Study of CT pulmonary angiography technique in pulmonary embolism-low dose and low concentration / 中华放射学杂志

ABSTRACT

Objective To evaluate the image quality and the diagnostic value of low radiation,low dose and isotonic low concentration iodine contrast pulmonary computed tomography angiography (CTPA) protocol in pulmonary embolism.Methods Eighty patients with clinic ally suspected pulmonary embolism and BMI＜28 kg/m2 underwent pulmonary CTA on a 64-MDCT scanner (GE Discovery CT750 HD).Eighty patients were divided into two groups (group An=40,80 kV,Auto mA,20 ml 270 mg I/ml,60％FBP+40％ ASIR; group Bn=40,120 kV,Auto mA,40 ml 370 mg I/ml,100％FBP).Image quality was assessed,using a five-point scoring scale.Intraarterial density was measured in the common pulmonary artery trunk,the main right and left pulmonary arteries,lobar arteries,and then the average CT value was calculated.Image quality score,Average CT value,noise,SNR,CNR,CTDIvol and DLP were compared between the two groups using t-test.The occurrence rate of the superior vena cava iodine contrast agent sclerosis artifacts and the positive rate of pulmonary embolism were compared between the two groups,using Chi-square test.Results PE was found in 33 patients (14 in group A,19 in group B),and there was no difference of the positive rate of PE between two groups (35.0％ vs 47.5％,x2=1.289,P＞0.05).Overall 4-6 pulmonary artery branches were clearly displayed in all the cases.The image quality scores for two groups were 3.9±0.6 and 4.0 ± 0.7,respectively.There was no statistical difference between two groups (t=0.632,P＞0.05).The superior vena cava iodine contrast agent sclerosis artifacts were reduced in group A (28 cases vs.36 cases,x 2=10.362,P＜0.01).The average CT value and noise in group A [(426.8 ± 84.8),(14.9 ± 1.5)HU,respectively] was higher than those in group B [(359.4±75.3),(7.4± 1.4)HU,respectively],which was statistically significant(t=3.758,22.848,respectively; P＜0.01).However,the SNR (28.8 ±6.3)and CNR (24.5±6.1) in group A were lower than those in group B(SNR 50.4± 14.7,CNR 42.9± 13.8).There was statistically significant difference between two groups (t=8.522,7.669,respectively; P＜0.01 both).The CTDIvol[(3.3±0.3)mGy]and DLP[(101.4± 11.9)mGy· cm] in group A were significantly lower than those in group B [CTDI vol (9.6±0.6)mGy,DLP (328.5 ± 37.3)mGy· cm].The difference between two groups was statistically significant(t=56.393,36.675,respectively,P＜0.01 both).Conclusions The low radiation,low dose and isotonic low concentration iodine contrast CTPA protocol shows pulmonary artery branches of 4-6 levels,reduces radiation exposure and contrast media volume compared with the conventional pulmonary CTA,and achieves the same positive rate of PE in comparison of the conventional CTPA.It can meet the clinical needs.