Ultrasonic Adaptive Sound Speed Estimation for the Diagnosis and Quantification of Hepatic Steatosis: A Pilot Study

Abstract

Purpose To evaluate the ability of a new ultrasound (US) method based on sound speed estimation (SSE) with respect to the detection, quantification, and grading of hepatic steatosis using magnetic resonance (MR) proton density fat fraction (PDFF) as the reference standard and to calculate one US fat index based on the patient’s SSE.

Materials and Methods This study received local IRB approval. Written informed consent was obtained from patients. We consecutively included N = 50 patients as the training cohort and a further N = 50 as the validation cohort who underwent both SSE and abdominal MR. Hepatic steatosis was classified according to MR-PDFF cutoffs as: S0 ≤ 6.5 %, S1 6.5 to 16.5 %, S2 16.5 to 22 %, S3 ≥ 22 %. Receiver operating curve analysis was performed to evaluate the diagnostic performance of SSE in the diagnosis of steatosis (S1–S3). Based on the optimal data fit derived from our study, we proposed a correspondence between the MR-PDFF and a US fat index. Coefficient of determination R2 was used to evaluate fit quality and was considered robust when R2 > 0.6.

Results The training and validation cohorts presented mean SSE values of 1.570 ± 0.026 and 1.568 ± 0.023 mm/µs for S0 and 1.521 ± 0.031 and 1.514 ± 0.019 mm/µs for S1–S3 (p < 0.01) patients, respectively. An SSE threshold of ≤ 1.537 mm/µs had a sensitivity of 80 % and a specificity of 85.7 % in the diagnosis of steatosis (S1-S3) in the training cohort. Robust correspondence between MR-PDFF and the US fat index was found both for the training (R2 = 0.73) and the validation cohort (R2 = 0.76).

Conclusion SSE can be used to detect, quantify and grade liver steatosis and to calculate a US fat index.

Zusammenfassung

Ziel Beurteilung der Leistungsfähigkeit einer innovativen Ultraschall-(US)-Methode auf Grundlage der Schallgeschwindigkeitsschätzung („sound speed estimation“ SSE) für den Nachweis, die Quantifizierung und Einstufung der Lebersteatose mit Magnetresonanz-(MR)-Protonendichtefettfraktion (PDFF) als Referenzstandard und die Berechnung eines US-Fettindex basierend auf der SSE des Patienten.

Material und Methoden Diese Studie erhielt eine lokale IRB-Zulassung. Eine schriftliche Einverständniserklärung der Patienten lag vor. Fortlaufend wurden N = 50 Patienten als Trainingskohorte und weitere N = 50 als Validierungskohorte eingeschlossen, bei denen sowohl eine SSE als auch eine abdominale MR durchgeführt wurde. Die hepatische Steatose wurde gemäß der MR-PDFF-Grenzwerte wie folgt klassifiziert: S0: ≤ 6,5 %, S1: 6,5 bis 16,5 %, S2: 16,5 bis 22 %, S3: ≥ 22%. Eine ROC-(„receiver operating curve“)-Analyse wurde durchgeführt, um die Leistung der SSE bei der Diagnose einer Steatose (S1–S3) zu ermitteln. Basierend auf der optimalen Datenanpassung, die aus unserer Studie abgeleitet wurde, schlugen wir eine Analogie zwischen MR-PDFF und einem US-Fettindex vor. Der Koeffizient der Bestimmung R2 wurde verwendet, um die Qualität der Anpassung zu bewerten und wurde als robust angesehen, wenn R2 > 0,6 betrug.

Ergebnisse Die Trainingskohorten zeigten mittlere SSE-Werte von 1,570 ± 0,026 für S0 und 1,521 ± 0,031 mm/μs für S1–S3-Patienten, während die Validierungskohorten für S0-Patienten 1,568 ± 0,023 und für S1–S3 1,514 ± 0,019 mm/μs aufwiesen (p < 0,01). Ein SSE-Grenzwert von ≤ 1,537 mm/μs hatte in der Trainingskohorte eine Sensitivität von 80 % und eine Spezifität von 85,7 % für die Diagnose der Steatose (S1–S3). Eine robuste Übereinstimmung zwischen MR-PDFF und dem US-Fettindex wurde sowohl für die Trainings- (R2 = 0,73) als auch für die Validierungskohorte (R2 = 0,76) ermittelt.

Schlussfolgerung SSE kann eingesetzt werden, um eine Lebersteatose zu detektieren, zu quantifizieren und zu einzustufen und um einen US-Fettindex zu berechnen.

Key words

ultrasound - NAFLD - PDFF - liver - steatosis

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