CN114452026B - An enamel caries detection system based on terahertz spectroscopy imaging - Google Patents

Abstract

The invention discloses an enamel caries detection system based on terahertz spectroscopy imaging, which utilizes the characteristics of strong penetrability, non-ionizing radiation, sensitivity to caries tissues and high contrast response difference of caries tissues and healthy tissues of terahertz waves, and realizes the non-ionizing radiation, accuracy, precision and intuitionistic detection of early enamel caries which is difficult to be detected and is hidden in position in the prior art.

Description

An enamel caries detection system based on terahertz spectroscopy imaging

Technical field

The present invention relates to terahertz spectroscopy imaging technology, and in particular to an enamel caries detection system based on terahertz spectroscopy imaging technology.

Background technique

According to the findings of the "Fourth National Oral Disease Epidemiological Survey Report" released in 2017, the caries rate in permanent teeth has been rising rapidly in my country from children to the elderly in recent years. Dental caries refers to a chronic infectious disease in which the inorganic matter of the dental hard tissue is demineralized and the organic matter is decomposed under the action of bacteria and other factors, resulting in chronic progressive destruction as the main change.

At present, the clinical detection methods for dental caries mainly use visual inspection, X-ray diagnosis, CT, laser fluorescence diagnosis, etc. Among them, visual inspection directly observes whether the teeth are damaged or changed color with the naked eye, but the diagnosis can only be made after cavities appear. X-ray diagnosis uses X-rays to irradiate teeth for two-dimensional transmission imaging, which can diagnose occult caries, proximal caries, etc. that are difficult to find. However, X-rays will produce certain biological effects when they pass through the human body. Although the radiation of oral X-ray detection The dose is very low, and pregnant women and children should still try to avoid exposure. Oral CT can reconstruct the three-dimensional morphology of teeth and can provide a more detailed diagnosis compared with dental X-rays. However, it is only suitable for the detection of larger or already formed caries. It is difficult to detect early caries and also contains ionizing radiation. of radioactive hazards. Laser fluorescence detection focuses on qualitative analysis, which is greatly affected by changes in the distribution uniformity of the tooth surface, and cannot detect proximal caries.

It can be seen from the above that existing detection methods are difficult to detect and identify early caries and hidden caries safely, accurately and accurately.

Contents of the invention

In view of the deficiencies in the prior art, the present invention proposes an enamel caries detection system based on terahertz spectroscopy imaging. The detection system utilizes the difference in response of caries tissue and healthy tissue to terahertz time domain transmission and reflection signals. Contrast is created in imaging, enabling early screening of enamel caries.

The specific technical solutions of the present invention are as follows:

An enamel caries detection system based on terahertz spectroscopy imaging, including: femtosecond laser generation and conduction unit, terahertz transmitting antenna, first polarized terahertz detection antenna, second polarized terahertz detection antenna, antenna control unit, synchronization unit, distance detection and control unit, spectral signal processing unit, imaging reconstruction unit and display unit; among which,

Femtosecond laser generation and transmission unit: used to generate linearly polarized terahertz pulse light;

Terahertz transmitting antenna: used to emit linearly polarized terahertz pulse light to the tooth being detected;

First polarized terahertz detection antenna: used to detect terahertz pulse light that passes through the tooth being detected;

Second polarization terahertz detection antenna: used to detect terahertz pulse light reflected from the tooth being detected;

Antenna control unit: used to rotate and control the azimuth angles of the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna to emit and detect terahertz pulse light in different linear polarization directions;

Synchronization unit: used to maintain the same rotation azimuth angle of the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna during rotation;

Distance detection and control unit: used to obtain the distance from the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna to the surface of the detected tooth, prevent collision, and calculate the thickness of the detected tooth;

Spectral signal processing unit: used to process the terahertz time domain spectrum signals detected by the first polarized terahertz detection antenna and the second polarized terahertz detection antenna;

Imaging reconstruction unit: Based on the data processed by the spectral signal processing unit, it generates a variety of imaging data of transmission and reflection of the detected teeth;

Display unit: used for external display of the imaging data reconstructed by the imaging reconstruction unit.

Preferably, the method for processing data by the spectral signal processing unit includes: calculating peak-to-peak values, fast Fourier transform, calculating time of flight, calculating refractive index and analyzing the degree of azimuthal anisotropy.

Preferably, the analysis of the degree of azimuth anisotropy is: at the same detection position, the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna are synchronously rotated at a fixed angle. Azimuth angle, generate and detect linearly polarized terahertz pulse light in different directions, record the time domain signal at each azimuth angle; after one rotation, count the peak-to-peak value of the terahertz pulse at each azimuth angle, and calculate the maximum among all azimuth angles The ratio of the peak-to-peak value to the minimum peak-to-peak value is regarded as the first degree of anisotropy. The ratio of the maximum peak-to-peak value in all azimuth angles to the peak-to-peak value at an angle orthogonal to the azimuth angle corresponding to the maximum peak-peak value is calculated and regarded as the second degree of anisotropy. For the degree of anisotropy, calculate the ratio of the maximum refractive index to the minimum refractive index at each azimuth angle, which is regarded as the third degree of anisotropy.

Preferably, the method for generating imaging data by the imaging reconstruction unit includes: peak-to-peak imaging, time-of-flight tomography, refractive index imaging, frequency domain amplitude imaging, frequency domain phase imaging and azimuthal anisotropy degree imaging.

Preferably, the azimuthal anisotropy degree imaging is as follows: the first anisotropy degree imaging uses the first anisotropy degree as the numerical size of the imaging pixel at the position, and the second anisotropy degree imaging uses the second anisotropy degree The degree is used as the numerical size of the imaging pixel at this position, and the third degree of anisotropy imaging uses the third degree of anisotropy as the numerical size of the imaging pixel at this position.

Compared with the prior art, the present invention has the following beneficial effects:

1. The detection system of the present invention uses terahertz waves for detection. Compared with X-rays that produce ionizing radiation, terahertz waves have lower photon energy, only about 4.1meV at 1THz, and will not cause harmful effects on biological tissues. Ionizing radiation is very suitable for detection of living biological tissue. Compared with visible light and infrared light, terahertz waves are more penetrating and are suitable for characterization of caries below the tooth surface.

2. The detection system of the present invention integrates terahertz wave transmission signals and reflection signals. The transmission signal at the carious location has a significant attenuation compared to the healthy location, and the refractive index can be calculated to identify enamel and dentin; the reflection signal can be time-delayed for time-of-flight tomography, and Fourier transform can be performed Perform spectrum imaging to achieve three-dimensional reconstruction.

3. The detection system of the present invention realizes synchronous rotation of the azimuth angles of the transmitting antenna and the detection antenna through the control unit and the synchronization unit, that is, while keeping the teeth stationary, the polarization direction of the terahertz excitation source is adjusted and polarization angle-dependent measurement is introduced. When healthy tooth enamel is radiated by terahertz waves with different polarization directions, it will produce an obvious angle-dependent phenomenon. However, for carious tooth enamel, this phenomenon will be significantly weakened. This characteristic parameter can be used for refined detection. Improved the accuracy of detection results.

Description of the drawings

In order to more clearly explain the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings that need to be used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description The drawings illustrate the implementation process and details of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic diagram of the enamel caries detection system based on terahertz spectroscopy imaging of the present invention;

Figure 2 is a flow chart of applying the detection system of the present invention to detect dental caries;

Explanation of reference numbers:

1-Enamel caries detection system based on terahertz spectroscopy imaging, 2-terahertz transmitting antenna, 3-first polarization terahertz detection antenna, 4-second polarization terahertz detection antenna, 5-antenna control unit, 6-synchronization Unit, 7-distance detection and control unit, 8-spectral signal processing unit, 9-imaging reconstruction unit, 10-display unit, 11-femtosecond laser generation and conduction unit.

Detailed ways

In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, as long as there is no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described here. Therefore, the protection scope of the present invention is not limited by the specific details disclosed below. Limitations of Examples.

In order to facilitate understanding of the above technical solutions of the present invention, the above technical solutions of the present invention will be described in detail below through specific embodiments.

As shown in Figure 1, the terahertz spectroscopy imaging enamel caries detection system 1 of the present invention includes: femtosecond laser generation and transmission unit 11, terahertz transmitting antenna 2, first polarized terahertz detection antenna 3, second polarized terahertz Detection antenna 4, antenna control unit 5, synchronization unit 6, distance detection and control unit 7, spectral signal processing unit 8, imaging reconstruction unit 9 and display unit 10.

The synchronization unit 6 is installed on the first circuit board, the spectral signal processing unit 8 is installed on the second circuit board, the distance detection and control unit 7 is installed on the third circuit board, the femtosecond laser generates and conducts The unit 11 is mounted on a fourth circuit board, said first, second, third and fourth circuit boards being connected to the main circuit board.

Femtosecond laser generation and transmission unit 11: used to generate linearly polarized terahertz pulse light.

Terahertz transmitting antenna 2: used to emit linearly polarized terahertz pulse light to the tooth being detected.

The first polarized terahertz detection antenna 3 is used to detect the terahertz pulse light that passes through the tooth to be detected.

The second polarized terahertz detection antenna 4 is used to detect the terahertz pulse light reflected from the tooth to be detected.

Antenna control unit 5: used to rotate and control the azimuth angles of the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna to emit and detect terahertz pulse light in different linear polarization directions.

In another embodiment, the antenna control unit 5 also includes a driver and a stepper motor.

Synchronization unit 6: used to maintain the same rotation azimuth angle of the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna during rotation.

Distance detection and control unit 7: used to obtain the distance from the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna to the surface of the detected tooth, prevent collision, and calculate the thickness of the detected tooth.

In another embodiment, the distance detection and control unit 7 includes a distance detection subunit and a distance control subunit. The distance detection subunit detects the distance between the transmitting antenna and the detection antenna from the tooth surface and the tooth thickness. The distance control subunit detects the distance according to the distance. The information collected by the detection subunit keeps the distance of the transmitting antenna and the detection antenna constant from the tooth surface.

In another embodiment, the sensor used by the distance detection and control unit 7 is a laser or ultrasonic sensor.

Spectral signal processing unit 8: used to process the terahertz time domain spectrum signals detected by the first polarized terahertz detection antenna and the second polarized terahertz detection antenna.

In another embodiment, the method for processing data by the spectral signal processing unit 8 includes: calculating peak-to-peak values, fast Fourier transform, calculating time of flight, calculating refractive index, and analyzing the degree of azimuthal anisotropy.

In another embodiment, the analysis of the degree of azimuthal anisotropy is as follows: at the same detection position, the terahertz transmitting antenna, the first polarized terahertz detection antenna and the second polarized terahertz detection antenna are synchronously rotated at a fixed angle. Hertz detects the azimuth angle of the antenna, generates and detects linearly polarized terahertz pulse light in different directions, and records the time domain signal at each azimuth angle; after one rotation, the peak-to-peak value of the terahertz pulse at each azimuth angle is counted, and all The ratio of the maximum peak-to-peak value and the minimum peak-to-peak value in the azimuth angle is regarded as the first degree of anisotropy. The ratio of the maximum peak-to-peak value in all azimuth angles to the peak-to-peak value at an angle orthogonal to the azimuth angle corresponding to the maximum peak-peak value is calculated, and is regarded as the first degree of anisotropy. For the second degree of anisotropy, the ratio of the maximum refractive index to the minimum refractive index at each azimuth angle is calculated, which is regarded as the third degree of anisotropy.

Imaging reconstruction unit 9: generates various imaging data of transmission and reflection of the detected tooth based on the data processed by the spectral signal processing unit.

In another embodiment, the method for generating imaging data by the imaging reconstruction unit 9 includes: peak-to-peak imaging, time-of-flight tomography, refractive index imaging, frequency domain amplitude imaging, frequency domain phase imaging and azimuth angle imaging. Imaging of degrees of heterosexuality.

In another embodiment, the azimuthal anisotropy degree imaging is: the first anisotropy degree imaging uses the first anisotropy degree as the numerical size of the imaging pixel at the position, and the second anisotropy degree imaging uses the The second degree of anisotropy is used as the numerical size of the imaging pixel at this position, and the third degree of anisotropy is used as the numerical size of the imaging pixel at this position.

Display unit 10: used to externally display the imaging data reconstructed by the imaging reconstruction unit.

Early screening of enamel caries can be achieved using the detection system of the present invention. A detection method is now provided as follows:

Step 1: Turn on the detection system and scan the terahertz transmission time domain information of the patient’s teeth. The size of the pores in the dental tissue at the site of caries is similar to the wavelength of the terahertz wave, so it will cause stronger terahertz wave scattering, and the transmission signal will show greater attenuation. Peak-to-peak imaging of the transmission signal is used to characterize the caries area. An important basis for contouring. There are obvious differences in the refractive index of enamel and dentin in the terahertz band. Using transmission time domain signals to calculate the refractive index for refractive index imaging can characterize the contours of enamel and dentin.

Terahertz transmission imaging:

For the tooth to be detected, scan the buccal surface of the entire tooth and collect the transmission time domain signals at all scanning positions. Use transmission signals to first distinguish the distribution ranges of different tooth tissues (mainly to distinguish between enamel and dentin), and then perform transmission imaging on the enamel area of concern to find the shadow of enamel caries.

(1)Refractive index imaging

Due to the different content of components of enamel and dentin, the difference in refractive index appears in the time domain transmission signal, which can be calculated as follows:

In the formula, ω is the angular frequency; c is the speed of light in vacuum; d is the tooth thickness; is the delay time between the tooth signal and the reference signal. The distribution range of enamel and dentin is distinguished based on the difference in refractive index.

(2) Transmission intensity imaging

For the enamel area, compared with the healthy location, the transmission signal shows strong attenuation, and in time-domain transmission imaging, it appears as a shadow dark spot, and based on this, a preliminary diagnosis is made of whether there is early enamel caries in the measured tooth.

Step 2: During the transmission scan in the first step, the reflection signal is collected simultaneously and peak-to-peak imaging in the reflection time domain is performed. When the depth of the characteristic structure inside the tooth changes, the time delay of the reflected signal changes. This principle can be used to analyze the reflected signal and perform time-of-flight tomography. Fourier transform is performed on the reflected time domain signal to obtain the frequency domain signal, and three-dimensional imaging is performed using frequency as the third dimension.

Terahertz reflection imaging:

The transmission signal and the reflection signal have a one-to-one correspondence, and in the reconstructed image, the pixel positions of the transmission image and the reflection image also have a one-to-one correspondence. Use reflected signals to perform terahertz time-of-flight tomography and spectrum imaging to obtain layering and depth information inside the teeth, and perform three-dimensional reconstruction. In addition to reflection imaging of the buccal surface of the tooth, a separate reflection imaging of the occlusal surface can be performed.

(1) Reflection intensity imaging.

When a terahertz pulse is incident on the air/tooth interface, part of the terahertz pulse will pass through the interface, part of it will be reflected from the interface, and part of it will scatter in different directions at the interface. The size of the tissue pores at the caries site has a similar scale to the wavelength of the terahertz wave, so it will cause stronger scattering of the terahertz wave, and the reflected signal will be weaker than that at the healthy site, which will appear in the image as dark spots.

(2) Terahertz time-of-flight chromatography.

In addition to the first reflection at the air/tooth interface, the terahertz pulse will also be reflected if there are other interfaces at different depths inside the tooth. The interior of the tooth has layered structures such as enamel, dentin, and pulp. Time-of-flight tomography can be used to obtain the depth information of each layered structure inside the tooth based on different reflection pulse delays and the refractive index of different tissues, and perform three-dimensional Structural reconstruction. In particular, if there is caries in the enamel, there will also be an interface between the healthy enamel/caries enamel and the carious enamel/healthy enamel. The terahertz pulse will be reflected at such an interface and be imaged in three dimensions. It manifests itself in the enamel, allowing the detection of caries buried beneath healthy enamel and determining its depth.

(3) Reflection spectrum imaging.

Fourier transform is performed on the measured reflection signal to transform the time domain signal into a frequency domain signal. By taking signals of different frequencies for imaging, the response values at different frequencies can be extracted, thereby achieving three-dimensional reconstruction.

Step 3: For further detection of the suspected caries area detected in the first two steps, the antenna control unit and the synchronization unit control the azimuth angles of the transmitting antenna and the detection antenna to rotate synchronously, that is, while keeping the teeth stationary, adjust too much. Due to the polarization direction of the Hertz pulse light, the internal structure of the tooth at the carious location is destroyed, and the anisotropy of the response to the terahertz waves in different polarization directions changes. It can produce significant contrast to the healthy location, and the degree of azimuthal anisotropy is imaged. Further clarify the outline of carious tissue. Multi-source data fusion is performed with the detection results of the first two steps to improve the accuracy of diagnosis.

Terahertz polarization angle-dependent imaging:

After the first two steps are completed, more serious enamel caries will be effectively detected. For some early-stage caries that are not yet serious, the contrast of the image is weak and are classified as suspected caries. Using terahertz polarization angle-dependent measurements to make more refined measurements improves the accuracy of early enamel caries screening.

(1) Detection of anisotropy of enamel.

Change the polarization direction of the incident terahertz wave, fix the interval step size, and measure the transmission and reflection anisotropy of the terahertz pulse. An angle-dependent image can be drawn at each measurement position. If caries occurs in the enamel, the internal tissue will be destroyed, and the angle-dependent image will show irregular anisotropy, which can be used as a diagnostic indicator of the presence of caries.

(2) Anisotropic degree imaging.

Imaging is performed using the first degree of anisotropy, the second degree of anisotropy and the third degree of anisotropy measured at different positions as pixel values. After caries develops, the degree of anisotropy decreases and dark spots appear in the image.

(3) Terahertz polarization angle-dependent imaging of enamel.

Three-dimensional imaging is performed using the polarization angle of the incident terahertz wave as the third dimension. If there are dark spots within the enamel, and the contrast between the dark spots and the surrounding healthy enamel changes irregularly when imaging at different polarization angles, it can be used as a diagnostic indicator of the presence of caries.

The enamel caries detection system based on terahertz spectroscopy imaging proposed by the present invention utilizes the strong penetrability of terahertz waves, non-ionizing radiation characteristics, sensitivity to caries tissue, and high contrast response of caries tissue and healthy tissue. The differential characteristics enable the accurate, precise and intuitive detection of early enamel caries that are hidden and difficult to detect using non-ionizing radiation, which is difficult to achieve in the existing technology. For the preliminary diagnosis of the location of dental caries and its surrounding tissue, polarized terahertz light is used to conduct anisotropic detection of the location to be examined, and the anisotropic response of the carious tissue and healthy tissue to the excitation of terahertz light with different polarization directions is used The significant difference is that by combining the two modes of transmission spectroscopy imaging and reflection spectroscopy imaging, based on the two translation directions and the three dimensions of frequency, anisotropic dimensions that are dependent on the polarization direction of the incident terahertz light are introduced to further Improve the detection accuracy of the location, size and shape of caries, and reduce the possibility of false detection and missed detection.

The embodiments described above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any person familiar with the art can make more possible changes and modifications to the technical solution of the present invention using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modifications are all equivalent embodiments of the present invention. Therefore, any equivalent changes made based on the ideas of the present invention that do not deviate from the content of the technical solution of the present invention shall be covered by the protection scope of the present invention.

Claims (5)

1. An enamel caries detection system based on terahertz spectroscopy imaging, comprising: the device comprises a femtosecond laser generating and conducting unit, a terahertz transmitting antenna, a first polarized terahertz detecting antenna, a second polarized terahertz detecting antenna, an antenna control unit, a synchronization unit, a distance detection and control unit, a spectrum signal processing unit, an imaging reconstruction unit and a display unit; wherein,,

femtosecond laser generation and conduction unit: for generating linearly polarized terahertz pulse light;

terahertz transmitting antenna: for emitting linearly polarized terahertz pulse light to the tooth to be detected;

first polarization terahertz detection antenna: the terahertz pulse light is used for detecting terahertz pulse light transmitted through the detected teeth;

second polarized terahertz detection antenna: the terahertz pulse light is used for detecting the terahertz pulse light reflected by the detected teeth;

an antenna control unit: the terahertz pulse light detection device comprises a terahertz transmitting antenna, a first polarized terahertz detecting antenna, a second polarized terahertz detecting antenna, a first polarization terahertz detecting antenna, a second polarization terahertz detecting antenna, a third polarization terahertz detecting antenna, a fourth polarization terahertz detecting antenna and a third polarization terahertz detecting antenna, wherein the azimuth angles are used for rotationally controlling the terahertz transmitting antenna, the first polarized terahertz detecting antenna and the second polarized terahertz detecting antenna so as to transmit and detect terahertz pulse light with different linear polarization directions;

synchronization unit: the rotating azimuth angles of the terahertz transmitting antenna, the first polarized terahertz detecting antenna and the second polarized terahertz detecting antenna are kept the same when the terahertz transmitting antenna, the first polarized terahertz detecting antenna and the second polarized terahertz detecting antenna are rotated;

distance detection and control unit: the method comprises the steps of obtaining distances from a terahertz transmitting antenna, a first polarized terahertz detecting antenna and a second polarized terahertz detecting antenna to the surface of a detected tooth, preventing collision, and calculating the thickness of the detected tooth;

spectral signal processing unit: the terahertz time-domain spectrum signal processing device is used for processing terahertz time-domain spectrum signals obtained by detection of the first polarized terahertz detection antenna and the second polarized terahertz detection antenna;

an imaging reconstruction unit: generating various imaging data of the transmission and reflection of the detected teeth according to the data processed by the spectrum signal processing unit;

and a display unit: for externally displaying the imaging data reconstructed by the imaging reconstruction unit.

2. The terahertz spectroscopy imaging-based enamel caries detection system according to claim 1, wherein the method of spectral signal processing unit processing data includes: calculating peak-to-peak, fast fourier transform, calculating time of flight, calculating refractive index and azimuthal anisotropy degree analysis.

3. The terahertz spectroscopy imaging-based enamel caries detection system according to claim 2, characterized in that the azimuthal anisotropy degree analysis is: synchronously stepping and rotating azimuth angles of the terahertz transmitting antenna, the first polarized terahertz detecting antenna and the second polarized terahertz detecting antenna at the same detection position by a fixed angle to generate and detect linear polarized terahertz pulse light in different directions, and recording time domain signals under each azimuth angle; after one rotation, counting peak-to-peak values of terahertz pulses under each azimuth, calculating the ratio of the maximum peak-to-peak value to the minimum peak-to-peak value in all azimuth, regarding the ratio as a first anisotropic degree, calculating the ratio of the maximum peak-to-peak value in all azimuth and the peak-to-peak value of an angle orthogonal to the azimuth corresponding to the maximum peak-to-peak value, regarding the ratio as a second anisotropic degree, and calculating the ratio of the maximum refractive index to the minimum refractive index under each azimuth, regarding the ratio as a third anisotropic degree.

4. The terahertz spectroscopy imaging-based enamel caries detection system according to claim 1, wherein the method of generating imaging data by the imaging reconstruction unit includes: peak-to-peak imaging, time-of-flight tomography, refractive index imaging, frequency domain amplitude imaging, frequency domain phase imaging, and azimuthal anisotropy extent imaging.

5. The terahertz spectroscopy imaging-based enamel caries detection system of claim 4, wherein the azimuthal anisotropy degree is imaged as: the first degree of anisotropy imaging takes the first degree of anisotropy as the numerical value of the imaging pixel of the position, the second degree of anisotropy imaging takes the second degree of anisotropy as the numerical value of the imaging pixel of the position, and the third degree of anisotropy imaging takes the third degree of anisotropy as the numerical value of the imaging pixel of the position.