Beschleunigung der kardiovaskulären MRT mittels paralleler Bildgebung: Grundlagen, praktische Aspekte, klinische Anwendungen und Perspektiven

Zusammenfassung

Moderne Verfahren der Magnetresonanztomographie (MRT) spielen eine zentrale Rolle für die nicht-invasive Diagnostik von Herz- und Gefäßerkrankungen. Kardiovaskuläre MRT erfordert eine sehr hohe Datenaufnahmegeschwindigkeit und Effektivität, deren Erfordernissen konventionelle MR-Datenakquisitionsstrategien nur eingeschränkt genügen. In diesen Strategien wird die Ortskodierung ausschließlich über eine sequenzielle Abfolge von Hochfrequenzimpulsen in Verbindung mit magnetischen Feldgradienten vorgenommen. Die parallele MRT (pMRT) umgeht diese Einschränkungen, indem zum Zweck der simultanen Ortskodierung zusätzlich das Signalintensitätsprofil von Hochfrequenzempfangsantennen benutzt wird. Der damit verbundene Geschwindigkeitszuwachs kann die kardiovaskuläre MR-Diagnostik auf vielfältige Weise verbessern: durch Verkürzung der Untersuchungszeiten, Verbesserung der räumlichen Auflösung bzw. ausreichende Abdeckung anatomischer Zielgebiete, Verbesserung der zeitlichen Auflösung, Erhöhung der Bildqualität, Überwindung physiologischer Grenzwerte, Detektion und Korrektur physiologischer Bewegungseinflüsse sowie Vereinfachung des Untersuchungsablaufes. Diese Übersichtsarbeit stellt für jede dieser Strategien Anwendungsbeispiele zur diagnostischen Bildgebung des Herzens und großer Gefäße vor. Zuvor wird eine Übersicht zu den wesentlichen Grundlagen der parallelen Bildgebung präsentiert. Anschließend werden elementare praktische Aspekte wie Einschränkungen im Signal-Rausch-Verhältnis, maßgeschneiderte Untersuchungsprotokolle und potenzielle Bildartefakte sowie klinische Anwendungsmöglichkeiten der parallelen Bildgebung in der kardiovaskulären MRT betrachtet. Abschließend werden aktuelle Forschungstrends und zukünftige Entwicklungen der kardiovaskulären MRT aus technischer und klinischer Sicht diskutiert.

Abstract

Cardiovascular Magnetic Resonance (CVMR) imaging has proven to be of clinical value for non-invasive diagnostic imaging of cardiovascular diseases. CVMR requires rapid imaging; however, the speed of conventional MRI is fundamentally limited due to its sequential approach to image acquisition, in which data points are collected one after the other in the presence of sequentially-applied magnetic field gradients and radiofrequency pulses. Parallel MRI uses arrays of radiofrequency coils to acquire multiple data points simultaneously, and thereby to increase imaging speed and efficiency beyond the limits of purely gradient-based approaches. The resulting improvements in imaging speed can be used in various ways, including shortening long examinations, improving spatial resolution and anatomic coverage, improving temporal resolution, enhancing image quality, overcoming physiological constraints, detecting and correcting for physiologic motion, and streamlining work flow. Examples of these strategies will be provided in this review, after some of the fundamentals of parallel imaging methods now in use for cardiovascular MRI are outlined. The emphasis will rest upon basic principles and clinical state-of-the art cardiovascular MRI applications. In addition, practical aspects such as signal-to-noise ratio considerations, tailored parallel imaging protocols and potential artifacts will be discussed, and current trends and future directions will be explored.

Cardiovascular MRI - parallel MR imaging - phased array technology - many element coil arrays

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