应用低管电压能谱CT成像降低肾动脉CTA对比剂用量

Low tube voltage gemstone spectral imaging for reducing contrast medium dose of renal CTA

目的探索低管电压宝石CT能谱成像(GSI)降低肾动脉CTA对比剂用量的应用价值。方法对48例临床怀疑肾血管源性高血压患者行肾动脉CTA,将其随机分为两组:常规组23例,应用常规扫描模式,管电压120kVp,对比剂剂量为1ml/kg体质量;GSI组25例,应用GSI扫描,对比剂剂量为0.5ml/kg体质量。重建GSI组数据,得到101组(40～140keV)单能量图像,从中选出腹主动脉与竖脊肌之间具有最佳CNR的单能量图像;对GSI组最佳单能量图像和常规组图像进行MIP、VR和CPR等后处理,分别在原始图像上测量具有最佳CNR的单能量图像和常规组混合能量图像中双侧肾动脉的CT值、噪声和CNR,并以5分法比较两组重建图像的图像质量,记录并比较两组成像的剂量长度乘积(DLP)。结果 GSI组内,(51±1)keV单能图像具有最佳CNR,与70keV图像相比CNR提高了72.00%(P=0.001)。GSI组中最佳CNR单能量图像的肾动脉的平均CT值(466.45±109.93)HU高于常规组的(317.32±49.93)HU(P<0.001),CNR(14.31±4.70)和主观评分(4.75±0.30)与常规组中混合能量图像[CNR:(17.07±9.60),主观评分:(4.64±0.17)]差异均无统计学意义(P=0.22、0.11)。GSI组的DLP(333.44±19.35)与常规组(340.08±127.06)差异亦无统计学意义(P=0.81)。结论51keV能谱CTA可降低对比剂用量,提高CT值,并维持与常规CTA相同的图像质量,可在具有潜在肾功能损害的患者中推荐使用。

Objective To investigate the utility of low tube voltage gemstone spectral imaging （GSI） for reducing contrast medium of renal CTA. Methods Forty-eight patients with suspected renal vascular hypertension underwent either conventional CTA with 120 kVp （conventional group） and normal contrast medium dose at 1 ml/kg （n=23） or spectral CTA with half contrast medium dose at 0.5 ml/kg （n=25, GSI group）. Totally 101 groups of monochromatic images （40—140 keV） were obtained from the spectral CTA, and from which an optimal energy level was selected for obtaining the best CNR for the abdominal aorta at the renal artery level relative to the erector spine muscle. CT value and noise of bilateral renal arteries and muscle from the optimal monochromatic images and conventional 120 kVp images were measured and assessed with 5-point scale. Dose-length product （DLP） was recorded. Results Images of （51±1）keV showed best CNR, and there was a 72.00% raise of CNR compared with 70 keV images. At this energy, the mean CT value of bilateral renal arteries of spectral CTA （466.45±109.93）HU was higher than that of conventional CTA （317.32±49.93）HU （P〈0.001）. CNR value and subjective image quality score of spectral CTA （14.31±4.70, 4.75±0.30） were compatible with those of conventional CTA （17.07±9.60, 4.64±0.17; P=0.22, 0.11）, and there was no statistical difference of DLP between conventional CTA （340.08±127.06） and spectral CTA （333.44±19.35, P=0.81）. Conclusion Spectral CTA with image reconstruction at 51 keV can reduce contrast medium dose, enhance CT value and provide compatible image quality. Low tube voltage monochromatic CT renal angiography should be an optional choice for patients with renal function impairment.