R2* Relaxometry for the Quantification of Hepatic Iron Overload: Biopsy-Based Calibration and Comparison with the Literature

 

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Abstract

Purpose: We compared the calibration of hepatic iron based on R2* relaxometry and liver biopsy with similar studies that have already been published to investigate the transferability of published calibration curves.

Materials and Methods: 17 patients with clinically suspected hepatic iron overload (HIO) were enrolled. All patients underwent liver biopsy and MRI of the liver using a multi-echo gradient echo sequence (TR = 200 ms; TE-initial 0.99 ms; Delta-TE 1.41 ms; 12 echos; flip-angle: 20 °). R2* parameter maps were analyzed using manually placed regions of interest and R2* values were correlated with liver iron concentration (LIC) obtained from liver biopsy. In addition, the results of our study were compared with 6 similar, already published studies.

Results: A linear relationship between R2* and LIC was found. Regression analysis yielded a correlation coefficient of 0.926, a slope of 0.024 (s mg/g) [95 % CI 0.013 – 0.024] and an intercept of 0.277 (mg/g) [95 % CI –0.328 – 2.49]. We found a significant correlation between the calibration curves obtained from our study in comparison to 3/6 similar studies. The other 3 studies used a different reference standard or sequence parameters which lead to a significant difference for slope, intercept or both in comparison to our data.

Conclusion: Calibration curves from published studies that are based on a correlation of liver biopsy and R2* can be used for the estimation of liver iron concentration, although different scanning parameters and post-processing protocols were used. Low initial TEs might be a prerequisite for pooling data for liver iron quantification.

Key Points:

• Calibration curves from different studies can be used for liver iron quantification

• For that purpose calibration curves from published studies should be based on liver biopsy

• Low initial TEs might be a prerequisite for pooling data for liver iron quantification

Citation Format:

• Henninger B., Zoller H., Rauch S. et al. R2* Relaxometry for the Quantification of Hepatic Iron Overload: Biopsy-Based Calibration and Comparison with the Literature. Fortschr Röntgenstr 2015; 187: 472 – 479

Zusammenfassung

Ziel: Ziel dieser Studie war es, die Kalibrierung des Lebereisens basierend auf R2*-Relaxometrie und Leberbiopsie mit ähnlichen, bereits veröffentlichten, Studien zu vergleichen um die Übertragbarkeit der veröffentlichten Eichkurven zu untersuchen.

Material und Methoden: 17 Patienten mit klinischem Verdacht auf pathologischer Eiseneinlagerung wurden in diese Studie eingeschlossen. Bei allen Patienten wurden eine Leberbiopsie und eine MRT der Leber zur Quantifizierung des Gewebeeisens durchgeführt. Die R2*-Relaxationszeit wurde in identischen ROIs mit einer Fett-gesättigten Multi-Echo-Gradienten-Echo-Sequenz mit 12 Echos gemessen (TR = 200 ms; TE-initial 0,99 ms; Delta-TE 1,41 ms; 12 echos; flip-angle: 20 °). Diese Ergebnisse wurden den aus der Biopsie gewonnenen Eisenkonzentrationen gegenübergestellt. Als Weiteres wurden die Ergebnisse unserer Studie mit 6 ähnlichen Studien verglichen.

Ergebnisse: Es konnte ein linearer Zusammenhang zwischen R2* und der Lebereisenkonzentration gezeigt werden. Die Regressionsanalyse ergab einen Korrelationskoeffizienten von 0,926, eine slope (Steigung) von 0,024 (s mg/g) [95 % CI 0,013 – 0,024] und einen intercept von 0,277 (mg/g) [95 % CI –0,328 – 2,49]. Eine signifikante Korrelation zwischen der Eichkurve unserer Studie und jenen bei 3/6 ähnlichen Studien konnte gezeigt werden. Die anderen 3 Studien verwendeten einen unterschiedlichen Referenzstandard oder Sequenzparameter, die im Vergleich mit unserer Studie zu einem signifikanten Unterschied in Steigung, Achsenabschnitt oder beiden führten.

Schlussfolgerung: Kalibrierungskurven von veröffentlichen Studien, die auf einer Korrelation von Leberbiopsie und R2* basieren, können für die Schätzung der Lebereisenkonzentration verwendet werden, obwohl verschiedene Scanparameter und Nachbearbeitungsprotokolle verwendet wurden. Niedrige initiale TEs könnten eine Voraussetzung für eine Zusammenlegung von Daten für die Quantifizierung von Lebereisen sein.

Kernaussagen:

• Eichkurven aus verschiedenen Studien können für die Quantifizierung von Lebereisen verwendet werden

• Zu diesem Zweck sollten Eichkurven aus veröffentlichten Studien auf einer Leberbiopsie basieren

• Niedrige initiale TEs könnten eine Voraussetzung für eine Zusammenlegung von Daten für die Quantifizierung von Lebereisen sein

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