Handbook of Biomedical Optics

738 Handbook of Biomedical Optics

substantially (Stratonnikov et al. 2003, Finlay et al. 2004a). Other

reactions, such as singlet-state sensitizer reactions, can also be

considered using a similar mechanism.

It is dicult or impossible to measure each of the photody-

namic reaction rate constants independently, particularly in

living tissue. However, by measuring the rate of oxygen con-

sumption in multicellular tumor spheroids, Foster et al. have

been able to measure quantities that relate directly to the ratios of

several of these constants (Foster et al. 1993, Nichols and Foster

1994, Georgakoudi et al. 1997, 1998), or to place ...