Repeatability and reproducibility of MRI apparent diffusion coefficient applied on four different regions of interest for patients with axial spondyloarthritis and healthy volunteers scanned twice within a week.

Jakob Møllenbach Møller,Stine Hangaard,Henrik S Thomsen,Ole Rintek Madsen,Inge J Sørensen,Mikkel Østergaard,Susanne J Pedersen

doi:10.1259/bjro.20200004

Abstract

Objectives:The apparent diffusion coefficient (ADC) may be used as a biomarker for diagnosis and/or monitoring treatment response in patients with axial spondyloarthritis (axSpA), but this requires reliable ADC measurements. This study assessed test–retest repeatability and reproducibility of ADC measurements using four different region of interest (ROI) settings.Methods:In this prospective study, the sacroiliac joints (SIJs) of 25 patients with axSpA and 24 age- and sex-matched healthy volunteers were imaged twice at a mean interval of 6.8 days in a 1.5 T scanner using, multishot echoplanar diffusion-weighted sequences. ADCs at four ROI settings were assessed: 5 mm and 10 mm anatomic band-shaped, 15 mm linear, and 40 mm2 circular.Results:Intraclass correlation coefficient (ICC) assessments showed that the interstudy repeatability was good for median ADC (ADCmed) and 95th-percentile ADC (ADC95) measurements in patients with axSpA (0.77–0.83 and 0.75–0.83, respectively), but poor-to-moderate in healthy subjects (0.27–0.55 and 0.13–0.37, respectively). For all ROI settings, intrareader reproducibility was excellent for ADCmed-measurements (ICC:0.85–0.99) and moderate-to-excellent for ADC95 measurements (ICC:0.68–0.96). The 5 mm ROI had the least estimated bias and highest level of agreement on Bland–Altman plots. The interreader reproducibility was moderate (ICC:0.71). The 15 mm linear ROI produced significantly greater ADCmed and ADC95 measurements than all other ROI settings (p < 0.01–0.02), except for the circular ROI ADC95 measurements.Conclusion:ROI settings influence ADC measurements. Interstudy repeatability of SIJ ADC measurements is independent of ROI settings. However, the 5 mm ROI showed the least bias and random error and seems preferable.Advances in knowledge:ADC measurements are affected by ROI settings, and this should be taken into account when assessing ADC maps.

Highlights

The chronic inflammatory disease axial spondyloarthritis causes severe pain and functional disability, and with time often structural bone damage and, ankylosis.[1]
For all region of interest (ROI) settings, both ADCmed and ADC95 measurements in patients with axial spondyloarthritis (axSpA) and healthy subjects were tested using one-sample t-tests, and the differences between MRI1 and MRI2 examinations were not significantly different from 0, indicating that there was no systematic bias
This study showed that there were no significant differences in interstudy repeatability at four ROI settings, and that interstudy repeatability was markedly better in patients with axSpA than in healthy subjects

Summary

Introduction

The chronic inflammatory disease axial spondyloarthritis (axSpA) causes severe pain and functional disability, and with time often structural bone damage and, ankylosis.[1]. Circular regions of interest (ROIs) of various sizes (70–90 mm2) have been used in predefined areas of the sacroiliac joints (SIJs),[3,5,7] as have circular or polynomial ROIs positioned on areas affected by BME.[4,6,7] One study used a linear ROI that extended from the bone marrow on one side of the joint to the other, covering both the iliac and sacral bone marrow and including the joint cavity.[8] Using an ROI that covers the bone marrow entirely was suggested recently.[9] Several relevant studies have measured interobserver reproducibility,[3,6,8] whereas few studies have measured intraobserver reproducibility.[3] to our knowledge, the interstudy repeatability of SIJ measurements has not been investigated (i.e. repeatability between two MRI scans performed within a short period, or test–retest reliability). We investigated variation, interstudy repeatability, and intra- and inter reader reproducibility of ADC measurements using four different types of standardized ROI settings in patients with axSpA and healthy subjects

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Conclusion