56 Chapter 2 Table 4b. 2 x 2 table of both observers assessing the MRA images. MRA Observer 1 Observer 2 - + - + 18a - 14 4 16 2 DSA b 65 + 2 63 4 61 Total 16 67 20 63 a b Number of patients without an aneurysm. Total number of aneurysms. The sensitivity and specificity for the detection of an aneurysm by CTA and CEMRA with their 95% Confidence Intervals (CI’s) are given in Table 5. There was no significant difference between the sensitivity and specificity of CTA and CEMRA tested with McNemar’s test. Cohen’s Kappa inter-observer agreement in rating CEMRA and CTA was 0.82 and 0.85 respectively for the detection of an aneurysm. ROC curves are given in Figure 2. The areas under the curve (95% CI) are 0.94 (0.90-0.99) and 0.96 (0.93-1) for CTA and 0.89 (0.79-0.99) and 0.91 (0.83-0.99) for CEMRA. The areas of CTA and CEMRA are not significantly different (p=0.30 for Observer 1 and p=0.24 for Observer 2). Table 5. Sensitivity and specificity (95% CI) of CTA and CEMRA for the detection of aneurysms. CTA CEMRA Obs 1 90.8 (81.0 – 96.5) 96.9 (89.3 – 99.6) Sensitivity Obs 2 92.3 (83.0 – 97.5) 93.8 (85.0 – 98.3) Obs 1 94.4 (72.7 – 99.9) 77.8 (52.4 – 93.6) Specificity Obs 2 94.4 (72.7 – 99.9) 88.9 (65.3 – 98.6) Figure 2. ROC curve for the detection of aneurysms by CTA and CEMRA by both observers.
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