INVESTIGATION OF THE SIGNAL-TO-NOISE RATIO ON A STATE-OF-THE-ART PET SYSTEM - MEASUREMENTS WITH THE EEC WHOLE-BODY PHANTOM

Aim: The spatial resolution of PET scanners can be improved by using s maller detector elements. This approach, however, results in poorer co unting statistics of the reconstructed images. Therefore, the aim of t his study was to investigate the influence oi different acquisition pa rameters on the signal-to-noise ratio (SNR) and thus to optimize PET i mage quality. Methods: The experiments were performed with the latest- generation whole-body PET system (ECAT Exact HR+, Siemens/CTI) using t he standard 2D and 3D data acquisition parameters recommended by the m anufacturer The EEC whole-body phantom with different inserts was used to simulate patient examinations of the thorax. Emission-and transmis sion scans were acquired with varying numbers of events and at differe nt settings oi the lower level energy discriminator. The influence of the number of counts on the SNR was parameterized using a simple model function. Results: For count rates frequently encountered in clinical PET studies, the emission scan has a stronger influence on the SNR in the reconstructed image than the transmission scan. The SNR can be im proved by using a higher setting of the lower energy level provided th at the total number of counts is kept constant. Based on the establish ed model function, the relative duration of the emission scan with res pect to the total acquisition time was optimized, yielding a value of about 75% for both the 2D and 3D mode. Conclusion: The presented pheno menological approach can readily be employed to optimize the SNR and t hus the quality of PET images acquired at different scanners or with d ifferent examination protocols.