Shamir Rai BSC, Presenter: Nothing to Disclose

Chesnal Dey Arepalli MD, Abstract Co-Author: Nothing to Disclose

Patrick McLaughlin FFR(RCSI), Abstract Co-Author: Nothing to Disclose

Rita Chiu MD, Abstract Co-Author: Nothing to Disclose

Savvas Nicolaou MD, Abstract Co-Author: Nothing to Disclose

Virtual non-contrast (VNC) images are derived from dual energy (DE) contrast enhanced CT scans. The purpose of this study is to evaluate the whether the VNC images derived from DE head CT angiography (CTA) are of diagnostic quality in patients presenting with acute stroke symptoms.

A total of 50 consecutive patients with acute stroke symptoms were retrospectively identified between Dec. 1, 2013 and Feb. 5, 2014 from a single institution’s emergency department. All the patients underwent both a non-contrast CT (NCCT) and DE head CTA at 100 kv and 140 kv. Quantitative analysis of the NCCT and the generated VNC Head images were performed using circular region of interests (ROIs) with an area of 22.8mm2 centered on both caudate heads (grey matter), internal capsules, corona radiata and centrum semiovale. The SNR and CNR were calculated. The CTDvol (mGy), DLP (mGycm) were recorded. The effective dose was calculated using the established ratio of 0.0021. Two radiologists, with combined 20 years of experience were blinded and retrospectively interpreted the VNC CT images in comparison to the routine NCCT, assessing for pathology and diagnostic acceptability. The VNC CT scans were graded 1 (non-diagnostic), 2 (decreased image quality, unlikely to be diagnostic), 3 (decreased image quality with potential to be diagnostic), 4 (decreased image quality but diagnostic), 5 (diagnostic study).

The median subjective score for assessment of the virtual non-contrast study for reader 1 and reader 2 were 4±1 and 4±0.75. The effective dose in the DE CTA scans was significantly lower than in the non-contrast CT heads (1.652 msv±0.1986 and 1.955 msv ±0.4843 respectively, (p <0.0001)). The quantitative measures of image quality demonstrated no significant difference in SNR of grey matter (p=0.0581). However, there was a significant difference noted between the CNR and SNR of the white matter between the virtual non-contrast and non-contrast heads, in favor of the non-contrast head (p < 0.0001).

VNC CT scans were determined to be diagnostic with reduced image quality. This has the potential to replace routine non-contrast studies.

Optimized head VNC CT protocols are currently in development. With enhancement in VNC CT algorithms, stroke assessment could be limited to a single DE CTA thereby reducing radiation exposure to the patient.

Rai, S, Arepalli, C, McLaughlin, P, Chiu, R, Nicolaou, S, Derivation of Virtual Non-contrast CT Head Images from Dual Energy Head CT Angiography Studies: Potential Feasibility of Replacing Routine Non-contrast Head CT with Virtual Non-contrast CT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14018828.html