Study on the optimized scanning conditions of cerebral CT angiography based on the angiographic CT head phantom

Abstract

Objective To study the impacts of different tube voltage and different noise index(NI) guided automatic tube current modulation on the image quality and radiation dose in cerebrovascular imaging and determine the optimal scanning condition. Methods PH3 angiographic CT head phantom was used for head CTA examination. Scanning protocols: all the scanning objectives were divided into three groups according to the different tube voltages of 80, 100 and 120 kV. Each group applied certain tube current (300, 400 mA) and automatic tube current modulation technique with NI from 3 to 10 to perform head CTA. There were 30 scanning proposals with different parameter combinations of tube voltage and tube current. The radiation dose [CT dose index volume (CTDIvol), dose length product (DLP) and effective dose (ED)], objective indicators of images(CT value of the blood vessels and its noise, CT value of brain tissue and its noise, signal-to-noise ratio, contrast-to-noise ratio) and the subjective scores of the five cerebrovascular segments were recorded. Differences of CT value of the blood vessels and its noise, CT value of brain tissue and its noise, signal-to-noise ratio and contrast-to-noise ratio between different tube voltages and tube currents were analyzed by One-Way ANOVA. Results When the tube voltage was certain, the CTDIvol, DLP and ED were all dropped while NI was increased from 3 to 10. Compared with group(120 kV, 300 mA), CTDIvol of group with 100 kV, 300 mA decreased 35.32% (12.22/34.59) , CTDIvol of group(100 kV, NI=6) decreased 46.72% (16.16/34.59) . Compared with group(100 kV, 300 mA), CTDIvol of group (100 kV, NI=6) decreased 17.61% (3.94/22.37) . When the tube voltage was certain and the tube current and NI were not certain, there is no statistical difference (P>0.05) between CT values of blood vessel and brain, while blood vessel noise, noise of brain, SNR and CNR showed statistical difference (P<0.05). When tube current and NI were certain while tube voltage was varied, all objective indicators discussed above all exhibited statistical difference (P<0.05). SNR and CNR of group(100 kV, NI=6) were higher than group(120 kV, 300 mA) with 6.31% (2.69/42.66) and 7.18% (2.64/36.78) , respectively. The tube voltage, NI and tube current had no effect on the subjective scores of first and second grade vessel but greater impact on the fourth and fifth grade vessel. Conclusion In the head CTA scanning, combined the use of NI 6 guided automatic adjustment tube current and low tube voltage (100 kV) technique not only can get better image quality but also significantly decreased the radiation dose. Key words: Tomography, X-ray computed; Radiation dosage; Comparative study