双源CT低剂量扫描在腰椎检查中的应用

Application of Dual-source Low-dose Computed Tomography in Lumber Examination

目的探讨双源CT腰椎检查中低剂量扫描方法及其临床应用价值。方法将2011年8月-2012年5月行双源CT腰椎检查的714例患者随机分为7组。均采用管电压120 kV,分别依次采用常规参考管电流量250 mAs和低管电流量240、230、220、210、200、190 mAs,且均采用CARE DOSE技术采集数据。扫描参数:准直器64 mm×0.6 mm,重建层厚0.75 mm,重建间隔0.7 mm,FOV 180～200 mm。采集图像后,测量腰3椎体的CT值及同层面的脊髓的CT值、背脊肌的CT值及噪声;腰5椎体的CT值及同层面的脊髓的CT值、背脊肌的CT值及噪声,并计算腰3、腰5椎体及相应层面脊髓的信噪比(SNR)和其相对于背脊肌的对比噪声比(CNR)。应用统计学软件对不同管电流下的CNR、SNR、盲法评分的数值以及射线剂量指数(CTDI)、剂量长度乘积(DLP)、有效剂量(ED)进行分析。结果第1组和第2组比较,图像的背脊肌SD值;腰3、腰5椎体和脊髓的SNR值进行比较,差异无统计学意义(P>0.05)。第1组与第3、4、5、6、7组比较,腰3、腰5低管电流量各组间图像的背脊肌SD值;腰3、腰5椎体和脊髓的SNR值与常规管电流量组间比较差异均有统计学意义(P<0.05)。腰3和腰5各组图像的椎体-背脊肌和脊髓-背脊肌CNR值分别行单因素方差分析,结果差异均无统计学意义(P>0.05)。结论双源CT腰椎检查时,通过阶段性逐步降低管电流量的方法,使诊断医生逐渐适应低剂量图像质量,从而实现现有设备的低剂量扫描的方法是可行的。对于体质量指数(BMI)≤25 kg/m2的患者,可以采用190 mAs的参考管电流量进行腰椎扫描,不仅降低了患者接受的辐射剂量,同时也能获得满足临床诊断的合格图像,并且保护患者和减小设备损耗。

Objective To evaluate the application of lower-dose scan protocol and clinical values of dual source CT （DSCT） in lumbar examination. Methods A total of 714 consecutive patients treated in our hospital between Auguest 2011 and May 2012 were orderly divided into seven groups. All participants underwent DSCT with the same tube voltage （120 kV） and care dose technology. One of seven groups was scanned with regular tube current （250 mAs）, while other groups were scanned with decreasing tube current （240, 230, 220, 210, 200, and 190 mAs）. All other scan parameters were identical in the whole scan process, such as collimator （64 mm×0.6 mm）, recon thickness （0.75 mm）, recon interval （0.7 mm）, and field of view （FOV） （180-200 mm）. We measured CT values and noise of centrum/myelon/erector spinae at the third and fifth lumbar level （L3/L5）, and calculated the signal noise rate （SNR） of the centrum and myelon at the L3/L5 level, and the contrast noise rate （CNR） of them was compared with erector spinae. Then, we analyzed the relation between these data （SNR/CNR） acquired in different current and the index of X-ray dose, including CTDI, DLP, and ED etc. Results No difference was observed in the SNR/SD values of the centrum and myelon at the L3/L5 between group 1 and 2 （P 〉 0.05）. However, compared with group 3, 4, 5, 6, and 7, there were obvious differences in the SNR values of centrurn/myelon at the L3/L5 level in group 1 （P 〈 0.05）. With one-way ANOVA, no difference was observed in the CNR values of all groups （P 〉 0.05）. Conclusions In the DSCT lumbar examinations, by means of gradually decreasing the tube current, diagnosticians can easily adapt to the lower-dose imaging, so as to make sense of the lower-dose DSCT protocol. For patients whose BMI values are less than 25 kg/m2, not only the radiation dose will be decreased with referred current （190 mAs）, but also suitable imaging can be acquired to satisfy the diagnosticians. Meanwhile, it can also protect the patients from over-dose radiation and reduce facilities depletion.