Combined application of low kV,low mAs, and iterative model reconstruction (IMR) in carotid CT angiography / 中华放射医学与防护杂志

ABSTRACT

Objective To evaluate the application value of combination of low kV,low mAs,and iterative model reconstruction (IMR) in carotid CT angiography.Methods Forty patients (BMI 20-25 kg/m2) were enrolled and randomly divided into routine dose group(20) and low dose group(20),The parameters in routine dose group were 120 kV,automatic mAs,and filter back projection(FBP);and that in low dose group were 80 kV,automatic mAs but upper limit 150 mAs,and FBP or IMR.All patients received the injection of 32 ml of iopamidol(370 mg I/100 ml) at a flow rate of 4 ml/s,followed by 50 ml normal saline at the same rate.The CT value and image noise(SD)of the aortic arch,left carotid artery bifurcation,and right carotid artery of rock bone were measured with region of interest(ROI) method,and then signal to noise ratios (SNR) and contrast to noise ratio (CNR)of image were calculated.The image quality was evaluated by two radiologists using a subjective four points scale on multiplanar reformated (MPR),maximum density projected (MIP) and volume rendered (VR) images.Volume CT dose index (CTDIvol),dose length product (DLP),and the effective dose (E) of each patient were recorded.Results CT values of carotid artery[(479.87 ± 70.28),(514.78 ± 82.69),(436.50 ± 89.87) HU] in low dose group were significantly higher than those in routine dose group [(295.63 ± 34.75),(325.09 ± 37.81),(286.93±36.46)HU](t =-6.47,-5.76,-3.66,P＜0.05).The SNR and CNR of IMR reconstructed image in low dose group were significantly higher than those of FBP reconstructed image in routine dose group (t =-7.54,-3.55,-5.31,-7.13,-5.28,-8.35,P＜0.05).The image quality of FBP reconstructed images in routine dose group and IMR reconstructed images in low dose group were all enough for diagnosis.The image quality of FBP reconstructed images in low dose group was significantly poorer than that in routine dose group and IMR reconstructed images in low dose group (Z =-2.87,-3.69,P ＜0.05).The effective dose in low dose group (0.57 ±0.13) mSv was 73％ less than that in routine dose group (2.22 ± 0.36) mSv.Conclusions Using low kV,low mAs,and IMR would help to obtain good carotid CT angiographic images and low radiation dose.