Biomedical Engineering Reference
In-Depth Information
sample. It should be noted that each of these descriptions is somewhat oversimplified in
that a great deal of design needs to be done to gain the specificity, accuracy, and sensitivity
required to measure these various low-level parameters in the noisy environment of the
body. For indirect fiber optic measurements, a miniaturized transducer (sometimes referred
to as on optode) is attached to the distal end of the fiber so the light interacts with this trans-
ducer and the transducer interacts with the sample. A displacement optode such as that
shown in Figure 17.23a can be used to monitor pressure or temperature changes by simply
causing less light to be specularly reflected into the fiber as the tip is moved. In addition,
fluorescent chemistry can be placed within a membrane on the distal tip of the fiber, as
shown in Figure 17.23b, in which the amount of fluorescent light produced is a measure
Optical
Fiber
Thin
Diaphragm
In
P > Po
Out
In
Po
Out
In
P < Po
Out
(a)
Membrane
Sample
Media
Light
in/out
Enclosed
Chemistry
(b)
FIGURE 17.23
Indirect fiber optic probe designs including (a) a thin reflectance diaphragm for pressure or
temperature measurements, and (b) an optode with some chemistry enclosed within a membrane at the distal
tip of the fiber, which can be used, for instance, to determine a particular analyte concentration using fluorescent
chemistry specific to the analyte of interest.
