Effect of Optode Separation on Brain Penetration in Adults
Near Infra-red Spectroscopy (NIRS) has been widely used to study intracerebral oxygenation and haemodynamics in neonates (1,2), but doubts have been raised over the penetration of NIR of the thick adult skull when using optode separations of 3–4 cm (3), as suggested by the classical estimates of scattering and absorption, and one commercial instrument has been shown to reflect only extra-cranial tissue perfusion. Indocyanine Green (ICG) is easily detected by NIRS and is unaffected in changes in oxygenation. This study investigates the amount of cerebral tissue seen by NIR at different optode separations using indocyanine green as a specific indicator of flow during selective clamping of the carotid arteries.
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