To Estimate Organ Dose Of Automatic Tube Current Modulated CT Based On Individual Characteristics

Objective: To study the influence of CT scanning parameters on the performance of ATCM technology,and use Monte Carlo simulation to calculate the organ dose of the subject in the ATCM working mode of CT examination,and analyze the correlation between the simulated organ dose and the dose indexes calculated based on the sectional image to obtain the relationship between the indexes,so as to realize the rapid and accurate estimation of the organ dose of the subject by using the individual characteristic dose value.Methods: Using the GE Revolution 256 CT machine and CT dose phantom,using the ATCM technology and changing the tube voltage,tube current,projection angle of the spherical tube,and the tube current modulation range,noise index,beam collimation width,and the distance between the examination table and the center point of the frame,observe the tube current curve and image quality of the sectional image.Use MCNP6 to build the CT source model,establish the digital model of the subject,use the CT dose phantom and the on-site measured CTDIvol to verify the dose and calculate the conversion factor under different scanning conditions,and simulate the organ dose of the subject;Calculate the SSDE and organ SSDE of the subject using the equivalent water diameter of the subject,and explore the relationship between the organ dose of the subject and CTDIvol,SSDE and organ SSDE.Results: When the tube voltage of the positioning image was changed to 120 k V,the radiation dose was lower and the image quality was better.The tube current of the positioning image has little effect on the image quality and radiation dose.Change the projection angle of the positioning image.When the angle is 90 ° and 180 °,the image quality is better and the radiation dose is lower.Changing the milliampere modulation range of the fault can give full play to ATCM technology when the milliampere modulation range is wide.When the noise index is 50,the tube current modulation curve is more obvious than other groups.Change the beam collimation width.When the collimation width is 80 mm,the total exposure required is greater than the beam collimation width of 40 mm.Change the distance between the table and the isocenter of the frame.When the center of the scanning part is placed at the isocenter of the frame,the image quality is good and the radiation dose is low.Compared with CTDIvol and SSDE,there is a stronger linear relationship between organ SSDE and organ dose.The fitting curves of organ SSDE and organ dose are as follows: Organ Doselung=0.98 * SSDElung,Organ Doseheart=0.98 * SSDEheart,Organ Doseliver=0.56 *SSDEliver,Organ Dosekidney=0.35 * SSDEkidney,Organ Dosespleen=0.36 * SSDEspleen,Organ Dosepancreas=0.42 * SSDEpancreas,Organ Doseblader=0.024 * SSDEbladder.Conclusion: By studying the influence of CT scanning parameters on the tube current modulation curve,it is found that when using ATCM technology,selecting appropriate parameters can obtain better image quality and reduce exposure;Perform linear correlation analysis and fitting between the organ dose obtained by Monte Carlo simulation and various CT radiation dose indicators,and use organ SSDE to estimate the organ dose of the subject has certain value,which can be used to optimize the scanning parameters.