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Proceedings Paper

Determination of the transport scattering coefficient of red blood cells
Author(s): A. Timothy Lovell; Jeremy C. Hebden; John C. Goldstone; Mark Cope
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Paper Abstract

There are no reliable values for the transport scattering coefficient (?'s) of whole blood, particularly at the high hematocrits found in-vivo. Existing values are largely based on single scattering measurements of scattering crosssection and angular scattering. The accuracy of the single scattering method is limited by the accuracy with which the g-value can be measured, as it is near 0.99. Diffuse measurements, coupled to diffusion theory models, are normally hampered by the relatively high absorption coefficient of oxy-hemoglobin even in the near infrared. Blood was drawn from 9 healthy volunteers, heparinised, and the cells washed twice with phosphate buffered saline. Oxyhemoglobin was converted to carbonmonoxide-hemoglobin, which has an absorption coefficient that is approximately 5% of that of oxy-hemoglobin in the near infrared region. Picosecond pulses of light were transmitted through an 80x60x20 mm cuvette and the resulting temporal point spread functions recorded with a streak camera. The data were fitted to a time-dependent diffusion model to derive values for ?'s and ?'a which is now valid because of the low ?a of carbonmonoxide-hemoglobin. The effect of changing the hematocrit was determined by stepwise dilution of the washed red cells with further phosphate buffered saline. Mean values for ?'s and ?a at 802 nm were 3.15±0.12 mm-1 and 0.0098±0.0004 mm-1 respectively for the hematocrit in the normal range. The undiluted red cells showed a small negative wavelength dependence for ?'s over the range 740 to 860 nm with a slope of -0.0045±0.0011 mm-1nm-1 which was highly significant (p=0.0001). The negative wavelength dependence of ?'s is compatible with Mie theory predictions of scattering by large particles. A near linear relationship between ?'s versus hematocrit (H) was found in this study (up to H=0.45) as opposed to the ?'s ° H( 1 Ñ H) or ?'s ° H(1 Ñ H)(1.4 Ñ H) macroscopic scattering coefficient relationship of others..

Paper Details

Date Published: 15 July 1999
PDF: 8 pages
Proc. SPIE 3597, Optical Tomography and Spectroscopy of Tissue III, (15 July 1999); doi: 10.1117/12.356795
Show Author Affiliations
A. Timothy Lovell, Univ. College London Medical School (United Kingdom)
Jeremy C. Hebden, Univ. College London (United Kingdom)
John C. Goldstone, Univ. College London Medical School (United Kingdom)
Mark Cope, Univ. College London (United Kingdom)

Published in SPIE Proceedings Vol. 3597:
Optical Tomography and Spectroscopy of Tissue III
Britton Chance; Robert R. Alfano; Bruce J. Tromberg, Editor(s)

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