CT管电压对鼻窦图像质量和辐射剂量的影响研究

目的探讨CT管电压在鼻窦扫描中对图像质量和辐射剂量的影响。方法利用离体头颅标本,在逐层扫描方式下,分别选择5种不同的管电压(70、80、100、120、140 kV),对鼻窦区域进行扫描。噪声指数(NI)厂家默认为9,自动管电流调制,Smart mA设置为对应管电压下的最大范围。探测器宽度为120 mm。进行骨算法和软组织算法重建,层厚均为0.625 mm。按照临床实践的基线重组横断面、冠状面和矢状面图像,层厚2 mm。在横断面的中心层面上,选择相应的兴趣区测量CT值均值和标准差,计算对比度噪声比(CNR)。同时记录CT容积剂量指数(CTDIvol)和剂量长度乘积(DLP),并计算图像品质因子(FOM)。两名放射诊断医师和1名主管技师采用双盲法对实验所得图像进行主观评价,5分制标准计分。结果实验所得影像质量均满足诊断要求。在骨算法重建下,管电压为100和80 kV的CNR分别为66.98、64.75,高于管电压为70、120、140 kV的CNR值(51.61、61.56、57.76)。CTDIvol最大值为34.11 mGy(140 kV),最小值为17.45 mGy(70 kV)。管电压100 kV时的FOM值为152.26。在软组织算法重建下,管电压为80 kV的CNR为195.62,显著高于管电压为70、100、120、140 kV组(139.46、154.49、148.06、155.58)。管电压80 kV时的FOM值为1273.56,显著高于管电压为70、100、120、140 kV组(1114.56、809.98、735.63、709.62)。结论CT头颅标本鼻窦逐层扫描中,临床怀疑骨质病变时,优先选择骨算法100 kV;临床怀疑软组织病变时,优先选择软组织算法80 kV时,所得的图像质量最佳且受检者辐射剂量较低。

Eeffects of tube voltage on image quality and radiation dose of paranasal sinus CT examination

Objective To explore the effects of tube voltage on the image quality and radiation dose of paranasal sinus CT on a 16 cm wide-detector CT. Methods The sinus area of head specimen was scanned with sequential scanning mode and tube voltages of 70, 80, 100, 120 and 140 kV, respectively. The parameters were set as follows:NI=9, automatic tube current modulation, Smart mA with the maximum range at the corresponding tube voltage, 120 mm detector width. The images were reconstructed with bone and soft tissue algorithms separately.The slice thickness was 0.625 mm for all reconstructed images. The axial, coronal and sagittal images were reformatted as 2 mm thickness with clinical baseline. The CT value and standard deviation (SD) were measured in the region of interest(ROI) of central axial image and the contrast-to-noise ratio (CNR) was calculated. The volume CT dose index(CTDI_vol) and dose length product (DLP) were recorded, and the figure of merit (FOM) of images was computed. The images obtained in the study were subjectively evaluated by two experienced radiologists and one technician using a five-point scoring system. Results The subjective evaluation of images obtained in the study met the diagnostic requirements. With the reconstruction of bone algorithm, the CNR at the tube voltages of 100 and 80 kV were 66.98 and 64.75, respectively, which was significantly higher than those at the tube voltages of 70, 120 and 140 kV (51.61, 61.56 and 57.76, respectively). The maximum and minimum CTDI_vol were 34.11 mGy at 140 kV and 17.45 mGy at 70 kV. The FOM value was 152.26 at 100 kV. With the reconstruction of soft tissue algorithm, the maximum CNR was 195.62 at 80 kV, which was markedly greater than those at 70, 100, 120 kV and 140 kV (139.46, 154.49,148.06 and 155.58 respectively). The maximum FOM value was 1273.56 at 80 kV, which was significantly higher than those at the tube voltages of 70, 100, 120 kV and 140 kV (1114.56, 809.98, 735.63 and 709.62, respectively). Conclusions For the sinus CT of head specimen, the scan protocols with 100 kV combined with bone reconstruction algorithm and 80 kV combined with soft tissue reconstruction algorithm can provide relatively lower radiation dose and good image quality.