Document Type : Original Paper
Division of Medical Radiation, Department of Nuclear Engineering, Shiraz University, Shiraz, Iran
Division of Nuclear Medicine and Molecular Imaging, Department of Medical Imaging, Geneva University Hospital, CH-1211 Geneva 4, Switzerland
Introduction: In Positron emission tomography (PET), a high amount of radiotracer is injected to form high-quality PET images causing a high risk of radiation damage to patients. On the other hand, reducing the injected dose would lead to poor image quality.
Material and methods: In this study, 18F-FDG PET/CT brain scans of 50 patients with head and neck malignant lesions were employed to assess the relationship between the amount of injected dose and the image quality through measuring 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 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 to reduce noise at different low-dose levels.
Results: Significant degradation of PET image quality and tumor detectability was observed with a decrease in the injected dose, leading to a remarkable increase in RMSE from 0.173 SUV (at 5%) to 1.454 SUV (at 1%). SUVmax bias greatly increased in low-dose-PET images 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 less than 1% in low-dose-PET images; however, this bias increased significantly after applying the post-reconstruction filter.
Conclusion: In conclusion, it is 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.