Clot Analogs Research Articles

Cyclic Aspiration in Mechanical Thrombectomy: Influencing Factors and Experimental Validation.

Mechanical thrombectomy is a fundamental intervention for acute ischemic stroke treatment. While conventional techniques are effective, cyclic aspiration (CyA) shows potential for better recanalization rates. We aim to investigate factors affecting CyA and compare them with static aspiration (StA). StA setup consisted of an aspiration pump connected to pressure transducer. CyA was tested with 5 subsequent iterations: single solenoid valve with air plus saline (i1) or saline alone (i2) as aspiration medium; 2 solenoid valves with air plus saline (i3) as aspiration medium; complete air removal and saline feeding (i4); and pressurized saline feeding (i5). To assess the efficacy of clot ingestion, the pressure transducer was replaced with a distal aspiration catheter. Moderately stiff clot analogs (15 mm) were used to investigate the ingestion quantified as clot relative weight loss. Additionally, the aspiration flow rate was assessed for each setup. With CyA i1, the amplitude of the achieved negative pressure waves declined with increasing frequencies but progressively increased with each subsequent iteration, achieving a maximum amplitude of 81 kPa for i5 at 1 Hz. Relative clot weight loss was significantly higher with i5 at 5 Hz than with StA (100% versus 37.8%; P = .05). Aspiration flow rate was lower with CyA than with StA (i5 at 5 Hz: 199.8 mL/min versus StA: 311 mL/min; P < .01). CyA with the appropriate setup may represent an encouraging innovation in mechanical thrombectomy, offering a promising pathway for improving efficacy in clot ingestion and recanalization. The observed benefits warrant confirmation in a clinical setting.

A hyper-viscoelastic uniaxial characterization of collagenous embolus analogs in acute ischemic stroke

PurposeAcute ischemic stroke is a leading cause of death and morbidity worldwide. Despite advances in medical technology, nearly 30% of strokes result in incomplete vessel recanalization. Recent studies have demonstrated that clot composition correlates with success rates of mechanical thrombectomy procedures. To understand clot behavior during thrombectomy, which exerts considerable strains on thrombi, in vitro studies must characterize the rate-dependent high-strain behavior of embolus analogs (EAs) with different formation conditions, which can be used to fit models of hyper-viscoelasticity. MethodsIn this study, the effect of collagen infiltration as a carotid-induced collagen-rich thrombosis surrogate is considered as a contributor to embolus analog high-strain stiffness, when compared to 40% hematocrit EAs. ResultsEA high-strain stiffnesses, characterized on a uniaxial load frame, increase by an order of magnitude for collagenous clot analogs. Chandler loop analogs show high-strain stiffnesses and clot compositions commensurate with previous reports of stroke patient clots, and collagenous clots show significant increase in stiffness when compared to stroke patient clots. Finally, hyper-viscoelastic curve fitting demonstrates the asymmetry between tension and compression. Nonlinear, rate-dependent models that consider clot-stiffening behavior match the high strain stiffness of clots fairly well. Furthermore, we demonstrate that the stability of the elastic energy needs to be considered to obtain optimal curve fits for high-strain, rate dependent data. ConclusionThis study provides a framework for the development of dynamically formed EAs that mimic the mechanical and structural properties of in vivo clots and provides parameters for numerical simulation of clot behavior with hyper-viscoelastic models.

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.

Experimental comparison of first-pass effect between direct thromboaspiration and combined thrombectomy in the setting of distal basilar occlusion.

Studies investigating endovascular therapy in vertebro-basilar stroke have led to controversial results in the past, but recent randomized trials seem to show an effectiveness superiority of endovascular therapy versus best medical treatment. However, uncertainty remains concerning many aspects of thrombectomy in acute basilar artery occlusion, notably technical considerations. This study compared the first-pass effect of direct thromboaspiration and combined thrombectomy in the setting of distal basilar occlusion. An in-vitro experimental set-up was used, consisting of a vascular phantom model and thrombus analogs of different consistencies to mimic human clots. Thrombus analogs were injected into the model through the vertebral artery and flowed to the basilar distal third to mimic a distal basilar occlusion. Ten procedures were performed for each thrombus analog stiffness and technique (direct thromboaspiration versus combined thrombectomy). Direct thromboaspiration showed an overall first-pass effect rate of 83.3% (25/30) and was particularly effective for ultra-soft and soft clot analogs, but decreased for hard clot analogs. Combined thrombectomy had an overall first-pass effect rate of 56.7% (17/30). The effect rate for ultra-soft and soft clot analogs was 60% and 50% for hard clot analogs. In the softer clot analogs, the stent-retriever device used for the combined thrombectomies tended to deviate the clot analog from a co-axial trajectory with the aspiration catheter. In the context of distal basilar occlusion, our in-vitro results showed that higher first-pass effect rates were achieved with direct thromboaspiration compared to combined thrombectomy in all types of thrombus analogs.

Can micro-guidewire advancement forces predict clot consistency and location to assist the first-line technique for mechanical thrombectomy?

The identification of specific clot characteristics before mechanical thrombectomy (MTB) might allow the selection of the most effective first-line technique, thus potentially improving the procedural outcome. We aimed to evaluate if the microwire push forces could extrapolate information on clot consistency and extension before MTB, based on clot mechanical properties. We measured in vitro the forces exerted on the proximal extremity of the guidewire during the advancement and retrieval of the guidewire through clot analogs of different compositions. In addition, we analyzed the forces exerted on the guidewire to extrapolate information about the location of the proximal and distal extremities of the clot analogs. The maximum forces recorded during the whole penetration phase were significantly different for hard and soft clots (median values, 55.6 mN vs 15.4 mN, respectively; P<0.0001). The maximum slope of the force curves recorded during the advancement of the guidewire for the first 3 s of penetration also significantly differentiated soft from hard clot analogs (7.6 mN/s vs 23.9 mN/s, respectively; P<0.0001). In addition, the qualitative analysis of the shape of the force curves obtained during the advancement and retrieval of the guidewire showed a good potential for the identification of the proximal and distal edges of the clot analogs. Our results demonstrated that it was possible to differentiate between soft and hard clot analogs. Furthermore, force measurements could give important information about the location of the clot extremities. Such an approach might support the selection of the first-line MTB technique, with the potential to improve the outcome.

MicroCT and Histological Analysis of Clot Composition in Acute Ischemic Stroke : AComparative Study of MT-Retrieved Clots and Clot Analogs.

Assessing clot composition on prethrombectomy computed tomography (CT) imaging may help in stroke treatment planning. In this study we seek to use microCT imaging of fabricated blood clots to understand the relationship between CT radiographic signals and the biological makeup. Clots (n = 10) retrieved by mechanical thrombectomy (MT) were collected, and 6clot analogs of varying RBC composition were made. We performed paired microCT and histological image analysis of all 16clots using aScanCo microCT 100 (4.9 µm resolution) and standard H&E staining (imaged at 40×). From these data types, first order statistic (FOS) radiomics were computed from microCT, and percent composition of RBCs (%RBC) was computed from histology. Polynomial and linear regression (LR) were used to build statistical models based on retrieved thrombus microCT and %RBC that were evaluated for their ability to predict the %RBC of clot analogs from mean HU. Correlation analyses of microCT FOS with composition were completed for both retrieved clots and analogs. The LR model fits relating MT-retrieved clot %RBC with mean (R2 = 0.625, p = 0.006) and standard deviation (R2 = 0.564, p < 0.05) in HUs on microCT were significant. Similarly, LR models relating analog histological %RBC to analog protocol %RBC (R2 = 0.915, p = 0.003) and mean HUs on microCT (R2 = 0.872, p = 0.007) were also significant. When the LR model built using MT-retrieved clots was used to predict analog %RBC from mean HUs, significant correlation was observed between predictions and actual histological %RBC (R2 = 0.852, p = 0.009). For retrieved clots, significant correlations were observed for energy and total energy with %RBC and %FP (|R| > 0.7, q < 0.01). Analogs further demonstrated significant correlation between FOS energy, total energy, variance and %WBC (|R| > 0.9, q < 0.01). MicroCT can be used to build models that predict AIS clot composition from routine CT parameters and help us to better understand radiomic signatures associated with clot composition and first pass outcomes. In future work, such observations can be used to better infer clot composition and inform thrombectomy prognostics from pretreatment CTs.

Impact on collateral flow of devices used for endovascular treatment of stroke: an in-vitro flow model

BackgroundCollateral blood supply of distal vessels has been linked to clinical outcome, infarct volume and recanalization rates in patients with large vessel occlusion. Our study aimed to explore the effects...

A novel method for preparing clot analogs under dynamic vortical flow for testing mechanical thrombectomy devices.

Clot analogs are essential in animal and in vitro experiments on mechanical thrombectomy devices for treating acute ischemic stroke. Clot analogs should be capable of reproducing a variety of arterial clots observed in clinical practice in terms of histological composition and mechanical properties. Bovine blood with added thrombin was stirred in a beaker so that clots could be formed under the condition of dynamic vortical flow. Static clots were also prepared without stirring, and the properties of the static clots and dynamic clots were compared. Histological and scanning electron microscopy experiments were performed. Compression and relaxation tests were performed to evaluate the mechanical properties of the two types of clots. Thromboembolism and thrombectomy tests were conducted in an in vitro circulation model. Compared to the static clots, the dynamic clots prepared under vortical flow displayed a higher fibrin content, and their fibrin network was denser and sturdier than that of the static clots. The stiffness of the dynamic clots was significantly higher than that of the static clots. The stress of both types of clots could decay quickly under large sustained strain. The static clots could break at the bifurcation in the vascular model, while the dynamic clots could be firmly stuck in the vascular model. Dynamic clots generated in dynamic vortical flow differ significantly from static clots in terms of their composition and mechanical properties, which may be beneficial information for preclinical research on mechanical thrombectomy devices.

Effect of Chandler loop shear and tubing size on thrombus architecture

Thrombosis can lead to a wide variety of life-threatening circumstances. As current thrombolytic drug screening models often poorly predict drug profiles, leading to failure of thrombolytic therapy or clinical translation, more representative clot substrates are necessary for drug evaluation. Utilizing a Chandler loop device to form clot analogs at high shear has gained popularity in stroke societies. However, shear-dependent clot microstructure has not been fully addressed and low shear conditions are often overlooked. We herein characterized the impact of wall shear rate (126 to 951 s−1) on clot properties in the Chandler loop. Different revolutions (20–60) per minute and tubing sizes (3.2 to 7.9 mm) were employed to create different sized clots to mimic various thrombosis applications. Increased shear resulted in decreased RBC counts (76.9 ± 4.3% to 17.6 ± 0.9%) and increased fibrin (10 to 60%) based on clot histology. Increased fibrin sheet morphology and platelet aggregates were observed at higher shear under scanning electron microscope. These results show the significant impact of shear and tubing size on resulting clot properties and demonstrate the capability of forming a variety of reproducible in-vivo-like clot analogs in the Chandler loop device controlling for simple parameters to tune clot characteristics.Graphical

Impact of stent-retriever tip design on distal embolization during mechanical thrombectomy: a randomized in vitro evaluation

BackgroundRepeated number of passes, clot fragmentation, and distal embolization during mechanical thrombectomy (MT) lead to worse clinical outcomes in acute ischemic stroke. This study aimed to assess the recanalization and...

NIMBUS geometric clot extractor for challenging clots: Real-world clinical experience and clot composition.

Revascularization rates following mechanical thrombectomy (MT) for acute ischemic stroke (AIS) remain suboptimal for patients with fibrin-rich, recalcitrant clots. The NIMBUS Geometric Clot Extractor has demonstrated promising in vitro revascularization rates using fibrin-rich clot analogs. This study assessed the retrieval rate and composition of clot using NIMBUS in a clinical setting. This retrospective study included patients who underwent MT with NIMBUS at two high-volume stroke centers between December 2019 and May 2021. NIMBUS was used for clots deemed challenging to remove at the interventionalist's discretion. At one of the centers, per pass clot was collected for histological analysis by an independent lab. A total of 37 patients (mean age 76.87 ± 11.73 years; 18 female; mean time from stroke onset 11.70 ± 6.41 h) were included. NIMBUS was used as first and second-line device in 5 and 32 patients, respectively. The main reason for using NIMBUS (32/37) was the failure of standard MT techniques after a mean 2.86 ± 1.48 number of passes. Substantial reperfusion (mTICI ≥2b) was achieved in 29/37 patients (78.4%) with a mean of 1.81 ± 1.00 NIMBUS passes (mean 4.68 ± 1.68 passes with all devices), and NIMBUS was the final device used in 79.3% (23/29) of those cases. Clot specimens from 18 cases underwent composition analysis. Fibrin and platelets represented 31.4 ± 13.7% and 28.8 ± 18.8% of clot components; 34.4 ± 19.5% were red blood cells. In this series, NIMBUS was effective in removing tough clots rich in fibrin and platelets in challenging real-world situations.

A swine model of pulmonary embolism with human-derived thrombi

Objectives: The development and evaluation of percutaneous thrombectomy devices for pulmonary embolism (PE) pose a need for standardized large in vivo models with representative anatomical and physiological conditions and clots analogs. In this study, we present a swine model of PE model employing human-derived clot analogs. Material and Methods: Baseline angiographic and physiological pressure measurements were obtained in six adult Yorkshire pigs (45–65 kg) and results were benchmarked for interspecies comparison with published human data using fluoroscopic examinations, intra-arterial pressure measurements, and histologic studies. Then, clot analogs were created ex vivo employing banked human blood and a subset incubated in iodinated contrast for fluoroscopic visualization. Clot analogs were then embolized via a femoral venous access and angiographic/physiological consequences were evaluated. Results: The main, right, and left pulmonary artery diameters were 24 ± 1.1 mm, 16.5 ± 0.8 mm, and 12.6 ± 1.2 mm, respectively. The angle between the main pulmonary artery at the bifurcation point was approximately 90–95°. The clot analogs were heterogeneous and had increased fibrin content along the clot length. The overall composition was 96.63% red blood cell (RBC)/3.37% fibrin in the initial section, 48.85% RBC/51.15% fibrin in the intermediate section, and 3.44% RBC/96.56% fibrin in the final section. Embolization of the clot analogs resulted in distal occlusion of the right and left pulmonary arteries. Conclusions: This swine model coupled with clot analog is able to accurately mimic human anatomical and physiological conditions in PE making it feasible for the evaluation of pulmonary thrombectomy devices.

Abstract Number ‐ 151: Impact of Stent‐Retriever Tip Design on Distal Embolization during Mechanical Thrombectomy

Introduction Mechanical thrombectomy (MT) is a widely performed procedure for acute ischemic stroke (AIS) due to large vessel occlusion. Repeated number of passes, clot fragmentation, and distal embolization during MT lead to worse clinical outcomes. We aim to evaluate the impact of different stent‐retriever (SR) distal tip designs on distal emboli generation during MT. Methods Fragment‐prone clot analogs (diameter = 3.53±0.14mm; length = 6.74±0.61mm) were used to create proximal middle cerebral artery (MCA‐M1) occlusions in an in vitro neurovascular model featuring a complete circle of Willis. The anatomical replica was connected to a flow loop with circulating saline at physiological flow rate and temperature; 100‐µm filters were placed at the neurovascular outflow points of the model to collect generated distal emboli. After initial embolization, experiments were randomized into one of the three treatment arms based on SR tip design: open‐end (Open‐SR: Solitaire 6.0×40mm), closed‐end (Closed‐SR: Embotrap II 5.0×33mm), and filter‐end (Filter‐SR: NeVa NET 5.5×37mm). A balloon guide catheter was inflated at the internal carotid artery C1 level immediately after SR deployment, and the SR was pulled out under continuous proximal pump aspiration. A total of 90 cases were performed (30 cases/treatment arm). A single attempt was performed per case and after each pass, distal emboli collected in the outflow filters were analyzed by an image processing algorithm. Successful first pass recanalization (FPR) was confirmed if no residual clot was observed at the initial location or in a distal branch of the model. Primary study endpoints were: FPR rate (%FPR), the size of the largest embolus (largest‐E), the total emboli count (total‐E), the total count of emboli larger than 1mm (total&gt;1mm‐E), and the total area of the filter covered by emboli (area‐E). Results FPR was achieved in 57.8% of cases (52/90): Filter‐SR achieved a non‐significantly higher %FPR (70%) than closed‐SR (50%) and open‐SR (53.3%) (p = 0.244). In comparison to open‐ and closed‐SR, filter‐SR significantly reduced the largest‐E (open‐SR = 1.66±0.68mm vs. closed‐SR = 1.77±0.90mm vs. filter‐SR = 1.22±0.77mm; p = 0.013) as well as the total&gt;1mm‐E (open‐SR = 2.27±2.33 vs. closed‐SR = 3.97±5.68 vs. filter‐SR = 0.93±1.28; p = 0.002), and the area‐E (open‐SR = 18.22±14.47mm2 vs. closed‐SR = 23.98±22.39mm2 vs. filter‐SR = 10.14±8.81mm2; p = 0.013). The differences between distal tip designs were not clearly evidenced in the total‐E (open‐SR = 22.7±10.75 vs. closed‐SR = 23.13±13.16 vs. filter‐SR = 20.63±12.77; p = 0.464). No significant differences were found between open‐ and closed‐SR (p&gt;0.05 in all metrics). Conclusions When facing fragment‐prone clots with low SR engagement, the filter‐SR significantly reduces the number of large clot fragments (&gt;1mm), the size of the largest embolus, and the overall surface area of clot fragments that embolize distally during an MT procedure.

Double stent-retriever as the first-line approach in mechanical thrombectomy: a randomized in vitro evaluation

BackgroundA repeated number of passes during mechanical thrombectomy leads to worse clinical outcomes in acute ischemic stroke. Initial experiences with the simultaneous double stent-retriever (double-SR) technique as the first-line treatment...

Construction and Validation of a Benchtop Model for Testing of Mechanical Thrombectomy Devices for Pulmonary Embolism.

This study aims to define the process of designing and manufacturing 3D printed and glass models of the pulmonary artery (PA) and utilizing them in a test bed for evaluation of devices for mechanical thrombectomy of pulmonary embolism (PE). Patient derived computed tomography angiography (CTA) images of the PA were digitally converted into a hollowed-out structure and translated into clear 3D printed and glass models. A test bed was created using a peristaltic pump and silicone tubing connected to the models. Human clot analogs were then prepared and injected within the models. Thrombectomy testing was done using clinically used predicates and baseline characteristics of the models were evaluated by independent interventionalists. The mean sizes of the main pulmonary artery (MPA) for the 3D printed model and glass model were 30.4mm and 29.2mm, mimicking those of the patient's PA obtained on CTA. Heterogeneous human clot analogs were created with fibrin composition ranging from 60 to 30%. Mechanical thrombectomy was successfully attempted by independent interventionalists. Both the 3D printed, and glass model were appraised as very good for multiple attributes. A complete test bed using 3D printed and glass models of the PA with human clot analogs was created for testing of mechanical thrombectomy devices for PE.

Numerical simulation of non-linear loading–unloading hysteresis behavior of blood clots

The stress–strain characteristics of a clot during loading/unloading mechanical cycles are significant features to assess the underlying mechanisms of thrombectomy, especially when multiple thrombectomy attempts are required. We investigated a damage model to predict loading/unloading response of clots. To study the validity of the model, we tested theoretical models to reproduce the experimentally obtained mechanical characteristics of clots under various conditions. Three types of clot analogs with different red blood cell (RBC) compositions were prepared. Cylindrical clot analogs were formed for the tensile and compression tests. Loading/unloading tests at 80% of strain were conducted, where the material parameters were determined by fitting the results to a theoretical curve combining the damage model and the elasto-plastic constitutive model. Through the computation for theoretical curves, unique characteristics of clots were revealed such that the hysteresis loss rate did not change by varying RBC contents, except for the clot created with 0% RBC composition, under compressive loading. In addition, the plastic strain decreased as the RBC content decreased under tensile loading, whereas it increased as the RBC content decreased under compressive loading. A three-dimensional finite element method (FEM) was employed with the determined parameters. The FEM could accurately reproduce the experimental stress–strain curves for all types of clot analogs and for both loading types up to a strain of 80%. The results indicate that the theoretical model which incorporates and combines the damage model and the elasto-plastic constitutive model is applicable to predict the non-linear stress–strain behavior of clots under loading and unloading.

Combined stent-retriever and aspiration intra-arterial thrombectomy performance for fragmentable blood clots: A proof-of-concept computational study

Mechanical thrombectomy (MT) treatment of acute ischemic stroke (AIS) patients typically involves use of stent retrievers or aspiration catheters alone or in combination. For in silico trials of AIS patients, it is crucial to incorporate the possibility of thrombus fragmentation during the intervention. This study focuses on two aspects of the thrombectomy simulation: i) Thrombus fragmentation on the basis of a failure model calibrated with experimental tests on clot analogs; ii) the combined stent-retriever and aspiration catheter MT procedure is modeled by adding both the proximal balloon guide catheter and the distal access catheter.The adopted failure criterion is based on maximum principal stress threshold value. If elements of the thrombus exceed this criterion during the retrieval simulation, then they are deleted from the calculation.Comparison with in-vitro tests indicates that the simulation correctly reproduces the procedures predicting thrombus fragmentation in the case of red blood cells rich thrombi, whereas non-fragmentation is predicted for fibrin-rich thrombi. Modeling of balloon guide catheter prevents clot fragments' embolization to further distal territories during MT procedure.

Novel synthetic clot analogs for in-vitro stroke modelling.

PurposeThe increased demand for training of mechanical thrombectomy in ischemic stroke and development of new recanalization devices urges the creation of new simulation models both for training and device assessment. Clots properties have shown to play a role in procedural planning and thrombectomy device effectiveness. In this study, we analyzed the characteristics and applicability of completely synthetic, animal-free clots in the setting of an in-vitro model of mechanical thrombectomy for training and device assessment.MethodsSynthetic clots based on agarose (n = 12) and silicone (n = 11) were evaluated in an in-vitro neurointervention simulation of mechanical thrombectomy with clot extraction devices. Calcified clots of mixed nature were simulated with addition of 3D printed structures. 9 clots were excluded due to insufficient vessel occlusion and failure to integrate with clot extraction device. Synthetic thrombi were characterized and compared using a categorical score-system on vessel occlusion, elasticity, fragmentation, adherence and device integration.ResultsBoth agarose-based and silicone-based clots demonstrated relevant flow arrest and a good integration with the clot extraction device. Silicone-based clots scored higher on adherence to the vessel wall and elasticity.ConclusionSelected synthetic clots can successfully be implemented in an in-vitro training environment of mechanical thrombectomy. The clots’ different properties might serve to mimic fibrin-rich and red blood cell-rich human thrombi.

Human “live cadaver” neurovascular model for proximal and distal mechanical thrombectomy in stroke

BackgroundPreclinical testing platforms that accurately replicate complex human cerebral vasculature are critical to advance neurointerventional knowledge, tools, and techniques. Here, we introduced and validated a human “live cadaveric” head-and-neck neurovascular...

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

BackgroundGrowing 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.MethodologyA 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.ResultsThe 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).ConclusionDifferent 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.