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Probleme und Chancen der Hochfeldmagnetresonanztomographie

Problems and chances of high field magnetic resonance imaging

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Zusammenfassung

Klinisches/methodisches Problem

Die räumliche, zeitliche oder spektrale Auflösung der MRT ist heute vielfach nicht ausreichend, um Submillimeterläsionen zu detektieren oder um die Dynamik des Herzschlags darzustellen.

Radiologische Standardverfahren

Zur Zeit sind MR-Tomographen bei 1,5 oder 3 T die Standardgeräte für klinische Untersuchungen.

Methodische Innovationen

Der Einsatz ultrahoher Magnetfelder von 7 T verspricht durch die Erhöhung des Signal-zu-Rausch-Verhältnisses eine deutliche Verbesserung der räumlichen und/oder zeitlichen Auflösung sowie die Generierung neuer Kontraste.

Leistungsfähigkeit

Mit der 7-T-MRT ist es gelungen, MR-Aufnahmen des Hirns routinemäßig mit 0,3 mm Auflösung zu akquirieren. Die theoretisch erwartete Verbesserung des Signal-zu-Rausch-Verhältnisses wird aber auf Grund von B1-Inhomogenitäten und Kontrastvariationen oft nicht erreicht.

Bewertung

Mit Hilfe der 7-T-MRT kann eine deutliche Erhöhung der räumlichen Auflösung erzielt werden. Techniken wie die Time-of-flight(TOF)-MR-Angiographie und suszeptibilitätsgewichtete Methoden (z. B. die neurofunktionelle MRT) profitieren in verstärktem Maße von den hohen Feldern. Sendefeldinhomogenitäten sind immer noch eine große Herausforderung für die Ultrahochfeld(UHF)-MRT und stellen auch ein nur teilweise gelöstes Sicherheitsproblem dar.

Empfehlung für die Praxis

Die UHF-MRT ist z. Z. auf spezielle Anwendungsgebiete beschränkt, und der erwartete Gewinn muss oft gegen technische Komplikationen bei der Datenaufnahme und Bildinterpretation abgewogen werden.

Abstract

Clinical/methodical issue

The spatial, temporal and spectral resolution in magnetic resonance imaging (MRI) is in many cases currently not sufficient to detect submillimeter lesions or to image the dynamics of the beating heart.

Standard radiological methods

At present MRI systems at 1.5 T and 3 T are the standard units for clinical imaging.

Methodical innovations

The use of ultrahigh magnetic fields of 7 T and higher increases the signal-to-noise ratio, which holds promise for a significant improvement of the spatial and/or temporal resolution as well as for new contrast mechanisms.

Performance

With 7 T MRI, images of the brain have been acquired routinely with a spatial resolution of 0.3 mm. The theoretical improvement of the signal-to-noise ratio is often not fully realized due to B1 inhomogeneities and contrast variations.

Achievements

With MRI at 7 T a notable increase in spatial resolution can be achieved. Methods such as time-of-flight MR angiography and susceptibility-weighted imaging (e.g. neurofunctional MRI, fMRI) profit especially from the higher field strengths. Transmission field inhomogeneities are still a major challenge for ultrahigh field (UHF) MRI and are also a partially unsolved safety problem.

Practical recommendations

The use of UHF MRI is currently limited to special applications and the expected gain of the high field must be weighed against technical limitations in both image acquisition and interpretation.

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Authors and Affiliations

  1. Erwin L. Hahn Institute for Magnetic Resonance Imaging, Institut für Diagnostische und Interventionelle Radiologie und Neuroradiologie, Universität Duisburg-Essen, Universitätsklinikum Essen, Arendahls Wiese 199, 45141, Essen, Deutschland

    M.E. Ladd

  2. Abt. Radiologie – Medizin Physik, Universitätsklinikum Freiburg , Breisacher Str. 60a, 79106, Freiburg, Deutschland

    M. Bock

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Ladd, M., Bock, M. Probleme und Chancen der Hochfeldmagnetresonanztomographie. Radiologe 53, 401–410 (2013). https://doi.org/10.1007/s00117-012-2344-x

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