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      Ultrahigh-field MRI: where it really makes a difference Translated title: Ultrahochfeld-MRT: wo es wirklich einen Unterschied macht

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          Abstract

          Background

          Currently, two major magnetic resonance (MR) vendors provide commercial 7‑T scanners that are approved by the Food and Drug Administration (FDA) for clinical application. There is growing interest in ultrahigh-field MRI because of the improved clinical results in terms of morphological detail, as well as functional and metabolic imaging capabilities.

          Materials and methods

          The 7‑T systems benefit from a higher signal-to-noise ratio, which scales supralinearly with field strength, a supralinear increase in the blood oxygenation level dependent (BOLD) contrast for functional MRI and susceptibility weighted imaging (SWI), and the chemical shift increases linearly with field strength with consequently higher spectral resolution.

          Results

          In multiple sclerosis (MS), 7‑T imaging enables visualization of cortical lesions, the central vein sign, and paramagnetic rim lesions, which may be beneficial for the differential diagnosis between MS and other neuroinflammatory diseases in challenging and inconclusive clinical presentations and are seen as promising biomarkers for prognosis and treatment monitoring. The recent development of high-resolution proton MR spectroscopic imaging in clinically reasonable scan times has provided new insights into tumor metabolism and tumor grading as well as into early metabolic changes that may precede inflammatory processes in MS. This technique also improves the detection of epileptogenic foci in the brain. Multi-nuclear clinical applications, such as sodium imaging, have shown great potential for the evaluation of repair tissue quality after cartilage transplantation and in the monitoring of newly developed cartilage regenerative drugs for osteoarthritis.

          Conclusion

          For special clinical applications, such as SWI in MS, MR spectroscopic imaging in tumors, MS and epilepsy, and sodium imaging in cartilage repair, 7T may become a new standard.

          Translated abstract

          Hintergrund

          Derzeit bieten 2 Hersteller von Geräten für die Magnetresonanztomographie (MRT) kommerzielle 7‑T-MRT-Geräte mit Zulassung der US-amerikanischen Food and Drug Administration (FDA) für die klinische Anwendung an. Es besteht ein zunehmendes Interesse an Ultrahochfeld-MRT sowohl aufgrund verbesserter klinischer Ergebnisse bei morphologischen Details als auch bei den funktionellen und metabolischen bildgebenden Möglichkeiten.

          Material und Methoden

          Vorteile der 7‑T-Technik sind ein höheres Signal-zu-Rausch-Verhältnis, das von 3 T auf 7 T sogar supralinear zunimmt, eine ebenfalls supralineare Zunahme des Blood-Oxygenation-Level-Dependent(BOLD)-Kontrasts für funktionelle MRT und die suszeptibilitätsgewichtete Bildgebung sowie die lineare Zunahme des Chemical Shift mit konsekutiv höherer spektraler Auflösung.

          Ergebnisse

          Bei multipler Sklerose (MS) ermöglicht die 7‑T-Technik die Visualisierung von kortikalen Läsionen, das zentrale Venenzeichen und den Nachweis von paramagnetischen Randsaumläsionen, die für die Differenzialdiagnose zwischen MS und anderen neuroinflammatorischen Erkrankungen bei schwierigen, unklaren klinischen Symptomen von Vorteil sein können sowie als vielversprechende Biomarker für Prognose- und Therapiemonitoring gesehen werden. Die kürzlich entwickelte hochauflösende Protonen-MR-Spektroskopie in klinisch noch vertretbaren Untersuchungszeiten liefert neue Einsichten in den Tumorstoffwechsel und das Grading von Tumoren, in frühe metabolische Veränderungen, die entzündlichen Prozessen bei MS vorausgehen können, und verbessert den Nachweis von epileptogenen Herden im Gehirn. Klinische Multi-Kern-Anwendungen, wie beispielsweise die Natriumbildgebung, weisen ein hohes Potenzial für die Evaluation der Qualität des Ersatzgewebes nach Knorpeltransplantationen und im Monitoring von neu entwickelten knorpelregenerativen Medikamenten zur Behandlung der Gelenkarthrose auf.

          Schlussfolgerung

          Für besondere klinische Anwendungen wie z. B. SWI bei MS, MR-spektroskopische Bildgebung beim Hirntumorgrading und Monitoring unter Therapie oder beim Nachweis von epileptischen Foci, und der Anwendung von Multikern-MR wie die Natriumbildgebung zur Qualitätsbeurteilung von Knorpelersatztherapien, hat 7T das Potenzial ein neuer bildgebender Standard zu werden.

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          Most cited references33

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          Slow expansion of multiple sclerosis iron rim lesions: pathology and 7 T magnetic resonance imaging

          In multiple sclerosis (MS), iron accumulates inside activated microglia/macrophages at edges of some chronic demyelinated lesions, forming rims. In susceptibility-based magnetic resonance imaging at 7 T, iron-laden microglia/macrophages induce a rim of decreased signal at lesion edges and have been associated with slowly expanding lesions. We aimed to determine (1) what lesion types and stages are associated with iron accumulation at their edges, (2) what cells at the lesion edges accumulate iron and what is their activation status, (3) how reliably can iron accumulation at the lesion edge be detected by 7 T magnetic resonance imaging (MRI), and (4) if lesions with rims enlarge over time in vivo, when compared to lesions without rims. Double-hemispheric brain sections of 28 MS cases were stained for iron, myelin, and microglia/macrophages. Prior to histology, 4 of these 28 cases were imaged at 7 T using post-mortem susceptibility-weighted imaging. In vivo, seven MS patients underwent annual neurological examinations and 7 T MRI for 3.5 years, using a fluid attenuated inversion recovery/susceptibility-weighted imaging fusion sequence. Pathologically, we found iron rims around slowly expanding and some inactive lesions but hardly around remyelinated shadow plaques. Iron in rims was mainly present in microglia/macrophages with a pro-inflammatory activation status, but only very rarely in astrocytes. Histological validation of post-mortem susceptibility-weighted imaging revealed a quantitative threshold of iron-laden microglia when a rim was visible. Slowly expanding lesions significantly exceeded this threshold, when compared with inactive lesions (p = 0.003). We show for the first time that rim lesions significantly expanded in vivo after 3.5 years, compared to lesions without rims (p = 0.003). Thus, slow expansion of MS lesions with rims, which reflects chronic lesion activity, may, in the future, become an MRI marker for disease activity in MS. Electronic supplementary material The online version of this article (doi:10.1007/s00401-016-1636-z) contains supplementary material, which is available to authorized users.
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            Autologous chondrocyte implantation compared with microfracture in the knee. A randomized trial.

            New methods have been used, with promising results, to treat full-thickness cartilage defects. The objective of the present study was to compare autologous chondrocyte implantation with microfracture in a randomized trial. We are not aware of any previous randomized studies comparing these methods. Eighty patients without general osteoarthritis who had a single symptomatic cartilage defect on the femoral condyle in a stable knee were treated with autologous chondrocyte implantation or microfracture (forty in each group). We used the International Cartilage Repair Society, Lysholm, Short Form-36 (SF-36), and Tegner forms to collect data. An independent observer performed a follow-up examination at twelve and twenty-four months. Two years postoperatively, arthroscopy with biopsy for histological evaluation was carried out. The histological evaluation was done by a pathologist and a clinical scientist, both of whom were blinded to each patient's treatment. In general, there were small differences between the two treatment groups. At two years, both groups had significant clinical improvement. According to the SF-36 physical component score at two years postoperatively, the improvement in the microfracture group was significantly better than that in the autologous chondrocyte implantation group (p = 0.004). Younger and more active patients did better in both groups. There were two failures in the autologous chondrocyte implantation group and one in the microfracture group. No serious complications were reported. Biopsy specimens were obtained from 84% of the patients, and histological evaluation of repair tissues showed no significant differences between the two groups. We did not find any association between the histological quality of the tissue and the clinical outcome according to the scores on the Lysholm or SF-36 form or the visual analog scale. Both methods had acceptable short-term clinical results. There was no significant difference in macroscopic or histological results between the two treatment groups and no association between the histological findings and the clinical outcome at the two-year time-point. Therapeutic study, Level I-1a (randomized controlled trial [significant difference]). See Instructions to Authors for a complete description of levels of evidence.
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              Magnetic susceptibility mapping of brain tissue in vivo using MRI phase data.

              Phase images in susceptibility-weighted MRI of brain provide excellent contrast. However, the phase is affected by tissue geometry and orientation relative to the main magnetic field (B(0)), and phase changes extend beyond areas of altered susceptibility. Magnetic susceptibility, on the other hand, is an intrinsic tissue property, closely reflecting tissue composition. Therefore, recently developed inverse Fourier-based methods were applied to calculate susceptibility maps from high-resolution phase images acquired at a single orientation at 7 T in the human brain (in vivo and fixed) and at 11.7 T in fixed marmoset brain. In susceptibility images, the contrast of cortical layers was more consistent than in phase images and was independent of the structures' orientation relative to B(0). The contrast of iron-rich deep-brain structures (red nucleus and substantia nigra) in susceptibility images agreed more closely with iron-dominated R(2) (*) images than the phase image contrast, which extended outside the structures. The mean susceptibility in these regions was significantly correlated with their estimated iron content. Susceptibility maps calculated using this method overcome the orientation-dependence and non-locality of phase image contrast and seem to reflect underlying tissue composition. Susceptibility images should be easier to interpret than phase images and could improve our understanding of the sources of susceptibility contrast. (c) 2009 Wiley-Liss, Inc.
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                Author and article information

                Contributors
                siegfried.trattnig@meduniwien.ac.at
                Journal
                Radiologie (Heidelb)
                Radiologie (Heidelb)
                Radiologie (Heidelberg, Germany)
                Springer Medizin (Heidelberg )
                2731-7048
                2731-7056
                16 August 2023
                16 August 2023
                2024
                : 64
                Issue : Suppl 1 Issue sponsor : This supplement is not sponsored by industry
                : 1-8
                Affiliations
                [1 ]High-Field MR Center – 7T MR, Department of Biomedical Imaging and Image-guided Therapy, Medical University Vienna, ( https://ror.org/05n3x4p02) Lazarettgasse 14, 1090 Vienna, Austria
                [2 ]Department of Neurology, Medical University of Vienna, ( https://ror.org/05n3x4p02) Währinger Gürtel 18–20, 1090 Vienna, Austria
                [3 ]GRID grid.419303.c, ISNI 0000 0001 2180 9405, Department of Imaging Methods, Institute of Measurement Science, , Slovak Academy of Sciences, ; Dubravska cesta 9, 84104 Bratislava, Slovakia
                [4 ]Medical University of Vienna, Comprehensive Center for Clinical Neurosciences & Mental Health, ( https://ror.org/05n3x4p02) Vienna, Austria
                Article
                1184
                10.1007/s00117-023-01184-x
                11602857
                37584681
                c4d38269-6ce2-481a-9cc9-e7e150fa3e1f
                © The Author(s) 2023

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 30 June 2023
                Funding
                Funded by: Medical University of Vienna
                Categories
                Review
                Custom metadata
                © Springer Medizin Verlag GmbH, ein Teil von Springer Nature 2024

                7 tesla,multiple sclerosis,spectroscopic imaging,susceptibility weighted imaging,sodium imaging,multiple sklerosa,spektroskopische bildgebung,suzeptibilitätsgewichtete bildgebung,natriumbildgebung

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