颈部能谱CT与常规CT扫描辐射剂量与图像质量的对比研究

Comparative study of radiation dose and image quality between spectral CT scanning and conventional scanning on neck

目的探讨颈部能谱CT与常规CT扫描辐射剂量与图像质量的差异。方法回顾性分析行颈部增强CT扫描的60例患者，其中行能谱CT成像的30例作为能谱扫描组，行常规CT扫描的30例作为常规扫描组。能谱扫描组采用管电压80、140kVp瞬时切换，管电流为默认值630mA，转速0．5s/周；常规扫描组管电压120kVp，管电流采用自动毫安技术（100—600mA），转速0.6s/周。对2组患者上、中、下颈部图像进行客观评价[噪声、对比信噪比（CNR）]、主观评分，并记录辐射剂量。采用独立样本t检验比较2组患者的辐射剂量，采用独立样本t检验和秩和检验比较各部位65、55keV单能量图像与常规扫描组混合能量图像的客观评价指标和主观评分。结果能谱扫描组和常规扫描组的CT剂量指数分别为17．77、（17．26±2．18）mGy，差异无统计学意义（t=-1．26，P=0．218）。上、中、下颈部能谱扫描组65keV图像噪声分别为（4．5±0．8）、（4．5±0．9）、（5．2±1．0）HU，常规扫描组上述部位噪声分别为（4．5±1．1）、（4．1±1．0）、（5．0±1．7）HU，差异均无统计学意义（t值分别为0．102、-1．362、-0．621，P均〉0．05）。上、中、下颈部能谱扫描组65keV图像评分分别为（4．1±0．3）、（4．7±0．5）、（3．8±0．7）分，常规扫描组上述部位图像评分分别为（4．1±0．4）、（4．6±0．5）、（3．5±0．6）分，两组差异无统计学意义（Z值分别为-0．286、-0．531、-1．568，P均〉0.05）。上、中、下颈部能谱扫描组55keV图像噪声分别为（5．4±0．9）、（5．6±1．1）、（6．6±1．6）HU，均大于常规图像噪声，差异均有统计学意义（t值分别为-3．614、-5．560、-3．784，P均〈0．05）。上、中颈部能谱扫描组55keV图像评分分别为（3．7±0．5）、（4．2±0．4）分，低于常规组图像，差异有统计学意义（z值分别为-2．541、-3．136，P均〈0．05）；下颈部能谱扫描组55keV图像评分为（3．3±0．8）分，和常规组图像差异无统计学意义（z=-1．318，P〉0．05）。上、中、下颈部常规扫描组图像CNR与能谱扫描组65、55keV图像CNR间的差异均无统计学意义（P均〉0．05）。结论颈部能谱CT与常规CT扫描辐射剂量和图像质量相当，65keV图像可以作为常规单能量图像使用。

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 significandy 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.