Standardized uptake values (SUVs) have been widely used in the diagnosis of malignant tumors and in clinical trials of tumor therapies as semiquantitative metrics of tumor 18 F-FDG uptake. However, SUVs for small lesions are liable to errors due to partialvolume effect and statistical noise. The purpose of this study was to evaluate the reproducibility and accuracy of maximum and peak SUV (SUV max and SUV peak , respectively) of small lesions in phantom experiments. Methods: We used a body phantom with 6 spheres in a quarter warm background. The PET data were acquired for 1,800 s in list-mode, from which data were extracted to generate 15 PET images for each of the 60-, 90-, 120-, 150-, and 180-s scanning times. The SUV max and SUV peak of the hot spheres in the 1,800-s scan were used as a reference (SUV ref,max and SUV ref,peak ). Coefficients of variation for both SUV max and SUV peak in hot spheres (CV max and CV peak ) were calculated to evaluate the variability of the SUVs. On the other hand, percentage differences between SUV max and SUV ref,max and between SUV peak and SUV ref,peak were calculated for evaluation of the accuracy of SUV. We additionally examined the coefficients of variation of background activity and the percentage background variability 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 CV max and CV peak increased as the sphere size became smaller and as the acquisition time became shorter. SUV max was generally overestimated as the scan time shortened and the sphere size increased. The SUV max and SUV peak of a 37-mm-diameter sphere for 60-s scans had average positive biases of 28.3% and 4.4%, compared with the reference. Conclusion: SUV max was variable and overestimated as the scan time decreased and the sphere size increased. In contrast, SUV peak was a more robust and accurate metric than SUV max . The measurements of SUV peak (or SUV peak normalized to lean body mass) in addition to SUV max are desirable for reproducible and accurate quantification in clinical situations.

The edge artifacts in the PET images reconstructed using the PSF algorithm increased with an increasing SBR. In the small spheres, the edge artifact was observed as a sharp peak at the center of spheres and could result in overestimation.

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The aim of this study was to evaluate differences in dopamine transporter SPECT images among different SPECT/CT devices and to determine the most appropriate region of interest (ROI) for semiquantitative evaluation. Methods: An anthropomorphic striatal phantom was filled with 123 I solutions of different striatumto-background radioactivity ratios. Data were acquired using 2 SPECT/CT devices equipped with low-to medium-energy generalpurpose and low-energy high-resolution (LEHR) collimators. The SPECT images were reconstructed by filtered backprojection with both attenuation and scatter correction and then were analyzed using specific binding ratio (SBR). The most appropriate of 7 ROI types was determined, and we then compared the linearity and recovery of SBR among the different SPECT/CT devices and collimators. Results: The linearity of SBR was excellent for all types of ROIs. The ROI contouring the striatum based on the CT images showed the best recovery of SBR using mean activity in the striatal ROI (SBR mean ) (47.8%). For this ROI, the recovery of SBR mean for SPECT/CT with a LEHR collimator with thick septa and a long hole length was 61.6%-significantly higher than that of other devices. Conclusion: The ROI contouring the striatum based on CT images was considered appropriate for evaluating dopamine transporter SPECT/CT. Among the different SPECT/CT devices, an LEHR collimator designed for 123I I imaging is recommended.

This study demonstrated that the NEC is not a useful metric for the evaluation of the image quality on TOF-PET images.