Effect of different scanning parameters on scattered radiation from wide-detector CT / 中华放射医学与防护杂志

ABSTRACT

Objective To explore the distribution characteristics on z-axis of scattered radiation from a wide-detector CT with different scan modes and detector widths.Methods The CT standard-dose phantom was scanned using a 16 cm wide detector Revolution CT.Thermoluminescent dosimeters (TLDs)were placed on the central axis (z-axis) of the scan hole at given intervals.As scan modes,both axial scan mode (using detector with width in 4,8 or 16 cm) and the helical scan mode (using detector with width in 4 and 8 cm) are used.The scan parameters were as followstube voltage 120 kV;effective tube current 200 mAs;scan length 16 cm;pitch (for helical scan)0.984 ∶ 1 and 0.516 ∶ 1,and all scans were repeated for 4 times.All TLDs were measured,after exposure,and divided by four for further analysis.Results The scattered radiation on z-axis was higher at the direction of human head than at the direction of human foot (Z=-2.366,-2.197,-2.366,-2.371,-2.028,-2.236,-2.028,P＜0.05).Under the axial scan,the difference in distribution of scattered radiation with different detector widths was statistically significant.The maximum increase for detector width of 4 cm and 16 cm was 67.5 μ Gy(x2=28.000,P＜0.05).Under the helical scan,the difference in distribution of scattered radiation with different detector widths was statistically significant (Z =-3.233,-2.982,P＜0.05).The largest distribution of scattered radiation was found when the detector width was 8 cm and the smallest at the detector width is 4 cm.The maximum increase for detector width of 8 and 4 cm was 97.67 μGy at a pitch of 0.516 ∶ 1.Furthermore,when the detector width and effective mAs were the same,the scattered radiation at a pitch of 0.516∶1 was greater than that at a pitch of 0.984 ∶ 1,with the statistically significant difference(Z =-3.296,-3.296,P＜0.05).The maximum increase was 49.95 μGy when the detector width was 8 cm.Conclusions In a 16 cm wide-detector CT,the selection of different detector widths can significantly influence the distribution of radiation field and related radiation values.Suitable detector width and relevant parameters shall be chosen according to the specific clinical requirements so as to reduce the radiation doses to workers,patients and carers.