摘要目的 研究肺部容积高分辨CT(volumetric high-resolution CT,VHRCT)的低剂量扫描方案,评价其诊断价值.方法 采用120 kV和10～250 mAs对Catphan 500体模行VHRCT扫描,层厚0.625 mm,记录图像的空间分辨力、密度分辨力、噪声及扫描剂量,制定低剂量VHRCT的扫描方案；105例在本院行常规剂量VHRCT检查的肺弥漫病变患者,复诊时行低剂量VHRCT,比较常规剂量与低剂量VHRCT对于肺弥漫病变的显示情况.结果 体模研究中,管电压120 kV,管电流120～250 mAs时,VHRCT图像的空间分辨力均为9 LP/cm；低于120 mAs时,随着管电流降低,VHRCT图像的空间分辨力和密度分辨力下降而噪声增加.临床研究中,对于肺弥漫病变各种征象的显示,低剂量VHRCT(120 kV,120 mAs)与常规剂量VHRCT(120 kV,250 mAs)比较差异无统计学意义(P＞0.05).扫描剂量较常规VHRCT降低52％.结论 采用120 kV和120 mAs行低剂量VHRCT,可以在保持图像的分辨能力及诊断价值的前提下显著降低放射剂量,其取代常规剂量VHRCT具有可行性.

abstractsObjective To explore the optimal low-dose protocol of volumetric high-resolution CT (VHRCT) of the lung and evaluate its diagnostic value.Methods Catphan phantom were scanned using GE Lightspeed VCT with different parmeters from 120 kV,10 mAs to 120 kV,250 mAs in 10 mAs increments.Other parameters included 0.969 pitch,20 mm scan coverage,0.625 mm collimation and 30 cm display field of view and bone recon kernel.The spatial and density resolution,noise and radiation dose of each scanning were measured to determine the low-dose VHRCT protocol.In clinical study,105 patients with diffuse lung diseases underwent standard-dose VHRCT with 120 kV,250 mA according to the clinical needs.Low-dose VHRCT was performed with 120 kV,120 mAs in follow-up.Two radiologists who were unaware of the CT technique reviewed randomized images for the detail of diffuse lung diseases,including linear or reticular opacities,micro-nodules or tree-in-bud patterns,bronchiolectasis,ground-glass opacities and emphysema using a 4-point scale.Results In phantom study,the spatial-resolution maintained at 9 LP/cm from 250 mAs to 120 mAs.Below 120 mAs,the spatial-resolution and density-resolution decreased and noise increased with the decrease of tube-current.In clinical study,there were no statistical differences between standard-dose and low-dose VHRCT in demonstrating the detail of diffuse lung diseases(P ＞0.05).The CTDIvol was 23.44 mGy at 250 mAs and 11.25 mGy at 120 mAs,with 52％dose reduction by low-dose VHRCT.Conclusions Low-dose VHRCT at 120 kV,120 mAs offers maximum dose reduction without compromising spatial resolution and diagnostic value.