Non-invasive and quantitative near-infrared haemoglobin spectrometry in the piglet brain during hypoxic stress, using a frequency-domain multidistance instrument†

Abstract

The frequency-domain multiple-distance (FDMD) method is capable of measuring the absolute absorption and reduced scattering coefficients of optically turbid media. Absolute measurement of absorption at two near-infrared (NIR) wavelengths makes possible the quantitation of tissue haemoglobin concentration and tissue haemoglobin oxygen-saturation (StO2). However, errors are introduced by the uncertainties of background absorption and the dissimilarities between real tissues and the simplified mathematical model on which these measurements are based. An FDMD-based tissue instrument has been used for the monitoring of tissue haemoglobin concentration and oxygenation in the brain of newborn piglets during periods of hypoxia and hyperoxia. These tissue haemoglobin saturation values were compared with arterial saturation (SaO2) and venous saturation (SvO2) measured by blood gas analyses. A linear correlation was observed between StO2 and the average of SaO2 and SvO2. However, StO2 is not equal to any fixed weighted average of SaO2 and SvO2 unless we introduce an effective background tissue absorption. The magnitude of the background absorption was about 0.08 cm(-1) at 758 nm and 0.06 cm(-1) at 830 nm, and it was nearly consistent between piglets. The origin of this 'effective' background absorption may be real, an artefact caused by the application of a simplified model to a complex sample, or a combination of factors.

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

“…The 75:25 ratio commonly used today originated from Mchedlishvili and is based on cerebrovascular resistance measurements. More recent studies have compared NIRS tissue oxygenation measurements to oxygenation measurements from arterial and venous blood samples, and have shown similar results to Mchedlishvili under normal physiologic conditions (Brun et al, 1997;Watzman et al, 2000;Hueber et al, 2001;Kusaka et al, 2002;Ferrari et al, 1989).…”

“…Because of its importance, there have been a number of studies that have attempted to measure the relative vascular distribution (Wiedeman, 1963;Moskalenko et al, 1980;Mchedlishvili, 1986;Brun et al, 1997;Watzman et al, 2000;Hueber et al, 2001;Kusaka et al, 2002). The 75:25 ratio commonly used today originated from Mchedlishvili and is based on cerebrovascular resistance measurements.…”

“…Hueber et al (2001) and Kusaka et al (2002) measured a vascular ratio of 50:50 under hypoxic conditions. Kusaka et al attributed this change to an increase in CBF caused by hypoxic arteriole vasodilation.…”

“…Cerebral oxygenation has been studied by measuring deoxyhemoglobin (Hb), oxy-hemoglobin (HbO 2 ), and cytochrome oxidase concentrations (Kusaka et al, 2002;Hueber et al, 2001;Watzman et al, 2000;Brun et al, 1997;Ferrari et al, 1989;Springett et al, 2000). Near-infrared spectroscopy has also been used to measure CBF using the near-infrared (NIR) tracer indocyanine green (ICG) (Patel et al, 1998;Springett et al, 2001;Brown et al, 2002).…”

Comparison of a layered slab and an atlas head model for Monte Carlo fitting of time-domain near-infrared spectroscopy data of the adult head

“…Various continuous-wave (CW), [1][2][3][4][5] frequency-domain (FD), [6][7][8][9][10][11][12][13][14] and time-domain (TD) [15][16][17][18][19] near-infrared spectroscopy (NIRS) approaches offer the ability to determine the absolute absorption and scattering coefficients of biological tissue. The retrieved optical absorption measured at multiple wavelengths allows quantification of different chromophores' concentrations within the tissue.…”