S.C. Fisica Sanitaria, San Giovanni Battista Hospital of Turin, Corso Bramante 88, Torino 10126, Italy.
Eur J Radiol. 2012 Nov;81(11):3172-7. doi: 10.1016/j.ejrad.2012.06.017. Epub 2012 Jul 18.
This study aims to investigate the consequences on dose and image quality of the choices of different combinations of NI and adaptive statistical iterative reconstruction (ASIR) percentage, the image quality parameters of GE CT equipment.
An anthropomorphic phantom was used to simulate the chest and upper abdomen of a standard weight patient. Images were acquired with tube current modulation and different values of noise index, in the range 10-22 for a slice thickness of 5mm and a tube voltage of 120 kV. For each selected noise index, several image series were reconstructed using different percentages of ASIR (0, 40, 50, 60, 70, 100). Quantitative noise was assessed at different phantom locations. Computed tomography dose index (CTDI) and dose length products (DLP) were recorded. Three radiologists reviewed the images in a blinded and randomized manner and assessed the subjective image quality by comparing the image series with the one acquired with the reference protocol (noise index 14, ASIR 40%). The perceived noise, contrast, edge sharpness and overall quality were graded on a scale from -2 (much worse) to +2 (much better).
A repeatable trend of noise reduction versus the percentage of ASIR was observed for different noise levels and phantom locations. The different combinations of noise index and percentage of ASIR to obtain a desired dose reduction were assessed. The subjective image quality evaluation evidenced a possible dose reduction between 24 and 40% as a consequence of an increment of ASIR percentage to 50 or 70%, respectively.
These results highlighted that the same patient dose reduction can be obtained with several combinations of noise index and percentages of ASIR, providing a model with which to choose these acquisition parameters in future optimization studies, with the aim of reducing patient dose by maintaining image quality in diagnostic levels.
本研究旨在探讨不同噪声指数（NI）和自适应统计迭代重建（ASIR）百分比组合选择对剂量和图像质量的影响，以及 GE CT 设备的图像质量参数。
使用人体模型模拟标准体重患者的胸部和上腹部。使用管电流调制和不同的噪声指数值（范围为 10-22），对 5mm 切片厚度和 120kV 管电压进行扫描。对于每个选定的噪声指数，使用不同的 ASIR 百分比（0、40、50、60、70、100）重建多个图像序列。在不同的体模位置评估定量噪声。记录计算机断层扫描剂量指数（CTDI）和剂量长度乘积（DLP）。三位放射科医生以盲法和随机方式对图像进行评估，并通过与参考方案（噪声指数 14，ASIR 40%）的图像序列进行比较，评估主观图像质量。通过从-2（差很多）到+2（好很多）的评分来评估感知噪声、对比度、边缘锐度和整体质量。
在不同的噪声水平和体模位置，观察到随着 ASIR 百分比的增加，噪声降低呈可重复的趋势。评估了获得所需剂量降低的不同噪声指数和 ASIR 百分比的组合。主观图像质量评估表明，由于 ASIR 百分比分别增加到 50%或 70%，可以实现 24%至 40%的剂量降低。
这些结果表明，可以通过几种噪声指数和 ASIR 百分比的组合获得相同的患者剂量降低，为未来的优化研究提供了一种选择这些采集参数的模型，旨在通过维持诊断水平的图像质量来降低患者剂量。
