Technical limitations of dual-energy CT in neuroradiology: 30-month institutional experience and review of literature

Julien Dinkel, Omid Khalilzadeh, Catherine M Phan, Ajit H Goenka, Albert J Yoo, Joshua A Hirsch, Rajiv Gupta
Journal of Neurointerventional Surgery 2015, 7 (8): 596-602

BACKGROUND: Dual-energy CT (DECT) has been shown to be a useful modality in neuroradiology.

OBJECTIVE: To assess failure modes and limitations of DECT in different neuroimaging applications.

PATIENTS AND METHODS: Dual-source DECT scans were performed in 72 patients over 30 months to differentiate contrast agent staining or extravasation from intracranial hemorrhage (ICH) (n=40); to differentiate calcium from ICH (n=2); for metal-artifact reduction (n=5); and for angiographic assessment (n=25). A three-material decomposition algorithm was used to obtain virtual non-contrast (VNC) and iodine (or calcium) overlay images. Images were analyzed in consensus by two board-certified radiologists to determine the success of the algorithm and to assess confounding factors. Furthermore, a dilution experiment using cylinders containing defined heparinized swine blood, normal saline, and selected iodine concentrations was conducted to assess other possible confounding factors.

RESULTS: Dual-energy analysis was successful in 65 (90.2%) patients. However, the algorithm failed when images were affected by beam hardening (n=3, 4.2%), the presence of a fourth material (parenchymal calcification) (n=3, 4.2%), or motion (n=1, 1.4%). In the dilution experiment, a saturation effect was seen at high iodine concentrations (≥37 mg/ml). VNC and iodine overlay images were not reliable above this concentration, and beam-hardening artifacts were noted.

CONCLUSIONS: DECT material decomposition is usually successful in neuroradiology. However, it can only distinguish up to three preselected materials. A fourth material such as parenchymal calcium may confound the analysis. Artifacts such as beam hardening, metallic streak, or saturation effect can also impair material decomposition.

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