Inter-Reader Agreement of Multi-Parametric MR Imaging for the Detection of Prostate Cancer: Evaluation of a Scoring System

Abstract

Purpose: Functional prostate MR is performed in varying combinations of T2-weighted images with diffusion-weighted imaging (DWI), dynamic contrast-enhanced MRI (DCE-MRI), and spectroscopic imaging (MRSI). Recently, a European consensus meeting proposed the use of a simple 5-point scale for estimating the probability of a lesion being malignant. The aim of the present study was to determine the inter-reader agreement of MR imaging using a scoring system based on the recommendations of the consensus.

Materials and Methods: The appearance of 108 predefined lesions in three different MR sequences (T2-weighted images, DWI, and DCE-MRI) in 50 functional prostate MR examinations were retrospectively scored by three blinded radiologists using a 5-point scale for each MR sequence. After scoring T2/DWI and T2/DWI/DCE-MRI, every lesion was graded based on its probability for malignancy. The inter-observer reliability was evaluated using Kappa statistics (ĸ).

Results: With respect to T2-weighted images, DWI and DCE-MRI ĸ was 0.49, 0.97, and 0.77, respectively. Combined scoring of T2-weighted images and DWI demonstrated correct tumor diagnosis (true positive) in 71 – 88 % (depending on reader) of cases (ĸ = 0.78). The accuracy was further improved to 88 – 96 % after scoring all three MR sequences including DCE-MRI (ĸ = 0.90).

Conclusion: The use of a simple 5-point scoring system for T2-weighted images, DWI, and DCE-MRI is feasible in functional prostate MRI and has high inter-observer reliability.

Zusammenfassung

Ziel: Die multiparametrische Prostata-MRT kombiniert anatomische Sequenzen (T1- und T2-gewichtete Sequenzen) mit funktionellen Sequenzen, wie der Diffusionsbildgebung (DWI), der dynamischen kontrastmittelverstärkten MRT (DCE-MRI) und der Spektroskopie (MRSI). Eine europäische Konsensus-Konferenz hat kürzlich die Benutzung einer 5-Punkte-Skala empfohlen, um die Malignitäts-Wahrscheinlichkeit einer Läsion zu stratifizieren. Ziel der vorliegenden Studie war die Bestimmung der Interobserver-Reliabilität unter Verwendung eines Scoringsystems auf der Basis der Konsensusempfehlungen.

Material und Methoden: Das Erscheinungsbild von insgesamt 108 vordefinierten Läsionen in 50 Prostata-MRT-Untersuchungen wurde retrospektiv von 3 geblindeten Untersuchern bewertet. Analog der Empfehlung der europäischen Konsensus-Konferenz wurde eine 5-Punkte-Skala für jede verwendete Sequenz (T2, DWI und DCE-MRI) verwendet. Zusätzlich erfolgte die Bewertung jeder Läsion für die Kombination aus T2 +DWI und für T2 +DWI+DCE-MRI, ob es sich um eine maligne Läsion handelt. Die Interobserver-Reliabilität wurde mittels Kappa-Statistik berechnet.

Ergebnisse: Kappa-Werte der 3 Untersucher waren: T2 0,49; DWI 0,97 und DCE-MRI 0,77. Die Tumordiagnose unter Verwendung von T2 +DWI war in 71 – 88 % (untersucherabhängig) der Fälle (ĸ = 0,78) korrekt. Unter Einschluss der DCE-MRI wurden 88 – 96 % der Läsionen korrekt als Tumor erkannt (ĸ = 0,90).

Schlussfolgerung: Die Benutzung eines 5-Punkte-Scoringsystems für T2-gewichtete Sequenzen, DWI und DCE-MRI zur Bewertung einer Prostataläsion ist praktikabel und weist eine hohe Interobserver-Reliabilität auf.

Key words

prostate - MR imaging - MR diffusion/perfusion - MR functional imaging - decision analysis

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