Buxton_1998_dynamics_in_blood_flow - MAGNETIC RESONANCE IN...

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Dynamics of Blood Flow and Oxygenation Changes During Brain Activation: The Balloon Model Richard B. Buxton, Eric C. Wong, Lawrence R. Frank A biomechanical model is presented for the dynamic changes in deoxyhemoglobin content during brain activation. The model incorporates the conflicting effects of dynamic changes in both blood oxygenation and blood volume. Calcu- lations based on the model show pronounced transients in the deoxyhemoglobin content and the blood"oxygenation level dependent (BOLD) signal measured with functional MAl, in- cluding initial dips and overshoots and a prolonged post- stimulus undershoot of the BOLD signal. Furthermore, these transient effects can occur in the presence of tight coupling of cerebral blood flow and oxygen metabolism throughout the activation period. An initial test of the model against experi- mental measurements of flow and BOLD changes during a finger-tapping task showed good agreement. Key words: functional magnetic resonance imaging; cerebral blood volume; cerebral blood flow; cerebral oxygen metabo- lism. INTRODUCTION Despite the widespread use of functional neuroimaging techniques, the physiological changes in the brain that accompany neural activation are still poorly understood. D~ring brain activation, a modest increase in the cerebral metabolic rate of oxygen (CMROzJ is accompanied by a much larger increase in local blood flow (1, 2). Because of this imbalance, local capillary and venous blood are more oxygenated during activation. The large increase in flow is the basis for mapping brain activation patterns with positron emission tomography (PET), and the de- crease in local de oxyhemoglobin concentration is the basis for functional magnetic resonance imaging (fMRI) exploiting the blood oxygenation level dependent (BOLD) effect (3-7). Recently, we proposed a possible explanation for the large flow increase as a result of tight coupling of flow and oxygen metabolism in the presence of limited oxygen delivery (8). This oxygen limitation model is based on the assumptions that essentially all of the oxygen that leaves the capillary is metabolized and that blood flow increases are accomplished by increased capillary blood velocity rather than capillary recruit- MRM 39:855-864 (1998) From the Departments of Radiology (R.B.B., E.C.W., LR.F.) and Psychiatry (E.C.W.), University of California at San Diego, San Diego, California. Address correspondence to: Richard B. Buxton, Ph.D., Associate Professor of Radiology, UCSD Medical Center, 200 West Arbor Drive, San Diego, CA 92103-8756. Received July 3, 1997; revised November 28, 1997; accepted February 9, 1998. 0740-3194/98 $3.00 Copyright @ 1998 by Williams All rights of reproduction in any form reserved. MAGNETIC RESONANCE IN MEDICINE
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This note was uploaded on 02/10/2010 for the course TBE 2300 taught by Professor Cudeback during the Spring '10 term at Webber.

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Buxton_1998_dynamics_in_blood_flow - MAGNETIC RESONANCE IN...

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