38 Chapter 2 Table 4. RPM BPND, RPM R1 and SUVr values obtained from the test scan are compared to corresponding values obtained from the retest scan for the original scan duration (0-60/80-130), and for the shortened scan duration (0-30/80-100) interpolated with cubic or POP-IP_2T4k_VB interpolation method. HC AD r2 Slope %TRT r2 Slope %TRT RPM BPND (0-60/80-130) 0.91 0.95 -1 ± 4 0.98 1.0 0 ± 4 Cubic RPM BPND (0-30/80-100) 0.90 0.96 -1 ± 4 0.98 0.98 0 ± 5 POP-IP_2T4k_VB RPM BPND (0-30/80-100) 0.90 0.96 -1 ± 4 0.97 1.0 0 ± 5 RPM R1 (0-60/80-130) 0.86 0.95 0 ± 6 0.94 0.96 0 ± 6 Cubic RPM R1 (0-30/80-100) 0.86 0.94 0 ± 6 0.94 0.96 0 ± 6 POP-IP_2T4k_VB RPM R1 (0-30/80-100) 0.86 0.95 0 ± 6 0.94 0.96 0 ± 6 SUVr (80-100) 0.86 0.97 -1 ± 5 0.96 1.05 -1 ± 7 Test-Retest Repeatability The RPM BPND values estimated for both test and retest scans using the shortest assessed scan duration (0–30/80–100) and POP-IP_2T4k_VB or cubic interpolation for the reference region correlated well (Table 4). The test-retest parametric correlations using the short scan duration and interpolated reference TAC (POP-IP_2T4k_VB and cubic interpolation methods) were similar to the correlations using the original scan duration. The TRT across all Hammers’ regions of interest for RPM BPND was − 1 %± 4 for HC and 0 %± 4 for AD patients using the original dual-time-window acquisition (Table 4). Furthermore, TRT for R1 was 0 %± 6 for both groups using the original dual-time-window acquisition. The TRT for BPND remained the same for HC when using the shortest dual-time-window 0–30/80–100 min with either of the interpolations methods (POP-IP_2T4k_VB or cubic interpolation). For AD patients, the TRT changed to 0 %± 5 when using the shortest dual-time-window 0–30/80–100 min with POP-IP_2T4k_VB or cubic interpolation. The TRT for R1 remained similar as with the original data (0 %± 6) for the shortest dual-time-window (0–30/80–100 min) both with POP-IP_2T4k_VB and cubic interpolation for both groups. TRT for SUVr80-100 min was − 1 %± 5 for HC and −1 %± 6 for AD patients (Table 4). Bland-Altman plots for the RPM BPND+1 illustrating TRT for all Hammers’ regions obtained with the original scan duration and the shortest scan duration with POP-IP_2T4k_VB reference region interpolation are presented in Figure 3c and d.
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