Evaluation of Virtual Noncontrast Images Obtained from Dual-Energy CTA for Diagnosing Subarachnoid Hemorrhage.

X.Y Jiang,Q.Y Liu,Q.Z Xie,X.J Mao,Z.J Yin,S.H Zhang,M.D Zhao,X.L Li

doi:10.3174/ajnr.a4223

Abstract

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.

Highlights

BACKGROUND AND PURPOSEThe virtual noncontrast images generated with iodine subtraction from dual-energy CTA images are expected to replace the true noncontrast images for radiation-dose reduction
Virtual noncontrast images are a reliable tool for diagnosing SAH, with the advantage of reducing the radiation dose
ABBREVIATIONS: TNC ⫽ true noncontrast; VNC ⫽ virtual noncontrast ubarachnoid hemorrhage is defined as the extravasation of blood into the spaces filled with CSF in the central nervous system.[1]

Summary

MATERIALS AND METHODS

Between May 2012 and January 2013, 55 patients with SAH and 29 patients who were suspected of having head disease but were diagnosed as not having SAH were included in the study. All patients underwent TNC brain CT with either additional head dual-energy CTA The causes for SAH included aneurysm (33 cases were diagnosed or suspected by CTA and 26 were confirmed by surgery or DSA), definite history of head injury (n ⫽ 6), vascular malformation (n ⫽ 1), and unclear causes (n ⫽ 15). In the control group (n ⫽ 29), there were 9 patients with essentially normal findings, 17 with lacunar infarction, 1 with subdural collection of fluid, 1 with a history of a cerebral hemorrhage operation 16 months previously, and 1 with a vascular malformation of the cerebellar hemisphere (but without SAH). For each dual-energy CTA examination, we reconstructed 2 image datasets with one at 140 kV and another at 100 kV with a 0.75-mm thickness/0.5-mm interval and transferred them to the workstation (syngo MultiModality; Siemens) for further processing. Statistical analyses were performed at the individual (patient) and lesion levels (each bleeding section representing a lesion)

RESULTS

CONCLUSIONS

Objective

DISCUSSION