摘要
目的探讨宽体探测器CT扫描中使用表浅辐射敏感器官剂量调制(ODM)技术时,选择不同探测器宽度及螺距对辐射剂量和图像质量的影响。方法以临床胸部扫描方案为基准,在其他参数相同情况下分别使用两种探测器宽度(40、80mm)和3种螺距(0.500、1.000和1.375)的组合,对胸部模体进行3种ODM模式扫描,分别为不使用ODM技术(ODMoff)、从扫描起始层至乳腺区240mm开启ODM(ODMpart)、全扫描范围320mm开启ODM(ODMall)。在右侧乳腺区域前方固定位置放置长杆电离室,每组扫描参数重复测量7次,记录容积CT剂量指数(CTDIvol)和平均乳腺皮肤剂量(Dav)值。重组冠状面5mm层厚肺及软组织算法图像,沿Z轴方向平均分为上部、中部和下部3部分,分别测算对比噪声比(CNR)和品质因子(FOM)。对探测器宽度分别为40、80mm的两组的CTDIvol、D、CNR的比较采用独立样本t检验,对3组螺距(0.500、1.000和1.375)及3种ODM模式间辐射剂量和CNR比较采用单因素方差分析。结果使用80mm探测器、螺距为0.992并部分开启ODM时FOM因子最大。3种不同ODM模式下,辐射剂量依次下降,3种ODM模式的CTDIvol和Dav差异均有统计学意义(P值分别为0.019、0.002)。探测器宽度增加剂量增加,不同探测器宽度(40、80mm)间的CTDIvol差异有统计学意义(t=-2.723,P=0.015),Dav差异无统计学意义(t=-0.908,P=0.377)。3种螺距下的CTDIvol和Dav差异均无统计学意义(P值分别为0.254、0.146)。3种不同ODM模式下,CNR依次下降,不同ODM模式间软组织图像CNR的差异无统计学意义(P=0.146),肺算法图像CNR的差异有统计学意义(F=4.460,P=0.030),其中ODMoff与ODMall间CNR的差异有统计学意义(P=0.009)。探测器宽度增加CNR增加,不同探测器宽度(40、80mm)间的肺算法图像CNR差异有统计学意义(t=-4.128,P=0.001),软组织图像CNR的差异无统计学意义(P=0.187)。不同螺距下的肺算法图像CNR差异无统计学意义(P=0.660);软组织图像CNR差异有统计学意义(F=11.756,P=0.001),其中与螺距为1.000时相比,螺距为0.500和1.375的CNR差异有统计学意义(P值分别为0.000、0.013)。肺及软组织算法图像上、中部CNR在3种不同ODM模式组间比较差异无统计学意义(P>0.05),下部在仅ODMall模式时与其他两组CNR的差异有统计学意义(P<0.05)。结论探测器宽度和螺距改变会对ODM技术的作用产生影响,继而影响到辐射剂量与影像质量。胸部CT扫描使用80mm探测器、螺距0.992并且部分开启ODM时,达到质量与剂量利益最优化。
Objective To explore the effects of detector width and pitch on radiation dose and image quality when using organ dose modulation (ODM) technology in a wide-area detector CT scanning. MethodsBased on the clinical chest scan protocol,3 sets of scans of the chest phantom were performed using any combination of two detector width (40 mm and 80 mm) and pitch (0.500,1.000 and 1.375) with the same parameters:1 Do not use ODM technology (ODM off),2 open ODM (ODM part) 240 mm from scan start layer to breast area,3 open ODM (ODM all) in full 320 mm scan range. A long rod ionization chamber was placed in the fixed position in front of the right breast area. The scanning parameters of each group were measured 7 times,and the volume computed tomography dose index (CTDIvol) and breast skin dose measurement values D were recorded and the mean was calculated and recorded as Dav. The coronal 5 mm thick images of lung and soft tissue algorithms were reformed. It was divided into three parts in the Z-axis direction,and the contrast-to-noise ratio (CNR) and figure of merit (FOM) were measured separately. Independent sample t test was used for CTDI and breast skin doses D and CNR at both detector widths. ANOVA was used for dose and CNR of three sets of pitch (0.500,1.000,and 1.375) and the three ODM techniques. ResultThe FOM factor was the largest when using an 80 mm detector with a pitch of 0.992 and partially turning on the ODM. The radiation dose of the three ODM groups decreased in turn,and the effect of ODM on CTDIvol (P=0.019) and breast skin dose (P=0.002) was statistically significant. The width of the detector increased and the dose was increased. The width of the detector was statistically significant for CTDIvol (t=-2.723,P=0.015). There was no statistically significant effect on the breast skin dose (t=-0.908, P=0.377). The effects of the pitch were not statistically significant for CTDIvol (P=0.254) and breast dose (P=0.146). The CNR of the three ODM groups decreased in turn,and the effect of ODM on the soft tissue image CNR was not statistically significant (P=0.146). The CNR of lung algorithm image (P=0.030) had significant effects. The multiple comparisons:only ODM all was significantly different from ODM off (P=0.009). With the increase of detector width,the values of CNR increased,the values of CNR (t=-4.128,P=0.001) of lung images were significantly affected. The effects on the soft tissue images were not statistically significant (P=0.187). There was no statistically significant difference in the effect of pitch on the CNR (P=0.660) of the lung images. The effects of the pitch on the values of CNR of soft tissue images (F=11.756,P=0.001) were statistically significant. By multiple comparisons,the difference of CNR between 0.500 (P=0.000) and 1.375 (P=0.013) was statistically significant compared with that when the pitch was 1.000. There was no significant difference among the three ODM modes (P>0.05) on the values of CNR of upper and middle parts of lung and soft tissue arithmetic images. The differences of CNR between ODM all and the other two groups were statistically significant (P<0.05) on the bottom part of images. ConclusionThe changes of detector width and pitch will affect the organs dose modulation technique,and then affect the radiation dose and image quality. When using 80 mm detector with the pitch of 0.992 and partially turning on ODM in chest CT scan,achieving the optimized benefits of quality and dose.
作者
张永县
牛延涛
张丽丽
郭森林
康天良
吴建兴
王世军
李伟
Zhang Yongxian;Niu Yantao;Zhang Lili;Guo Senlin;Kang Tianliang;Wu Jianxing;Wang Shijun;Li Wei(Department of Radiology,Beijing Tongren Hospital,Capital Medical University,Beijing 100730,China)
出处
《中华放射学杂志》
CAS
CSCD
北大核心
2019年第6期464-469,共6页
Chinese Journal of Radiology
基金
北京市卫生系统高层次卫生技术人才培养计划(20143019)
北京市医院管理局临床医学发展专项经费(ZYLX201704).
关键词
辐射剂量
图像质量
器官剂量调制
表浅辐射敏感器官
Radiation dosage
Image quality
Organ dose modulation
Superficial radiation sensitive organ
作者简介
通信作者:牛延涛,Email:ytniu163@163.com.
