Device for measuring the velocity of capillary blood flow

 

The invention relates to medical instrumentation and can be used to control blood flow in the capillaries of the superficial tissues of man and experimental animals. The device includes a two-beam interferometer, comprising sequentially installed on the optical axis of the lighting unit consisting of a low-coherence source of radiation and the lens flat beam splitter oriented at an angle of 45to the optical axis of the interferometer plane-parallel plate in the plane of the placement of the measurement object, a planar reflector mounted on the move reflected from the flat beam splitter beam and located in a plane optically conjugate with a luminous body of the low-coherence source of radiation, the first photodetector mounted on the move reflected from a flat reflector and held flat beam splitter beam, and the second photodetector. The latter is installed on the move reflected from the measurement object and held flat beam splitter beam. Photodetectors are installed symmetrically with respect to the flat beam splitter. Their outputs connected to the inputs schema subtraction, the output of which is connected to the input of bandpass Wuxi what if">determined from the equality s/2=dtgwhere s is the linear size of the lighting unit, defined in the direction perpendicular to the direction of the radiation, d is the distance from the light Assembly to the plane-parallel plate. The device is designed to reduce the time of measurement of blood flow. 2 Il.

The invention relates to medical instrumentation and can be used to control blood flow in the capillaries poverchnostnich tissues of man and experimental animals.

A device for measuring the velocity of capillary blood flow (Siavash Y. et al. Diagnostic blood flow monitoring during therapeutic interventions using color Doppler optical coherence tomography. Proc. SPIE. Vol 3251. P 126-132), which is a fiber Michelson interferometer in which the reference reflector is installed on the modulator optical path, equipped with a measurement system to move it. Behind the exit window of the interferometer is a photodetector. The photodetector is electrically connected to the processing unit of the signal. The device analyzes the spectrum reflected from the test object radiation. The amount of blood flow is determined by the Doppler shift of the frequency imposed on postoyanniye be attributed to the difficulty of manufacturing the scanner unit reference reflector.

A device for measuring the velocity of capillary blood flow (Uly-anov S. S., Tuchin V. V. Partially developed speckle-field dynamics for blood microcirculation and biovibration parameters measurement. Proc. SPIE. V. 1922. P. 284), comprising sequentially installed on the optical axis of the lighting unit consisting of a low-coherence source of radiation and the lens flat beam splitter oriented at an angle of 45to the optical axis, a plane-parallel plate in the plane of the placement of the object mounted on the move reflected from the flat beam splitter beam flat reflector, and a flat reflector is located in a plane optically conjugate with a luminous body of the source of coherent radiation, mounted on the move reflected from a flat reflector and held flat beam splitter beam photodetector, the band-pass amplifier and a power meter, and the output of the bandpass amplifier is connected to the input of the power meter. This unit is adopted for the prototype.

The main disadvantage of the prototype is the low speed measurement. Really useful information contained in the Doppler spectral component reflected from the object radiation (Siavash Y. et al. Diagnostic blood flow monitoring during therapeutic interv frequency radiation, reflected from moving with the velocity V of the blood;

- the angle between the incident radiation and the velocity vector of blood;

0- wavelength radiation source.

The presence of Doppler frequency offset leads to a temporal modulation of the intensity of the output interference signal, which is

where I0=<EE0*>

Ip=<EEp*>

I0, Ip- the intensity of the reference and object light beams, respectively; and

E0Ep- the amplitudes of the reference and object waves, respectively,

<...> - the operation of averaging over time,

- the initial phase shift between the interfering beams;

t - time.

Detection of the interference signal produced by the photodetector.

However, when measuring scanning over the surface of the object is accompanied by temporal modulation of the intensity of the reflected radiation 1R, due to the roughness of the surface of the skin, which leads to an additional modulation of the spectrum of the reflected signal.

Assuming the diameter of the probe spots on the surface of the object is equal to 20 μm. ametra, that is 2 microns (Parks V. J. The range of spekle metrology // Exp.Mech. 1980. V. 20. No. 6. P. 181). Therefore, when the scanning speed of the spot VSC=1 mm/s with a characteristic modulation frequency FM of the reected light intensity is equal to

The speed of blood flow in capillaries V=0-1,5 mm/s (K. Caro. Mechanics of blood circulation. M: Peace. 1981. S. 473), i.e., Vcp=0.75 mm/s At a wavelength of probing radiation of 0.83 μm, the average Doppler frequency offset in accordance with formula (1) is equal to (cos=1)

When increasing the scanning speed (Vck=2mm/s spurious frequency shift overlaps the Doppler shift frequency that carries useful information. Since the intensity of radiation reflected from the skin surface by several orders of magnitude, greater than the intensity of radiation scattered by the particles moving blood (Helicon C. M. and other Coherent optical tomography microinhomogeneities of biological tissues. Letters vieth. 1995. So 61. C. 2. With 149-153), the measurement becomes impossible.

The objective of the invention is to reduce the time of measurement of blood flow. The problem is solved in that the device for measuring the speed cap the optical axis of the lighting unit, consisting of a low-coherence source of radiation and a lens, a flat light-totaltel, oriented at an angle of 45to the optical axis of the interferometer plane-parallel plate in the plane of the placement of the measurement object, a planar reflector mounted on the move reflected from the flat beam splitter beam and located in a plane optically conjugate with a luminous body of the low-coherence source of radiation, a photodetector mounted on the move reflected from a flat reflector and held flat beam splitter beam, bandpass amplier and power meter, and the output of the bandpass amplifier is connected to the input of the power meter according to the invention is further provided with a second photodetector mounted on the move reflected from the measurement object and held flat beam splitter beam, and schema subtraction, the inputs of which are connected to the outputs of the photodetectors and the output to the input of the bandpass amplifier, and first and second photodetectors are installed symmetrically with respect to the flat beam splitter, and the light Assembly is deflected from the optical axis by the angledetermined from the equality

s/2=d

Required technical result is achieved by the fact that in the inventive device in the output signal components are eliminated, containing parasitic modulation of the spectrum.

In Fig.1 shows a diagram of the device of Fig.2 - scheme of the interference beams of the reference and object light beams after passing through the beam splitter.

Device for measuring the velocity of capillary blood flow contains the light Assembly 1 consisting of a source of low-coherence light 2 and the lens 3, the flat beam splitter 4, is oriented at an angle of 45to the optical axis OO’ of the interferometer plane-parallel plate 5 located in the plane of the placement of the measurement object, a flat reflector 6, mounted on the move reflected from the flat beam splitter 4 beam and located in a plane optically conjugate with a luminous body of the low-coherence source of radiation 2, the first sensor 7 mounted on the move reflected from a flat reflector 6 and past the flat beam splitter beam 4, the second sensor 8 mounted on the move reflected from the measurement object and held flat beam splitter beam 4, scheme and 11 and the difference compensator stroke 12, installed between the flat beam splitter 4 and the flat reflector 6. The input bandpass amplifier 10 is connected to the output of the circuit subtracting 9 and the output to the input of the power meter 11. The first 7 and second 8 photodetectors are installed symmetrically with respect to the flat beam splitter 4. The lighting unit 1 is deflected from the optical axis OO’ of the interferometer at an angledetermined from the equality

s/2=dtg,

where s is the linear size of the lighting unit 1, defined in the direction perpendicular to the direction of the radiation, d is the distance from the lighting unit 1 to plane-parallel plate 5.

The device operates as follows. The radiation source 2 (Fig.1) by means of the lens 3 is focused on the surface of the plane-parallel plate 5. During the measurements, the surface of the test object is combined with the plane of plane-parallel plates 5. Therefore, the focusing of radiation in plane-parallel plate is focusing on the object surface. Focus provides local control of blood flow.

The flat beam splitter 4 deflects part of the light from the low-coherence source 2 on a flat reflector 6 (flat mirror is mind lines:

radiation reflected from the flat beam splitter 4, extends in the direction of the first photodetector 7;

radiation, proprosed flat beam splitter 4, in the direction of the second photodetector 8.

The reference light after reflection from the flat reflector 6 also falls on two of the photodetector 7 and 8. The sensors register the result of interference of object and reference light beams.

Consider equation interference (2). Imagine the light wave EP, reflected from an object as a sum of waves Ebcarrying useful information, and spurious signal Es(light reflected from the surface of the skin). Then the equation (2) can be represented as follows:

where Is=<EEs*> - the intensity of the parasitic signal,

Ib=<EEb*> - the intensity of the useful signal.

In equation (3) there are no cross members, due to the interaction of waves E0and EsEsand Eb. The control flow is at a depth h from the surface of the object, which exceeds the coherence length of the radiation source. Therefore, for these pairs of waves will not satisfy the condition of interferen the physical essence of the achieved technical result on the example of the interference beams of the reference and object light beams after passing through one of the beam-splitting surfaces of the flat beam splitter 4. In Fig.2 depicts a fragment of the flat beam splitter, where

7, 8 photodetectors;

a, b is incident on the beam splitter reference and object beams, respectively; and

a7b7- the output beams of the reference and object light beams, respectively, extending in the direction of the photodetector 7;

a8b8- the output beams of the reference and object light beams, respectively, extending in the direction of the photodetector 8;

n is the refractive index of the material of the beam splitter (n>1).

Suppose that the phase difference between the reference and object b rays at the point M is equal to. After passing through the beam splitter, the phase of the beam b at the point M will experience a jump on the TT in accordance with the law of reflection from an optically more dense medium (the hydrographic system of Lansberg. Optics. "Science". M: 1976. S. 475).

Then due to the interference of rays (a7b7) and (a8b8) the intensity of the light fluxes detected by the photodetectors will be determined by the following expression.

The photodetector 7:

The photodetector 8:

The output signals of the photodetectors U7and U8proportional to the intensities of light potl, we can write: U7=I7and U8=I8. In the schema subtraction 9 (Fig.1) is the subtraction of the output signals of the photodetectors U7and U8. In the end, the components of the signals containing the parasitic modulation of the spectrum are eliminated, and there is only one interference member:

The spectral composition of the output signal U according to (6) is determined by the distribution of mikropotokami blood velocity, and spatial orientation vectors of their velocities. The lower and upper limits of the bandwidth of the amplifier 10 (Fig.1) define the frequency analysis of blood flow velocity. Almost borders are set respectively equal to 300 Hz and 1500 Hz. The integral value of the blood flow will be determined by the readings of the power meter 11.

Almost for the implementation of the considered device as a source of low-coherence radiation 2 (Fig.1) can be used superluminescent diode with a wavelength of 0.83 μm and a coherence length of 30 μm. The low coherence length of the radiation source allows local control of blood flow in the depth of the object. At this spatial resolution in depth is the same, obviously, Oldowan plane-parallel plate compensator 12, placed in the reference arm of the interferometer. The thickness of the compensator determines the position of the zero stroke difference of the interfering light beams. Therefore, changing the thickness of the compensator accordingly, it is possible to vary the desired measuring depth of flow. The maximum depth analysis of blood flow is determined by the degree of exceeding the level of the useful signal above the noise level, i.e. the signal - to-noise ratio. Modern element base allows you to control the blood flow at a depth of up to 1.5 mm

The specified deviation block light from the optical axis by the angledictated by the need for symmetrical installation of two photodetectors relative to the beam splitter. The device uses a beam splitter that divides the incident radiation is reflected on and proprosed in the ratio of 1:1. The requirement of symmetry of the installation of sensors necessary for the identity of the analyzed light fluxes. In the inventive device, the low-coherence source of radiation is mounted for movement perpendicular to the direction of radiation. Moving source provides the bias (scan) Sonderweg light spot on the surface of the object.

As follows from verrazanno from the object radiation is not an obstacle to increase the speed of scanning the surface of the test object.

Thus, based on the above, the claimed combination of features in the device allows to solve the problem, namely, to reduce the time of measurement of blood flow velocity.

Claims

Device for measuring the velocity of capillary blood flow, containing a two-beam interferometer, comprising sequentially installed on the optical axis of the lighting unit consisting of a low-coherence source of radiation and the lens flat beam splitter oriented at an angle of 45to the optical axis of the interferometer plane-parallel plate in the plane of the placement of the measurement object, a planar reflector mounted on the move reflected from the flat beam splitter beam and located in a plane optically conjugate with a luminous body of the low-coherence source of radiation, a photodetector mounted on the move reflected from a flat reflector and held flat beam splitter beam, bandpass amplier and power meter, and the output of the bandpass amplifier is connected to the input of the power meter, characterized in that it is further provided with a second sensor, fitted the passages which are connected to the outputs of photodetectors, and the output to the input of the bandpass amplifier, and first and second photodetectors are installed symmetrically with respect to the flat beam splitter, and the light Assembly is deflected from the optical axis by the angledetermined from the equality s/2=dtgwhere s is the linear size of the lighting unit, defined in the direction perpendicular to the direction of the radiation, d is the distance from the light Assembly to the plane-parallel plate.

 

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