Noninvasive Measurement of Regional Cerebral Blood Flow by Near-Infrared Spectroscopy and Indocyanine Green

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Abstract
Clinicians lack a practical method for measuring CBF rapidly, repeatedly, and noninvasively at the bedside. A new noninvasive technique for estimation of cerebral hemodynamics by use of near-infrared spectroscopy (NIRS) and an intravenously infused tracer dye is proposed. Kinetics of the infrared tracer indocyanine green were monitored on the intact skull in pigs. According to an algorithm derived from fluorescein flowmetry, a relative blood flow index (BFI) was calculated. Data obtained were compared with cerebral and galeal blood flow values assessed by radioactive microspheres under baseline conditions and during hemorrhagic shock and resuscitation. Blood flow index correlated significantly ( rs = 0.814, P < 0.001) with cortical blood flow but not with galeal blood flow ( rs = 0.258). However, limits of agreement between BFI and CBF are rather wide (± 38.2 ± 6.4 mL 100 g−1 min−1) and require further studies. Data presented demonstrate that detection of tracer kinetics in the cerebrovasculature by NIRS may serve as valuable tool for the noninvasive estimation of regional CBF. Indocyanine green dilution curves monitored noninvasively on the intact skull by NIRS reflect dye passage through the cerebral, not extracerebral, circulation.