Ngaile J E, Msaki P, Kazema R
Directorate of Radiation Control, Tanzania Atomic Energy Commission, PO Box 743 Arusha, Tanzania.
Radiat Prot Dosimetry. 2012 Jan;148(2):189-201. doi: 10.1093/rpd/ncr021. Epub 2011 Feb 25.
Since patient doses from computed tomography (CT) are relatively high, risk-benefit analysis requires dose to patients and image quality be optimised. The aim of this study was to develop a patient-dependent optimisation technique that uses patient diameter to select a combination of CT scanning parameters that minimise dose delivered to patients undergoing abdominal CT examinations. The study was performed using cylindrical phantoms of diameters ranging from 16 to 40 cm in order to establish the relationship between image degradation, CT scanning techniques, patient dose and patient size from two CT scanners. These relationships were established by scanning the phantoms using standard scanning technique followed by selected combinations of scanning parameters. The image noises through phantom images were determined using region of interest software available in both scanners. The energy depositions to the X-ray detector through phantoms were determined from measurements of CT dose index in air corrected for attenuation of the phantom materials. The results demonstrate that exposure settings (milliampere seconds) could be reduced by up to 82 % for smaller phantom relative to standard milliampere seconds, while detector signal could be reduced by up to 93 % for smaller phantom relative to energy depositions required when scanned using standard scanning protocols. It was further revealed that the use of the object-specific scanning parameters on studies performed with phantom of different diameters could reduce the incident radiation to small size object by up to 86 % to obtain the same image quality required for standard adult object. In view of the earlier mentioned fact, substantial dose saving from small-sized adults and children patients undergoing abdomen CT examinations could be achieved through optimal adjustment of CT scanning technique based on the patient transverse diameter.
由于计算机断层扫描（CT）对患者的辐射剂量相对较高，因此风险效益分析要求对患者剂量和图像质量进行优化。本研究的目的是开发一种基于患者个体的优化技术，该技术利用患者直径来选择CT扫描参数的组合，以尽量减少接受腹部CT检查患者所接受的剂量。本研究使用直径范围为16至40厘米的圆柱形体模进行，以建立两台CT扫描仪的图像质量下降、CT扫描技术、患者剂量和患者体型之间的关系。通过使用标准扫描技术扫描体模，然后选择扫描参数的组合来建立这些关系。使用两台扫描仪中都有的感兴趣区域软件来确定体模图像中的图像噪声。通过对体模材料衰减进行校正后，根据空气中CT剂量指数的测量值来确定X射线探测器通过体模的能量沉积。结果表明，相对于标准毫安秒，较小体模的曝光设置（毫安秒）最多可降低82%，而相对于使用标准扫描协议扫描时所需的能量沉积，较小体模的探测器信号最多可降低93%。进一步的研究表明，在对不同直径体模进行的研究中使用特定对象的扫描参数，对于小尺寸对象，可将入射辐射最多降低86%，以获得标准成年对象所需的相同图像质量。鉴于上述事实，通过根据患者横向直径对CT扫描技术进行优化调整，可大幅减少接受腹部CT检查的小尺寸成人和儿童患者的剂量。
