Die Analyse aortaler Hämodynamik und Gefäßwandparameter mittels fluss-sensitiver in-vivo 4D-MRT bei 3 Tesla

Zusammenfassung

Moderne fluss- oder bewegungssensitive Phasenkontrast MR-Bildgebung, auch „velocity mapping” genannt, erlaubt in einer Messung die Abbildung der 3-dimensionalen Gefäßmorphologie mitsamt der zeitaufgelösten Erfassung der Blutflussgeschwindigkeiten in den drei Raumrichtungen (3-direktional). Dabei kann die Blutströmung im gesamten Gefäßgebiet mit vollständiger räumlicher und zeitlicher Abdeckung, d. h. entlang des gesamten EKG-Zyklus, erfasst werden. In Kombination mit geeigneter Software werden die Darstellung und die qualitative Analyse normaler und pathologischer Hämodynamik möglich. Dies erlaubt, unabhängig von vordefinierten 2-dimensionalen Schichten, die freie Orientierung im 3D-Datenvolumen und die entsprechende Möglichkeit der lückenlosen Evaluierung beliebiger Gefäßabschnitte. So kann die 4-Dimensionalität der Daten vollständig ausgenutzt werden, um zusätzliche Aussagen und ein besseres Verständnis der zum Teil komplexen zeitlichen und räumlichen Änderungen des Blutflussverhaltens zu erreichen. Damit hat diese Technik das Potenzial, die Limitationen bestehender diagnostischer Verfahren zu überwinden und neue Parameter in die Diagnostik einzubringen, insbesondere vor dem Hintergrund der aktuell wachsenden Bedeutung von Faktoren wie Wandschubspannung und Oszillationsindex in der Diskussion um das Fortschreiten stenosierender und dilatativer Gefäßpathologien. Darüber hinaus können einfache, empirische Kriterien zur Indikationsstellung und Therapieentscheidung durch funktionelle Parameter bereichert oder ersetzt werden. Wir stellen einen Überblick der Literatur und Fallbeispiele vor, die das Verständnis für die methodischen Grundlagen und die zukünftigen Möglichkeiten erweitern sollen. Dabei steht die Erfassung und Visualisierung vaskulärer Hämodynamik insbesondere in den großen Gefäßen wie der thorakalen Aorta im Vordergrund.

Abstract

Modern phase contrast MR imaging at 3 Tesla allows the depiction of 3D morphology as well as the acquisition of time-resolved blood flow velocities in 3 directions. In combination with state-of-the-art visualization and data processing software, the qualitative and quantitative analysis of hemodynamic changes associated with vascular pathologies is possible. The 4D nature of the acquired data permits free orientation within the vascular system of interest and offers the opportunity to quantify blood flow and derived vessel wall parameters at any desired location within the data volume without being dependent on predefined 2D slices. The technique has the potential of overcoming the limitations of current diagnostic strategies and of implementing new diagnostic parameters. In light of the recent discussions regarding the influence of the wall shear stress and the oscillatory shear index on the genesis of arteriosclerosis and dilatative vascular processes, flow-sensitive 4D MRI may provide the missing diagnostic link. Instead of relying on experience-based parameters such as aneurysm size, new hemodynamic considerations can deepen our understanding of vascular pathologies. This overview reviews the underlying methodology at 3T, the literature on time-resolved 3D MR velocity mapping, and presents case examples. By presenting the pre- and postoperative assessment of hemodynamics in a thoracic aortic aneurysm and the detailed analysis of blood flow in a patient with coarctation we underline the potential of time-resolved 3D phase contrast MR at 3T for hemodynamic assessment of vascular pathologies, especially in the thoracic aorta.

Key words

hemodynamics/flow dynamics - vascular - aorta - aneurysm - MR imaging - velocity mapping

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