CT轴扫描和螺旋扫描模式对颅脑急诊患者影像质量与辐射剂量的影响

The Effect of Axial and Spiral Scan Mode in Emergency Head CT on Image Quality and Radiation Dosage

目的:探讨CT轴扫描和螺旋扫描模式对颅脑影像质量和辐射剂量的影响,为颅脑急诊CT患者合理选择扫描模式提供依据。方法:20例患者,急诊CT扫描采用螺旋扫描模式,首次复查时采用轴扫描模式。管电压120 k V,管电流290 m A,球管转速0.8 s,层厚5 mm,间隔5 mm,螺距0.969∶1,标准重建算法。测量脑灰质和脑白质CT值和背景噪声,计算SNR和CNR,并对图像噪声、颅底伪影、脑灰、白质对比显示情况进行主观评分,扫描后从CT剂量报告中调取辐射剂量值。两种扫描模式影像质量组间比较采用配对t检验和独立样本卡方检验。结果:轴扫描模式时脑灰、白质CT值分别为(38.02±2.23)HU和(27.01±1.72)HU,螺旋扫描时脑灰、白质CT值分别为(37.76±2.22)HU和(26.99±1.69)HU。CT轴扫描和螺旋扫描模式时,脑白质CT值、SNR和CNR差异没有统计学意义(P>0.05,t=0.045,0.119,0.502),图像噪声、颅底伪影、脑灰、白质对比显示主观评分结果没有统计学意义(P>0.05,χ2=3.142,0.0,3.159)。有效剂量在螺旋扫描模式时为66 m Sv,在轴扫描模式时为43 m Sv,但螺旋扫描模式扫描时间短,后处理重组图像对影像诊断有意义。结论:从影像质量和辐射剂量两方面考虑,对颅脑急诊患者CT检查时首选轴扫描模式,但对躁动不合作患者或体位不合作患者应选择螺旋扫描模式。

Objective： to study the effect of axial and spiral scan mode in head CT on image quality and radiation dosage, and provide the evidence for emergency patient to choice the reasonable scanning mode. Methods： A total of 20 patients were taken the emergency CT with spiral scan mode and with axial scan mode in the first recheck. Scan parameters： 120 kV, 290 mA, 0.8 s/rol, slice thickness 5 ram, scanning interval 5 mm, pitch 0.969：1, standard reconstruction algorithm. To measure the CT value and background noise of the white matter and grey matter and calculate the SNR and CNR, and evaluate image noise, artifacts of the skull base, gray matter-white matter differentiation. After scanning, the radiation dosage was obtained from the dose report. Paired sample t test and chi-square test were used to compare the difference of image quality between two scanning modes. Results： Using axial scanning mode, the CT value of grey matter and white matter was （38.02± 2.23）HU and （27.01 ± 1.72）HU respectively, and using spiral scanning mode, the CT value of grey matter and white matter was （37.76±2.22） HU and （26.99± 1.69） HU respectively. There is no significant difference in CT value, SNR, CNR between two modes （P〉 0.05, t = 0.045, 0.119, 0.502）. There is no significant difference in image noise, artifacts of the skull base, the scores of grey matter-white matter differentiation between two modes （P 〉 0.05, χ2 = 3.142, 0.0, 3.159）. Effective doses was 66 mSv in spiral mode, and 43 mSv in axial mode, but the scanning time of spiral mode is shorter, and the reconstruction is helpful to the diagnosis. Conclusions： In term of both image quality and radiation dosage, the axial scanning mode is the preferred choice in the emergency head CT, but spiral scanning mode should be taken for the restless and non-cooperative patients.