Background/Purpose: Effusion-synovitis (ES) on knee MRI has been identified as an important biomarker of OA. Semi-automated software methods offer objective measurements of ES volume on MRI, but efficiency is crucial, especially for studies involving many MRIs. We developed a quantitative measurement of ES using the single axial slice with the largest area of ES, evaluated the reliability of the new single-slice quantitative measurement of ES, and correlated this measurement of ES with the previously validated method based on multi-slice quantitative measurement of ES and with a validated semi-quantitative scoring of ES to demonstrate that the single-slice ES method is a valid substitute.

Methods: OAI participants with radiographic OA (i.e., Kellgren-Lawrence [KL] 2,3) in at least 1 knee at baseline with prior semi-quantitative assessment of ES by a MSK radiologist were randomly selected (n=50 knees; 1 knee per participant). Four non-expert readers were trained to use custom semi-automated software and a programmed multi-button mouse (see Figure 1) to measure ES volume on 3T MRI (see Figure 2) under the direction of a MSK radiologist, and then read scans from the KL 2,3 sample blinded to prior assessments (twice for 3 readers; once for 1 reader). Intra- and inter-reader reliability was evaluated based on intraclass correlation coefficients (ICC) from a linear mixed model with random effects for knee, reader, and interaction between knee and reader. We assessed agreement with the mean absolute difference (MAD). In a subset of the FNIH study (n=301), one reader measured single-slice ES volume, blinded to the prior multi-slice quantitative measurements of ES. We estimated the Spearman correlation coefficient between single-slice and multi-slice volume of ES in the FNIH subset. Validity was evaluated based on Spearman correlation between single-slice ES volume and semi-quantitative ES MRI Osteoarthritis Knee Score (MOAKS) in the KL 2,3 sample and the FNIH subset. 95% confidence intervals (CI) were generated from bias-corrected and acceleration-adjusted bootstrap.

Results: In this sample of KL 2,3 knees, the mean single-slice ES volume was 312.8 mm³ with standard deviation 218.4 mm³. The intra-reader ICC was 0.96 (95%CI 0.93-0.97) and inter-reader ICC was 0.90 (95%CI 0.87-0.95); the intra-reader MAD was 36 mm³ (95%CI 28-44) and inter-reader MAD was 61 mm³ (95%CI 48-75). The estimated correlation between single-slice and multi-slice ES volume was 0.75 (95%CI 0.68-0.81; Figure 3). Correlation between single-slice ES volume and MOAKS ES was 0.62 (95%CI 0.39-0.79) in the KL 2,3 sample and 0.67 (95%CI 0.59-0.73) in the FNIH subset (Figure 4A), while correlation between multi-slice ES volume and MOAKS ES was 0.74 (95%CI 0.68-0.79) in the FNIH subset (Figure 4B).

Conclusion: The more efficient single-slice quantitative measurement of ES had excellent intra-and inter-reader reliability with non-expert readers, and good correlation with both the multi-slice quantitative ES measurement and MOAKS semi-quantitative assessment of ES. Single-slice quantitative measurement is an efficient surrogate for multi-slice assessment, having shown similar validity based on comparison to semi-quantitative scoring by experienced MSK radiologists.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/reliability-and-validity-of-single-axial-slice-vs-multiple-slice-quantitative-measurement-of-the-volume-of-effusion-synovitis-on-3t-knee-mri-in-knees-with-osteoarthritis/