Collateral Flow Patterns Research Articles

Patterns of venous collateral development after splenic vein occlusion associated with surgical and oncological outcomes after distal pancreatectomy.

Splenic vein occlusion (SpVO) due to a pancreatic tumor may result in the development of collateral circulation and left-sided portal hypertension. This study aimed to investigate the impact of SpVO on distal pancreatectomy (DP) and provide insights about the management of such cases. This retrospective analysis included 124 patients who underwent DP from 2014 to 2022. A subgroup analysis was performed on 88 patients who underwent DP for pancreatic ductal adenocarcinoma (PDAC). SpVO was found in 26 (20.8%) patients. The patients with SpVO had significantly larger splenic volumes and lower platelet counts. Compared to the patients with patent splenic veins (SpVs), the patients with SpVO underwent significantly longer operations (p = 0.006), with a higher incidence of postoperative complications (p = 0.002). We classified the collateral routes associated with SpVO into five patterns. The most common pattern was the left gastroepiploic vein type, which was associated with a tumor of the pancreatic body. In patients with PDAC, SpVO was associated with larger tumors, microscopic vascular permeation, and peritoneal recurrence. However, the differences between overall and recurrence-free survival rates in the patients with SpVO vs those with patent SpVs were not significant. SpVO causes left-sided portal hypertension, which can be a risk for perioperative complications in DP. Operative planning based on the classification of collateral flow patterns may help prevent intraoperative congestion and perioperative complications.

Perfusion Defects and Collateral Flow Patterns in Acute Small Subcortical Infarction: a 4D Dynamic MRI Study

The hemodynamic changes of acute small subcortical infarction (SSI) are not well understood. We evaluate the hemodynamic changes and collaterals in acute SSI using perfusion magnetic resonance imaging (MRI). A total of 103 patients with acute SSI in penetrating artery territories were recruited and underwent MRI within 24 h of stroke onset. Using 4D dynamic perfusion MRI, they were divided into three patterns: 25 (24%) with normal perfusion, 31 (30%) with compensated perfusion, and 47 (46%) with hypoperfusion. The development of anterograde or retrograde collaterals was also evaluated. Patients with hypoperfusion pattern had the highest rate of early neurological deterioration (32%, p = 0.007), the largest initial and final infarction volumes (p < 0.001 and p = 0.029), the lowest relative cerebral blood flow (0.63, p < 0.001), and the lowest rate of anterograde and retrograde collaterals (19%, p < 0.001; 66%, p = 0.002). The anterograde collaterals were associated with higher relative cerebral blood volume (0.91 vs. 0.77; p = 0.024) and a higher rate of deep cerebral microbleeds (48 vs. 21%; p = 0.028), whereas retrograde collaterals were associated with higher systolic and diastolic blood pressure (p = 0.031 and 0.020), smaller initial infarction volume (0.81 vs. 1.34 ml, p = 0.031), and a higher rate of lobar cerebral microbleeds (30 vs. 0%; p = 0.013). Both anterograde and retrograde collaterals may play a critical role in maintaining cerebral perfusion and can have an impact on patient clinical outcomes. Further studies are warranted to verify these findings and to investigate effective treatments.

Which Acute Ischemic Stroke Patients Are Fast Progressors?: Results From the ESCAPE Trial Control Arm.

Fast infarct progression in acute ischemic stroke has a severe impact on patient prognosis and benefit of endovascular thrombectomy. In this post hoc analysis of the ESCAPE trial (Endovascular Treatment for Small Core and Proximal Occlusion Ischemic Stroke), we identified acute ischemic stroke patients with rapid infarct growth and investigated their baseline clinical and imaging characteristics. Control arm patients were included if they had follow-up imaging at 2-8 hours without substantial recanalization, and if their baseline Alberta Stroke Program Early CT Score was ≥9. Fast infarct progression was defined as Alberta Stroke Program Early CT Score decay ≥3 points from baseline to 2- to 8-hour follow-up imaging. Clinical and imaging baseline characteristics were compared between fast progressors and other patients, and occlusion site and collateral flow patterns were assessed in detail. Fast infarct progression occurred in 15 of 43 included patients (34.9%). Fast progressors had worse collaterals (poor in 3/15 [20%] versus 0/28 patients, P=0.021) and more carotid-T or -L occlusions (8/15 [53.4%] versus 3/28[10.7%], P=0.021). In 8 out of 15 (53.3%), occlusion site and circle of Willis configuration prevented collateral flow via the anterior or posterior cerebral artery. Most patients with fast infarct progression had terminal carotid occlusions and impaired collateral flow via the anterior or posterior cerebral artery, indicating that occlusion location and intracranial vascular anatomy are relevant for infarct progression.

The Clinical Contribution of Neurovascular Ultrasonography in Acute Ischemic Stroke.

Patients with acute ischemic stroke receive computed tomography angiogram (CTA) and digital subtraction angiogram (DSA) for clinical evaluation. Current guidelines lack in defining indications for transcranial Doppler (TCD) and/or carotid duplex ultrasonography (CUS) in acute stroke evaluation or follow-up cerebrovascular imaging after reperfusion. We investigated the clinical utility of performing additional TCD/CUS after reperfusion in guiding postacute care stroke management. Retrospective review of acute ischemic stroke patients admitted to a comprehensive stroke center with CTA head and neck and/or DSA followed by TCD/CUS. Cases were reviewed by two authors to determine if TCD/CUS provided additional diagnostic information to aid management. A nominal group process, using a third author, achieved consensus in cases of disagreements. Only 25 of 198 patients had CTA or DSA followed by TCD/CUS. Ten (40%) cases showed new clinical information from CUS aiding management. Of those with TCD, 5 patients (22.7%) had findings that impacted management. These clinical scenarios included detection of mobile thrombus requiring anticoagulation; distinguishing carotid near-occlusion from occlusion; confirming hemodynamic significance of intra/extracranial stenosis helping emergent stenting/endarterectomy; detecting hyperperfusion on TCDs causing symptoms; and establishing chronicity of carotid stenosis based on collateral flow patterns, which deferred further intervention. Our experience shows that TCD/CUS may offer additional diagnostic information assisting postacute care management in small subset of patients with acute ischemic stroke. Larger studies are needed to research the clinical impact and cost-effectiveness of additional imaging and inform clinical guidelines for selecting patients who will benefit from these additional studies.

Spatiotemporal dynamics of pial collateral blood flow following permanent middle cerebral artery occlusion in a rat model of sensory-based protection: a Doppler optical coherence tomography study.

.There is a growing recognition regarding the importance of pial collateral flow in the protection from impending ischemic stroke both in preclinical and clinical studies. Collateral flow is also a major player in sensory stimulation-based protection from impending ischemic stroke. Doppler optical coherence tomography has been employed to image spatiotemporal patterns of collateral flow within the dorsal branches of the middle cerebral artery (MCA) as it provides a powerful tool for quantitative in vivo flow parameters imaging (velocity, flux, direction of flow, and radius of imaged branches). It was employed prior to and following dorsal permanent MCA occlusion (pMCAo) in rat models of treatment by protective sensory stimulation, untreated controls, or sham surgery controls. Unexpectedly, following pMCAo in the majority of subjects, some MCA branches continued to show anterograde blood flow patterns over time despite severing of the MCA. Further, in the presence of protective sensory stimulation, the anterograde velocity and flux were stronger and lasted longer than in retrograde flow branches, even within different branches of single subjects, but stimulated retrograde branches showed stronger flow parameters at 24 h. Our study suggests that the spatiotemporal patterns of collateral-based dorsal MCA flow are dynamic and provide a detailed description on the differential effects of protective sensory stimulation.

Pencil Beam Presaturation Magnetic Resonance Imaging Helps to Identify Patients at Risk for Intolerance to Temporary Internal Carotid Artery Occlusion During Carotid Endarterectomy and Carotid Artery Stenting

There has been no effective method to predict ischemic intolerance to temporary internal carotid artery (ICA) occlusion during carotid artery reconstruction. Pencil beam presaturation (BeamSAT) pulse suppresses the flow signal of the target vessel in magnetic resonance angiography (MRA). Applying this method, we constructed ICA-selective MRA images. The aim of this study was to identify patients at risk for ischemic intolerance by ICA-selective MRA. By evaluating flow of anterior communicating artery (Acom) and A1 portion of anterior cerebral artery with ICA-selective MRA and posterior communicating artery (Pcom) with conventional MRA, we investigated associations of these collateral flow patterns with ischemic intolerance and decrease of regional cerebral oxygen saturation. The study included 58 patients who underwent carotid endarterectomy or carotid artery stenting. Six of 7 patients without Acom flow and Pcom flow demonstrated ischemic intolerance, whereas all patients (n= 51) with Acom and/or Pcom flow demonstrated tolerance. The accuracy of this prediction model according to Acom and Pcom flow patterns for ischemic intolerance was 0.98 (P=0.01, binomial test). Regional cerebral oxygen saturation decrease after ICA occlusion was significantly larger in patients without Acom flow and Pcom flow (12.0%± 6.0%) than in patients with Acom flow and Pcom flow (3.0% ± 3.1%, P < 0.01) and in patients with Acom flow but no Pcom flow (2.4% ± 5.2%, P < 0.01). These findings support the importance of Acom flow as a collateral route. ICA-selective MRA enables prediction of ischemic intolerance to temporary ICA occlusion during carotid endarterectomy or carotid artery stenting. This method provides valuable information regarding probability of an ischemic complication.

Blood Flow Lateralization and Collateral Compensatory Mechanisms in Patients With Carotid Artery Stenosis.

Background and Purpose—Four-dimensional phase-contrast magnetic resonance imaging enables quantification of blood flow rate (BFR; mL/min) in multiple cerebral arteries simultaneously, making it a promising technique for hemodynamic investigation in patients with stroke. The aim of this study was to quantify the hemodynamic disturbance and the compensatory pattern of collateral flow in patients with symptomatic carotid stenosis.Methods—Thirty-eight patients (mean, 72 years; 27 men) with symptomatic carotid stenosis (≥50%) or occlusion were investigated using 4-dimensional phase-contrast magnetic resonance imaging. For each patient, BFR was measured in 19 arteries/locations. The ipsilateral side to the symptomatic carotid stenosis was compared with the contralateral side.Results—Internal carotid artery BFR was lower on the ipsilateral side (134±87 versus 261±95 mL/min; P<0.001). BFR in anterior cerebral artery (A1 segment) was lower on ipsilateral side (35±58 versus 119±72 mL/min; P<0.001). Anterior cerebral artery territory bilaterally was primarily supplied by contralateral internal carotid artery. The ipsilateral internal carotid artery mainly supplied the ipsilateral middle cerebral artery (MCA) territory. MCA was also supplied by a reversed BFR found in the ophthalmic and the posterior communicating artery routes on the ipsilateral side (−5±28 versus 10±28 mL/min, P=0.001, and −2±12 versus 6±6 mL/min, P=0.03, respectively). Despite these compensations, BFR in MCA was lower on the ipsilateral side, and this laterality was more pronounced in patients with severe carotid stenosis (≥70%). Although comparing ipsilateral MCA BFR between stenosis groups (<70% and ≥70%), there was no difference (P=0.95).Conclusions—With a novel approach using 4-dimensional phase-contrast magnetic resonance imaging, we could simultaneously quantify and rank the importance of collateral routes in patients with carotid stenosis. An important observation was that contralateral internal carotid artery mainly secured the bilateral anterior cerebral artery territory. Because of the collateral recruitment, compromised BFR in MCA is not necessarily related to the degree of carotid stenosis. These findings highlight the importance of simultaneous investigation of the hemodynamics of the entire cerebral arterial tree.

Visualizing artery-specific blood flow patterns above the circle of Willis with vessel-encoded arterial spin labeling.

PurposeTo establish the feasibility of using vessel‐encoded pseudocontinuous arterial spin labeling (VEPCASL) for noninvasive vascular territory imaging (VTI) and artery‐specific dynamic angiography of a large number of arterial branches above the circle of Willis within a clinically feasible scan time.Methods3D time‐of‐flight angiography was used to select a labeling plane and establish 7 pairs of encoding cycles. These were used for VEPCASL VTI and dynamic 2D angiography (8 min and 3 min acquisition times, respectively) in healthy volunteers, allowing the separation of signals arising from 13 arterial branches (including extracranial arteries) in postprocessing. To demonstrate the clinical potential of this approach, VEPCASL angiography was also applied in 5 patients with brain arteriovenous malformation (AVM).ResultsIn healthy volunteers, the artery‐specific filling of the vascular tree and resulting perfusion territories were well depicted. SNRs were approximately 5 times higher than those achievable with single‐artery selective methods. Blood supply to the AVMs was well visualized in all cases, showing the main feeding arteries and venous drainage.ConclusionsVEPCASL is a highly efficient method for both VTI and dynamic angiography of a large number of arterial branches, providing a comprehensive picture of vascular flow patterns and the effect on downstream tissue perfusion within an acceptable scan time. Automation of labeling plane and vessel‐encoding selection would improve robustness and efficiency, and further refinement could allow quantitative blood flow measurements to be obtained. This technique shows promise for visualizing the blood supply to lesions and collateral flow patterns.

Posterior circulation involvement and collateral flow pattern in moyamoya disease with the RNF213 polymorphism.

Moyamoya disease is a chronic cerebrovascular disorder characterized by progressive stenosis of the circle of Willis with a compensatory collateral vessel network. Recent studies have identified the ring finger protein 213 gene (RNF213) as the unique susceptibility gene for moyamoya disease. The purpose of this study was to compare clinical features of moyamoya disease, especially angiographic findings, between patients with and without the RNF213 mutation. Blood samples from 35 patients with moyamoya disease were obtained between May 2016 and May 2017. Information on age at the time of diagnosis, sex, and initial symptom were obtained via retrospective chart review. Angiographic records were evaluated. RNF213 variants were detected in the 28 of 35 patients (80%), including all pediatric patients (100%) and 18 of 25 adult patients (72%) in our cohort. Leptomeningeal collateral flow from posterior to anterior circulation was more frequent in the RNF213-negative group than in the RNF213-positive group (100% versus 38.9%; p = 0.020). Posterior cerebral arterial territorial involvement was more frequently observed in RNF213-positive patients than in RNF213-negative patients (50% versus 0%; p = 0.027). RNF213 may play a significant role in the development of collateral anastomoses.

Simultaneous acquisition of perfusion image and dynamic MR angiography using time-encoded pseudo-continuous ASL.

PurposeBoth dynamic magnetic resonance angiography (4D‐MRA) and perfusion imaging can be acquired by using arterial spin labeling (ASL). While 4D‐MRA highlights large vessel pathology, such as stenosis or collateral blood flow patterns, perfusion imaging provides information on the microvascular status. Therefore, a complete picture of the cerebral hemodynamic condition could be obtained by combining the two techniques. Here, we propose a novel technique for simultaneous acquisition of 4D‐MRA and perfusion imaging using time‐encoded pseudo‐continuous arterial spin labeling.MethodsThe time‐encoded pseudo‐continuous arterial spin labeling module consisted of a first subbolus that was optimized for perfusion imaging by using a labeling duration of 1800 ms, whereas the other six subboli of 130 ms were used for encoding the passage of the labeled spins through the arterial system for 4D‐MRA acquisition. After the entire labeling module, a multishot 3D turbo‐field echo‐planar‐imaging readout was executed for the 4D‐MRA acquisition, immediately followed by a single‐shot, multislice echo‐planar‐imaging readout for perfusion imaging. The optimal excitation flip angle for the 3D turbo‐field echo‐planar‐imaging readout was investigated by evaluating the image quality of the 4D‐MRA and perfusion images as well as the accuracy of the estimated cerebral blood flow values.ResultsWhen using 36 excitation radiofrequency pulses with flip angles of 5 or 7.5°, the saturation effects of the 3D turbo‐field echo‐planar‐imaging readout on the perfusion images were relatively moderate and after correction, there were no statistically significant differences between the obtained cerebral blood flow values and those from traditional time‐encoded pseudo‐continuous arterial spin labeling.ConclusionsThis study demonstrated that simultaneous acquisition of 4D‐MRA and perfusion images can be achieved by using time‐encoded pseudo‐continuous arterial spin labeling. Magn Reson Med 79:2676–2684, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Compensatory patterns of collateral flow in stroke patients with unilateral and bilateral carotid stenosis.

BackgroundCollateral pathways are important in maintaining adequate cerebral blood flow in patients with carotid stenosis. We aimed to evaluate the hemodynamic patterns in relation to carotid stenosis in acute stroke patients.MethodsConsecutive 586 stroke patients in a hospital based cohort were included in the present study. Carotid duplex was performed to identify patients with absolute minimal diameter reductions of 50 % or greater in their internal carotid arteries (ICAs). Color velocity imaging quantification ultrasound (CVIQ) was used to measure extracranial arterial blood flow volume (BFV) in bilateral common carotid arteries (CCAs) and bilateral vertebral arteries (VAs). The absolute values of BFV and the ratios were compared between patients with and without ICA stenosis.ResultsAmong 586 acute ischemic stroke patients (mean age: 67.5 ± 12.4y), ICA stenosis was detected in 112 patients (19.1 %), including unilateral ICA stenosis in 81 patients (13.8 %) and bilateral ICA stenosis in 31 patients (5.3 %). Among patients with unilateral ICA stenosis, the BFV in contralateral CCA was significantly higher than that in ipsilateral CCA (325.5 ± 99.8 mL/min vs. 242.2 ± 112.2 mL/min, P < 0.001). Among patients with bilateral ICA stenosis, the sum of BFV in bilateral VAs accounted for 22 % of the whole cerebral blood flow, which was significantly higher than that in those without ICA stenosis (14.8 %, P < 0.001) or with unilateral ICA stenosis (16.9 %, P = 0.007).ConclusionsIn patients with unilateral carotid stenosis, contralateral carotid blood flow increases to compensate decreased blood flow, while posterior circulation may compensate for the decreased brain perfusion in those with bilateral carotid stenosis.

Abstract 159: Posterior Communicating Artery Flow Diversion in Middle Cerebral Artery Stroke: Angiographic Evidence from IMS III

Background: Only 20% of adults have a “fetal” posterior communicating artery (PCOMM) with carotid flow to the posterior cerebral artery. Dynamic pressure changes at the circle of Willis due to proximal artery occlusion may restore such collateral blood flow patterns. We investigated the findings and implications of PCOMM blood flow in middle cerebral artery (MCA) stroke at angiography in IMS III. Methods: The angiography core lab prospectively evaluated PCOMM blood flow and collateral circulation in proximal MCA or M1 occlusion. Proximal or distal M1 occlusion was noted with PCOMM flow scored (0-2) on ipsilateral carotid injections before and after endovascular therapy, correlating PCOMM status with ASITN/SIR leptomeningeal collateral grade, TICI reperfusion and subsequent clinical outcomes. Results: 122 patients with M1 occlusion at angiography (60 proximal, 62 distal) had peri-procedural evaluation of PCOMM status and associated collateral grade. Ipsilateral carotid injections revealed PCOMM flow diversion in 87/122 (71%) prior to revascularization, including 41/60 (68%) in proximal M1 and 46/62 (74%) in distal M1 (p=0.61) occlusions. After treatment, PCOMM patency was noted in 86/122 (71%), with 40/60 (67%) in proximal M1 and 46/62 (74%) in distal M1 (p=0.48) occlusions. Decrease in PCOMM score after therapy was noted in 11/122 (9%); 9/11 (82%) had mTICI 2B-3 reperfusion compared to 48/111 (43%) mTICI 2B-3 reperfusion in those with PCOMM unchanged (p=0.03). PCOMM flow (n=85) was associated with worse ASITN/SIR collaterals (median 2, IQR 2-3) than those without (n=29; median 3, IQR 2-3), p=0.09. PCOMM patency before treatment had 90-day mRS median of 4 (2-6) versus 3 (1-4), p=0.37. Conclusions: PCOMM flow diversion is common in MCA stroke, revealing an inverse correlation with leptomeningeal collaterals and dynamic changes following reperfusion.

Abstract WP57: ASL MR Perfusion Imaging Detects Collateral Blood Flow Patterns and Dynamic Changes After Treatment in Acute Ischemic Stroke

Introduction: Vessel-encoded arterial spin labeling (ASL) perfusion MRI is a new non-invasive method that is able to assess collateral blood flow and the perfusion territories of the brain feeding arteries. Hypothesis: Collateral blood flow imaging with ASL MRI is feasible in acute stroke patients and can be used to study the relationship between infarct location, perfusion territories and collateral patterns, together with dynamic changes after treatment. Method: Consecutive acute stroke patients were imaged within 24 hours of onset. Follow-up imaging was performed at discharge and/or 30 days to assess changes in vascular distribution and final infarct size. The imaging protocol contained a vessel-encoded pseudo-continuous ASL, DWI and MRA sequence. Results: Twenty stroke patients were included (NIHSS, 10; range, 0-23). Twelve patients were treated with tPA and 3 with additional endovascular therapy. Median time from initial imaging to follow-up was 25 days (range, 3-36). 80% of the exams were interpretable. Thirteen subjects (70%) had an ischemic lesion within the expected perfusion territory; 12 within the internal carotid artery (ICA) territory and 3 from basilar artery. In 5 patients (25%), the infarct zone was fed through collateral pathways. Figure A demonstrates a patient with a left ICA occlusion and collateral flow through the anterior and posterior-communicating artery. In 2 of the 5 patients with collaterals there was a shift in the vascular distribution at FU with decline of collateralisation. Figure B shows a patient with a right-sided ICA dissection directly post endovascular therapy with collateral flow from the basilar artery and normalization of the vascular distribution after 30 days. Conclusion: ASL can access perfusion territories and collateral blood flow in acute stroke. It may potentially be used to identify brain tissue without adequate collateral blood flow and stratify patients suitable for appropriate (endovascular) therapy.

Reflux of Anterior Spinal Artery Predicts Recurrent Posterior Circulation Stroke in Bilateral Vertebral Artery Disease

Predictive value of reflux of anterior spinal artery for recurrent posterior circulation ischemia in bilateral vertebral arteries steno-occlusive disease was evaluated. We retrospectively reviewed 55 patients with symptomatic posterior circulation stroke caused by bilateral stenotic (>70%) lesions of the vertebral artery. We investigated any correlation of clinical and angiographic characteristics including collateral flow patterns, with recurrent stroke. Risk factors for poor 3-month functional outcome were also evaluated. Recurrent posterior circulation stroke was observed in 15 (27.3%) patients. Multivariable analysis using Cox proportional hazards model showed anterior spinal artery reflux as a significant risk factor for stroke recurrence (adjusted hazard ratio, 19.3 [95% confidence interval, 5.35-69.9]; P<0.001). Anterior spinal artery reflux was also correlated with poor functional outcome (modified Rankin Scale score, 3-6; adjusted odds ratio, 7.41 [95% confidence interval, 1.24-44.4]; P=0.028). In patients with symptomatic bilateral vertebral artery occlusive disease, anterior spinal artery reflux predicted recurrent posterior circulation stroke and poor functional outcome.

Minimally Invasive Monitoring of Chronic Central Venous Catheter Patency in Mice Using Digital Subtraction Angiography (DSA).

BackgroundRepetitive administration of medication or contrast agents is frequently performed in mice. The introduction of vascular access mini-ports (VAMP) for mice allows long-term vascular catheterization, hereby eliminating the need for repeated vessel puncture. With catheter occlusion being the most commonly reported complication of chronic jugular vein catheterization, we tested whether digital subtraction angiography (DSA) can be utilized to evaluate VAMP patency in mice.MethodsTwenty-three mice underwent catheterization of the jugular vein and subcutaneous implantation of a VAMP. The VAMP was flushed every second day with 50 μL of heparinized saline solution (25 IU/ml). DSA was performed during injection of 100 μL of an iodine based contrast agent using an industrial X-ray inspection system intraoperatively, as well as 7±2 and 14±2 days post implantation.ResultsDSA allowed localization of catheter tip position, to rule out dislocation, kinking or occlusion of a microcatheter, and to evaluate parent vessel patency. In addition, we observed different ante- and retrograde collateral flow patterns in case of jugular vein occlusion. More exactly, 30% of animals showed parent vessel occlusion after 7±2 days in our setting. At this time point, nevertheless, all VAMPs verified intravascular contrast administration. After 14±2 days, intravascular contrast injection was verified in 70% of the implanted VAMPs, whereas at this point of time 5 animals had died or were sacrificed and in 2 mice parent vessel occlusion hampered intravascular contrast injection. Notably, no occlusion of the catheter itself was observed.ConclusionFrom our observations we conclude DSA to be a fast and valuable minimally invasive tool for investigation of catheter and parent vessel patency and for anatomical studies of collateral blood flow in animals as small as mice.

Collateral circulation via the circle of Willis in patients with carotid artery steno-occlusive disease: evaluation on 3-T 4D MRA using arterial spin labelling

To evaluate whether 3-T four-dimensional (4D) arterial spin-labelling (ASL) -based magnetic resonance angiography (MRA) is useful for assessing the collateral circulation via the circle of Willis in patients with carotid artery steno-occlusive disease. Institutional review board approval and prior written informed consent from all patients were obtained. The inclusion criteria were fulfilled by 13 patients with carotid artery steno-occlusive disease. All underwent 4D-ASL MRA at 3T and digital subtraction angiography (DSA). The flow-sensitive alternating inversion recovery (FAIR) preparation scheme with look-locker sampling was used for spin labeling. At 300-ms intervals seven dynamic scans were obtained with a spatial resolution of 0.5×0.5×0.6mm(3). The collateral flow via the circle of Willis was read on 4D-ASL MRA and DSA images by two sets of two independent readers each. κ statistics were used to assess interobserver and intermodality agreement. On DSA, collateral flow via the anterior communicating artery (AcomA) was observed in six patients, via the posterior communicating artery (PcomA) in four patients, and via both the AcomA and PcomA in three patients. With respect to the qualitative evaluation of 4D-ASL MRA images, interobserver agreement was excellent for all items (κ=1). 4D-ASL MRA and DSA consensus readings agreed on the type of collateral flow pattern in 10 of the 13 patients (77%). Intermodality agreement was good (κ=0.606; 95% confidence interval (CI): 0.215-0.997). 3T 4D-ASL MRA may be a useful tool for the evaluation of the collateral circulation in patients with carotid artery steno-occlusive disease.

Abstract 138: Perfusion Imaging of Intracranial Atherosclerotic Disease in SAMMPRIS

Background: Noninvasive perfusion imaging with CT (CTP) or MRI (PWI) provides key physiologic data regarding hemodynamics of intracranial atherosclerotic disease (ICAD). Parameters of delayed perfusion such as Tmax, time to peak (TTP), mean transit time (MTT) and cerebral blood volume (CBV) or flow (CBF) may disclose important mechanisms of stroke in ICAD. We analyzed CTP and PWI acquired in SAMMPRIS to identify the principal perfusion patterns, correlation with conventional angiography and potential links with clinical outcome. Methods: CTP and PWI were identified in the SAMMPRIS imaging archive. Perfusion datasets were processed with Olea Sphere® to yield Tmax, TTP, MTT, CBV and CBF maps graded by 2 expert readers to identify markers of decreased, normal, or increased perfusion in the symptomatic territory. The resultant multiparametric perfusion patterns were correlated with clinical and angiographic variables, using Fisher’s exact test and Kaplan-Meier methods followed by log-rank tests. Results: Perfusion imaging was available in 59 subjects at baseline and 42 at follow-up. Baseline perfusion included Tmax (decreased in 2, normal in 18, increased in 39); TTP (decreased in 2, normal in 18, increased in 39); MTT (decreased in 2, normal in 27, increased in 30); CBV (decreased in 5, normal in 42, increased in 12); CBF (decreased in 7, normal in 48, increased in 4). The baseline Tmax increases in 66% of subjects were associated with the combined (TICI and collaterals) diminished angiographic flow patterns (p=0.016) and with increased 30-day SIT (p=0.015). Baseline CBV changes were associated with stroke as a qualifying event (p=0.007), NIHSS (p=0.039), presenting symptoms of hypoperfusion (p=0.071), severity of stenosis (p=0.015), and angiographic flow patterns (p=0.009). Follow-up CTP or PWI revealed similar patterns to baseline, although delay maps normalized in patients after stenting. Conclusions: Noninvasive perfusion imaging with CT or MRI discloses delayed flow caused by ICAD, often compensated by autoregulatory vasodilation (increased CBV) to maintain CBF in the downstream territory. Perfusion imaging parameters may reflect angiographic collateral flow patterns in ICAD, warranting further investigation as predictors of stroke risk.

Improved dynamic CT angiography visualization by flow territory masking

Backgound and Purpose: Computerized tomography (CT) perfusion (or CTP) source images from CT scanners with small detector widths can be used to create a dynamic CT angiogram (CTA) similar to digital subtraction angiography (DSA). Because CTP studies use a single intravenous injection, all arterial territories enhance simultaneously, and individual arterial territories [i.e., anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA)] cannot be delineated. This limits the ability to assess collateral flow patterns on dynamic CTAs. The aim of this study was to devise and test a postprocessing method to selectively color-label the major arterial territories on dynamic CTA. Materials and Methods: We identified 22 acute-stroke patients who underwent CTP on a 320-slice CT scanner within 6 h from symptom onset. For each case, two investigators independently generated an arterial territory map from CTP bolus arrival maps using a semiautomated method. The volumes of the arterial territories were calculated for each map and the average relative difference between these volumes was calculated for each case as a measure of interrater agreement. Arterial territory maps were superimposed on the dynamic CTA to create a vessel-selective dynamic CTA with color-coding of the main arterial territories. Two experts rated the arterial territory maps and the color-coded CTAs for consistency with expected arterial territories on a 3-point scale (excellent, moderate, poor). Results: Arterial territory maps were generated for all 22 patients. The median difference in arterial territory volumes between investigators was 2.2% [interquartile range (IQR) 0.6-8.5%]. Based on expert review, the arterial territory maps and the vessel-selective dynamic CTAs showed excellent consistency with the expected arterial territories in 18 of 22 patients, moderate consistency in 2 patients, and poor consistency in another 2 patients. Conclusion: Using a novel postprocessing technique, arterial territory maps and dynamic CTAs with vessel-selective color-coding can be derived from a standard CTP scan. These maps may be used to noninvasively assess collateral flow in patients with acute stroke.

Cerebral collateral flow defines topography and evolution of molecular penumbra in experimental ischemic stroke

Intracranial collaterals are dynamically recruited after arterial occlusion and are emerging as a strong determinant of tissue outcome in both human and experimental ischemic stroke. The relationship between collateral flow and ischemic penumbra remains largely unexplored in pre-clinical studies. The aim of the present study was to investigate the pattern of collateral flow with regard to penumbral tissue after transient middle cerebral artery (MCA) occlusion in rats. MCA was transiently occluded (90min) by intraluminal filament in adult male Wistar rats (n=25). Intracranial collateral flow was studied in terms of perfusion deficit and biosignal fluctuation analyses using multi-site laser Doppler monitoring. Molecular penumbra was defined by topographical mapping and quantitative signal analysis of Heat Shock Protein 70kDa (HSP70) immunohistochemistry. Functional deficit and infarct volume were assessed 24h after ischemia induction. The results show that functional performance of intracranial collaterals during MCA occlusion inversely correlated with HSP70 immunoreactive areas in both the cortex and the striatum, as well as with infarct size and functional deficit. Intracranial collateral flow was associated with reduced areas of both molecular penumbra and ischemic core and increased areas of intact tissue in rats subjected to MCA occlusion followed by reperfusion. Our findings prompt the development of collateral therapeutics to provide tissue-saving strategies in the hyper-acute phase of ischemic stroke prior to recanalization therapy.

Carotid I's, L's and T's: collaterals shape the outcome of intracranial carotid occlusion in acute ischemic stroke

BackgroundCollaterals may affect revascularization, ischemic severity, and clinical outcomes in acute stroke owing to internal carotid artery (ICA) occlusion.ObjectiveTo examine the hypothesis that morphology of occlusive thrombus and collateral flow...