The phantom and clinical study of low-dose protocol of volumetric high resolution CT

Abstract

Objective 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. Key words: Lung diseases; Volumetric high-resolution CT; Phantoms; Low dose scanning