多层 CT 检查的加权 CTDI(∞)估计。

Estimation of the weighted CTDI(∞) for multislice CT examinations.

机构信息

Department of Radiology, Massachusetts General Hospital, Boston, MA 02114, USA.

出版信息

Med Phys. 2012 Feb;39(2):901-5. doi: 10.1118/1.3678990.

DOI:10.1118/1.3678990

PMID:22320799

Abstract

PURPOSE

The aim of this study was to examine the variations of CT dose index (CTDI) efficiencies, ε(CTDI(100))=CTDI(100)/CTDI(∞), with bowtie filters and CT scanner types.

METHODS

This was an extension of our previous study [Li, Zhang, and Liu, Phys. Med. Biol. 56, 5789-5803 (2011)]. A validated Monte Carlo program was used to calculate ε(CTDI(100)) on a Siemens Somatom Definition scanner. The ε(CTDI(100)) dependencies on tube voltages and beam widths were tested in previous studies. The influences of different bowtie filters and CT scanner types were examined in this work. The authors tested the variations of ε(CTDI(100)) with bowtie filters on the Siemens Definition scanner. The authors also analyzed the published CTDI measurements of four independent studies on five scanners of four models from three manufacturers.

RESULTS

On the Siemens Definition scanner, the difference in ε(CTDI(W)) between using the head and body bowtie filters was 2.5% (maximum) in the CT scans of the 32-cm phantom, and 1.7% (maximum) in the CT scans of the 16-cm phantom. Compared with CTDI(W), the weighted CTDI(∞) increased by 30.5% (on average) in the 32-cm phantom, and by 20.0% (on average) in the 16-cm phantom. These results were approximately the same for 80-140 kV and 1-40 mm beam widths (4.2% maximum deviation). The differences in ε(CTDI(100)) between the simulations and the direct measurements of four previous studies were 1.3%-5.0% at the center∕periphery of the 16-cm∕32-cm phantom (on average).

CONCLUSIONS

Compared with CTDI(vol), the equilibrium dose for large scan lengths is 30.5% higher in the 32-cm phantom, and is 20.0% higher in the 16-cm phantom. The relative increases are practically independent of tube voltages (80-140 kV), beam widths (up to 4 cm), and the CT scanners covered in this study.

摘要

目的

本研究旨在探讨锥形束滤光器和 CT 扫描仪类型对 CT 剂量指数（CTDI）效率 ε(CTDI(100))=CTDI(100)/CTDI(∞)的影响。

方法

这是我们之前研究的扩展[Li、Zhang 和 Liu，Phys. Med. Biol. 56, 5789-5803 (2011)]。我们使用经过验证的蒙特卡罗程序在西门子 Somatom Definition 扫描仪上计算 ε(CTDI(100))。之前的研究已经测试了 ε(CTDI(100)) 对管电压和射束宽度的依赖性。本工作中检验了不同锥形束滤光器和 CT 扫描仪类型的影响。作者在西门子 Definition 扫描仪上测试了锥形束滤光器对 ε(CTDI(100))的影响。作者还分析了来自三个制造商的四个型号的五台扫描仪的四个独立研究的已发表 CTDI 测量值。

结果

在西门子 Definition 扫描仪上，在 32-cm 体模的 CT 扫描中，使用头部和体部锥形束滤光器的 ε(CTDI(W)) 之间的差异最大为 2.5%，在 16-cm 体模的 CT 扫描中，最大为 1.7%。与 CTDI(W)相比，在 32-cm 体模中，加权 CTDI(∞)增加了 30.5%（平均），在 16-cm 体模中增加了 20.0%（平均）。在 80-140kV 和 1-40mm 射束宽度（最大偏差 4.2%）下，结果大致相同。在四个先前研究的模拟和直接测量之间，在 16-cm/32-cm 体模的中心/外围，ε(CTDI(100))的差异为 1.3%-5.0%（平均）。