Heterogeneity of cognitive impairment in progressive supranuclear palsy, Parkinson's disease, and Alzheimer's disease

Standardized uptake values (SUV) have been widely used in diagnosis of malignant tumors and in clinical trials of tumor therapies as a semi-quantitative metrics of tumor FDG uptake. However, SUV for small lesions is liable to errors due to partial volume effect and statistical noise. The purpose of this study was to evaluate the reproducibility and accuracy of SUVmax and SUVpeak of small lesions in phantom experiments. Methods: We used a NEMA IEC body phantom with 6 spheres in 1/4 warm background. The PET data were acquired for 1,800 seconds in a list-mode, from which data were extracted to generate a total of 15 PET images for each of 60, 90, 120, 150, and 180 second scanning time. The SUVmax and SUVpeak of the hot spheres in the 1,800 second scan were used as a reference (SUVref, max and SUVref, peak). Coefficients of variation for both SUVmax and SUVpeak in hot spheres (CVmax and CVpeak) were calculated to evaluate the variability of the SUVs. On the other hand, percent differences between SUVmax and SUVref, max and between SUVpeak and SUVref, peak were calculated for evaluation of the accuracy of SUV (%Diffmax and %Diffpeak). We additionally examined the coefficients of variation of background activity (CVbackground) and the percent background variability (N10mm) as parameters for the physical assessment of image quality. Results: Visibility of a 10-mm-diameter hot sphere was considerably different among scan frames. The CVmax and CVpeak increased as the sphere size became smaller and as the acquisition time became shorter. SUVmax were generally overestimated as the scan time shortened and the sphere size increased. The SUVmax and SUVpeak of 37-mm-diameter sphere for 60-second scans had average positive biases of 28.3% and 4.4% compared with the reference. Conclusion: SUVmax was variable and overestimated as the scan time decreased and the sphere size increased. In contrast, SUVpeak was a more robust and accurate metric than SUVmax. The measurements of SUVpeak (or SULpeak) in addition to SUVmax are desirable for reproducible and accurate quantification in clinical situations.