Comparison of time-resolved and -unresolved measurements of deoxyhemoglobin in brain.
Continuous (CW) and pulsed light were used for the noninvasive measurement of hemoglobin oxygenation in tissues. A dual wavelength method of continuous illumination spectroscopy used 760 nm (deoxyhemoglobin peak) and 800 nm (an oxyhemoglobin-deoxyhemoglobin isosbestic point) to measure the kinetics and extent of oxyhemoglobin deoxygenation in brains during mild ischemia/hypoxia. Absorption and scattering were modeled in an artificial milk/yeast blood system, which gave an exponential relationship between absorption and optical path length to a depth of 7 cm. Time-resolved spectroscopy (10-ps resolution) afforded a display of the times and distances of arrival of photons emitted by the cat brain in response to a 10-ps input pulse. The emitted photons rose to a peak in a fraction of a nanosecond and declined exponentially over a few nanoseconds. The half-time of exponential decay corresponds to photon migration over a distance of 4 cm. Exponential light emission continued for several more nanoseconds when the brain was encased by the skull, which plays a key role in prolonging light emission. The exponential decline of light intensity has a value [exp(-microL)], where L is the path length determined from the time/distance scale and mu is the characteristic of the migration of light in the brain. The factor mu is increased by increasing absorption, and mu' = epsilon C where epsilon and C are the Beer-Lambert parameters of extinction coefficient (epsilon) and concentration (C). Thus, deoxyhemoglobin can be quantified in brain tissues.
Chance
B
B
Department of Biochemistry, University of Pennsylvania, Philadelphia 19104.
Leigh
J S
JS
Miyake
H
H
Smith
D S
DS
Nioka
S
S
Greenfeld
R
R
Finander
M
M
Kaufmann
K
K
Levy
W
W
Young
M
M
D000818:Animals; D001921:Brain / Q000378:metabolism; D001923:Brain Chemistry; D002545:Brain Ischemia / Q000378:metabolism; D002415:Cats; D006454:Hemoglobins / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D002534:Hypoxia, Brain / Q000378:metabolism; D007700:Kinetics; D010108:Oxyhemoglobins / Q000378:metabolism; D013053:Spectrophotometry
D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin