# Perfusion stability in acute stroke: An observational study exploiting repeated CTP imaging

## TL;DR

This study examines the consistency of CT perfusion imaging in acute stroke patients over time, finding that perfusion metrics remain stable despite variability in volume estimates.

## Contribution

The study provides empirical evidence on the temporal stability of perfusion imaging in acute stroke, challenging assumptions about linear infarct growth.

## Key findings

- Repeated CTP showed minimal systematic bias in infarct core and hypoperfusion volumes at the group level.
- Intensity-based metrics like Tmax and CBF demonstrated lower variability compared to volume estimates.
- Findings suggest perfusion imaging reflects hemodynamic state rather than time-dependent tissue progression.

## Abstract

CT perfusion (CTP) is widely used to assess infarct core in acute stroke, yet real-world data on its reproducibility and temporal dynamics are limited.

We retrospectively identified patients with repeated CTP scans. Core and hypoperfusion volumes were quantified using standard thresholds (CBF <30 %, Tmax >6 s). Clinical and imaging data were reviewed to identify cases with disruptive events. We analyzed scan-to-scan differences in core volume, hypoperfusion volume, ASPECTS, and intensity metrics, including median Tmax (in hypoperfusion), CBF, and NCCT HU (in core), using Bland-Altman analysis and assessed their association with time between scans.

Among 32 patients with repeated CTP (26 with repeated NCCT), three were excluded due to disruptive events. In the remaining 29 cases, mean scan-to-scan differences for infarct core volume (4.8 ± 19.6 mL), hypoperfusion volume (3.86 ± 39.1 mL), and ASPECTS (–0.4 ± 1.6) indicated minimal systematic bias at the group level but substantial variability. Correlation coefficients were high (r = 0.90, 0.93, and 0.70, respectively; all p < 0.0001), and no statistically significant paired differences or association with scan interval were observed. Intensity-based metrics likewise showed minimal bias with lower variability (Tmax –0.3 ± 1.07 s; CBF –3.11 ± 7.3 %; NCCT HU –3.0 ± 4.9 %), high correlations (Tmax r = 0.87, CBF r = 0.91, NCCT HU r = 0.69; all p < 0.02), and no association with time between scans.

Repeated CTP showed no systematic group-level scan-to-scan bias suggestive of infarct growth, while a substantial degree of variability was observed, with intensity-based metrics demonstrating lower variability than volume estimates. These findings support temporal consistency of perfusion-derived metrics at the group level and question the applicability of linear infarct growth rate (IGR) concepts to perfusion imaging, which primarily reflects a hemodynamic state rather than time-dependent tissue progression.