CN110095081B - Method and device for measuring tissue morphology and optical parameters based on space frequency domain imaging - Google Patents
Method and device for measuring tissue morphology and optical parameters based on space frequency domain imaging Download PDFInfo
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Abstract
The invention provides a method for detecting the morphology and optical parameters of a complex tissue body based on space frequency domain imaging, which comprises the following steps: firstly, a light source generates modulated light with certain spatial frequency; secondly, calibrating the system by using a reference plane; thirdly, projecting the modulated light to a tissue body to be detected, and collecting a reflected light image scattered by the sample by a camera; fourthly, acquiring a three-dimensional surface shape by utilizing a Fourier profilometry; fifthly, correcting the image illumination according to the height and the angle; performing line-by-line Fourier transform, decomposing direct current and alternating current frequency spectrum components, and performing inverse Fourier transform to obtain direct current and alternating current component images; and seventhly, matching and fitting to obtain optical parameters. The method can obtain the surface shape and optical parameter information only by single imaging; meanwhile, the illuminance error caused by the complex surface shape is corrected, and the measurement speed and the measurement precision are high.
Description
Technical Field
The invention belongs to the technical field of optics and measurement, and particularly relates to a method for measuring the morphology and optical parameters of a tissue body based on spatial frequency domain imaging, and a measuring device for measuring the morphology and optical parameters of the tissue body based on spatial frequency domain imaging, which is suitable for measuring the absorption coefficient and the reduced scattering coefficient of biological tissues.
Background
Chinese patent publication No. CN105510253A, "apparatus and method for detecting optical properties of agricultural product tissue by spatial frequency domain imaging", discloses a spatial frequency domain imaging technique, which projects sinusoidally modulated light with a certain spatial frequency onto a tissue sample to be measured, collects a diffuse reflection illuminance image after tissue scattering by a camera, and matches the absorption coefficient and reduced scattering coefficient of the tissue point by using a specific light transmission model, such as the paper "Cuccia J D, Bevilacqua F, Durkin JA, et al. Since the absorption coefficient is generally related to chemical components and the reduced scattering coefficient is generally related to physical properties such as microstructure, the optical property detection can be used for diagnosis of diseases and quality detection of agricultural products.
The space frequency domain imaging technology can perform wide field imaging and has the advantages of non-contact and large-area detection. However, the traditional spatial frequency domain imaging adopts a three-phase shift method for demodulation, that is, 3 diffuse reflection images with different phases under the same modulation frequency are required to be collected so as to analyze the modulation depth under the modulation frequency; in order to obtain the absorption coefficient and the reduction scattering coefficient at the same time, the modulation depth under 2 or more modulation frequencies needs to be measured, a sample to be measured needs to be imaged for multiple times, and the real-time performance of measurement is reduced. In addition, when the surface heights of the tissue body to be measured are inconsistent, the structured light projected to the surface of the tissue body does not meet the sine distribution rule, and the illuminance collected by the camera is interfered by the surface shape of the tissue body, so that data distortion is caused, and the accuracy of optical parameter measurement is influenced. Chinese patent CN105466889B, "a method for acquiring illuminance on the surface of a complex tissue in spatial frequency domain imaging", proposes a method for reducing acquisition errors of illuminance data by modifying a projected gray scale picture and modifying an image acquired by a CCD camera, but this method needs to calculate the three-dimensional height of the tissue surface and then re-image, which further restricts the real-time performance of measurement.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method for measuring the morphology and the optical parameters of a tissue body based on a space frequency domain imaging technology, which is easy to implement and simple and convenient to operate, can detect the three-dimensional surface shape and the optical characteristics of a complex tissue body by only one-time imaging, corrects the illumination error caused by the surface shape, and improves the measurement speed and the accuracy. The invention also aims to provide a measuring device for measuring the tissue morphology and the optical parameters based on the space frequency domain imaging
In order to achieve the purpose, the invention adopts the following technical measures:
a method for measuring the morphology and optical parameters of a tissue body based on a spatial frequency domain imaging technology comprises the following steps: (1) generating a spatial frequency f by the upper computerxThe two-dimensional sine wave of (1) modulates the gray picture, controls the projector to project the picture, and generates sine modulated light, wherein the light intensity of the sine modulated light in the x direction changes in a sine mode;
(2) the upper computer controls the projector to project the sine wave modulation gray level picture in the step (1) onto the standard diffuse reflection plate, and then controls the CCD camera to collect a reference light field illuminance distribution image signal I on the standard diffuse reflection plate0(x, y) the upper computer receives the signal I of the CCD camera0(x, y) displaying a fringe image; the standard diffuse reflection plate is located on a reference plane, the projector and the CCD camera are located at the same height above the reference plane, so that an image projected by the projector is clearly projected on the reference plane, meanwhile, the CCD camera completely collects the image on the reference plane, the optical axis of the projector is perpendicular to the reference plane, the optical axis of the CCD camera is intersected with the normal direction of the reference plane to form an included angle A, wherein x and y are coordinates of an image signal, the y direction is perpendicular to the x direction and represents the stripe direction in a reference light field, H is the perpendicular distance from the CCD camera to the reference plane, d is the distance from the center of the projector to the center of the CCD camera, and r is the distance between the center of the projector0(x, y) is the reflectance of a standard diffuse reflector, a known value;
(3) placing the tissue body to be detected on a reference plane, projecting a sine modulation gray picture onto the tissue body to be detected through a projector, collecting a deformed light field illuminance distribution image signal I (x, y) scattered by the tissue body through a CCD (charge coupled device) camera, and receiving the signal I (x, y) of the CCD camera by an upper computer to display a deformed stripe image;
(4) obtaining the three-dimensional shape of the tissue body to be detected through Fourier transform profilometry, and accordingly distributing the illuminance of the deformed light fieldCorrecting the image signal I (x, y) to obtain a corrected signal Icorrected(x,y)；
(5) Then obtaining modulation depth MTF through line-by-line Fourier transform and frequency spectrum data decompositionDC(x,y)、MTFAC(x,y)；
(6) Dispersing the absorption coefficient and the reduction scattering coefficient in the optical parameter range of the tissue body to be detected according to the optical parameter range of the tissue body to be detected before the step (1), and combining the absorption coefficient and the reduction scattering coefficient to obtain a plurality of groups of optical parameters; obtaining the spatial distribution of diffuse reflection light of the tissue body model corresponding to each group of optical parameters under the excitation of an infinite narrow vertical light beam by utilizing Monte Carlo simulation; calculating Modulation Transfer Functions (MTF) corresponding to all the tissue models according to the Fourier transform relation between the space domain and the frequency domain, and establishing a database;
(7) and (5) matching and fitting the modulation depth in the step (5) with a model in a database to obtain an absorption coefficient and a reduced scattering coefficient.
Further, the fourier transform profilometry described in step (4) comprises the steps of:
s01, the upper computer performs Fourier transform on each row of data of the signals I (x, y) in the step (3) line by line along the y direction, and a band-pass filter is selected to filter out fundamental frequency components of the signals I (x, y) modulated by the surface height of the tissue to be detected; obtaining the fundamental frequency distribution of the deformed optical field
Wherein A is the amplitude of the harmonic, r (x, y) is the non-uniform reflectivity of the surface of the tissue to be measured,
is the phase distribution of the deformed fringe image;
s02, in order to eliminate the influence of additional phase modulation caused by divergent illumination of the projection system, the upper computer performs comparison on the signal I in the step (2)0(x, y) also carrying out the processing of the step (4) to obtain the fundamental frequency distribution of the original light field
Wherein r is0(x, y) is the reflectance of a standard diffuse reflection plate,
is the phase distribution of the fringe image;
s03, enabling the upper computer to distribute g from fundamental frequency of the deformed light field1Fundamental frequency distribution g of (x, y) and reference light field0(x, y) is calculated according to the formula:
s04, calculating a phase modulation value caused by the height of the tissue body to be detected by the upper computer according to the imaginary part of S (x, y) obtained in the step S01
the upper computer can obtain a real phase function according to the phase expansion
S05, the upper computer further selects a phase value
And (3) converting to obtain the height value distribution h (x, y) of the tissue to be detected:
wherein d is the distance between the center of the projector and the center of the CCD camera, H is the vertical distance between the CCD camera and the reference plane, and fxModulating the spatial frequency of the light for a two-dimensional sine wave;
s06, the upper computer compares the height value distribution h (x, y) of the tissue body to be detectedCorrecting the signal I (x, y) obtained in the step (3) to obtain the diffuse reflection light intensity distribution I of the surface of the tissue body to be measuredsurf(x,y)：
Wherein theta (x, y) is an included angle between the normal direction of the surface of the tissue body and the optical axis of the CCD, and can be obtained according to the three-dimensional surface shape and the space geometric relation of the tissue body;
adjusting the light intensity distribution I of the light according to a sinecos(x, y) and the actual light intensity distribution I influenced by the height of the surface of the tissue to be measuredreal(x, y) pairs Isurf(x, y) to obtain a corrected signal Icorrected(x,y)：
Wherein
And
respectively representing the fourier change and the inverse fourier transform:
further, the step (5) comprises the following steps:
s07. the upper computer compares the signal IcorrectedFourier transform is carried out on (x, y) line by line, a filter is adopted to decompose the direct current component and the alternating current component, then inverse Fourier transform is carried out on the direct current component and the alternating current component respectively to obtain a direct current DC frequency spectrum image signal Icorrected,DC(x, y) and alternating AC spectral image signal Icorrected,AC(x,y)；
S08, according to the method of the step S07, the signal I in the step (2) is processed0(x, y) processing line by line to obtain DC frequency spectrum image signal I0,DC(x, y) and alternating AC spectral image signal I0,AC(x,y)；
S09. the signals obtained at steps S07 and S08 are input according to the modulation depth formula: i iscorrected,DC(x,y)、Icorrected,AC(x,y)、I0,DC(x,y)、I0,AC(x, y), obtaining the direct current DC spectrum modulation depth MTF of each signalDC(x, y) and AC spectral modulation depth MTFAC(x,y)：
Wherein r is0(x, y) is the reflectance of a standard diffuse reflector, a known value.
Through the technical measures in the step (4), the light intensity of the diffuse reflection image of the tissue body to be measured is corrected according to the three-dimensional shape of the tissue body to be measured, so that the illuminance acquisition error caused by the inconsistency of the surface height and the angle of the tissue body with a complex shape during imaging of the CCD camera is reduced, and the measurement accuracy is improved. The existing method is to modify the projected gray pattern according to the height distribution, then image and revise the image, i.e. 2 times of imaging are needed, and the 2 projected lights are different.
The square law algorithm is improved through the step S06, the improved algorithm does not need to correct the light source and then image again, but directly corrects the illumination change caused by the difference of the distance from the light source to the tissue surface and the difference of the distance from the tissue surface to the CCD through calculation, and in addition, the improved algorithm takes the change of the Lambert illumination with the angle into consideration, and a third term 1/cos [ theta (x, y) ] is introduced. Through the measure of the step (5), the direct current modulation depth and the alternating current modulation depth of each part of the diffuse reflection image can be obtained only by shooting the tissue to be detected once, the absorption coefficient and the reduced scattering coefficient of each part of the tissue to be detected can be obtained through fitting of the data, compared with the existing three-phase shift demodulation technology which needs to collect 3 diffuse reflection images with different phases under the same modulation frequency, the imaging frequency is greatly reduced, the measurement speed is improved, and the real-time measurement of the optical parameters of the biological tissue can be realized. The existing method requires lifting the DC and AC components from 3 different phases, i.e. 3 images are required; if the error caused by the height of the object needs to be corrected, 3 × 2 to 6 times of imaging is needed, the measurement speed is increased, and the real-time measurement of the optical parameters of the biological tissue can be realized.
The device comprises a digital projector, a CCD camera, a polaroid, an upper computer and a standard diffuse reflection plate, and the connection relation is as follows: the upper computer is connected with the projector through a signal line and controls the projector to project patterns to generate sine modulation light with spatial frequency; the standard diffuse reflection plate is positioned on a reference plane, the projector and the CCD camera are positioned at the same height above the reference plane, the optical axis of the projector is perpendicular to the reference plane, the optical axis of the CCD camera and the normal direction of the reference plane are intersected to form an included angle A, so that an image projected by the projector is clearly projected on the reference plane, and meanwhile, the CCD camera completely collects the image on the reference plane; the upper computer is connected with the CCD camera through a signal line, receives pictures shot by the CCD camera and processes image data, and the absorption coefficient and the constraint scattering coefficient of each part of the tissue body to be detected are obtained through the method; polarizing plates are arranged in front of the projector and the CCD camera and used for reducing the specular reflection light received by the camera; the diffuse reflectance of a standard diffuse reflector is uniform and of a known value (e.g., 97%). At present, the measurement requirements can be met by a commercial projector, an upper computer, a CCD camera for laboratory use and a linear polaroid.
Compared with the prior art, the invention has the following advantages and effects:
the invention realizes that the absorption coefficient and the reduced scattering coefficient of each part of the tissue to be measured can be obtained only by single shooting, greatly reduces the imaging times, improves the measuring speed and can realize the real-time measurement of the optical parameters of the biological tissue compared with the prior three-phase shift demodulation technology. And the light intensity of the diffuse reflection image of the tissue to be measured is corrected according to the three-dimensional shape of the tissue to be measured, so that the light illumination acquisition error caused by the inconsistency of the surface height and angle of the tissue with a complex shape during the imaging of a CCD camera is reduced, and the measurement accuracy is improved.
Drawings
FIG. 1 is a schematic diagram of a measuring apparatus for measuring tissue morphology and optical parameters based on spatial frequency domain imaging;
FIG. 2 is a block diagram of a method for measuring tissue morphology and optical parameters based on spatial frequency domain imaging.
Wherein: the method comprises the following steps of 1-a digital projector, 2-a CCD camera, 3-an upper computer, 4-a polarizing film, 5-a polarizing film, 6-a standard diffuse reflection plate, 7-a tissue sample to be detected, 8-a reference plane, 9-a stripe image and 10-a deformed stripe image.
Detailed Description
The invention will be further described with reference to the accompanying drawings and specific embodiments which are described herein and which are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or exceeding the scope of the invention as defined.
Example 1:
referring to fig. 1, a left-side straight stripe pattern in fig. 1 is a schematic diagram of an incident sine-modulated light, and a curved stripe pattern on an upper computer 3 is a schematic diagram of an image captured by a CCD; the standard diffuse reflection plate 6 has uniform and known diffuse reflection rate, and the tissue sample 7 to be detected is animal skin, liver, agricultural products, fruits and vegetables and the like.
A method for measuring the morphology and optical parameters of a tissue body based on a spatial frequency domain imaging technology comprises the following steps:
K1. the projector 1 and the CCD camera 2 are located at the same height above a reference plane 8, the optical axis of the projector 1 is perpendicular to the reference plane 8, the optical axis of the CCD camera 2 intersects with the normal direction of the reference plane 8 to form an included angle A, the included angle A is 15 degrees, the height of the projector 1 and the height and the angle of the CCD camera 2 are adjusted, an image projected by the projector 1 is clearly projected on the reference plane, meanwhile, the CCD camera 2 completely collects the image on the reference plane, and the projector and the CCD camera are in signal connection with an upper computer 3 through signal lines;
K2. the upper computer 3 generates a spatial frequency fxThe two-dimensional sine wave of (1) modulates the gray picture, controls the projector to project the picture, and generates sine modulated light, wherein the intensity of the sine modulated light in the x direction is changed in a sine way, like a stripe image 9 on the left side in fig. 1;
K3. a standard diffuse reflection plate 6 is arranged on a reference plane 8, a sine modulation gray picture is projected onto the standard diffuse reflection plate 6 through a projector 1, and a CCD camera 2 collects a reference light field illuminance distribution image signal I on the standard diffuse reflection plate 60(x, y), the diffuse reflectance r of the standard diffuse reflection plate 60(x, y) is uniform and is a known value of 97%, the upper computer 3 receives a display stripe image 9 of the CCD camera 2, wherein x and y are coordinates of an image signal, and the y direction is perpendicular to the x direction and represents the stripe direction in the reference light field;
K4. placing a tissue body 7 to be detected on a reference plane 8, projecting a sine modulation gray picture onto the tissue body 7 to be detected through a projector 1, collecting a deformed light field illuminance distribution image signal I (x, y) scattered by the tissue body 7 by a CCD camera 2, and receiving the signal I (x, y) of the CCD camera 2 by an upper computer 3 to display a deformed stripe image 10;
K5. the upper computer compares the signal I (x, y) and the signal I0(x, y) for every y-th image signal along y-directioniThe line data is subjected to Fourier transform line by line, and y is more than or equal to 1i≤ny，nyIs an image signal I0(x, y), the number of pixels in the y direction in I (x, y), and I (x, y)0The gray scale distribution function of (x, y) is converted into a frequency distribution function g1(x, y) and g0(x, y), inputting the distance d between the center of the projector 1 and the center of the CCD camera 2 and the vertical distance H between the CCD camera 2 and the reference plane, and solving the height value distribution H (x, y) of the tissue to be detected;
specifically, the method comprises the following steps: J1. filtering out the surface height modulation of the tissue body to be measured by selecting a band-pass filterObtaining the fundamental frequency distribution g of the deformed light field by the fundamental frequency component of the diffuse reflection illuminance distribution image signal I (x, y)1(x, y) wherein
A is the amplitude of the harmonic, r (x, y) is the non-uniform reflectivity of the surface of the tissue to be measured,
is the phase distribution of the deformed fringe image;
J2. upper computer to signal I0(x, y) also processed in step J1 to obtain the fundamental frequency distribution g of the reference light field0(x, y) wherein
A is the amplitude of the harmonic, r0(x, y) is the reflectance of a standard diffuse reflector,
is the phase distribution of the fringe image;
J3. the upper computer is based on the fundamental frequency distribution g of the deformed light field1Fundamental frequency distribution g of (x, y) and reference light field0(x, y) calculating s (x, y) according to the formula:
J4. calculating the phase modulation value caused by the height of the tissue body to be measured according to the imaginary part of s (x, y) obtained in the step J3
J5. the upper computer performs the exhibition according to the menstrual phaseAfter the phase is opened, the real phase function can be obtained
J6. Then the phase value
And (3) converting to obtain the height value distribution h (x, y) of the tissue to be detected:
where d is the distance between the center of the projector 1 and the center of the CCD camera 2, H is the perpendicular distance between the CCD camera 2 and the reference plane, and fxModulating the spatial frequency of the light for a two-dimensional sine wave;
the method for calculating the height value distribution h (x, y) of the tissue to be measured in the steps J1-J6 can refer to Wei Sheng and the like, and the extraction of object-plane phase based on Fourier transform profilometry, Nanchang university journal, 2007, 6 months, 31, 3 rd, 260-261.
K6. The upper computer corrects the signal I (x, y) obtained in the step K4 according to the height value distribution h (x, y) of the tissue body to be detected to obtain a diffuse reflection light intensity distribution signal I on the surface of the tissue body to be detectedsurf(x,y)：
Theta (x, y) is an included angle between the normal direction of the surface of the tissue body and the optical axis of the CCD, and can be obtained according to the three-dimensional surface shape and the space geometric relationship;
because the structural light projected on the surface of the tissue body does not meet the sine distribution rule due to the inconsistent height of the surface of the tissue body to be detected, I is required to obtain the diffuse reflection light intensity distribution image of the tissue body to be detected under the sine modulation lightsurf(x, y) to obtain a corrected signal Icorrected(x,y)：
Wherein
And
respectively representing a Fourier change and an inverse Fourier transform, Icos(x, y) represents the intensity distribution of the sinusoidally modulated light, Ireal(x, y) represents the actual light intensity distribution highly influenced by the surface of the tissue to be measured:
K7. for signal Icorrected(x, y) and signal I0(x, y) respectively carrying out Fourier transform line by line, adopting a filter to decompose the direct current component and the alternating current component, then respectively carrying out inverse Fourier transform on the direct current component and the alternating current component to obtain a direct current DC frequency spectrum image signal Icorrected,DC(x,y)、I0,DC(x, y) and alternating AC spectral image signal Icorrected,AC(x,y)、I0,AC(x, y); finally, the direct current DC frequency spectrum modulation depth MTF of the image is obtained according to a modulation depth formulaDC(x, y) and AC spectral modulation depth MTFAC(x,y)：
Wherein r is0(x, y) is the reflectance of a standard diffuse reflector;
specifically, step K7 includes the steps of: G1. for the signal I in step K6correctedFourier transform is performed on (x, y) lines by line, and a filter is used for each lineDecomposing the line spectrum signal into two parts of frequency spectrums corresponding to Direct Current (DC) and Alternating Current (AC); then, the DC frequency spectrum and the AC frequency spectrum are respectively subjected to inverse Fourier transform to obtain a signal IcorrectedDC component I of the line signal in (x, y)DCAnd an alternating current component IAC(ii) a For signal IcorrectedEach line of (x, y) is subjected to fourier transform, spectral decomposition and inverse fourier transform processing until the signal of the whole image is obtained: i iscorrected,DC(x, y) and Icorrected,AC(x,y)。
G2. Signal I is obtained using step G10I of (x, y)0,DC(x, y) and I0,AC(x,y)。
G3. And (3) calculating to obtain modulation depth:
wherein r is0(x, y) is the reflectance of a standard diffuse reflector, a known value.
K8. Discretizing an absorption coefficient and an approximative scattering coefficient within the optical parameter range of the tissue body to be detected in advance according to the optical parameter range of the tissue body to be detected, and combining the absorption coefficient and the approximative scattering coefficient to obtain a plurality of groups of optical parameters; obtaining the spatial distribution of diffuse reflection light of the tissue body model corresponding to each group of optical parameters under the excitation of an infinite narrow vertical light beam by utilizing Monte Carlo simulation; and calculating Modulation Transfer Functions (MTF) corresponding to all the tissue body models according to the Fourier transform relation between the space domain and the frequency domain, and establishing a database. Spatial domain: in image processing, an image can be understood as a spatial domain or an image space, and a processing object is an image pixel; frequency domain: the spatial frequency is used as an independent variable to describe the characteristics of the image, the change of the pixel value of an image on the space can be decomposed into linear superposition of simple vibration functions with different amplitudes, spatial frequencies and phases, and the composition and distribution of various spatial frequency components in the image are called as an image frequency spectrum. The space domain and the frequency domain can be mutually converted, two-dimensional discrete Fourier transform or wavelet transform is carried out on the image, and the image can be converted from the space domain to the frequency domain; which in turn may be transformed back into the spatial domain image by a corresponding inverse transform.
K9. From the obtained modulation depth MTFDC(x,y)、MTFAC(x, y) matching and fitting with the model in the database to obtain the absorption coefficient and the reduced scattering coefficient of all parts of the tissue body.
Chinese patent 105816151B, a method for reconstructing optical parameters of uniform tissue based on spatial frequency domain measurement, discloses a process of establishing an optical parameter database in steps K8 and K9, establishing a frequency domain transfer function variation curve of a tissue body corresponding to optical parameters along with frequency, and matching and fitting a model in a modulation depth and transfer function relation database to obtain an absorption coefficient and a reduced scattering coefficient.
Claims (2)
1. A method for measuring the morphology and optical parameters of a tissue body based on spatial frequency domain imaging is characterized by comprising the following steps:
(1) the upper computer generates a space frequency fxThe two-dimensional sine wave of (1) modulates the gray picture, controls the projector to project the picture, and generates sine modulated light, wherein the light intensity of the sine modulated light in the x direction is changed in a sine mode;
(2) selecting a standard diffuse reflection plate to be arranged on a reference plane, projecting a sine wave modulation gray picture onto the standard diffuse reflection plate, and collecting a reference light field illuminance distribution image signal I on the standard diffuse reflection plate by a CCD (charge coupled device) camera0(x, y) the upper computer receives the signal I of the CCD camera0(x, y) displaying a fringe image, wherein x and y are coordinates of the image signal, and the y direction is perpendicular to the x direction and represents the fringe direction in the reference light field;
(3) placing the tissue body to be detected on a reference plane, projecting sine modulation light onto the tissue body to be detected, collecting a deformed light field illuminance distribution image signal I (x, y) scattered by the tissue body by a CCD camera, and receiving the signal I (x, y) of the CCD camera by an upper computer to display a deformed stripe image;
(4) the upper computer aligns the signal I (x, y) along the imageFourier transform is carried out on each row of data line by line in the y direction of the signals, the fundamental frequency component of a deformed light field diffuse reflection illuminance distribution image signal I (x, y) which is modulated by the surface height of the tissue to be measured is filtered out by selecting a band-pass filter, and the fundamental frequency distribution g of the deformed light field is obtained1(x, y) wherein
(5) The upper computer compares the signal I in the step (2)0(x, y) also carrying out the processing of the step (4) to obtain the fundamental frequency distribution of the original light field
Wherein r is0(x, y) is the reflectance of a standard diffuse reflector,
is the phase distribution of the fringe image;
a is the amplitude of the harmonic, r (x, y) is the non-uniform reflectivity of the surface of the tissue to be measured,
is the phase distribution of the deformed fringe image, r0(x, y) is the reflectance of a standard diffuse reflector,
is the phase distribution of the fringe image;
(6) the upper computer is based on the fundamental frequency distribution g of the deformed light field1Fundamental frequency distribution g of (x, y) and reference light field0(x, y) is calculated according to the formula:
(7) the upper computer calculates a phase modulation value caused by the height of the tissue body to be measured according to the imaginary part of s (x, y) obtained in the step (6)
(8) the upper computer can obtain a real phase function according to the phase expansion
(9) The upper computer then adjusts the phase value
And (3) converting to obtain the height value distribution h (x, y) of the tissue to be detected:
wherein d is the distance between the center of the projector and the center of the CCD camera, H is the vertical distance between the CCD camera and the reference plane, and fxModulating the spatial frequency of the light for a two-dimensional sine wave;
(10) the upper computer corrects the signals I (x, y) obtained in the step (3) according to the height value distribution h (x, y) of the tissue body to be detected to obtain diffuse reflection light intensity distribution signals I of the surface of the tissue body to be detectedsurf(x,y)：
Wherein theta (x, y) is an included angle between the normal direction of the surface of the tissue body and the optical axis of the CCD, and can be obtained according to the three-dimensional surface shape and the space geometric relation of the tissue body;
(11) adjusting the light intensity distribution I of the light according to a sinecos(x, y) and the actual light intensity distribution I highly influenced by the surface of the tissue to be measuredreal(x, y) pairs Isurf(x, y) to obtain a corrected signal Icorrected(x,y)：
Wherein
And
inverse fourier transform and inverse fourier transform are indicated respectively:
(12) upper computer to signal IcorrectedFourier transform is carried out on (x, y) line by line, a filter is adopted to decompose the direct current component and the alternating current component, then inverse Fourier transform is carried out on the direct current component and the alternating current component respectively to obtain a direct current DC frequency spectrum image signal Icorrected,DC(x, y) and alternating AC spectral image signal Icorrected,AC(x,y)；
(13) According to the method of step (12), for the signal I in step (2)0(x, y) processing line by line to obtain DC frequency spectrum image signal I0,DC(x, y) and alternating AC spectral image signal I0,AC(x,y)；
Inputting the signals obtained in the steps (12) and (13) according to a modulation depth formula: i iscorrected,DC(x,y)、Icorrected,AC(x,y)、I0,DC(x,y)、I0,AC(x, y), obtaining the direct current DC spectrum modulation depth MTF of each signalDC(x, y) and AC spectral modulation depth MTFAC(x,y)：
Wherein r is0(x, y) is the reflectance of a standard diffuse reflector, a known value;
(14) dispersing the absorption coefficient and the reduction scattering coefficient in the optical parameter range of the tissue body to be detected according to the optical parameter range of the tissue body to be detected before the step (1), and combining the absorption coefficient and the reduction scattering coefficient to obtain a plurality of groups of optical parameters; obtaining the spatial distribution of diffuse reflection light of the tissue body model corresponding to each group of optical parameters under the excitation of an infinite narrow vertical light beam by utilizing Monte Carlo simulation; calculating Modulation Transfer Functions (MTF) corresponding to all the tissue body models according to the Fourier transform relation between the space domain and the frequency domain, and establishing a database;
(15) and (5) matching and fitting the modulation depth in the step (13) with a model in a database to obtain an absorption coefficient and a reduced scattering coefficient.
2. The device for measuring the morphology of the tissue body and the optical parameters based on the spatial frequency domain imaging is characterized by comprising a digital projector, a CCD camera, a polaroid, an upper computer and a standard diffuse reflection plate, wherein the connection relation is as follows: the upper computer is connected with the projector through a signal line, and controls the projector to project patterns and generate sine modulation light with spatial frequency; the standard diffuse reflection plate is positioned on a reference plane, the projector and the CCD camera are positioned at the same height above the reference plane, the optical axis of the projector is perpendicular to the reference plane, the optical axis of the CCD camera and the normal direction of the reference plane are intersected to form an included angle A, so that an image projected by the projector is clearly projected on the reference plane, and meanwhile, the CCD camera completely collects the image on the reference plane; the upper computer is connected with the CCD camera through a signal line, and receives pictures shot by the CCD camera and processes image data.
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