The Primary Study Of The Image Quality And Radiation Dose Of High-pitch CTPA With IR Algorithms And Low Tube Voltage In Patients With Pulmonary Embolism

Objective: According to the body mass index(BMI) of the tested patients,to assess the image quality and radiation dose of prospective-ECG triggered high-pitch spiral scan of CT pulmonary angiography(CTPA) using low tube voltage and iterative reconstruction(IR) algorithms in patients with pulmonary embolism and the feasibility of it in the diagnosis for pulmonary embolism.Methods: From June 2014 to February 2015, 150 consecutive patients who had suspected pulmonary embolism underwent CTPA, 76 patients were eventurely conformed with pulmonary embolism. 31 of those are male, the others are female. Ages were from 44 to 86 years old, the average was 69 ± 9.2 years old. There were 50 patients with normal BMI(<25 kg/m2) in the whole patients with pulmonary embolism, 80 k V tube voltage for 25 patients(groupⅠ), 100 k V tube voltage for the other 25 patients(group Ⅱ). The other 26 patients with pulmonary embolism are overweight with abnormal BMI(≥ 25 kg/m2), 100 k V tube voltage for 15 patients(group Ⅲ), 120 k V tube voltage for the other 11 patients(group Ⅳ). The sex, BMI, heart rate and the scan time are matched between groupⅠandⅡand group Ⅲ and Ⅳ, there are no significance between each group. CTPA was performed on a dual source CT system(the second generation) by the scan mode of prospective-ECG triggered high-pitch spiral scan. Acquisition parameters were as follows: gantry rotation time 280 ms, single sector reconstructed temporal resolution 75 ms, detector collimation 2 × 64 × 0.6 mm, pitch 3.4 and tube current time product was 320 m As per rotation. Parameters for image reconstruction of a slice thickness and increment were 0.75 mm and 0.7 mm. IR algorithms(convolution kernel I26f) were used for groupⅠand group Ⅲ, IR algorithms and FBP reconstructed algorithms(convolution kernel B26f) were used for groupⅡand group Ⅳ.Before the examination giving all the tested patients a vein remaining needlleiv in antecubital vein, during the examination 50 ml of iodinated contrast material and 22 ml of saline was injected at the speed of 5.0 ml/s by using a dual-syringe injector. The CT attenuation of pulmonary artery(main pulmonary artery, the artery of pulmonary trunk, the artery of pulmonary lobe), the value of Hounsfield unit of the emboli, image noise, signal-to-noise ratio, contrast-to-noise ratio and image quality between IR and FBP were compared respectively reconstruction in group Ⅱ and group Ⅳ. According to the BMI, the CT attenuation of pulmonary artery(main pulmonary artery, the artery of pulmonary trunk, the artery of pulmonary lobe),the value of Hounsfield unit of the emboli, image noise, signal-to-noise ratio, contrast-to-noise ratio, image quality scores and effective radiation dose were compared respectively in each matched groups(groupⅠwith IR algorithms and group Ⅱwith FBP algorithms, group Ⅲ with IR algorithms and group Ⅳ with FBP algorithms).Results:(1) In group Ⅱand Ⅳ, the image noise with IR was significantly lower than that with FBP(P< 0.01), and the signal-to-noise ratio and contrast-to-noise ratio with IR were significantly higher than with that FBP(P < 0.01); while there was no significant difference in CT attenuation of pulmonary artery(main pulmonary artery, the artery of pulmonary trunk,the artery of pulmonary lobe) and the value of Hounsfield unit of the emboli.(2) In groupⅠ with IR and groupⅡwith FBP, the CT attenuation of pulmonary artery and the image noise in group Ⅰ with IR were significant higher than group Ⅱ with FBP, while there were no significant difference in signal-to-noise ratio, contrast-to-noise ratio and image quality scores between the two groups. The effective radiation dose of groupⅠwas 53.85% lower than that of groupⅡ(0.78 ± 0.14 m Sv vs. 1.69 ± 0.42 m Sv, P < 0.01).(3) In group Ⅲ with IR and group Ⅳ with FBP, there were no significant differences in CT attenuation of pulmonary artery, the image noise, signal-to-noise ratio, contrast-to-noise ratio and image quality scores. The effective radiation dose of group Ⅲ was 42.38% lower than that of group Ⅳ(1.55 ± 0.11 m Sv vs 2.69 ± 0.10 m Sv, P < 0.01).Conclusion:(1) In PE patients with normal BMI, compared with CTPA using prospective-ECG triggered high-pitch spiral scan with FBP reconstruction algorithms and 100 k V tube voltage, CTPA using prospective-ECG triggered high-pitch spiral scan with IR algorithms and 80 k V tube voltage can decreased approximately 53.85% of the radiation dose(average 0.78 m Sv) with the same image quality.(2) In PE patients with abnormal BMI, compared with CTPA using prospective-ECG triggered high-pitch spiral scan with FBP reconstruction algorithms and 120 k V tube voltage, CTPA using prospective-ECG triggered high-pitch spiral scan with IR algorithms and 100 k V tube voltage can decreased approximately 42.38% of the radiation dose(average 1.55 m Sv) with the same image quality. In conclusion, CTPA with IR algorithms and reduced tube voltage can be used for the diagnosis of PE.