Rationale and Objectives
Computed tomography angiography source imaging (CTA-SI) in acute ischemic stroke improves detection rate and estimation of extent of cerebral infarction. This study compared the new components color-coded perfusion weighted map (PWM) and color-coded perfused blood volume (PBV) derived from CTA data with CTA-SI for the visualization of cerebral infarction.
Materials and Methods
Fifty patients (women = 30; mean age = 74.9 ± 13.3 years) underwent nonenhanced computed tomography and CTA for suspected acute ischemic stroke. PWM, PBV, and CTA-SI were reconstructed with identical slice thickness of 1.0 mm with commercial software. Extent of infarction was measured using the Alberta Stroke Program Early Computed Tomography Score (ASPECTS). For statistical analysis, Spearman’s R correlation and paired-samples t -test was used. P < .05 was considered significant.
Results
PBV had superior sensitivity for detection of cerebral infarction with 0.88 compared to PWM and CTA-SI with 0.79 and 0.76, respectively. The accuracy of correct diagnosis was superior for PBV with 0.82 compared to PWM and CTA-SI with 0.76, respectively. ASPECTS of PWM and PBV showed strong correlation with CTA-SI with r = 0.903 ( P < .001) and r = 0.866 ( P < .001), respectively. Mean ASPECTS of CTA-SI (6.24 ± 3.62) revealed no significant difference with PWM (6.26 ± 3.45), but a significant difference with PBV (5.62 ± 3.41; P < .02).
Conclusions
PWM was equal to CTA-SI in detection of cerebral infarction and estimation of extent of cerebral ischemia. Although PBV was superior to CTA-SI in detection of cerebral infarction, PBV seems to overestimate the extent of critical cerebral ischemia. Therefore, CTA-SI information is not identical to PBV and further clinical evaluation is mandatory.
Stroke is one of the major diseases resulting in death or permanent disability worldwide. In Western countries, the age adjusted incidence rate is about 180 per 100,000 per year . Most strokes are caused by acute ischemia because of occlusion of a cerebral artery. Major efforts were made in the past to improve patient selection in thrombolysis therapy and to predict patient outcome . Sophisticated imaging strategies are considered the key technique to meet these demands. Both, computed tomography (CT) and magnetic resonance imaging (MRI), have been proven to be feasible for acute stroke imaging . CT is the most frequently used method due to its wide availability and nonenhanced CT (NECT) of the brain is the basis of any thrombolysis therapy. In addition to NECT, contrast-enhanced CT angiography (CTA) is frequently used in acute stroke imaging to visualize the cerebral vasculature . However, CTA data also include hemodynamic information . The so named CTA source imaging (CTA-SI) has proven better visualization of the infarcted brain tissue as well as improved prediction of patient outcome in acute ischemic stroke in several studies .
Commercial software now allows the fast and standardized postprocessing of CTA data with calculation of color-coded perfusion weighted map (PWM) images and color-coded perfused blood volume (PBV) images to extract hemodynamic information of the whole brain. PWM is the color-coded visualization of the CTA-SI, whereas PBV is based on the subtraction of NECT and CTA data sets and visualizes the cerebral blood volume with a defined color-coded map. Both methods are considered to visualize mainly the irreversible infarcted brain tissue.
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Materials and methods
Study Population
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Imaging Protocol
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Postprocessing
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Image Analysis
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Statistics
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Table 1
Calculation of Sensitivity, Specificity, and Accuracy
Sensitivity=TruepositivesTruepositives+false negatives Sensitivity
=
True
positives
True
positives
+
false negatives Specificity=True negativesTrue negatives+falsepositives Specificity
=
True negatives
True negatives
+
false
positives Accuracy=True positives+true negativesTrue positives+false positives+true negatives+false negatives Accuracy
=
True positives
+
true negatives
True positives
+
false positives
+
true negatives
+
false negatives
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Results
Study Population
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Table 2
Descriptive Data of Study Population
Mean age (n = 50) 74.9 ± 13.3 years (30.8-93.6) Mean age women (n = 30) 78.4 ± 10.7 years (49.2-93.6) Mean age men (n = 20) 69.7 ± 15.3 years (30.8-92.4) Onset-to-imaging time interval 3.08 ± 2.44 hours (0.3-12.0) NIHSS on admission 11.5 ± 5.1 (0-22) Delay of follow-up imaging 1.41 ± 1.51 days (1-10)
n, number; NIHSS, National Institute of Health Stroke Scale. All values displayed as mean ± standard deviation (range).
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Sensitivity and Specificity Statistics
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Table 3
Sensitivity, Specificity, and Accuracy
CTA-SI PWM PBV True positives 32 33 37 False positives 2 3 4 True negatives 6 5 4 False negatives 10 9 5 Sensitivity 0.76 0.79 0.88 Specificity 0.75 0.63 0.50 Accuracy 0.76 0.76 0.82
CTA-SI, computed tomography angiography source imaging; PWM, perfusion weighted map; PBV, perfused blood volume.
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Correlation Statistics for Extent of Cerebral Ischemia
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Discussion
Sensitivity and Specificity
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Extent of Cerebral Ischemia
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Limitations of this Study
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