Measurement of Cerebral Perfusion Indices from the Early Phase of [¹⁸F]MK6240 Dynamic Tau PET Imaging

Comparison of direct R₁ estimates obtained from SRTM2 and indirect blood-based R₁ estimates obtained from 1T2kv model with [¹⁸F]MK6240. (A) Correlation plot. Red line represents total-least-square regression, and black line is line of identity. (B) Corresponding Bland–Altman plot showing agreement in R₁ estimates between 2 methods. Solid red line represents mean difference, dashed red lines show mean difference ± 1.96 SD, and black line is zero line for reference. Blue dots represent CN subjects, and orange dots represents MCI/AD subjects. Data points are for all subjects, and brain time–activity curves were surveyed using atlases in MNI template space.

Comparison of SRTM2 R₁ estimates obtained from [¹⁸F]MK6240 and [¹¹C]PiB paired scans. (A and B) Correlation and Bland–Altman plots of R₁ estimates for all paired [¹⁸F]MK6240 and [¹¹C]PiB scans (49 pairs). (C and D) Correlation and Bland–Altman plots of R₁ estimates for paired scans acquired within 15 d (29 pairs). (E and F) Correlation and Bland–Altman plots of R₁ estimates for paired scans acquired on same day (18 pairs). In correlation plots (A, C, and E), solid red lines represent total-least-square regressions and black lines are lines of identity. In Bland–Altman plots (B, D, and F), solid red lines represent mean difference, dashed red lines show mean difference ± 1.96 SD, and black lines are zero lines for references. Blue and orange dots represent brain regions corresponding to CN subjects and MCI/AD subjects, respectively. Data points are for all subjects, and brain time–activity curves were surveyed using atlases in MNI template space.

Bar plots showing differences in regional R₁ measurements among CN, MCI, and AD groups for analysis performed using FreeSurfer parcellation. (A) Plots with CN, MCI, and AD groups presented separately. (B) Plots presented while grouping MCI and AD groups. Asterisks indicate differences that were statistically significant between groups as assessed from unpaired 2-tailed t test assuming unequal variance and after Bonferroni adjustment (P < 0.0013). Asterisks in A resulted from comparison between CN and AD groups. Asterisk in B resulted from comparison between CN and MCI/AD groups. Error bars represent SD measured within each group.

Parametric maps and corresponding MR structural images in CN subject and AD subject. First row shows magnetization-prepared rapid gradient echo as anatomic reference. Second row shows parametric [¹¹C]PiB DVR images as measure of amyloid burden. Third row shows late [¹⁸F]MK6240 SUV ratio for images from 90 to 120 min as measure of tau load. Fourth row shows parametric images of R₁ computed from [¹⁸F]MK6240 dynamic data. Arrows indicate areas of reduced cerebral perfusion and corresponding to high tau load. MPRAGE = magnetization-prepared rapid gradient echo; DVR = distribution volume ratio; SUVR = SUV ratio; SUVR_90–120 = SUV ratio for images from 90 to 120 min.