Page 91 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

Chapter 4 scans (split 1 vs split 2). To evaluate test-retest variability, 50% count scans were compared to the mean since split scans could not be directly compared as this would yield 4 comparisons (Figure 4.2). Calculation of test-retest RCs was as follows (Equation 4-8): Eq. 4 Eq. 5 Eq. 6 Eq. 7 Eq. 8 where d is the relative difference between day 1 (SUV1) and day 2 (SUV2) for original data; di,j is the relative difference of each split i (split 1 and split 2) on each day j (days 1 and 2) compared to the average SUVi,j; SD is the standard deviation of relative test-retest differences (SDsplit was scaled by factor 2 since SUVs were compared to the mean SUVi,j). RCs of intrascan variability were calculated using eq. 4, 6, and 8. Figure 4.2: Schematic representation of assessment of test-retest variability of original 100% count scans and split 50% count scans, respectively. Note that, in contrast with original scans, split scans cannot be directly compared, as this would yield 4 individual comparisons underestimating true test-retest variability. 90