The present invention relates to devices and methods for measuring the pH of
blood in the vicinity of a vulnerable plaque. A balloon including an opto-electric
device may be positioned proximate a vulnerable plaque. The balloon can be inflated
to partially occlude blood flow enabling interaction between lipid laden blood
and pH-sensitive material either within the balloon or on the wall(s) of the balloon.
The selected pH-sensitive material is one whose optical properties change as a
function of the pH of blood in the vasculature. An opto-electric device may be
used for measuring the optical property and/or the change in the optical characteristics
of the pH-sensitive compound.