Scan Technology Research Of Low-dose Chest CT

Currently,CT examination’s clinical applications are more widely, protection issues of subjects have received increasing attention.However, reduce the radiation dose of CT examinations which will reduce the quality of CT images, increase the rate of misdiagnosis.It is necessary that reduce the radiation dose subjects, while ensuring the CT images to meet the requirements of clinical diagnosis, thereby promoting the rational use of CT.In the course of clinical practice, spatial resolution is a core indicator of CT image quality evaluation,it is crucial to obtain diagnostic information and correct diagnosis of diseases.The main methods of spatial resolution measurements are line pair method and MTF method,correlation analysis between the two methods has great significance for the routine quality control of CT.Objective1.This research was about the spatial resolution reflected in the image of CT through two different low dose scanning conditions,and the correlation between the two methods.2.Studied the possibility of Q2 factor as a evaluation standard for low-dose chest CT scan programs.Methods1.Using GE LightSpeed 16 CT scanned located midline CPT 528 module of Catphan 500 phantom.Scan conditions: Routine chest scanning conditions(120kV 200mA)and low dose conditions(Voltage:80kV、100kV、120kV、140kV four gears;Current:10mA~60mA,10 mA increased). Each scan conditions were used CPT486 module measuring noise. Adjusted the window with and window level,observed distinguishable lines on the card under different scanning conditions.The PSFs on the different locations were measured via the program composed by Matlab r2011 b,and then on two-dimensional Fourier transformation of PSF to get modulation transfer function(MTF). Finally,use SAS8.2 software statistical analyze 10% MTF values and visual value in order to search the correlation between MTF method and line pairs method.2.Using routine chest scanning conditions(120kV 200mA) and low-dose scanning conditions(Voltage:80kV、100kV、120kV、140kV four gears;Current:10mA~60mA,10 mA increased) for the torso phantom(320mm × 140mm) scanned. Using unfors / 8201023-C Xi pencil ionization chamber measure CTDI100, and calculate CTDIW, calculated according to the pitch CTDIvol. Combining the MTF value and noise σ in order to calculate factor Q2, select Q2 factor larger scanning programs(120kV 50 mA, 120 kV 60mA) for patients with pulmonary nodules scanned.The images for subjective evaluation.Compare the nodules detection rate.Results1.Spatial resolution under standard condition was higher than low dose conditions.When the MTF is 10% the corresponding spatial resolution and visual values obtained by lines pair method are consistent(t’=0.18 P=0.8556). Under low-dose conditions,part of MTF curves influenced by noise leading MTF value increased.2.Although, under the conditions of low-dose scan(120kV 50 mA, 120 kV 60mA) noise and artifacts increased in mediastinal area under mediastinal window level compared with the standard scanning condition. But the lung window level was still able to distinguish between lung pulmonary nodules and surrounding anatomical structures. The nodules detection rate with no significant difference between the two conditions.Conclusions1.Verified the consistency between the 10% MTF value and visual values of line pairs method. Provided an objective basis for subjective measurements of CT spatial resolution.2.Through experiments on standard scanning conditions, and low-dose scanning conditions diagnostic accuracy for statistical analysis, proved that Q2 factor as an evaluation standard for low-dose scanning programs is feasible. Provided a viable way in order to solve the current low-dose scanning conditions are quite different situation.Accordingly,promote the use of low dose CT in clinical, reduce the radiation dose of subjects.