颞骨CT扫描方案对晶体剂量影响的研究

目的 探讨颞骨CT的不同扫描方式对眼晶体剂量的影响。方法 在相同管电压和有效mAs下,对成人离体头颅标本分别行横断位和冠状位的标准单层连续扫描、常规多层螺旋扫描以及改良的多层螺旋扫描。分析各种扫描方式的CT容积剂量指数(CTDI_vol)和剂量长度乘积(DLP),计算被检体有效剂量,并使用热释光剂量片测量晶体的器官剂量。结果 单层连续扫描时总体有效剂量为1.21 mSv,横断位扫描的晶体剂量为50.96 mGy,冠状位晶体剂量为1.73 mGy;常规多层螺旋扫描的有效剂量为0.803 mSv,晶体剂量为40.17 mGy;改良的多层螺旋扫描的有效剂量为0.803 mSv,晶体剂量为10.33 mGy。结论 相同管电压和有效mAs下,单层连续横断位和冠状位扫描的总体有效剂量和晶体剂量分别是常规螺旋扫描的1.51和1.31倍。改良的多层螺旋CT扫描方式可将螺旋扫描时的晶体剂量降低74.3%,可作为临床颞骨CT扫描的选择方式。

Radiation dose to lens in different CT scanning protocols of temporal bone

Objective To investigate the radiation dose to the lens of patients in temporal bone CT scanning with different protocols. Methods With the same values of kV and effective mAs, the tranaxial and coronal scans of exsomatize cadaveric head was performed with conventional sequential scan mode, routine multi-slice helical scan and modified multi-slice helical scan, respectively. The values of CT volume dose index (CTDI_vol) and dose length product (DLP) at various scanning mode were anylyzed, and effective doses of subject were calculated. Organ doses of the lens were measured with thermoluminescence dosimetry (TLD). Results When sequential scan mode was selected, gross effective dose was 1.21 mSv, while organ doses to lens were 50.96 and 1.73 mGy separately in axial and coronal slice scan, respectively. Effective dose was 0.803mSv at helical scanning, while dose to lens was 40.17 mGy. With modified helical scan mode, the effective dose was similar to routine helical scan, but dose to lens was 10.33 mGy which was significant lower than that of routine helical scan (40.17 mGy). Conclusions With the same values of kV and effective mAs, the effective doses and lens dose obtained in sequential axial and coronal scan were 1.51 times and 1.31 times higher than helical scan, respectively. With modified helical scan mode thinner slice images could be used to reformat axial, coronal and sagittal plane images, and lens dose was reduced by 74.3%. The modified helical CT scan mode of temporal bone could be selected in the clinical application.