The accuracy of ischemic core perfusion thresholds varies according to time to recanalization in stroke patients treated with mechanical thrombectomy: A comprehensive whole-brain computed tomography perfusion study

Abstract

Computed tomography perfusion (CTP) allows the estimation of pretreatment ischemic core after acute ischemic stroke. However, CTP-derived ischemic core may overestimate final infarct volume. We aimed to evaluate the accuracy of CTP-derived ischemic core for the prediction of final infarct volume according to time from stroke onset to recanalization in 104 patients achieving complete recanalization after mechanical thrombectomy who had a pretreatment CTP and a 24-h follow-up MRI-DWI. A range of CTP thresholds was explored in perfusion maps at constant increments for ischemic core calculation. Time to recanalization modified significantly the association between ischemic core and DWI lesion in a non-linear fashion (p-interaction = 0.018). Patients with recanalization before 4.5 h had significantly lower intraclass correlation coefficient (ICC) values between CTP-predicted ischemic core and DWI lesion (n = 54; best threshold relative cerebral blood flow (rCBF) < 25%, ICC = 0.673, 95% CI = 0.495-0.797) than those with later recanalization (n = 50; best threshold rCBF < 30%, ICC = 0.887, 95% CI = 0.811-0.935, p = 0.013), as well as poorer spatial lesion agreement. The significance of the associations between CTP-derived ischemic core and clinical outcome at 90 days was lost in patients recanalized before 4.5 h. CTP-derived ischemic core must be interpreted with caution given its dependency on time to recanalization, primarily in patients with higher chances of early recanalization.

Keywords: Computed tomography perfusion; ischemic core; ischemic stroke; recanalization; thrombectomy.

Figure 1.

Intraclass correlation coefficient (ICC) and 95% confidence intervals (95%CI) between volume of ischemic core defined on CT perfusion and final infarct volume defined on DWI for the set of relative (a) and absolute (b) thresholds analyzed on cerebral blood flow (CBF) and cerebral blood volume (CBV) maps.

Figure 2.

Individual best threshold (patient level) depending on the time from symptom onset to recanalization. The best fitting (highest r²) was observed in cubic regression models and the plateau was reached for every threshold in the range between 240 and 420 min: rCBF (a, 240–350 min), rCBV (b, 280–420 min), aCBF (c, 250–370 min) and aCBV (d, 260–380 min).

Figure 3.

Intraclass correlation coefficient (ICC) and 95% confidence intervals (95% CI) between the volume of ischemic core defined on CT perfusion and final infarct volume defined on DWI depending on time from symptom onset to recanalization (complete recanalization before or after 4.5 h from symptom onset). Higher ICC values were found in patients with later recanalization for every analyzed threshold: rCBF (a), rCBV (b), aCBF (c) and aCBV (d).

Figure 4.

Volume difference between DWI final infarct and CTP ischemic core defined with a set of relative CBF thresholds. *p < 0.01 and **p < 0.005 for the comparison of volume differences according to recanalization groups (<4.5 h vs. ≥ 4.5 h).

Figure 5.

Odds ratios (OR) and 95% confidence intervals (95%CI) of the association between ischemic core defined with different absolute and relative thresholds and functional outcome. The significant associations are shown in bold (p < 0.05). A range of absolute and relative thresholds are significantly associated with functional outcome on the whole cohort of patients, fewer in the subset of patients recanalized after 4.5 h from symptom onset but no associations were found in those recanalized earlier.