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Key Points

Question听 In patients with proximal anterior circulation occlusion stroke presenting in the extended window, are rates of favorable outcomes at 90 days comparable in the patients selected for thrombectomy with noncontrast computed tomography vs patients selected with computed tomography perfusion or magnetic resonance imaging?

Findings听 In a multicenter cohort of 1604 patients in the extended window with large-vessel occlusion, patients selected by noncontrast computed tomography had comparable clinical and safety outcomes with patients selected by computed tomography perfusion or magnetic resonance imaging.

Meaning听 These findings suggest noncontrast computed tomography alone may be used as an alternative to advanced imaging in selecting patients with late-presenting large-vessel occlusion for mechanical thrombectomy.

Importance听 Advanced imaging for patient selection in mechanical thrombectomy is not widely available.

Objective听 To compare the clinical outcomes of patients selected for mechanical thrombectomy by noncontrast computed tomography (CT) vs those selected by computed tomography perfusion (CTP) or magnetic resonance imaging (MRI) in the extended time window.

Design, Setting, and Participants听 This multinational cohort study included consecutive patients with proximal anterior circulation occlusion stroke presenting within 6 to 24 hours of time last seen well from January 2014 to December 2020. This study was conducted at 15 sites across 5 countries in Europe and North America. The duration of follow-up was 90 days from stroke onset.

Exposures听 Computed tomography with Alberta Stroke Program Early CT Score, CTP, or MRI.

Main Outcomes and Measures听 The primary end point was the distribution of modified Rankin Scale (mRS) scores at 90 days (ordinal shift). Secondary outcomes included the rates of 90-day functional independence (mRS scores of 0-2), symptomatic intracranial hemorrhage, and 90-day mortality.

Results听 Of 2304 patients screened for eligibility, 1604 patients were included, with a median (IQR) age of 70 (59-80) years; 848 (52.9%) were women. A total of 534 patients were selected to undergo mechanical thrombectomy by CT, 752 by CTP, and 318 by MRI. After adjustment of confounders, there was no difference in 90-day ordinal mRS shift between patients selected by CT vs CTP (adjusted odds ratio [aOR], 0.95 [95% CI, 0.77-1.17]; P鈥�=鈥�.64) or CT vs MRI (aOR, 0.95 [95% CI, 0.8-1.13]; P鈥�=鈥�.55). The rates of 90-day functional independence (mRS scores 0-2 vs 3-6) were similar between patients selected by CT vs CTP (aOR, 0.90 [95% CI, 0.7-1.16]; P鈥�=鈥�.42) but lower in patients selected by MRI than CT (aOR, 0.79 [95% CI, 0.64-0.98]; P鈥�=鈥�.03). Successful reperfusion was more common in the CT and CTP groups compared with the MRI group (474 [88.9%] and 670 [89.5%] vs 250 [78.9%]; P鈥�&濒迟;鈥�.001). No significant differences in symptomatic intracranial hemorrhage (CT, 42 [8.1%]; CTP, 43 [5.8%]; MRI, 15 [4.7%]; P鈥�=鈥�.11) or 90-day mortality (CT, 125 [23.4%]; CTP, 159 [21.1%]; MRI, 62 [19.5%]; P鈥�=鈥�.38) were observed.

Conclusions and Relevance听 In patients undergoing proximal anterior circulation mechanical thrombectomy in the extended time window, there were no significant differences in the clinical outcomes of patients selected with noncontrast CT compared with those selected with CTP or MRI. These findings have the potential to widen the indication for treating patients in the extended window using a simpler and more widespread noncontrast CT鈥搊nly paradigm.

The DAWN and DEFUSE 3 trials were 2 landmark stroke trials that changed the paradigm of care for patients with large-vessel occlusion stroke who present within 6 to 24 hours from symptom onset (defined as time last seen well [TLSW]), opening the indications of endovascular treatment for this extended time window.^1,2 Advanced imaging with magnetic resonance imaging (MRI) or computed tomography perfusion (CTP) demonstrating clinical or tissue mismatch were the mainstay of triage entry for these 2 studies and are currently recommended in the American Stroke Association and European Stroke Organization guidelines for the selection of these patients.^3,4

Access to acute MRI or CTP is not readily available or performed across many stroke centers in the US⁵ or globally.^6,7 A correlation between the Alberta Stroke Program Early CT Score (ASPECTS) on noncontrast CT (NCCT) and CTP has been demonstrated in several studies,⁸ with CT being potentially more sensitive than relative cerebral blood flow for irreversible injury in the later time window.⁹ However, there is known interrater variability in the interpretation of ASPECTS.¹⁰

An important notion is to distinguish triage performed to identify patients who can benefit from treatment (the appropriate goal of imaging) and triage performed to identify patients who may have better outcomes than others (an inappropriate goal in the context of individual medical care). Better clinical outcomes can be observed among patients selected on optimal CTP parameters, but this selection may improve overall statistics at the cost of denying care to many patients who could benefit.^9,11 Moreover, CTP is vulnerable to infarct core overestimation, which may inappropriately exclude patients from treatment.^11,12 It is not well established whether advanced neuroimaging is indispensable or if NCCT may be sufficient for identifying patients with large-vessel occlusion likely to benefit from endovascular thrombectomy who present in the extended window.

The objective of this study was to evaluate clinical outcomes in patients with proximal anterior circulation occlusion stroke presenting in the extended time window who were selected by NCCT and CT angiography, compared with patients selected via advanced imaging with CTP or MRI. The prespecified hypothesis was that there were no significant differences in the outcomes of patients selected for thrombectomy using NCCT compared with patients selected with advanced imaging with CTP or MRI.

Local institutional review board or ethics committee approval was obtained from all sites. Written informed consent was waived because of the retrospective nature of this study and because the research was considered no more than minimal risk. This was an investigator-initiated study. The study funder had no role in the study design, analysis, management, or writing of this report. The corresponding author (T.N.N.) and lead statistician (M.M.Q.) had access to all data in the study. Anonymized data are available on reasonable request to the corresponding author.

The CT for Late Endovascular Reperfusion (CLEAR) study () was a multicenter cohort study of consecutive patients with proximal anterior circulation stroke undergoing mechanical thrombectomy (MT) in the extended time window, defined as a period from TLSW to arterial puncture between 6 to 24 hours. Patients were recruited at 15 sites across 5 countries in Europe and North America between January 1, 2014, and December 31, 2020. Pretreatment imaging protocols are listed in eTable 1 in the Supplement. A description of the change in protocol imaging selection across the study period is reported in eTable 2 in the Supplement. ASPECTS was site adjudicated based on the last NCCT image before thrombectomy.

Quiz Ref IDThe study cohort for this analysis included consecutive patients meeting the following criteria: baseline National Institutes of Health Stroke Scale (NIHSS) scores of 6 or more, occlusion of the internal carotid artery or proximal middle cerebral artery (M1/M2 segments), prestroke modified Rankin Scale (mRS) scores of 0 to 2, and TLSW to treatment of 6 to 24 hours. These criteria mirror the broader range of inclusion of patients encompassing both the DAWN and DEFUSE3 trials, with the addition of M2 occlusions. A subset of patients in the CLEAR study were included in the DAWN study (2 sites, up to 45 patients) or the DEFUSE-3 study (3 sites, 18 patients).

The CLEAR study cohort was categorized according to the imaging modality used to select the patient for endovascular therapy: NCCT with CT angiography, CTP, or MRI. If both NCCT and CTP were used, the patient was classified as selected by CTP. If both CTP and MRI were used, the patient was classified as selected by MRI. Patients presenting with large-vessel occlusion stroke presenting in an early time window (0 to <6 hours from TLSW), prestroke baseline mRS scores of 3 to 5, or large-vessel occlusion of the posterior circulation were excluded (Figure 1).

Quiz Ref IDThe primary end point was the distribution of mRS score at 90 days (ordinal shift analysis). The secondary clinical outcomes included the rate of 90-day functional independence (mRS scores of 0-2) as well as workflow metrics including TLSW to arterial puncture, time from door to puncture, and postprocedure successful reperfusion (defined as grade 2b or 3 [>50% of the affected territory] on the modified Treatment in Cerebral Infarction [mTICI] scale). A standard approach to mRS assessment was used (eTable 3 in the Supplement). The safety end points included postprocedural symptomatic intracranial hemorrhage (as defined in the European Cooperative Acute Stroke Study III: intracranial hemorrhage that is associated with deterioration in NIHSS of 4 or more points and the main reason for neurological deterioration) and 90-day mortality.¹³

For the continuous variables, we tested the normal distribution of the data with the Shapiro-Wilk test. As the normality tests showed significant results, the data were deemed nonnormal, and hence, continuous data are presented as median (IQR) values. Nonparametric Kruskal-Wallis tests were used to assess for differences in continuous variables by imaging modality. For categorical variables, 蠂² tests (or Fisher exact tests, when appropriate) were used to examine differences in the distribution by imaging modality.

For the outcome of functional independence at 90 days, a logistic regression model was used to estimate the likelihood of functional independence (mRS scores of 0-2). Clustering by sites was accounted for using a generalized estimating equation. The model was fitted using PROC GENMOD in SAS version 9.4 (SAS Institute), with the specifications of logit link function and binomial distribution. An independent correlation structure was assumed for the within-site clustering of patients. The independent correlation structure had the smallest quasilikelihood independence criterion value. Crude and adjusted odds ratios (ORs) with 95% CIs were obtained for each parameter of interest. The following characteristics were selected as covariates of interest a priori: age, NIHSS score at baseline, sex, baseline mRS scores, hypertension, atrial fibrillation, diabetes, transfer status, intravenous thrombolysis, baseline ASPECTS, site of occlusion, and TLSW to arterial puncture.

For the distribution of 90-day mRS scores (ordinal mRS shift), a multinomial ordinal logistic regression was applied to estimate a 1-point shift toward the lowered ordered value, indicating a better outcome. The model was fitted using PROC GENMOD in SAS version 9.4 with the cumulative logit link function and multinomial distribution. An independent correlation structure was assumed for the within-site clustering of patients.

All statistical computations were performed on SAS version 9.4. All tests were 2-sided, and a P value less than .05 was considered significant.

There were 2304 patients with internal carotid artery or proximal middle cerebral artery occlusions recruited in the CLEAR study, of whom 1768 had a premorbid mRS score of 0 to 2. Of these, 1604 patients had baseline NIHSS scores of 6 or more and descriptive data of the key variables, constituting the primary analysis cohort (median [IQR] age, 70 [59-80] years; 848 women [52.9%]; Figure 1). Patients were selected for MT on the basis of the following modalities: NCCT with angiography (n鈥�=鈥�534), CTP (n鈥�=鈥�752), and MRI (n鈥�=鈥�318). Computed tomography angiography was performed in 1303 of 1334 patients (98%), whereas MRI and magnetic resonance angiography were the primary modalities for large-vessel occlusion selection in 270 patients. Data variables are summarized in Table 1.

There was no difference in age, sex, baseline mRS score, and diabetes across the 3 modalities. Median (IQR) baseline NIHSS scores were marginally higher in the NCCT-selected group than the CTP-selected and MRI-selected groups, respectively (NCCT, 17 [13-21]; CTP, 16 [11-19]; MRI, 16 [12-21]; P鈥�&濒迟;鈥�.001). Quiz Ref IDPatients selected by NCCT had higher rates of hypertension (NCCT, 385 [72.1%]; CTP, 544 [72.3%]; MRI, 205 [64.5%]; P鈥�=鈥�.02) and atrial fibrillation (NCCT, 191 [35.8%]; CTP, 219 [29.1%]; MRI, 117 [36.8%]; P鈥�=鈥�.01) and more frequently presented as transfers (NCCT, 362 [67.8%]; CTP, 422 [56.1%]; MRI, 222 [69.8%]; P鈥�<鈥�.001) (Table 1). Intravenous thrombolysis was more frequent in patients selected by MRI (136 [42.8%]), followed by NCCT (126 [23.6%]) and CTP (91 [12.1%]; P鈥�&濒迟;鈥�.001).

The median (IQR) ASPECTS score was 8 (7-9) across the 3 groups. Internal carotid artery occlusion was more common in the MRI and NCCT groups compared with the CTP group (103 [32.4%] vs 161 [30.2%] vs 162 [21.5%], respectively; P鈥�&濒迟;鈥�.001). The M2 occlusions were more common in the CTP than CT and MRI groups (160 [21.3%] vs 73 [13.7%] vs 39 [12.3%], respectively; P鈥�&濒迟;鈥�.001).

Time last seen well to puncture was shorter in patients who underwent NCCT selection (median [IQR], 10.4 [7.8-14.4] hours) compared with CTP selection (median [IQR], 11.3 [8.4-15.2] hours) and MRI selection (median [IQR], 12.4 [9.4-15.4] hours; P鈥�&濒迟;鈥�.001). In a subgroup analysis of patients who presented directly to the endovascular center (n鈥�=鈥�598) with available door arrival time (n鈥�=鈥�484), there were shorter door-to-puncture times for NCCT (median [IQR],76 [50-107] minutes) compared with CTP (median [IQR], 93 [72-118] minutes) and MRI (median [IQR], 98 [78-135] minutes; P鈥�&濒迟;鈥�.001).

Successful reperfusion (mTICI scores 2b-3) was more common in the NCCT group (474 [88.9%]) and CTP group (670 [89.5%]) compared with the MRI group (250 [78.9%]; P鈥�&濒迟;鈥�.001). General anesthesia was more commonly used in the NCCT group (133 [25.5%]) than the CTP group (128 [17.5%]) and MRI group (54 [17.0%]; P鈥�=鈥�.001).

Discharge NIHSS scores were lower among patients selected with NCCT (median [IQR], 7 [3-17]) and CTP (median [IQR], 6 [2-14]) than those undergoing MRI (median [IQR], 11 [3-19]; P鈥�&濒迟;鈥�.001). Overall, symptomatic intracranial hemorrhage was present in 6.3% (n鈥�=鈥�100) of this cohort and was similar between the 3 imaging modalities (NCCT, 42 [8.1%]; CTP, 43 [5.8%]; MRI, 15 [4.7%]; P鈥�=鈥�.11). In addition, mortality at 90 days was similar between the 3 groups (NCCT, 125 [23.4%]; CTP, 159 [21.1%]; MRI, 62 [19.5%]; P鈥�=鈥�.38) (Table 1).

A 90-day mRS score of 0 to 2 was observed in 220 patients selected by NCCT (41.2%), 333 selected by CTP (44.3%), and 123 selected by MRI (38.7%) (Table 1). The crude and adjusted odds of independent outcomes (mRS score 0-2) by imaging modality, baseline characteristics, and metrics are presented in Table 2. Of the 1604 patients in the primary cohort, complete information for multivariate analysis was available in 1530 patients (NCCT, 480; CTP, 735; MRI, 315). In the multivariable analysis, after adjusting for these factors, odds of functional independence at 90 days (mRS scores, 0-2) was similar between patients selected by CTP and NCCT (adjusted OR [aOR], 0.90 [95% CI, 0.70-1.16]; P鈥�=鈥�.42). However, there were lower odds of independent outcomes for patients selected by MRI than those selected by NCCT (aOR, 0.79 [95% CI, 0.63-0.98]; P鈥�=鈥�.03). Among other factors, age, baseline NIHSS score, baseline mRS score, diabetes, transfer status, and baseline ASPECTS were associated with independent outcomes at 90 days (Table 2).

In the multivariable analysis, after adjusting for the mentioned factors, there was no difference in 90-day ordinal mRS shift between patients selected by NCCT vs CTP (aOR, 0.95 [95% CI, 0.77-1.17]; P鈥�=鈥�.64) or patients selected by NCCT vs MRI (aOR, 0.95 [95% CI, 0.80-1.13]; P鈥�=鈥�.55; Table 3; Figure 2). On multivariate analysis, increasing age (OR, 0.97 [95% CI, 0.96-0.99]; P鈥�<鈥�.001), higher baseline NIHSS scores (OR, 0.91 [95% CI, 0.89-0.92]; P鈥�<鈥�.001), higher baseline mRS scores (ORs: score of 1, 0.68 [95% CI, 0.54-0.86]; P鈥�=鈥�.001; score of 2, 0.48 [95% CI, 0.34-0.65]; P鈥�<鈥�.001), diabetes (on univariate analysis only; OR, 0.77 [95% CI, 0.62-0.96]; P鈥�=鈥�.02), internal carotid artery occlusion (OR, 0.83 [95% CI, 0.69-1.0]; P鈥�=鈥�.049), and having been transferred (OR, 0.79 [95% CI, 0.67-0.92]; P鈥�=鈥�.002) were associated with decreased odds of a 1-point shift toward the lowered ordered value, indicating a worse prognosis. Conversely, an increasing ASPECTS score (OR, 1.18 [95% CI, 1.13-1.24]; P鈥�<鈥�.001) was associated with increased odds of a 1-point shift, indicating an improved prognosis.

In a sensitivity analysis confined to patients who arrived locally and were not transferred (n鈥�=鈥�598), odds of functional independence at 90 days (mRS scores, 0-2) were similar on the multivariate analysis between patients selected by NCCT vs CTP (aOR, 0.71 [95% CI, 0.42-1.21]; P鈥�=鈥�.21), and patients selected by NCCT vs MRI (aOR, 0.69 [95% CI, 0.36-1.33]; P鈥�=鈥�.27; eTable 4 in the Supplement). Similarly, there was no difference in ordinal mRS shifts between patients selected by NCCT vs CTP (aOR, 0.74 [95% CI, 0.46-1.18]; P鈥�=鈥�.21) or patients selected by NCCT vs MRI (aOR, 0.78 [95% CI, 0.54-1.12]; P鈥�=鈥�.18) for those arriving locally.

In a sensitivity analysis on the association of time as a continuous variable from 2014 to 2020 with available data in 1425 patients, odds of a good outcome at 90 days (mRS scores 0-2) were no different between patients selected by NCCT vs CTP (aOR, 0.88 [95% CI, 0.67-1.15]; P鈥�=鈥�.35) and patients selected by NCCT vs MRI (aOR, 0.85 [95% CI, 0.64-1.14]; P鈥�=鈥�.29). Similarly, no significant differences were observed in ordinal mRS shift between patients selected by NCCT vs CTP (aOR, 0.92 [95% CI, 0.75-1.12]; P鈥�=鈥�.39) and those selected by NCCT vs MRI (aOR, 1.01 [95% CI, 0.85-1.21]; P鈥�=鈥�.92).

In a separate analysis, patients who were reperfused (mTICI 2b/3) had better odds of good clinical outcome compared with those who were not reperfused (mTICI 0, 1, or 2a) (aOR, 6.31 [95% CI, 4.45-8.95]; P鈥�&濒迟;鈥�.001). Of the 3 imaging modalities, the odds of a favorable outcome with reperfusion were highest in patients selected with MRI (aOR, 8.9 [95% CI, 6.7-11.9]; P鈥�<鈥�.001) followed by NCCT (aOR, 6.1 [95% CI, 2.2-16.5]; P鈥�<鈥�.001) and CTP (aOR, 5.1 [95% CI, 2.9-9.2]; P鈥�<鈥�.001; eTable 5 in the Supplement).

The CLEAR study demonstrated that in patients with stroke due to occlusion of the internal carotid or proximal middle cerebral artery (M1/M2 segments) presenting within 6 to 24 hours from TLSW and undergoing mechanical thrombectomy, favorable functional outcomes defined by both ordinal shift and dichotomized analysis of the mRS scores at 90 days were equivalent for patients selected by NCCT compared with patients selected by CTP or MRI. The rate of functional independence at 90 days among patients in the CLEAR study who were treated using NCCT was comparable with that of patients treated in the DAWN and DEFUSE-3 trials. There was no evidence of a greater risk of symptomatic hemorrhage or death according to the imaging modality used in patient selection. Quiz Ref IDNotably, door-to-puncture time, a workflow metric of stroke care,¹⁴ was shorter in patients selected by NCCT than CTP and MRI. To our knowledge, this is the largest multicenter study to date assessing selection of patients in the extended time window with NCCT compared with CTP or MRI.

These findings have the potential to support the adoption of a more pragmatic selection of patients for MT in the extended window, simply based on NCCT and proximal anterior circulation large-vessel occlusion. Quiz Ref IDThis selection could occur as an alternative to CTP-based or MRI-based selection paradigms, the second of which are not widely available across the globe,⁷ associated with potential treatment delays,^15,16 cost, contrast load, radiation exposure, and resource use. On the other hand, it is important to note that management of patients in the NCCT group in the CLEAR study were not aligned with the American Stroke Association or European Stroke Organization guidelines.

In the extended time window, the concept of clinical core mismatch was used to guide patient selection in the DAWN trial,¹ with additional and controversial criteria¹⁷ for study entry based on age and core infarct volume. The DEFUSE-3 trial relied on perfusion imaging assessment for the qualification of mismatch and study eligibility.² While our study did not prespecify study entry based on clinical-core mismatch, NCCT-based selection in this analysis led to equivalent outcomes compared with patients selected by CTP or MRI. Two factors may explain the equivalence of outcome by the different imaging modality selection. First, prior reports demonstrated a moderate correlation between NCCT ASPECTS and CTP core volumes,^8,18 with a stronger correlation in patients in the extended (6-24鈥揾our) vs early (0-6鈥揾our) time window.¹⁹ Second, among similar ASPECTS levels, the presence of clinical core mismatch does not decline over time, even when presenting in the extended time window.²⁰

The rates of 90-day functional independence in our study were numerically but not significantly lower in the NCCT compared with the CTP group (41.2% vs 44.3%; P鈥�=鈥�.21). This apparent difference disappeared on multivariate analysis, which is likely explained by higher NIHSS scores, transfers, and internal carotid artery occlusions in the NCCT compared with the CTP group. On multivariate dichotomized mRS score analysis, patients selected by NCCT had higher rates of 90-day functional independence compared with patients selected by MRI (41.2% vs 38.7%; aOR, 0.79 [95% CI, 0.63-0.98]; P鈥�=鈥�.03), which was likely explained by a higher rate of reperfusion in the NCCT compared with the MRI group (88.9% vs 78.9%; P鈥�&濒迟;鈥�.001). In a reperfusion sensitivity analysis, patients who achieved reperfusion had greater odds of good outcomes than patients who were not reperfused. There was a higher likelihood of functional independence in patients who were reperfused and selected by MRI compared with CT or CTP.

The findings in our study are concordant with other studies. The Heidelberg group evaluated thrombectomy of patients in the extended window using Highly Effective Reperfusion Using Multiple Endovascular Devices (HERMES)鈥搇ike criteria and found equivalent outcomes in patients treated in the extended window with an ASPECTS-based selection paradigm.²¹ The Trevo multicenter registry evaluated the association of imaging modality with thrombectomy outcomes in both the early and extended windows.⁷ Computed tomography perfusion did not confer better 90-day outcomes in the extended window than NCCT. In a 2-site analysis of patients in the extended time window in Switzerland, MT was effective in the presence of a clinical-ASPECTS mismatch as defined by the DAWN study criteria but not effective in its absence.²² Another study suggested that NCCT-ASPECTS鈥揵ased selection paradigms for late MT have similar 90-day outcomes as the DAWN and DEFUSE-3 studies.²³ In a network of stroke centers in Houston, Texas, hospitals with NCCT as the initial imaging choice were more likely to perform MT than hospitals with NCCT and CTP as the primary approach, without any difference in clinical outcomes.²⁴

While this study did not specify patient inclusion based on ASPECTS thresholds, most sites used ASPECTS of 6 or more to treat patients in the extended window (eTable 1 in the Supplement). The median (IQR) NCCT ASPECTS of 8 (7-9) in this study reflects that most patients selected for MT had high NCCT ASPECTS. As the IQR for ASPECTS score ranged from 7 to 9 in this cohort, this suggests an ASPECTS of 7 or more may be considered if one were to select patients with NCCT for thrombectomy in the extended window. Whether one should select patients with lower NCCT ASPECTS is unknown, because these patients were not well represented in our study.

In the absence of data on the number of patients denied thrombectomy and their outcomes, we could only compare aggregate results of patients who were ultimately treated. While the end results were similar, this does not mean that the same patients were selected in or out, and all triage methods may be inaccurate. Outside randomized trials, this may be impossible to determine. Two randomized trials are in progress to provide more definitive evidence of a simplified imaging protocol in the extended window: the MR CLEAN LATE trial (Endovascular Treatment of Acute Ischemic Stroke in the Netherlands for Late Arrivals; ) and the RESILIENT-Extended trial (Randomization of Endovascular Treatment in Acute Ischemic Stroke in the Extended Time Window; ).

The strength of our study was the large number of patients across multiple centers and countries. To decrease bias, we excluded patients with missing data to conduct a complete case analysis with the final cohort of 1530 patients.

Our study was limited to patients with baseline mRS scores of 0 to 2, occlusion of the internal carotid or proximal middle cerebral artery (M1/M2 segments), with median (IQR) ASPECTS of 8 (7-9). Hence our study鈥檚 findings cannot be applied to other patients.

The retrospective design of our study may have led to selection bias, thereby limiting the generalization of results. While we encouraged enrollment of consecutive patients in the study period, this was not monitored. There was no independent imaging core laboratory in this study. Differences in imaging interpretation, selection paradigms, and automatic CTP processing software across the multiple centers could introduce bias. We did not measure core volumes across the patients selected by CTP or MRI, other than by their CT or diffusion-weighted imaging鈥揳djudicated ASPECTS scores. Collateral score was not measured; most sites reported that CT angiography collaterals were not routinely used in their imaging triage (eTable 1 in the Supplement). Thus, we could only compare various imaging modalities without knowing the explicit criteria used to select patients. In this analysis, we have data for patients treated; we do not know the proportions of patients who were excluded by the triage process, nor could we compare treatment effect sizes, given the lack of patients who were medically managed.

In patients with large-vessel occlusion of the internal carotid artery and proximal middle cerebral artery (M1/M2 segments) undergoing MT in the time window of 6 to 24 hours after TLSW, selection by NCCT yielded no significant difference in clinical and safety outcomes compared with advanced imaging with CTP or MRI. These findings have the potential to widen the indication for treating patients in the extended window using the simpler, less costly, and easier to implement NCCT imaging as an alternative to CTP or MRI.

Accepted for Publication: September 17, 2021.

Published Online: November 8, 2021. doi:10.1001/jamaneurol.2021.4082

Corresponding Authors: Thanh N. Nguyen, MD, Department of Neurology and Radiology, Boston Medical Center, 725 Albany St, Neurology 7th Floor, Boston, MA 02118 (thanh.nguyen@bmc.org); Raul G. Nogueira, MD, Department of Neurology, Grady Memorial Hospital, Emory University School of Medicine, 80 Jesse Hill Jr Drive SE, Atlanta, GA 30303 (raul.g.nogueira@emory.edu).

Correction: This article was corrected on January 10, 2022, to fix an error in the byline.

Open Access: This is an open access article distributed under the terms of the CC-BY-NC-ND License. 漏 2021 Nguyen TN et al. 榴莲视频 Neurology.

Author Contributions: Drs Nguyen and Qureshi had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Nguyen, Abdalkader, Qureshi, Sheth, Siegler, Castonguay, Jovin, Zaidat, Nogueira.

Acquisition, analysis, or interpretation of data: Nguyen, Nagel, Qureshi, Ribo, Caparros, Haussen, Mohammaden, Sheth, Ortega-Gutierrez, Siegler, Zaidi, Oliv茅-Gadea, Henon, M枚hlenbruch, Castonguay, Nannoni, Kaesmacher, Puri, Seker, Farooqui, Salazar-Marioni, Kuhn, Kaliaev, Farzin, Boisseau, Masoud, Lopez, Rana, Kareem, Sathya, Klein, Kassem, Ringleb, Cordonnier, Gralla, Fischer, Michel, Raymond, Zaidat, Nogueira.

Drafting of the manuscript: Nguyen, Qureshi, Sheth, Castonguay, Farooqui, Salazar-Marioni, Kaliaev, Farzin, Kareem, Klein.

Critical revision of the manuscript for important intellectual content: Abdalkader, Nagel, Ribo, Caparros, Haussen, Mohammaden, Sheth, Ortega-Gutierrez, Siegler, Zaidi, Oliv茅-Gadea, Henon, M枚hlenbruch, Castonguay, Nannoni, Kaesmacher, Puri, Seker, Kuhn, Boisseau, Masoud, Lopez, Rana, Sathya, Kassem, Ringleb, Cordonnier, Gralla, Fischer, Michel, Jovin, Raymond, Zaidat, Nogueira.

Statistical analysis: Qureshi, Sheth, Castonguay, Kaesmacher, Farooqui, Farzin, Nogueira.

Obtained funding: Nguyen, Castonguay, Michel, Zaidat.

Administrative, technical, or material support: Nguyen, Abdalkader, Mohammaden, Ortega-Gutierrez, Siegler, Zaidi, Castonguay, Kaliaev, Lopez, Kareem, Cordonnier, Gralla, Michel.

Supervision: Nguyen, Sheth, Ortega-Gutierrez, Puri, Kuhn, Ringleb, Jovin, Raymond, Zaidat, Nogueira.

Other鈥攄ata collection: Kareem.

Other鈥揷ontribution of data: Nagel.

Conflict of Interest Disclosures: Dr Nguyen reported research support from Medtronic and the Society of Vascular and Interventional Neurology with data safety monitoring board involvement for Thrombectomy for Emergent Salvage of Large Anterior Circulation Ischemic Stroke (TESLA), Endovascular Therapy for Low NIHSS Ischemic Strokes (ENDOLOW), a Randomized Controlled Trial to Optimize Patient鈥檚 Selection for Endovascular Treatment in Acute Ischemic Stroke (SELECT 2), pRESET for Occlusive Stroke Treatment (PROST), Carotid Revascularization and Medical Management for Asymptomatic Carotid Stenosis Trial (CREST-2), and Workflow Optimization to Reduce Time to Endovascular Reperfusion in Stroke Treatment (WE-TRUST) trials. Dr Nagel reported personal fees for consultancy for Brainomix and payment for lectures including speaker bureaus with Boehringer Ingelheim and Pfizer outside the submitted work. Dr Ribo reported being a cofounder of Anaconda Biomed; a consultant with Methinks, Medtronic, Cerenovus, Apta Targets, Anaconda Biomed, and Philips; and grants from CVAid, outside the submitted work. Dr Haussen reported being a consultant for Stryker, Vesalio, Cerenovus, and Jacobs Institute and holding stock options with VizAi during the conduct of the study. Dr Siegler reported consulting fees from Ceribell and speakers鈥� bureau involvement with AstraZeneca outside the submitted work. Dr Ortega-Gutierrez reports being a consultant for Medtronic and Stryker Neurovascular and receiving grants from Stryker, IschemiaView, Viz.ai, and Siemens. Dr M枚hlenbruch reports consultancy at Medtronic, MicroVention, and Stryker; grants or grants pending from Medtronic, Stryker, Balt, and MicroVention (money paid to his institution); and payment for lectures including service on speakers鈥� bureaus from Medtronic, MicroVention, and Stryker, outside the submitted work. Dr Zaidat reported consulting fees for Stryker, Medtronic, Cerenovus, and Penumbra; research grants from Stryker, Medtronic, Cerenovus, Penumbra, and Genentech; in addition, Dr Zaidat had a patent for Ischemic Stroke issued. Dr Sheth reported research grants from the National Institutes of Health (grants U18EB029353 and R01NS121154) and American Academy of Neurology/the Society of Vascular and Interventional Neurology and consultancy fees from Penumbra and Cerenovus. Dr Fischer reported research grants from Medtronic (BEYOND SWIFT and SWIFT DIRECT); serving as consultant for Medtronic, Stryker, CSL Behring; and participating in an advisory board for Alexion/Portola outside the submitted work. Dr Jovin reported being an investigator with Stryker (DAWN and AURORA trials); an advisor or investor for Anaconda, Route92, VizAi, FreeOx, Methinks, and Blockade Medical; a recipient of personal fees, data safety monitoring board, and steering committee fees from Cerenovus and grants from Medtronic; an advisor and stockholder for Corindus; and a member of a medical committee for Contego outside the submitted work. Dr Nogueira reported involvement with Stryker as part of the DAWN trial; the Trevo-2 trial and Trevo registry steering committee; Medtronic as part of the SWIFT/SWIFT-PRIME steering committee and STAR trial core laboratory; Penumbra as part of the 3D Trial executive committee; Cerenovus/Neuravi as part of the ENDOLOW Trial, EXCELLENT Registry, and ARISE-2 trial steering committee; Phenox as part of the PROST Trial; Imperative Care as part of the Imperative Trial; and Philips as part of the WE-TRUST trial. Dr Nogueira also reported consulting fees for advisory roles with Anaconda, Biogen, Cerenovus, Genentech, Hybernia, Imperative Care, Medtronic, Phenox, Philips, Prolong Pharmaceuticals, Stryker Neurovascular, Shanghai Wallaby, and Synchron and stock options for advisory roles with Astrocyte, Brainomix, Cerebrotech, Ceretrieve, Corindus Vascular Robotics, Vesalio, Viz-AI, RapidPulse, and Perfuze; and investments in Viz-AI, Perfuze, Cerebrotech, Reist/Q'Apel Medical, Truvic, and Viseon. Dr Kaesmacher reported grants from SAMW/Bangerter Foundation, Swiss Stroke Society, and CTU Bern outside the submitted work. Dr Puri reported personal fees from Stryker Neurovascular, Cerenovus, Medtronic, Merit, CereVasc, Microvention, and Arsenal Medical; stocks with InNeuroCo, Galaxy, NTI, Agile, and Perfuze; and grants from the National Institutes of Health outside the submitted work. Dr Kaliaev reported grants from Medtronic and SVIN during the conduct of the study. Dr Ringleb reported personal fees from Boehringer Ingelheim, Bayer, Bristol Myers Squibb, and Pfizer outside the submitted work. Dr Cordonnier reported personal fees from Boehringer Ingelheim and advisory board participation from Bristol Myers Squibb, AstraZeneca, and Biogen outside the submitted work. Dr Gralla reported grants from Medtronic (SWIFT DIRECT trial) and SNF outside the submitted work. Dr Michel reported grants from Swiss National Science Foundation and Swiss Heart Foundation outside the submitted work. No other disclosures were reported.

Additional Contributions: We would like to acknowledge the following persons who contributed to this work: Oscar Bolanos, Medtronic; Margaret Lavoye, RN, Boston Medical Center; Kristine Below, BS, Umera Paracha, MD, Sakshi Kaul, DO, MS, Mercy Health St. Vincent Medical Center; Viraj M. Moholkar, BS. These individuals were not compensated for their contributions. We express gratitude to all CLEAR study investigators.