FIGURE 13.7. Schematic model of hemoglobin oximetry changes that occur following functional activation.

FIGURE 13.7

Schematic model of hemoglobin oximetry changes that occur following functional activation. The time course of hemoglobin changes may be different in gyri, which contain the capillary beds, and sulci, which contain large venous structures. (A) Following functional activation, there may be a brief increase in deoxyhemoglobin concentrations in the cortex, corresponding to an immediate burst in oxidative metabolism preceding functional perfusion changes. This phase is often referred to as the initial dip in the blood-oxygen level dependent fMRI signal or the first phase of the 610 nm optical response. (B) Within seconds, functional recruitment of blood volume and flow reverse the initial increase in deoxyhemoglobin, “washing out” and eventually decreasing deoxyhemoglobin concentrations below baseline. (C,D) The functional blood volume and flow changes may peak in the capillary beds and cortex before peaking in the sulci, or in the large venous structures, generating the BOLD signal and the second phase of the 610 nm optical response. (E) Eventually, functional changes subside and the brain returns to baseline. Note: Time courses displayed are hypothetical and are illustrated to explain a possible model of hemoglobin oximetry changes with functional activation.

From: Chapter 13, Intraoperative Optical Imaging

Cover of In Vivo Optical Imaging of Brain Function
In Vivo Optical Imaging of Brain Function. 2nd edition.
Frostig RD, editor.
Boca Raton (FL): CRC Press/Taylor & Francis; 2009.
Copyright © 2009, Taylor & Francis Group, LLC.

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