DE4414679B4 - Method for determining the degree of oxygenation of an object - Google Patents

Abstract

Method for determining the degree of oxygenation of an object (18) which contains at least two substances which absorb light differently depending on the wavelength in which the concentrations of the two substances are measured, the object (18) containing the two substances being detected by a light beam ( 14) having at least two different wavelengths (λ ₁ , λ ₂ ), which are respectively tuned to a wavelength range or a wavelength for which the at least two substances have an absorption, is scanned in a two-dimensional grid by means of a beam deflection device (12), characterized in that an object (18) containing the two substances is provided for measurement, in which the first of the two substances is an oxidized form of the second substance and the second of the two substances is a reduced form of the first substance, that of the signals generated during the scanning at two adjacent Stell s s and ds + s in the object (18) the local absorption changes at the points s, the local concentration changes at the point s ...

Description

The The invention relates to a method for determining the degree of oxygenation an object according to the Preamble of claim 1 specified characteristics.

In many areas of medical diagnostics, it is important to quantify the degree of tissue oxygenation. Particularly in ophthalmology, there is a great clinical need for a spatially and temporally resolved measurement of oxygen metabolism substances in the retina. The three cell layers of the retina are known to be supplied by two independent blood vessel systems with oxygen, the photoreceptors are supplied by the choroid and the bipolar and Amakrinzellen and the nerve cells of retinal vessels. It is clinically necessary to determine the degree of oxygenation of the retina in the various layers, whereby, in particular, the oxidation states of hemoglobin and cytochrome aa _{3 represent} a measure of the quality of the oxygen supply in the tissue.

In the not previously published German patent application DE 43 22 043.6-52 a method is described for measuring the flow rate of a liquid, in particular of the blood, by determining a frequency shift of a laser beam reflected in the liquid according to the optical Doppler effect. According to this method, a two-dimensional raster-scan is performed by means of the laser beam and a number of N measurements are formed at each sampling point corresponding to the reflected light, where N is an integer equal to or greater than 2. From the temporal variation of the thus measured intensity of the reflected light at the respective sampling point, the Doppler shift is calculated and from this the flow rate of the liquid at each point of the grid is determined. The patent application further describes a device for carrying out the method.

In the document EP 26 046 A1 For example, a method and apparatus for quantitative monitoring of gaseous pollutants, for example above a chemical factory, are described. Two infrared lasers emit a sample light beam and a reference light beam. These are modulated with different frequencies or phases and combined into a light beam that scans two-dimensionally an area to be monitored. A portion of the light is backscattered or reflected so that it returns to the apparatus and is detected by isolating the modulated portions of the light by means of frequency or phase selective amplifiers. The extinction ratio of sample light beam and reference light beam serves as a measure of the concentration. In this way, the concentrations of one or more gases can be measured simultaneously when the laser wavelengths of the sample light beams are tuned to absorption wavelengths of the gases.

In the document WO 93/15391 A1 a structure and a method for infrared laser absorption spectroscopy by means of radio frequency modulation in a sample gas cell compared to a calibrated reference cell is shown. To detect the presence of several different isotopes of an element, laser illumination is performed at wavelengths characteristic of the isotope absorption. In various embodiments, a tunable laser diode and, on the other hand, two laser diodes which emit different wavelengths are used on the one hand.

The document DE 26 078 169 relates to a method for determining the vertical concentration profile of contaminants or natural components in the atmosphere. Two or more locating laser beams in a missile are periodically deflected perpendicular to the direction of flight, so that three-dimensional concentration profiles can be detected. A comparative absorption measurement is carried out, whereby pollutants at a certain position are detected by the different positioning laser beams at different times, so that the height of the position can be determined. Each locating laser beam has a laser beam of different wavelengths, one of which is selectively absorbed by one type of gas, while the other receives no absorption as a reference. The detection takes place by means of an optical heterodyne measurement, wherein the laser primary light serves as a local oscillator.

Hemoglobin and cytochrome aa ₃ show an absorption coefficient dependent on the state of oxidation in the near infrared light. Therefore, it is known that the concentration of oxygenated hemoglobin and oxidized cytochrome aa ₃ can be determined with infrared light. In the tissue, infrared light is strongly scattered but only very slightly absorbed, with the scattering coefficient in the fatty tissue being in the order of 400 cm ^-1 . The determination of the concentration C of a substance of interest can be based on Lambert-Beer's law: I = I 0 e - [.mu.C + μ a + μ s ] t (1)

In this formula, t represents the mean optical path length of the photons, μ the molar absorption coefficient of the substance under investigation, μa the total absorption coefficient of all other substances present, μ _a , the scattering coefficient, I ₀ the irradiated light intensity and I after absorption and scattered light intensity. It is irrelevant whether the measurement is carried out in transmitted light or reflected light.

Assuming that the total absorption coefficient μ and the scattering coefficient μ _{s are} spatially constant for an extended object, the result for a measured light intensity in a specific location s (x, y, z) of the object is: I = I 0 e - [.mu.C (s) + μ a + μ s ] t (2)

By measuring I at two adjacent locations s and s + ds, the quantity can be calculated from equation (2) dA (s) = -In [I (ds + s) / I (s)] = μdC (s) t (3) With dC (s) = C (s + ds) -C (s) determine. In this case, In is the natural logarithm, dA is the absorption change and dC (s) is the local change of the concentration C. Thus, with known absorption coefficient μ by measuring the absorption change at adjacent points dA (s) according to equation (3) determine the corresponding concentration change dC (s).

Hemoglobin in oxidized form - hereinafter referred to as Hb0 ₂ - preferably absorbs light of wavelength λ ₁ = 850 nm, while hemoglobin in reduced form - hereinafter called HbR - absorbs light preferably with a local maximum at about λ ₂ = 720 nm. The same applies to the chromophores cytochrome aa ₃ , which absorb in reduced form preferably at short wavelengths λ ₁ <700 nm and in oxidized form preferably at longer wavelengths of about λ ₂ = 880 nm. Such substances absorb light differently depending on the wavelength, whereby maximum absorption is given for at least one wavelength range or one wavelength.

Of these, The invention is based on the object, a method to propose a spatially and temporally resolved Measurement of the concentrations of substances reach, which accordingly the oxygenation have different absorption bands. Furthermore, especially the pulsatile nature of oxygen metabolism locally and temporally resolved can be represented. The method and should give a high accuracy.

The solution This task is performed according to the characterizing Features of claim 1.

The method according to the invention belongs to scanning laser pulse oximetry and comprises the combination of measuring the concentrations of at least two substances which have different absorption bands depending on the degree of oxygenation, ie for different wavelengths or wavelength ranges, a maximum absorption of the filling light. Thus, this method allows in particular the measurement of the concentration of oxidized or reduced hemoglobin or optionally of the chromophores cytochrome aa ₃ by absorption measurement and the known laser scanning technique, which can be represented by specifying the scanning of the pulsatile nature of the oxygen metabolism dissolved in time and space. According to the invention, the object to be examined is scanned in a grid-like manner by means of a laser scanning system and simultaneously with two laser sources of different wavelengths. The method can be used for incident light, wherein the incident light beam is reflected, as well as for devices using the transmitted light principle.

The different wavelengths of the two laser sources are specified according to the substances to be examined, the wavelengths being tuned in particular to the maximum of the absorption of the substances to be investigated. Thus, to measure the concentrations of hemoglobin, the wavelengths of substantially 720 nm and 850 nm are given, while for measuring the concentrations of cytochrome aa _3, the wavelengths of preferably 700 nm and 880 nm are given. Appropriately, a virtually simultaneous scanning of the substances takes place. The local derivatives of the concentration curves of the two substances are detected and after local integration, the local concentrations of the two substances, in particular of oxidized and reduced hemoglobin or the chromophores cytochrome aa ₃ itself found. The relative values of the concentration gradients and concentrations are determined, especially since the optical path lengths of the photons are not immediately known, above all because of the strong scattering. In addition, it should be noted that the photons do not propagate ideally straightforward due to the large scattering, whereby a strong attenuation of the measurement signal and a limitation of the local resolution is due, but for diagnostic statements, a qualitative determination of the concentrations is sufficient.

In contrast to all previously known methods, the measurement according to the invention of the concentrations of substances which have a dependent on the wavelength of the incident light and independent of each other absorption behavior, in particular of HbO ₂ and HbR and cytochrome aa ₃ in oxidized and reduced form simultaneously three-dimensional spatial resolution, time-resolved, non-invasive and fast. In ophthalmology, no enlargement of the pupil of the examined eye is required. The method enables the temporally and three-dimensionally spatially resolved measurement of the concentrations of oxidized and reduced hemoglobin or chromophores cytochrome aa ₃ , wherein, in combination with the measurement of the flow rate, the spatially resolved measurement of the oxygen consumption is carried out.

The uses of the method according to the invention in ophthalmology extend to all diseases of the retina and the choroid, in which there is circulatory or metabolically caused disturbances of the oxygen supply. Typical applications are studies on the oxygen situation of the retina and the choroid in diabetic retinopathy, in arterial and venous occlusions, in glaucoma diseases and in macular degeneration. For medical applications outside the field of ophthalmology, in particular the spatially and temporally resolved determination of the concentration of oxidized and reduced hemoglobin or cytochrome aa _{3 of} the skin and other organs such as the heart, liver, intestine and brain in intraoperative use referenced.

Further special embodiments and advantages are in the subclaims and the following description of two embodiments. The invention will be explained in more detail with reference to the drawings. It demonstrate:

1 a schematic representation of an apparatus for performing the method,

2 a schematic diagram of another embodiment of the device.

1 shows a schematic diagram of two laser sources 1 . 2 , which each light rays 3 . 4 emit at different wavelengths λ ₁ and λ ₂ . For example, the wavelength λ ₁ = 720 nm and the wavelength λ _2, for example 850 nm. By means of a suitable optical element 6 become the two laser beams 3 . 4 to a single beam of light 8th united. The optical element 6 can be designed as a semitransparent mirror. Preferably, the optical element 6 is formed as a mirror with wavelength-dependent reflection such that it reflects light having a wavelength greater than a predetermined wavelength of, for example, 780 nm, but transmits light of a wavelength below the predetermined wavelength unaffected. The united ray of light 8th passes through an optical element to be explained below 10 , which serves to separate the returning light beam, to a beam deflection device 12 ,

This beam deflection device 12 can in particular according to the from DE 41 03 298 C2 be formed prior art device. The beam deflection device 12 consists generally of two periodically rotatable mirrors, which the incident light beam, here the common light beam 8th , along two mutually orthogonal axes deflect. In this case, one of the two mirrors oscillates rapidly and directs the light beam in a line, while the second mirror oscillates comparatively slowly and deflects the light beam in a direction perpendicular to the line direction of the first mirror. This leads to a grid-shaped two-dimensional deflection of the common light beam 4 , The the beam deflection device 12 leaving, now directionally variable light beam 14 is by means of suitable lenses 16 on the object to be examined 18 , z. As the retina of the eye, focused and scans this two-dimensional and grid-shaped.

The object 18 Scattered and reflected light sets the same optical path through the lens system 16 and the beam deflecting device 12 back and is by means of the already mentioned optical element 10 from the illuminating, common light beam 8th separated. The thus separated light beam 20 then becomes an optical element 22 directed, which is designed to separate the returning light beam according to different wavelengths. This is the optical element 22 preferably formed as a mirror, which reflects light of a wavelength greater than, for example, 780 nm, but leaves light with a wavelength of less than, for example, 780 nm unaffected. The reflected and scattered by the object light beam is thus in two light beams 23 . 24 divided according to the wavelengths λ ₁ = 720 nm and λ ₂ = 850 nm. The two separate reflected light beams 23 . 24 be on two separate detectors 26 . 27 steered, which measure the respective light intensity.

By digitizing these detector signals, two two-dimensional images I (s, λ ₁ ) and I (s, λ ₂ ) result simultaneously according to the two wavelengths λ ₁ and λ ₂ . From these two two-dimensional images, the absorption changes dA (s, λ ₁ ) and dA (s, λ ₂ ) are determined in accordance with the aforementioned equation (3). From the absorption changes, the local concentration changes dC ₁ (s) and dC ₂ (s) of the oxidized and reduced hemoglobin or cytochrome aa _{3 are then} calculated. The local concentrations C ₁ (s) and C ₂ (s) of the two substances investigated are determined from the obtained local derivatives of the concentration curves of the two substances for suitable, in particular local integration certainly.

In a particular embodiment of the invention, a plurality of such image pairs I (s, λ ₁ ) and I (s, λ ₂ ) are successively recorded for a predetermined period of time, preferably at least 1 second in a fast sequence, so that, for example, 20 image pairs per second be available. Furthermore, a simultaneous determination of the electrocardiogram takes place during the recording of said images, so that a temporal assignment of the substance concentrations of each retinal point to the heartbeat takes place within the scope of this invention.

Further will be done in a convenient way digitizing the images in such a way that electronically already part of the explained Evaluations carried out becomes. So it is expedient the explained local absorbance change done electronically and before digitization, creating a considerable shortening the time required to evaluate the data is achieved.

2 shows an alternative embodiment, with respect to the matching components to the description of 1 referenced. The object 18 reflected and scattered light beam 20 becomes after separation from the illuminating light beam ( 8th ) by means of the optical element 10 directly to a single detector 28 directed. In addition, there is a modulation of the intensities of the two laser sources 1 . 2 such that during the time of scanning for a line only one of the two laser sources 1 . 2 is turned on while the second one is off. Conversely, for the duration of the next line, the second laser is turned on and the first laser is turned off. This alternating switching on and off of the two lasers 1 . 2 will continue until the entire picture is taken. By corresponding digitization of the detector signals is thus also obtained two two-dimensional images I (s, λ ₁ ) and I (s, λ ₂ ), from which according to the above, the local concentrations C ₁ (s) and C ₂ (s) of the two substances be determined. To capture a two-dimensional image is compared with the basis of 1 described method requires twice the time. On the other hand, the alternative proposed method has the advantage that only a single detector 28 and a single digitizing device are required.

It should be noted that even with the basis of 2 explained method, several images, as already explained, for a period of at least 1 sec. In a rapid sequence can be successively recorded and also by the simultaneous determination of the electrocardiogram during the recording also the temporal allocation of the oxygen concentrations of each retinal point to the heartbeat can take place.

In a particular embodiment of the invention, the combination of the above-explained scanning laser pulse oximetry with the method of scanning laser Doppler velocimetry. Here, the laser scanning system according to one of the basis of the 1 or 2 explained method designed and thus there is a simultaneous measurement of the two wavelengths or the images of the two wavelengths are recorded in alternating scan lines. In addition, the scanning is preferably carried out according to the method described in the cited patent application P 43 22 043.6-52 method or of the device described therein. In this case, not several two-dimensional images are successively recorded, but it is scanned each line of an image in rapid succession several times, at least twice, and only then is moved to the next line. Thus, once again two two-dimensional images I (s, λ ₁ ) and I (s, λ ₂ ) are generated, but each individual point of these images is scanned several times during the recording in a very fast sequence. The consequences of the N measured values, where an integer equal to or greater than 2, are stored for each individual measuring point. By analyzing the temporal variation in the sequence of the measured intensity of the reflected light at each point, the flow velocity of the blood at each measuring point is determined on the basis of the optical Doppler effect, as described in P 43 22 043. The inventive combination of the measurement of the flow rate with the measurement of the concentrations of the two substances, in particular oxidized or reduced hemoglobin or chromophores cytochrome aa ₃ , allows completely new statements. For example, by multiplying the flow rate by the local concentration values, the oxygen consumption can be measured in a locally resolved manner.

at All the above-described realizations can be by appropriate Preparation of the images the two-dimensionally resolved pulsation retinal oxygenation, combined with flow rate in the third process, as a movie pose. From this presentation can derived further quantitative parameters such as pulse wave velocity become.

In any of the above-described implementations, the laser scanning system may be preferably designed as a confocal optical system. Here, in front of the detector for measuring the intensity of the reflected light, there is a very small diaphragm whose position is optically conjugate to the focal plane of the scanning light beam. This ensures that light that reflects from a narrow environment around the focal plane and thus at the Focusing the small aperture is able to pass this aperture almost unhindered and can be detected, but that such light, which is reflected from a position at a distance from the focal plane and therefore not focused on the small aperture, is effectively suppressed. This results in an additional spatial resolution in the depth, so that the measurements can be made selectively in individual layers of the object. By suitable adjustment of the focal plane of the scanning light beam, the oxygen situation of the retina and the choroid can thus be measured and considered separately from one another.

The proposed method of laser scanning pulse oximetry is not limited to the substances mentioned here hemoglobin and cytochrome aa ₃ . It can be used in the same way for the measurement of the concentrations of all substances which have different absorption bands, in particular according to their degree of oxygenation, ie have different absorption levels for different wavelengths or wavelength ranges.

1

first laser source with wavelength λ ₁

2

second laser source with wavelength λ ₂

3

Laser beam, wavelength λ ₁

4

Laser beam, wavelength λ ₂

6

optical element for the union of 3 and 4

8th

united beam of light

10

optical Element for separating the back and forth light beam

12

Beam deflection device

14

direction variable beam of light

16

lens system

18

to examining object

20

from the object 18 reflected and scattered light beam

22

optical element for the separation of 20

23

Light beam, wavelength λ ₁

24

Light beam, wavelength λ ₂

26-28

detector

Claims (41)

Method for determining the degree of oxygenation of an object ( 18 ) containing at least two substances that absorb light differently depending on the wavelength in which the concentrations of the two substances are measured, wherein the object containing the two substances ( 18 ) of a light beam ( 14 ) having at least two different wavelengths (λ ₁ , λ ₂ ), which are each tuned to a wavelength range or a wavelength for which the at least two substances have an absorption, two-dimensionally in a grid shape by means of a beam deflection device ( 12 ) is scanned, characterized in that an object containing the two substances ( 18 ) is provided for measurement, in which the first of the two substances is an oxidized form of the second substance and the second of the two substances is a reduced form of the first substance, that of the signals generated at the sampling at two adjacent locations s and ds + s in the object ( 18 ) the local absorption changes at the points s, the local concentration changes at the point s from the local absorption changes at the point (s) and the local concentrations at the point s from the local concentration changes at the point s of the two substances are determined; the local degree of oxygenation of the object based on the local concentration of the two substances ( 18 ) for a plurality of places s in the object ( 18 ) is determined from the signals at two adjacent locations s and ds + s. Method according to claim 1, characterized in that that the first substance is oxidized hemoglobin and the second substance reduced hemoglobin is. A method according to claim 1, characterized in that the first substance is oxidized chromophore cytochrome aa ₃ and the second substance is chromophore reduced cytochrome aa ₃ . A method according to claim 1, 2 or 3, characterized in that the two substances at the two wavelengths (λ ₁ , λ ₂ ) have the highest possible absorption. Method according to one of claims 1 to 4, characterized that the two substances are substances of oxygen metabolism. Method according to one of claims 1 to 5, characterized in that the two wavelengths (λ ₁ , λ ₂ ) are in the near infrared. Method according to one of claims 1 to 6, characterized in that the substances are scanned simultaneously, that by digitizing the signals corresponding to the different wavelengths (λ ₁ , λ ₂ ) at least two two-dimensional images are obtained depending on the location and the wavelength and / / or the local derivatives of the concentration profiles of the substances are detected, and that after local integration, the local concentrations of the at least two substances are determined. Method according to one of claims 1 to 7, characterized in that laser beams ( 3 . 4 ) of at least two laser sources ( 1 . 2 ) to a Light beam ( 8th ), which is connected via the common beam deflection device ( 12 ) for scanning the object ( 18 ) is provided. Method according to one of claims 1 to 8, characterized in that the common light beam ( 8th ), which contains light with the at least two wavelengths (λ ₁ , λ ₂ ), at the same time the object ( 18 ) and that of the object ( 18 ) emitted scattered light beam ( 20 ) after separation according to the wavelengths ( 21 . 22 ) at least two detectors ( 26 . 27 ) is supplied. Method according to one of claims 1 to 9, characterized in that the object ( 18 ) emitted and scattered light beam ( 20 ) after separation from the illuminating, common light beam ( 8th ) directly onto a single detector ( 28 ), wherein the intensities of the at least two laser sources ( 1 . 2 ) are modulated such that the scanning of the object line by line alternately with the light of one of the laser sources ( 1 . 2 ) is carried out. Method according to one of claims 1 to 10, characterized that for a predetermined time in rapid succession, the concentration changes be detected and that by simultaneous determination of a temporal Assignment of the concentrations of substances to the heartbeat is performed. Method according to claim 11, characterized in that the time duration is at least one second and / or the simultaneous one Determination by means of electrocardiogram takes place and / or that the detection the concentration changes taking into account at least two two-dimensional images the sampling points and the wavelengths he follows. Method according to one of claims 1 to 12, characterized that the substances in a liquid are included, and that a measurement of the flow rate of the liquid by determining a frequency shift of one of the in the liquid reflected laser beam according to the Doppler effect takes place, each line of an image in rapid succession at least is sampled twice and only then in the same way the next lines be sampled at each sampling point corresponding to the reflected Light a number N measured values is formed, where N is a whole Number is equal to or greater than 2, and that from the temporal variation of the thus measured intensity of the reflected Light at each sampling point, the Doppler shift calculated and from this the flow speed is determined at each point of the grid. Method according to one of claims 1 to 13, characterized in that the scanning in at least two levels in different depths of the object ( 18 ) is carried out. Method according to claim 14, characterized in that that a laser scanning system with confocal arrangement is used and wherein the sampling and measurement in at least two different Focal planes performed becomes. A method according to claim 15, characterized in that a measurement in different areas of the object ( 18 ) is performed by the choice of the wavelength of the laser light. A method according to claim 16, characterized in that for the measurement in different areas of the object ( 18 ) two different laser sources ( 1 . 2 ) are used. Method according to one of claims 13 to 16, characterized that the intensity during the the scanning of reflected light measured at fixed time intervals becomes. Method according to claim 18, characterized that the scanning is along a line, along the sampled line recorded and stored a number of M readings which reflects the reflected light intensities at M individual points along the sampled line, the sample being along said line N times in and that following for at least another line along the object repeats this scan becomes. Method according to claim 19, characterized that the sampling is carried out at equal time intervals. Method according to one of claims 13 to 20, characterized in that the matrix of M × N measured values acquired per scanned line, containing N lines of locally resolved and M columns of the time resolved reflected light intensity of a Spectral analysis are subjected and from this the frequency distribution the temporal variation of the reflected light intensity determined and that from the thus determined frequency distribution the Velocity distribution of the moving parts of the liquid is determined at the respective point of the object. Method according to claim 21, characterized that for the spectral analysis is performed a discrete Fourier transform. Method according to one of claims 13 to 22, characterized in that according to the calculation At each point of the scanned two-dimensional field of the object, a matrix of MxL velocities is determined at the typical flow rate which reflects the flow rate at a localized resolution. Method according to claim 23, characterized that the matrix of M × L Speeds in a picture is made visible. Method according to one of claims 1 to 24, characterized that the capture of readings synchronizes to the heartbeat becomes. Method according to one of claims 1 to 25, characterized in that one of the object ( 18 ) returning light beam ( 20 ) from the light beam ( 8th ) by means of an optical element ( 10 ), which between one the laser beams ( 3 . 4 ) uniting optical element ( 6 ) and the beam deflection device ( 12 ) is separated, and that the separate light beam either via an optical element ( 22 ), which performs the separation according to the wavelengths (λ ₁ , λ ₂ ), two detectors ( 26 . 27 ) or a common detector ( 28 ) is supplied. Method according to claim 26, characterized in that the optical element ( 6 . 10 ) is designed as a semitransparent mirror or a mirror with wavelength dependent reflection such that it reflects light having a wavelength greater than a predetermined wavelength, but allows light of a wavelength below this predetermined wavelength to pass through substantially unaffected. A method according to claim 27, characterized in that the predetermined wavelength to one between the wavelengths (λ ₁ , λ ₂ ) of the two laser sources ( 1 . 2 ) value is set. Method according to one of claims 1 to 25, characterized in that the laser beam through the beam deflection device ( 12 ) is periodically deflected in two mutually perpendicular directions by a control and control electronics for performing the scanning and for determining the measured values combined laser scanning system and that the analysis of the measured values obtained by means of a computer. A method according to claim 29, characterized in that the focal plane of the scanning laser beam by means of a lens system ( 16 ) for imaging the scanning laser beam on the object to be examined ( 18 ) is adjusted and that the beam with two periodically and synchronously moving mirrors for deflecting the illuminating laser beam is deflected in two dimensions orthogonal to the optical axis. Method according to claim 30, characterized in that that the second mirror oscillates at high frequency (f) and the Laser beam moved along a line of the object being examined, the scan being along the respective line of the object N times, where N is an integer equal to or greater than 2, along the respective line for each of the M points N × the measurement at equal intervals of 1 / f. Method according to one of claims 30 or 31, characterized that the center of the second mirror in the middle of the distance is arranged between the first mirror and its axis of rotation and that the rays from the first mirror go directly to the second mirror and vice versa and / or that the first mirror via an arm with his belonging Rotary axis is coupled, wherein the length of the arm is substantially equal as big as the said distance is. Method according to one of Claims 29 to 32, characterized that M × N Readings are digitized and stored in the computer, where a matrix of M × N Measured values is stored, whose N lines are resolved locally and their M columns temporally resolved the reflected light intensity at the individual points. A method according to claim 33, characterized in that after the storage of the location-time matrix for the line of the object by means of the first mirror of the laser beam substantially perpendicular to the direction of the first scanned line on at least one adjacent line of the object ( 18 ) and the location-time matrix is stored correspondingly for this line, with L-matrices each having M × N measured values being stored and / or evaluated by the computer in accordance with the number L of sampled lines. A method according to claim 33 or 34, characterized that spectral analysis by a suitable signal processor or a hardware Fourier transformer is carried out. Method according to one of claims 26 to 35, characterized in that the returning light beam ( 20 ) is detected with an avalanche photodiode. Method according to one of claims 26 to 36, characterized in that a polarization-sensitive optical system is used, and in that a decoupling device is used, which is formed so sensitive to polarization that only such reflected light, which is linearly polarized in a direction to the illuminated beam to the western 90 ° rotated direction to the detector ( 26 . 27 . 28 ) is reflected, and / or by a 1/4 wavelength plate, the polarization direction of the reflected light is rotated by 90 ° compared to the polarization direction of the laser source. Method according to claim 37, characterized in that that a linearly polarized light source is used or that unpolarized laser light by means of a polarizer linear is polarized. A method according to claim 37, characterized in that the 1/4 wavelength plate between the object ( 18 ) and the decoupling element is arranged. Method according to one of Claims 26 to 39, characterized that at the second mirror with the frequency (f) moving the return time after scanning along a line of the object for extraction is used by data, where for the respective scanned line one time to the first location-time matrix moved second place-time matrix is detected, and that the said two Space-time matrices separated from each other Fourier-transformed and then under consideration of the shift set of the Fourier transform to an overall spectrum be combined. Method according to one of claims 26 to 40, characterized by using it for laser Doppler flowmetry, being at every point of a studied area the measured flow velocity with the ratio of of stationary components and those of moving components Light intensity multiplied by the ratio of the analysis of the frequency spectra is formed.