1. ^*Department of Physics and Astronomy, Cerebrovascular Research Center, University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A.
2. ^†Department of Neurology, Cerebrovascular Research Center, University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A.

Correspondence: Joseph P Culver, NMR Center, Massachusetts General Hospital, Bldg. 149, 13th Street, Charlestown, MA 02129, U.S.A.; e-mail: jculver@nmr.mgh.harvard.edu

Received 4 December 2002; Revised 16 April 2003; Accepted 17 April 2003.

Abstract

Diffuse optical tomography (DOT) is an attractive approach for evaluating stroke physiology. It provides hemodynamic and metabolic imaging with unique potential for continuous noninvasive bedside imaging in humans. To date there have been few quantitative spatial-temporal studies of stroke pathophysiology based on diffuse optical signatures. The authors report DOT images of hemodynamic and metabolic contrasts using a rat middle cerebral artery occlusion (MCAO) stroke model. This study used a novel DOT device that concurrently obtains coregistered images of relative cerebral blood volume (rCBV), tissue-averaged hemoglobin oxygen saturation (Sto₂), and relative cerebral blood flow (rCBF). The authors demonstrate how these hemodynamic measures can be synthesized to calculate an index of the oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen consumption (CMRo₂). Temporary (60-minute) MCAO was performed on five rats. Ischemic changes, averaged over the 60 minutes of occlusion, were as follows: rCBF = 0.42 0.04, rCBV = 1.02 0.04, Sto₂ = -11 2%, rOEF = 1.39 0.06 and rCMRo₂ = 0.59 0.07. Although rOEF increased in response to decreased blood flow, rCMRo₂ decreased. The sensitivity of this method of DOT analysis is discussed in terms of assumptions about baseline physiology, and the diffuse optical results are compared with positron emission tomography, magnetic resonance imaging, and histology observations in the literature.