The butterfly effect: improving brain cone-beam CT image artifacts for stroke assessment using a novel dual-axis trajectory

Abstract

Background: Cone-beam computed tomography (CBCT) imaging of the brain can be performed in the angiography suite to support various neurovascular procedures. Relying on CBCT brain imaging solely, however, still lacks full diagnostic confidence due to the inferior image quality compared with CT and various imaging artifacts that persist even with modern CBCT.

Objective: To perform a detailed evaluation of image artifact improvement using a new CBCT protocol which implements a novel dual-axis 'butterfly' trajectory.

Methods: Our study included 94 scans from 47 patients who received CBCT imaging for assessment of either ischemia or hemorrhage during a neurovascular procedure. Both a traditional uni-axis 'circular' and novel dual-axis 'butterfly' protocol were performed on each patient (same-patient control). Each brain scan was divided into six regions and scored out of 3 based on six artifacts originating from various physics-based and patient-based sources.

Results: The dual-axis trajectory produces CBCT images with significantly fewer image artifacts than the traditional circular scan (whole brain average artifact score, AS: 0.20 vs 0.33), with the greatest improvement in bone beam hardening (AS: 0.13 vs 0.78) and cone-beam artifacts (AS: 0.04 vs 0.55).

Conclusions: Recent developments in CBCT imaging protocols have significantly improved image artifacts, which has improved diagnostic confidence for stroke and supports a direct-to-angiography suite transfer approach for patients with acute ischemic stroke.

Keywords: Angiography; Brain; CT; Stroke; Technology.

Figure 1

Cone-beam CT (CBCT) image artifact assessment scale: (1) beam hardening: streaks caused by dense bones (i.e., skull); (2) undersampling: view or ray aliasing, fine stripes radiating from the edges of dense structures; (3) inhomogeneity: darkness on one side of the brain vs the other; (4) cone-beam effect: dark bands at top and/or bottom of image; (5) patient motion: misregistration artifacts, blurry image or appearance of shading or streaking. (6) metallic artifacts: severe streaking artifacts radiating from a metallic object (i.e., dental fillings, surgical clips, or stents).

Figure 2

Average artifact scores for 10 s circular versus 8 s butterfly scans for the whole brain (A) and specific brain regions (B–D). Left-side and right-side scores for each region were not significantly different and were therefore averaged together.

Figure 3

Three patient examples (A–C) demonstrated improved cone-beam (upper yellow square) and beam hardening (lower yellow square) for circular (left) versus dual axis ‘butterfly’ (right) scans.