JP3322953B2 - Blood flow distribution measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blood flow distribution measuring device, and more particularly to a blood flow distribution measuring device which irradiates a living body with laser light and receives reflected light to measure blood flow.

[0002]

2. Description of the Related Art At present, there are two methods for measuring skin blood flow, the hydrogen clearance method and the laser blood flow meter, which are used to measure microcirculation dynamics in plastic surgery and dermatology. Have been. Above all, a laser blood flow meter irradiates the skin with laser light, receives scattered light from red blood cells circulating in the skin with an optical system such as a fiber system, and converts the scattered light intensity into an electric signal with a light receiving element. Further, the blood flow velocity and the blood flow rate of the skin are measured from the magnitude of the scattered light intensity and the time variation, and the measurement can be performed non-invasively.

[0003] Such a laser blood flow meter can be roughly classified into a configuration for performing one-point measurement and a configuration for performing two-dimensional measurement in terms of configuration. In the one-point measuring device, laser light from a laser light source is guided to a measurement site by an optical fiber, and scattered light from a living body is also guided to a light receiving element by an optical fiber to be photoelectrically converted. The blood flow rate is a value composed of the speed and volume of blood flowing through the measurement unit. However, such a laser blood flow meter analyzes the frequency and magnitude of the scattered light intensity from the living body and obtains a high value in the frequency range of the scattered light intensity. The blood flow velocity is obtained from the degree of spread to the area, the value corresponding to the blood volume is obtained from the magnitude of the signal, and the value corresponding to the blood flow is obtained from the product of the two. This configuration is based on the concept that blood flow information is derived from the entire frequency band from low frequency to high frequency of the scattered light intensity measured from the living body.

[0004]

On the other hand, a configuration as shown in FIG. 4 is known as a device for obtaining a two-dimensional blood flow distribution in a non-contact manner. In FIG. 4, reference numeral 47 denotes a perforated mirror, and a laser beam 49 from a laser light source 48 passes through a hole 50 of the perforated mirror 47, and rotates the deflecting mirror 52 in the direction of the arrow 54 or 55 via the lens 51. Is used to select a position on the living body surface 53 and irradiate.

[0005] The scattered light from the measurement point is imaged on the light receiving element 57 from the deflection mirror 52 by the lens 51 and the lens 56.

The light receiving element 57 photoelectrically converts the scattered light intensity, amplifies only an AC signal having blood flow information, and analyzes the frequency to obtain blood flow information at a measurement point. The measurement of the scattered light is performed while the deflection mirror 52 is stopped. By repeating these measurement points in a grid-like process of moving, stopping, and measuring, the planar distribution of blood flow can be measured.

In this method, the intensity of the scattered light is measured at each measurement point at a standstill, so that the intensity of the scattered light from the living body in all frequency bands can be measured. Therefore, the blood flow velocity and the blood volume can be obtained, and the two-dimensional distribution of the blood flow can be displayed, similarly to the conventional one-point laser blood flow meter.

However, in the method in which the position of the irradiation light is two-dimensionally scanned by a mechanical means such as the deflection mirror 52, unnecessary measurement waiting time is required for the following two measurements. The first is the problem of the moment of inertia of the deflecting mirror 52. When the irradiation light is moved from the previous measurement point to the next measurement point and stopped, vibration occurs due to the moment of inertia of the mirror, and it takes time to completely stop. On the other hand, while the scattered light is received, measurement cannot be performed unless the mirror is stationary.
2 needs a waiting time to completely stop.

Now, to show the importance of this waiting time,
Comparing the measurement time and the waiting time, the galvano scanner mirror, which is often used as a deflection mirror,
It is known that the time during which the vibration at the time of stopping is attenuated and settles is about several ms, and this time is set to 5 ms.

[0010] The time required for one point measurement is several hundred H in the frequency band of the scattered light intensity containing blood flow information from the living body.
z or more, and if this is 500 Hz or more, it takes about 2 ms. If the measurement frequency band is further extended to a lower frequency band, the time required for this measurement becomes longer. Therefore, the measurement time at one point is the sum of the waiting time and the measurement time, which is 7 ms. That is, 5/7 of the measurement time is a completely useless time for acquiring blood flow information.

A second problem is that electric vibration is generated at the stage of AC amplification necessary after converting scattered light from a living body into an electric signal by a photoelectric conversion element. That is, by the electric high-pass filter at the time of AC amplification,
The change in light quantity when the irradiation light moves from the measurement point to the measurement point appears as a differential waveform. The time to wait for the signal to attenuate and settle may become a useless loss time for measurement. Since this time is added to the estimation of the measurement time, the measurement becomes more inefficient in terms of time.

As a two-dimensional measuring device, Japanese Patent Publication No.
There is a blood flow device that performs blood flow measurement at multiple measurement points in a non-contact manner as described in Japanese Patent No. 28133. Fig. 5
2 shows the device described in No. 28133. In FIG. 5, a laser beam 40 from a light source (not shown) is converted into a sheet light beam by a cylindrical lens 41, and is applied to a living body surface 43 via a deflection mirror 42. The scattered light from the living body is converted to lens
4 and the scattered light is received by the light receiving element array 45 having the pixel arrangement direction in the same direction as the longitudinal direction of the sheet light.

Then, a scattered light intensity signal at time t is measured at each pixel, and the result is compared with the signal intensity at time t + Δt, and a change in this signal is set as a value corresponding to the activity of blood flow. Is displayed as a blood flow distribution in correspondence with the irradiation site.

In this state, since the measurement is performed on one line, the deflection mirror 42 is rotated as indicated by an arrow 46 instead of moving the object to be measured in order to measure the distribution of the plane, so that the measurement is performed in the longitudinal direction of the sheet light. To move the measurement line in the vertical direction. In this apparatus, since a value corresponding to the blood flow at each point can be easily obtained, there is a feature that the number of pixels constituting one blood flow distribution screen can be increased accordingly.
In this configuration, although the number of pixels is small as a light receiving element, such as a CCD element, an element that outputs a time-division output signal that is not a continuous output can be used. Blood flow images can be measured.

The apparatus described in Japanese Patent Publication No. Hei 5-28133 handles enormous information of two dimensions as compared with one-point measurement, so that blood flow information at each pixel, that is, at each measurement point can be easily obtained. Is considered.

In Japanese Patent Publication No. 5-28133, scattered light is measured twice before and after at a certain time interval at each measurement point, and the magnitude of the change in the two measurements is used to determine the blood at the measurement point. We want the "activity" of the flow.

With such a method of acquiring the change of the measurement value twice, the load on the analysis unit is greatly reduced, and thus the distribution of the blood flow state having a large number of pixels can be displayed.

However, this method is different from the one-point measuring device described above or the device shown in FIG.
It is based on the concept of measuring the state of blood flow from only certain frequency components, so that the output is a two-dimensional distribution of values expressed as "activity" of the blood flow, Unlike the one-point measurement device described above or the blood flow equivalent value output by the device of FIG. 4 based on this, it is understood that a simple measurement value is output instead of a precise measurement value. Must evaluate the measurement results.

An object of the present invention is to realize a measurement in a shorter time in an apparatus for precisely and two-dimensionally measuring a blood flow rate, similarly to the configuration in which one-point measurement is repeated as shown in FIG. The blood flow distribution is measured without wasting time due to the moment of inertia of the deflecting mirror.

As a method of shortening the vibration time of the deflecting mirror due to the moment of inertia, it is conceivable to reduce the moment of inertia of the deflecting mirror. However, in the present invention, the use of the deflecting mirror itself is limited to at least one axis scanning. A configuration that basically addresses the problem by making it unnecessary is adopted.

[0021]

In order to solve the above-mentioned problems, in the present invention, an irradiation means for expanding a laser beam and irradiating the surface of a living body to be measured with an image conjugate to an irradiation surface of the irradiation means is provided. A light receiving optical system configured to form an image of a point on a light receiving surface and sharing at least a part of an optical element of the optical system of the irradiating means, and an irradiation optical axis and a light receiving optical axis in common Means for scanning around one axis above, a light receiving element array in which a plurality of light receiving elements are arranged on the light receiving surface, that is, an image plane conjugate to the irradiation surface, and amplifying a signal of each light receiving element row by AC. Means, means for independently selecting an output signal from each of the AC amplifying means, and analysis means for measuring blood flow information at multiple points of a living body based on a time-series signal of the selected light-receiving element output signal. Configuration was adopted.

[0022]

According to the above arrangement, at least one axis of the two-dimensional scanning can be electrically performed by selecting the output signal of each element of the light receiving element array, so that the measurement time can be reduced. it can.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

In the present invention, instead of using a two-axis deflecting mirror in the configuration of FIG. 4, a light receiving element array is provided at a position conjugate to the measurement surface, and two-dimensional scanning is performed using only at least one axis of the deflecting mirror. Perform

At this time, similarly to the apparatus shown in FIG. 5, the luminous flux of the irradiation light is a sheet luminous flux or a plane luminous flux, and the measurement point is moved by sequentially designating the elements in the light receiving element array for obtaining the measurement signal. However, as will be described later, unlike the apparatus of FIG. 5, a light receiving element array for photoelectrically converting scattered light from a living body is arranged at a position optically conjugate to a measurement object. If not used, the above-mentioned selection of the light receiving element cannot be established.

Unlike the configuration using the CCD shown in FIG. 5, the signals from the respective light receiving elements are amplified in parallel by independent signal processing systems so that the output of a desired element can be selected at a desired timing. .

Unlike the idea of mechanically moving the irradiation light as shown in FIG. 4 with such a configuration, attention is focused on by electrically switching pixel signals from each element of the light receiving element array. Selects the signal of the element and measures the two-dimensional distribution. It can measure the intensity of scattered light from the living body in all frequency bands at each measurement point, and wastes measurement time by moving the irradiation light mechanically. Can be eliminated.

This apparatus irradiates an expanded laser beam to an object and measures scattered light from a living body with a light receiving element composed of a plurality of pixels. The signal from each light receiving element can be independently amplified and processed, and the signal By designating the element from which the signal is to be extracted, a signal at a specific position can be extracted and analyzed. Further, the intensity of the scattered light from the light receiving element array can be measured in parallel, and the measurement can be performed in a shorter time.

FIGS. 1 and 2 show a specific configuration. The laser light from the laser light source 1 is converted into a sheet light flux 3 by the lens 2. Then, the light is once collected by the lens 4 and reflected by the mirror 5. Since the mirror 5 is located at the focal point of the sheet light beam 3, the light beam reflected by the mirror 5 becomes the sheet light beam again.

The light beam 3 is changed in direction while being spread by the deflection mirror 6, and then is converted into a sheet-like parallel light by the lens 7 having the focal point of the lens 4 as the focal position, and is irradiated on the living body surface 8. .

The scattered light 9 from the living body is condensed by the lens 7 to become parallel light, reflected by the deflecting mirror 6, passes through the imaging lens 10, and forms an image on the photodiode array 11.

This photodiode array 11 has a CC
Unlike D, a plurality of photodiodes 13a to 13c
(FIG. 2) are arranged on a line.

Unlike the configuration shown in FIG. 5, the light receiving surface 12 and the living body surface 8 on the photodiode array are optically conjugated by the lenses 7 and 10.

The lens 7 also exists as a component of the irradiation optical system, and the lens 7 is a collimator as the irradiation optical system. Photodiode array 11
Are installed such that the direction in which the photodiodes 13 a to 13 c are arranged in one line is the same as the longitudinal direction of the sheet light beam 3.

FIG. 2 shows a signal processing system, in which the photodiodes 13a to 13a of the photodiode array 11 are arranged.
The photocurrent signals photoelectrically converted for each of the photodiodes 3c are converted into current-to-voltage conversion circuits 14a to 14c provided independently for each photodiode.
After being converted to a voltage at 14c, the AC amplifiers 15a to 15c
After being amplified by c, the signal is switched by the analog multiplexer 16 so that a signal for each measurement point can be selected. The low-frequency cutoff frequency of each of the AC amplifiers 15a to 15c is about 100 Hz, and has a purpose of removing a DC signal other than blood flow information from a living body, for example, a DC component due to direct return light from the skin surface. Here, it is important that the AC amplifiers 15a to 15c are provided after the photodiodes 13a to 13c of the photodiode array 11, not after the analog multiplexer 16.

In the actual blood flow distribution measurement, there may be a portion where the scattering characteristics are significantly different in the plane of the measurement range. For example, in the measurement of the tip of the hand, the scattered light from a ring attached to the finger returns a stronger return light than the scattered light from the skin, and the base on which the hand is placed is placed between the fingers. Is returned, but if the reflectance of the table is low,
Light hardly returns. As described above, when a DC signal from a photodiode in a certain area is stronger or weaker than an adjacent photodiode, if an AC amplifier is provided after the analog multiplexer, a difference between DC signals of the photodiodes 13a to 13c can be obtained. May be input to the AC amplifier as a step-like signal, and a differential waveform may appear from the output of the AC amplifier. However, in the configuration of FIG. It is not necessary to be affected by the extreme level difference of the signal.

The scattered light intensity signal selected by the analog multiplexer 16 is converted into a digital value by an AD converter 17 and then a power spectrum is obtained by an FFT circuit 18.
The microcomputer 19 calculates a blood flow corresponding to the photodiode 13a from the power spectrum.

The photodiodes 13a to 13c are sequentially selected by the analog multiplexer 16 to measure one line. According to the above-described method, in the measurement of one line, useless waiting time other than the measurement is not required, and the measurement can be performed in a short time.

When this is extended two-dimensionally, the deflecting mirror 6 is rotated to move the measuring point in a direction perpendicular to the longitudinal direction of the sheet light beam 3. Here, the deflecting mirror used is sufficient to be simply used for the purpose of moving the measurement position, similarly to the prior art shown in FIG. 5, and the deflection mirror shown in FIG. It is not necessary to use an expensive one such as the deflection mirror 52.

Here, the number of measurement points in this embodiment is 32 × 3.
Estimate the measurement time when two points are assumed. The measurement time at each measurement point is set to 2 ms as in the case of the related art. In practice, the analog multiplexer 16 also has time to complete the switching, which is on the order of a few μs and can be ignored.

Assuming that the time required for the deflection mirror 6 to completely stop is 5 ms as described in the section of the prior art, the total measurement time is (2 ms × 32 + 5 ms) × 32 = 2.2 s. Now, the total measurement time in the configuration of FIG. 4 for performing a measurement equivalent to the present invention is (2 ms + 5 ms) × 32 × 32 = 7
Therefore, in the present invention, the measurement time is reduced to about 1/3.

As a method of shortening the time, although not shown, signals from two elements of the photodiode array are simultaneously analyzed by a multiplexer and an A / D converter in which two elements are arranged in parallel. By arranging the diode array in the upper and lower stages, the illuminating sheet luminous flux is spread so as to illuminate the two stages, and the analysis is performed at the same time to further reduce the half.
It is also possible to shorten the time.

As described above, wasteful time due to the moment of inertia of the deflecting mirror can be omitted, and the blood flow distribution can be accurately and two-dimensionally measured in a shorter time.

The basic embodiment has been described above.
An embodiment that further considers safety will be described. In the present invention, the spread laser light is applied, and the intensity of the scattered light from the living body is received by a light receiving element array including a plurality of light receiving elements. Then, a scattered light intensity signal from each light receiving element is electrically switched to select a measurement point.

In this configuration, while one of the pixels is electrically selected, the measuring point corresponding to the other pixel is also irradiated with the laser beam. Is irradiated only, and the irradiation energy of the laser light irradiated during this period does not contribute to the measurement. When irradiating a living body with a laser beam, it is desirable that the energy of the laser beam irradiated on the living body be small from the viewpoint of safety.

FIG. 3 shows a configuration in which the energy of the laser beam applied to the living body is reduced. Here, the measurement for one line is shown. The light beam 21 from the laser light source 20 is turned into a sheet light beam by the lens 22. Next, the light is condensed by the lens 23, is totally reflected by the prism 24, and changes its direction by 90 degrees, and further changes its direction by 90 degrees by the mirror 25.

Next, the measurement area 28 of the living body surface 27 is irradiated in a sheet shape through the lens 26. The light beam 33 from the other laser light source 32 becomes a sheet light beam by the lens 34. Next, the light is condensed by the lens 35, and the prism 2
4, the light is totally reflected and turned 90 degrees, and the mirror 25 turns the light 90 degrees further.

Next, the measurement area 36 on the living body surface 27 is irradiated via the lens 26. The scattered light 29 from the living body is photoelectrically converted by the photodiode array 31 at the image forming position via the lens 26 and the lens 30.

The signal from the photodiode array 31 is analyzed by a current-voltage conversion circuit (not shown), an AC amplifier, an analog multiplexer, an FFT circuit and a microcomputer 37 in the same manner as in the embodiment of FIG. The blood flow is measured by the microcomputer 37 while measuring the measurement points corresponding to the range of the measurement area 28.
, Only the light source 20 is driven by the drive circuit 38, and only the light source 32 outputs the laser beam 33 by the drive circuit 39 while the measurement area 36 is being measured.

With such a configuration, the irradiation time at each measurement point in one measurement of one line is halved compared to the case of irradiating the whole with one light beam, and the irradiation energy to the living body can be suppressed low. Can be.

[0051]

As is apparent from the above description, according to the present invention, an irradiation means for expanding a laser beam and irradiating the surface of a living body to be measured, and an image of an image point conjugate to an irradiation surface of the irradiation means are received. A light receiving optical system that is configured to form an image on a surface and shares at least a part of the optical element of the optical system of the irradiating means; Means for scanning as a center, the light-receiving surface, that is, a light-receiving element array in which a plurality of light-receiving elements are arranged on an image plane conjugate to the irradiation surface, and means for AC-amplifying a signal of each light-receiving element array; It employs a configuration including means for independently selecting an output signal from each AC amplification means, and analysis means for measuring blood flow information at a number of points in a living body based on a time-series signal of the selected light-receiving element output signal. The two-dimensional scanning At least for one axis, the measurement can be performed electrically by selecting the output signal of each element in the light receiving element array, so that the measurement time can be significantly reduced and the blood flow distribution can be precisely two-dimensionally measured. An excellent blood flow measuring device can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an optical system of a blood flow distribution measuring device employing the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a measuring circuit of the blood flow distribution measuring device employing the present invention.

FIG. 3 is an explanatory diagram showing a different configuration of a blood flow distribution measuring device employing the present invention.

FIG. 4 is an explanatory diagram showing a configuration of a conventional two-dimensional blood flow measuring device.

FIG. 5 is an explanatory diagram showing a different configuration of a conventional two-dimensional blood flow measuring device.

[Explanation of symbols]

1, 48, 20, 32, 32 Laser light source 2, 4, 7, 10, 22, 23, 26, 30, 34 Lens 35, 44, 44, 44, 51, 56 Lens 3, 3, 21 Sheet luminous flux 5, 25 Mirror 6, 42, 52 Deflection mirror 8, 27, 43, 53 Biological surface 9, 29 Scattered light 11, 31 Photodiode array 12 Light receiving surface 13a to 13c Photodiode 16 Analog multiplexer 18 FFT circuit 19, 37 Microcomputer 24 Prism Reference Signs List 33 Laser beam 36 Measurement area 38, 39 Drive circuit 40 Laser beam 41 Cylindrical lens 45 Light receiving element array 47 Perforated mirror 49 Laser beam 57 Light receiving element

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-28348 (JP, A) JP-A-3-32641 (JP, A) JP-A-55-75668 (JP, A) JP-A-1- 256924 (JP, A) JP 5-28133 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/026

Claims (4)

(57) [Claims] An irradiating means for expanding a laser beam to irradiate a living body surface to be measured; and an image of an image point conjugate to an irradiating surface of the irradiating means is formed on a light receiving surface. A light receiving optical system that shares some optical elements of the optical system of the irradiating unit, a unit that scans the living body surface around one axis in common with the irradiating optical axis and the receiving optical axis, and the light receiving surface, that is, A light-receiving element array in which a plurality of light-receiving elements are arranged on an image plane conjugate to the irradiation surface; a means for AC-amplifying a signal of each light-receiving element row; and an output signal independently from each of the AC-amplifying means. A blood flow distribution measuring device comprising: selecting means; and analyzing means for measuring blood flow information at a number of points in a living body based on the time-series signal of the selected light receiving element output signal. 2. The blood flow distribution measuring device according to claim 1, wherein the direction of the spread of the irradiation laser light on the irradiation surface is the same as the direction of the arrangement of the light receiving element rows. 3. The light receiving optical system is constituted by a coaxial spherical optical system including two optical elements, and among the two optical elements, an optical element shared with an optical system of an irradiation unit transmits the irradiation light. The blood flow distribution measuring device according to claim 1, wherein the light is emitted as a parallel light beam. 4. A luminous flux of the irradiation laser light is selected such that a plurality of luminous fluxes of the irradiation laser light are provided, and a light beam of the irradiation laser light is selected so as to selectively irradiate a subject surface corresponding to at least a light receiving element selected by the signal selection means. The blood flow distribution measuring device according to claim 1, wherein the total irradiation energy to the blood flow is reduced.