Figure 2a:

Perfusion maps. True-value and perfusion maps of digital phantom (section 16, box-shaped R[t], and CBV [5 mL/100 g]) are shown with identical color lookup table (not shown). The color scale is automatically adjusted for visual assessment in each map of CBF, CBV, and MTT. A constant window level and window width (8 and 16 seconds, respectively) are used for T_max. In the true-value maps of CBF and MTT, seven columns with different CBF or MTT show different colors. However, there is no vertical color gradient, because all seven rows have identical CBF or MTT and only the delay is different. The true-CBV image is uniform in color, because all 49 tiles have the same CBV value in a section. (a) CT perfusion. Delay-dependent vertical gradation is apparent in most of CBF (G1, P1, P2, T1, T2, PM1, ST1, and ST2) and MTT (G1, H, P1, P2, T1, T2, PM1, PM2, ST1, and ST2). In CBV, a delay-dependent vertical gradient is observed in H and T1. MTT dependency is also noted in G2, H, S1, T1, T2, and ST2 as a horizontal gradient. (b) Perfusion-weighted imaging. Delay dependency is apparent in most algorithms for CBF and MTT maps. Delay-dependent vertical gradient on CBV map is observed for P. MTT dependency is also noted for G, S1, and ST2 as a horizontal gradient. N.A. = not available.