| 1. |
- Kvernby, Sofia, 1987-
(författare)
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Myocardial Tissue Characterization Using Magnetic Resonance Imaging
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In cardiovascular disease, which is the most common cause of death in the world, early diagnosis is crucial for disease outcome. Diagnosis of cardiovascular disease can be challenging, though. Quantification of myocardial T1 and T2 relaxation times with MRI has demonstrated to be a promising method for characterizing myocardial tissue, but long measurement times have hampered clinical use. The overall aim of this doctoral thesis was to develop, validate and, in patient studies, evaluate a very fast three-dimensional method for simultaneous quantification of myocardial T1 and T2 relaxation times with whole coverage of the left ventricle.The 3D-QALAS method is presented in Paper I of this thesis. It is a method that simultaneous measures both T1 and T2 relaxation times in a three-dimensional volume of the heart. The method requires 15 heartbeats, to produce 13 short-axis slices of the left ventricle with voxelwise information of both T1 and T2 relaxation times. The 3D-QALAS method was validated in phantoms and in 10 healthy volunteers by comparing the method with reference methods and demonstrated good accuracy and robustness both in-vitro and in-vivo.In Paper II, the 3D-QALAS method was carefully validated in-vivo by investigating accuracy and precision in 10 healthy volunteers, while the clinical feasibility of the method was investigated in 23 patients with various cardiac pathologies. Repeated independent and dependent scans together with the intra-scan repeatability, demonstrated all a very good precision for the 3D-QALAS method in healthy volunteers.In Paper III and IV, the 3D-QALAS method was applied and evaluated in patient cohorts where the heart muscle alters over time. In Paper III, patients with severe aortic stenosis underwent MRI examinations with 3D-QALAS before, 3 months after and 12 months after aortic valve surgery. Changes in T1 and T2 were observed, which might be used as markers of myocardial changes with respect to edema and fibrosis, which may develop due to increased workload over a long period of time.In study IV, 3D-QALAS was used to investigate 10 breast cancer patients treated with radiation therapy prior to treatment, 2-3 weeks into treatment, and one and 6 months after completion of treatment, to investigate any changes in T1 and T2 and further if they can be correlated to unwanted irradiation of the heart during radiation therapy.
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| 2. |
- Blystad, Ida, 1972-, et al.
(författare)
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Quantitative MRI using relaxometry in malignant gliomas detects contrast enhancement in peritumoral oedema
- 2020
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Malignant gliomas are primary brain tumours with an infiltrative growth pattern, often with contrast enhancement on magnetic resonance imaging (MRI). However, it is well known that tumour infiltration extends beyond the visible contrast enhancement. The aim of this study was to investigate if there is contrast enhancement not detected visually in the peritumoral oedema of malignant gliomas by using relaxometry with synthetic MRI. 25 patients who had brain tumours with a radiological appearance of malignant glioma were prospectively included. A quantitative MR-sequence measuring longitudinal relaxation (R-1), transverse relaxation (R-2) and proton density (PD), was added to the standard MRI protocol before surgery. Five patients were excluded, and in 20 patients, synthetic MR images were created from the quantitative scans. Manual regions of interest (ROIs) outlined the visibly contrast-enhancing border of the tumours and the peritumoral area. Contrast enhancement was quantified by subtraction of native images from post GD-images, creating an R-1-difference-map. The quantitative R-1-difference-maps showed significant contrast enhancement in the peritumoral area (0.047) compared to normal appearing white matter (0.032), p = 0.048. Relaxometry detects contrast enhancement in the peritumoral area of malignant gliomas. This could represent infiltrative tumour growth.
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| 3. |
- Chougar, Lydia, et al.
(författare)
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Signal Intensity within Cerebral Venous Sinuses on Synthetic MRI
- 2020
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Ingår i: MAGNETIC RESONANCE IN MEDICAL SCIENCES. - : JPN SOC MAGNETIC RESONANCE MEDICINE. - 1347-3182 .- 1880-2206. ; 19:1, s. 56-63
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Flowing blood sometimes appears bright on synthetic T-1-weighted images, which could be misdiagnosed as a thrombus. This study aimed to investigate the frequency of hyperintensity within cerebral venous sinuses on synthetic MR images and to evaluate the influence of increasing flow rates on signal intensity using a flow phantom. Materials and Methods: Imaging data, including synthetic and conventional MRI scans, from 22 patients were retrospectively analyzed. Signal intensities at eight locations of cerebral venous sinuses on synthetic images were graded using the following three-point scale: 0, "dark vessel"; 1, "hyperintensity within the walls"; and 2, "hyperintensity within the lumen:" A phantom with gadolinium solution inside a U-shaped tube was acquired without flow and then with increasing flow rates (60, 100, 200, 300, 400 ml/min). Results: Considering all sinus locations, the venous signal intensity on synthetic T-1-weighted images was graded as 2 in 79.8% of the patients. On synthetic T-2-weighted images, all sinuses were graded as 0. On fluid-attenuated inversion recovery (FLAIR) images, sinuses were almost always graded as 0 (99.4%). In the phantom study, the signal initially became brighter on synthetic T-1-weighted images as the flow rate increased. Above a certain flow rate, the signal started to decrease. Conclusion: High signal intensity within the cerebral venous sinuses is a frequent finding on synthetic T-1-weighted images. This corresponds to the hyperintensity noted at certain flow rates in the phantom experiment.
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| 4. |
- Hagiwara, Akifumi, et al.
(författare)
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SyMRI of the Brain : Rapid Quantification of Relaxation Rates and Proton Density, With Synthetic MRI, Automatic Brain Segmentation, and Myelin Measurement
- 2017
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Ingår i: Investigative Radiology. - : Lippincott Williams & Wilkins. - 0020-9996 .- 1536-0210. ; 52:10, s. 647-657
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Forskningsöversikt (refereegranskat)abstract
- Conventional magnetic resonance images are usually evaluated using the image signal contrast between tissues and not based on their absolute signal intensities. Quantification of tissue parameters, such as relaxation rates and proton density, would provide an absolute scale; however, these methods have mainly been performed in a research setting. The development of rapid quantification, with scan times in the order of 6 minutes for full head coverage, has provided the prerequisites for clinical use. The aim of this review article was to introduce a specific quantification method and synthesis of contrast-weighted images based on the acquired absolute values, and to present automatic segmentation of brain tissues and measurement of myelin based on the quantitative values, along with application of these techniques to various brain diseases. The entire technique is referred to as "SyMRI" in this review. SyMRI has shown promising results in previous studies when used for multiple sclerosis, brain metastases, Sturge-Weber syndrome, idiopathic normal pressure hydrocephalus, meningitis, and postmortem imaging.
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| 5. |
- Ouellette, R., et al.
(författare)
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Validation of Rapid Magnetic Resonance Myelin Imaging in Multiple Sclerosis
- 2020
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Ingår i: Annals of Neurology. - : Wiley. - 0364-5134 .- 1531-8249. ; 87:5, s. 710-724
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Magnetic resonance imaging (MRI) is essential for multiple sclerosis diagnostics but is conventionally not specific to demyelination. Myelin imaging is often hampered by long scanning times, complex postprocessing, or lack of clinical approval. This study aimed to assess the specificity, robustness, and clinical value of Rapid Estimation of Myelin for Diagnostic Imaging, a new myelin imaging technique based on time-efficient simultaneous T1/T2 relaxometry and proton density mapping in multiple sclerosis. Methods: Rapid myelin imaging was applied using 3T MRI ex vivo in 3 multiple sclerosis brain samples and in vivo in a prospective cohort of 71 multiple sclerosis patients and 21 age/sex-matched healthy controls, with scan–rescan repeatability in a subcohort. Disability in patients was assessed by the Expanded Disability Status Scale and the Symbol Digit Modalities Test at baseline and 2-year follow-up. Results: Rapid myelin imaging correlated with myelin-related stains (proteolipid protein immunostaining and Luxol fast blue) and demonstrated good precision. Multiple sclerosis patients had, relative to controls, lower normalized whole-brain and normal-appearing white matter myelin fractions, which correlated with baseline cognitive and physical disability. Longitudinally, these myelin fractions correlated with follow-up physical disability, even with correction for baseline disability. Interpretation: Rapid Estimation of Myelin for Diagnostic Imaging provides robust myelin quantification that detects diffuse demyelination in normal-appearing tissue in multiple sclerosis, which is associated with both cognitive and clinical disability. Because the technique is fast, with automatic postprocessing and US Food and Drug Administration/CE clinical approval, it can be a clinically feasible biomarker that may be suitable to monitor myelin dynamics and evaluate treatments aiming at remyelination.
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| 6. |
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| 7. |
- Warntjes, Marcel, Jan Bertus, 1973-, et al.
(författare)
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Rapid magnetic resonance quantification on the brain : Optimization for clinical usage
- 2008
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 60:2, s. 320-329
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented for rapid simultaneous quantification of the longitudinal T1 relaxation, the transverse T2 relaxation, the proton density (PD), and the amplitude of the local radio frequency B 1 field. All four parameters are measured in one single scan by means of a multislice, multiecho, and multidelay acquisition. It is based on a previously reported method, which was substantially improved for routine clinical usage. The improvements comprise of the use of a multislice spin-echo technique, a background phase correction, and a spin system simulation to compensate for the slice-selective RF pulse profile effects. The aim of the optimization was to achieve the optimal result for the quantification of magnetic resonance parameters within a clinically acceptable time. One benchmark was high-resolution coverage of the brain within 5 min. In this scan time the measured intersubject standard deviation (SD) in a group of volunteers was 2% to 8%, depending on the tissue (voxel size = 0.8 x 0.8 x 5 mm). As an example, the method was applied to a patient with multiple sclerosis in whom the diseased tissue could clearly be distinguished from healthy reference values. Additionally it was shown that, using the approach of synthetic MRI, both accurate conventional contrast images as well as quantification maps can be generated based on the same scan. © 2008 Wiley-Liss, Inc.
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