Noninvasive MRI-Based Liver Iron Quantification: Methodic Approaches, Practical Applicability and Significance Nicht invasive MRT-basierte Bestimmung des Leber-Eisen-Gehalts: Methodische Ansätze, Anwendbarkeit in der Praxis und Aussagekraft

Correspondence Dr. Arthur P. Wunderlich Klinik für Diagnostische und Interventionelle Radiologie, Universitätsklinikum Ulm Albert-Einstein-Allee 23 D-89070 Ulm Germany Tel.: ++ 49/7 31/500610 86 Fax: ++ 49/7 31/500611 08 [email protected] Pathophysiology of iron overload ▼ Normal iron content plays an important role in the physiological processes of the human body. A disturbance to the precisely regulated iron metabolism system has serious consequences. Therefore, for example, iron overload results in oxidative damage to membrane lipids and proteins and in DNA damage that can cause mitochondrial and lysosomal dysfunction, changes in gene expression, and changes in tumor suppressor genes (p53). Organ damage due to iron overload primarily affects the heart and liver as well as the endocrine organs, i. e., the pituitary gland, pancreas, thyroid, parathyroid, and gonads [1]. Cardiac insufficiency and arrhythmia as a result of myocardial siderosis are the most 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 timeconsuming 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 multicontrast 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-Echosowie die Gradienten-Echo-Methode. Bei Letzterer gibt es prinzipiell mehrere Ansätze zur Datenauswertung, mit unterschiedlichen Voraussetzungen fürAufnahmetechnik undNachverarbeitung: 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-BestimmungalsdritterAnsatz zurAuswertung 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. Review 1031