Functional photoacoustic microscopy is a valuable tool in quantifying hemoglobin oxygenation within single vessels. In several functional studies with this tool, quantitative sO2 measurements were taken both in vitro and in vivo. Although in vitro measurements of sO₂ showed high agreement with expected values from premade samples, in practice, in vivo measurements were less accurate. The reported values of 70%-100% sO₂ in the arteries present large deviations from the expected range of 95-100%. Several factors, such as fluence wavelength dependence, optical wavelength range, and transducer central frequency have been suggested and investigated in order to understand these discrepancies. Despite additional knowledge of systematic errors arising from such factors, measuring the absolute value of sO₂ in vivo remains a challenge. All previous studies assumed linear dependence of the photoacoustic signal on absorption and used the linear least squares model. However, several factors, such as wavelength calibration errors, photodiode-wavelength dependence, and intensity dependent non-linearity, all of which may have a significant effect on the final calculation, have not been investigated. Here we evaluate both in vitro and in vivo the effects on sO₂ measurements of photodiode wavelength dependence, laser wavelength accuracy, and intensity dependent absorption of oxygenated and deoxygenated hemoglobin. We show that these factors may contribute significantly to the deviations in sO₂ calculations in vivo.

Date Published: 28 February 2011
PDF: 8 pages
Proc. SPIE 7899, Photons Plus Ultrasound: Imaging and Sensing 2011, 78993C (28 February 2011); doi: 10.1117/12.875287

Published in SPIE Proceedings Vol. 7899:
Photons Plus Ultrasound: Imaging and Sensing 2011
Alexander A. Oraevsky; Lihong V. Wang, Editor(s)