96 Chapter 6 Interobserver agreement and reader preference Table 4 shows the median IOA (κ), specified results for expert and non-expert readers, and the difficulty and preference scores assigned by the various readers. Detailed IOA results between individual readers are provided in Supplement 3. Group IOA (Krippendorff’s alpha) for all readers was 0.39 (mrTRG), 0.40 (modTRG), 0.43 (DWI patterns), and 0.18 (Split scar). Overall, IOA was higher for the expert readers, except for the split scar sign which showed similarly low IOA for all readers. Most readers selected scoring systems incorporating DWI (modified TRG, DWI pattern) as their preferred response method (selected by 68–73% vs. 5–18% for the mrTRG and split scar). This preference was also reflected in the difficulty scores. Figure 2 Impact of image quality. Upper row shows the sagittal (A) and axial (B) T2-weighted images and DWI scan (C) of a male patient with an MRI that was graded as good quality. The fibrotic tumour bed is indicated by the white arrows in A and arrowheads in B. * indicates shine through of luminal fluid with a typical star shape on DWI. The majority of readers scored this case as a complete response with a TRG score of 1-2, no suspicious signal on DWI (modified TRG score 0; DWI Pattern C-) and with a positive split scar sign. The bottom row shows the T2-weighted (D; E) and DWI (F) images of a male patient where image quality was graded as below average. Much variation was observed between readers: mrTRG scores ranged from 2-5, modified TRG scores ranged from 0-2, DWI pattern scores included A+, B-, B+, and C+, and a split scar sign was detected by 1 out of 22 readers.
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