Journal article (peer-reviewed)abstract
- Purpose: Magnetic resonance spectroscopic imaging (MRSI), under low-spatial resolution settings, often suffers signal contamination from neighboring voxels due to ringing artifacts. Spatial localization can be improved by constraining the point-spread-function (PSF). Here the effectiveness of the two-dimensional PSF-Choice technique in providing improved spatial localization for MRSI is demonstrated. Theory and methods: The PSF-Choice technique constrains the PSF to a desired shape by manipulating the weighting of RF excitation pulse throughout phase-encode steps. Based on a Point REsolved SpectroScopy (PRESS)-type sequence, PSF-Choice encoding was implemented along two dimensions to excite a two-dimensional Gaussian profile, by replacing the usual RF excitation pulse with a train of pulses that is modified at each phase-encoding step. The method was proven mathematically, and demonstrated experimentally in phantoms containing prostate relevant metabolic compounds of choline, creatine and citrate. Results: Using a dedicated prostate-mimicking spectroscopy phantom surrounded by oil, it was found that there is significantly less signal contamination from oil for PSF-Choice encoding compared with standard phase encoding. In particular, with standard phase encoding, there was a significant difference (p = 0.014) between ratios of Choline + Creatine to Citrate for voxels well within the phantom compared to voxels within the phantom but near the boundary with oil. The ratios in boundary voxels were also significantly different (p = 0.035) from reference values obtained using the prostate phantom with no oil present. In contrast, no significant differences were found in comparisons of these ratios when encoding with PSF-Choice. Conclusion: The PSF-Choice scheme applied along two dimensions produces MR spectroscopic images with substantially reduced truncation artifacts and spectral contamination. © 2018 Elsevier Inc.
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