Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R₂* Analysis: First Experience

 

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Abstract

Purpose MR transverse relaxation rate R₂* has been shown to be useful for monitoring liver iron overload. A sequence enabling acquisition of the whole liver in a single breath hold is now available, thus allowing volumetric hepatic R₂* distribution studies. We evaluated the feasibility of computer-assisted whole liver segmentation of 3 D multi-gradient-echo MRI data, and compared whole liver R₂* determination to analyzing only a single slice. Also, segmental R₂* differences were studied.

Materials and Methods The liver of 44 patients, investigated by multi-gradient echo MRI at 1.5 T, was segmented and divided into nine segments. Segmental R₂* values were examined for all patients together and with respect to two criteria: average R₂* values, and reason for iron overload. Correlation of single-slice and volumetric data was tested with Spearman’s rank test, segmental and group differences were evaluated by analysis of variance.

Results Whole-liver R₂* values correlated excellent to single slice data (p < 0.001). The lowest R₂* occurred in segment 1 (S1), differences of S1 with regard to other segments were significant in five cases and highly significant in two cases. Patients with high average R₂* showed significant differences between S1 and segments 2, 6, and 7. Disease-related differences with respect to S1 were significant in segments 3 to 5 and 7.

Conclusion Our results suggest inhomogeneous hepatic iron distribution. Low R₂* in S1 may be explained by its special vascularization.

Key Points 

• Hepatic R₂* distribution is not as homogeneous as previously thought.

• Liver segments might have a functional relevance.

• Segmental and total liver R₂* values coincide best in segment 8.

Citation Format

• Wunderlich AP, Cario H, Kannengießer S et al. Volumetric Evaluation of 3D Multi-Gradient-Echo MRI Data to Assess Whole Liver Iron Distribution by Segmental R₂* Analysis: First Experience. Fortschr Röntgenstr 2023; 195: 224 – 233

Zusammenfassung

Ziel Die transversale MR-Relaxationsrate R₂* hat sich als nützlich für die Überwachung der Eisenüberladung der Leber erwiesen. Mittlerweile steht eine Sequenz zur Verfügung, die die Erfassung der gesamten Leber in einem einzigen Atemzug ermöglicht. Das erlaubt volumetrische Studien der hepatischen R₂*-Verteilung. Unser Ziel war es, die Machbarkeit einer computergestützten Segmentierung der gesamten Leber aus 3D-Multigradientenecho-MRT-Daten zu untersuchen. Darüber hinaus haben wir untersucht, ob die Bestimmung des R₂*-Wertes der gesamten Leber mit der Analyse einer einzelnen Schicht vergleichbar ist. Schließlich wurden die segmentalen R₂*-Unterschiede bewertet.

Methoden 44 Patienten wurden mittels Multi-Gradientenecho-MRT bei 1,5 T untersucht. Die Leber wurde segmentiert und in neun Segmente unterteilt. Die segmentalen R₂*-Werte wurden für alle Patienten zusammen und unterteilt nach zwei Kriterien analysiert: durchschnittliche R₂*-Werte und vorherrschender Grund für die Eisenüberladung. Die Korrelation von Einzelschicht- und volumetrischen Daten wurde mit dem Spearman-Rangtest geprüft, während Segment- und Gruppenunterschiede durch Varianzanalyse bewertet wurden.

Ergebnisse Die R₂*-Werte der Gesamtleber korrelierten hervorragend mit den Einzelschichtdaten (p < 0,001). Die niedrigsten R₂*-Werte traten in Segment 1 (S1) auf, die Unterschiede zwischen S1 und anderen Segmenten waren in fünf Fällen signifikant und in zwei Fällen hochsignifikant. Patienten mit niedrigem R₂* wiesen keine signifikanten Unterschiede auf, Patienten mit hohem R₂* zeigten signifikante Unterschiede zwischen S1 und den Segmenten 2, 6 und 7. Krankheitsbedingte Unterschiede zu S1 waren in den Segmenten 3 bis 5 und 7 signifikant.

Schlussfolgerungen Die Ergebnisse dieser Studie deuten auf eine Inhomogenität der hepatischen Eisenverteilung hin. Während der niedrige R₂*-Wert in S1 durch seine besondere Gefäßversorgung erklärt werden kann, sollte die Ursache für segmentale Unterschiede, möglicherweise bedingt durch spezifische Krankheitsbilder, weiter untersucht werden.

Kernaussagen: 

• Die R₂*-Verteilung in der Leber ist nicht so homogen wie bisher angenommen.

• Dies deutet darauf, dass die Lebersegmente nicht nur eine anatomische, sondern auch eine funktionelle Bedeutung haben.

• Die beste Übereinstimmung des R₂*-Werts eines einzelnen Segments mit dem der gesamten Leber fanden wir in Segment 8.

Publication History

Received: 13 July 2022

Accepted: 21 October 2022

Article published online:
28 December 2022

© 2023. Thieme. All rights reserved.

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

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