This paper describes the use of pulsed photoacoustic spectroscopy (PPAS) to monitor the concentration and oxygenation state of blood in vitro and in vivo. Measurements of blood oxygenation in the brain are described. It is well known that hemoglobin is the primary oxygen carrier in blood and that this molecule exhibits absorption bands in several regions of the visible spectrum which are specific to its oxidation state [1,2]. The region between 700-900 nm is noteworthy since it is both a window region in tissue with relatively low absorption and since oxy- and deoxy- hemoglobin absorption bands near 840 nm and 740 nm respectively are relatively strong. A number of spectroscopic studies of blood oxygenation have been made. One approach includes a class of methods termed photon diffusion or photon tomography that relies on a fact that brain tissue is strongly scattering and that light injected into the brain through the skull can be detected after scattering at a second location on the skull . Analysis has shown that the relative absorption spectra of oxy and deoxy hemoglobin can be obtained by such methods. However, quantitative measurements necessary to determine the concentrations of absorbing species require knowledge of the absorption pathlength. In photon diffusion this pathlength is at best known as a statistical quantity. A description of the signal formation process in photon diffusion found in the literature generally involves analysis of the response in specific portions of the time or spatial domain . PAS methods on the other hand monitor light absorption and while affected by scattering they do not involve scattering as part of the detection process itself. In addition, the PAS method described in this paper uses a fiber probe for delivery of the exciting light and hence it can deliver light at depths unattainable by conventional methods if the fiber is allowed to penetrate the tissue. The method can also be used to study the spectral response of hemoglobin and other compounds in strongly absorbing spectral regions not exclusively in a window region.
|Original language||English (US)|
|Journal||Progress in Natural Science|
|Issue number||SPEC. ISS.|
|State||Published - 1996|
ASJC Scopus subject areas
- Materials Science(all)