40 Chapter 2 (Table 2). Comparisons of RPM BPND obtained with the shortest scanning interval (0–30/80–100) to plasma input DVR-1, SRTM BPND and RPM BPND derived from the original scan duration (0–60/80–130) showed that POP-IP_2T4k_VB interpolation had a minimal and acceptable bias of ~ 5 % (Table 3). Since RPM BPND is the main parameter outcome for [18F]flortaucipir, shortening the scan duration to 0–30/80–100 min with POP-IP_2T4k_VB interpolation for the reference region will provide quantitative acceptable accurate results. However, when individual regions are assessed, relatively higher bias (~ 8 %) was observed in regions with higher tau uptake (RPM DVR > 2) (Supplementary Figure 1). From Table 3, it is evident that SUVr(80-100 min) presents over-/underestimations when compared to DVR-1, SRTM BPND and RPM BPND (using 0–60/80–130 min scan duration data). In contrast, parameters estimated using a shortened scan duration data had a much better correspondence with the parameters estimated using the whole scan duration data (0–60/80–130 min). Although with a shortened scan duration, a 50-min scanning time is required, which is 30 min more than that required for a static scan; SUVr is still semi-quantitative. Moreover, it is known that SUVr might be effected by blood flow changes overtime, and hence is an unreliable parameter for longitudinal studies, whereas using the shortened dual-time-window protocol (0–30/80–100), a flow estimate (R1) to evaluate the effect of flow can be estimated and therefore is apt for longitudinal studies. Moreover with the proposed method, only 50 min of actual scanning time is required on contrast to 110 min of actual scan duration (decreasing the patient burden by 60 min of scanning). Dynamic [18F]flortaucipir PET scans can be used to estimate both the specific binding of the tracer to tau pathology (BPND) and as well as rCBF (R1) using RPM. Perfusion imaging is a reliable biomarker to assess neuronal dysfunction in neurodegenerative diseases [30]. R1 is an estimate of the relative blood flow, and it has been shown that it has a high correlation with [18F]FDG uptake [30] and so an accurate estimation of R1 is also necessary. The current study demonstrated that shortening the scan duration to 0–30/80–100 min had negligible effects on R1 estimations. As such, it can be safely assumed that the scanning protocol can be reduced to 0–30/80–100 min with minimal bias (~ 7 % on average). If the implementation for POP-IP_2T4k_VB interpolation is not possible, use of cubic interpolation is a reliable alternative to interpolate the gap between the dual-time-windows for the reference region. Unfortunately, further reduction of the acquisition time for the first part was not possible since the bias in the estimated parameters was increasing as the scan duration was being reduced (Figure 2). A reason could be that as the peak approaches, further loss of information makes it difficult to estimate the efflux kinetics of [18F]flortaucipir. Further reduction of the second part of the scan
RkJQdWJsaXNoZXIy MjY0ODMw