The potential of point-spread-function reconstruction and time-of-flight to reduce FDG dose in PET/CT imaging

Objectives The incorporation of the Point Spread Function (PSF) into the system model improves spatial resolution uniformity. Time-of-Flight (TOF) information improves image signal-to-noise (SNR). We assess the potential of PSF and TOF to allow the injected dose to be reduced without compromising image quality.

Methods A total of 10 patients were scanned on a Biograph 6 PET/CT (Siemens Molecular Imaging) first with 370 MBq of FDG injected, followed within 5 days by a second scan with 185 MBq injected. The protocol was standardized to control start of imaging post injection, imaging time per bed position and patient glucose level. The data set with 370 MBq was reconstructed with fully 3D Ordinary Poisson (OP) Ordered Subset Expectation Maximization (OSEM) with PSF. The data set with 185 MBq was reconstructed with 3D OP OSEM with PSF and TOF. The image contrast and SNR were compared for the two sets of images acquired for each patient and for specific lesions. As the scans were acquired within 5 days of each other, the reproducibility of the Standard Uptake Values (SUVs) could also be assessed assuming the patient received no treatment between the two scans.

Results Our results show that incorporation of TOF information into the PSF reconstruction process can compensate for the increased noise due to reduced injected dose when imaging for the same scan time. We observed no significant difference in the image SNR between the 370 MBq and 185 MBq scans for the same lesions.

Conclusions The use of PSF with TOF compensates for the increased noise due to the lower, 185 MBq injected dose and results in an image SNR comparable to that of the 370 MBq injected dose.