医用CT仪上基于衰减的曝光量和峰值电压自动控制基本等式（英文）

Attenuation Based Governing Equations for Automatic mAs and kVp Controls in Medical X-ray CT Imaging

为了给患者以最少的辐射剂量而不影响诊断,现行医用CT仪都有基于噪声指标的自动曝光量控制。峰值电压对于图像质量和辐射剂量影响都很大,因此自动峰值电压控制很重要。本文从图像质量和辐射剂量优化的第一原理出发,给出基于衰减的曝光量和峰值电压同时自动控制的一般等式。此等式可用于单独曝光量自动控制或者单独峰值电压自动控制。对于单独暴光量自动控制,此等式要求对患者体厚度毎增加一厘米,曝光量要增加3.8%。对于单独峰值电压自动控制,此等式要求对患者体厚度每增加一厘米,峰值电压要平均增加1.53%。如果患者体厚度是常数,此等式要求平均百分比曝光量增加是百分比峰值电压减少的2.49倍。这些等式应该可以在现行医用CT仪上用于曝光量和峰值电压的自动控制。

Automatic exposure control based on noise index has been commonly implemented in current medical X-ray CT scanners in order to minimise radiation dose to patients while maintaining image quality for patient diagnosis. Automatic peak voltage control is also desirable as it is an important scanning parameter that has significant impact on both image quality and radiation dose. In this paper, a general attenuation based governing equation for simultaneous automatic controls of both mAs and kVp is presented which was derived from the first principle of radiation dose and image quality optimisation. This equation can be applied separately for automatic mAs control only or automatic kVp control only. The equation for automatic re_As control only states that the mAs should be increased by 3.8% for every lcm increase of the patient body＇s sectional thickness if the peak voltage is kept constant. For automatic kVp control only, the equation states that the peak voltage should be increased by 1.53% percent on average for every 1 cm increase of the patient＇s body sizes if the mAs is kept as a constant. For a constant body thickness, the equation states that the average percentage mAs reduction should be 2.49 times the percentage peak voltage increase. The implementation of these equations in medical CT scanners has been described in a recent Australian patent.