Abstract
In the Netherlands about 40.000 patients yearly suffer from stroke or TIA. In 20-30% of these cases a stenosis in the carotid artery is found. This stenosis is caused by atherosclerotic plaque formation. Symptoms are thought to be the result of cerebral embolism by formation of thrombi at the plaque
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and the luminal obstruction which causes reduced blood flow to the brain. Endarterectomy has proven beneficial in the prevention of stroke by removal of this stenosis, but carries a risk for complications. However, a new treatment option has been proposed: carotid artery stenting. Although this is a very promising less-invasive treatment, it has not yet proven to be as effective as surgery. Therefore the ICSS trial has been started. We studied the participating patients of the ICSS using a new technique; the multislice CT scanner.
The possibilities of the multislice CT for neurovascular applications are explained.
We studied how we could improve image quality in combination with radiation dose reduction. It turned out that the use of lower kilovoltage settings can improve image quality at lower total patient dose.
We compared the ICSS population to 100 patients without cerebrovascular disease, and assessed the presence and size of the segments of the circle of Willis both in patients and controls. In ICSS patients we found significantly more absent or hypoplastic segments in the anterior part of the circle. This suggests that incompleteness of the circle may be a risk factor for the development of symptoms in case of carotid stenosis by preventing collateral supply.
Next, we compared various techniques to measure the degree of stenosis using MSCT and compared this to DSA as standard of reference. The use of visual estimation outperformed the other techniques for all four observers and resulted in comparable inter-observer variability as repeated DSA measurements.
To evaluate the potentials of CT perfusion, first the reproducibility of CT perfusion measurements was determined. We concluded that MTT is the most reproducible CTP parameter in patients with unilateral symptomatic CAS. Measurement variability in CBV and CBF can be improved if CTP ratios instead of CTP values are used.
Last, we determined whether pre-treatment CT perfusion analysis in patients with unilateral symptomatic carotid artery stenosis can be used to distinguish between groups of patients that will respond differently to carotid revascularization, in terms of changes in cerebral perfusion.
Based on the previous study we used relative MTT defined as difference in MTT between two hemispheres, to distinguish three groups of patients. Sixteen patients (44%) came in group 1, 12 patients (33%) in group 2, and in eight patients (22%) in group 3. Only patients with the largest MTT difference (group 3) showed significant improvement of CBF, CBV and MTT. This indicates that the relative MTT before treatment may be used as parameter that can predict hemodynamic response to treatment. The results imply that knowledge of perfusion values may not only increase our insight in the hemodynamics, but in future also may help to select patients that benefit most from treatment.
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