Handbook of Biomedical Optics

Photodynamic Therapy 743

maximum 630 nm), Photofrin (630 nm), and PpIX (635 nm),

which have absorption maxima in the region where hemoglobin

is highly absorbing. Because the concentration of hemoglobin

is generally orders of magnitude greater than that of the sensi-

tizer, its absorption easily overwhelms that of the sensitizer if

the absorption peaks of the two coincide. For sensitizers with

longer-wavelength absorption peaks, such as mTHPC (658 nm),

MLu (732 nm), and BPD (690 nm), the long-wavelength absorp-

tion peak coincides with a relatively at, featureless region of the

hemoglobin absorption spectrum, making detection much easier.

In the extreme case of MLu, with an absorption peak at

732 nm, the absorption of the sensiti ...