Jiang X Y, Zhang S H, Xie Q Z, Yin Z J, Liu Q Y, Zhao M D, Li X L, Mao X J
From the Departments of Radiology (X.Y.J., Z.J.Y., Q.Y.L., M.D.Z., X.L.L., X.J.M.)
Department of Radiology (S.H.Z.), Shandong Cancer Hospital and Institute, Shandong, P.R. China.
AJNR Am J Neuroradiol. 2015 May;36(5):855-60. doi: 10.3174/ajnr.A4223. Epub 2015 Jan 22.
The virtual noncontrast images generated with iodine subtraction from dual-energy CTA images are expected to replace the true noncontrast images for radiation-dose reduction. This study assessed the feasibility of virtual noncontrast images for diagnosing SAH.
Eighty-four patients with or without SAH underwent true noncontrast brain CT (the criterion standard for diagnosing SAH). Among them, 37 patients underwent an additional head dual-energy angiography, and the other patients underwent head and neck dual-energy angiography. Virtual noncontrast images were produced on a dedicated dual-energy postprocessing workstation and reconstructed in orientation and section width identical to those in true noncontrast images. The findings on the virtual noncontrast and true noncontrast images were compared at both the individual level and the lesion level. Image noise of the virtual noncontrast and true noncontrast images was also measured and compared. The volume CT dose index and dose-length product were recorded for the radiation-dose analysis.
The sensitivity, specificity, positive predictive value, and negative predictive value of virtual noncontrast images at the individual level and the lesion level were 94.5%, 100%, 100%, 90.6% and 86.7%, 96.9%, 91.8%, 94.8%, respectively. The agreement in the diagnosis of SAH on true noncontrast and virtual noncontrast images reached 92.3% at the individual level and 85.1% at the lesion level. The virtual noncontrast images showed a higher image noise level. The volume CT dose index and dose-length product were obviously reduced without the true noncontrast brain CT scan.
Virtual noncontrast images are a reliable tool for diagnosing SAH, with the advantage of reducing the radiation dose.
利用双能量CT血管造影（CTA）图像进行碘减影生成的虚拟平扫图像有望替代真正的平扫图像以降低辐射剂量。本研究评估了虚拟平扫图像用于诊断蛛网膜下腔出血（SAH）的可行性。
84例有或无SAH的患者接受了真正的脑部平扫CT（诊断SAH的标准方法）。其中，37例患者额外接受了头部双能量血管造影，其他患者接受了头颈部双能量血管造影。在专用的双能量后处理工作站上生成虚拟平扫图像，并以与真正平扫图像相同的方向和层厚进行重建。在个体层面和病灶层面比较虚拟平扫图像与真正平扫图像的表现。还测量并比较了虚拟平扫图像与真正平扫图像的图像噪声。记录容积CT剂量指数和剂量长度乘积以进行辐射剂量分析。
虚拟平扫图像在个体层面和病灶层面的敏感性、特异性、阳性预测值和阴性预测值分别为94.5%、100%、100%、90.6%和86.7%、96.9%、91.8%、94.8%。真正平扫图像与虚拟平扫图像对SAH诊断的一致性在个体层面达到92.3%，在病灶层面达到85.1%。虚拟平扫图像显示出更高的图像噪声水平。在不进行真正的脑部平扫CT扫描的情况下，容积CT剂量指数和剂量长度乘积明显降低。
虚拟平扫图像是诊断SAH的可靠工具，具有降低辐射剂量的优势。
