Abstract
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Objectives: Pediatric patients are more susceptible to the radiation due to longer life expectancy and vigorous cell reproduction. As newly introduced PET with higher sensitive detector, it is possible to maintain the image quality of FDG-PET on pediatric patients and reduce the injected tracer dose, which can lower the radiation dose to the patient. Therefore, this research aims to analyze the quantitative and qualitative image quality of FDG-PET on simulated low-dose imaging studies and find the optimal low-dose recommendation for pediatric patients.
Methods: 7 cases (age 2 to 14 years old) were acquired on a SiPM-based detector PET/CT scanner (uMI780, United Imaging Healthcare, Shanghai, China). The acquisition settings were 3-minute PET acquisition per bed position and the injection dose was around 0.1mCi/kg. All cases were retrospectively reconstructed with different levels of simulated dose reduction and then were compared with full dose images in sequence. Simulated 1/2 dose, 1/4 dose, 1/8 dose images were produced via reconstruction using 90s (1/2 dose), 45s (1/4 dose) and 22.5s (1/8 dose) data from the acquired list data. A combination of two physicians’ evaluation of various low-dose images and quantitative measurement of SUV mean value, SUV peak and volume were used for image quality evaluation. Two physicians (3- and 7-year experience) assessed image quality using a Likert-scale to rank the quality of images and to see if the low-dose images were clinically acceptable (1, unacceptable image quality; 2, suboptimal image quality; 3, acceptable image quality; 4, good image quality; 5, excellent image quality). VOIs with radius of 20mm were placed at the same position of different levels of low-dose images on normal hepatic tissue to compare the variability and bias of SUV peak and SUV mean among different images. The VOIs were placed on the lesions, and the volume was as large as possible to cover the whole lesion.
Results: A total of 21 lesions in 7 cases were successfully identified and no lesion was omitted compared to standard-dose images. The image quality was all clinically acceptable according to the qualitative evaluation of two physicians. The Likert-scale grades of 1/2 dose, 1/4 dose and 1/8 dose images were 4.14±0.69, 3.85±1.21,3.28±0.75, respectively. The deviations of quantitative measurement between low-dose and standard dose images are all under 25%. For 1/2 dose images, the difference of SUV peak, SUV mean and lesion volume are lower than 15% compared with full-dose images. The deviation of 1/4 dose images ranges from 0% to 19.91%. 1/8 dose images have the most dramatic variation from 0 % to 26.97%. Conclusions: Our results demonstrates that dose reduction is feasible without compromising the diagnostic image quality or influence quantitative measurement. Considering the fluctuation of 1/2 dose images is minimum and combining with the results of two physicians, 1/2 dose reduction (0.05 mCi/kg) might be potentially feasible and worthy for further exploration. The values are calculated based on the following equations: [(A-B)/B][asterisk]100% A: SUVpeak, SUVmean, Volume of low dose B: SUVpeak, SUVmean, Volume of standard dose
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