Framework to generate perfusion map from CT and CTA images in patients with acute ischemic stroke: A longitudinal and cross-sectional study

TL;DR

This work addresses the lack of access to 4D-CTP perfusion imaging in the hyperacute stroke window by introducing a CT/CTA-derived predicted perfusion map (PPM). It implements a VTrails-based pipeline that computes a voxelwise time-of-arrival map from digitally subtracted images, producing a unitless PPM that aligns with $T_{max}$ maps from 4D-CTP in 18 patients (mean correlation $r_s = 0.7893$, SD $=0.049$). In a large cross-sectional cohort of $n=2110$, PPM-derived signals map to expected infarct-related symptoms, showing associations with left/right motor, gaze, and language regions in GLM analyses. The results support using PPM as an early, imaging-efficient surrogate for perfusion to guide treatment decisions when 4D-CTP is unavailable.

Abstract

Stroke is a leading cause of disability and death. Effective treatment decisions require early and informative vascular imaging. 4D perfusion imaging is ideal but rarely available within the first hour after stroke, whereas plain CT and CTA usually are. Hence, we propose a framework to extract a predicted perfusion map (PPM) derived from CT and CTA images. In all eighteen patients, we found significantly high spatial similarity (with average Spearman's correlation = 0.7893) between our predicted perfusion map (PPM) and the T-max map derived from 4D-CTP. Voxelwise correlations between the PPM and National Institutes of Health Stroke Scale (NIHSS) subscores for L/R hand motor, gaze, and language on a large cohort of 2,110 subjects reliably mapped symptoms to expected infarct locations. Therefore our PPM could serve as an alternative for 4D perfusion imaging, if the latter is unavailable, to investigate blood perfusion in the first hours after hospital admission.

Figures (3)

• Figure 1: Preprocessing steps in VTrails and the estimation of the predicted perfusion map.
• Figure 2: 2A: Two typical examples of the PPM and the T-max map. Each row consists of three sub-figures, from left to right, the PPM, the T-max map, and the smoothed T-max map overlay on our PPM's smoothed version. In the predicted perfusion and T-max maps, dark red represents the area with a high risk of permanent brain damage, whereas blue represents the area with a low risk. The overlap map was created for illustrative purposes to highlight the overlap between two brain images. The units in the predicted perfusion and the T-max maps are dimensionless and seconds, respectively. Note that: L = left hemisphere. 2B: Spearman ranks plotted against age for all subjects. Each dot represents each subject's spatial similarity index (Spearman's correlation coefficient). The dotted line shows no significant correlation between age and the spatial similarity index between the two modalities.
• Figure 3: Four GLM models in which different NIHSS subscores were used as covariates. 3A: Left-hand motor score, 3B: Right-hand motor score, 3C: Best gaze score, 3D: Best language score. Each section shows the brain in sagittal, coronal and axial views with a mean intensity projection of the voxelwise significance scores for each GLM contrast (darker = more significant). Section 3A also shows the SPM design matrix with the tested contrast over the variable of interest. L = left hemisphere.