技术说明：用于评估基于计算机断层扫描器官的管电流调制技术的剂量和图像质量影响的体模研究。

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography organ-based tube current modulation technique.

作者信息

Gandhi Diksha, Crotty Dominic J, Stevens Grant M, Schmidt Taly Gilat

机构信息

Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin 53201.

GE Healthcare, Waukesha, Wisconsin 53188.

出版信息

Med Phys. 2015 Nov;42(11):6572-8. doi: 10.1118/1.4933197.

DOI:10.1118/1.4933197

PMID:26520748

Abstract

PURPOSE

This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison.

METHODS

Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated.

RESULTS

ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%-20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA.

CONCLUSIONS

ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol.

摘要

目的

本技术说明通过实验和模拟体模研究，对一种临床可用的基于器官剂量的管电流调制（ODM）技术的剂量和图像质量性能进行量化。所研究的ODM实施方案降低了前位源位置的管电流，而没有增加后位位置的电流，不过也对这种方法进行了评估以作比较。

方法

在一台配备ODM的扫描仪（Optima CT660，GE医疗集团，英国查尔方特圣贾尔斯）上，对头部和胸部体模进行120 kV的轴向CT扫描。剂量计对ODM和三维调制（SmartmA）设置下的乳腺、肺、心脏、脊柱、晶状体和脑区的剂量进行量化。利用实验数据进行验证的蒙特卡洛模拟，在28个体素化头部体模和10个胸部体模上进行，以量化器官剂量和噪声标准差。还研究了增加后位管电流的剂量和噪声效应。

结果

相对于SmartmA，ODM降低了所有实验剂量计的剂量，各剂量计的平均剂量降低幅度为：乳腺31%、肺21%、心脏24%、脊柱6%、晶状体19%、脑11%，模拟验证研究也得到了类似结果。在体模库研究中，所有体模的平均剂量降低幅度为：乳腺34%、肺20%、脊柱8%、晶状体20%、脑8%。ODM使重建图像中的噪声标准差增加了6% - 20%，前位区域的噪声增加通常更大。增加后位管电流对乳腺和晶状体的剂量降低效果与ODM相似，脊柱剂量增加，噪声效应范围为噪声降低2%至噪声增加16%。在噪声与SmartmA相等时，ODM使胸部和头部扫描的估计有效剂量分别增加了4%和8%。相对于SmartmA，增加后位管电流使有效剂量进一步增加，胸部增加15%，头部增加18%。