The Application of Z-axis Tube-current Modulation Technique in MSCT neck Scanning

Objective To study the effect of Z-axis tube-current modulation technique to image quality(image noise level) and radiation dose of MSCT(16-slice CT) in neck scanning.Methods Consecutive 120 patients underwent neck CT were randomly divided into two groups:Z-axis tube-current modulation(ZTCM) group(test group) and constant tube-current(CTC) group(contrast group).The desired noise level of ZTCM group was 7.5HU and the dynamic tube-current range was 40～500mA,the tube-current of CTC group was set 250mA,while the other scan parameters remained totally same.CTDIvol and DLP of two groups,the tubecurrent of image at thyroid isthmus slice of ZTCM group were recorded respectively.The noise index level of image at angle of mandible,isthmus of thyroid,suprasternal notch were measured and compared.The qualities of Images were classified in three levels(excellent,good,poor) with double blind method.Results CTDIvol,DLP and the tube-current of image at thyroid isthmus slice ZTCM group were 21.4 mGy,210.5mGy·cm and 120.5mA,those of CTC were 13.8 mGy??292.8 mGy· cm and 250mA,ZTCM group increased 55%,decreased 28% and decreased 52% respectively as compared with CTC group.The noise index of image at angle of mandible and isthmus of thyroid were 7.36 HU and 7.05 HU in ZTCM group,those were a little higher than CTC group of 5.64HU and 4.85 HU,the noise index of image at suprasternal notch was 7.23HU in ZTCM group,it was significantly lower than CTC group of 13.24HU,the cases of excellent images in ZTCM group was significantly higher than that of CTC group(P 0.05).Conclusion ZTCM technique dynamically modulates tube current every gantry rotation according to the patients' habitus,thickness and density of scan position,it realizes individuation and keep images qualities constant of different slice.It decreases the total radiation dose and improves image quality in neck CT scanning.It is valuable and promising in neck CT scan.