Johan Wassélius

Background/Objectives: Beam-hardening artifacts from the skull base reduce image quality in routine non-contrast head CT, particularly in the posterior fossa. Virtual monoenergetic images (VMIs) reconstructed from dual-layer spectral CT have been shown to reduce these artifacts, but previous studies have generally been limited by small cohorts or evaluation of only a limited range of monoenergetic reconstructions. The aim of this study was to comprehensively evaluate image quality and posterior fossa artifact reduction across the monoenergetic spectrum in a large cohort of normal head CT examinations. Methods: Consecutive adult patients undergoing non-contrast head CT on a dual-layer spectral CT system were retrospectively included if no intracranial pathology was identified on clinical interpretation. Regions of interest were placed in predefined posterior fossa and supratentorial locations in conventional images and automatically propagated to VMIs reconstructed from 40 to 200 keV. Image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), attenuation, and a posterior fossa artifact index were quantified. Two neuroradiologists independently performed qualitative image quality assessment. Results: A total of 188 examinations were included in the quantitative analysis and 40 in the qualitative assessment. Compared with conventional images, VMIs reconstructed at ≥50 keV demonstrated significantly reduced image noise in the posterior fossa together with a higher SNR, while the CNR was improved between 40 and 80 keV. Qualitative assessment likewise demonstrated superior overall image quality and reduced artifact severity, with the highest ratings generally obtained for reconstructions around 60 keV. Improvements became marginal above approximately 80 keV. Conclusions: Virtual monoenergetic reconstructions from dual-layer spectral CT improve posterior fossa image quality by reducing beam-hardening artifacts while maintaining favorable image noise and tissue contrast. Intermediate-energy reconstructions (approximately 50–70 keV) provide the most favorable balance between beam-hardening artifact reduction, image noise, and tissue contrast, supporting their use as an image optimization strategy for non-contrast head CT. Whether these technical improvements translate into improved diagnostic performance should be evaluated in future studies including patients with posterior fossa pathology.

Purpose: Subterminal intracranial Internal Carotid Artery (ICA-I) occlusion is a lesser-known stroke subtype which may delay access to endovascular thrombectomy (EVT). We compared clinical presentation, imaging characteristics, treatment delays, outcomes, and diagnostic accuracy between EVT-treated patients with ICA-I and carotid terminus (ICA-T) occlusions. Methods: All EVT-treated patients with intracranial ICA occlusions registered in two Swedish national quality registers (2016–2022) were included. Outcomes included pre- and postoperative National Institutes of Health Stroke Scale (NIHSS), successful recanalization, and 90-day modified Rankin Scale. Perfusion images and original radiology reports from one comprehensive stroke center were analyzed to assess the relationship between collateral anatomical variants, stroke severity, perfusion deficits, and diagnostic accuracy. Results: Among 6163 EVT-treated patients, 356 had ICA-I occlusions and 657 had ICA-T occlusions. Median baseline NIHSS was lower in ICA-I occlusions (17 vs. 19), but variability in NIHSS and modified Alberta Stroke Program Early CT Score were higher (both p < 0.001). ICA-I occlusions were associated with EVT treatment delays, but recanalization rates, 24-hour NIHSS, and 90-day functional outcomes were similar between groups. In exploratory hypothesis-generating sub-group analyses of ICA-I occlusions, anterior collateral variants were associated with stroke severity, and fetal-type posterior cerebral artery variants were associated with larger perfusion deficits. In a sub-group analysis, ICA-I occlusions were correctly identified in 31% of baseline radiology reports compared with 57% of ICA-T occlusions. Conclusion: ICA-I occlusions show greater clinical and radiological heterogeneity, are frequently underrecognized on baseline imaging, and are associated with longer treatment delays than ICA-T occlusions. Increased awareness may improve acute stroke triage and reduce delays to treatment.

BACKGROUND: Detection of ischemia and intracranial hemorrhage (ICH) directly after endovascular thrombectomy (EVT) could enable earlier diagnosis and treatment. We evaluated whether post-EVT Sine Spin cone-beam computed tomography (CBCT) on the Siemens ARTIS Icono biplane system at the end of the procedure can predict ischemia and ICH on subsequent follow-up computed tomography (FUCT) within 48 hours. METHODS: Adult patients undergoing EVT in 2024 with available CBCT and FUCT were included. Two interventional neuroradiologists independently evaluated the CBCT examinations for ischemia, ICH (including Heidelberg classification), and image quality. FUCT, annotated by a neuroradiologist, was used as reference standard. Large ischemia was defined as ischemia involving ≥3 predefined vascular territories. RESULTS: Of 331 patients with EVT, 225 had both CBCT and FUCT, of which 197 (88%) were successfully recanalized. Ischemia was observed in 127 (56%) and ICH in 64 (28%) of the FUCTs. For ICH, sensitivity was 75%/77% (reviewer 1/reviewer 2), specificity 85%/84%, and positive predictive value 67% for both reviewers, negative predictive value 92%/91%, and accuracy 84%/83%. Accuracy for large ischemia (n=24, 11%) was 78%/67%. Sensitivity for correctly located ischemia on CBCT was 48%/73%, with specificity of 87%/60%, positive predictive value of 82%/71%, negative predictive value of 56%/63%, and accuracy of 65%/68%. CBCT was rated overall nondiagnostic in 0%/1% of the cases. For the posterior fossa specifically, 6%/16% of examinations were rated nondiagnostic. CONCLUSIONS: Sine Spin CBCT on the Siemens ARTIS Icono biplane system after EVT showed high accuracy for predicting ICH and large ischemia on FUCT. CBCT may help identify patients needing closer monitoring or early neurosurgical intervention.

Introduction: We compared image quality of first- and second generation SOMATOM On.site mobile head CT with vendor-matched stationary head CT in neurosurgical ICU patients. Methods: Retrospective paired study of 100 ICU patients, 50 mobile CT v1 and 50 mobile CT v2, paired with stationary CT, yielding 200 head CT exams. Four radiologists blinded to image characteristics scored five tasks on a four-point scale: supratentorial cortical and deep image quality, infratentorial image quality and artifact severity. Quantitative metrics were attenuation and noise from four standardized ROIs, and grey-white matter contrast-to-noise ratio. Results: MobCT v2 received higher reader scores than paired stationary CT for overall image quality, supratentorial cortical and deep image quality, and equal to stationary CT for infratentorial image quality and artifact severity. Mobile CT v1 was rated lower than paired stationary CT, and lower than mobile CT v2, for all tasks. Attenuation, noise, and CNR were similar across groups. Radiation dose favoured mobile CT v2 with a median Dose Length Product (DLP) of 39.6 mGy·cm compared to 50.1 mGy·cm for mobile CTv1. Conclusion: The second generation On.site mobile CT yielded superior image quality versus the first generation and comparable to contemporary stationary CT with similar quantitative metrics. These findings support a broader adoption of point-of-care head CT.

Introduction: Changes in long-term survival after stroke at the population level are incompletely characterized, particularly using recent data and stratified by stroke type. Patients and methods: This nationwide, register-based cohort study used data from the Swedish Stroke Register (Riksstroke) and the Swedish Causes of Death Register. Adults (⩾18 years) hospitalized with ischemic stroke or intracerebral hemorrhage in Sweden during either 2013 or 2020 were included. Patients were followed for 3 years after the index stroke. The primary outcome was the difference in all-cause mortality within 3 years. Survival was assessed using Kaplan–Meier analyses and Cox proportional hazards regression, stratified by stroke type. Results: The study included 42,926 patients. Among patients with ischemic stroke, 3-year survival increased from 63.8% in 2013 to 69.3% in 2020, corresponding to an absolute difference of 5.5 percentage points, with survival differences increasing progressively during follow-up. Ischemic stroke in 2020 was associated with a lower risk of 3-year mortality compared with 2013 in both unadjusted (hazard ratio (HR), 0.83; 95% CI, 0.80–0.86) and multivariable analyses (adjusted HR, 0.92; 95% CI, 0.89–0.96). Survival improvements after ischemic stroke were most pronounced among patients aged 75 years or older. In contrast, long-term survival after intracerebral hemorrhage did not change between cohorts (3-year survival, 50.9% in both years; adjusted HR, 0.97; 95% CI, 0.89–1.05). Conclusions: In this nationwide cohort study, 3-year survival after ischemic stroke improved between 2013 and 2020, particularly among patients aged 75 years or older, whereas long-term survival after intracerebral hemorrhage remained unchanged. These findings suggest a contemporary population-level improvement in long-term survival after ischemic stroke over a relatively short calendar period and indicate that survival differences between cohorts increased progressively over long-term follow-up.

The diagnostic accuracy of AIDOC-VO, the first commercial artificial intelligence tool for intracranial large-and medium-vessel occlusion (LVO/MeVO) detection on head-and-neck CT angiography (CTA), was evaluated in a multicenter emergency setting. A prospective diagnostic-accuracy study of 3,031 adult CT angiograms (mean age, 67.3 years ± 16.4 [SD]; 1,549 females) acquired March–July 2024 across a ten-hospital region was performed. The AI model was compared with clinical radiology reporting. Examinations flagged positive or doubt by either the AI model or report underwent blinded rereading for reference-standard establishment. Of 3,031 CT angiograms, valid AI model output was yielded for 2,804 (92.5%), of which 224/2,804 (8.0%) had vessel occlusion (VO) on referencestandard reading. For VO detection within intended use (218/224), sensitivity was 81.7% (178/218) (clinical report: 81.2% [177/218]; P =.91), and specificity was 99.6% (2,569/2,580) (clinical report: 99.3% [2,561/2,580]; P =.12). LVO sensitivity was 92.8% (64/69) (clinical report: 87.0% [60/69]; P =.42) and MeVO sensitivity was 76.1% (121/159) (clinical report: 79.2% [126/159]; P =.55). The AI model identified VOs missed by radiologists in 42 examinations, for an enhanced detection rate of 18.8% (42/224; 15 per 1,000 CT angiograms), and generated 11 false alerts (3.9 per 1,000 CT angiograms). Performance did not differ significantly from clinical radiology reporting. ©RSNA, 2026

Background: Accurate volumetry and imaging characterization of chronic subdural hematoma (cSDH) are essential for prognostication and treatment planning, but manual assessment is time-consuming and therefore underutilized. Methods: We retrospectively analyzed preoperative non-contrast CT (NCCT) scans of 257 patients undergoing first-time surgery for uni- or bilateral cSDH. Hematoma volumes were measured manually using a semi-automated area-outlining tool on every second axial slice and compared with the volumes estimated through the ABC/2 formula. Hematoma attenuation patterns and components were categorized, and interrater reliability was assessed for volume, maximum diameter, and imaging features using intraclass correlation coefficients (ICCs) and Cohen’s κ. Results: A total of 339 hematomas were evaluated. Manual and ABC/2 volume measurements correlated strongly (R² = 0.83, ICC [3, 1] = 0.90). The interrater agreement for manual volumetry was excellent (ICC [2, 1] = 0.96). Agreement was also excellent for maximum diameter (ICC [2, 1] > 0.9) and good for midline shift assessment (κ = 0.81). Agreement was moderate for the identification of fresh clots, trabeculations, and laminations (κ = 0.62–0.72) but poor for general attenuation patterns (κ = 0.44). Conclusions: The manual volumetry of cSDH is feasible and highly reproducible between raters of different experience levels. These results provide a robust reference standard for the validation of automated volumetry tools and support the implementation of quantitative hematoma assessment in future clinical trials and routine care.

Introduction: Endovascular thrombectomy (EVT) is a significant improvement in the care of acute ischemic stroke (AIS) patients, but only a small portion of patients receive treatment. Our aim was to analyze EVT implementation in Sweden according to a set of key performance indicators (KPIs) for procedural and implementational effectiveness. Methods: A nationwide prospective registry-based observational study using data from 2018, 2020, and 2022 from the Swedish quality registries for stroke care (Riksstroke and EVAS) and official population statistics. Effectiveness was analyzed using a set of predefined KPIs. To describe procedural and implementation effectiveness in a single comprehensible measure population success rate was derived by multiplying the EVT rate with successful recanalization. Results: Between 2018 and 2022 EVTs in Sweden increased from 874 to 1474 procedures per year. Correspondingly, the EVT rate (EVT/AIS) increased from 4.1% to 7.3%. Implementation was heterogenous with a six-fold difference between the highest and lowest regions. EVT rates were generally highest in regions with comprehensive stroke centers (CSCs). Procedural effectiveness were similar between all CSCs. The population success-rate increased from 3.4% to 6.4% during the period with large differences between CSCs (range 3.4%–12.4%, in 2022). Conclusions: By including KPIs for procedural and implementational effectiveness, it is possible to evaluate EVT implementation for the entire stroke population, which is the ultimate objective for healthcare. The population success-rate is capturing procedural implementation effectiveness in a single measure comprehensible for all stake holders and facilitate comparisons over time and between regions, even between regions with different stroke incidence.

Purpose: Techniques for endovascular thrombectomy in acute ischemic stroke due to medium or distal vessel occlusions (MDVO) need to be improved, and first-line aspiration is emerging as a promising technique. The objective was to describe first-pass and final reperfusion rates with a triaxial direct aspiration first pass technique (ADAPT) and a novel, quadriaxial technique (QUATTRO-ADAPT) using RED43 Reperfusion Catheters to target MDVOs. Methods: This retrospective study collected data from 11 stroke centers in Europe and North America between 2023 and 2025. Patients with primary, isolated MDVOs who underwent thrombectomy using first-line aspiration with RED43 Reperfusion Catheters were included. Primary outcome was first-pass successful reperfusion rate (modified Treatment In Cerebral Infarction score ≥ 2b). Additionally, final reperfusion rates, complications and functional outcomes up to 90 days were evaluated. Results: We included 85 cases. Median age was 74 years (IQR 67–81) and median National Institutes of Health Stroke Scale score 9 (IQR 6–15). The majority (69.4%) had an occlusion of the co- or nondominant M2 segment of the middle cerebral artery. First-pass successful reperfusion was 63.5% overall, with 55.6% for the triaxial ADAPT and 69.4% for the quadriaxial QUATTRO-ADAPT. Final successful reperfusion was achieved in 96.5%. Complications included vessel perforations (2.4%), subarachnoid hemorrhage (3.5%), parenchymal hematoma type 2 (2.4%), and symptomatic intracerebral hemorrhage (1.2%). Functional independence (modified Rankin Scale 0–2) at 90 days was observed in 58.7%. Conclusion: This study shows that first-line aspiration, especially in a quadriaxial approach, can be effective and safe. These findings should be evaluated in prospective trials.