Biomedical Engineering Reference
In-Depth Information
Sample
medium
Light from Source
Fixed
Path Length
Light to Detector
(a)
Sample
medium
Cladding
Light In
Light Out
Core
Evanescent light
wave interacts with
the media
(b)
Sample
medium
Distal Fiber Tip
Returned light
Delivery fiber
Receiving fiber
Fiber optic delivery
of light
(c)
FIGURE 17.22
Direct fiber optic probe designs including (a) absorption probe using two side firing fibers, (b)
an evanescent wave probe in which the light transmits from the core to the sample and back into the core, and (c) a
multifiber design for use in distinguishing normal from cancerous tissue by directly measuring autofluorescence or
Raman spectra.
precancerous lesions using direct measurement of tissue autofluorescence or Raman spec-
trum. Interferometers, such as the Fabrey-Perot type described in Section 17.3.4, have been
designed using partially reflecting mirrors built into a fiber optic, and any physical change
imparted on the fiber, such as that due to fluctuations in body temperature or pressure, can
be directly measured by the fiber in the form of a change in the interference pattern of the
light. Finally, the fiber optic probe for measurement of tissue optical properties, described
in Section 17.2.4, is another example of a direct probe that measures reflections from the
