<title>Local determination of hemoglobin concentration and degree of oxygenation in tissue by pulsed photoacoustic spectroscopy</title>

Abstract

Pulsed-photoacoustic spectroscopy (PPAS) in the near-infrared portion of the optical spectrum was used as a local technique for quantitative monitoring of tissue hemoglobin concentration and its oxygenation state. A pulsed, tunable optical source coupled to a 1mm-diameter optical fiber cable was used to deliver optical energy to the tissue under study. The fiber was placed either on the exterior surface or inserted into the tissue. An ultrasonic signal was produced in the tissue as a result of the absorbed light pulse energy. Since the rate of conversion of laser light energy to heat was rapid and the laser pulse was much shorter than the tissue thermal-diffusion length, the ultrasonic signal amplitude was proportional to the energy absorbed. Spectra of absorbing compounds were obtained by measuring the variation in the acoustic signal with source wavelength. In contrast with near-infrared spectroscopic techniques that measure diffuse light transmission and assume knowledge of the pathlength of light traveling through tissues in order to determine the absorption coefficient, the photoacoustic response is produced directly by light absorption. Light scattering merely modifies the spatial distribution of the absorbed energy. Our studies demonstrate that photoacoustic spectra obtained both in-vitro and in-vivo allow determination of relative changes in the concentration of oxy-and de-oxyhemoglobin.

Quantitative spectroscopic photoacoustic imaging: a review

“…Using a low frequency ultrasound detector (<1 MHz), Fainchtein et al 62,63 made measurements of the wavelength dependence of the amplitude of the peak of the PA wave which showed qualitative agreement with the absorption spectrum of blood (710 to 870 nm), both for blood in a cuvette and in a canine arterial-venous shunt. The measured spectrum changed approximately as expected as the level of oxygen in the blood was varied, but no quantitative estimates were made.…”

“…Subsequently μ eff was measured from the slope of the curve, and μ 0 s calculated from it, by use of the known μ a . Rather than measuring the diffuse reflectance, Fainchtein et al 62,63 modeled it as approximately R d∞ ≈ expð−7μ a ∕μ eff Þ. Note that in both cases an additional optical measurement, or an additional assumption, is required to allow both μ a and μ 0 s to be estimated from the PA signal.…”

Imaging brain hemodynamic changes during rat forepaw electrical stimulation using functional photoacoustic microscopy

“…By taking advantage of the ultrasonic detection, PA imaging can provide better spatial resolution than DOI. In addition, by leveraging the intrinsic oxygen-dependent spectral absorption properties of hemoglobin, it has been shown that this technique can detect changes in SO 2 and total hemoglobin concentration (HbT) related to blood volume and flow independently in single vessels (Fainchtein et al, 2000). This is a fascinating feature for a label-free functional brain imaging system.…”

Noninvasive imaging of hemoglobin concentration and oxygenation in the rat brain using high-resolution photoacoustic tomography

“…Photoacoustic detection of deeply embedded absorbing objects colored with bovine hemoglobin was achieved by Esenaliev et al 9 More recently, Kolkman et al 12 explored the photoacoustic imaging of blood vessels in human skin. Fainchtein et al 17 studied photoacoustic measurements on in vitro and in vivo blood samples and proved that this technique can assess relative changes in concentrations of both oxygenated hemoglobin ͑HbO 2 ͒ and deoxygenated hemoglobin ͑Hb͒. Single-wavelength photoacoustic detection was used by Esenaliev et al 18 to monitor relative changes in blood oxygenation in vitro.…”