Imaging local cerebral blood flow by Xenon-enhanced computed tomography ? Technical optimization procedures

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Abstract
Methods are described for non-invasive, computer-assisted serial scanning throghout the human brain during eight minutes of inhalation of 27%–30% Xenon gas in order to measure local cerebral blood flow (LCBF). Optimized Xenonenhanced computed tomography (XeCT) was achieved by 5-second scanning at one-minute intervals utilizing a state-of-the-art CT scanner and rapid delivery of Xenon gas via a face mask. Values for local brain-blood partition coefficients (Lλ) measured in vivo were utilized to calculate LCBF values. Previous methods assumed Lλ values to be normal, introducing the risk of systematic errors, because Lλ values differ throughout normal brain and may be altered by disease. Color-coded maps of Lλ and LCBF values were formatted directly onto CT images for exact correlation of function with anatomic and pathologic observations (spatial resolution: 26.5 cubic mm). Results were compared among eight normal volunteers, aged between 50 and 88 years. Mean cortical gray matter blood flow was 46.3±7.7, for subcortical gray matter was 50.3±13.2 and for white matter was 18.8±3.2. Modern CT scanners provide stability, improved signal to noise ratio and minimal radiation scatter. Combining these advantages with rapid Xenon saturation of the blood provides correlations of Lλ and LCBF with images of normal and abnormal brain in a safe, useful and non-invasive manner.