Search

This paper presents vibration-based methods for detecting and quantifying delaminations in composite structures. Three different delamination sizes were considered numerically and experimentally. Our approach combines and compares finite element method (FEM) numerical analysis and experimental measurements to find the location of structural delaminations and identify their severity. First, we noticed that a low-frequency modal study comparing pristine and damaged plates could not provide local damage information. Hence, a high frequency-modal analysis was performed to obtain the local damage information. The damaged mode shapes corresponding to resonance frequencies that cause significant local vibration (high amplitude) over the damaged regions were calculated numerically. The result shows the capability of damage identification (location and size of structural delaminations) within the high-frequency modal analysis. The numerical results were validated experimentally. The experiments include electromechanical impedance spectroscopy (EMIS) and scanning laser Doppler vibrometer (SLDV) techniques. The EMIS experiment was implemented to predict the resonance frequencies which cause significant local vibration over the delamination regions. The spectra of the electromechanical response resemble the vibration response of the structure and detect the new resonances created by the presence of the delamination. The test plate’s experimental resonance peaks show a good match with the resonance frequencies of the numerical modal analysis. The SLDV experiments measured the local vibration over the investigated scanning areas. The operational vibration shapes corresponding to predicted resonance frequencies were created. These experimental mode shapes may visually measure the delaminations by observing intense local vibration over the delamination zones. Comparing the numerical mode shapes and the operational vibration shapes shows a good match between numerical and experimental results.

Background Acute ischemic stroke attributed to basilar artery occlusion (BAO) results in high rates of death and significant morbidity. Endovascular thrombectomy an effective treatment for BAO, but imaging parameters that predict a favorable response to thrombectomy are not well defined. We determined which imaging parameters were associated with poor outcome in patients with BAO treated by thrombectomy. Methods We performed a retrospective cohort study of patients with BAO who underwent thrombectomy at multiple international stroke centers. All patients underwent computed tomography or magnetic resonance perfusion imaging before treatment. Clinical and imaging variables were measured and correlated to poor functional outcomes (modified Rankin scale score ≥4) after thrombectomy. Imaging variables included the following: Critical Area Perfusion Score, Posterior Circulation Alberta Stroke Program Early Computed Tomography Score, ischemic core volume (30% cerebral blood flow on computed tomography perfusion or diffusion‐weighted imaging), and volume of time to maximum >10 seconds. Clinical and imaging variables associated with poor functional outcome were assessed by a multivariable binary logistic regression analysis. Results A total of 102 patients were included in the study. Median patient age was 66.5 years (interquartile range [IQR], 55–78), median presentation National Institutes of Health Stroke Scale score was 14 (IQR, 7–23), and the median time from last seen normal was 4 hours (IQR, 1:52–9:20). Patient age (odds ratio [OR], 1.37 per 5‐year increment [95% CI, 1.08–1.72]; P=0.008), presentation National Institutes of Health Stroke Scale score (OR, 1.11 [95% CI, 1.04–1.18]; P=0.001), successful reperfusion after thrombectomy (OR, 0.03 [95% CI, 0.003–0.25]; P=0.002), Posterior Circulation Alberta Stroke Program Early Computed Tomography Score ≤6 (OR, 11.40 [95% CI, 1.73–75]; P=0.011), and Critical Area Perfusion Score >3 (OR, 26.22 [95% CI, 1.07–642]; P =0.045) independently predicted poor outcome after BAO thrombectomy. Ischemic core volume (30% cerebral blood flow) and volume of time to maximum >10 seconds did not predict poor outcome. Conclusion Age, National Institutes of Health Stroke Scale presentation, unsuccessful reperfusion, Critical Area Perfusion Score >3, and Posterior Circulation Alberta Stroke Program Early Computed Tomography Score ≤6 are independently associated with poor outcome after BAO thrombectomy.

Introduction There is limited information on retained wires during neuro interventional ischemic cases, although there is a wealth of information on cardiac cases. Retained wires can present with thrombosis, perforation, or may be followed for longer period of time, with no complications. Changes in outcome vary on the ability of the wire to migrate, the size of the vessel adjacent to the wire, and the difficulty in retrieving the retained item. Methods We present a case report on a 56‐year‐old man who presented in 2018 with a left internal carotid occlusion horizontal petrous level, with no early signs of stroke on CT, and 106 mL penumbra on CT perfusion (CTP), with dense expressive and receptive aphasia. Results Patient developed hemiparesis while sitting sitting up, and drops in blood pressure, below the presenting blood pressure of 200 over 100 mmHg. The patient was taken for emergent thrombectomy. Patient underwent petrous thrombectomy with a residual high grade stenosis. This was followed by cavernous angioplasty, and Wingspan stenting. We attempted to cross the stenosis with a Gateway balloon and Synchro2 microwire. The wire tip was trapped and separated after extensive rotation, with a retained 5 mm tip. After inspecting the wire, there is no clear evidence of any a retained product. The tip was secured with a Wingspan stent. After thrombectomy and stenting aphasia improved. Four days later the patient developed worsening aphasia, and was found to have stent reocclusion. During CT angiography (CTA) it became apparent that a small wire extended from the left internal carotid petrous segment at the level of the wingspan stent down to the descending aorta. CT angiography of the chest and abdomen after reperfusion found that the wire was anchored in the left internal carotid, and extended down to the renal artery. Thrombus was aspirated, and ICA reconstructed with coronary stents in the petrous, and self‐expanding stents in the cervical segments, with TICI 3 reperfusion. Follow‐up imaging with CT chest and abdomen at six months, one year, and four years found the wire to be still anchored to the left internal carotid stent, and stable in the superior mesenteric artery. There is no evidence of thrombus formation, or distal embolization. We examined a Synchro2 microwire ex vivo were able to detach the tip, and have the inner core unravel up to a meter in length. Given that the wire shaft did not appear to be altered, the retained product was likely an unraveled inner core. Conclusions Retained neurovascular products can predispose to reocclusion, and should be secured. Once secured the course can be benign. When a wire with a wound core is fractured, unwound core can remain behind with the wire appearing as if it has been fully retrieved.

Introduction: Prompt detection of intracranial hemorrhage (ICH) on a non-contrast head CT (NCCT) is critical to initial patient triage. Several ICH detection and notification programs now exist, but none presently generate locations or segmentations of suspected ICH, and false-positive notifications are not easily identified. We investigated an enhanced ICH detection tool with heightened immunity to false-positive diagnosis. Methods: NCCT scans from 3 large databases were evaluated for the presence of an ICH (IPH, IVH, SAH or SDH) of >0.4 ml by the automated RAPID ICH 3.0 software module and compared to a consensus detection from 3 neuroradiology experts. Scans were excluded for (1) severe CT acquisition artifacts, (2) prior neurosurgical procedures or (3) intravenous contrast administration. ICH detection accuracy, sensitivity, specificity, positive predictive value, negative predictive value, and positive and negative likelihood ratios by RAPID ICH 3 were determined. Results: A total of 790 studies were included. RAPID ICH 3.0 correctly identified 399/411 ICH-positive cases and 378/379 ICH-negative cases, resulting in a sensitivity of 98.08% and specificity 99.74%, positive predictive value 99.75%, and negative predictive value 96.92% for ICH detection. The positive and negative likelihood ratios for ICH detection were similarly favorable at 367.93 and 0.03 respectively. Mean processing time was Conclusions: In this large data set of nearly 800 patients, the RAPID ICH 3.0 automated software maintained a high sensitivity for detection of ICH, while essentially eliminating false positive identifications, leading to very high positive predictive value.

OBJECTIVE Perfusion imaging identifies anterior circulation stroke patients who respond favorably to endovascular thrombectomy (ET), but its role in basilar artery occlusion (BAO) is unknown. We hypothesized that BAO patients with limited regions of severe hypoperfusion (time to reach maximum concentration in seconds [Tmax] > 10) would have a favorable response to ET compared to patients with more extensive regions involved. METHODS We performed a multicenter retrospective cohort study of BAO patients with perfusion imaging prior to ET. We prespecified a Critical Area Perfusion Score (CAPS; 0-6 points), which quantified severe hypoperfusion (Tmax > 10) in cerebellum (1 point/hemisphere), pons (2 points), and midbrain and/or thalamus (2 points). Patients were dichotomized into favorable (CAPS ≤ 3) and unfavorable (CAPS > 3) groups. The primary outcome was a favorable functional outcome 90 days after ET (modified Rankin Scale = 0-3). RESULTS One hundred three patients were included. CAPS ≤ 3 patients (87%) had a lower median National Institutes of Health Stroke Scale score (NIHSS; 12.5, interquartile range [IQR] = 7-22) compared to CAPS > 3 patients (13%; 23, IQR = 19-36; p = 0.01). Reperfusion was achieved in 84% of all patients, with no difference between CAPS groups (p = 0.42). Sixty-four percent of reperfused CAPS ≤ 3 patients had a favorable outcome compared to 8% of nonreperfused CAPS ≤ 3 patients (odds ratio [OR] = 21.0, 95% confidence interval [CI] = 2.6-170; p 3 patients had a favorable outcome, regardless of reperfusion. In a multivariate regression analysis, CAPS ≤ 3 was a robust independent predictor of favorable outcome after adjustment for reperfusion, age, and pre-ET NIHSS (OR = 39.25, 95% CI = 1.34->999, p = 0.04). INTERPRETATION BAO patients with limited regions of severe hypoperfusion had a favorable response to reperfusion following ET. However, patients with more extensive regions of hypoperfusion in critical brain regions did not benefit from endovascular reperfusion. ANN NEUROL 2021.

Background Mixed data exist regarding the association between hyperglycemia and functional outcome after acute ischemic stroke when accounting for the impact of leptomeningeal collateral flow. We sought to determine whether collateral status modifies the association between treatment group and functional outcome in a subset of patients with large vessel occlusion enrolled in the Stroke Hyperglycemia Insulin Network Effort (SHINE) trial. Methods In this post-hoc analysis, we analyzed patients enrolled into the SHINE trial with anterior circulation large vessel occlusion who underwent imaging with CT angiography prior to glucose control treatment group assignment. The primary analysis assessed the degree to which collateral status modified the effect between treatment group and functional outcome as defined by the 90-day modified Rankin Scale score. Logistic regression was used to model the data, with adjustments made for thrombectomy status, age, post-perfusion thrombolysis in cerebral infarction (TICI) score, tissue plasminogen activator (tPA) use, and baseline National Institutes of Health Stroke Scale (NIHSS) score. Five SHINE trial centers contributed data for this analysis. Statistical significance was defined as a p-value Results Among the 1151 patients in the SHINE trial, 57 with angiographic data were included in this sub-analysis, of whom 19 had poor collaterals and 38 had good collaterals. While collateral status had no effect (p = 0.855) on the association between glucose control treatment group and functional outcome, patients with good collaterals were more likely to have a favorable functional outcome (p = 0.001, OR 5.02; 95% CI 1.37–16.0). Conclusions In a post-hoc analysis using a subset of patients with angiographic data enrolled in the SHINE trial, collateral status did not modify the association between glucose control treatment group and functional outcome. However, consistent with prior studies, there was a significant association between good collateral status and favorable outcome in patients with large vessel occlusion stroke. Trial registration ClinicalTrials.gov Identifier is NCT01369069. Registration date is June 8, 2011.

Delamination is one of the most common and dangerous failure modes for composites because it takes place and grows in the absence of any visible surface damage. The successful implementation of delamination detection in aerospace composite structures is always challenging due to the general anisotropic behavior of composites and multilayer delamination scenarios. This article presents a numerical and experimental investigation to detect and characterize the multilayer delaminations in carbon fiber–reinforced polymer composite plates using guided waves and wavenumber analysis. Multiphysics three-dimensional finite element simulations of the composite plate with five different delamination scenarios are conducted to provide the out-of-plane wave motion for wavenumber analysis. The out-of-plane results from finite element simulations of one delamination and two delaminations are validated by the scanning laser Doppler vibrometer measurements. It is found that the wavenumber analysis can identify the plies between which the delamination occurs and evaluate the delamination severity by comparing the new wavenumbers due to the trapped waves in the delamination regions, which is potentially related to delamination severity. Both numerical and experimental results demonstrate a good capability for the detection and characterization of multilayer delaminations in composite structures.

Background and Purpose: Rapid detection of large vessel occlusion (LVO) is essential for rapid triage for thrombectomy to salvage at-risk tissue. Early detection of LVO on noncontrast CT head (NCCT) could facilitate triage before advanced imaging is obtained. RAPID hyperdense vessel sign (HVS), a new fully automated software- tool for HVS detection is compared to experienced radiologists, for early LVO detection on NCCT, and validated with CTA. Methods: Scans were selected from a database of 335 scans, of which 166 were selected by stratified random selection. Images were evaluated by the Rapid automated software, and six readers, two radiologists, and four neuroradiologists. The Rapid algorithm returns a score between zero and one, and a threshold of 0.5 was applied of HVS. Radiologists read each scan twice, 30 days apart. A scan rating confidence scale was used, from “very confident of absence,” to “very confident of HVS,” and a separate “technically inadequate” rating, and this was compared to the Rapid HVS score. “Very Confident,” or “Confident” rated scans were considered HVS positive. Results: Demographics: 54% were men. Ages ranged 23 - 94 with a median of 65. GE, Philips, Siemens, and Toshiba scanners are represented. Agreement with RAPID for HVS detection was 75% to 84%. Below a HVS score of 0.4 the proportion of LVO positive scans was 46% (indeterminate), between 0.4 and 0.6 the proportion was 62.5% (probable), and above 0.6 the proportion was 90% (likely). The scan rating confidence grade correlated with the Rapid HVS score. The software identified 53% of the LVOs, comparable to human readers (26-57%) A clinical practice simulation of RAPID followed by a reader identified 61.3% (p=0.02 vs readers alone). Among the 61 patients with no LVO on CTA, readers had a false positive rate of less than 7% as compared to 15% for the software. Median software processing time was 54 seconds. Conclusions: Expert readers, and the Rapid software, detect an HVS in about 50% of CT head images with LVO on CTA. When Rapid software is used in tandem with an experienced reader, HVS can be detected in up to two thirds of patients with LVO on CTA. This high percentage of early LVO detection would facilitate faster triage of patients for more advanced imaging and/or therapeutic interventions.

Introduction: Acute ischemic stroke due to basilar artery occlusion (AIS-BAO) results in significant morbidity and mortality. Endovascular thrombectomy (ET) has not been shown to improve outcomes in AIS-BAO patients in randomized trials, which may be due to insufficient selection before ET. We determined whether the Critical Area Perfusion Score (CAPS) and posterior circulation ASPECTS (PC-ASPECTS) predict a favorable response to ET. Methods: We performed a multicenter retrospective study of AIS-BAO patients with perfusion imaging prior to ET. PC-ASPECTS was determined on NCCT by evaluating the cerebellum (1 point/hemisphere), pons (2 points), midbrain (2 points), thalamus (1 point/hemisphere), and posterior cerebral artery (1 point/hemisphere) territories, and points were subtracted for hypodensity in these regions. CAPS was quantified severe hypoperfusion (Tmax >10s) in cerebellum (1 point/hemisphere), pons (2 points), midbrain and/or thalamus (2 points). The primary outcome was a favorable outcome 90-days after ET (modified Rankin Scale [mRS] 0-3). Results: 89 patients were included. CAPS (AUC=0.70 [95% CI: 0.59-0.80]; p=0.002) and PC-ASPECTS (AUC=0.63 [95% CI: 0.52-0.75]; p=0.034) both predicted favorable outcomes in a receiver operating curve analysis, but there was no difference between the two (p=0.434). After dichotomization, patients with favorable CAPS (≤3) and PC-ASPECTS (≥7) were more likely to achieve a good functional outcome after successful reperfusion after ET (Figure). However, an unfavorable CAPS (>3) was associated with poor outcomes despite successful thrombectomy in all patients, whereas 22% of patients with unfavorable PC-ASPECTS ( Conclusions: CAPS and PC-ASPECTS both identify AIS-BAO patients who are likely to have a favorable clinical response to ET. CAPS, but not PC-ASPECTS, appears to accurately identify a subgroup in whom ET may be futile.

This chapter is dedicated to the discussion of fundamental aspect of composite materials. The basic principles and notations of anisotropic elasticity theory are reviewed in tensor notations and then converted to Voigt matrix notations. Strain–displacement and stress–strain relations, equation of motion in terms of stresses, and the equation of motion in terms of displacements are introduced. Attention is next focused on the unidirectional composite lamina: formulae for the estimation of lamina elastic properties from the properties of the constituent fiber and matrix were presented in principal axes. The elastic constants in the longitudinal (L), transverse (T), in-plane shear (LT), and transverse shear (23) directions are deduced and the corresponding stiffness and compliance matrices are presented and related to the constitutive fiber and matrix properties. The properties of the rotated unidirectional lamina are considered next, first under the plane-stress (2D) assumption, and then in the fully 3D case. The 2D and 3D rotation matrices are deduced and applied to obtain the rotated 2D and 3D compliance and stiffness matrices. The proof of some of the more intricate steps during this process is also given as separate sections.

Cerebral perfusion imaging may be used to identify the ischemic core in acute ischemic stroke (AIS) patients with a large vessel occlusion of the anterior circulation; however, perfusion parameters that predict the ischemic core in AIS patients with a basilar artery occlusion (BAO) are poorly described. We determined which cerebral perfusion parameters best predict the ischemic core after successful endovascular thrombectomy (EVT) in BAO patients.We performed multicenter retrospective study of BAO patients with perfusion imaging before EVT and a DWI after successful EVT. The ischemic core was defined as regions on CTP, which were co-registered to the final DWI infarct. Various time-to-maximum (Tmax) and cerebral blood flow (CBF) thresholds were compared to final infarct volume to determine the best predictor of the final infarct.28 patients were included in the analysis for this study. Tmax8s (rPre-EVT CT perfusion imaging is useful to predict the final ischemic infarct volume in BAO patients. Tmax8s and Tmax10s were the strongest predictors of the post-EVT final infarct volume.

Introduction : Rationale: Bilateral vertebral artery occlusion with collateral reconstitution is a rare finding. Compared to patients with acute occlusion, symptom progression may be much slower [1]. Atherosclerotic risk factors lead to occlusion, including hypertension and hyperlipidemia, but it is unclear what leads to collateral reconstitution [2]. These patients may have collateral circulation from anterior and posterior circulation sources that are well developed [1] [2]. Sufficient collateral flow correlates with lower rates of hemorrhagic transformation following recanalization [3] [4]. However, given the risk of spontaneous hemorrhage from microvascular collaterals, the hemorrhagic risk associated with thrombolytic therapy in patients with moyamoya collaterals, due to the fragility of these vessels [5], must be balanced with the benefit of therapy in the presence of severe neurologic deficits along with the mortality and morbidity that may stem from the occlusion. Patient concerns: 67 year old Caucasian male with past medical history of coronary artery disease, abdominal aortic aneurysm, hypertension, history of tobacco use and type 2 diabetes mellitus presents with acute right‐sided weakness. Methods : Diagnoses: On admission, CTA Head and Neck suggested chronic total occlusion of bilateral V4 segments from their origin to the midportion with tandem bilateral high‐grade stenoses throughout the imaged distal V2 and V3 segments bilaterally. MRI could not be obtained because of old lumbar fusion spinal hardware. Cerebral angiography showed microvascular reconstitution, analogous to moyamoya, with slow mid basilar flow, which could be either due to occlusion or competitive flow from top of the basilar collaterals. Interventions: Patient received intra‐arterial integrilin and tPA thrombolysis with TICI 1 reperfusion. Results : Outcomes: Patient presented with NIHSS 18 notable for right sided weakness (2/5 strength in his right upper extremity and 1/5 strength in RLE), bilateral hemianopia, severe dysarthria and right gaze preference. Patient had significant improvement in his exam the next day following thrombolysis. Notably, patient had 5/5 strength in his right upper and right lower extremities compared to his strength on presentation. Repeat head CT on the following day after thrombolysis showed left pontine infarct. Repeat NIHSS was 3 at 24 hours for partial hemianopia, minor nasolabial flattening and mild dysarthria. Conclusions : Conclusion: Bilateral intracranial vertebral artery stenosis and occlusion commonly occurs distal to PICA and near the vertebrobasilar junction [2]. Proximal (specifically areas supplied by PICA) and distal territories within the posterior circulation are often infarcted [2], which can yield a unique exam upon presentation that can help accurately guide diagnosis and treatment when appropriately recognized. The involvement of collateral circulation can play a crucial role in patients undergoing endovascular revascularization therapy [6]. In the setting of bilateral vertebral occlusion with microvascular reconstitution, patients can still undergo catheter based thrombolysis, but not thrombectomy.

This paper addresses a forward problem using an analytical global–local (AGL) method based on the physics of the Lamb wave propagation in the presence of a crack in the complex structure which would be beneficial for the inverse problem of damage detection. Discontinuity in a structure acts as a damage source and interacts with a Lamb wave. The global analytical solution determines the wave generation by a transmitter, wave propagation through the structure, and detection by a receiver. The local analytical solution determines the scattering coefficients for the Lamb waves at the discontinuity location. These frequency-dependent scatter coefficients are calculated considering transmission, reflection, and mode conversion. An analytical method called “complex mode expansion with vector projection (CMEP)” is used to calculate the scattering coefficients of Lamb wave modes from geometric discontinuities. The scattered wave field from a discontinuity is expanded in terms of complex Lamb wave modes with unknown scatter coefficients. These unknown coefficients are obtained from the boundary conditions using a vector projection utilizing the power expression. Two test cases are considered in this paper: (a) a plate with a pristine stiffener and (b) a plate with a cracked stiffener. Complex-valued scattering coefficients are calculated from 50 to 350 kHz for S0 incident waves. Scatter coefficients are compared for both cases to identify the suitable frequency range to excite a Lamb wave to detect the crack. The frequency-dependent complex-valued scattering coefficients are then inserted into the global analytical model. Therefore, in combination AGL method provides the exact analytical Lamb wave solution for the simulation of Lamb wave propagation and interaction with a discontinuity. By comparing the waveforms for both pristine stiffener and cracked stiffener, the crack can be detected. An FEM transient analysis was also performed to calculate the scattered wave signals. FEM results agree well with the AGL predicted results. An experiment was also performed to validate the AGL result. The obtained experimental results match well with the CMEP analytical predictions. The present AGL method is a highly computationally efficient simulation approach which allows performing virtual experiments for structural health monitoring applications.

The guided wave technique is commonly used in the health monitoring of thin-walled structures because the guided waves can propagate far in the structures without much energy loss. However, understanding of the wave propagation in bounded layered structures is still lacking. In this study, the Lamb wave field of single- and multi-layer plates excited by surface-mounted piezoelectric wafer active sensors is theoretically analyzed using the normal mode expansion method, which is based on the elastodynamic reciprocity relation and utilizes the orthogonality relations of the Lamb wave modes. The mode participation factors of Lamb wave in single- and multi-layer isotropic plates are derived. The time domain responses are obtained through the inverse Fourier transform of the structural response spectrum, which is obtained by multiplying the transfer function with the excitation frequency spectrum. The developed normal mode expansion method is first applied to an aluminum single-layer plate. The obtained analytical tuning curves and out-of-plane velocity of the plate are in good agreement with the numerical and experimental results. Finally, the analytical wave responses of an aluminum–adhesive–steel triple-layer plate are verified through comparison with the finite element analysis and experiment. The proposed normal mode expansion method provides a reliable and accurate calculation of the wave field in single- and multi-layer plates.

BACKGROUND Acute promyelocytic leukemia (APL) has long been associated with coagulation disorders. The proposed mechanism is a combination of fibrinolysis, proteolysis, platelet dysfunction, thrombocytopenia, and possibly disseminated intravascular coagulation. Hemorrhagic complications are prominent. OBSERVATIONS In this case, a 25-year-old female with newly diagnosed APL developed extensive cerebral venous thrombosis (CVT) and was initiated on a protocol with idarubicin and all-trans retinoic acid. The general recommendation for treating CVT is anticoagulation to stabilize the existing thrombus and prevent propagation. The patient was initiated on a heparin drip, but her clinical course was complicated by subdural hemorrhage (SDH) and epidural hemorrhage in the setting of thrombocytopenia. Anticoagulation was held, and her CVT propagated on follow-up imaging. To restart anticoagulation for CVT with a limited risk of SDH, the authors pursued middle meningeal artery (MMA) embolization. The patient was transitioned to apixaban and discharged to home. LESSONS MMA embolization enables safe anticoagulation in patients with concomitant CVT and SDH. The authors report the complex clinical course and effective management of this rare clinical scenario.

This paper presents an ultrasonic guided wave tomography for detecting and sizing delaminations in composites using pure shear horizontal (SH) wave. In this method, pure SH0 wave excitation was achieved using the adjustable angle beam transducers (ABT) in quasi-isotropic composite plates. First, a 3-mm quasi-isotropic composite plate with simulated delaminations by Teflon inserts was manufactured. Then, the ABT tuning angle of SH0 mode was calculated from the theoretical phase-velocity dispersion curve based on Snell’s law. Experiments were conducted on the 3-mm quasi-isotropic composite plate for pure SH0 wave excitation and delamination detection. It was found that a significant decrease in the signal amplitude was observed due to the delaminations. Finally, a linear scanning approach in 0° and 90° directions was conducted to cover the whole delamination area. The collected signals were used to visualize the damage through damage imaging methods. SH0 wave tomography based on the reconstruction algorithm for probabilistic inspection of defects (RAPID) was applied for delamination detection and characterization. The experimental results show that the SH0 wave tomography has a good performance for delamination detection, size estimation, and localization in aerospace composites.

Background and Purpose: The novel coronavirus of 2019 (COVID-19) has been associated with worse outcomes for hospitalized patients across the US and worldwide. Our study investigates the effect of the pandemic on functional outcomes for patients presenting with stroke-like symptoms in two high-volume Tele-Stroke networks. Methods: We performed retrospective chart review of 7689 consecutive patients seen through two Tele-Stroke networks (Medical University of South Carolina and Augusta University) from July 2019 through May 2020. Discharge outcomes were assessed using modified Rankin scale (mRS). We dichotomized patients to preCOVID-19 pandemic (July 2019 to February 2020) and during COVID-19 pandemic (March to May 2020). Results: During COVID, a higher percentage of patients received intravenous tissue plasminogen activator (tPA) (14.2% vs 11.3% before, p=0.001), despite a similar baseline NIHSS. Also, patients during the pandemic had a shorter symptom-onset to hospital door time (288 vs 353, P=0.012). Demographics were similar between groups, other than older age in patients presenting during COVID (66.02 vs 65.15 before, p=0.04) (table 1). During the pandemic, a higher percentage of patients had a poor functional outcome, as defined by mRS 3-6 (35.7% vs 30% before, p=0.012), and a higher percentage died or were discharged to hospice (7.0% vs 5.1%, p=0.000). Conclusions: Despite earlier ED presentation and increased tPA administration, our results demonstrate worse discharge outcomes during the pandemic in two large telestroke networks. Changes in workflow and resulting delays during COVID-19 may explain these findings.

Barely visible impact damage (BVID) due to low velocity impact events in composite aircraft structures are becoming prevalent. BVID can have an adverse effect on the strength and safety of the structure. During aircraft inspections it can be extremely difficult to visually detect BVID. Moreover, it is also a challenge to ascertain if the BVID has in-fact caused internal damage to the structure or not. This paper describes a method to ascertain whether or not internal damage happened during the impact event by analyzing the high-frequency information contained in the recorded acoustic emission signal signature. Multiple 2 mm quasi-isotropic carbon fiber reinforced polymer (CFRP) composite coupons were impacted using the ASTM D7136 standard in a drop weight impact testing machine to determine the mass, height and energy parameters to obtain approximately 1” impact damage size in the coupons iteratively. For subsequent impact tests, four piezoelectric wafer active sensors (PWAS) were bonded at specific locations on each coupon to record the acoustic emission (AE) signals during the impact event using the MISTRAS micro-II digital AE system. Impact tests were conducted on these instrumented 2 mm coupons using previously calculated energies that would create either no damage or 1” impact damage in the coupons. The obtained AE waveforms and their frequency spectrums were analyzed to distinguish between different AE signatures. From the analysis of the recorded AE signals, it was verified if the structure had indeed been damaged due to the impact event or not. Using our proposed structural health monitoring technique, it could be possible to rapidly identify impact events that cause damage to the structure in real-time and distinguish them from impact events that do not cause damage to the structure. An invention disclosure describing our acoustic emission structural health monitoring technique has been filed and is in the process of becoming a provisional patent.