Absence of selective deep white matter ischemia in chronic carotid disease: a positron emission tomographic study of regional oxygen extraction.

BACKGROUND AND PURPOSE: Deep white matter may be the location of an internal arterial border zone. The purpose of this study was to determine whether the deep white matter was subject to a greater degree of ischemia than was the cortex among patients with chronic carotid occlusion. METHODS: Thirty-six patients with carotid occlusion and structurally normal deep white matter were studied with positron emission tomography. Measurements of oxygen extraction fraction were made in superficial (cortical and subcortical) regions in the middle cerebral artery territory and in deep white matter (internal border zone) regions. The presence of selective ischemia of the deep white matter was assessed by the ratio of deep white matter:superficial oxygen extraction fraction. Ipsilateral hemispheric ratios among patients were assessed as a group as compared with contralateral hemispheric ratios and as compared with normal hemispheric ratios from 15 control volunteers. RESULTS: Mean deep white matter to superficial oxygen extraction fraction ratios (+/-95% confidence limits) were 0.99 (+/-0.07), 1.01 (+/-0.06), and 1.02 (+/-0.08) for ipsilateral, contralateral, and normal hemispheres, respectively. No statistically significant difference was found between ipsilateral and contralateral (P = .691) or normal hemispheres (P = .68), nor was any statistically significant difference found when the analysis was limited to patients with increased superficial oxygen extraction fraction (n = 9). Individual deep white matter:superficial ratios were within the normal range for all patients. CONCLUSION: Normal deep white matter among patients with carotid occlusion is not subject to a greater degree of ischemia than is the overlying cortex. It is unlikely that deep white matter infarctions observed among patients with carotid occlusion are owing to chronic selective hemodynamic compromise occurring at an internal arterial border zone.

Count-based PET method for predicting ischemic stroke in patients with symptomatic carotid arterial occlusion.

PURPOSE: To test the ability of a count-based positron emission tomographic (PET) method, without arterial sampling, for the measurement of regional cerebral oxygen extraction fraction (OEF) to predict ischemic stroke in patients with symptomatic carotid arterial occlusion. MATERIALS AND METHODS: The outcome analysis of a blinded prospective study designed to determine if increased OEF was an independent predictor of stroke in patients with symptoms and with carotid occlusion was repeated by substituting a count-based method of OEF measurement for the original quantitative technique. The performance of the quantitative and count-based methods was assessed by using Kaplan-Meier cumulative survival functions (log-rank, [p < .05]). Receiver operating characteristic (ROC) curves for both methods were generated. RESULTS: Thirteen ipsilateral strokes occurred during a mean follow-up of 3.1 years for 81 patients. All ipsilateral strokes occurred in 50 patients with increased count-based OEF (P = .002, sensitivity 100%, specificity 46%). Sixty-eight patients underwent complete quantitative studies, which allowed comparison of OEF methods. Both the count-based and the quantitative methods were predictive of stroke in this subgroup (P = .005 and .025, respectively). ROC analysis demonstrated a greater area under the curve for the count-based OEF method. CONCLUSION: Count-based PET measurement of OEF without arterial sampling accurately predicts stroke in patients with carotid occlusion.