Device for contactless determination of volumetric flow

 

The invention relates to medicine, to medical devices for measuring blood flow velocity and can be used to assess blood flow in the eye, skin, surgery for intraoperative studies of blood flow in various organs, for the study of microcirculatory blood flow in grafts in plastic surgery and cosmetology. Device for contactless determination of volumetric flow consists of a laser light source, the condenser aperture diaphragm, lens, sensor, device for recording and processing the signal of the photodetector, which further comprises an inclined mirror with a hole. The device allows to determine the volumetric flow in the surface layers of various organs and tissues, while in its design takes into account the requirements of the laser safety requirements of such devices, as well as improved signal-to-noise ratio, simplified construction of the apparatus as a whole. 2 Il.

The invention relates to medicine, to medical devices for measuring blood flow velocity and can be used to assess blood flow in otorhinolaryngology (in the mucous membranes of upper respiratory tract), skin, surgery for intrapersonal in plastic surgery and cosmetology.

A known method for contactless evaluation of blood flow in biological tissues, based on registration of fluctuations of intensity of laser radiation scattered at the site perfoirmance tissue [1, 2]. Perfusely the volume of tissue illuminated with coherent lasernet radiation, which is scattered on the structural elements of blood moving in tissue and optical inhomogeneities in the tissue. Diffuse radiation is converted into an electrical signal which is proportional to the intensity of this radiation, by means of a sensor. The system calculates the frequency spectrum of the electrical signal P(f), where f is the frequency. Next, calculate values of zero M0and the first M1spectral moments of the formula [1]:

Zero spectral moment M0will be proportional to the average concentration of moving blood cells, the first spectral moment M1refers to the average perfusion and first normalized spectral moment of N1defined by the formula:

directly proportional to the average velocity of blood cells [1].

The described method is implemented in a relatively large kolichestvennyh organs [3, 4, 5]. In particular, a device for contactless study of the microcirculation in the tissues of the eye, described in [6]. Diagram of the device depicted in Fig.1. The laser radiation source 1 passes through the polarizer 9, becomes linear polarization and is focused by the condenser 2 in the plane of the intermediate focus. Next, the laser light passes through the aperture diaphragm 3 and the lens 4, which focuses the laser radiation in the plane of the examined object 5. Between the lens and the object is placed a quarter-wave plate 11, through which the laser light becomes circular polarization. Laser radiation scattered by the object 5, passes through the quarter wave plate 11 in the opposite direction and acquires a polarization orthogonal initial and using the lens 4 and the polarization divider 8 is directed through the polarizer 10 on the photodetector 6 for photovoltaic registration of the scattered radiation, and then the signal from the photodetector 6 is supplied to the device for recording and processing the signal of the photodetector 7. Further signal processing is to calculate its power spectrum and the determination by the formulas (1) to(3) parameter values M0shall I check and signal processing 7. In this scheme, the polarizer and quarter-wave plate is used to guide on the photodetector all scattered radiation using a polarizing beam divider. The optical system is assembled so that the plane of the P0P1and P2was optically coupled [6].

The disadvantage of this device is the complexity of the optical system using a polarizing beam divider, a quarter-wave plates and polarizers to separate the laser beam illuminating the analyzed tissue and scattered radiation directed to the photodetector. This requires further adjustment, as well as the intensity of the radiation directed to the photodetector is significantly reduced as a result of reflection on a large number of glass surfaces, which leads to the need to increase the power of the probing laser radiation to achieve an acceptable signal to noise. It should also be noted that in laser systems for medical purposes the maximum power of the laser radiation substantially limited to the security requirements [7, 8].

First proposed device for contactless determination of volumetric blood flow, Katy plot perfoirmance fabric, sensor for photoelectric registration of the scattered radiation, the device for recording and processing the signal of the photodetector, characterized in that it further comprises a flat mirror, facing the reflecting surface to the lens installed between the condenser lens in the plane of the intermediate focus of the laser beam inclined to the axis of the laser beam with a hole located on the axis of the laser beam.

The device shown in Fig.2 and consists of:

1 - the source of laser radiation

2 - condenser

3 - aperture stop

4 - lens

5 - analyzed object

6 photodetector

7 is a device for recording and processing the signal of the photodetector

8 - inclined mirror

9 - hole in an inclined mirror 8.

Laser radiation emitted by the laser source 1 is focused by the condenser 2 in the plane of the intermediate focus. Passing through the opening 9 in an inclined mirror 8, which is placed in the plane of the intermediate focus, the laser light then passes through the aperture diaphragm 3 and is focused by lens 4 in the plane of the examined object 5. Diffuse perfuziruemami tissues examined object 5 radiation passing through the lens 4 and reflected from the radiation does not fall on the photodetector 6, and goes through the hole 9 in an inclined mirror 8. The photodetector 6 converts the scattered radiation into an electrical signal proportional to the intensity of radiation, and this signal is processed in the device registration and signal processing 7, that is to calculate its power spectrum and the determination by the formulas (1) to(3) parameter values M0, M1and N1characterizing blood flow in the test section of the cloth.

As can be seen from the above, the proposed device is simpler, uses fewer parts, which reduces the reflection of laser radiation from their surfaces and, consequently, the lower the loss of signal power that is manifested by the increase of the ratio signal/noise, and reducing the required power of the laser light source, which is important for safety when using this product in medicine.

Bibliography

1. R. Bonner and R. Nossal, "Model for laser Doppler measurements of blood flow in tissue", Appl. Opt. 20, pp.2097-2107 (1981).

2. M. D. Stem, "Laser Doppler Velocimetry in Blood and Multiply Scattering Fluids: Theory", Appl. Opt. 24, 1968 (1985).

3. Y. Aizu, T. Asakura "Coherent Optical Techniques for Diagnostics of retinal Blood Flow", J. Biomed. Opt. Vol. 4, No. 1, pp.61-75, Jan. 1999.

4. F. F. M. de Mul, J. Van Spijker, D. Van der Plas et al. Mini Laser Doppler (blood) Flow Monitor With Diode Laser SGeiser, U. Diermann, C. E. Riva Compact Laser Doppler Choroidal Flowmeter", J. Biomed. Opt. Vol. 4, No. 4, pp. 459-464, oct. 1999.

7. Sanitary norms and rules for design and operation of lasers, No. 5804-91. - M.: 1991. - 94 C.

8. American National Standards Institute, 1993, ANSI Z-2.1, New York.

Claims

Device for contactless determination of volumetric blood flow, containing a laser emitter, a condenser lens that focuses the laser light on the study plot perfoirmance tissue, a sensor for photoelectric registration of the scattered radiation, the device for recording and processing the signal of the photodetector, characterized in that it further comprises a flat mirror, facing the reflecting surface to the lens installed between the condenser lens in the plane of the intermediate focus of the laser beam inclined to the axis of the laser beam and having an aperture, the axis of the laser beam passes through the indicated hole in the mirror.

 

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