Digital Optical and Scanning Probe Microscopy for Inspection and Manipulation of Biocells - Bioanalysis Advanced Materials Methods and Devices - page 94

of thermal and biochemical exchanges and is important, for example, in general
physiological thermal regulation. Optical monitoring of the blood flux has an
obvious advantage due to its nonintrusive character. Various methods have been
used to study blood in the microcirculation by analysis of the light scattered from
moving blood; these are based on such optical phenomena as the Doppler effect [ 6 ],
speckle photography (Fercher and Briers [ 7 ], Asakura and Takai [ 8 ], Briers [ 9 , 10 ]),
and the dynamic behavior of laser speckles (Fujii et al. [ 45 ], Aizu and Asakura
[ 12 ]). The application of these phenomena is particularly attractive and promising
because of the non-invasive character of the measurements (that is without causing
any disturbance) and the possibility of implementing these techniques in vivo. In
this section real time blood microcirculation monitoring is described. This uses
CCD recording of the sequences of the dynamic biospeckle patterns produced when
a tissue under study is illuminated with a laser beam with direct digital cross-
correlation analysis of the patterns [ 13 , 14 ].

7.6.3 Biospeckle Dynamics

The dynamics of speckle patterns produced by a moving rough surface have been
extensively studied for velocity measurements (e.g., [ 11 , 12 ]). However, the
spatio-temporal properties of biospeckle are essentially different from those of
the speckle patterns formed by a moving rough surface due to the effect of the
multiple scattering and different velocities of the scatterers. This effect is important
for Laser Doppler measurements as well, but the description of the scattered light
using speckles has the advantage of including multiple scattering, even if we
consider the simplest case of multiple scattering from the “single” rough surface.
For single-point measurements, the intensity fluctuations measured at the point
are characterized by the time-correlation length defined by the time at which the
normalized temporal autocorrelation function of intensity fluctuations falls to 1/ e .
This statistical quantity is inversely proportional to the fluctuating speed of the
speckle intensity. Its reciprocal value measures the velocity of a diffuse object at
least for the speckles scattered once. A more general description of dynamic
speckle patterns is based on the use of multidimensional space-time cross-
correlation functions. The normalized cross-correlation function of the fluctuating
component

D I ¼ I < I >

of the speckle intensity is

h D I ðr 1 ; t 1 ; ÞD I ðr 2 ; t 2 Þ i

gD I ð r 1 ; r 2 ; t 1 ; t 2 Þ¼

i :

(7.1)

h D I ð r 1 ; t 1 ; Þ > <D I ð r 2 ; t 2 Þ

The parameter g , characterizes the mutual correlation of two biospeckle images
and varies from 0 to 1. Dynamic speckles have two fundamental motions of
speckles. For the first type of the speckle motion called “translation” the speckles
move as a whole, and their shape remains unchanged even under considerable