  In this study, 18F-FDG PET/CT brain scans of 50 patients with head and neck
malignant lesions were employed to systematically assess the relationship
between the amount of injected dose (10%, 8%, 6%, 5%, 4%, 3%, 2%, and 1% of
standard dose) and the image quality through measuring standard image quality
metrics (peak-signal-to-noise-ration (PSNR), structural similarity index
(SSIM), root mean square error (RMSE), and standard uptake value (SUV) bias)
for the whole head region as well as within the malignant lesions, considering
the standard-dose PET images as reference. Furthermore, we evaluated the impact
of post-reconstruction Gaussian filtering on the PET images in order to reduce
noise and improve the signal-to-noise ratio at different low-dose levels.
Significant degradation of PET image quality and tumor detectability was
observed with a decrease in the injected dose by more than 5%, leading to a
remarkable increase in RMSE from 0.173 SUV (at 5%) to 1.454 SUV (at 1%). The
quantitative investigation of the malignant lesions demonstrated that SUVmax
bias greatly increased in low-dose PET images (in particular at 1%, 2%, 3%
levels) before applying the post-reconstruction filter, while applying the
Gaussian filter on low-dose PET images led to a significant reduction in SUVmax
bias. The SUVmean bias within the malignant lesions was negligible (less than
1%) in low-dose PET images; however, this bias increased significantly after
applying the post-reconstruction filter. In conclusion, it is strongly
recommended that the SUVmax bias and SUVmean bias in low-dose PET images should
be considered prior to and following the application of the post-reconstruction
Guassain filter, respectively.
