CN105466889B - The acquisition method of complex organization's body surface face illuminance in a kind of spatial frequency domain imaging - Google Patents

Abstract

The present invention relates to a collection method of complex tissue surface illuminance in space frequency domain imaging, comprising: ① generating a grayscale image with a modulation frequency, loading it into a digital micromirror device, and projecting a laser light source onto the digital micromirror device On the surface, the light projected by the digital micromirror device is a sinusoidal modulated light with a certain spatial frequency. The surface of the diffuse reflection plate is selected as the reference plane for system calibration, and a three-dimensional height map of the surface of the complex tissue is obtained; ②Modification step ① The distribution of gray values in a grayscale image. Load the modified grayscale image to the digital micromirror device to output light on the complex tissue body, so that the illuminance distribution on the surface of the complex tissue body meets the law of sinusoidal distribution, and the CCD camera collects the illuminance distribution image on the surface of the complex tissue body; The image of the illumination distribution on the surface of the complex tissue collected by the camera is corrected. The invention can reduce the illuminance data collection error caused by the non-uniform height, and improve the light projection efficiency and projection precision.

Description

A Method for Acquisition of Illuminance on Complex Tissue Surface in Spatial Frequency Domain Imaging

technical field

The invention belongs to the technical field of biomedical engineering, and in particular relates to a method for collecting light intensity on complex tissue surfaces in space frequency domain imaging.

Background technique

Spatial frequency domain imaging is an emerging medical imaging technique. The reflectance spectroscopy or diffuse reflectance spectroscopy techniques commonly used in the past can only measure a certain point of optical parameter values (absorption coefficient and scattering coefficient), and cannot perform imaging of a wide range of optical parameter values. The spatial frequency domain imaging can perform wide-field imaging to meet the requirements of large-area detection. Spatial frequency domain imaging belongs to the category of diffuse light imaging. Its principle is: choose a diffuse reflector with known diffuse reflectance (usually 97%-100%) as a reference plane, and separate sinusoidal modulated light with a certain spatial frequency Projected to the tissue to be tested and the reference plane, the CCD camera collects the diffuse reflection light distribution on the surface of the tissue to be tested and the reference plane under the excitation of sinusoidal modulation light, and combines with a specific light transmission model to reconstruct the tissue carrying the tissue The distribution of optical parameters of functional information and clinicopathological information, so as to complete the optical parameter imaging of the entire tissue to be measured.

Spatial frequency domain imaging requires that all points on the surface of the tissue to be measured are at the same height as the reference plane, so it is mostly used for optical parameter imaging of planar tissue with a uniform surface. When spatial frequency domain imaging is used to image the optical parameters of a complex tissue with a certain outline, since each point on the surface of the complex tissue is not at the same height as the reference plane, it will bring two adverse effects on the collection of surface illuminance :

1. The height of each point on the surface of the complex tissue is not uniform, so that the illuminance projected on the reference plane and the corresponding point on the surface of the complex tissue are different, so the sinusoidal modulated light projected on the surface of the complex tissue does not satisfy the sinusoidal distribution law;

2. Since the distance between each point on the surface of the complex tissue and the CCD camera is not the same, the illuminance distribution on the surface of the complex tissue collected by the CCD camera will inevitably be disturbed by the height modulation, which makes the useful data appear to some extent distortion.

Contents of the invention

In order to make up for the defects of space-frequency domain imaging and to overcome the lack of light intensity collection for complex tissue surfaces with outlines, the present invention proposes a method for collecting surface light intensity of complex tissue bodies in space-frequency domain imaging. This method can make The sinusoidally modulated light projected onto the surface of the complex tissue satisfies the sinusoidal regular distribution, which reduces the illuminance acquisition error caused by the non-uniform height, and eliminates the above two adverse effects. Main technical scheme of the present invention is divided into following two steps:

A method for collecting surface illuminance of complex tissues in space-frequency domain imaging, using a space-frequency domain imaging system with a contour acquisition function, including a laser light source (8), a digital micromirror device (9), a CCD camera (12), Computer (13), five parts of diffuse reflection plate (11), the projection area of digital micromirror device and the collection area of CCD camera overlap, and the aperture stop of CCD camera and digital micromirror device are at the same level height, complex organization body The method of collecting surface illuminance is:

①Generate a grayscale image with modulation frequency, load it into the digital micromirror device, project the laser light source onto the surface of the digital micromirror device, and the light projected by the digital micromirror device is sinusoidal modulated light with a certain spatial frequency . The surface of the diffuse reflector is selected as the reference plane for system calibration, and the sinusoidal modulated light is projected onto the reference plane and the surface of the complex tissue respectively. The illuminance distribution images of the reference plane and the surface of the complex tissue are collected by the CCD camera respectively, and the computer recognizes the change of the phase difference in the two images collected before and after, and the height difference distribution between the surface of the complex tissue and the reference plane can be obtained, so as to obtain the complex 3D height map of the tissue surface;

②According to the three-dimensional height map of the complex tissue surface obtained in step ①, modify the gray value distribution in the gray image in step ①. Load the modified grayscale image to the digital micromirror device to output light on the complex tissue body, so that the illuminance distribution on the surface of the complex tissue body meets the sinusoidal distribution law, and the illuminance distribution image on the surface of the complex tissue body is collected by the CCD camera;

③According to the characteristics of the Lambertian surface diffuse reflection model, the light intensity emitted from the complex tissue surface is inversely proportional to the square of the distance, and the illuminance distribution image of the complex tissue surface collected by the CCD camera is corrected.

The beneficial effects of the present invention are: since the sinusoidally modulated light projected onto the surface of the complex tissue satisfies the distribution of the sinusoidal law, and the illuminance received by the corresponding point of the reference plane is the same, the complex tissue is equivalent to being at the same height as the reference plane The planar organization greatly reduces the illuminance data collection error caused by the non-uniform height. The digital micromirror device is used to precisely control the light output, so that the light intensity received by each point on the surface of the complex tissue is easy to adjust, and the light projection efficiency and projection accuracy are improved.

Description of drawings

Figure 1 is a diagram of the internal structure of a digital micromirror device

Figure 2 is a structural diagram of a pixel micromirror module in a digital micromirror device

Figure 3 is a structural diagram of the spatial frequency domain imaging system with contour acquisition function

Specific implementation

Figure 1 is a diagram of the internal structure of a digital micromirror device, which consists of 912*1140 pixel micromirror modules (1), each pixel micromirror module has a surface area of 7.56*7.56um ² , and one pixel micromirror module represents a Pixels, the output image is composed of these pixels. The digital micromirror device controls all pixel micromirror modules to output light by receiving corresponding grayscale electrical signal data representing brightness. The electrical signal data here is a gray-scale picture (2) with a resolution of 912*1140 and 2 ⁿ gray levels, which is generated by a computer using programming software. Load the generated grayscale image onto the circuit board of the digital micromirror device. Each pixel micromirror module can identify the grayscale value of its corresponding pixel in the grayscale image. When light is projected onto the surface of the pixel micromirror module, its The output illuminance is proportional to the gray value. Therefore, when the laser light source is projected onto the digital micromirror device, the image output by the digital micromirror device is exactly the same as the input grayscale image, maintaining all the light distribution of the grayscale image, which is controlled by the input grayscale image By outputting images, the precise modulation and correction of single-point illumination on the surface of complex tissues can be completed.

Fig. 2 is the structural representation of a pixel micromirror module in the digital micromirror device, a pixel micromirror module is made up of pixel micromirror (3), the pillar (4) of supporting micromirror, mirror frame (7), electrode one (5) and electrode two (6). Between the pixel micromirror and the mirror frame, an air gap is generated by removing part of the organic sacrificial layer by plasma etching, and the mirror frame is integrated on the chip. The material of the pixel micromirror is aluminum alloy, and the electrode 1 and electrode 2 can change their own voltages under the drive of electrical signal data, and generate electrostatic attraction between the pixel micromirror. According to the different positions of the electrostatic attraction, the pixel micromirror can produce deflection angles in two directions. When the pixel micromirror is subjected to the electrostatic attraction of electrode 1, it produces a deflection angle of +10° from the horizontal direction. At this time, the pixel micromirror can reflect the incident light to the target; when the pixel micromirror is subjected to the electrostatic attraction of electrode 2, A deflection angle of -10° from the horizontal direction is generated, the incident light is absorbed by the absorption plane, and the incident light cannot be reflected to the target. Inside the digital micromirror device, each pixel micromirror module automatically recognizes the grayscale value of its corresponding pixel in the input grayscale picture, and the control electrode maintains the time (duty cycle) of +10° deflection angle per second, When light is projected onto the DMD, an image consistent with the input grayscale image can be projected.

Fig. 3 is based on the space-frequency domain imaging system structural diagram with profile acquisition function of the present invention, and it is made up of laser light source (8), digital micromirror device (9), CCD camera (12), computer (13), diffuse reflection Plate (11) is made up of five parts. The projected area of the digital micromirror coincides with the collection area of the CCD camera, and the aperture stop of the CCD camera is at the same level as the digital micromirror, and the diffuse reflectance of the diffuse reflection plate is 97%. In Figure 3, the specific implementation of light intensity collection on the surface of complex tissues is as follows:

① Generate a grayscale image (14) with modulation frequency by computer programming software, and load it into the digital micromirror device. The laser light source is projected onto the surface of the digital micromirror device, and the light projected by the digital micromirror device is a sinusoidal modulated light with a certain spatial frequency. Select the surface of the diffuse reflector as the reference plane for system calibration, and project the sinusoidal modulated light onto the reference plane and the surface of the complex tissue respectively (10). The illuminance distribution of the plane obeys the law of sinusoidal distribution. The illuminance distribution images of the reference plane and the surface of the complex tissue are collected by the CCD camera respectively, and the computer recognizes the change of the phase difference in the two images collected before and after, and the height difference distribution between the surface of the complex tissue and the reference plane can be obtained as follows:

d is the distance between the digital micromirror device and the aperture diaphragm of the CCD camera, and l is the height from the digital micromirror device to the reference plane, Indicates the phase difference value of the two images collected twice before and after by the CCD camera, f is the spatial frequency of the sinusoidally modulated light, x and y represent the coordinates, and the three-dimensional height map of the complex tissue surface can be obtained according to this method;

②According to the inverse square law, the illuminance is inversely proportional to the square of the distance from the point light source. Digital micromirror devices are used as secondary light sources, and because of their small size, they can be used as point light sources. Compared with the reference plane, the complex tissue body is closer to the digital micromirror device, and the light intensity received by its surface is relatively strong. In order to make the illuminance distribution projected on the surface of the complex tissue body satisfy the sinusoidal distribution law, it is necessary to adjust the gray level in step ① The picture is modified.

Assume that the gray value distribution of the gray image in step ① is G ₀ (x,y). Due to the close proximity of complex organoids to the digital micromirror device, images with lower grayscale values should be used. According to the inverse square law, the distribution of the gray value G(x, y) of the gray image used for projecting sinusoidally modulated light on complex tissues should be:

G(x,y)=[G ₀ (x,y)×(lh(x,y)) ² ]/l ²

l and h(x,y) are known, and they are the distance from the digital micromirror device to the reference plane in ① and the height distribution on the surface of the complex tissue, respectively. Load the modified image onto the circuit board of the digital micromirror device, and when projecting sinusoidally modulated light on complex tissues, use the modified grayscale image whose gray value distribution is G(x,y) to control the digital micromirror device The output image of the complex tissue body can achieve the purpose that the illumination distribution on the surface of the complex tissue obeys the law of sinusoidal distribution.

③ After the CCD camera collects the illuminance on the surface of the complex tissue, it is necessary to correct the collected illuminance distribution image. According to the characteristics of the diffuse reflection model of the Lambertian body surface, the light intensity emitted from the surface of the complex tissue body is inversely proportional to the square of the distance. Assuming that the pixel value of the illuminance image on the surface of the complex tissue collected by the CCD camera is A ₀ (x,y), the corrected pixel value A(x,y) is:

A(x,y)＝[A ₀ (x,y)×(lh(x,y) ² )]/l ²

l and h(x,y) are known, which are respectively the distance from the digital micromirror device to the reference plane in ① and the height distribution of the complex tissue surface. The above three steps can be used to complete the imaging of the complex tissue surface in the space frequency domain The collection of illuminance.

Claims (1)

1. the acquisition method of complex organization's body surface face illuminance, function is obtained using with profile in a kind of spatial frequency domain imaging Spatial frequency domain imaging system, including LASER Light Source (8), digital micromirror device (9), CCD camera (12), computer (13), diffusing reflection (11) five parts of plate, the projected area of digital micromirror device and the collection area of CCD camera overlap, and the aperture of CCD camera Diaphragm and digital micromirror device are in same level height, and the acquisition method of complex organization's body surface face illuminance is：

1. one gray scale picture for carrying modulating frequency of generation, is loaded into digital micromirror device, and laser light source projects are micro- to numeral Mirror device surface, the light that digital micromirror device is launched are the electroencephalogram with certain space frequency, choose diffusing reflection plate surface System calibrating is carried out as a reference plane, and electroencephalogram is projected to reference planes and complex organization's body surface face respectively；By CCD Camera gathers the intensity of illumination distribution image in reference planes and complex organization's body surface face respectively, is collected twice before and after computer identification Image in phase difference change, the height difference that can obtain complex organization's body surface face and reference planes is distributed, so as to be answered The three-dimensional height map on miscellaneous organizer surface；

2. the three-dimensional height map in the complex organization's body surface face 1. obtained according to step, the amendment step 1. gray scale in middle gray scale picture Distribution value；Amended gray scale picture is loaded into digital micromirror device light output is carried out to complex organization's body, make complex organization's body The intensity of illumination distribution on surface meets Sine distribution rule, and the intensity of illumination distribution image in complex organization's body surface face is gathered by CCD camera；

3. according to the characteristics of the diffusing reflection model of lambert's body surface face, the light intensity sent from complex organization's body surface face is inversely proportional to the flat of distance Side, the intensity of illumination distribution image in the complex organization's body surface face collected to CCD camera are corrected.