Study On Effective Dose And Image Quality Of PET/CT And SPECT?SPECT/CT

Objective:To investigate the effective dose and the relationship beteween effective dose and image quality of PET/CT and SPECT/CT.Materials and Methods:PET/CT equipment:Discovery ST-16 and Discovery Elite PET/CT.SPECT/CT equipments:GE NM/CT 640 and Symbia T.Anthropomorphic phantom RS-550 was used to acquire the effective dose caused by CT in PET/CT and SPECT/CT.CT acquisition conditions were as follows.PET/CT:?in both ST-16 and Elite:tube voltage 120kV,pitch 1.375,rotation speed 0.8s,noise index ranged from 8 to 30,and the interval was 2,low limit of automatic tube current was 30mA,high limit ranged from 200 to 350mA,the interval was 50mA.?auto-tube current 30-250mA,noise index(NI)8-30,the interval was 2,the other conditions used our clinical acquisition conditions:tube voltage 120kV,pitch 1.75 for ST-16,0.984 for Elite,rotation speed 0.8s for ST-16,0.5s for Elite.?low limit of auto tube current was 30mA,high limit ranged from 210 to 350mA,the interval was 20mA,NI 14,the other conditions were the same as those in(1).?pitch 1.75,1.375 0.938 for ST-16,1.375,0.984 for Elite,tube voltage 120kV,auto tube current 30-250mA,NI 14,rotation speed 0.8s for ST-16,0.5s for Elite.?rotation speed 0.5s,0.8s,1.0s for both,tube voltage 120kV,auto tube current 30-250mA,NI 14,pitch 1.75 for ST-16,0.984 for Elite.SPECT/CT:GE NM/CT 640:tube voltage 120kV,tube current 30mA,rotation speed 0.5s,pitch 0.9381.375,1.75?SymbiaT:1)tube voltage 130kV,rotation speed 1.0s,quality reference milliseconds 50-130mAs,the interval was 20mAs,pitch 0.95?1.35?1.75?2)quality reference milliseconds 90mAs,pitch1.35,rotation speed 1.0s,tube voltage 80Kv?110kV?130kV.The anthropomorphic phantom Model RS-550 was scanned by clinical methods.The dose-length product(DLP)was recorded and the effective dose(EDCT)was calculated,and the image was analyzed on the GE Xeleris workstation to calculate the noise,signal to noise ratio,contrast to noise ratio,and figure of merit of the main organs in the abdomen.Results:1)The effective dose of CT in PET/CT decreases with the increase of the noise index and pitch,increases with the increase of tube current and rotation speed.The whole body effective dose caused by CT part of PET/CT is lower in Elite PET/CT than that in ST-16 When the same acquisition conditions are used for scanning.2)The effective dose of CT in SPECT/CT decreases with the increase of pitch,increases with the increase of tube current and tube voltage.3)The noise of imaging of PET/CT and SPECT/CT decreases with the increase of effective dose,the SNR and CNR increases with the increase of effective dose,but the FOM does not show significant change.Conclusion:The effective dose caused by CT scan in PET/CT and SPECT/CT could be effectively reduced by appropriate choice of acquisition conditions according to different clinical needs,and the image quality is related to effective dose.The image quality indicators and effective dose should all be considered for the best CT acquisition.