Application of low tube voltage and reduced contrast medium in CT pulmonary angiography / 中华放射医学与防护杂志

ABSTRACT

Objective:To explore the feasibility of 60 kV tube voltage combined with reduced contrast medium in CT pulmonary angiography (CTPA).Methods:Totally 60 outpatients and inpatients with a body mass index (BMI) of less than 25 kg/m 2 who had suspected pulmonary embolism and were arranged for CTPA examination were enrolled in this study. They were divided into a control group and an test group according to the random number table method. A protocol with a conventional dose was adopted in the control group. This scheme consisted of 100 kV tube voltage and injection of 50 ml of contrast medium at the rate of 4.5 ml/s. A scheme with a low dose was employed in the experimental group. Specifically, this scheme involved 60 kV tube voltage scheme and injection of 30 ml of contrast medium mixed with 20 ml of normal saline at a rate of 4.5 ml/s. The objective image quality was assessed by measuring the Hounsfield units (HU) of five regions of interest (ROIs), i. e., pulmonary trunk, right and left pulmonary arteries, and right and left lower lobar arteries, and the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) were calculated. Moreover, the radiation doses were recorded. The subjective image quality was assessed by radiologists using a 5-point scale based on the overall image quality and the enhancement homogeneity of pulmonary arteries. The noise, SNR, CNR, and radiation dose of the two groups were compared using the Mann-Whitney U test, and the differences in the subjective image quality between the two groups were compared using the χ2 test. Results:All images met the requirements for clinical diagnosis. The two groups did not show significant differences in the overall subjective quality of CTPA images and enhancement scores ( P > 0.05), and in the average attenuation values of the pulmonary trunk and the left and right lower lobar arteries ( P > 0.05), but exhibited statistical differences in the average attenuation values of the left and right pulmonary arteries ( t = 2.75, 3.91, P < 0.05). There was no significant difference in the average background noise between the two groups ( P > 0.05). The test group had higher CNR of the left pulmonary artery and higher SNR and CNR of the right pulmonary artery than the control group, with statistically significant differences ( t = 0.04, 2.41, 3.08, P < 0.05). There was no significant difference in the SNR and CNR of other pulmonary artery branches between the two groups ( P > 0.05). The test group had an average effective dose of 1.24 mSv for CTPA, which was about one-third of that of the control group, with statistically significant differences ( t = 21.65, P < 0.05). Conclusions:The scheme of 60 kV tube voltage and reduced contrast medium for CTPA is feasible for patients with BMI < 25 kg/m 2. Using this scheme, the radiation and iodine dose can be reduced without affecting image quality.