Figure 4b: (a, b) Interreader agreement for percentage of change in blood flow measured with perfusion CT. Bland-Altman plots show that when each observer was allowed to select the section that he or she thought was most representative of the tumor, there was significantly greater interobserver variability (SD, 0.22) for the single-section technique than for the multisection technique (SD, 0.10; P = .01). Bars represent mean differences, and corresponding 95% confidence intervals are shown.