Anthropomorphic Phantom Study Of Radiation Dose And Image Quality For PET/CT

第一部分 Study of effective dose and influence factors for PET/CT patientsObjective:The aim of the study was to investigate the effective dose of patient caused by PET/CT to provide data basis for decreasing the radiation dose.Materials and Methods:The effective dose was the sum of the dose caused by CT and PET. The dose caused by PET was calculated by the radioactivity of the radiopharmaceutical injected. The dose caused by CT was determined by acquisition for the anthropomorphic phantom(Model RS-550). PET/CT system of GE Discovery ST-16 and Discovery Elite was used to simulate clinical PET/CT situation for the anthropomorphic phantom. CT acquisition conditions were as follows:tube voltage 120kV, tube current 30-250mA, pitch 0.938,1.375 and 1.75.Scan range was divided into body scan and head-neck scan to simulate clinical PET/CT. The dose-length product (DLP) was recorded and the effective dose (EDCT) was calculated with EDCTk.DLP.Results:1)The effective dose caused by PET was 3.16-8.96 mSv for a patient with45-85kg weight with injection dose 3.70-5.55MBq/kg (0.08-0.15mCi/kg) of 18F-FDG, increased linearly with weight and injection dose and independent of the PET acquisition conditions.2) The effective dose caused by CT increases linearly with increasing tube current when the pitch was fixed, Discovery Elite increased larger than Discovery ST. However, when the tube current fixed, the effective dose reduce with increasing pitch. Under the different acquisition condition(30-250mA), total the effective dose of two PET/CT was 1.40-27.68 mSv. The effective dose of Discovery Elite was lower than Discovery ST, upon the condition of clinical scan conditions.Conclusions:There is no big variation for effective dose by PET for a certain patient, however there is much difference for the effective dose caused by CT under the different acquisition conditions. It shows that the radiation dose caused by CT in PET/CT could be effectively reduced by appropriate choice of acquisition conditions according to different clinical needs.第二部分 Effect on image quality and radiation dose in a phantom study for PET/CTObjective:To investigate the effect on image quality and radiation dose of Anthropomorphic phantom caused by PET/CT to provide data basis for decreasing the radiation dose.Materials and Methods:PET/CT system of GE Discovery ST-16 was used to simulate clinical PET/CT situation for the anthropomorphic phantom. The dose caused by CT was determined by acquisition for the Anthropomorphic phantom (Model RS-550). CT acquisition conditions were as follows:tube voltage 120 kV, tube current 30-250 mA, pitch 0.938,1.375 and 1.75. Scan range was divided into body scan and head-neck scan to simulate clinical PET/CT. The noise (SD) was recorded and the signal-to-noise ratio and the figure of merit were calculated with different formulas.Results:The noise decreased with increasing effective dose, when the effective dose was less than 15 mSv, the noise decreased rapidly, however, when the effective dose was more than 15 mSv, the decrease of noise was not significant. The signal-to noise ratio and contrast-to-noise ratio increased with increasing effective dose. However, the figure of merit was fixed, when the radiation dose increased under the different acquisition condition. All indicators of ATCM were superior to the fixed tube current mode.Conclusions:The image quality of CT in PET/CT could not significantly improve by increasing effective dose, when The image quality reaches to certain level. The radiation dose caused by CT in PET/CT could be effectively reduced by appropriate choice of acquisition conditions according to different clinical needs.