Marieke van Rosmalen

Chapter 3 46 We developed a scoring system with categories of abnormality of nerve thickening ( Figure 3.1 ). Scans were scored using a 3-point scale (1 = no nerve thickening, 2 = possible nerve thickening, 3 = definite nerve thickening). Examples of abnormality were selected from a subset of all included patients by two experienced (2 years and > 30 years) neuroradiologists (AG, TW) via discussion and consensus. The examples were saved using the “Teaching Tool” in PACS IDS7 19.3.12 (SectraAB, Linköping, Sweden). With this tool raters can scroll through images and compare them with the target image. The radiologists scored all images using PACS IDS7. The degree of abnormality was assessed by the overall impression of the entire brachial plexus. Images were presented to raters in the same order, blinded to clinical status of the subjects and on screens with similar resolution. Statistical analysis Statistical analyses was performed using IBM SPSS Statistics (Version 25, Armonk, New York, United States). To analyze patient characteristics we used independent samples t tests. The interrater variability of qualitative assessments of brachial plexus MRI was determined by Cohen’s kappa as coefficient for measure of agreement because we evaluated categorized data with limited categories. We interpreted a kappa value of 0.00 – 0.20 as no agreement, 0.21 – 0.39 as minimal, 0.40 – 0.59 as weak, 0.60 – 0.79 as moderate, 0.80 – 0.90 as strong and > 0.90 as almost perfect agreement. 9 p < 0.05 was considered significant.We calculated sensitivity and specificity per rater using receiver operating characteristic curves. Figure 3.1 The brachial plexus scoring system Representative images of the scoring system used to define categories of abnormality, i.e. category 1 = no nerve thickening, 2 = possible nerve thickening, 3 = definite nerve thickening. Each category represents an example of a Maximum Intensity Projection (MIP) and 3D short-tau inversion recovery (STIR) image.