Aug 2026· Journal of Magnetic Resonance Imaging· 0 citations· 43 references
Medicine
TL;DR
This review critically appraise how CT and MRI are integrated hierarchically across these scenarios, and how emerging fast MRI and quantitative biomarkers may reshape future selection paradigms.
Abstract
The management of acute ischemic stroke has shifted from rigid time-based protocols to imaging-driven, tissue-based reperfusion strategies. Non-contrast CT and CT angiography remain the indispensable frontline for rapid triage, particularly in community and low-resource settings. However, magnetic resonance imaging (MRI) provides unique biological information that complements CT-based assessment: Diffusion-weighted imaging (DWI) detects cellular ischemia within minutes without contrast; DWI-fluid-attenuated inversion recovery (FLAIR) mismatch serves as a tissue clock for unknown-onset stroke; susceptibility-weighted imaging (SWI) aids thrombus characterization; and MRI resolves the posterior fossa without beam-hardening artifact. Low-field portable MRI further extends these capabilities to the bedside where conventional scanners are unavailable. This review examines four convergent trends within this transition: expanding thrombectomy to large-core infarction, extending thrombolysis through tissue-based selection, advancing recanalization in posterior-circulation stroke while defining boundaries for medium- and distal-vessel occlusions, and simplifying imaging workflows through fast MRI protocols, quantitative CT biomarkers, and artificial intelligence (AI). Landmark trials have established that treatment benefit is determined by tissue viability rather than clock time, while recent negative trials define critical boundaries beyond which intervention may cause harm. We critically appraise how CT and MRI are integrated hierarchically across these scenarios, and how emerging fast MRI and quantitative biomarkers may reshape future selection paradigms. EVIDENCE LEVEL: 3-4. TECHNICAL EFFICACY: 3.
The current clinical evidence base is reviewed, including the role of LF-MRI in supporting stroke-type classification and tissue confirmation, in wake-up and unknown-onset stroke for tissue-based triage, and in post-therapeutic settings to enable serial assessment after thrombolysis or thrombectomy.
A. Sorby-Adams, N. Pintér, Keith W. Muir et al.· Stroke· 0 citations
Although digital subtraction angiography remains the gold standard for the diagnosis and treatment planning of intracranial arteriovenous shunts (AVS), including arteriovenous malformations and arteriovenous fistulas, non-invasive imaging is increasingly sought for comprehensive evaluation. Magnetic resonance imaging (MRI) plays a crucial role in AVS detection, identification of feeding arteries and draining veins, localization of shunt points, classification of subtypes, assessment of venous reflux and congestion, and evaluation of post-treatment residual or recurrent lesions. Clinical techniques such as time-of-flight MR angiography (MRA), contrast-enhanced time-resolved MRA, susceptibility-weighted imaging, and arterial spin labeling (ASL) are established for these assessments. Recent advances have expanded MRI capabilities: Ultrashort echo time MRA can overcome turbulent flow-related signal loss and susceptibility artifacts, improving visualization of complex nidus architecture; compressed sensing substantially accelerates three-dimensional and four-dimensional (4D)-MRA while maintaining diagnostic quality; ASL-based 4D-MRA provides high-temporal-resolution dynamic evaluation without contrast, with vessel-selective techniques enabling independent assessment of individual vascular territories; and high-resolution vessel wall imaging shows promise for risk stratification. Emerging artificial intelligence applications enable automated AVS segmentation and characterization, with potential to enhance image quality and reduce scan times. This review summarizes current MRI techniques, recent innovations, and future perspectives in the non-invasive assessment of intracranial AVS.
Akihiko Sakata, Koji Fujimoto, M. Iima et al.· Diagnostic and Interventiona...· 0 citations
Low-field magnetic resonance imaging (LF-MRI) has recently emerged as a novel approach to extend MRI capability into critical care environments and offers a unique opportunity to support repeated imaging during periods when neurological examination is unreliable or limited.
Lina Zheng, Z. Law, X. Nie et al.· Stroke· 0 citations
Accurate delineation of infarct core and ischemic penumbra in acute ischemic stroke primarily relies on computed tomography perfusion (CTP), where the arterial input function (AIF) is essential for reliable perfusion quantification. However, reliable and fast AIF selection remains challenging in clinical practice due to noise, vascular heterogeneity, and inter-patient variability in bolus dynamics. In this study, we propose TriAIF-RWKV, a three-stage framework for robust and automated AIF extraction. Specifically, ACSANet is first employed for spatial vascular localization using axial and channel-aware attention mechanisms, thereby narrowing the candidate arterial region and reducing the AIF search space. Then, a Dilated-RWKV network is introduced to model temporal intensity dynamics from a global sequence perspective, allowing robust identification of AIF-consistent patterns. Finally, a physiology-informed scoring strategy is used to select the optimal AIF by evaluating baseline stability, peak enhancement, and washout characteristics. Extensive experiments on CTP datasets were conducted from multiple perspectives, including AIF waveform fidelity, perfusion parameter estimation, and lesion-level analysis. The results demonstrate that the proposed method achieved high agreement with expert-selected AIFs, with a global waveform PCC of 0.973, peak correlation of 0.942, and TTP correlation of 0.973 with a mean error of 0.923 s. Furthermore, the proposed method provides more consistent downstream perfusion quantification, achieving higher consistency of CTP-derived parameters and improved lesion-to-normal tissue discrimination compared with existing approaches. These results highlight its potential for reliable clinical perfusion assessment.
Lei Lei, Yu Shen, Dawei Wang et al.· Entropy· 0 citations
Standard CT perfusion mismatch and hypoperfusion intensity ratio formulas are undefined when ischemic core or Tmax>6 s equals zero. Such “imaging-quiescent” patients remain uncharacterized. We quantified their prevalence and used DWI to separate CTP-undetected ischemia from DWI-negative presentations.
We conducted a single-center retrospective cohort study of 188 consecutive patients receiving intravenous thrombolysis between January 2023 and October 2025. Patients were classified into four CTP phenotypes based on the presence of rCBF<30% core and Tmax>6 s hypoperfusion: A (classic mismatch), B (core without hypoperfusion), C (pure penumbra), and D (imaging-quiescent, both volumes = 0 mL). Group D was further subdivided by post-thrombolysis DWI into D1 (DWI-positive), D2 (DWI-negative), and D3 (DWI unavailable). The primary outcome was 90-day modified Rankin Scale 0–2. Analyses included Kruskal–Wallis tests, multivariable logistic regression, two one-sided tests, and false discovery rate adjustment.
Of 188 thrombolysed patients, 168 had classifiable CTP phenotypes and 161 had 90-day mRS data. Group D was the largest phenotype (
n
= 69, 41.1%), with a favorable outcome rate of 84.6%, comparable to Group C (83.9%) and higher than Group A (55.9%). Among 62 Group D patients with DWI, 42 (60.9%) were DWI-positive (D1) and 20 (29.0%) were DWI-negative (D2). D1 patients had higher NIHSS (median 4 vs. 2), more posterior circulation involvement (38.1% vs. 5.0%), and lower favorable outcome rates (80.5% vs. 94.1%); 65% of D2 patients achieved mRS = 0. Group A had 51.4% large-vessel occlusion versus 4.4% in Group D. In multivariable regression (EPV = 17, AUC = 0.823), NIHSS was the strongest predictor of favorable outcome (OR 0.83 per point, 95% CI 0.75–0.91;
p
< 0.001).
The imaging-quiescent phenotype is not a single entity but a composite of three operationally defined subgroups (D3 reflecting absent MRI data rather than a distinct biological entity), with approximately 30% being DWI-negative, a population enriched for stroke mimics or transient ischemic events. DWI reclassified nearly one-third of CTP-quiescent patients and may improve diagnostic precision. These findings are hypothesis-generating and suggest that post-thrombolysis DWI may improve diagnostic characterization of CTP-quiescent patients; prospective study is required before any change to pre-thrombolysis workflow can be recommended.
Songqi Hou, Rui Wang, Xiao-Bin Chen et al.· Frontiers in Neuroscience· 0 citations
BACKGROUND
The therapeutic landscape of acute ischemic stroke (AIS) has been transformed by expanding endovascular therapy (EVT) criteria. With the incorporation of MR perfusion imaging in the 2026 AHA/ASA Guidelines for the early management of patients with AIS to support EVT patient selection, there is renewed energy and focus on the clinical applications of different MR perfusion techniques in AIS. A reliable, contrast-free perfusion technique with acceptable acquisition time and capability to identify salvageable tissue and assess collateral status may be utilized in certain clinical contexts. Arterial spin labeling (ASL) is a clinically feasible technique that can be considered as a valuable modality within stroke workflows and MRI-based EVT selection protocols, particularly in patients with renal insufficiency, contrast allergy, and contrast-limited settings. Although ASL has been investigated in multiple previous studies, its systematic integration into contemporary acute stroke clinical workflows has yet to be routinely adopted and standardized practical guidance in this regard is lacking. Furthermore, ASL is not yet validated in prospective EVT-selection trials to support timely reperfusion decisions.
METHODS AND PURPOSE
This state-of-practice paper was developed on behalf of the American Society of Functional Neuroradiology (ASFNR) by an expert panel of neuroradiologists with expertise in cerebrovascular imaging and MR perfusion. We appraise the current evidence, clinical applications, implications for therapeutic decision-making, and translational barriers of ASL in AIS triage and EVT patient selection. We also discuss ASL challenges related to workforce capacity and reimbursement, and propose recommendations for future clinical validation and implementation.
CONCLUSION
ASL may serve as a valuable adjunct within MRI-based stroke workflows by providing complementary information on ischemic penumbra and collateral status. However, validation through multicenter prospective studies for EVT patient selection, standardized acquisition protocols, and automated postprocessing quantification pipelines are needed before ASL can be routinely integrated into time-sensitive stroke workflows.
M. Gad, D. Tsang, Aakanksha Sriwastwa et al.· AJNR. American journal of ne...· 0 citations
