Absolute measurements of local chromophore concentrations using pulsed photoacoustic spectroscopy

J. Laufer; C. Elwell; D. Delpy; P. Beard

doi:10.1117/12.657372

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6 March 2006 Absolute measurements of local chromophore concentrations using pulsed photoacoustic spectroscopy

J. Laufer, C. Elwell, D. Delpy, P. Beard

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Proceedings Volume 6086, Photons Plus Ultrasound: Imaging and Sensing 2006: The Seventh Conference on Biomedical Thermoacoustics, Optoacoustics, and Acousto-optics; 60861J (2006) https://doi.org/10.1117/12.657372
Event: SPIE BiOS, 2006, San Jose, California, United States

Abstract

Photoacoustic spectroscopy has the potential to make non-invasive, spatially resolved measurements of absolute chromophore concentrations. This has a wide range of possible applications, for example the mapping of endogenous chromophores such as oxy- (HbO₂) and deoxyhaemoglobin (HHb) or externally administered contrast agents designed to target specific tissues or molecular processes. In this study we used near-infrared photoacoustic spectroscopy to determine the absolute concentrations of HbO₂ and HHb in a tissue phantom. The phantom consisted of three blood filled capillaries (Ø460microns) suspended at depths between 3mm and 9mm in a 2.5% Intralipid solution which also contained 2% blood in order to simulate the background optical attenuation in biological tissue. The blood oxygen saturation (SO₂) of the blood circulating in the capillaries was varied using a membrane oxygenator. At each SO₂ level, nanosecond pulses emitted by an OPO laser system that was tuneable over the wavelength range from 740nm to 1040nm illuminated the phantom. The generated photoacoustic waves were recorded using a single Fabry-Perot ultrasound detector and used to obtain a depth profile of the location of the tubes. The amplitudes of the part of the photoacoustic signal that corresponded to the capillaries and the surface of the Intralipid/blood mixture were plotted as a function of wavelength. The output of a diffusion theory based model of the wavelength dependence of the photoacoustic signal amplitude was then fitted to these spectra. This enabled the quantitative determination of absolute HbO₂ and HHb concentrations in the capillaries and the Intralipid/blood mixture from which the total haemoglobin concentrations and blood SO₂ were calculated. Based on these measurements, the smallest chromophore concentrations that can be detected in biological tissue were estimated.

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J. Laufer, C. Elwell, D. Delpy, and P. Beard "Absolute measurements of local chromophore concentrations using pulsed photoacoustic spectroscopy", Proc. SPIE 6086, Photons Plus Ultrasound: Imaging and Sensing 2006: The Seventh Conference on Biomedical Thermoacoustics, Optoacoustics, and Acousto-optics, 60861J (6 March 2006); https://doi.org/10.1117/12.657372

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