Marieke van Rosmalen

Chapter 3 48 Table 3.2 Assessment of brachial plexus MRI by two raters. Category 1 Category 2 Category 3 Total Cohen’s kappa (SE) 95% CI p value Rater 1 (number of cases) 25 17 8 50 Rater 2 (number of cases) 21 4 25 50 Cases of agreement 16 2 8 26 (52%) 0.30 (0.08) 0.14 - 0.46 < 0.0001 Abbreviations: SE = standard error; CI = confidence interval. Kappa coefficients for assessment of images performed with 1.5T and 3.0T scanners were 0.26 (SE 0.13, 95% CI 0.00 – 0.56, p = 0.032) and 0.26 (SE 0.10, 95% CI 0.07 – 0.49, p = 0.012), respectively. Figure 3.2 Examples of interrater disagreement Subject A was rated as “possible nerve thickening” by rater 1 and as “no nerve thickening” by rater 2. Subject B and C were rated as “possible nerve thickening” by rater 1 and as “definite nerve thickening” by rater 2. This figure shows the difficulties in classifying subtle nerve thickening as either normal or as thickening. Each subject represents an example of a Maximum Intensity Projection (MIP) and 3D short-tau inversion recovery (STIR) image.