SU-E-I-85: Impact of Partial Volume Effect On PET Image: Quantification Aspect.
PURPOSE
Partial Volume Effect (PVE) is not taken to account in clinical routine although it is one of the major sources of error in quantification in PET image especially in small size lesion. Depending on its size, the uptake lesion is underestimated. It mainly depends on the spatial resolution of the system and the chosen sampling. The purpose of this study is to highlight this difference witch characterizes the camera.


METHODS
This study was performed on a new generation PET/CT (Siemens mCT), fitted with four rings and time of flight (TOF). We used an anthropomorphic TORSO phantom representing a patient. Spheres of various diameters (6 to 33mm) were introduced into the lungs (air density) and the thorax (water density). Total whole body concentration were between 3 and 5 MBq/kg. SUV (Standardized Uptake Value) values were fixed successively 2, 4 and 8. We compare those values with the maximal uptake level using SUVmax and SUVmean on PET acquisition. Parameters reconstructions were: 2 iterations, 21 subsets, gaussian filter (FWHM=2mm), matrix size 200×200 pixels, True X algorithm (OSEM+PSF) and TOF with acquisition time of 150 s. Results were expressed as mean +-sd.


RESULTS
The reproducibility for each acquisition of SUV max and mean was high (respectively r=0.96, p=0.0003 and r=0.95, p=0.0004). The largest sphere (diameter 33mm) was considered as the reference for the normalization of results. The average results of SUVmax normalized in water and air compared to theorical value were respectively below 4% and 20% for diameter below 14mm. For diameter under 14 mm it decreases drastically. For SUVmean the decay is progressive under 26mm in each medium.


CONCLUSION
Following the SUVmax, wich is the clinical quantification parameter in PET images, PVE occurs at 14mm corresponding to 3 times the spatial resolution. These characteristics show the limits of the performance of our TEP camera.