Collateral Map Research Articles

3D mobile regression vision transformer for collateral imaging in acute ischemic stroke.

The accurate and timely assessment of the collateral perfusion status is crucial in the diagnosis and treatment of patients with acute ischemic stroke. Previous works have shown that collateral imaging, derived from CT angiography, MR perfusion, and MR angiography, aids in evaluating the collateral status. However, such methods are time-consuming and/or sub-optimal due to the nature of manual processing and heuristics. Recently, deep learning approaches have shown to be promising for generating collateral imaging. These, however, suffer from the computational complexity and cost. In this study, we propose a mobile, lightweight deep regression neural network for collateral imaging in acute ischemic stroke, leveraging dynamic susceptibility contrast MR perfusion (DSC-MRP). Built based upon lightweight convolution and Transformer architectures, the proposed model manages the balance between the model complexity and performance. We evaluated the performance of the proposed model in generating the five-phase collateral maps, including arterial, capillary, early venous, late venous, and delayed phases, using DSC-MRP from 952 patients. In comparison with various deep learning models, the proposed method was superior to the competitors with similar complexity and was comparable to the competitors of high complexity. The results suggest that the proposed model is able to facilitate rapid and precise assessment of the collateral status of patients with acute ischemic stroke, leading to improved patient care and outcome.

The collateral map: prediction of lesion growth and penumbra after acute anterior circulation ischemic stroke

ObjectivesThis study evaluated the collateral map’s ability to predict lesion growth and penumbra after acute anterior circulation ischemic strokes.MethodsThis was a retrospective analysis of selected data from a prospectively collected database. The lesion growth ratio was the ratio of the follow-up lesion volume to the baseline lesion volume on diffusion-weighted imaging (DWI). The time-to-maximum (Tmax)/DWI ratio was the ratio of the baseline Tmax > 6 s volume to the baseline lesion volume. The collateral ratio was the ratio of the hypoperfused lesion volume of the phase_FU (phase with the hypoperfused lesions most approximate to the follow-up DWI lesion) to the hypoperfused lesion volume of the phase_baseline of the collateral map. Multiple logistic regression analyses were conducted to identify independent predictors of lesion growth. The concordance correlation coefficients of Tmax/DWI ratio and collateral ratio for lesion growth ratio were analyzed.ResultsFifty-two patients, including twenty-six males (mean age, 74 years), were included. Intermediate (OR, 1234.5; p < 0.001) and poor collateral perfusion grades (OR, 664.7; p = 0.006) were independently associated with lesion growth. Phase_FUs were immediately preceded phases of the phase_baselines in intermediate or poor collateral perfusion grades. The concordance correlation coefficients of the Tmax/DWI ratio and collateral ratio for the lesion growth ratio were 0.28 (95% CI, 0.17–0.38) and 0.88 (95% CI, 0.82–0.92), respectively.ConclusionPrecise prediction of lesion growth and penumbra can be possible using collateral maps, allowing for personalized application of recanalization treatments. Further studies are needed to generalize the findings of this study.Clinical relevance statementPrecise prediction of lesion growth and penumbra can be possible using collateral maps, allowing for personalized application of recanalization treatments.Key Points• Cell viability in cerebral ischemia due to proximal arterial steno-occlusion mainly depends on the collateral circulation.• The collateral map shows salvageable brain extent, which can survive by recanalization treatments after acute anterior circulation ischemic stroke.• Precise estimation of salvageable brain makes it possible to make patient-specific treatment decision.

Impact of Collateral Circulation on Futile Endovascular Thrombectomy in Acute Anterior Circulation Ischemic Stroke.

Collateral circulation is associated with the differential treatment effect of endovascular thrombectomy (EVT) in acute ischemic stroke. We aimed to verify the ability of the collateral map to predict futile EVT in patients with acute anterior circulation ischemic stroke. This secondary analysis of a prospective observational study included data from participants underwent EVT for acute ischemic stroke due to occlusion of the internal carotid artery and/or the middle cerebral artery within 8 hours of symptom onset. Multiple logistic regression analyses were conducted to identify independent predictors of futile recanalization (modified Rankin scale score at 90 days of 4-6 despite of successful reperfusion). In a total of 214 participants, older age (odds ratio [OR], 2.40; 95% confidence interval [CI], 1.56 to 3.67; p<0.001), higher baseline National Institutes of Health Stroke Scale (NIHSS) scores (OR, 1.12; 95% CI, 1.04 to 1.21; p=0.004), very poor collateral perfusion grade (OR, 35.09; 95% CI, 3.50 to 351.33; p=0.002), longer door-to-puncture time (OR, 1.08; 95% CI, 1.02 to 1.14; p=0.009), and failed reperfusion (OR, 3.73; 95% CI, 1.30 to 10.76; p=0.015) were associated with unfavorable functional outcomes. In 184 participants who achieved successful reperfusion, older age (OR, 2.30; 95% CI, 1.44 to 3.67; p<0.001), higher baseline NIHSS scores (OR, 1.12; 95% CI, 1.03 to 1.22; p=0.006), very poor collateral perfusion grade (OR, 4.96; 95% CI, 1.42 to 17.37; p=0.012), and longer door-to-reperfusion time (OR, 1.09; 95% CI, 1.03 to 1.15; p=0.003) were associated with unfavorable functional outcomes. The assessment of collateral perfusion status using the collateral map can predict futile EVT, which may help select ineligible patients for EVT, thereby potentially reducing the rate of futile EVT.

A 3D Multi-task Regression and Ordinal Regression Deep Neural Network for Collateral Imaging from Dynamic Susceptibility Contrast-Enhanced MR perfusion in Acute Ischemic Stroke

Background and ObjectiveCerebral collaterals have been identified as one of the primary determinants for treatment options in acute ischemic stroke. Several works have been proposed, but these have not been adopted for a routine clinical usage due to their manual and heuristic nature as well as inconsistency and instability of the assessment. Herein, we present an advanced deep learning-based method that can automatically generate a multiphase collateral imaging (collateral map) derived from dynamic susceptibility contrast-enhanced MR perfusion (DSC-MRP) in an accurate and robust manner. MethodsWe develop a 3D multi-task regression and ordinal regression deep neural network for generating collateral maps from DSC-MRP, which formulates the prediction of collateral maps as both a regression task and an ordinal regression task. For an ordinal regression task, we introduce a spacing-decreasing discretization (SDD) strategy to represent the intensity of the collateral status on a discrete, ordinal scale. We also devise loss functions to achieve effective and efficient multi-task learning. ResultsWe systematically evaluated the performance of the proposed network using DSC-MRP from 802 patients. On average, the proposed network achieved ≥0.900 squared correlation coefficient (R-Squared), ≥0.916 Tanimoto measure (TM), ≥0.0913 structural similarity index measure (SSIM), and ≤0.564 × 10−1 mean absolute error (MAE), outperforming eight competing models that have been recently developed in medical imaging and computer vision. We also found that the proposed network could provide an improved contrast between the low and high intensity regions in the collateral maps, which is a key to an accurate evaluation of the collateral status. ConclusionsThe experimental results demonstrate that the proposed network is able to generate collateral maps with high accuracy, facilitating a timely and prompt assessment of the collateral status in clinlcs. The future study will entail the optimization of the proposed network and its clinical evalution in a prospective manner.

Collateral and permeability imaging derived from dynamic contrast material-enhanced MR angiography in prediction of PH 2 hemorrhagic transformation after acute ischemic stroke: a pilot study.

To evaluate the role of collateral and permeability imaging derived from dynamic contrast material-enhanced magnetic resonance angiography to predict PH 2 hemorrhagic transformation in acute ischemic stroke. The secondary analysis of a published data from participants with acute ischemic stroke. The multiphase collateral map and permeability imaging were generated by using dynamic signals from dynamic contrast material-enhanced magnetic resonance angiography obtained at admission. To identify independent predictors of PH 2 hemorrhagic transformation, age, sex, risk factors, baseline National Institutes of Health Stoke Scale (NIHSS) score, baseline DWI lesion volume, collateral-perfusion status, mode of treatment, and successful early reperfusion were evaluated with multiple logistic regression analyses and the significance of permeability imaging in prediction of PH 2 hemorrhagic transformation was evaluated by subgroup analysis. In 115 participants, including 70 males (mean (SD) age, 69 (12) years), PH 2 hemorrhagic transformation occurred in 6 participants with very poor collateral-perfusion status (MAC 0). MAC 0 (OR, 0.06; 95% CI, 0.01, 0.74; P = .03) was independently associated with PH 2 hemorrhagic transformation. In 22 participants with MAC 0, the permeable signal on Kep permeability imaging was the only significant characteristic associated with PH 2 hemorrhagic transformation (P = .009). The specificity of Kep permeability imaging was 93.8% (95% confidence interval: 69.8, 99.8) in predicting PH 2 hemorrhagic transformation. Individual-based prediction of PH 2 hemorrhagic transformation in patients with acute ischemic stroke may be possible with multiphase collateral map and permeability imaging derived from dynamic contrast material-enhanced magnetic resonance angiography.

Multiphase MR Angiography Collateral Map: Functional Outcome after Acute Anterior Circulation Ischemic Stroke.

Background Collateral circulation determines tissue fate and affects treatment result in acute ischemic stroke. A precise method for collateral estimation in an optimal imaging protocol is necessary to make an appropriate treatment decision for acute ischemic stroke. Purpose To verify the value of multiphase collateral imaging data sets (MR angiography collateral map) derived from dynamic contrast material-enhanced MR angiography for predicting functional outcomes after acute ischemic stroke. Materials and Methods This secondary analysis of an ongoing prospective observational study included data from participants with acute ischemic stroke due to occlusion or stenosis of the unilateral internal carotid artery and/or M1 segment of the middle cerebral artery who were evaluated within 8 hours of symptom onset. Data were obtained from March 2016 through August 2018. The collateral grading based on the MR angiography collateral map was estimated by using six-scale MR acute ischemic stroke collateral (MAC) scores. To identify independent predictors of favorable functional outcomes, age, sex, risk factors, baseline National Institutes of Health Stroke Scale (NIHSS) score, baseline diffusion-weighted imaging (DWI) lesion volume, site of steno-occlusion, collateral grade, mode of treatment, and early reperfusion were evaluated with multiple logistic regression analyses. Results One hundred fifty-four participants (mean age ± standard deviation, 69 years ± 13; 99 men) were evaluated. Younger age (odds ratio [OR], 0.45; 95% confidence interval [CI]: 0.29, 0.70; P < .001), lower baseline NIHSS score (OR, 0.85; 95% CI: 0.78, 0.94; P < .001), MAC score of 3 (OR, 27; 95% CI: 4.0, 179; P < .001), MAC score of 4 (OR, 17; 95% CI: 2.1, 134; P = .007), MAC score of 5 (OR, 27; 95% CI: 2.5, 306; P = .007), and successful early reperfusion (OR, 7.5; 95% CI: 2.6, 22; P < .001) were independently associated with favorable functional outcomes in multivariable analysis. There was a linear negative association between collateral perfusion grades and functional outcomes (P < .001). Conclusion An MR angiography collateral map was clinically reliable for collateral estimation in patients with acute ischemic stroke. This map provided patient-specific pacing information for ischemic progression. © RSNA, 2020.

Abstract TP82: Factors Associated With Good Collateral Flow in Acute Stroke Patients With Large Vessel Occlusion

Introduction: Retrograde collateral flow is critical to maintain tissue perfusion despite large vessel occlusion. However, the premorbid factors associated with good collateral flow remain unclear, with substantial discrepancies in the literature. Methods: Patients from the registries of 6 French stroke centres with the following criteria were included: (1) acute stroke with isolated M1 occlusion ( i.e , without tandem occlusion) referred for thrombectomy between May 2015 and March 2017; and (2) baseline brain MRI, including diffusion weighted imaging, MR-angiography and dynamic susceptibility-contrast perfusion-weighted imaging (PWI). A collateral flow map derived from PWI source data was automatically generated, replicating Kim et al’s previously validated method (Ann. Neurol., 2014). Collateral flow was dichotomized into good and poor. The association between good collateral flow and baseline clinical, biological and radiological variables was studied. Results: One hundred and sixteen patients were included, of which 66 (57%) had good collaterals. As expected, the latter patients had lower admission NIHSS (median: 15 vs . 18, P=0.005) and lower baseline DWI lesion volume (median: 7ml vs . 32ml, P&lt;0.001) than patient with poor collaterals. Onset-to-imaging delay and M1 occlusion site (proximal vs . distal) were similar in both groups (123min vs . 118min, P=0.75; 70% vs. 68%, P=0.85, respectively). There was no significant (P&gt;0.05) difference in gender, age, history of hypertension or diabetes, current smoking, baseline blood glucose and use of statins or antiplatelets between the good and poor collaterals groups. Conclusions: Despite the expected association between PWI-derived collateral flow and baseline clinical and radiological stroke severity in our sample of acute M1 occlusions, there was no association with premorbid factors previously found associated in some -but not all- studies. Our findings suggest that collateral flow is predominantly explained by genetic factors.

Abstract WMP13: Multiphase MRA Collateral Map: Prediction of Tissue Outcome and Penumbra in Patients With Acute Ischemic Stroke in the Anterior Circulation

Background and Purpose: We developed the MRA collateral map derived from dynamic MR angiography and grading methods with significant linear association with functional outcomes of patients with acute ischemic stroke (AIS). This study is to verify the value of the MRA collateral map for predicting tissue outcome and penumbra in patients with AIS. Materials and Methods: From a prospectively maintained registry, patients with AIS due to occlusion or stenosis of the unilateral ICA and/or M1 MCA within 8 hours of symptom onset were included. The collateral-perfusion grading based on the MRA collateral map was estimated using 6-scale MAC. Changes of infarct area were divided into two groups with and without infarct growth (IG + and IG - ). Areas of baseline DWI lesion, Tmax &gt; 6s, and decreased collateral-perfusion on each phases of the MRA collateral map, and infarct lesion on follow-up image were compared by visual assessment. Results: One hundred thirty-five patients, including 85 males (mean age, 69 years old), were included. Shorter onset-to-door times (OR=1.04, 95% CI=1.01-1.08) and successful early reperfusion (OR=0.19, 95% CI=0.05-0.66) were independently associated with IG - in multivariate analysis. In subgroup analysis, good collateral-perfusion status was associated with IG - (OR=0.30, 95% CI=0.10-0.91). In IG + group, the infarction grew within hypoperfused area on the phase of the MRA collateral map immediately before the phase that matches the baseline DWI lesion. There was no infarct growth beyond hypoperfused area on the capillary phase of the MRA collateral map in both IG + and IG - groups. The area of Tmax &gt; 6s matched with the hypoperfused area on capillary phase of the MRA collateral map in 83% of patients. Conclusion: In this study, tissue fate in AIS was dependent on early reperfusion. In case of unsuccessful early reperfusion, it was associated with collateral-perfusion status. We suggest that the extent of penumbra can be estimated by the MRA collateral map.

A Novel Collateral Imaging Method Derived from Time-Resolved Dynamic Contrast-Enhanced MR Angiography in Acute Ischemic Stroke: A Pilot Study.

Assessment of the collateral status has been emphasized for appropriate treatment decisions in patients with acute ischemic stroke. The purpose of this study was to introduce a multiphase MRA collateral imaging method (collateral map) derived from time-resolved dynamic contrast-enhanced MRA and to verify the value of the multiphase MRA collateral map in acute ischemic stroke by comparing it with the multiphase collateral imaging method (MRP collateral map) derived from dynamic susceptibility contrast-enhanced MR perfusion. From a prospectively maintained registry of acute ischemic stroke, MR imaging data of patients with acute ischemic stroke caused by steno-occlusive lesions of the unilateral ICA and/or the M1 segment of the MCA were analyzed. We generated collateral maps using dynamic signals from dynamic contrast-enhanced MRA and DSC-MRP using a Matlab-based in-house program and graded the collateral scores of the multiphase MRA collateral map and the MRP collateral map independently. Interobserver reliabilities and intermethod agreement between both collateral maps for collateral grading were tested. Seventy-one paired multiphase MRA and MRP collateral maps from 67 patients were analyzed. The interobserver reliabilities for collateral grading using multiphase MRA or MRP collateral maps were excellent (weighted κ = 0.964 and 0.956, respectively). The agreement between both collateral maps was also excellent (weighted κ = 0.884; 95% confidence interval, 0.819-0.949). We demonstrated that the dynamic signals of dynamic contrast-enhanced MRA could be used to generate multiphase collateral images and showed the possibility of the multiphase MRA collateral map as a useful collateral imaging method in acute ischemic stroke.

Abstract 160: Better Collaterals Are Independently Associated With Post-thrombolysis Recanalization Before Thrombectomy

Introduction: In acute stroke with large-vessel occlusion (LVO), the goal of intravenous thrombolysis (IVT) is to achieve early recanalization (ER). Over and above occlusion site and thrombus length, better collaterals might also facilitate ER, for instance by improving delivery of the thrombolytic agent to both ends of the thrombus. In this proof-of-concept study, we tested the hypothesis that good collaterals independently predict post-IVT recanalization before thrombectomy. Methods: Patients from the registries of 6 French stroke centres with the following criteria were included: (1) acute stroke with LVO treated with IVT and referred for thrombectomy between May 2015 and March 2017; (2) pre-IVT brain MRI, including diffusion weighted imaging, T2*, MR-angiography and dynamic susceptibility-contrast perfusion-weighted imaging (PWI); and (3) ER evaluated ≤3hrs from IVT start on either first angiographic run or non-invasive imaging. A collateral flow map derived from PWI source data was automatically generated, replicating Kim et al’s previously validated method (Ann. Neurol., 2014). Thrombus length was measured on T2*-based susceptibility vessel sign. Results: Of 224 eligible patients, 37 (16%) experienced ER. ER occurred in 10/83 (12%), 17/116 (15%) and 10/25 (40%) patients with poor/moderate, good and excellent collaterals, respectively. In multivariable analysis, better collaterals were independently associated with ER ( P =0.029), together with shorter thrombus ( P &lt;0.001) and more distal occlusion site ( P =0.010). Conclusions: In our sample of stroke patients imaged with PWI before IVT and intended for thrombectomy, better collaterals were independently associated with post-IVT recanalization, supporting our hypothesis. These findings strengthen the idea that advanced imaging may play a key role for personalized medicine in the thrombectomy era by identifying LVO patients most likely to benefit from IVT.

Abstract TP57: Predicting Regional Tissue Fate in Ischemic Stroke Using Color Coded mCTA-based Collaterals Assessment

Background and Purpose: Multiphase CT angiography (mCTA) assessment of collaterals has been proven to be predictive of tissue fate on follow-up imaging following an acute stroke. We used the GE FastStroke Software, a novel mCTA image analysis and visualization tool that color codes pial arteries and veins based on delay in vessel enhancement to predict regional tissue fate. Red colored collaterals represented no delay in enhancement, green represented a one phase delay and blue two phase delays. Methods: Forty patients with M1-middle cerebral artery occlusions were selected from the prospective database ProVeIT. Baseline CT as well as 24 to 36-hour CT/MRI were analyzed and scored regionally using the Alberta Stroke Program early CT scoring (ASPECTS). Regional vessel filling was assessed using color coded collateral maps, and given a score of 1,2 or 3 based on the predominant color of collaterals (1=blue, 2=green, 3=red). A score of 0 was given if there was less than 50% regional filling compared to the contralateral side. Logistic regression method was used to correlate collateral assessment with tissue fate, adjusting for baseline ASPECTS. Results: 280 cortical regions were assessed (M1 to M6, Insula). When blue color was predominant, risk of subsequent infarction was 48% (27/56). Green and red colors were associated with 33% (37/111) and 14% (13/88) of subsequent infarction, respectively. A score of 0 had an 80% (20/25) risk of infarction. Using logistic regression methods, collaterals assessment met statistical significance in tissue fate correlation (p&lt;0.001). Conclusions: Collateral scoring using color coded collateral maps was highly predictive of subsequent infarction risk. Further work is needed to understand the impact of fast endovascular reperfusion in influencing tissue outcome.

Abstract WMP24: CT Angiography Collateral Gradient Mapping: Validation of a Novel Imaging Technique in Acute Ischemic Stroke

Background: CT angiography (CTA) is routinely acquired in acute ischemic stroke, providing data on extent of collaterals yet current techniques compromise either spatial or temporal resolution. We developed and validated a novel imaging technique from standard or single-phase CTA to discriminate both the spatial and temporal blood flow features in leptomeningeal collaterals. Methods: Consecutive acute ischemic stroke patient data, including single-phase CTA (sCTA) followed immediately by digital subtraction angiography (DSA), in the setting of ICA or proximal MCA occlusions were analyzed. Three-dimensional (3D) reconstruction and surface mapping of collateral flow gradients on sCTA was performed. Quantitative output of flow gradients in individual collateral vessels was correlated with DSA ASITN collateral grade. Results: 75 consecutive cases of acute stroke due to ICA or proximal MCA occlusion were analyzed with contemporaneous sCTA and DSA. Automatic post-processing of collateral gradient maps and generation of quantitative data output followed 3D reconstruction and segmentation of sCTA. sCTA collateral gradient mapping was feasible in all cases, compared to limitations in availability of DSA collateral grades. Poor collateral status on DSA (ASITN 0-1) was evident as limited extent and color-mapped gradients on sCTA. In contrast, sCTA gradient mapping provided more detailed distinction between subjects of intermediate or partial DSA collaterals (ASITN 2) and also amongst complete, but delayed DSA collaterals (ASITN 3). sCTA gradient mapping provided quantitative data on the delay of collateral flow in individual cortical vessels. Conclusions: CTA collateral gradient mapping can routinely provide detailed data on both the extent and delay of collaterals, using standard sCTA acquisition. This novel imaging technique may provide key information to distinguish the wide variability of ASITN grades 2-3, most commonly encountered in acute stroke.

A map of collateral uses and flows

All flows of secured funding in the financial system are met by flows of collateral in the opposite direction. A network depicting secured funding flows thus implicitly reveals a network of collateral flows. Collateral can also be presented as its own network to show collateral arrangements with bilateral counterparties, triparty banks and central counterparties; the purpose and incentives of collateral exchanges; and the participants involved. We create a collateral map to show how this function of the financial system works, especially with secured funding and derivatives activity. This paper provides insights into the increased demand for collateral, the reduced capacity for banks to act as collateral intermediaries and examples of risks and vulnerabilities in collateral flows.

A Map of Collateral Uses and Flows

All flows of secured funding in the financial system are met by flows of collateral in the opposite direction. A network depicting secured funding flows thus implicitly reveals a network of collateral flows. Collateral can also be presented as its own network to show collateral arrangements with bilateral counterparties, triparty banks, and central counterparties; the purpose and incentives of collateral exchanges; and participants involved. We create a collateral map to show how this function of the financial system works, especially with secured funding and derivatives activity. This paper provides insights into the increased demand for collateral, the reduced capacity for banks to act as collateral intermediaries, and examples of risks and vulnerabilities in collateral flows.

Abstract W MP15: A Novel Magnetic Resonance Imaging Approach for Collateral Flow Imaging in Ischemic Stroke

Background: Assessing the status of collateral circulation is important in acute ischemic stroke. However, digital subtraction angiography(DSA) which is considered as the gold standard for evaluation of collaterals is invasive and has a risk of thrombotic complications. Dedicated MRI sequences for evaluation of collateral flow can be generated using perfusion-weighted imaging(PWI) source data. We compared a novel collateral flow imaging technique with DSA for determining collateral circulation in the setting of acute stroke. Methods: Consecutive patients who were eligible for recanalization therapy underwent MRI and DSA for acute MCA infarction at a university medical center. A collateral flow map derived from PWI source data was generated by manual or semi-automatic post-processing. Collateral grading based on collateral flow map was performed and compared with DSA (Figure). Results: Of 68 patients, 42(61.8%) had M1 occlusion and 26(38.2%) had ICA occlusion. The time interval between MRI scanning and the start of DSA was 50.8±28.6 minutes. Both the collateral flow map and DSA showed good inter-observer agreement of collateral grade(weighted κ-coefficients=0.817 for collateral flow map and 0.757 for DSA). There was good correlation between MRI- and DSA-based collateral grades: 68% had the same grade in the same patient(weighted κ-coefficient=0.653). In most patients who had mismatches between the two modalities, the collateral grade was higher in MRI-based vs. DSA-based assessment. Conclusion: MRI techniques for assessment of collaterals are rapidly being developed, which may provide insight on collateral perfusion in patients who are not otherwise candidates for conventional angiography and may potentially replace it in the future. Figure . Typical examples of collateral flow map- (left panel) and digital subtraction angiography (right panel)-based collateral grade. All DSAs show proximal MCA occlusions (white arrows).

Abstract T P41: Determination of Collateral Supply Patterns Using MR or CT Perfusion Imaging

Introduction: In this study, we sought to develop a collateral flow mapping method based on MR or CT perfusion imaging and compare this method with the digital subtraction angiography (DSA) method. Methods: Ischemic tissue supplied by collateral flow is likely to have delayed tracer arrival but relatively normal flow. In this study, abnormal Tmax (&gt; 6 sec), MTT (4 sec or greater than unaffected hemisphere) and CBF (&lt;40% of unaffected hemisphere) were labeled with green, red and blue, respectively (Fig. A). Any perfusion patterns can then be represented by a combination of this integrated RGB maps (Integrated Collateral flow Maps, iCMaps). 24 patients were included in this study. DSA images were obtained from all patients, whereas MR and CT perfusion images were acquired from 15 and 9 patients, respectively, within 30 hours after MCA occlusion. iCMaps collateral flow was scored independently as follows. iCMaps without any perfusion abnormality was assigned “1”. iCMaps with white as the dominant perfusion pattern was assigned a “5”; while those with a dominant green and yellow pattern were assigned a “2” or a “3”, depending on the relative green and yellow volume. Finally, iCMaps with a white region surrounded with yellow and green was assigned a “4”. Examples of iCMaps scoring are shown in Fig. B. Using a DSA scoring method in the literature5, a score of 1-5 was given independently based on the degree of retrograde collateralization (5: poor collateralization). Results: Good correlation was found between the MR perfusion iCMaps and DSA (DSA=0.70*MR iCMaps+0.54, R=0.75). Moderate correlation was obtained between the CT perfusion iCMaps and DSA (DSA=0.51*CT iCMaps+1.9, R=0.56). Conclusions: Based on the different characteristics of Tmax, MTT and CBF maps, the proposed MR or CT perfusion based iCMaps method can provide DSA comparable collateral flow information.

Graphical tools for interactive image interpretation

This paper describes BROWSE, an interactive raster image display facility which is a major component of a larger integrated Map Assisted Photo-interpretation System (MAPS), being developed as a prototype interactive aid for photo-interpretation. Application areas for this research include image cartography, land use studies and reconnaissance, as well as image database organization, storage, and retrieval. BROWSE is a window-oriented display manager which supports raster image display, overlay of graphical data such as map descriptions and image processing segmentations, and the specification and generation of 3D shaded surface models. Digitized imagery from black and white and color aerial mapping photographs is displayed by BROWSE at multiple levels of resolution and allows for dynamic positioning, zooming, expansion or shrinking of the image window. Map data represented as vectors and polygons can be superimposed on the imagery through image-to-map registration. Access to collateral map databases and terrain models may be accomplished using the BROWSE graphical interface. Finally, the window representation gives a convenient communication mechanism for passing image fragments to image interpretation programs, which generally run as separate processes. The results of such processing can be returned to BROWSE for further processing by the user. We will discuss the rationale behind the design of BROWSE as well as its application to domains including aerial photo-interpretation and 3D cartography.