Hypoperfusion Intensity Ratio Research Articles

The Los Angeles motor scale (LAMS) is independently associated with CT perfusion collateral status markers

Background and aimThe Los Angeles Motor Scale (LAMS) is an objective tool that has been used to rapidly assess and predict the presence of large vessel occlusion (LVO) in the pre-hospital setting successfully in several studies. However, studies assessing the relationship between LAMS score and CT perfusion collateral status (CS) markers such as cerebral blood volume (CBV) index, and hypoperfusion intensity ratio (HIR) are sparse. Our study therefore aims to assess the association of admission LAMS score with established CTP CS markers CBV Index and HIR in AIS-LVO cases. Materials and MethodsIn this prospectively collected, retrospectively reviewed analysis, inclusion criteria were as follows: a) CT angiography (CTA) confirmed anterior circulation LVO from 9/1/2017 to 10/01/2023, and b) diagnostic CT perfusion (CTP). Logistic regression analysis was performed to assess the relationship between admission LAMS with CTP CS markers HIR and CBV Index. p ≤ 0.05 was considered significant. ResultsIn total, 285 consecutive patients (median age = 69 years; 56 % female) met our inclusion criteria. Multivariable logistic regression analysis adjusting for sex, age, ASPECTS, tPA, premorbid mRS, admission NIH stroke scale, prior history of TIA, stroke, atrial fibrillation, diabetes mellitus, hyperlipidemia, coronary artery disease and hypertension, admission LAMS was found to be independently associated with CBV Index (adjusted OR:0.82, p < 0.01), and HIR (adjusted OR:0.59, p < 0.05). ConclusionLAMS is independently associated with CTP CS markers, CBV index and HIR. This finding suggests that LAMS may also provide an indirect estimate of CS.

Hypoperfusion intensity ratio and hemorrhagic transformation in patients with successful recanalization after thrombectomy.

Hemorrhagic transformation remains a potentially devastating complication of acute ischemic stroke. We aimed to evaluate whether the hypoperfusion intensity ratio (HIR), a parameter derived from CT perfusion imaging, is associated with the development of hemorrhagic transformation in patients with anterior large-artery occlusion who had undergone thrombectomy. We retrospectively reviewed data from consecutive acute ischemic stroke patients who had achieved successful recanalization (thrombolysis in cerebral infarction score ≥ 2b) between January 2020 and December 2023. HIR was defined as the ratio of the volume of lesions with a time-to-maximum (TMax) > 6 s to those with a Tmax > 10 s delay. The primary outcome, based on the European Cooperative Acute Stroke Study, was hemorrhagic transformation (HT), diagnosed by follow-up imaging assessment in 24 h windows, and radiologically classified as hemorrhagic infarction (HI) and parenchymal hematoma (PH). The secondary outcome was a 3-month mRS score of ≥3. Among 168 patients, 35/168 developed hemorrhagic transformation HT; 14/168 developed hemorrhagic infarction HI, and 21/168 developed parenchymal hematoma PH. After adjusting the latent covariates, increased hypoperfusion intensity ratio (per 0.1, adjusted OR [aOR] 1.68, 95% CI 1.26-2.25), ASPECTS (aOR 0.44, 95% CI 0.27-0.72), onset-to-puncture (aOR 1.01, 95% CI 1.00-1.02), and cardioembolism (aOR 5.6, 95% CI 1.59-19.7) were associated with hemorrhagic transformation in multivariable regression. The receiver operating characteristic curve indicated that HIR can predict HT accurately (area under the curve = 0.81; 95% CI, 0.738-0.882; P < 0.001) and predict PH (area under the curve = 0.801; 95% CI, 0.727-0.875; P < 0.001). Upon admission, hypoperfusion intensity ratio, an imaging parameter, predicted hemorrhagic transformation after reperfusion therapy in this patient population.ABBREVIATIONS: HT = hemorrhagic transformation; HIR = hypoperfusion intensity ratio; LVO = left vessel occlusion; EVT = endovascular thrombectomy; AIS = arterial ischemic stroke; OTP = onset-to-puncture; HI = hemorrhagic infarction; PH = parenchymal hematoma.

Association of blood pressure and outcomes differs upon cerebral perfusion post-thrombectomy in patients with acute ischemic stroke

BackgroundThe relationship between post-endovascular thrombectomy (EVT) blood pressure (BP) and outcomes in patients with acute ischemic stroke (AIS) remains contentious. We aimed to explore whether this association differs with different...

Importance of computed tomography perfusion on assessing collateral circulation and prognosis of patients with acute anterior circulation large vessel occlusion after endovascular therapy

This study probed the importance of computed tomography perfusion (CTP) on assessing collateral circulation and prognosis in patients with acute anterior circulation large vessel occlusion (AAC-LVO) after endovascular therapy (EVT). Retrospective analysis was performed on the case data of 124 AAC-LVO patients who achieved EVT in the First People's Hospital of Lianyungang. All patients received computed tomography (CT) examination. Based on the multi-phase computed tomography angiography (mCTA) score, patients were separated into poor collateral circulation group and good collateral circulation group. Based on modified Rankin scale (mRS) score, patients were separated into good prognosis group and poor prognosis group. The receiver operating characteristic (ROC) curve was used to measure the efficacy of CTP parameters in predicting good collateral circulation or good prognosis. Correlation between CTP parameters with mCTA collateral and 90-day mRS circulation score was analyzed using the Spearman correlation analysis. The age and admission national Institutes of Health stroke scale (NIHSS) scores of the good collateral circulation group were lower than the poor collateral circulation group, and low perfusion area volume with Tmax > 6 s (VTmax>6s), infarct core area volume (VCBF<30%)and hypoperfusion intensity ratio (HIR) were also lower. The mCTA collateral cycle score was negatively related to VTmax>6 s, VCBF<30% and HIR. The area under the curve (AUC) values of VTmax>6 s and VCBF<30% and HIR for predicting good collateral circulation were 0.763, 0.884 and 0.842, respectively, which suggested that perfusion parameters VTmax>6 s, VCBF<30% and HIR could effectively indicate the status of patients’ collateral circulation. Relative to the poor prognosis group, patients in the good prognosis group possessed lower admission NIHSS score, younger age, smaller final infarct volume, lower HIR, VCBF<30%, VTmax>6s, Alberta Stroke Program Early CT(ASPECT) score, and higher mCTA score. Spearman correlation analysis unveiled that ASPECT score, mCTA score and 90-day mRS were negatively correlated. The final infarct volume, perfusion parameters HIR and VCBF<30% were positively correlated with 90-day mRS. ROC analysis showed that all variates had good prognostic value for acute anterior circulation great vessel occlusion patients, while VCBF<30% and HIR had high diagnostic value for prognosis. To sum up, CTP can provide a comprehensive imaging assessment of the collateral circulation of patients with AAC-LVO and has a higher predictive value for the prognosis assessment of patients with EVT in terms of VCBF<30%, HIR score and mCTA collateral circulation score.

Long term outcome after endovascular treatment for large ischemic core acute stroke is associated with hypoperfusion intensity ratio and onset-to-reperfusion time.

Endovascular treatment (EVT) is effective for large vessel occlusion (LVO) stroke with smaller volumes of CT perfusion (CTP)-defined core. However, the influence of perfusion imaging during thrombectomy on the functional outcomes of patients with large ischemic core (LIC) stroke at both early and late time windows is uncertain in real-world practice. A retrospective analysis was performed on 99 patients who underwent computed tomography angiography (CTA) and CT perfusion (CTP)-Rapid Processing of Perfusion and Diffusion (RAPID) before EVT and had a baseline ischemic core ≥ 50 mL and/or Alberta Stroke Program Early CT Score (ASPECTS) score of 0-5. The primary outcome was the three-month modified Rankin Scale (mRS) score. Data were analyzed by binary logistic regression and receiver operating characteristic (ROC) curves. A fair outcome (mRS, 0-3) was found in 34 of the 99 patients while 65 had a poor prognosis (mRS, 4-6). The multivariate logistic regression analysis showed that onset-to-reperfusion (OTR) time (odds ratio [OR], 1.004; 95% confidence interval [CI], 1.001-1.007; p = 0.008), ischemic core (OR, 1.066; 95% CI, 1.024-1.111; p = 0.008), and the hypoperfusion intensity ratio (HIR) (OR, 70.898; 95% CI, 1.130-4450.152; p = 0.044) were independent predictors of outcome. The combined results of ischemic core, HIR, and OTR time showed good performance with an area under the ROC curve (AUC) of 0.937, significantly higher than the individual variables (p < 0.05) using DeLong's test. Higher HIR and longer OTR time in large core stroke patients were independently associated with unfavorable three-month outcomes after EVT.

Sex alters the effect of perfusion deficits on functional outcome in patients with acute ischemic stroke undergoing mechanical thrombectomy.

The discourse surrounding differences in cerebral hemodynamics and clinical outcomes among male and female patients treated with mechanical thrombectomy (MT) for acute ischemic stroke (AIS) remains unresolved. We aimed to elucidate these differences by employing computed tomography perfusion (CTP) imaging before MT and examining the influence of perfusion deficits on the 90-day functional outcome. This single-center retrospective analysis involved patients with anterior circulation AIS treated with MT at the Comprehensive Stroke Center, University Hospital, Krakow from January 2019 to July 2023. We compared male and female patients in terms of baseline characteristics, CTP deficits, hypoperfusion intensity ratio (HIR, defined as T10max/T6max) and complications. The endpoints included the 90-day excellent functional outcome, defined as modified Rankin Score (mRS)<2, and the 90-day mortality rate. We included 794 patients, of whom 408 were female (51.4%). Female patients had a smaller early infarct volume (median: 7 mL; IQR: [0-24.8] vs 10 mL [0-33], p=0.004), smaller penumbra volume (77.5 mL [46-117] vs 99.5 mL [59.8-140], p<0.001), lower HIR (0.34 [0.16-0.5] vs 0.37 [0.2-9.53], p=0.043) and were less likely to achieve an excellent functional outcome (55.6% vs 66.1%, p=0.003). For every 10 mL increase in early infarct volume, the odds for achieving an excellent outcome were lower in females (odds ratio (OR): 0.82 [95% confidence interval: 0.73-0.92]) compared to males (OR: 0.96 [0.88-1.04]), whereas the risk of death was higher for females (OR: 1.25 [1.13-1.39] than for males (OR: 1.05 [0.98-1.14]). Despite more favorable cerebral hemodynamic profile, female AIS patients have worse outcomes than their male counterparts. This effect seems to be independently mediated by the more pronounced impact of early infarct volume on the prognosis in female patients. These findings underscore the possible explanatory power arising for from sex-specific interpretation of early infarct volume in clinical practice.

Large vessel occlusive stroke with milder baseline severity shows better collaterals and reduced harm from thrombectomy transfer delays.

Patients with large vessel occlusion (LVO) stroke presenting with milder baseline clinical severity are common and require endovascular thrombectomy. However, such patients are difficult to recognize using pre-hospital severity-based triage tools and therefore are likely to require a secondary inter-hospital transfer if transported to a non-thrombectomy center. Given the potential for milder severity to represent better underlying cerebrovascular collateral circulation, it is unknown whether transfer delays are still associated with poorer post-stroke outcomes in this patient group. We primarily aimed to examine whether the harmful effect of inter-hospital transfer delay for thrombectomy was different for LVO patients with mild or severe deficits. Secondarily, we also investigated whether imaging markers of collateral circulation were different between severity groups. Registry data from two large Australian thrombectomy centers were used to identify all directly presenting and secondarily transferred LVO patients undergoing thrombectomy, divided into those with lower (NIHSS < 10) and higher (NIHSS ⩾ 10) baseline deficits. The primary outcome was the functional independence or return to baseline defined as modified Rankin Scale 0-2 or baseline at 90 days. Patients with complete baseline CT-perfusion data were analyzed for imaging markers of collateral circulation by baseline severity group. A total of 1210 LVO patients undergoing thrombectomy were included, of which 273 (22.6%) had lower baseline severity. Despite similar thrombolysis and recanalization rates, transferred patients had lower odds of achieving the primary outcome compared to the primary presentation to a thrombectomy center, where baseline severity was higher (adjusted odds ratio (aOR) 0.759 (95% CI 0.576-0.999)), but not when severity was lower (aOR 1.357 (95% CI 0.764-2.409), p-interaction = 0.122). In the imaging analysis of 436 patients, those with milder severity showed smaller median ischemic core volumes (12.6 (IQR 0.0-17.9) vs 27.5 (IQR 6.5-37.1) mL, p < 0.001)), higher median perfusion mismatch ratio (10.8 (IQR 4.8-54.5) vs 6.6 (IQR 3.5-16.5), p < 0.001), and lower median hypoperfusion intensity ratio (0.25 (IQR 0.18-0.38) vs 0.40 (IQR 0.22-0.57), p < 0.001). Patients receiving secondary inter-hospital transfer for thrombectomy had poorer outcomes compared to those presenting directly to a thrombectomy center if baseline deficits were severe, but this difference was not observed when baseline deficits were milder. This result may potentially be due to our secondary findings of significantly improved collateral circulation markers in lower-severity LVO patients. As such, failure of pre-hospital screening tools to detect lower-severity LVO patients for pre-hospital bypass to a thrombectomy center may not necessarily deleteriously affect outcome. Anonymized data not published within this article will be made available on request from any qualified investigator.

Does TyG Index Correlate with Infarct Core Progression Measured by CTP Hypoperfusion Intensity Ratio in Stroke Patients Undergoing Reperfusion Therapy? (P5-5.027)

Does TyG Index Correlate with Infarct Core Progression Measured by CTP Hypoperfusion Intensity Ratio in Stroke Patients Undergoing Reperfusion Therapy? (P5-5.027)

Clinico-radiological features of intracranial atherosclerosis-related large vessel occlusion prior to endovascular treatment

The identification of large vessel occlusion with underlying intracranial atherosclerotic disease (ICAS-LVO) before endovascular treatment (EVT) continues to be a challenge. We aimed to analyze baseline clinical-radiological features associated with ICAS-LVO that could lead to a prompt identification. We performed a retrospective cross-sectional study of consecutive patients with stroke treated with EVT from January 2020 to April 2022. We included anterior LVO involving intracranial internal carotid artery and middle cerebral artery. We analyzed baseline clinical and radiological variables associated with ICAS-LVO and evaluated the diagnostic value of a multivariate logistic regression model to identify ICAS-LVO before EVT. ICAS-LVO was defined as presence of angiographic residual stenosis or a trend to re-occlusion during EVT procedure. A total of 338 patients were included in the study. Of them, 28 patients (8.3%) presented with ICAS-LVO. After adjusting for confounders, absence of atrial fibrillation (OR 9.33, 95% CI 1.11–78.42; p = 0.040), lower hypoperfusion intensity ratio (HIR [Tmax > 10 s/Tmax > 6 s ratio], (OR 0.69, 95% CI 0.50–0.95; p = 0.025), symptomatic intracranial artery calcification (IAC, OR .15, 95% CI 1.64–26.42, p = 0.006), a more proximal occlusion (ICA, MCA-M1: OR 4.00, 95% CI 1.23–13.03; p = 0.021), and smoking (OR 2.91, 95% CI 1.08–7.90; p = 0.035) were associated with ICAS-LVO. The clinico-radiological model showed an overall well capability to identify ICAS-LVO (AUC = 0.88, 95% CI 0.83–0.94; p < 0.001). In conclusion, a combination of clinical and radiological features available before EVT can help to identify an ICAS-LVO. This approach could be useful to perform a rapid assessment of underlying etiology and suggest specific pathophysiology-based measures. Prospective studies are needed to validate these findings in other populations.

Abstract WP138: Collateral Status Measured by Hypoperfusion Intensity Ratio Correlates With Infarct Core Size and Growth Rate in MCA Medium Vessel Occlusions &lt;6 Hours and 6-24 Hours Post Onset

Purpose: Hypoperfusion intensity ratio (HIR) derived from CT perfusion (CTP) has shown to be a useful surrogate marker of collateral status, but prior studies focused on ICA/M1 large vessel occlusions (LVO). We aimed to determine: associations between HIR and clinical/imaging metrics of stroke severity for M2 and M3 medium vessel occlusions (MVO), any differences between &lt;6h and 6-24h from onset as MVO often present later than LVO, and what optimal HIR threshold describes infarct growth rate (IGR) &gt;10mL/h (fast progressor). Methods: We retrospectively analyzed consecutive patients arriving within 24h from onset, with M2 or M3 occlusion on CTA, and had concurrent CTP. RAPID generated maps of infarct core defined as rCBF&lt;30% and HIR defined as Tmax&gt;10s/Tmax&gt;6s. IGR was defined as core size/onset-to-CTP time. ASPECTS and NIHSS data were also collected. Correlations were tested using Spearman's rank analysis, for the cohort and separately for &lt;6h and 6-24h subgroups. Difference in HIR between subgroups was tested using Mann-Whitney U. Optimal threshold for IGR&gt;10mL/h was determined by ROC analysis. Results: 78 patients included with median (IQR) age of 79 (64-84), onset of 7.5h (2.5-14.5), NIHSS of 12 (7-18), ASPECTS of 7 (9-10), core size of 4 mL (0-22), and IGR of 0.57 mL/h (0-2.8). 63 M2 and 15 M3 occlusions identified with median HIR of 0.35 (0.06-0.52). For the cohort, HIR was highly correlated to core size r=0.740 and IGR r=0.710, moderately correlated to NIHSS r=0.474 and ASPECTS r=-0.331 (all p&lt;0.003). 28 and 50 patients presented &lt;6h and 6-24h, respectively, without significant difference in HIR, median 0.31 vs 0.36 (p=0.543). For &lt;6h, HIR was moderately correlated to core size r=0.672, IGR r=0.639, NIHSS r=0.435, and ASPECTS r=-0.496 (all p&lt;0.021). For 6-24h, HIR was highly correlated to core size r=0.791 and IGR r=0.777, moderately correlated to NIHSS r=0.502 and ASPECTS r=-0.376 (all p&lt;0.007). ROC analysis showed AUC of 0.860 (p&lt;0.001) for IGR&gt;10mL/h, with optimal HIR threshold at 0.43 for sensitivity of 100% [95% CI: 59.0-100], specificity of 64.8% [95% CI: 52.5-75.5]. Conclusion: In acute MCA MVO strokes &lt;6h and 6-24h, HIR as marker of collateral status is moderate to highly correlated to stroke severity, especially size and growth rate of the infarct core.

Abstract WP117: Improvement of Collateral Status in Thrombectomy-Eligible Stroke Patients During Inter-Hospital Transfer: Association With Clinical Factors and Outcome

Background: Ischemic stroke patients who are eligible for endovascular therapy (EVT), can be transferred from a primary stroke center (PSC) to an EVT-capable comprehensive stroke center (CSC). Little is known about the dynamics of the collateral circulation in this time-window. We aimed to explore changes in collateral status during inter-hospital transfer among patients with poor collaterals on presentation to the PSC. Methods: Data from patients with an anterior circulation large vessel occlusion (LVO), transferred to two CSCs were prospectively collected. A CT perfusion was obtained at the PSC followed by an MRI immediately on arrival at the CSC. The hypoperfusion intensity ratio (HIR), a measure of collateral blood flow, was calculated as the ratio of the Tmax volumes of &gt;10s and &gt;6s. Only patients with stable LVO at the CSC and poor collateral status at the PSC (HIR ≥ 0.40) were included. An HIR &lt; 0.40 in the CSC and a difference ≥ 0.10 was considered as HIR improvement. Results: Data from 104 patients with perfusion imaging at both PSC and CSC, were analyzed. Of them, we included 59 patients with an HIR ≥ 0.40 at the PSC. Sixteen (27%) patients experienced HIR improvement during transfer (Figure 1) . A smaller baseline core volume was independently associated with HIR improvement (OR for every 10 ml increase = 0.46 {95%CI 0.21-0.81}; p=0.03). Collateral improvement was associated with slower infarct growth during transfer (2.45 {95%CI 1.03-3.62} vs 7.77 {95%CI 4.56-17.86} ml/h; p&lt;0.01) and a better functional outcome at 90 days post stroke (median mRS 3 {IQR 1-5} vs 4 {IQR 4-6}; p=0.01). Conclusion: During inter-hospital transfer spontaneous improvement in collateral status, as measured by HIR, is commonly seen, and associated with a smaller infarct core at the PSC, slower infarct growth during transfer, and better functional outcomes. Future neuroprotective trials targeted at collateral improvement, might consider the use of the HIR change as a surrogate outcome marker.

Abstract 129: An Automated Perfusion Collateral Score as a Tool to Predict Inter-Hospital Infarct Growth and Functional Outcome

Background: The accuracy of infarct growth prediction based on collateral scores, assessed on CT perfusion (CTP) and CT angiography, has been modest. We aimed to investigate the accuracy of infarct growth prediction using a novel collateral score based on two CTP parameters. Methods: Patients were included from CRISP2, a multi-center prospective cohort study of stroke patients with an anterior circulation large vessel occlusion who are transferred from a primary stroke center (PSC) to a comprehensive stroke center (CSC). CTP was performed at the PSC, and MRI was performed immediately after arrival at the CSC. The inter-hospital infarct growth rate was calculated as the difference between the co-registered infarct volumes on MRI and CTP divided by the time interval between the scans, with fast inter-hospital growth ≥ 5ml/h. The hypoperfusion intensity ratio (HIR) was defined as the ratio of the volumes of Tmax &gt;6s and Tmax &gt;10s, and the CBV index as the ratio of mean CBV values within the Tmax &gt;6s volume and the mean CBV in normal brain regions. An automated collateral score, based on the HIR and CBV index, was calculated from the CTP images at the PSC ( Fig 1A ). Results: Of 183 patients who were included, 111 (61%) were classified as having good collaterals and 72 (39%) as poor. Patients with poor collaterals experienced more rapid early infarct growth (median 2.19 ml/h IQR [0.32, 5.46] vs 7.92 [4.23, 16.23]; p-value &lt;0.001) and had worse 90-day functional outcomes (p=0.01). The combined collateral score, based on both HIR and CBVindex, showed a trend towards better prediction of fast infarct growth compared to HIR alone (HIR ≥ 0.40 = poor collaterals) and CBV alone (CBVindex &lt; 0.85 = poor collaterals) ( Fig 1B ). Conclusion: A perfusion collateral score, based on HIR and CBV index, is strongly associated with inter-hospital infarct growth rate and functional outcome. This automated tool can aid in patient selection for (neuroprotective) treatment strategies and transfer decisions.

Abstract 23: Results of CRISP2: CTP and CTA Assessment of Collaterals Predicts Inter-Hospital Infarct Growth

Background: Acute ischemic stroke patients with a large vessel occlusion (LVO) who present in a primary stroke center (PSC) without endovascular treatment capability, are often transferred to a comprehensive stroke center (CSC) for thrombectomy. CRISP2 was a prospective NIH funded multi-center study that aimed to determine characteristics associated with infarct growth during inter-hospital transfer. Methods: Data from patients with an anterior circulation LVO transferred to two CSCs were collected. A CT perfusion (CTP) was obtained at the PSC followed by an MRI at the CSC, before consideration of thrombectomy. The inter-hospital infarct growth rate was defined as the difference between the co-registered infarct volumes on MRI and CTP, divided by the time between the two scans. Multivariable logistic regression was used to determine characteristics associated with fast inter-hospital progression, defined as a growth rate ≥ 5ml/h. The hypoperfusion intensity ratio (HIR) was calculated automatically from the CTP, while the Tan collateral score was visually rated on baseline CT angiography. Results: A total of 183 patients, of whom 45% were fast progressors, were included. Baseline characteristics are presented in Table 1 . An HIR ≥0.40 identified fast infarct growth with a sensitivity of 0.76 (95%CI 0.65-0.84) and a specificity of 0.55 (95%CI 0.44-0.65), whereas for Tan 0-1 sensitivity was 0.37 (95%CI 0.27-0.48) and specificity 0.93 (95%CI 0.86-0.97). In multivariable models, baseline core volume and poor collaterals defined as either an HIR ≥ 0.40 (aOR = 2.18 (95%CI 1.10-4.42); p = 0.03) or a Tan score of 0-1 (aOR = 4.74 (95%CI 1.90-13.07); p=0.001), remained independently associated with fast infarct growth. Conclusion: An HIR ≥ 0.40 is a predictor of fast inter-hospital infarct growth with high sensitivity and a Tan score of 0-1 predicts fast growth with high specificity. These are promising imaging markers for patient selection in future neuroprotective trials.

Abstract WP140: Perfusion Collateral Index Predicts Infarct Growth in Successfully Reperfused Patients With Acute Ischemic Stroke

Introduction: Robust collaterals are associated with lower rates of infarct growth and improved clinical outcomes in patients with acute ischemic stroke. Perfusion Collateral Index (PCI) and Hypoperfusion Intensity Ratio (HIR) have been shown to correlate with angiographic collaterals. We aimed to assess and compare the ability of PCI and HIR to predict infarct growth in anterior circulation large vessel occlusion (AC LVO) patients who underwent successful reperfusion. Methods: In this retrospective study, AC LVO stroke patients were included if they had pretreatment perfusion (CT or MR), successful reperfusion (mTICI &gt; 2b), and follow up MRI within 24 hours from treatment. HIR (defined as volume of Tmax &gt;10 sec/volume of Tmax &gt;6 sec) was calculated by RAPID software (Version 5.0.4). PCI (defined as volume of delay 2-6 seconds x rCBV) was calculated using Olea software (SP.23). Infarct growth was calculated by subtracting baseline ischemic core (ADC &lt;620 х 10 –6 mm2/s on MRI or rCBF &lt;30% on CTP) from post-treatment MRI volume of DWI hyperintensity. Results: A total of 80 patients were included; 46 female, age (mean + SD): 70.2 + 13.1 years, NIHSS (median, IQR): 14, 8-19, and time from stroke-onset to reperfusion (mean + SD): 389 + 236 minutes. The infarct growth volume was 27 + 52 mL (mean + SD); 47 patients (58.7%) had infarct growth &gt; 10 mL. ROC analysis for prediction of infarct growth &gt; 10 mL revealed AUC/sensitivity/specificity of 0.70/55.3/84.8 for PCI at threshold &lt;60, which was significantly higher (P=0.006) than HIR at threshold of &gt;0.4 (0.50/74.5/24.2) (Figure). Multivariate logistic regression showed PCI (p=0.004) and time-to treatment (p=0.024) were the only independent variables to predict infarct growth. Conclusion: In conclusion, in patients with AC LVO stroke, poor baseline collateral perfusion defined by PCI &lt;60 predicts infarction growth &gt; 10 mL despite successful reperfusion. PCI was superior to HIR in the prediction of infarct growth.

Abstract TP142: Perfusion Profiles to Identify Acute Extracranial Internal Carotid Artery Atherosclerosis-Related Stroke Prior to Endovascular Therapy

Introduction: Perfusion imaging has been used to assess collateral status in patients with acute ischemic stroke secondary to anterior large-vessel occlusion. We aimed to evaluate the hypoperfusion intensity ratio (HIR), a surrogate of collateral status, in acute stroke secondary to extracranial atherosclerosis disease (AD) compared with extracranial non-AD etiologies prior to EVT. Methods: We retrospectively reviewed the data of consecutive EVT stroke patients in our prospectively collected registry from January 2019 to December 2022. Inclusion criteria: patients with anterior circulation stroke with concomitant extracranial internal carotid artery (ICA) disease with 70-100% stenosis per NASCET criteria and patients who underwent computed tomography perfusion (CTP) before EVT. Patients were divided into those with extracranial AD and non-AD based on clinical and radiological characteristics. HIR was calculated as the volume of ischemic brain tissue with a Tmax&gt;10s divided by a Tmax&gt;6s. A relative CBF&lt;30% was also obtained. Multivariable regression was used to identify the HIR independently associated with extracranial ICA AD-related stroke; adjusted odds ratio with 95%CIs were calculated using the non-AD group as a reference. Results: Among all 624 EVT patients, 79 met inclusion criteria. Of these patients (21 women [36.2%]; median age 67 [60-75] years), 58 (72.5%) had extracranial ICA AD. Patients in the AD group had significantly lower CBF&lt;30% (median 8ml [0-17] vs 19ml [9-36]), lower Tmax&gt;10s (median 29ml [11-69] vs 68ml [38-117]), and lower HIR (median 0.27 [0.13-0.45] vs 0.49 [0.42-0.59]). There was no significant difference in time from last know well to CTP between groups. Lower HIR was independently associated with AD after adjusting for variables related to AD (Figure1). Conclusions: Low HIR values was a predictor of stroke secondary to extracranial ICA AD and could be helpful to differentiate from other non-AD etiologies prior to EVT.

Abstract TP141: Understanding Potential Limitations of CTP Imaging in Early Window Large Vessel Anterior Circulation Strokes

Background: Computerized tomography perfusion (CTP) imaging serves as a valuable modality for the assessment of individuals with a large vessel anterior circulation stroke. Current literature proposes that employing CTP imaging in patients within the initial time frame of less than 8 hours, may lead to an overestimation of the projected infarct core, specifically when utilizing cerebral blood flow (CBF) less than 30%. The hypoperfusion intensity ratio (HIR) may result in overestimation. We sought to further investigate the interplay of CTP parameters in patients presenting within 8 hours of symptom onset of stroke, to assess the accuracy of core infarct estimation. Methods: A retrospective cohort study analyzing patients with large vessel anterior occlusion (LVAO) who underwent CTP and mechanical thrombectomy within 24 hours of symptom onset between January 2017 to December 2022. RAPID software estimates the infarct core using CBF &lt;30%. DWI-MRI determined final infarct volume. A multivariate logistic regression model was employed to assess the impact of HIR and reperfusion success on outcomes. Results: Ninety-seven patients were identified within an 8-hour time window. CBF&lt;30% overestimated core infarct volume (mL) in 22 patients (22.6%) with a mean of 15.72 (range 4.4-37.7) and a median of 22.85. Of these, 2 patients experienced poor reperfusion (9%) while 20 had successful reperfusion (91%). Of the patients who did have successful reperfusion, an average of 13.57mL core was overpredicted compared to the DWI volumes. A multivariate logistic regression model adjusting for degree of reperfusion, administration of thrombolytic, and time from symptom onset showed that HIR strongly predicted the probability of core estimation with an odds ratio of 148.6, 95% CI [21.0-1048.8], (p&lt;0.001). Conclusion: HIR exceeding 0.4 demonstrates a predictive capacity for core overestimation in early-window LVAO patients. Our study affirms this observation with statistical significance. The integration of HIR as a parameter for early-window LVAO core computation shows promise, and has potential ramifications for patient selection for thrombectomy. In this context, utilization of further databases is imperative for validation and broader application of HIR.

Abstract WP118: Ischemic Core Volumes and Collateral Status Have Diurnal Fluctuations - A Retrospective Cohort Study of 18137 Patients Using Automated Perfusion Imaging

Introduction: Circadian rhythms have recently been shown to influence stroke incidence and progression of infarct. We aimed to describe the diurnal variations in the incidence and perfusion profiles of patients with ischemic stroke using a large, multi-center, automated imaging database. Methods: The RAPID Insights database was queried from 02/01/2016 to 01/31/2022 for patients with perfusion imaging and automated detection of an ischemic stroke due to a presumed large vessel occlusion. Exclusion criteria included: patient age ≤25, mismatch volume of &lt;0 cc, and failure to register a positive value on either cerebral blood flow (CBF) reduction of 38% less than normal or total mismatch volume. Imaging time was subdivided into three epochs: Night: 23:00h-06:59h and Day: 07:00h-14:59h, and Evening: 15:00h-22:59h. Perfusion parameters were defined as the following: core volume was defined as CBF of &lt;30% of normal, penumbra was defined as a Tmax delay of &gt;6 seconds minus core volume, and collateral circulation was estimated with the Hypoperfusion Intensity Ratio (HIR = [Tmax&gt;10s]/[Tmax&gt;6s]), where a higher HIR suggests poorer collateral status. All perfusion parameters were analyzed on a 24-hour continuous cycle. Statistical significance was tested using a sinusoidal regression analysis. Results: A total of 18,137 cases were analyzed. The peak incidence of ischemic stroke occurred around noon. A sinusoidal pattern was present, with larger ischemic core volumes and higher HIR during the night compared to the day: peak ischemic core volume of 23.40 cc occurred with imaging performed at 3:56 AM (p&lt;0.001) and peak HIR of 0.35 at 3:40 AM (p&lt;0.001). Conclusion: We found that ischemic core volumes were larger and collateral status worse at nighttime compared to daytime in this large national database. These findings support the notion that poor collateral recruitment with subsequent larger ischemic stroke volumes may occur at night. Fig 1. Logarithmic values of ischemic core volumes and hypoperfusion intensity ratios (HIR) are plotted against a 24-hour cycle, demonstrating a sinusoidal pattern for both.

Abstract TP190: Higher Pre-Hospital Blood Pressure is Associated With Lower Mismatch Volume and Poorer Collateral Status in Patients With Acute Ischemic Stroke Due to Large Vessel Occlusions

Introduction: Immediately after AIS onset, blood pressure variability (BPV) arises as the result of a complex interplay between brain and systemic physiological hemodynamic responses. In this study, we examined the effect of BPV on early infarct growth in patients with large vessel occlusions (LVO) during their prehospital transfer. Methods: We included consecutive patients with AIS-LVO from 2 large comprehensive stroke centers. We collected the BP values from emergency medical services arrival to hospital admission. Patients with &lt;3 BP recordings were excluded. BPV was assessed using the standard deviation (SD) of the systolic (SBPv), diastolic (DBPv), and mean BP (MBPv). Initial infarct volume (IIV) was defined as rCBF &lt;30%, penumbra area as time to maximum concentration (Tmax) &gt;6s, and mismatch volume as the difference between these two volumes (Tmax 6 - rCBF&lt;30%). Collateral status was evaluated using the hypoperfusion intensity ratio (HIR), defined as the Tmax&gt;10s/Tmax&gt;6s ratio. We used linear regression to investigate associations between these variables, using log-transformation to achieve normality, and final exponentiation for a better interpretability of the results. Results: We included 171 patients, mean age was 70.9± 13.7, 51.5% female, 88.3% white, median NIHSS was 15. Mean BP: SBP=12.37 + 6.8, DBP=10.2 + 7.1, and MBP=8.9 + 5.9. CTP values: rCBF &gt;30% (5 [IQR 0.001 - 22]), Tmax &gt;6s (103 [60.5 - 158.5]), and HIR (0.38 [0.17 - 0.54]). Higher SBP variability was significantly associated with lower mismatch volumes. Furthermore, higher SBP tertiles were associated with worse collaterals (high HIR) (Figure) . Conclusion: Pre-hospital BPV is associated with lower mismatch volume, likely mediated by the effect of BP on collateral status. Our findings are consistent with previous studies; the association between higher pre-treatment blood pressure and poorer collaterals might be due to an imbalance in the need of increasing perfusion to the ischemic tissue.

Abstract TP131: Computed Tomography Perfusion Imaging Patterns Are Similar Before and After Interfacility Transfer of Ischemic Stroke Patients

Background: Large vessel occlusion (LVO) stroke patients are often transferred from regional hospitals to comprehensive stroke centers (CSC) for thrombectomy. The need for repeat imaging at CSCs prior to intervention is unclear. We compared regional hospital and CSC perfusion imaging results for interfacility transfers in a single health system. Methods: We analyzed a cohort of patients in western Michigan who received CT perfusion imaging before and after transfer to a CSC. Perfusion mismatch (MM), core infarct volume (CIV), and favorability of imaging for mechanical thrombectomy (MT) candidacy were compared between the regional and CSC studies. A favorable imaging profile was defined as the presence of LVO, MM volume &gt;10 mL, and MM/CIV ratio of &gt;1.2. Linear regression was used to examine predictors of infarct growth during transfer. Results: Over a 10-month period, 25 patients met inclusion criteria. The median age was 76 (IQR 66-81), 60% were male, median NIHSS was 11 (IQR 2-18), and most patients had occlusion of the internal carotid or middle cerebral arteries (72%). The median time from last known well to initial CT was 250 minutes (IQR 85-620). Regional median MM volume was 52 mL (IQR 8-97), CIV was 0 mL (IQR 0-13), and hypoperfusion intensity ratio (HIR) was 0.25 (IQR 0-0.34). The median time between CTs was 152 minutes (IQR 139-226). The median change in MM volume was -3 mL (IQR -27-3) and median CIV growth rate was 0 mL/hr (IQR 0-2.0). In a multivariable regression model, higher HIR (β=23.2, p=0.012) and minutes between imaging studies (β=0.10, p=0.021) were associated with CIV growth. Sixteen patients (64%) had favorable imaging profiles for MT at the regional hospital. Of these, 15 (93.8%) continued to have a favorable CSC imaging profiles and 9 (56.2%) underwent MT. Of the 9 patients without favorable regional imaging profiles, 1 (11.1%) had a favorable CSC imaging profile and 2 (22.2%) underwent MT. Conclusion: In our sample, regional and CSC perfusion imaging patterns were similar and patients infrequently crossed thresholds for MT candidacy between studies. Initial HIR and longer delays between were independently associated with infarct growth during transfers, however overall infarct growth was very small.

Abstract WMP66: Detecting Medium Vessel Occlusions and Collateral Assessment With Multimodality AI Approach

Introduction: Recent advances and the use of Artificial intelligence (AI) is changing the standards of care in stroke patients. AI software has a high sensitivity and specificity for identifying Large Vessel Occlusions (LVOs), but the accuracy for detecting Medium Vessel Occlusions (MeVOs) is limited. We investigated the performance of the combination of two different AI modules for the identification of MeVOs. Methods: 150 patients with MeVOs were identified on CTA, using CTP to help localize the lesions, from retrospective databases at the MUSC, Stanford, and Royal Melbourne. Additionally, 55 patients with LVOs on CTA were included. A neuroradiologist confirmed the occluded vessel on CTA for each patient. LVOs were defined as occlusions of the intracranial ICA or horizontal segment of the M1. MeVOs were defined at M2, M3, ACA (A2/A3), or PCA (P2/P3) occlusions. All cases were processed through Rapid LVO, the Rapid Vessel Density module (which assesses hemispheric differences in blood vessel density), and Rapid CTP (Ischemaview Inc., Menlo Park, CA), [AZ1] using automated hypoperfusion intensity ratio (HIR) on CT perfusion (CTP), which estimates collateral flow, differed in LVOs vs. MeVOs. Results: Rapid LVO alone identified occlusions in 41/150 (27.3%) of MeVO patients. Rapid Vessel Density maps identified an additional 38/150 (25.3%) patients with either a 20-25% vessel density reduction or 26-40% reduction. Together, these two modules identified 79/150 (52.6%) of MeVO patients. 54/55 (98.1%) of the LVOs were detected by the Rapid LVO module. The mean HIR was lower in MeVO vs. LVO patients (0.25 vs. 0.45, P-value &lt; 0.001). Patients with M1 or ICA occlusions (LVOs) had average HIRs of 0.46 and 0.47 respectively. Patients with M2, M3, ACA, or PCA occlusions (MeVOs) had average HIRs of 0.30, 0.14, 0.22, and 0.20 respectively. Conclusion: MeVos detection was almost doubled with the use of the RapidAI Vessel Density in conjunction with the LVO module.