Liu Wenyun, Ding Xiaobo, Kong Boyu, Fan Baoyan, Chen Liang
Department of Radiology, The First Hospital of Jilin University, Changchun, Jilin 130021, China.
Department of Radiology, The First Hospital of Jilin University, Changchun, Jilin 130021, China. Email:
Chin Med J (Engl). 2014;127(7):1284-8.
Currently there is a trend towards reducing radiation dose while maintaining image quality during computer tomography (CT) examination. This results from the concerns about radiation exposure from CT and the potential increase in the incidence of radiation induced carcinogenesis. This study aimed to investigate the lowest radiation dose for maintaining good image quality in adult chest scanning using GE CT equipment.
Seventy-two adult patients were examined by Gemstone Spectral CT. They were randomly divided into six groups. We set up a different value of noise index (NI) when evaluating each group every other number from 13.0 to 23.0. The original images were acquired with a slice of 5 mm thickness. For each group, several image series were reconstructed using different levels of adaptive statistical iterative reconstruction (ASIR) (30%, 50%, and 70%). We got a total of 18 image sequences of different combinations of NI and ASIR percentage. On one hand, quantitative indicators, such as CT value and standard deviation (SD), were assessed at the region of interest. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The volume CT dose index (CTDI) and dose length product (DLP) were recorded. On the other hand, two radiologists with ≥ 5 years of experience blindly reviewed the subjective image quality using the standards we had previously set.
The different combinations of noise index and ASIR were assessed. There was no significant difference in CT values among the 18 image sequences. The SD value was reduced with the noise index's reduction or ASIR's increase. There was a trend towards gradually lower SNR and CNR with an NI increase. The CTDI and DLP were diminishing as the NI increased. The scores from subjective image quality evaluation were reduced in all groups as the ASIR increased.
Increasing NI can reduce radiation dose. With the premise of maintaining the same image quality, using a suitable percentage of ASIR can increase the value of NI. To assure image quality, we concluded that when the NI was set at 17.0 and ASIR was 50%, the image quality could be optimal for not only satisfying the requirements of clinical diagnosis, but also achieving the purpose of low-dose scanning.
目前在计算机断层扫描（CT）检查中存在一种在保持图像质量的同时降低辐射剂量的趋势。这源于对CT辐射暴露的担忧以及辐射诱发癌症发生率可能增加的情况。本研究旨在调查使用GE CT设备进行成人胸部扫描时保持良好图像质量的最低辐射剂量。
72例成年患者接受了宝石能谱CT检查。他们被随机分为六组。在评估每组时，我们每隔一个数字从13.0到23.0设置不同的噪声指数（NI）值。原始图像以5毫米层厚采集。对于每组，使用不同水平的自适应统计迭代重建（ASIR）（30%、50%和70%）重建了几个图像系列。我们总共得到了18个不同NI和ASIR百分比组合的图像序列。一方面，在感兴趣区域评估定量指标，如CT值和标准差（SD）。计算信噪比（SNR）和对比噪声比（CNR）。记录容积CT剂量指数（CTDI）和剂量长度乘积（DLP）。另一方面，两名具有≥5年经验的放射科医生使用我们之前设定的标准对主观图像质量进行盲法评估。
对噪声指数和ASIR的不同组合进行了评估。18个图像序列之间的CT值无显著差异。SD值随着噪声指数的降低或ASIR的增加而降低。随着NI的增加，SNR和CNR有逐渐降低的趋势。随着NI的增加，CTDI和DLP逐渐减小。随着ASIR的增加，所有组的主观图像质量评估得分均降低。
增加NI可以降低辐射剂量。在保持相同图像质量的前提下，使用合适百分比的ASIR可以提高NI值。为确保图像质量，我们得出结论，当NI设置为17.0且ASIR为50%时，图像质量不仅可以满足临床诊断要求，还能达到低剂量扫描的目的，可能是最佳的。
