Reliability, Reproducibility and Prognostic Accuracy of the Alberta Stroke Program Early CT Score on CT Perfusion and Non-Contrast CT in Hyperacute Stroke

Abstract

Background: Alberta Stroke Program Early CT Score (ASPECTS) assesses early ischemic change on non-contrast CT (NCCT). We hypothesised that assessing ASPECTS regions on CT Perfusion (CTP) rather than NCCT would improve inter-rater agreement and prognostic accuracy, particularly in patients presenting early after stroke onset. Methods: Ischemic stroke patients treated with intravenous alteplase from 2009 to 2014 at our institution were included in this study. Inter-rater agreement and prognostic accuracy of ASPECTS across modalities were analysed by the time between stroke onset and initial NCCT, dichotomized 1st quartile versus quartiles 2-4, referred to as epochs. ASPECTS was assessed by 2 independent raters, blinded to stroke onset time, with agreement determined by weighted kappa (κ_w). Prognostic accuracy for favourable outcome (modified Rankin Scale 0-2) was assessed using the receiver-operating characteristic analysis. Results: A total of 227 participants were included. There was significant time-by-CT modality interaction for ASPECTS, p < 0.0001. The inter-rater agreement of ASPECTS on NCCT significantly increased as onset to CT time increased (κ_w epoch 1 = 0.76 vs. κ_w epoch 2-4 = 0.89, p = 0.04), whereas agreement using CTP parameters was stable across epochs. Inter-rater agreement for CTP-ASPECTS was significantly higher than NCCT in early epoch: Tmax κ_w = 0.96, p = 0.002; cerebral blood volume (CBV) κ_w = 0.95, p = 0.003; cerebral blood flow (CBF) κ_w = 0.94, p = 0.006, with no differences in the later epochs. Prognostic accuracy of ASPECTS on NCCT in epoch 1 were (area under the ROC curves [AUC] = 0.52, 95% CI 0.48-0.56), CBV (AUC = 0.55, 95% CI 0.42-0.69, CBF (AUC = 0.58, 95% CI 0.46-0.71) and Tmax (AUC = 0.62, 95% CI 0.49-0.75), p = 0.46 between modalities. Conclusions: CTP can improve reliability when assessing the extent of ischemic changes, particularly in patients imaged early after stroke onset.

Noncontrast CT versus Perfusion‐Based Core Estimation in Large Vessel Occlusion: The Blood Pressure after Endovascular Stroke Therapy Study

“…For this reason, we grouped patients according to the presence of any early infarct signs (ASPECTS <10) and those with unfavorable ASPECTS scores (ASPECTS <6), which should improve the inter‐rater reliability in our cohort. Furthermore, the reliability between raters is thought to be poorest in the acute phase of stroke (eg, <3 or <6 hours), but may improve when the noncontrast CT scan is acquired later in the evolution of infarction, as in the present study. Additionally, we found a clear and significant trend in a lower ASPECTS among patients who present later in the course of their infarction, which further serves to validate these independent assessments.…”

“…Of 485 enrolled patients in the overall BEST study, 177 underwent CTP and were included in the analyses. The median age was 69 years (interquartile range [IQR]: 57-81), 87 were female (49%), with a median baseline NIHSS of 17 (IQR: [11][12][13][14][15][16][17][18][19][20]. Seventy-two patients (41%) presented in the early window.…”

Mechanical Thrombectomy for Acute Stroke: Early versus Late Time Window Outcomes

“…Early ischemic changes can be assessed on CT scan by the ASPECTS 20 . However, inter‐rater reliability, infarct core assessment, and prediction of good outcome utilizing CT‐ASPECTS are moderate 21 . Salvageable penumbra due to collaterals has been shown to predict outcome in patients undergoing MT 22 .…”

NCCT and CTA-based imaging protocol for endovascular treatment selection in late presenting or wake-up strokes

“…There is evidence to suggest that ASPECTS in NCCT may be safely used to select ischemic stroke patients for EVT,22 23 and it has been shown to have a good sensitivity in the definition of infarct core, especially in LPS 24. The analysis of early ischemic changes in NCCT has been associated with a moderate inter-rater reliability,25 but it increases significantly with time since stroke onset 26. Our strict clinical selection criteria for treatment in the WUS/LPS group—namely, the presence of moderate and severe deficits (NIHSS ≥12) and small infarct cores (ASPECTS ≥7)—aimed at maximizing the likelihood of the existence of a significant volume of salvageable tissue and, at the same time, reducing the risk of sICH after recanalization 27.…”