FIG 3. An explanation of how the ACV, determined as the ratio of the number of pixels above the 80% masking level to the number above the 70% level, is validated. In this setting, the ACVs derived from the eight cortical areas should be homogeneous, because the actual tracer accumulation in the cortical area is uniform regardless of the regions.

A, Phantom MR image.

B, Phantom ¹²³I-IMP SPECT scan.