Biophotonics_Concepts_to_Applications

The relative intensity of the backscattered light that enters the collectionfiber
depends on the sizes and concentrations in the tissue of scattering components (e.g.,
nuclei, mitochondria, and connective tissue) and absorbing components (e.g.,
hemoglobin and oxyhemoglobin) [ 2 ]. Because the sizes and densities of these
biological units change when the tissue becomes diseased, the ESS process assists
pathologists in diagnosing the development of abnormal cell growth. By using
appropriate mathematical models, the measured reflectance spectrum can be ana-
lyzed to yield scattering and absorption coefficients of the tissue sample. The values
of these optical parameters depend on the cell morphology (the cell form and
structure), the extracellular matrix (the biological constituents lying outside of the
cell), and the biochemistry and vascular structure of the tissue sample. Because
these tissue characteristics undergo predictable changes during the progression of a
disease, the variations in the optical properties with time can be used to get
information about the status of a tissue disease.

Example 9.8Consider the photon collection volume in Fig.9.12to be a

simple semicircular curved cylinder of tissue with a diameter 2a = 200μm. If

the separation between thefiber cores is 350μm and the center of the cylinder

has a maximum depth of 175μm, what is the volume of the cylinder?

Solution: The depth of 175μm means the center of the cylinder is simply a

semicircle with a radius of r = 175μm. Thus the length of the cylinder is

πr=π(175μm) = 550μm and its cross sectional area isπa^2 μm^2 =π(100)^2

μm^2 =π 104 μm^2. Then the volume is

V¼ðcylinder cross sectionÞðlengthÞ¼ðp 104 lm^2 Þð 550 lmÞ

¼ 0 :017 mm^3 :

Collection

fiber

Illumination

fiber

Photon collection region

350 μm

Scattering elements

in the tissue

Fig. 9.12 Example of an
ESS probe with separate
illumination and collection
fibers

274 9 Spectroscopic Methodologies