Susceptibility Vessel Sign and Cardioembolic Etiology in the THRACE Trial

Stent Retriever Deployment Tracing Susceptibility Vessel Sign in the M2 Branch Predicts the Effective First-Pass Reperfusion in Thrombectomy for M1 Occlusion

BACKGROUND AND PURPOSE

Successful first-pass reperfusion is associated with better functional outcomes after mechanical thrombectomy (MT) for acute ischemic stroke, but its treatment strategies remain unclear.

MATERIALS AND METHODS

We retrospectively recruited patients who underwent MT for M1 occlusion between December 2020 and May 2023 at our institution. The locations of susceptibility vessel sign (SVS) on magnetic resonance imaging were classified into M1 only, M1 to single M2 branch, or M1 to both M2 branches. Patients were included in the SVS tracing group when the stent retriever of the first pass covered the entire SVS length. Successful reperfusion was defined as a modified Thrombolysis in Cerebral Infarction scale 2b-3. Any intracranial hemorrhage detected at 24-hour postoperatively was included as a hemorrhagic complication.

RESULTS

The SVS was detected in M1 only, M1 to single M2 branch, and M1 to both M2 branches in 8, 22, and 4 patients, respectively. Among the 34 patients, 27 were included in the SVS-tracing group. Successful first-pass reperfusion was significantly more frequent in the SVS-tracing group compared with the non-SVS tracing group (odds ratio, 14.4; 95% confidence interval, 2.0 - 101; P = 0.007). The procedural time was significantly reduced in the SVS tracing group (median, 29 [interquartile range, 22 - 49] minute vs. 63 [43 - 106] minute; P = 0.043). There was a trend toward less frequent hemorrhagic complications in the SVS tracing group (odds ratio, 0.17; 95% confidence interval, 0.029 - 1.0; P = 0.052).

CONCLUSIONS

This study provides a thrombus imaging-based MT strategy to efficiently achieve first-pass reperfusion in M1 occlusion.

Imaging diagnosis of intracranial atherosclerosis stenosis-related large vessel occlusion before and during endovascular therapy

It is becoming increasingly important to identify the type of stroke, especially the mechanism of occlusion, before and during its treatment. In the case of intracranial atherosclerotic stenosis-related large vessel occlusion, it is necessary to develop a treatment strategy that includes not only mechanical thrombectomy but also adjunctive therapies such as primary or rescue therapy (percutaneous angioplasty, intracranial/carotid stenting, local fibrinolysis) and perioperative antithrombotic therapy. However, in clinical practice we often encounter cases where it is difficult to identify the occlusive mechanism before endovascular treatment because of insufficient information in the minimal circumstances of the hyperacute phase of stroke. Here we focus on the imaging diagnosis before and during treatment of intracranial atherosclerotic stenosis-related large vessel occlusion with in situ thrombotic occlusion as the mechanism of thrombotic occlusion, based on previous reports. We describe the diagnosis of intracranial atherosclerotic stenosis-related large vessel occlusion from the perspectives of "thrombus imaging," "perfusion," and "occlusion margin."

Factors That Influence Susceptibility Vessel Sign in Patients With Acute Stroke Referred for Mechanical Thrombectomy

Background and Purpose

The presence of a Susceptibility Vessel Sign (SVS) in the acute phase of proximal occlusion ischemic stroke indicates the presence of deoxyhemoglobin in the thrombus. Thrombi composition changes over time. The aim of this study was to investigate whether the absence of SVS is associated with a shorter symptom onset to imaging time.

Methods

We retrospectively analyzed all patients referred for mechanical thrombectomy at Besançon University Hospital between 1 January 2015 and 31 December 2020 for whom readable T2^*-weighted imaging was available. We compared patient characteristics according to the presence or absence of an SVS. We also studied the subgroup for whom the exact symptom onset time was known. We performed a univariate statistical analysis, then a multivariate analysis on the variables that were statistically significant in the univariate analysis.

Results

Of the 389 patients included, 309 (79.4%) were SVS+. We found no significant relationship between SVS– and the time between symptom onset and imaging in the whole cohort. In the multivariate analysis, SVS– was associated with anticoagulant treatment (p < 0.01), and SVS+ with age (p = 0.023) and carotid terminus occlusion (p = 0.042). In the known symptom onset subgroup, SVS– was significantly associated with a shorter symptom onset -imaging time (p < 0.001), and this was confirmed in the multivariate analysis (p = 0.011; OR 0.911; 95% CI [0.844; 0.972]).

Conclusion

In the acute phase of proximal occlusion ischemic stroke, absence of SVS was associated with a shorter symptom onset–imaging time for patients with a known symptom onset time.

Characterising acute ischaemic stroke thrombi: insights from histology, imaging and emerging impedance-based technologies

Treatment of acute ischaemic stroke (AIS) focuses on rapid recanalisation of the occluded artery. In recent years, advent of mechanical thrombectomy devices and new procedures have accelerated the analysis of thrombi retrieved during the endovascular thrombectomy procedure. Despite ongoing developments and progress in AIS imaging techniques, it is not yet possible to conclude definitively regarding thrombus characteristics that could advise on the probable efficacy of thrombolysis or thrombectomy in advance of treatment. Intraprocedural devices with dignostic capabilities or new clinical imaging approaches are needed for better treatment of AIS patients. In this review, what is known about the composition of the thrombi that cause strokes and the evidence that thrombus composition has an impact on success of acute stroke treatment has been examined. This review also discusses the evidence that AIS thrombus composition varies with aetiology, questioning if suspected aetiology could be a useful indicator to stroke physicians to help decide the best acute course of treatment. Furthermore, this review discusses the evidence that current widely used radiological imaging tools can predict thrombus composition. Further use of new emerging technologies based on bioimpedance, as imaging modalities for diagnosing AIS and new medical device tools for detecting thrombus composition in situ has been introduced. Whether bioimpedance would be beneficial for gaining new insights into in situ thrombus composition that could guide choice of optimum treatment approach is also reviewed.

Predictive value of thrombus susceptibility for cardioembolic stroke by quantitative susceptibility mapping

BACKGROUND

The hypointense blooming signal of thrombi on susceptibility-weighted imaging (SWI), known as the susceptibility vessel sign (SVS), is predictive of cardioembolic stroke. The SVS originates from the local magnetic susceptibility effect; thus, the susceptibility value of thrombi may provide useful information in discriminating stroke etiology. We aim to utilize quantitative susceptibility mapping (QSM) to assess thrombus's susceptibility value in acute ischemic stroke patients and explore the relationship of thrombus susceptibility with cardioembolic stroke.

METHODS

From 2018 to 2020, 132 consecutive acute ischemic stroke patients with middle cerebral artery occlusion were recruited within 48 hours of onset. All patients underwent a three-dimensional multi-echo SWI scan using a 3 Tesla magnetic resonance imaging scanner. The SVS presence and the diameter of the SVS-related hypointense signal were assessed on SWI. QSM was applied to compute the susceptibility value of the thrombus. The receiver operating characteristic (ROC) methodology was used to define the optimal cutoff value of the susceptibility in QSM and the diameter on SWI for predicting cardioembolic stroke.

RESULTS

The SVS was identified in 93 (70.5%) patients with symptomatic middle cerebral artery occlusion and was significantly associated with cardioembolism. The hyperintense signal on QSM in the corresponding middle cerebral artery occlusion was present in 116 (87.9%) patients. ROC analysis indicated that thrombus susceptibility had a greater area under the curve than that of the SVS diameter (0.88 vs. 0.70, P<0.001) and that the optimal cutoff value of thrombus susceptibility for cardioembolism was 0.35 ppm. Multivariate analysis demonstrated that thrombus susceptibility (≥0.35 ppm) was an independent predictor of cardioembolic stroke (odds ratio =20.75; 95% CI, 7.19-59.87; P<0.001), with sensitivity, specificity, a positive predictive value, and a negative predictive value of 85.2%, 80.8%, 75.4%, and 88.7%, respectively, while the SVS presence showed sensitivity, specificity, a positive predictive value, and a negative predictive value of 90.7%, 43.6%, 87.2%, and 52.7%, respectively.

CONCLUSIONS

Thrombus susceptibility provides superior diagnostic performance over the SVS for discriminating between cardioembolism and other stroke subtypes. Quantitative susceptibility measurements of thrombi may help predict cardioembolic stroke in patients with acute middle cerebral artery occlusion.

[Susceptibility vessel sign in subacute stroke patients with large vessel occlusion]

OBJECTIVE

To investigate the presentation of susceptibility vessel sign (SVS) in subacute stroke patients with large vessel occlusion.

METHODS

We collected consecutive stroke patients who were admitted to Peking University First Hospital from December 2017 to August 2019 retrospectively. Those who had intracranial large vessel occlusion and received sensitivity weighted imaging (SWI) within 3 to 14 days after stroke onset were included in our analysis. The diagnosis of large vessel occlusion was based on magnetic resonance angiography (MRA), CT angiography (CTA) or digital subtraction angiography (DSA). The demographic information, clinical characteristics and imaging results were obtained from medical record. The occurrence rates of SVS sign were compared between stroke patients with cardioembolism (CE) and large artery atherosclerosis (LAA). In the sensitivity analysis, we performed a subgroup analysis in those patients who received SWI within 7 to 14 days after stroke onset. We also compared the occurrence rate of SVS sign between the patients with and without atrial fibrillation.

RESULTS

A total of 51 patients, 19 females and 32 males, with an average age of (63.04±11.23) years were analyzed in this study. Compared with LAA group, the patients in CE group were older and more likely to have an atrial fibrillation (P < 0.05). There were no significant differences between the CE group and LAA group in gender, hypertension, diabetes, coronary heart disease, hyperlipidemia, smoking, or National Institute of Health stroke scale(NIHSS) score at admission. SVS sign was found in 30 patients. Of whom, 3 were in CE group and 27 in LAA group. The occurrence rate of SVS sign was higher in the LAA group than in the CE group significantly (65.9% vs. 30.0%, P=0.039). The subgroup analysis showed that, in the patients who received SWI examination within 7 to 14 days after stroke onset, the differences between the two groups were still statistically significant (0 vs. 72.7%, P=0.006). Another sensitivity analysis showed that, the rate of SVS in the patients with atrial fibrillation was significantly lower than those patients without atrial fibrillation (25% vs. 65.1%, P=0.043).

CONCLUSION

In subacute stroke patients, the occurrence rate of SVS sign in CE group was lower than that of LAA group. The significance of SVS sign in the differentiation of stroke subtype needs further validation.

In Vitro Study of Blood Clot Identification and Composition Assessment by Different Magnetic Resonance Sequences

Background

Growing data suggest that clot composition can impact revascularization outcomes and can potentially guide treatment strategies for stroke patients with large vessel occlusion. We performed an in vitro study to determine which magnetic resonance (MR) signaling characteristics correlate with clot compositions.

Methodology

A total of 25 clot analogs were prepared by mixing human plasma and red blood cells (RBCs) with five different combinations (five samples for each combination), namely, Group A, fibrin-rich (95% plasma:5% RBCs); Group B, fibrin-rich (75% plasma:25% RBCs); Group C, intermediate (50% plasma:50% RBCs); Group D, RBC-rich (25% plasma:75% RBCs), and Group E, RBC-rich (5% plasma:95% RBCs). The prepared samples were then scanned with quantitative T2* mapping, T2 fast spin-echo (FSE), T2 gradient-echo (GRE), fluid-attenuated inversion recovery (FLAIR), and susceptibility-weighted angiography (SWAN). Thrombus-T2* relaxation time (TT2*RT) and signal intensity (SI) from different scanning sequences were measured in all groups. SIs between different groups were compared using a one-way analysis of variance. Correlation between TT2*RT and SI was determined using the Pearson correlation test.

Results

The average TT2*RT decreased from 126 ms to 37 ms from fibrin-rich to RBC-rich clots (Groups A to E). Mean SIs of Groups D and E were lower than Groups A, B, and C on T2 mapping, T2 FSE, T2 GRE, FLAIR, and SWAN images (p < 0.00001). TT2*RT and SI were positively correlated on T2 mapping (R = 0.9628, p = 0.009).

Conclusion

Different compositions of blood clots can show different TT2*RT and SI on MR imaging. Quantitative T2* mapping and multicontrast MR scanning can help in the characterization of clots causing large vessel occlusion, which is useful to establish treatment strategies for stroke patients.

Impact of Clot Shape on Successful M1 Endovascular Reperfusion

Objectives: The susceptibility-vessel-sign (SVS) allows thrombus visualization, length estimation and composition, and it may impact reperfusion during mechanical thrombectomy (MT). SVS can also describe thrombus shape in the occluded artery: in the straight M1-segment (S-shaped), or in an angulated/traversing a bifurcation segment (A-shaped). We determined whether SVS clot shape influenced reperfusion and outcomes after MT for proximal middle-cerebral-artery (M1) occlusions.

Methods: Between May 2015 and March 2018, consecutive patients who underwent MT at one comprehensive stroke center and who had a baseline MRI with a T2^* sequence were included. Clinical, procedural and radiographic data, including clot shape on SVS [angulated/bifurcation (A-SVS) vs. straight (S-SVS)] and length were assessed. Primary outcome was successful reperfusion (TICI 2b-3). Secondary outcome were MT complication rates, MT reperfusion time, and clinical outcome at 90-days. Predictors of outcome were assessed with univariate and multivariate analyses.

Results: A total of 62 patients were included. 56% (35/62) had an A-SVS. Clots were significantly longer in the A-SVS group (19 mm vs. 8 mm p = 0.0002). Groups were otherwise well-matched with regard to baseline characteristics. There was a significantly lower rate of successful reperfusion in the A-SVS cohort (83%) compared to the S-SVS cohort (96%) in multivariable analysis [OR 0.04 (95% CI, 0.002–0.58), p = 0.02]. There was no significant difference in long term clinical outcome between groups.

Conclusion: Clot shape as determined on T2^* imaging, in patients presenting with M1 occlusion appears to be a predictor of successful reperfusion after MT. Angulated and bifurcating clots are associated with poorer rates of successful reperfusion.

FLAIR vascular hyperintensity-DWI mismatch most likely to benefit from recanalization and good outcome after stroke

We assessed the value of fluid-attenuated inversion recovery vascular hyperintensity (FVH)-diffusion-weighted imaging (DWI) mismatch in predicting revascularization and functional outcome in stroke patients with large vessel occlusion (LVO) after endovascular thrombectomy (EVT).Seventy-two acute stroke patients within 6 hour of stroke onset who received EVT were enrolled. FVH-DWI mismatch, revascularization (mTICI score), functional outcome (mRS at 3 months) and other clinical data were collected. Statistical analysis was performed to predict revascularization and functional outcome after stroke.Twenty-nine patients (60.42%) had FVH-DWI mismatch in patients with complete revascularization and 8 patients (33.33%) had FVH-DWI mismatch in patients with no/partial revascularization, and there was significant difference in 2 groups (t = 4.698; P = .045). The good functional outcome group (37/72; 51.39%) had higher FVH score (4.38 ± 1.53 vs 3.49 ± 1.52; t = 2.478; P = .016), higher FVH-DWI mismatch ratio (81.25% vs 48.15%; t = 10.862; P = .002), higher complete revascularization ratio (83.78% vs 48.57%; t = 10.036; P = .002) than the poor functional outcome group (35/72; 48.61%). Spearman's rank correlation analysis revealed that FVH-DWI mismatch was positively correlated with complete revascularization (r = 0.255; P = .030) and good functional outcome (r = 0.417; P = .000). Multivariable logistic regression analysis demonstrated that FVH-DWI mismatch was independently associated with complete revascularization (OR, 0.328; 95% CI, 0.117-0.915; P = .033) and good functional outcome (OR, 0.169; 95% CI, 0.061-0.468; P = .001).Assessments of FVH-DWI mismatch before thrombectomy therapy might be useful for predicting revascularization and functional outcome in stroke patients with LVO.

Correlation of imaging and histopathology of thrombi in acute ischemic stroke with etiology and outcome

Mechanical thrombectomy has become the stand of care for patients with large vessel occlusions, yet major improvements in thrombectomy speed, efficacy, and completeness can still be achieved. High rates of clot fragmentation and failure to remove the clot resulting in poor neurological outcomes suggest that in order to further advance the field of stroke intervention we must turn our attention towards understanding the science of clot. Accurately identifying the composition of the occlusive clot prior to intervention could significantly influence the success of the revascularization strategy used to treat them. Numerous features of thromboemboli could be studied and characterized, including quantitative histomorphometry and diagnostic imaging characteristics. Each of these features might logically predict superior thrombectomy outcomes with one device or another. This article aims to review the current literature on histopathological composition of acute ischemic stroke clots, with a particular focus on the correlation between clot composition and diagnostic imaging, stroke etiology and revascularization outcomes.

Two-Layered Susceptibility Vessel Sign and High Overestimation Ratio on MRI Are Predictive of Cardioembolic Stroke

In a prospective study among patients in the THRombectomie des Artères Cerebrales trial, we analyzed the diagnostic accuracy of 2 imaging biomarkers, the 2-layered susceptibility vessel sign and a high overestimation ratio, obtained on pretreatment brain T2* sequences, to identify cardioembolic stroke etiology (107/260 patients). In combination, these 2 biomarkers, on 1.5T or 3T systems (159 and 101 patients, respectively), demonstrated high specificity (0.77 at 1.5T and 1 at 3T) and their simultaneous presence is highly associated with cardioembolism.

Validation of overestimation ratio and TL-SVS as imaging biomarker of cardioembolic stroke and time from onset to MRI

OBJECTIVE

We aimed to determine in the "THRACE" trial, the clinical and MRI technical parameters associated with the two-layered susceptibility vessel sign (TL-SVS) and the overestimation ratio (overR).

MATERIALS AND METHODS

Patients with pre-treatment brain gradient echo (GRE) sequence and an etiological work-up were identified. Two readers reviewed TL-SVS, i.e., a SVS with a linear low-intense signal core surrounded by a higher intensity and measured the overR as the width of SVS divided by the width of the artery. Binomial and ordinal logistic regression respectively tested the association between TL-SVS and quartiles of overR with patient characteristics, cardioembolic stroke (CES), time from onset to imaging, and GRE sequence parameters (inter slice gap, slice thickness, echo time, flip angle, voxel size, and field strength).

RESULTS

Among 258 included patients, 102 patients were examined by 3 Tesla MRI and 156 by 1.5 Tesla MRI. Intra- and inter-reader agreements for quartiles of overR and TL-SVS were good to excellent. The median overR was 1.59 (IQR, 1.30 to 1.86). TL-SVS was present in 101 patients (39.2%, 95%CI, 33.1 to 45.1%). In multivariate analysis, only CES was associated with overR quartiles (OR, 1.83; 95%CI, 1.11 to 2.99), and every 60 min increase from onset to MRI time was associated with TL-SVS (OR, 1.72; 95%CI, 1.10 to 2.67). MRI technical parameters were statistically associated with neither overR nor TL-SVS.

CONCLUSION

Independent of GRE sequence parameters, an increased overR was associated to CES, while the TL-SVS is independently related to a longer time from onset to MRI.

KEY POINTS

• An imaging biomarker would be useful to predict the etiology of stroke in order to adapt secondary prevention of stroke. • The two-layered susceptibility vessel sign and the overestimation ratio are paramagnetic effect derived markers that vary according to the MRI machines and sequence parameters. • Independent of sequence parameters, an increased overestimation ratio was associated to cardioembolic stroke, while the two-layered susceptibility vessel sign is independently related to a longer time from onset to MRI.

Correlation of imaging and histopathology of thrombi in acute ischemic stroke with etiology and outcome: a systematic review

BACKGROUND AND PURPOSE

Studying the imaging and histopathologic characteristics of thrombi in ischemic stroke could provide insights into stroke etiology and ideal treatment strategies. We conducted a systematic review of imaging and histologic characteristics of thrombi in acute ischemic stroke.

MATERIALS AND METHODS

We identified all studies published between January 2005 and December 2015 that reported findings related to histologic and/or imaging characteristics of thrombi in acute ischemic stroke secondary to large vessel occlusion. The five outcomes examined in this study were (1) association between histologic composition of thrombi and stroke etiology; (2) association between histologic composition of thrombi and angiographic outcomes; (3) association between thrombi imaging and histologic characteristics; (4) association between thrombi imaging characteristics and angiographic outcomes; and (5) association between imaging characteristics of thrombi and stroke etiology. A meta-analysis was performed using a random effects model.

RESULTS

There was no significant difference in the proportion of red blood cell (RBC)-rich thrombi between cardioembolic and large artery atherosclerosis etiologies (OR 1.62, 95% CI 0.1 to 28.0, p=0.63). Patients with a hyperdense artery sign had a higher odds of having RBC-rich thrombi than those without a hyperdense artery sign (OR 9.0, 95% CI 2.6 to 31.2, p<0.01). Patients with a good angiographic outcome had a mean thrombus Hounsfield unit (HU) of 55.1±3.1 compared with a mean HU of 48.4±1.9 for patients with a poor angiographic outcome (mean standard difference 6.5, 95% CI 2.7 to 10.2, p<0.001). There was no association between imaging characteristics and stroke etiology (OR 1.13, 95% CI 0.32 to 4.00, p=0.85).

CONCLUSIONS

The hyperdense artery sign is associated with RBC-rich thrombi and improved recanalization rates. However, there was no association between the histopathological characteristics of thrombi and stroke etiology and angiographic outcomes.