Jae-Kwan Cha

Background and ObjectivesCraniocervical artery dissection (CCAD) is a major cause of stroke in young adults, yet its recurrence risk remains poorly defined because of delayed enrollment in prior re...

Background: Stroke registries have advanced cerebrovascular research but usually reduce neuroimaging to categorical variables, losing multidimensional information. We describe the CRCS‐K (Clinical Research Collaboration for Stroke in Korea) Imaging Repository, a multicenter platform integrating stroke imaging, artificial intelligence‐based quantification, and clinical and outcome data through a dedicated research platform, Artificial Intelligence Powered Stroke Clinical‐Image Archive Network (AISCAN). Methods: Building upon the nationwide CRCS‐K registry, the Imaging Repository collected all computed tomography, magnetic resonance, and angiographic studies obtained during index hospitalization from consecutive patients with acute ischemic stroke at 18 stroke centers. Images underwent centralized deidentification, quality verification, sequence classification, and artificial intelligence‐based quantification. As a proof‐of‐concept application, we examined associations of pretreatment imaging modality with treatment workflow and functional outcomes after intravenous thrombolysis or endovascular treatment. Results: From June 2022 through May 2025, 225 159 imaging sequences were collected from 20 792 patients. AI modules generated standardized numeric features including ischemic lesion volumes, perfusion parameters, white matter hyperintensity burden, and cerebral microbleed counts. Magnetic resonance‐first workflows varied substantially across centers, from 1.0% to 56.7%. Greater pretreatment imaging sequence burden was associated with longer door‐to‐treatment times after intravenous thrombolysis and endovascular treatment. In overlap‐weighted analyses, magnetic resonance‐based versus computed tomography‐based imaging was associated with directionally lower, but not statistically significant, odds of a favorable 3‐month outcome after intravenous thrombolysis (odds ratio [OR], 0.90 [95% CI, 0.70–1.18]) and endovascular treatment (OR, 0.89 [95% CI, 0.65–1.21]). Conclusions: Prospective, sequence‐level retention of all stroke neuroimaging is feasible at network scale and can be integrated with artificial intelligence‐derived features and clinical outcomes. This resource enables real‐world investigation of imaging workflows and outcomes.

BACKGROUND: Recent trials established the efficacy of thrombectomy for large-core stroke by utilizing the Alberta Stroke Program Early Computed Tomography Score (ASPECTS) as a pragmatic tool. However, whether this topographical scoring captures the therapeutic ceiling, or the upper threshold of infarct volume where the benefit of reperfusion diminishes, remains unclear. METHODS: Leveraging a nationwide multicenter registry in Korea (2022–2024), we compared the prognostic value of quantitative volumetry and ASPECTS in thrombectomy-treated patients. We analyzed discordance between ASPECTS and volumetry derived from diffusion-weighted imaging, computed tomography perfusion, and noncontrast computed tomography. The primary outcome was poor functional outcome (90-day modified Rankin Scale score 5–6). To estimate treatment effects across specific volume spectra, we conducted target trial emulations that stratified causal estimates by volumetric thresholds, with the ordinal 90-day modified Rankin Scale score shift as the primary outcome. RESULTS: Among 552 patients, the mean age was 70.4±12.6 years, and 319 (57.8%) were men. Patients classified as large core by ASPECTS but not by diffusion-weighted imaging volumetry (ASPECTS-only large core) had poor outcome proportions comparable to the both small-core group (11.8% versus 11.7%), with no excess risk after adjustment. Conversely, volumetric confirmation of large core across diffusion-weighted imaging, computed tomography perfusion, and noncontrast computed tomography consistently predicted poor prognosis regardless of ASPECTS (adjusted odds ratio, 6.92 [95% CI, 2.58–19.34] for the diffusion-weighted imaging–only large-core group). In the target trial emulations, the overall benefit of thrombectomy was attenuated (common odds ratio, 0.56 [95% CI, 0.31–1.03]). Stratified analyses delineated a therapeutic ceiling, with benefit in the 50 to 110 mL range (common odds ratio, 0.38 [95% CI, 0.15–0.97]) disappearing in extensive infarctions >110 mL. CONCLUSIONS: Quantitative volumetry provided better prognostic discrimination and identified ≥110 mL as a therapeutic ceiling where the benefit of thrombectomy becomes negligible. These findings advocate integrating volumetric thresholds into patient selection to minimize futile reperfusion and prioritize safety, serving as a critical refinement to current topographical scoring.

Background Adults aged 80 years and older are the fastest-growing segment of the stroke population. Whether contemporary advances in stroke care have produced sustained outcome gains in this group during the past decade, including the post-pandemic era, has not been examined in nationwide longitudinal data with concurrent age-specific comparison. Methods Using the Clinical Research Collaboration for Stroke in Korea-National Institutes of Health (CRCS-K-NIH) registry, we analyzed consecutive adults with acute ischemic stroke admitted within 7 days of symptom onset between 2011 and 2022. Patients aged 80 years and older formed the primary cohort; those aged 18-79 years served as comparators. Primary outcomes were 3-month utility-weighted modified Rankin Scale (UW-mRS) and 1-year all-cause mortality. Non-linear trends and age-group-by-year interaction were modeled using restricted cubic splines adjusted for sex, age, and baseline NIHSS. Results Of 83,953 patients, 18,514 (22.1%) were aged 80 years and older; their proportion rose from 17.4% to 27.3%. Despite treatment intensification (endovascular thrombectomy 4.2% to 10.6%; oral anticoagulation for atrial fibrillation 52.5% to 76.9%), 1-year mortality in this group fell from 27.5% in 2011 to 19.4% in 2019, then rose to 23.7% by 2022; 3-month UW-mRS improved from 0.47 to 0.51 over the same period, then stagnated at 0.48. Restricted cubic splines confirmed significant nonlinearity in both outcomes after adjustment for sex, age, and NIHSS (P < 0.01 for both). Younger patients showed no comparable functional deterioration. Age-group-by-year interaction was significant for 3-month UW-mRS (P < 0.001) but not for 1-year mortality (P = 0.058), which showed a similar direction in both age groups. Conclusion In this nationwide registry, patients aged 80 years and older experienced an age-specific inflection of functional recovery gains after 2019 despite continued intensification of acute stroke care. Sustaining outcome gains in this population may require attention to post-acute care infrastructure.

Background: Whether comprehensive prestroke risk factor (RF) management—defined by the extent to which existing major RFs meet prespecified treatment and biomarker criteria—is associated with 3‐month functional outcomes after ischemic stroke remains unclear. Methods: We analyzed patients with ischemic stroke from the CRCS‐K‐NIH (Clinical Research Collaborations for Stroke in Korea‐National Institutes for Health) registry (2011–2022), a multicenter stroke registry in Korea. Hypertension, diabetes, dyslipidemia, and atrial fibrillation were considered as major RFs for ischemic stroke. Comprehensive prestroke RF management was categorized as well controlled (all present RFs meeting study‐defined control criteria), partially controlled (some RFs meeting this criteria), or poorly controlled (no RFs meeting this criteria). The primary outcome was 3‐month modified Rankin Scale score of 0 to 2, indicating functional independence (good outcome). Results: Among 63 570 patients with ≥1 major RFs, 28.6% were poorly controlled, 35.6% partially controlled, and 35.8% well controlled. The rate of 3‐month good outcome was 66.0% among those with 1 RF, 60.8% in 2, and 55.0% in ≥3. After multivariable adjustment, both well‐controlled and partially controlled groups had significantly higher odds of achieving good 3‐month outcomes compared with poorly controlled patients, consistently across RF burden strata(well controlled: adjusted odds ratio, 1.16 [95% CI, 1.08–1.25] for 1 RF, 1.34 [95% CI, 1.21–1.48] for 2, and 1.23 [95% CI, 1.03–1.48] for ≥3; partially controlled: 1.16 [95% CI, 1.06–1.26] for 2; 1.22 [95% CI, 1.05–1.42] for ≥3) and in the overall cohort (well controlled: 1.22 [95% CI, 1.15–1.29], partially controlled: 1.14 [95% CI, 1.07–1.22]). Conclusions: Comprehensive prestroke RF management, defined by study‐specific treatment‐ and biomarker‐based criteria, was independently associated with a higher likelihood of favorable 3‐month outcomes across levels of RF burden. These findings suggest that effective prestroke management of existing RFs may improve poststroke functional outcomes, regardless of the number of RFs present.

Background: In atrial fibrillation (AF), cerebral microbleed (CMB) burden guides anticoagulation decisions, yet AF is itself inconsistently associated with CMBs, a paradox unexplained by frameworks that treat CMBs as a unitary marker of small vessel disease. We hypothesized that the white matter hyperintensity (WMH) context in which CMBs arise modifies their vascular meaning, and that this context-dependence underlies the inconsistent AF–CMB association. Methods: From a multicenter Korean stroke registry, we analyzed 5,735 first-ever ischemic stroke patients imaged at nine centers using susceptibility-weighted MRI. WMH volume and CMB count were extracted by validated deep learning pipelines. Patients were cross-classified by age-adjusted WMH residual (median split) and CMB count (≥2) into four groups. The AF–CMB association was estimated by multivariable logistic regression within each WMH stratum with formal interaction testing. Spatial CMB distribution was analyzed against the Automated Anatomical Labeling atlas. Results: In the full cohort (mean age 69.5 years; 57.7% male), AF was not associated with CMBs (OR 1.04; 95% CI 0.87–1.25). Stratification yielded divergent estimates: the adjusted AF OR was 1.46 (1.11–1.93; P = 0.007) in the WMH-low stratum and 0.95 (0.73–1.22; P = 0.665) in the WMH-high stratum, with significant interaction (OR 0.56; P < 0.001). The discordant phenotype (low WMH, high CMB; 8.9%) was enriched for AF (28.0%) and showed fronto-temporal cortical predominance with deep structure sparing. AF independently reduced the proportion of deep CMBs (IRR 0.80; P = 0.040). The interaction was preserved across prespecified sensitivity analyses. Conclusions: The AF–CMB association is confined to patients with low WMH burden relative to age and is accompanied by a topographically distinct CMB distribution. Clinical assessment of small vessel disease based on WMH alone may overlook a CMB phenotype linked to AF.

Background and Purpose: Ambient air pollution is an established risk factor for incident stroke, but whether post-discharge pollutant exposure influences stroke recurrence remains unknown. We investigated the association between post-discharge exposure to six ambient air pollutants and stroke recurrence in patients with acute ischemic stroke. Methods: We analyzed data from 27,346 patients in the CRCS-K-NIH nationwide multicenter registry of acute ischemic stroke patients (2014–2021) with confirmed ischemic stroke, residential address data, and matched air quality records. The primary exposure was the 3-month post-discharge average concentration of PM ₁₀ , PM _2.5 , NO₂, SO₂, CO, and O₃, assessed at the district level using inverse-distance weighted interpolation. The primary outcome was stroke recurrence from 3 to 15 months post-discharge. Cause-specific Cox proportional hazards models accounting for the multilevel data structure were used, with all-cause mortality as a competing risk. Restricted cubic splines assessed nonlinear dose-response relationships. Results: During follow-up (median 364.8 days), 765 patients experienced stroke recurrence and 471 died. Among the six pollutants, only SO₂ showed a statistically significant association with recurrence (P for overall association in the restricted cubic spline analysis = 0.024). A potential threshold was identified at approximately 8.2 ppb, above which recurrence risk increased progressively (P for non-linearity = 0.095). The association was numerically stronger among older adults (≥75 years; P for interaction = 0.051) and women (P for interaction = 0.062). The highest SO₂ concentrations were observed in harbor cities (Incheon, Ulsan, Busan), consistent with maritime shipping emissions. No significant associations were observed for the other five pollutants. Conclusions: Elevated post-discharge SO₂ exposure is associated with increased stroke recurrence risk, particularly in harbor regions and among older adults and women. These findings support incorporating ambient air quality monitoring into secondary stroke prevention strategies.

BACKGROUND: Hemorrhagic transformation (HT) after recanalization therapy remains a critical concern in acute ischemic stroke management. While severe hemorrhages clearly worsen outcomes, the prognostic impact of mild HT and its optimal prediction methods remain uncertain. In this study, we aimed to evaluate the clinical significance of all HT subtypes and develop automated HT prediction models based on noncontrast computed tomography (CT) images. METHODS: We analyzed 2211 patients receiving intravenous thrombolysis, endovascular thrombectomy, or both from the multicenter Clinical Research Collaboration for Stroke in Korea Imaging repository (2022–2024). HT was classified on follow-up imaging of magnetic resonance or CT. Baseline ischemic lesion volume and Alberta Stroke Program Early CT Score–based net water uptake were quantified on baseline noncontrast CT. Multivariable regression was used to assess the association of HT and 90-day modified Rankin Scale scores. The performance of HT prediction models was compared, the automated imaging model versus established scores (hemorrhage after thrombolysis score and SEDAN), using the area under the curve. RESULTS: HT occurred in 41.2% of patients (hemorrhagic infarction [HI] 1: 13.8% and HI2: 16.8%, parenchymal hematoma [PH] 1: 6.5% and PH2: 4.1%). All HT subtypes independently predicted worse functional outcomes with stepwise increasing odds ratios: HI1 (1.77 [95% CI, 1.40–2.22]), HI2 (2.83 [95% CI, 2.27–3.53]), PH1 (4.65 [95% CI, 3.41–6.36]), and PH2 (14.76 [95% CI, 9.61–22.90]). This association persisted across treatment modalities and vascular territories. For PH prediction, the automated imaging model (noncontrast CT imaging markers combined with clinical variables) achieved superior performance (area under the curve, 0.77 [95% CI, 0.73–0.80]) compared with hemorrhage after thrombolysis score (0.71 [95% CI, 0.68–0.75]) and SEDAN (0.72 [95% CI, 0.69–0.76]) scores (both P <0.01 for area under the curve comparison). CONCLUSIONS: Even mild HI was independently associated with poor functional outcomes after reperfusion therapy. Automated noncontrast CT–derived biomarkers provide superior HT risk prediction compared with conventional scores, offering a practical tool for individualized stroke management in the reperfusion era.