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Standardized uptake values (SUV) are commonly used in FDG PET to characterize suspicious high uptakes. To better understand the reliability and the limits of SUV, we studied the accuracy of uptake estimates as a function of a number of parameters using phantom data acquired on the CPET. Methods: Using the Data Spectrum thorax phantom in which spheres were inserted, we studied the effect of the sphere sizes, of out-of-the-field-of-view activity (OFOVA), of the emission scan duration and of attenuation and partial volume effect (PVE) corrections upon biases in tumor-to-normal tissue uptake ratio (TNR) estimates. Considering a specific acquisition and processing protocol as a reference, we determined the changes in TNR when modifying this protocol. Results: For a true TNR of 8, estimated TNR were strongly dependent on lesion size, but also on the acquisition and processing protocol. Depending on the method used to derive the attenuation map, estimated TNR could change by more than 50% for lung spheres less than 2 cm in diameter. Using PVE correction, TNR increased by a factor greater than 2 for spheres less than 2 cm in diameter. The very method used to estimate sphere activity from the reconstructed images could also change the TNR by more than 50%. Even with CT-based attenuation correction and PVE correction, TNR estimates remained underestimated by more than 20% in lesions less than 2 cm in diameter. Conclusion: Biases in uptake estimates strongly depend on the acquisition and processing protocols. This suggests that comparing SUV between studies make sense only if the scanner and the acquisition and processing protocols are strictly identical. Index Terms--PET, quantification, standardized uptake values.

Quantitation in Emission Tomography (PET and SPECT) requires that several physical factors are taken into account. Attenuation, which can be determined on SPECT and PET devices, can be corrected using transmission tomography. Here we quantitatively compared the relative performance of transmission scans in SPECT and PET using a calibrated liquid solution with a linear attenuation coefficient ([Mu]) nearly equivalent to that of skeletal cranium bone over the range of energies 50 to 600 keV. We showed that contrast recovery are similar in PET and SPECT for large structures (> 30 mm), but higher in PET as object size decreases.

The influence of the collimator on the contrast recovery of hyperfixation was studied using a dual-headed single photon emission computed tomography (SPECT) system with standard clinical acquisition parameters. Three parallel collimator sets and two fan beam collimator sets were tested with a Jaszczak phantom. The six spheres of the phantom were filled with 99mTc, and four background levels were progressively obtained by adding radioactivity to the cylinder of the phantom, providing four hyperfixation levels. The effects of angular sampling and reconstruction filters have been tested. The statistical analysis was performed with analysis of variance (ANOVA). This study demonstrates the advantage of ultra-high resolution fan beam collimators for contrast recovery of hyperfixation with SPECT when using 64 projections over 360 [degrees], in particular when the contrast is low. We also demonstrate that fan beam collimators permit smaller size hyperfixation detection. Index Terms - Fan beam collimators, hyperfixation detectability, SPECT.