Characterizing the effects of noncontrast head CT reconstruction kernel and slice thickness parameters on the...

There are multiple commercially available, Food and Drug Administration (FDA)-cleared, artificial intelligence (AI)-based tools automating stroke evaluation in noncontrast computed tomography (NCCT). This study assessed the impact of variations in reconstruction kernel and slice thickness on two outputs of such a system: hypodense volume and Alberta Stroke Program Early CT Score (ASPECTS).

The NCCT series image data of 67 patients imaged with a CT stroke protocol were reconstructed with four kernels (H10s-smooth, H40s-medium, H60s-sharp, and H70h-very sharp) and three slice thicknesses (1.5, 3.0, and 5.0 mm) to create 1 reference condition (H40s/5.0 mm) and 11 nonreference conditions. The 12 reconstructions per patient were processed with a commercially available FDA-cleared software package that yields total hypodense volume (mL) and ASPECTS. A mixed-effect model was used to test the difference in hypodense volume, and an ordered logistic model was used to test the difference in e-ASPECTS.

Hypodense volume differences from the reference condition ranged from $-14.6$ to 1.1 mL and were significant for all nonreference kernels (H10s $p=0.025$ , H60s $p<0.001$ , and H70h $p<0.001$ ) and for thinner slices (1.5 mm $p<0.001$ and 3.0 mm $p=0.002$ ). e-ASPECTS was invariant to the nonreference kernels and slice thicknesses, with a mean difference ranging from $-0.1$ to 0.5. No significant differences were found for any kernel or slice thickness (all $p>0.05$ ).

Automated hypodense volume measured with a commercially available, FDA-cleared software package is substantially impacted by reconstruction kernel and slice thickness. Conversely, automated ASPECTS is invariant to these reconstruction parameters.