Viscoelasticity-Based Magnetic Resonance Elastography for the Assessment of Liver Fibrosis in Hepatitis C Patients after Liver Transplantation

Abstract

Purpose: Despite advantages in antiviral therapy of hepatitis C (HCV) in recent years, progressing liver fibrosis remains a major problem for patients suffering from hepatitis C after liver transplantation. Therefore, effective non-invasive methods for the assessment of liver fibrosis are needed in order to guide treatment decisions and predict prognosis in these patients. The aim of this study was to prospectively assess the diagnostic accuracy of viscoelasticity-based magnetic resonance (MR) elastography for the assessment of liver fibrosis in HCV patients after liver transplantation.

Materials and Methods: After IRB approval, a total of 25 patients, who had received a liver graft due to chronic hepatitis C underwent both liver biopsy and MR elastography. Two viscoelastic constants, the shear elasticity μ and the powerlaw exponent α were calculated by fitting the frequency function of the complex shear modulus with the viscoelastic springpot-model.

Results: A strong positive correlation between shear elasticity μ and the stage of fibrosis could be found (R = 0.486, p = 0.0136). The area under the receiver operating curve (AUROC) of MR elastography based on μ for diagnosis of severe fibrosis (F ≥ 3) was 0.87 and 0.65 for diagnosis of significant fibrosis (F ≥ 2). The powerlaw exponent α did not correlate with the stage of fibrosis.

Conclusion: MR elastography represents a promising non-invasive procedure for the assessment of higher grades of fibrosis in HCV patients after liver transplantation. The poor correlation for lower grades of fibrosis suggests unknown mechanical interactions in the transplanted liver.

Zusammenfassung

Ziel: Trotz einiger Fortschritte auf dem Gebiet der antiviralen Therapie der Hepatitis C (HCV) in den letzten Jahren bleibt die fortschreitende Leberfibrose des Transplantats ein Hauptproblem der Patienten nach Lebertransplantation. Zur Prognosebestimmung sowie zur Festlegung von Therapiepfaden dieser Patienten sind nicht invasive Methoden zur Fibrosegradbestimmung daher von großer Bedeutung. Ziel der vorliegenden Studie war es, prospektiv die Aussagekraft der Magnetresonanz(MR)-Elastografie in der Diagnostik der Leberfibrose bei HCV-Patienten nach Lebertransplantation zu bestimmen.

Material und Methoden: Bei insgesamt 25 Patienten, die an unserem Zentrum eine Lebertransplantation auf dem Boden einer HCV-Zirrhose erhalten hatten, wurde eine Leberbiopsie durchgeführt und das Resultat der histopathologischen Fibrosegradbestimmung mit den Ergebnissen der ebenfalls durchgeführten MR-Elastografie verglichen. Entsprechend des viskoelastischen Springpot-Modells wurden die Scherelastiziät μ sowie der Exponent des Potenzgesetzes α mittels Daten-Fit berechnet.

Ergebnisse: Es konnte eine starke Korrelation zwischen der Scherelastizität µ und dem Fibrosegrad (R = 0,486, p = 0,0136) gezeigt werden. Die AUROC (area under the receiver operating curve) der MR-Elastografie betrug 0,87 für den Nachweis einer schwerwiegenden Fibrose (F ≥ 3) sowie 0,65 für die Diagnose einer signifikanten Fibrose (F ≥ 2). Der Exponent α korrelierte nicht mit dem Fibrosegrad.

Schlussfolgerung: Die MR-Elastografie stellt ein vielversprechendes nicht invasives Verfahren zur Bestimmung höherer Leberfibrosegrade bei lebertransplantierten Patienten dar. Die geringe Korrelation bei niedrigen Fibrosegraden deutet auf noch unbekannte mechanische Wechselwirkungen im Transplantat hin.

Key words

transplantation - tissue characterization - surgery - fibrosis, liver - MR-imaging

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