Comparative study of radiation dose and image quality between spectral CT scanning and conventional scanning on neck / 中华放射学杂志

ABSTRACT

Objective To investigate the radiation dose and image quality of spectral and conventional CT scan in neck.Methods Sixty patients with enhanced neck CT scan were analyzed retrospectively.The 30 patients with spectral CT scan were included in spectral CT group,and the 30 patients with conventional CT scan were included in conventional CT group.The tube voltage,tube current and rotation speed of the spectral CT group were fast switching with 80 and 140 kVp,630 mA and 0.5 s,respectively.The scanning parameters of conventional CT group were 120 kVp,auto tube current (100 to 600 mA),and 0.6 s,respectively.The objective evaluation [noise and (contrast to noise ratio) CNR] and subjective scores in the upper,middle and lower neck were evaluated.The radiation dose was also evaluated in the two groups.The independent-samples t test was used in comparison of the radiation dose.The independent-samples t test and the rank sum test were used to compare the objective and subjective image quality.Results The CT dose index of spectral and conventional scan in the neck were 17.77 mGy and (17.26±2.18) mGy,respectively without significant difference (t=-1.26,P=0.218).The noises of 65 keV images in upper,middle and lower neck were (4.5 ± 0.8),(4.5 ± 0.9),(5.2 ± 1.0) HU,and the noises of conventional CT images in above-mentioned regions were (4.5± 1.1),(4.1± 1.0),(5.0± 1.7) HU.There was no significant differences (t=0.102,-1.362,-0.621;P＞0.05).The subjective scores of 65 keV images in upper,middle and lower neck were (4.1 ± 0.3),(4.7 ± 0.5),(3.8 ± 0.7),while the subjective scores of conventional CT images in associated region were (4.1±0.4),(4.6 ±0.5),(3.5 ±0.6),wihtout significant differences (Z=-0.286,-0.531,-1.568;P＞0.05).The noises of 55 keV images in upper,middle and lower neck were (5.4±0.9),(5.6± 1.1),(6.6± 1.6) HU,which were significantly higher than noise of conventional images (t=-3.614,-5.560,-3.784;P＜0.05).The subjective scores of 55 keV images in upper and middle neck were (3.7±0.5),(4.2±0.4),which were significantly lower than those of conventional images (Z=-2.541,-3.136;P＜0.05).The subjective score of 55 keV images in lower neck was (3.3±0.8),which was no significant difference in comparison with conventional image (Z=-1.318,P＞0.05).There was no significant difference between the CNR of conventional images and CNR of spectral images with 65 keV and 55 keV in upper,middle and lower neck (P＞0.05).Conclusion The radiation dose and the image quality of spectral CT scan are same to the conventional CT scan in the neck,the 65 keV monochromatic images can be used routinely.