Experimental comparison of SUV measurement between two generations of PET scanners

Objectives Many institutions are now equipped with at least two PET scans with possible significant different performances. Comparing PET scans in follow-up study when it was not possible to perform exams on the same scanner could become challenging. This study aims at proposing an experimental set-up to assess the SUV enhancement between a new and an old brand PET camera.

Methods The GE Discovery LS (DLS) PET system (2D mode) was compared against the Siemens Biograph mCT 40 (with the extended FOV and TOF options). The modified IEC phantom (mIEC), as suggested by Brambilla, together with a head phantom and a second IEC phantom placed on each side of the mIEC were employed to simulate the outside FOV activity. The background (BKG) activity ratio between the 3 phantoms were chosen based on the evaluation of reconstructed activity computed on 30 patients. The initial BKG activity matched the clinical local prescribed concentration activity to ensure a realistic prompts count rate. The spheres of the mIEC were filled with a 9:1 ratio relative to BKG (TBR) except the biggest one filled with air. Ten consecutive acquisitions were performed with an appropriate duration in order to preserve an identical statistical level on each set of sinograms. All images were reconstructed using the OSEM algorithm provided by each manufacturer with the standard clinical settings.

Results The variability of the SUVmax varied from 5% to 18% whatever the sphere volume or scanners used. The mean SUV (SUVmean), calculated with a 3D thresholding (25% of the SUVmax), showed a variability ranged from 2% to 10%. The SUVmax enhancement between mCT and DLS was 1.4 and 2.7 for the largest and the smallest sphere respectively. The SUVmean enhancement was less pronounced and ranged from 1.25 to 2.2 for hot spheres and was 0.5 for the sphere filled with air.

Conclusions The proposed set-up acquisition takes the advantage of preserving clinical count rate. The SUVmax enhancement could reach a ratio of 2.7 for a small lesion, a 9:1 TBR and a standard body diameter. The TBR relative to air was better recovered by a factor 2 for the latest PET system