5.8 Development of Diagnostic Speckle-Optical Criteria for …
429
Methods of measurements. The measurement was conducted with an experimental
setup shown in Fig. 5.38. In a series of conducted experiments, laser irradiation
illuminated a small area of skin of 2 × 2 mm
2 through a light guide path.
The scattered irradiation was gathered with the second light guide and transmitted
to the photomultiplier. The photoelectrical signal from PMT, which is proportional
to the irradiation intensity, was digitalized with a 12-discharge ADC and recorded
in the form of integral numbers into a file, which includes 4096 numbers. Signal
measurement accuracy was 1/2000 of the average signal level. Methods of measurements and working principle of the device were described in more detail in the works
[80, 81]. Essential distinction is that the frequency range for blood flow determination is broadened considerably into the high-frequency area as the blood flow is
characterized by a signal of higher frequency [78].
The measurements were conducted 10 times in each point. Thus, the total number
of measurements in each point was 40,960. Then, the sensor was shifted with a step
of 10 mm in accordance with the net marked on the inside of the hand. In such a
way, the area of 300 mm
2 was scanned.
Two series of experiments were conducted, in one of which the blood flow was
normal and in the other one it increased as a result on therapeutic impact (warming
ointment “Finalgon” was rubbed into).
Random characteristics of the speckle signal. The speckle signal is formed as
the result of coherent composition of many wave elements scattered on moving
particles. In our case, such elements are cells, which form skin, and blood cells,
and erythrocytes are in the first place. Modeling of coherent dispersion for simple
macroscopic homogeneous systems shows that the average velocity of particle movement is proportional to fluctuation frequency. Today, there are no adequate models,
which describe light dispersion from the tissue of complex models such as biological tissues. Muscle tissue along with the adjoining skin suffers constant non-regular
microvibrations conditional on the tremor, contraction of separate fibers and groups
of muscles, but along with this they also have their own velocity relative to vessels.
The average velocity of erythrocyte movement appears to be higher than the velocity
of shift of covering tissues. Part of the light scattered by the blood cells is smaller
than the light scattered by skin as the density of erythrocytes is less than the density
of covering tissues.
However, both theoretical estimation [78, 84] and experimental data [75, 84,
132–134] obtained by foreign authors and by us give the possibility to assert with
confidence that movement of blood cells affects greater in the area of high-frequency
fluctuations.
Thus, processing of a random signal, which reflects intensity of a scattered
speckle-field, should be directed to the analysis of change of high-frequency components in the spectrum. From this point of view, the analysis of the whole spectrum is
optimal. Informative parameters of the spectrum can be diverse [41, 44, 85, 132–134,
163] though as it mentioned above none of them reflects directly either the number
of blood particles or their velocity because of complexity of the physical model.
This connection is of correlation character and is often ascertained during tests.
The following parameters can be mentioned: the average frequency, half-breadth
429
Methods of measurements. The measurement was conducted with an experimental
setup shown in Fig. 5.38. In a series of conducted experiments, laser irradiation
illuminated a small area of skin of 2 × 2 mm
2 through a light guide path.
The scattered irradiation was gathered with the second light guide and transmitted
to the photomultiplier. The photoelectrical signal from PMT, which is proportional
to the irradiation intensity, was digitalized with a 12-discharge ADC and recorded
in the form of integral numbers into a file, which includes 4096 numbers. Signal
measurement accuracy was 1/2000 of the average signal level. Methods of measurements and working principle of the device were described in more detail in the works
[80, 81]. Essential distinction is that the frequency range for blood flow determination is broadened considerably into the high-frequency area as the blood flow is
characterized by a signal of higher frequency [78].
The measurements were conducted 10 times in each point. Thus, the total number
of measurements in each point was 40,960. Then, the sensor was shifted with a step
of 10 mm in accordance with the net marked on the inside of the hand. In such a
way, the area of 300 mm
2 was scanned.
Two series of experiments were conducted, in one of which the blood flow was
normal and in the other one it increased as a result on therapeutic impact (warming
ointment “Finalgon” was rubbed into).
Random characteristics of the speckle signal. The speckle signal is formed as
the result of coherent composition of many wave elements scattered on moving
particles. In our case, such elements are cells, which form skin, and blood cells,
and erythrocytes are in the first place. Modeling of coherent dispersion for simple
macroscopic homogeneous systems shows that the average velocity of particle movement is proportional to fluctuation frequency. Today, there are no adequate models,
which describe light dispersion from the tissue of complex models such as biological tissues. Muscle tissue along with the adjoining skin suffers constant non-regular
microvibrations conditional on the tremor, contraction of separate fibers and groups
of muscles, but along with this they also have their own velocity relative to vessels.
The average velocity of erythrocyte movement appears to be higher than the velocity
of shift of covering tissues. Part of the light scattered by the blood cells is smaller
than the light scattered by skin as the density of erythrocytes is less than the density
of covering tissues.
However, both theoretical estimation [78, 84] and experimental data [75, 84,
132–134] obtained by foreign authors and by us give the possibility to assert with
confidence that movement of blood cells affects greater in the area of high-frequency
fluctuations.
Thus, processing of a random signal, which reflects intensity of a scattered
speckle-field, should be directed to the analysis of change of high-frequency components in the spectrum. From this point of view, the analysis of the whole spectrum is
optimal. Informative parameters of the spectrum can be diverse [41, 44, 85, 132–134,
163] though as it mentioned above none of them reflects directly either the number
of blood particles or their velocity because of complexity of the physical model.
This connection is of correlation character and is often ascertained during tests.
The following parameters can be mentioned: the average frequency, half-breadth