Expert consensus on optimal acquisition and development of the International Bowel Ultrasound Segmental Activity Score (IBUS-SAS): a reliability and inter-rater variability study on intestinal ultrasonography in Crohn's Disease

Background and aims Intestinal ultrasound (IUS) is an accurate, patient-centered monitoring tool that objectively evaluates Crohn’s disease (CD) activity. However, no current, widely accepted, reproducible activity index exists to facilitate consistent IUS identification of inflammatory activity. The aim of this study is to identify key parameters of CD inflammation on IUS, evaluate their reliability and develop an IUS index reflecting segmental activity. Methods There were 3 phases: 1) expert consensus Delphi method to derive measures of IUS activity; 2) an initial, multi-expert case acquisition and expert-interpretation of 20 blinded cases to measure inter-rater reliability for individual measures; 3) refinement of case acquisition and interpretation by 12 international experts, with 30 blinded case reads with reliability assessment and development of a segmental activity score. Results Delphi Consensus: Eleven experts representing 7 countries identified four key parameters including (1) bowel wall thickness (BWT) (2) bowel wall stratification (3) hyperemia of the wall [color Doppler imaging] and (4) inflammatory mesenteric fat. Blind Read: Each variable exhibited moderate to substantial reliability. Optimal, standardized image and cineloop acquisition were established. Second Blind Read and score development: intra-class correlation coefficient (ICC) for BWT was almost perfect 0.96 (0.94-0.98). All 4 parameters correlated with the global disease activity assessment and were included in the final International Bowel Ultrasound Segmental Activity Score with almost perfect ICC [0.97 (0.95-0.99, p<0.001)]. Conclusions Using expert consensus and standardized approaches, identification of key activity measurements on IUS has been achieved and a segmental activity score has been proposed, demonstrating excellent reliability.