Noninvasive MRI-Based Liver Iron Quantification: Methodic Approaches, Practical Applicability and Significance

Abstract

Due to the dependence of transverse relaxation times T₂ and T₂* on tissue iron content, MRI offers different options for the determination of iron concentration. These are the time-consuming spin-echo sequence as well as the gradient-echo sequence. For the latter, several data analysis approaches have been proposed, with different requirements for acquisition and post-processing: the mathematically challenging R₂* analysis and the signal-intensity ratio method with its high demand on the signal homogeneity of MR images. Furthermore, special procedures currently under evaluation are presented as future prospects: quantitative susceptibility imaging, as a third approach for analyzing gradient echo data, and multi-contrast spin-echo using repeated refocusing pulses. MR theory, as far as needed for understanding the methods, is briefly depicted.

Key points:

• Description of underlying technology of different MRI-based procedures for liver iron quantification

• Applicability of these methods in clinical practice

• Validity of the methods, i. e. positive and negative predictive value, if available

Citation Format:

• Wunderlich AP, Cario H, Juchems MS et al. Noninvasive MRI-Based Liver Iron Quantification: Methodic Approaches, Practical Applicability and Significance. Fortschr Röntgenstr 2016; 188: 1031 – 1036

Zusammenfassung

Aufgrund des Einflusses des Gewebe-Eisengehalts auf die transversalen Relaxationszeiten T₂ und T₂* bietet die MRT verschiedene Möglichkeiten zur In-vivo-Bestimmung der Eisenkonzentration. Dies sind im Einzelnen die zeitaufwändige Spin-Echo- sowie die Gradienten-Echo-Methode. Bei Letzterer gibt es prinzipiell mehrere Ansätze zur Datenauswertung, mit unterschiedlichen Voraussetzungen für Aufnahmetechnik und Nachverarbeitung: Einerseits die mathematisch anspruchsvolle R₂*-Analyse, andererseits das Signalintensitätsverfahren, das hohe Anforderungen an die Signalhomogenität der MRT-Bilder stellt. Darauf aufbauende bzw. weiterführende Methoden sind: Die quantitative Suszeptibilitäts-Bestimmung als dritter Ansatz zur Auswertung von Gradienten-Echo-Daten, sowie die Multi-Kontrast Spin-Echo-Technik mit wiederholten Refokussierungspulsen. Die Theorie der MRT, sofern für das Verständnis der Methoden notwendig, wird in aller Kürze beleuchtet.

Key words

abdomen - MR-imaging - iron

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