Exploring the relationship between embolic acute stroke distribution and supra-aortic vessel patency: key findings from an in vitro model study.

BACKGROUND: We investigated differences in intracranial embolus distribution through communicating arteries in relation to supra-aortic vessel (SAV) patency. METHODS: For this experimental analysis, we created a silicone model of the extracranial and intracranial circulations using a blood-mimicking fluid under physiological pulsatile flow. We examined the sequence of embolus lodgment on injecting 104 frangible clot analogues (406 emboli) through the right internal carotid artery (CA) as SAV patency changed: (a) all SAV patent (baseline), (b) emboli from a CA occlusion, (c) emboli contralateral to a CA occlusion and (d) occlusion of the posterior circulation. The statistical analysis included a descriptive analysis of thrombi location after occlusion (absolute and relative frequencies). Sequences of occlusions were displayed in Sankey flow charts for the four SAV conditions. Associations between SAV conditions and occlusion location were tested by Fisher's exact test. Two-sided p values were compared with a significance level of 0.05. RESULTS: The total number of emboli was 406 (median fragments/clot: 4 (IQR: 3-5)). Embolus lodgment was dependent on SAV patency (p<0.0001). In all scenarios, embolism lodging in the anterior cerebral artery (ACA) occurred after a previous middle cerebral artery (MCA) embolism (MCA first lodge: 96%, 100/104). The rate of ipsilateral ACA embolism was 28.9% (28/97) at baseline, decreasing significantly when emboli originated from an occluded CA (16%, 14/88). There were more bihemispheric embolisations in cases of contralateral CA occlusion (37%, 45/122), with bilateral ACA embolisms preceding contralateral MCA embolism in 56% of cases (14/25 opposite MCA and ACA embolism). CONCLUSIONS: All emboli in the ACA occurred after a previous ipsilateral MCA embolism. Bihemispheric embolisms were rare, except when there was a coexisting occlusion in either CA, particularly in cases of a contralateral CA occlusion.

Making acute ischemic stroke thrombi visible in MRI imaging.

Knowledge of thrombus behavior and visualization on MRI in acute ischemic stroke is less than optimal. However, MRI sequences could be enhanced based on the typical T1 and T2 relaxation times of the target tissues, which mainly determine their signal intensities on imaging. We studied the relaxation times of a broad spectrum of clot analogs along with their image characteristics of three sequences analyzed: a T1-weighted turbo inversion-recovery sequence (T1w Turbo IR), a T1-weighted turbo spin echo with fat suppression (T1w TSE SPIR), and a T2-weighted 3D TSE with magnetization refocusing to remove T1 dependence (T2w TSE DRIVE). We compared their imaging behavior with the intensity values of normal brain tissue using the same imaging protocols as for clots. Each histological and biochemical clot component contributed to each of the relaxation times. Overall, histological composition correlated strongly with T1 times, and iron content, specifically, with T2 relaxation time. Using decision trees, fibrin content was selected as the primary biomarker for T1 relaxation times, inducing an increase. Up to four clot subgroups could be defined based on its distinctive T1 relaxation time. Clot signal intensity in the T1 and T2-weighted images varied significantly according to T1 and T2 relaxation times. Moreover, in comparison with normal brain tissue intensity values, T2w DRIVE images depict thrombi according to the principle of the more fibrin, the higher the intensity, and in T1w TSE, the more erythrocytes, the higher the intensity. These findings could facilitate improvements in MRI sequences for clot visualization and indicate that T2w DRIVE and T1w TSE sequences should depict the vast majority of acute ischemic stroke thrombi as more hyperintense than surrounding tissues.

Predictors of Successful First-Pass Thrombectomy with a Balloon Guide Catheter: Results of a Decision Tree Analysis.

Complete recanalization after a single retrieval maneuver is an interventional goal in acute ischemic stroke and an independent factor for good clinical outcome. Anatomical biomarkers for predicting clot removal difficulties have not been comprehensively analyzed and await unused. We retrospectively evaluated 200 consecutive patients who suffered acute stroke and occlusion of the anterior circulation and were treated with mechanical thrombectomy through a balloon guide catheter (BGC). The primary objective was to evaluate the influence of carotid tortuosity and BGC positioning on the one-pass Modified Thrombolysis in Cerebral Infarction Scale (mTICI) 3 rate, and secondarily, the influence of communicating arteries on the angiographic results. After the first-pass mTICI 3, recanalization fell from 51 to 13%. The regression models and decision tree (supervised machine learning) results concurred: carotid tortuosity was the main constraint on efficacy, reducing the likelihood of mTICI 3 after one pass to 30%. BGC positioning was relevant only in carotid arteries without elongation: BGCs located in the distal internal carotid artery (ICA) had a 70% probability of complete recanalization after one pass, dropping to 43% if located in the proximal ICA. These findings demonstrate that first-pass mTICI 3 is influenced by anatomical and interventional factors capable of being anticipated, enabling the BGC technique to be adapted to patient's anatomy to enhance effectivity.

Clot Analog Attenuation in Non-contrast CT Predicts Histology: an Experimental Study Using Machine Learning.

Exact histological clot composition remains unknown. The purpose of this study was to identify the best imaging variables to be extrapolated on clot composition and clarify variability in the imaging of thrombi by non-contrast CT. Using a CT-phantom and covering a wide range of histologies, we analyzed 80 clot analogs with respect to X-ray attenuation at 24 and 48 h after production. The mean, maximum, and minimum HU values for the axial and coronal reconstructions were recorded. Each thrombus underwent a corresponding histological analysis, together with a laboratory analysis of water and iron contents. Decision trees, a type of supervised machine learning, were used to select the primary variable altering attenuation and the best parameter for predicting histology. The decision trees selected red blood cells (RBCs) for correlation with all attenuation parameters (p < 0.001). Conversely, maximum attenuation on axial CT offered the greatest accuracy for discriminating up to four groups of clot histology (p < 0.001). Similar RBC-rich thrombi displayed variable imaging associated with different iron (p = 0.023) and white blood cell contents (p = 0.019). Water content varied among the different histologies but did not in itself account for the differences in attenuation. Independent factors determining clot attenuation were the RBCs (ß = 0.33, CI = 0.219-0.441, p < 0.001) followed by the iron content (ß = 0.005, CI = 0.0002-0.009, p = 0.042). Our findings suggest that it is possible to extract more and valuable information from NCCT that can be extrapolated to provide insights into clot histological and chemical composition.

Variability in the decision-making process of acute ischemic stroke in difficult clinical and radiological constellations: analysis based on a cross-sectional interview-administered stroke questionnaire.

BACKGROUND AND PURPOSE: Notwithstanding guidelines, indications for mechanical thrombectomy (MT) in acute ischemic stroke are multifactorial and can be complex. Our aim was to exploratively evaluate decision-making on the advisability of performing MT in cases presented as an interview-administered questionnaire. METHODS: Fifty international raters assessed 12 cases and decided to recommend or exclude MT. Each case contained a brief summary of clinical information and eight representative images of the initial multimodal CT. The demographic characteristics and stroke protocols were recorded for raters. For each case, the reasons for excluding MT were recorded. Uni- and multivariate logistic regression analysis were performed for the different demographic and case characteristics to identify factors that might influence decision-making. RESULTS: All raters performed MT (median MTs/hospital/year [IQR], 100 [50-141]) with a median of 7 years of experience as first operator (IQR, 4-12). Per case, diversity in decision-making ranged between 1 (case 6, 100% yes MT) and 0.50 (case 12, 54.2% yes MT and 45.8% no MT). The most common reasons for excluding MT were small CBV/CBF mismatch (17%, 102/600), size of infarct core on the CBV map (15.2%, 91/600), and low NIHSS score (National Institute of Health Stroke Scale, 8.3%, 50/600). All clinical and radiological characteristics significantly affected the decision regarding MT, but the general characteristics of the raters were not a factor. CONCLUSIONS: Clinical and imaging characteristics influenced the decision regarding MT in stroke. Nevertheless, a consensus was reached in only a minority of cases, revealing the current divergence of opinion regarding therapeutic decisions in difficult cases. KEY POINTS: • This is the first study to explore differences in decision-making in respect of mechanical thrombectomy in ischemic stroke with complex clinical and radiological constellations. • Fifty experienced international neurointerventionalists answered this interview-administered stroke questionnaire and made decisions as to whether to recommend or disadvise thrombectomy in 12 selected cases. • Diversity in decision-making for thrombectomy ranged from 1 (100% of raters offered the same answer) to 0.5 (50% indicated mechanical thrombectomy). There was a consensus in only a minority of cases, revealing the current disparity of opinion regarding therapeutic decisions in difficult cases.

Impact of Working Experience on Image Perception and Image Evaluation Approaches in Stroke Imaging: Results of an Eye-Tracking Study.

PURPOSE: Higher rates of missed pathologies, caused by a lack of professional experience or systematic search, suggest that a methodical approach to radiological analysis can be learned. Thus, the aim of this study is to investigate the efficiency of different principles of screening stroke CTs for cerebrovascular diseases between radiologists and neuroradiologists with different levels of experience in relation to professional experience. METHODS: A set of anonymous CT images of 20 patients, with a suspected stroke, was individually presented to 12 radiologists with different levels of professional experience. Meanwhile, their fixation position was recorded by an eye-tracking system. For statistical analysis, the interobserver variability and accuracy of lesion detection were evaluated, taking the individual level of professional experience into account. RESULTS: The sensitivity of the observer depends on the professional experience, also determined by a systematic observation sequence and knowledge of the course of the disease. The duration of eye fixation with inexperienced assessors was significantly longer for conspicuous findings, while experienced assessors were more likely to fix clinically relevant regions. The retention time of ocular fixation in important pathological findings did not differ significantly between those groups. CONCLUSION: Our results indicate that experienced radiologists are reducing the number of missed findings through a systematic approach and targeted inspection of important regions. Through raising the awareness of analyzing CT images in systematic patterns, physicians at all levels of experience seem to be able to improve their performance. KEY POINTS: · Experienced radiologists improve detection rates through targeted inspection of clinically important regions.. · Experienced radiologists reduce time spent on analysis through focused visual attention.. · All levels of experience improve their performance by analyzing CT images systematically.. CITATION FORMAT: · Kammerer S, Schülke C, Leclaire MD et al. Impact of Working Experience on Image Perception and Image Evaluation Approaches in Stroke Imaging: Results of an Eye-Tracking Study. Fortschr Röntgenstr 2019; 191: 836 - 844.

Low rates of recanalization for wide-necked aneurysms treated with stenting after balloon-assisted coiling: combination of techniques delivers stable and improved results during follow-up.

PURPOSE: In the treatment of wide-necked aneurysms, stenting may be required after balloon-assisted coiling (BAC) for reconstructing the lumen/flow of the parent artery in cases of coil herniation. The potential benefits and complications of both techniques remain unclear when used together. Our aim was to assess the safety and long-term angiographic outcomes of stenting after BAC. METHODS: Retrospective review of 87 unruptured wide necked aneurysms (in 80 patients) treated with BAC and requiring stent placement at the final stage of the procedure due to coil prolapse. Aneurysm characteristics, technical issues, clinical records, and MR results were assessed. Post-treatment and follow-up angiograms were evaluated by two independent reviewers and categorized as "stable," "further thrombosis," or "recanalization." RESULTS: The mean maximum diameter was 9.1 ± 4.7 mm and aspect ratio 1.20 ± 0.47. Complete and near-complete initial occlusion were observed in 53 (60.9%) and 28 (32.2%) of all treated aneurysms, respectively. Angiographic follow-up (80 aneurysms; mean, 34.68 ± 25.26 months) revealed stability and further thrombosis in 92.4% (74/80). Recanalization was observed in six cases (7.5%, 6/83), four of which were retreated. No significantly different outcomes were found in terms of aneurysm size (p = 0.641). Transient and reversible procedure-related complications occurred in eight (9.2%), minor permanent deficits in 2.3%, and major deficits, including death, in four cases (4.6%). CONCLUSION: Our results suggest that treatment of wide-necked aneuryms with stent placement after BAC yields low recanalization rates and enhanced angiographic outcomes in long-term follow-up.