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| 2. |
- Alamidi, Daniel, et al.
(author)
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Variable Flip Angle 3D Ultrashort Echo Time (UTE) T-1 Mapping of Mouse Lung: A Repeatability Assessment
- 2018
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 48:3, s. 846-852
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Journal article (peer-reviewed)abstract
- Background: Lung T-1 is a potential translational biomarker of lung disease. The precision and repeatability of variable flip angle (VFA) T-1 mapping using modern 3D ultrashort echo time (UTE) imaging of the whole lung needs to be established before it can be used to assess response to disease and therapy. Purpose: To evaluate the feasibility of regional lung T-1 quantification with VFA 3D-UTE and to investigate long-and short-term T-1 repeatability in the lungs of naive mice. Field strength/Sequence: 3D free-breathing radial UTE (8 mu s) at 4.7T. Assessment: VFA 3D-UTE T-1 calculations were validated against T-1 values measured with inversion recovery (IR) in phantoms. Lung T-1 and proton density (S-0) measurements of whole lung and muscle were repeated five times over 1 month in free-breathing naive mice. Two consecutive T-1 measurements were performed during one of the imaging sessions. Statistical Tests: Agreement in T-1 between VFA 3D-UTE and IR in phantoms was assessed using Bland-Altman and Pearson's correlation analysis. The T-1 repeatability in mice was evaluated using coefficient of variation (CV), repeated-measures analysis of variance (ANOVA), and paired t-test. Results: Good T-1 agreement between the VFA 3D-UTE and IR methods was found in phantoms. T-1 in lung and muscle showed a 5% and 3% CV (1255 +/- 63 msec and 1432 +/- 42 msec, respectively, mean +/- SD) with no changes in T-1 or S-0 over a month. Consecutive measurements resulted in an increase of 2% in both lung T-1 and S-0. Data Conclusion: VFA 3D-UTE shows promise as a reliable T-1 mapping method that enables full lung coverage, high signal-to-noise ratio (similar to 25), and spatial resolution (300 mu m) in freely breathing animals. The precision of the VFA 3D-UTE method will enable better design and powering of studies.
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| 3. |
- Alsaqal, Salem, et al.
(author)
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The Combination of MR Elastography and Proton Density Fat Fraction Improves Diagnosis of Nonalcoholic Steatohepatitis.
- 2022
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In: Journal of Magnetic Resonance Imaging. - : John Wiley & Sons. - 1053-1807 .- 1522-2586. ; 56:2, s. -379
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Journal article (peer-reviewed)abstract
- BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is rapidly increasing worldwide. It is subdivided into nonalcoholic fatty liver (NAFL) and the more aggressive form, nonalcoholic steatohepatitis (NASH), which carries a higher risk of developing fibrosis and cirrhosis. There is currently no reliable non-invasive method for differentiating NASH from NAFL.PURPOSE: To investigate the ability of magnetic resonance imaging (MRI)-based imaging biomarkers to diagnose NASH and moderate fibrosis as well as assess their repeatability.STUDY TYPE: Prospective.SUBJECTS: Sixty-eight participants (41% women) with biopsy-proven NAFLD (53 NASH and 15 NAFL). Thirty participants underwent a second MRI in order to assess repeatability.FIELD STRENGTH/SEQUENCE: 3.0 T; MR elastography (MRE) (a spin-echo echo-planar imaging [SE-EPI] sequence with motion-encoding gradients), MR proton density fat fraction (PDFF) and R2* mapping (a multi-echo three-dimensional gradient-echo sequence), T1 mapping (a single-point saturation-recovery technique), and diffusion-weighted imaging (SE-EPI sequence).ASSESSMENT: Quantitative MRI measurements were obtained and assessed alone and in combination with biochemical markers (cytokeratin-18 [CK18] M30, alanine transaminase [ALT], and aspartate transaminase [AST]) using logistic regression models. Models that could differentiate between NASH and NAFL and between moderate to advanced fibrosis (F2-4) and no or mild fibrosis (F0-1), based on the histopathological results, were identified.STATISTICAL TESTS: Independent samples t-test, Pearson's chi-squared test, area under the receiver operating characteristic curve (AUROC), Spearman's correlation, intra-individual coefficient of variation, and intraclass correlation coefficient (ICC). Statistical significance was set at P < 0.05.RESULTS: There was a significant difference between the NASH and NAFL groups with liver stiffness assessed with MRE, CK18 M30, and ALT, with an AUROC of 0.74, 0.76, and 0.70, respectively. Both MRE and PDFF contributed significantly to a bivariate model for diagnosing NASH (AUROC = 0.84). MRE could significantly differentiate between F2-4 and F0-1 (AUROC = 0.74). A model combining MRE with AST improved the diagnosis of F2-4 (AUROC = 0.83). The ICC for repeatability was 0.94 and 0.99 for MRE and PDFF, respectively.DATA CONCLUSION: MRE can potentially diagnose NASH and differentiate between fibrosis stages. Combining MRE with PDFF improves the diagnosis of NASH.LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 2.
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| 4. |
- Andersson, Thord, et al.
(author)
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Consistent intensity inhomogeneity correction in water-fat MRI
- 2015
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In: Journal of Magnetic Resonance Imaging. - : Wiley-Blackwell. - 1053-1807 .- 1522-2586. ; 42:2
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Journal article (peer-reviewed)abstract
- PURPOSE: To quantitatively and qualitatively evaluate the water-signal performance of the consistent intensity inhomogeneity correction (CIIC) method to correct for intensity inhomogeneitiesMETHODS: Water-fat volumes were acquired using 1.5 Tesla (T) and 3.0T symmetrically sampled 2-point Dixon three-dimensional MRI. Two datasets: (i) 10 muscle tissue regions of interest (ROIs) from 10 subjects acquired with both 1.5T and 3.0T whole-body MRI. (ii) Seven liver tissue ROIs from 36 patients imaged using 1.5T MRI at six time points after Gd-EOB-DTPA injection. The performance of CIIC was evaluated quantitatively by analyzing its impact on the dispersion and bias of the water image ROI intensities, and qualitatively using side-by-side image comparisons.RESULTS: CIIC significantly ( P1.5T≤2.3×10-4,P3.0T≤1.0×10-6) decreased the nonphysiological intensity variance while preserving the average intensity levels. The side-by-side comparisons showed improved intensity consistency ( Pint≤10-6) while not introducing artifacts ( Part=0.024) nor changed appearances ( Papp≤10-6).CONCLUSION: CIIC improves the spatiotemporal intensity consistency in regions of a homogenous tissue type.
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| 5. |
- Berggren, Klas, et al.
(author)
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Super-Resolution Cine Image Enhancement for Fetal Cardiac Magnetic Resonance Imaging
- 2022
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 56:1, s. 223-231
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Journal article (peer-reviewed)abstract
- BackgroundFetal cardiac magnetic resonance imaging (MRI) improves the diagnosis of congenital heart defects, but is sensitive to fetal motion due to long image acquisition time. This may be overcome with faster image acquisition with low resolution, followed by image enhancement to provide clinically useful images.PurposeTo combine phase-encoding undersampling with super-resolution neural networks to achieve high-resolution fetal cine cardiac MR images with short acquisition time.Study TypeProspective.SubjectsTwenty-eight fetuses (gestational week 36 [interquartile range 33–38 weeks]).Field Strength/Sequence1.5 T, balanced steady-state free precession (bSSFP) cine sequence.AssessmentImages were acquired using fully sampled Doppler ultrasound-gated clinical bSSFP cine as reference, with equivalent cine sequences with decreased phase-encoding resolution (25%, 33%, and 50% of clinical standard). Two super-resolution methods based on convolutional neural networks were proposed and evaluated (phasrGAN and phasrresnet). Data were partitioned into training (36 cine slices), validation (3 cine slices), and test sets (67 cine slices) without overlap. Conventional reconstruction methods using bicubic interpolation and k-space zeropadding were used for comparison. Three blinded observers scored image quality between 1 and 10.Statistical TestsImage scores are reported as median [interquartile range] and were compared using Mann–Whitney's nonparametric test with P < 0.05 showing statistically significant differences.ResultsBoth proposed methods showed no significant difference in image quality compared to clinical images (8 [7–8.5]) down to 33% (phasrGAN 8 [6.5–8]; phasrresnet 8 [7–8], all P ≥ 0.19) phase-encoding resolution, i.e., up to three times faster image acquisition, whereas bicubic interpolation and k-space zeropadding showed significantly lower quality for 33% phase-encoding resolution (both 7 [6–8]).Data ConclusionSuper-resolution enhancement can be used for fetal cine cardiac MRI to reduce image acquisition time while maintaining image quality. This may lead to an improved success rate for fetal cine MR imaging, as the impact of fetal motion is lessened by shortened acquisitions.Level of Evidence1Technical EfficacyStage 2
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| 6. |
- Bergvall, Erik, et al.
(author)
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A fast and highly automated approach to myocardial motion analysis using phase contrast magnetic resonance imaging.
- 2006
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 23:5, s. 652-661
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Journal article (peer-reviewed)abstract
- Purpose: To develop a fast and highly automated method for calculating two-dimensional myocardial motion and deformation using velocity encoded magnetic resonance imaging. Materials and Methods: Two-dimensional phase contrast magnetic resonance imaging was used to acquire time resolved velocity maps of the myocardium. Cardiac motion was calculated by an iterative integration-regularization scheme of low computational cost. Image segmentation was performed using active appearance models. Results: Validation of motion tracking was performed in N = 47 subjects using saturation grid-tagging and closely followed "tag-lines." Image segmentation was validated vs. manual delineation. Conclusion: The speed and limited user interaction gives the method good potential for use in clinical practice.
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| 7. |
- Bjerner, Tomas, et al.
(author)
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Evaluation of nonperfused myocardial ischemia with MRI and an intravascular USPIO contrast agent in an ex vivo pig model
- 2000
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In: Journal of Magnetic Resonance Imaging. - 1053-1807 .- 1522-2586. ; 12:6, s. 866-872
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Journal article (peer-reviewed)abstract
- The ultrasmall superparamagnetic iron oxide (USPIO) preparation NC100150 Injection (Clariscan; Nycomed Imaging, Oslo, Norway) was tested for its ability to delineate nonperfused myocardium under steady-state conditions. An experimental animal model of focal myocardial ischemia induced by ligation of the distal part of the left anterior descending artery was used. The contrast agent was administered in four doses: 0, 4, 8, and 12 mg Fe/kg body weight. Magnetic resonance examination ex vivo, including T1-, T2-, and T2*-weighted sequences, was performed. Nonperfused myocardium was determined by fluorescein. The best delineation of nonperfused myocardium was found with a T1-weighted inversion recovery/turbo spin-echo sequence and doses of 4 and 8 mg Fe/kg body weight, where 95% of the volume was discernible at the dose of 4 mg Fe/kg body weight. The results suggest that steady-state imaging by T1-weighted sequence with the use of NC100150 Injection to delineate nonperfused myocardium is feasible. J. Magn. Reson. Imaging 2000;12:866-872.
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| 9. |
- Briley Saebo, Karen, et al.
(author)
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Long-term imaging effects in rat liver after a single injection of an iron oxide nanoparticle based MR contrast agent
- 2004
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 20:4, s. 622-631
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Journal article (peer-reviewed)abstract
- PURPOSE: To investigate the duration of liver R2* enhancement and pharmacokinetics following administration of an iron oxide nanoparticle in a rat model.MATERIALS AND METHODS: Rats were injected with 0, 1, 2, or 5 mg Fe/kg of NC100150 Injection, and quantitative in vivo 1/T2* liver measurements were obtained between 1 and 133 days after injection. The concentration of NC100150 Injection was determined by relaxometry methods in ex vivo rat liver homogenate.RESULTS: At all dose levels, 1/T2* remained greater than control values up to 63 days after injection. In the highest dose group, 1/T2* was above control levels during the entire 133 day time-course investigated. There were no quantifiable amounts of NC100150 Injection present 63 days after injection in any of the dose groups. The half-life of NC100150 Injection in rat liver was dose dependent. For the lowest dose group, the degradation of the particles could be defined by a mono-exponential function with a half-life of eight days. For the 2 and 5 mg Fe/kg dose groups, the degradation was bi-exponential with a fast initial decay of seven to eight days followed by a slow terminal decay of 43-46 days.CONCLUSION: NC100150 Injection exhibits prolonged 1/T2* enhancement in rat liver. The liver enhancement persisted at time points when the concentration of iron oxide particles present in the liver was below method detection limits. The prolonged 1/T2* enhancement is likely a result of the particle breakdown products and the induction of ferritin and hemosiderin with increasing iron cores/loading factors.
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