Is the detectability of the spot sign on CT angiography depending on slice thickness and reconstruction type?

The spot sign is a validated imaging marker widely used in CT angiography (CTA) to detect active bleeding and a higher risk of hematoma expansion in patients with intracerebral hemorrhage (ICH). The aim of this study was to investigate the detectability of spot signs on thin multiplanar projection reconstruction (MPR) images compared to thicker maximum intensity projection (MIP) images.

In this retrospective analysis, we assessed imaging data of 146 patients with primary hypertensive/microangiopathic ICH who received emergency non-contrast computed tomography (NCCT) and CTA. Two experienced radiologists, blinded to each other, evaluated images of thin (1 mm) MPR images and thick (3 mm) MIP images on the presence of spot signs and performed a consensus reading. Kappa tests were used for data comparison.

In total, spot signs were observed in 27 cases (=18.5 %) in both thin MPR and thick MIP slices. Detectability of the spot sign did not differ in 1 mm MPR images and 3 mm MIP images (Cohen's kappa, 1.0; p = 0.00). Also, when the readings of the two radiologists were analyzed separately, results for MPR and MIP slices were similar (MPR: Cohen's kappa, 0.81, p = 0.00; MIP: Cohen's kappa, 0.74; p = 0.00).

No significant difference in the detectability of the spot sign could be demonstrated when comparing 1 mm MPR images with 3 mm MIP images.