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Stroke, Vol 8, 380-382, Copyright © 1977 by American Heart Association

ARTICLES

Spectrum subtraction technique for minimizing extracranial influence on cerebral blood flow measurements by 133xenon inhalation

J Risberg, BP Uzzell and WD Obrist

Estimates of regional cerebral blood flow (rCBF) by the 133Xe inhalation method are influenced by isotope contamination from slow clearing extracerebral tissues. Subtraction of x-ray (31 kev) from gamma-ray counts (81 kev) has been suggested as a means of yielding clearance curves that are relatively free of such contamination. In the present study, rCBF measurements based on the total 133Xe spectrum (x- ray plus gamma) were compared with those derived from the subtracted spectrum (x-ray minus gamma) in 20 young controls, using a two- compartmental analysis of the clearance curves. In comparison with addition, the subtraction data gave substantially higher estimates of blood flow for the slow (second) compartment. This, along with a shift in the relative weights of the two compartments, indicated a decreased contribution of slow tissue components, consistent with a reduction in extracerebral contamination. Blood flow values obtained by subtraction were in good agreement with those reported for the intracarotid injection method. A limitation of the subtraction technique, however, is the relatively high dose of isotope required for adequate signal-to- noise ratios.