Comparison of Image Quality and Spatial Resolution Between 18F, 68Ga and 64Cu Phantom Measurements Using a Digital Biograph Vision PET/CT

Background:

The PET nuclide and reconstruction method can have a considerable influence on spatial resolution and image quality of PET/CT scans, which can, for example, influence the diagnosis in oncology. The individual impact of the positron energy of 18 F, 68 Ga and 64 Cu on spatial resolution and image quality of PET/CT scans acquired using a clinical, digital scanner was compared. Furthermore, the impact of different reconstruction parameters on image quality and spatial resolution was evaluated for 18 F-FDG PET/CT scans acquired with a scanner of the newest generation.
Methods:
PET/CT scans of a Jaszczak phantom and a NEMA PET body phantom, filled with 18 F-FDG, 68 Ga-HCl and 64 Cu-HCl, respectively, were performed on a Siemens Biograph Vision. Images were assessed using spatial resolution and image quality (Recovery Coefficients (RC), coefficient of variation within the background, Contrast Recovery Coefficient (CRC), Contrast-Noise-Ratio (CNR), and relative count error in lung insert). In a subsequent analysis, the scan of the NEMA PET body phantom filled with 18 F-FDG was reconstructed applying different parameters (with/without the application of Point Spread Function (PSF), Time of Flight (ToF) or post-filtering; matrix size). Spatial resolution and quantitative image quality were compared between reconstructions.
Results:
We found that image quality was comparable between 18 F-FDG and 64 Cu-HCl PET/CT measurements featuring similar maximal endpoint energy. In comparison, RC, CRC and CNR were worse in 68 Ga-HCl data, despite similar count rates. Spatial resolution was up to 18 % worse in 68 Ga-HCl compared to 18 F-FDG images. Post-filtering of 18 F-FDG acquisitions changed image quality the most and reduced spatial resolution by 52 % if a Gaussian filter with 5 mm FWHM was applied. ToF measurements especially improved the recovery of the smallest lesion (RC mean = 1.07 compared to 0.65 without ToF) and improved spatial resolution by 29 %.
Conclusions:
The positron energy of PET nuclides influences spatial resolution and image quality of digital PET/CT scans. Image quality of 68 Ga-HCl PET/CT images was worse compared to 18 F-FDG and 64 Cu-HCl, respectively, despite similar count rates. Reconstruction parameters have a high impact on image quality and spatial resolution and should be considered when comparing images of different scanners or centers.