Noninvasive Measurement of Cerebral Blood Flow in Adults Using Near-Infrared Spectroscopy and Indocyanine Green: A Pilot Study

Abstract

This pilot study was designed to determine the feasibility of measuring cerebral blood flow noninvasively after an intravenous bolus of indocyanine green using near-infrared spectroscopy and pulse dye-densitometry. Feasibility aside, this study did not attempt to validate the measured values of cerebral blood flow against an established method of measurement. Twelve healthy volunteers were investigated after peripheral intravenous injection of indocyanine green. Arterial and cerebral changes in indocyanine green concentration were measured using pulse dye-densitometry and near-infrared spectroscopy, respectively. Two methods of calculating cerebral blood flow were used, and a blood flow index was also estimated. Absolute cerebral blood flow was calculated using a modification of the Fick principle and a deconvolution algorithm to derive the impulse residue function. Mean (range) estimated cerebral blood flow for the Fick method was 8.2 mL/100 g/min (4.2-16.2 mL/100 g/min) and 8.3 mL/100 g/min (4.7-15.3 mL/100 g/min) for the impulse residue function method. The impulse residue function method provided a more precise intrasubject estimation of cerebral blood flow compared with the modified Fick principle, with a coefficient of variation of 10.1% versus 25.5%. The blood flow index was 8.6 mg/sec (range: 5.6-17.3 mg/sec) with an intrasubject coefficient of variation of 12.0%. Estimation of cerebral blood flow using near-infrared spectroscopy and pulse dye-densitometry can be made at the bedside after intravenous injection of indocyanine green, and the precision can be improved using a deconvolution algorithm. Notwithstanding the low values obtained for absolute cerebral blood flow, further investigation and validation of this bedside technique is warranted.

Measurement of Cerebral Oxidative Metabolism with Near-Infrared Spectroscopy: A Validation Study

“…It has been shown that over 50% of the illuminated tissue volume in adults can be comprised of extra-cerebral tissue (Steinbrink et al, 2001). This signal contamination has been shown to cause a significant underestimation of CBF, and presumably the same would apply to CMRO 2 (Gora et al, 2002).…”

Near-Infrared Spectroscopy

“…ICG can act as a Fick tracer, similar to that of an inert gas. The rate of arrival of ICG in the brain, a few seconds after the rapid injection of ICG, can be observed by NIRS (Gora et al, 2002). ICG is introduced rapidly and its rate of accumulation is measured over time.…”

“…Blood flow can be measured as a ratio of ICG accumulated to the quantity of ICG introduced over a given time (Perrey, 2008). The accumulation of ICG in the brain will be dependent on both arterial inflow and venous outflow (Gora et al, 2002). The method of measuring CBF relies on several assumptions: first, blood flow must be constant for the period of measurement.…”

“…And finally, the measurements should be made within the cerebrovascular transit time (four to six seconds), because then the venous outflow is negligible and the measured increase in cerebral ICG concentration can be assumed to be entirely the result of arterial inflow of the tracer. ICG meets up with these assumptions and can thus be used as the specific tracer in CBF measurements (Gora et al, 2002). The amount of tracer delivered to the brain can be calculated from the area under the curve of the arterial ICG concentration change measured by the dye-densitometer A disadvantage of CBV and CBF determinations with NIRS in combination with ICG is that it is invasive since it requires arterial cannulation, repeated blood withdrawals, and reinfusions (Guenette et al, 2011).…”

Towards Non-Invasive Bedside Monitoring of Cerebral Blood Flow and Oxygen Metabolism in Brain-Injured Patients with Near-Infrared Spectroscopy

“…For CBF measurements, the measured ICG tissue concentration curve is comprised of both cerebral and non-cerebral components that are highly correlated. Using tracer kinetic models to recover CBF from a contaminated curve would result in an underestimation of CBF Gora et al, 2002;Owen-Reece et al, 1996). Solutions to overcoming this challenge have been proposed, including more advanced instrumentation as well as analytical approaches, with the main goal of increasing sensitivity to cerebral components.…”