ABSTRACT
Objective To compare the iodine contrast agent dosage,radiation dose and image quality in CT pulmonary angiogra-phy (CTPA)with low tube voltage and high tube current in 64-slice spiral CT.Methods 60 patients with suspected pulmonary em-bolism in our hospital were randomly chosen and divided into three groups:Group Ⅰ:20 patients,using 120 kV,180 mA,contrast dose of 70 mL.Group Ⅱ:20 patients,using 100 kV,280 mA,contrast dose of 50 mL.Group Ⅲ:20 patients,using 80 kV,automat-ic tube current modulation techniques (300-500 mA),comparative dose of 30 mL.CT values and image noise of three pulmonary central areas and a segment branch were measured in each group.Objective indicators,subjective image quality assessment,CT dose index volume (CTDIvol),dose-length product (DLP)and effective absorbed dose (ED)were compared in three groups to evaluate the value of low kV,high mA with low-contrast dose in CTPA.Analysis of variance and t-test was used for data analysis.Results Compared with those of the standard method of CTPA,all pulmonary dry in two groups of low dose were well displayed.There was no statistical significance between each two groups in image quality score (P > 0.05),but was statistical significance in CT values, noise,SNR and CNR (P < 0.01).The CT radiation dose,CTDIvol and DLP of Group Ⅱ and Group Ⅲ were significantly lower than those of Group Ⅰ (P < 0.01).Conclusion Compared with traditional methods,low dose contrast agent injections under 80 kV could reduce the dose of contrast agent and the effect of hardening artifacts due to contrast agent in superior vena cava on right pul-monary artery.It is helpful to reduce the risk of contrast induced nephropathy and reduce patients’exposure to X-ray radiation.
ABSTRACT
Objective To investigate the effect of spectral CT monochromatic images for improving imaging quality in hepatic venography.Methods Thirty patients underwent spectral CT examination on a GE Discovery CT 750 HD scanner.During portal phase,1.25 mm slice thickness polychromatic images and optimal monochromatic images were obtained,and volume rendering and maximum intensity projection were created to show the hepatic veins respectively.The overall imaging quality was evaluated on a five-point scale by two radiologists.Inter-observer agreement in subjective image quality grading was assessed by Kappa statistics.Paired-sample t test were used to compare hepatic vein attenuation,hepatic parenchyma attenuation,CT value difference between the hepatic vein and the liver parenchyma,image noise,vein-to-liver contrast-to-noise ratio (CNR),the image quality score of hepatic venography between the two image data sets.Results The monochromatic images at 50 keV were found to demonstrate the best CNR for hepatic vein.The hepatic vein attenuation[(329 ± 47) HU],hepatic parenchyma attenuation [(178 ± 33) HU],CT value difference between the hepatic vein and the liver parenchyma [(151 ± 33) HU],image noise (17.33 ±4.18),CNR(9.13 ±2.65),the image quality score(4.2 ±0.6) of optimal monochromatic images were significantly higher than those of polychromatic images[(149 ± 18) HU],[(107 ± 14) HU],[(43 ±11) HU],12.55 ± 3.02,3.53 ± 1.03,3.1 ± 0.8 (t values were 24.79,13.95,18.85,9.07,13.25 and 12.04,respectively,P ＜ 0.01).In the comparison of image quality,Kappa value was 0.81 with optimal monochromatic images and 0.69 with polychromatic images.Conclusion Monochromatic images of spectral CT could improve CNR for displaying hepatic vein and improve the image quality compared to the conventional polychromatic images.