A phantom study of the effects of tube voltage combined with organ dose modulation on radiation dose and image quality in chest CT

Objective To investigate the effects of different tube voltages on the dose of superficial radiation-sensitive organs and image quality when using organ dose modulation(ODM) in chest CT. Methods Based on clinical chest CT protocol with the sameother parameters, chest phantom was scanned using 140, 120, 100, and 80 kv (100 kV was the recommended by the CT system) without ODM (ODM off) or with ODM from the starting layer to the breast area (ODM part). A long rod ionization chamber was placed iat a fixed position in front of the right breast area. The scans were repeated for 7 times with each group of scanning parameters and dose values were measured for each scanning, the CTDIvol and breast skin dose measurements(D) were recorded. Coronal images of 5 mm thickness for the lung and soft tissue algorithms were reformatted. The images were divided into 8 parts along the z axis direction, the contrast noise ratios(CNR) for every region were measured. For CTDIvol, D, CNR for different ODM and tube voltage scanning modes, two factor non-repeat test ANOVA was performed. LSD method was used for comparison among groups. Results The CTDIvol was lowest at 80 kV, and the breast skin dose measurement was lowest at 100 kV, CTDIvol decreased in turn from140 to 80 kV (F=105.579 5, P 0.05), and the difference was significant at 80 kV(P 0.05). Conclusions In clinical practice, with the tube voltage not less than the recommended(100 kV), the optimal reduction of breast radiation dose can be achieved by reducing kV and using ODM on the premise of resonable image quality. Key words: Organ dose modulation; Superficial radiation sensitive organ; Image quality; Radiation dose; Tube voltage