CN118941658A - Method for extracting confocal curved surface for attenuation coefficient imaging by beam matching method - Google Patents
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Abstract
The invention discloses a method for extracting a confocal curved surface by a beam comparison and carrying out attenuation coefficient imaging, which relates to the technical field of attenuation coefficient imaging and comprises the steps of carrying out simulation modeling based on a confocal OCT signal; changing the Rayleigh range in the confocal effect of the system by changing the incident beam diameter; carrying out confocal parameter extraction through the confocal effects of different Rayleigh ranges; and performing confocal correction on the acquired OCT data. The invention has the beneficial effects that: the method for extracting the confocal curved surface by the beam matching method and carrying out attenuation coefficient imaging can be used for constructing a model to extract the confocal parameters by changing the Rayleigh range in the confocal function, and the confocal parameters can be extracted without moving the focal plane position.
Description
Technical Field
The invention relates to the technical field of attenuation coefficient imaging, in particular to a method for extracting a confocal curved surface by a beam comparison method to perform attenuation coefficient imaging.
Background
Optical coherence tomography (Optical Coherence Tomography, OCT) is a low coherence optical interference imaging technique that can provide non-invasive, volumetric and real-time in vivo images of microscopic tissues, with image resolution up to the micrometer scale. But only provides morphological information of the tissue, quantitative analysis of tissue properties helps to more accurately distinguish diseased tissue from normal tissue. The optical attenuation coefficient (Optical Attenuation Coefficient, OAC) can measure the rate of attenuation of incident light as it passes through the medium, thereby allowing quantitative analysis of the tissue. In fact OAC analysis has been widely used for quantitative assessment and differentiation of various tissue types, quantification of OAC based on OCT data allows applications for in vivo diagnosis, such as imaging of atherosclerotic plaques, glaucoma assessment, differentiation of bladder normal tissue from cancerous tissue, and examination of the colon, and imaging of cerebral cortex after stroke. Furthermore, the measurement of OAC can also be used to assess vascularity in human burn scars and the development of acne scars and to monitor the effect of photodynamic therapy on skin lesions.
The measurement of the attenuation coefficient is a measure of the speed at which incident light attenuates as it passes through the medium and is a parameter of the properties of the medium. Light loss in tissue is typically caused by a combination of absorption and scattering, and as it propagates through the medium, irradiance of the beam follows Lambert-Beer's law, and various methods have been proposed to extract attenuation coefficient values from OCT images, which are related to the two general models proposed: single and multiple scatter models, which model should be used is determined by the type of tissue of interest. The earliest determination of attenuation coefficients from OCT data was typically based on fitting an exponential curve through the OCT depth profile, so that tissue was required to have a relatively uniform attenuation coefficient over a certain depth, and averaging of a large number of measured data points was required to obtain a reliable estimate by nonlinear least squares fitting, so that only relatively global attenuation coefficient measurements could be achieved. Later studies proposed a depth-resolved model based on a single scattering model that allowed the estimation of the attenuation coefficient for each pixel to have a higher resolution attenuation coefficient capability and without the need for pre-segmentation. The method relies on two assumptions: the ratio of the total attenuation of light over the imaging depth range to the back-scattered light received by the OCT system is a constant. But this method does not take into account the effect of the axial Point Spread Function (PSF) of the optics used, which can have a large impact on the calculation of the attenuation coefficient. Subsequent studies based on this model excluded the axial point spread function consideration based on single mode fiber, modeled the co-ordinates Jiao Hanshu of the OCT system, and divided the acquired OCT signal by co-ordinates Jiao Hanshu to recover the ideal attenuation signal. It is necessary to obtain the confocal parameters of OCT without prior knowledge, and current research involves fitting the confocal function directly in the model, but the method can only be applied to homogeneous media. And through the twice scanning, the sample information of the twice scanning is ensured to be consistent, but the focal plane position is changed, so that the corresponding confocal parameters can be extracted through the signals of the twice scanning, but signals with consistent sample information and different focal plane positions can be almost impossible to acquire in clinical application.
Disclosure of Invention
The present invention has been made in view of the above-described problems.
Therefore, the technical problems solved by the invention are as follows: the prior art method for measuring the attenuation coefficient has the problems that the confocal effect can influence the intensity distribution of the OCT signal, so that errors are generated in calculating the attenuation coefficient, the confocal effect needs to be eliminated for calculation, and the confocal parameter in the OCT signal is extracted under the condition of no priori knowledge.
In order to solve the technical problems, the invention provides the following technical scheme: a method for extracting confocal curved surface to carry out attenuation coefficient imaging by using a beam matching method comprises the steps of carrying out simulation modeling based on confocal OCT signals; changing the Rayleigh range in the confocal effect of the system by changing the incident beam diameter; carrying out confocal parameter extraction through the confocal effects of different Rayleigh ranges; and performing confocal correction on the acquired OCT data.
As a preferable scheme of the method for extracting confocal curved surfaces for attenuation coefficient imaging by using the beam matching method, the invention comprises the following steps: the simulation modeling based on the confocal OCT signal comprises modeling the OCT signal based on a single scattering model of light, wherein the OCT signal is composed of an exponential decay signal, a sensitivity roll-off signal, a proportionality constant, copolymerization Jiao Hanshu and multiplicative and additive noise, and the Fourier domain OCT signal at a physical depth z in a sample is expressed as:
I(z)＝h(z)Cαe-2μzS(z)+N(z)
Wherein h (z) is an axial point spread function based on a single-mode fiber, C represents a scale factor, alpha represents a backscattering coefficient, mu represents an attenuation coefficient, and roll-off Σ represents measurement sensitivity, and N (z) represents noise floor.
As a preferable scheme of the method for extracting confocal curved surfaces for attenuation coefficient imaging by using the beam matching method, the invention comprises the following steps: the simulation modeling based on the confocal OCT signal further comprises adding additive noise and multiplicative noise with SNR of 10, and fitting the focal position and the Rayleigh range as free parameters by comparing the two signals, wherein a fitting model is expressed as:
Where b is the diameter ratio of the two beams, z 0 represents the focal plane depth position, z R represents the apparent Rayleigh range, both of which are parameters of the confocal function, obtained by fitting as described above.
As a preferable scheme of the method for extracting confocal curved surfaces for attenuation coefficient imaging by using the beam matching method, the invention comprises the following steps: the method comprises the steps of changing the Rayleigh range in the confocal effect of a system by changing the diameter of an incident beam, diluting 20% Intralipid solution by distilled water, filling in a cuvette, imaging by placing in a sample arm at an inclined angle of 10 degrees, adjusting the position of a focal plane from the surface of the sample by the sample arm, acquiring different NA at the same focal depth twice, acquiring OCT signals of different confocal functions by changing NA, acquiring 1024B scans of 512×1024 each time, and averaging the middle 120B scans.
As a preferable scheme of the method for extracting confocal curved surfaces for attenuation coefficient imaging by using the beam matching method, the invention comprises the following steps: the method includes changing NA by using a beam expanding method, expanding Gaussian beam with diameter of 2.8mm to 5.6mm, under the condition that the focal length of a 1310 nanometer light source and a focusing lens is 30 mm, the focusing spot size of the beam with diameter of 2.8mm is 17.9 microns, expanding the diameter of the beam, reducing the focusing spot, and improving the transverse resolution to two times, which is expressed as:
Wherein Δd is the focal spot diameter, λ 0 is the light source center wavelength 1310nm, f is the focal length of the focusing lens 30mm, d is the beam diameter on the focusing lens, the beam diameter is changed from 2.8mm to 5.6mm, and the rayleigh range is changed, expressed as:
The change of the Rayleigh range is carried out while the confocal function is changed, the apparent Rayleigh range of B scanning with 2 times of difference between NA is 4 times, the larger the beam diameter is, the smaller the Rayleigh range is, the larger the influence of copolymerization Jiao Hanshu on the intensity distribution of OCT signals is, the full width at half maximum of the confocal function is narrowed, and the known Rayleigh range ratio is obtained by acquiring OCT signals with different beam diameters to meet the change of the Rayleigh range in a fitting model.
As a preferable scheme of the method for extracting confocal curved surfaces for attenuation coefficient imaging by using the beam matching method, the invention comprises the following steps: the confocal parameter extraction through the confocal effect of different Rayleigh ranges is carried out on an SS-OCT system, the central wavelength of a sweep laser light source is 1310 nanometers, a data acquisition card carries out analog-to-digital conversion on the acquired signals at the sampling rate of 100MS/s, and a digitized interference spectrum is temporarily stored in a memory of the data acquisition card board;
The data acquisition card is driven by an external k clock provided by a laser source, and spectrum is sampled to a linear wave number space through the k clock;
The data acquisition program is established on the Visual Studio platform and is used for acquiring data and storing spectrum signals to realize B scanning and C scanning, and the data processing comprises the steps of shaping, fourier transformation, fixed mode noise removal, depth-related background noise subtraction and sensitivity roll-off removal of the acquired spectrum signals.
As a preferable scheme of the method for extracting confocal curved surfaces for attenuation coefficient imaging by using the beam matching method, the invention comprises the following steps: the confocal correction of the acquired OCT data comprises fitting the focal plane position z 0 and the apparent Rayleigh range z R of I 1, so that copolymerization Jiao Hanshu h (z) of I 1 is obtained, the original OCT signal without the influence of a confocal function is obtained by dividing I 1 (z) by h (z), and then the attenuation coefficient is calculated by a depth resolution method and is expressed as:
Where μz is the attenuation coefficient of z depth, iz is the OCT signal of z depth, iz at the current time has subtracted the depth dependent background noise N (z), the confocal function h (z) and roll-off S (z) are excluded, and is achieved by dividing the acquired h (z) and S (z) in the Fourier domain OCT signal, and δ is the axial size of the pixel. This is done for each column of OCT signals to obtain the final attenuation coefficient image.
Another object of the present invention is to provide a system for extracting a confocal curved surface for attenuation coefficient imaging by using a beam matching method, which can construct a model extraction copolymer Jiao Canshu by changing the rayleigh range in a confocal function, so as to solve the problem that the current confocal function extraction technology needs to accurately move the focal plane position for two times of imaging.
As a preferable scheme of the system for extracting confocal curved surfaces for attenuation coefficient imaging by the beam comparison and fitting method, the invention comprises the following steps: the system comprises a simulation modeling module, a confocal parameter extraction module, a copolymerization Jiao Jiaozheng module and a Rayleigh range changing module; the simulation modeling module is used for performing simulation modeling based on the confocal OCT signal; the confocal parameter extraction module is used for extracting the confocal parameters through the confocal effects of different Rayleigh ranges; the confocal correction module is used for copolymerizing Jiao Jiaozheng the acquired OCT data; the Rayleigh range modification module is used for changing the Rayleigh range in the confocal effect of the system by changing the diameter of an incident beam.
A computer device comprising a memory storing a computer program and a processor executing the computer program is a step of performing a beam-matching method to extract a confocal curved surface for an attenuation coefficient imaging method.
A computer readable storage medium having stored thereon a computer program which when executed by a processor performs the steps of a beam-matching method for extracting a confocal curved surface for an attenuation coefficient imaging method.
The invention has the beneficial effects that: the method for extracting the confocal curved surface by the beam matching method and carrying out attenuation coefficient imaging can be used for constructing a model to extract the confocal parameters by changing the Rayleigh range in the confocal function, and the confocal parameters can be extracted without moving the focal plane position.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is an overall flowchart of a method for extracting a confocal curved surface for attenuation coefficient imaging by a beam matching method according to a first embodiment of the present invention.
Fig. 2 is a simulation diagram of confocal OCT signals of a method for extracting a confocal curved surface for attenuation coefficient imaging by using a beam matching method according to a first embodiment of the present invention, where the left side is a schematic diagram of signals with rayleigh ranges of ZR 1=200 and ZR 2=800 micrometers, and the right side is a result of dividing and logarithmizing two signals and a fitting graph.
Fig. 3 is a confocal correction flowchart of a method for extracting a confocal curved surface for attenuation coefficient imaging by a beam matching method according to a first embodiment of the present invention.
Fig. 4 is a solution B scan of different depths intralipid of focus of a method for extracting a confocal curved surface for attenuation coefficient imaging by a beam matching method according to a first embodiment of the present invention.
Fig. 5 is a intralipid solution imaging diagram of a method for extracting confocal curved surfaces by using a beam matching method to perform attenuation coefficient imaging, wherein the method is provided by a first embodiment of the invention, intralipid solution imaging is sequentially performed on 5.6mm beams with different focal depths from left to right, average a scanning contrast of sub-imaging is performed when the focal depths are 921 micrometers, corresponding focal positions and rayleigh ranges of focal surfaces of the different 5.6mm beams are extracted by using the beam matching method, and three signals of intralipid solution imaging of the 5.6mm beams with different focal depths are corrected.
Fig. 6 is a graph of depth-resolved attenuation coefficients of intralipid solutions with different focal depths before and after correction of an attenuation coefficient imaging method by extracting a confocal curved surface by a beam matching method according to a first embodiment of the present invention.
Fig. 7 is a B-scan of a layered titania phantom with a scale of 200 μm in each dimension for a method for performing attenuation coefficient imaging by extracting a confocal curved surface by beam-matching according to a second embodiment of the present invention.
Fig. 8 is a B-scan of a layered titania phantom with a scale of 400 μm in each dimension for a method for performing attenuation coefficient imaging by extracting a confocal curved surface by beam-matching according to a second embodiment of the present invention.
Fig. 9 is an image of a titanium oxide phantom attenuation coefficient after a confocal curve is extracted by a beam matching method to perform an attenuation coefficient imaging method according to a second embodiment of the present invention, (a) is a scale of 200 μm in each dimension, and (b) corresponds to the average attenuation coefficient and standard deviation of the corresponding layer in (a).
FIG. 10 is a schematic diagram showing an exemplary system for extracting a confocal curved surface for attenuation coefficient imaging by a beam-matching method according to a third embodiment of the present invention
Detailed Description
So that the manner in which the above recited objects, features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments, some of which are illustrated in the appended drawings. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Example 1
Referring to fig. 1-6, for one embodiment of the present invention, a method for extracting a confocal curved surface for attenuation coefficient imaging by using a beam matching method is provided, including:
S1: simulation modeling was performed based on confocal OCT signals.
Furthermore, performing simulation modeling based on the confocal OCT signal includes modeling the OCT signal based on a single scattering model of light, and forming the OCT signal from an exponentially decaying signal, a sensitivity roll-off signal, a proportionality constant, a co-ordination Jiao Hanshu, and multiplicative and additive noise, where the fourier domain OCT signal at the physical depth z in the sample is expressed as:
I(z)＝h(z)Cαe-2μzS(z)+N(z)
Wherein h (z) is an axial point spread function based on a single-mode fiber, C represents a scale factor, alpha represents a backscattering coefficient, mu represents an attenuation coefficient, and roll-off Sigma represents measurement sensitivity, N (z) represents noise floor, obtained by sample arm not placing sample empty acquisition. To determine the common characteristics of two scans of z 0 (focal plane position) and z R (rayleigh range) in the axial point spread function with the same sample depth position, two a scans with different beam diameters with different rayleigh ranges being identical in structure, the other terms in the fourier domain OCT signal at physical depth z in the sample except h (z) are identical, so the ratio of the confocal functions can be described by the ratio of the intensities of the two a scans. Two rayleigh ranges are simulated differently based on fourier domain OCT signals at physical depth Z in the sample, and two OCT signals with the same other factors are simulated with attenuation coefficients equal to 2 as shown in fig. 2, with apparent rayleigh ranges Z R1 =200 and Z R2 =800 microns at a focal plane position of 900 microns on the sample surface, with additive and multiplicative noise with SNR of 10 added.
It should be noted that, performing simulation modeling based on confocal OCT signals further includes adding additive and multiplicative noise with SNR of 10, and fitting the focal position and rayleigh range as free parameters by comparing the two signals, where the fitting model is expressed as:
Where b is the diameter ratio of the two beams, z 0 represents the focal plane depth position, z R represents the apparent Rayleigh range, both of which are parameters of the confocal function, obtained by fitting.
It should also be noted that the prior simulation is due to the change in OCT signal intensity distribution caused by the effect of the confocal function when actually acquiring data.
S2: the rayleigh range in the confocal effect of the system is changed by changing the incident beam diameter.
Furthermore, in order to realize my invention on a uniform scattering model, the rayleigh range in the confocal effect of the system is changed by changing the diameter of an incident beam, the system comprises diluting 20% of intralipid solution by distilled water, filling the solution in a cuvette, placing the solution in a sample arm for imaging at an inclined angle of 10 degrees, adjusting the position of a focal plane from the surface of the sample by the sample arm, acquiring different NA (NA) twice by the same focal depth, wherein NA is the numerical aperture of a focusing lens in an OCT (optical coherence tomography) system, describing the size of the light-receiving cone angle of the lens, increasing the numerical aperture of the focusing lens can reduce the focusing light spot, thereby improving the spatial resolution, but the deeper can be reduced, OCT signals of different confocal functions are obtained by changing NA, 1024B scans of 512×1024 are acquired each time, and the middle 120B scans are averaged. First, the study of the sample intralipid solution on the extraction of confocal surfaces is a standard homogeneous sample, intralipid solutions of different scattering coefficients can be obtained by dilution, and the application of the proposed method on this sample is an essential step. Referring to fig. 4, (a) - (c) the intralipid solution average B-scan with sample arm collimator at 5.6mm, the focal plane depth was progressively deeper. (d) - (e) the other conditions were the same as those of (a) to (c) except that the sample arm collimator was 2.8 mm. The scale bar is 400 μm in each dimension.
It should be noted that, changing NA by using the beam expanding method, expanding a gaussian beam with a diameter of 2.8mm to 5.6mm, and in the case of a 1310 nm light source and a focusing lens focal length of 30 mm, the focused spot size of the beam with a diameter of 2.8mm is 17.9 μm, and expanding the diameter of the beam reduces the focused spot, and improves the lateral resolution to two times, expressed as:
Wherein Δd is the focal spot diameter, λ 0 is the light source center wavelength 1310nm, f is the focal length of the focusing lens 30mm, d is the beam diameter on the focusing lens, the beam diameter is changed from 2.8mm to 5.6mm, and the rayleigh range is changed, expressed as:
the change of the Rayleigh range is carried out while the confocal function is changed, the apparent Rayleigh range of B scanning with 2 times of difference between NA is 4 times, the larger the beam diameter is, the smaller the Rayleigh range is, the larger the influence of copolymerization Jiao Hanshu on the intensity distribution of OCT signals is, the full width at half maximum of the confocal function is narrowed, and the known Rayleigh range ratio is obtained by acquiring OCT signals with different beam diameters to meet the change of the Rayleigh range in a fitting model. Figure 4 shows that intralipid solutions at different NA's average B-scan at different focal positions, especially at large NA's, the focal position significantly affects the intensity distribution of the B-scan. Three fixed focal plane positions were collected for the experiment, three dimensional scans of two different NA's, and data of the same focal plane position and different NA's were used for fitting.
Since the reference arm is also added with the beam expanding system, correction of the power of the reference arm needs to be considered, the influence of different SNR (signal to noise ratio) can be well removed by adding a constant as a free variable in a fitting model, the shape influence of a point spread function of 5.6mm light beam imaging at different focal plane positions on the whole average A scanning is shown in FIG. 5 (a), and the average A scanning of different NA at the same focal plane depth is shown in FIG. 5 (b), because previous researches have proved that the confocal effect can be well reflected when the focal plane is inside a sample, so that the focal plane is placed under the surface of the sample in experimental selection, and the data for fitting can be obtained by subtracting the pairs of signals. The focal plane depth and apparent rayleigh range from the fitting result are applied to data without excluding confocal effects, as shown in fig. 5 (c), where the fitting result R square is greater than 0.95 and the standard deviation of the fitting focal plane position is less than 10 μm. The attenuation coefficient was calculated using depth resolution, and it is seen from fig. 6 that the average a-scan in which the confocal was not corrected was far apart, and after correction was near its nominal value at 1310 nm.
S3: and carrying out confocal parameter extraction through the confocal effects of different Rayleigh ranges.
Furthermore, the confocal parameter extraction by the confocal effect of different Rayleigh ranges is included in an SS-OCT system, the central wavelength of a sweep laser light source is 1310 nanometers, a data acquisition card carries out analog-to-digital conversion on the acquired signals at the sampling rate of 100MS/s, and a digitized interference spectrum is temporarily stored in a memory of the data acquisition card board; the data acquisition card is driven by an external k clock provided by a laser source, and spectrum is sampled to a linear wave number space through the k clock; the data acquisition program is established on the Visual Studio platform and is used for acquiring data and storing spectrum signals to realize B scanning and C scanning, wherein single scanning along the depth z direction in the OCT imaging process is called A scanning, B scanning is a two-dimensional cross section image formed by splicing a series of A scanning along the X direction, wherein the light beam is continuously scanned through different deflection angles of an X vibrating mirror, a group of three-dimensional images, namely C scanning, formed by a plurality of B scanning converted along the Y direction are acquired through deflection of a Y vibrating mirror on the basis of the B scanning, the data processing comprises shaping, fourier transformation and fixed pattern noise removal of the acquired spectrum signals, and sensitivity roll-off is eliminated after the depth-related background noise is subtracted.
S4: and performing confocal correction on the acquired OCT data.
Further, performing confocal correction on the acquired OCT data includes fitting the focal plane position z 0 and the apparent rayleigh range z R of I 1 to obtain a copolymerization Jiao Hanshu h (z) of I 1, dividing I 1 (z) by h (z) to obtain an original OCT signal without the influence of a confocal function, and calculating an attenuation coefficient by a depth resolution method, where the attenuation coefficient is expressed as:
Where μz is the attenuation coefficient of z depth, iz is the OCT signal of z depth, iz at the current time has subtracted the depth dependent background noise N (z), the confocal function h (z) and roll-off S (z) are excluded, and is achieved by dividing the acquired h (z) and S (z) in the Fourier domain OCT signal, and δ is the axial size of the pixel. This is done for each column of OCT signals to obtain the final attenuation coefficient image. The flow is shown in fig. 3.
Example 2
Referring to fig. 7-9, for one embodiment of the present invention, a method for extracting a confocal curved surface by using a beam matching method to perform attenuation coefficient imaging is provided, and in order to verify the beneficial effects of the present invention, scientific demonstration is performed through economic benefit calculation and simulation experiments.
First, to evaluate the effect of the proposed beam-matching method in a multilayer sample, a series of optical multilayer samples consisting of titanium oxide powder and PDMS were prepared, and the formulated slurry was cast into glass molds of different thickness for curing, with the scattering coefficient controlled by varying the weight percentage of titanium oxide. Three films with different scattering coefficients are stacked for a plurality of times, the concentrations are respectively 0.136w%, 0.273w% and 1.33w%, the films with the same scattering coefficient are ensured to have the same physical characteristics, the thickness is 50 μm except the concentration of 1.33w%, and the other thicknesses are 150 μm, so that the aim of preventing light from being attenuated completely due to the overlarge scattering coefficient without reaching the ideal experimental depth is achieved.
Still with a beam combination of 2.8mm and 5.6mm, the imaging method still performs three-dimensional imaging at a scan angle of 10 degrees, avoiding specular reflection, and the scale is 200 microns in each dimension after an average of 120B scans, as shown in fig. 7. The confocal parameters were extracted according to the previous method for homogeneous samples. The actual focal plane position is not flat, and in order to obtain the actual focal plane position, a single A scan is adopted for fitting, namely, a B scan is adopted for 1024 times for fitting, and the fitted focal plane position is fitted into a curved surface by using a quadratic polynomial. In addition, the experimental objective was not to calculate the scattering coefficient of a titanium oxide sample of a specified concentration by reduction, but to ensure reproducibility of uniform scattering characteristics of layers of different depths within the sample. The fitting result is shown in fig. 8, the focal plane extracted by using the beam-to-fitting method is smoothed by fitting a second order polynomial, the scale is 400 micrometers in each dimension, the focal plane is a downward convex curved surface as can be seen from the distribution of speckles in the original B-scan, and the fitted focal plane is very close to the trend. And correcting confocal effect by fitting results, namely substituting free parameter results z 0、zR in fitting results into the OCT signals for Jiao Hanshu h (z), dividing the column of OCT signals I (z) by h (z) in vector form to obtain OCT signals without influence of confocal functions, calculating attenuation coefficients by a depth resolution method, and layering to count attenuation coefficient distribution of titanium oxide samples with different concentrations, wherein fig. 9 (a) is a graph of corrected attenuation coefficients of focal planes under the condition that the samples are deep, and layers with the same titanium oxide concentration show similar attenuation coefficients irrespective of depths of the layers in the samples. The relatively large standard deviation reflects the fact that the different layers are not completely uniform, as shown in fig. 9 (b).
The result shows that the invention provides a method for acquiring the system confocal function without moving the focal plane position, and the focal plane position can be extracted more accurately under the condition of deeper focal plane, so that the accuracy of attenuation coefficient calculation is improved.
Example 3
Referring to fig. 10, for an embodiment of the present invention, a system for extracting a confocal curved surface by using a beam matching method to perform attenuation coefficient imaging is provided, where the system includes a simulation modeling module, a rayleigh range modification module, a confocal parameter extraction module, and a copolymerization Jiao Jiaozheng module;
The simulation modeling module is used for performing simulation modeling based on the confocal OCT signals; the confocal parameter extraction module is used for extracting the confocal parameters through the confocal effects of different Rayleigh ranges; the confocal correction module is used for copolymerizing Jiao Jiaozheng the acquired OCT data; the Rayleigh range modification module is used for changing the Rayleigh range in the confocal effect of the system by changing the diameter of an incident beam.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a personal computer, a server, a network device, etc.) to perform all or part of the steps of the method of the embodiments of the present invention. And the aforementioned storage medium includes: a usb disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.
Logic and/or steps represented in the flowcharts or otherwise described herein, e.g., a ordered listing of executable instructions for implementing logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium may even be paper or other suitable medium upon which the program is printed, as the program may be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory.
It is to be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, the various steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, may be implemented using any one or combination of the following techniques, as is well known in the art: discrete logic circuits having logic gates for implementing logic functions on data signals, application specific integrated circuits having suitable combinational logic gates, programmable Gate Arrays (PGAs), field Programmable Gate Arrays (FPGAs), and the like. It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
Claims (10)
1. The method for extracting the confocal curved surface by using the light beam matching method to carry out attenuation coefficient imaging is characterized by comprising the following steps of:
Performing simulation modeling based on the confocal OCT signal;
Changing the Rayleigh range in the confocal effect of the system by changing the incident beam diameter;
Carrying out confocal parameter extraction through the confocal effects of different Rayleigh ranges;
and performing confocal correction on the acquired OCT data.
2. The method for extracting confocal curved surfaces for attenuation coefficient imaging by using a beam matching method as claimed in claim 1, wherein the method comprises the following steps: the simulation modeling based on the confocal OCT signal comprises modeling the OCT signal based on a single scattering model of light, wherein the OCT signal is composed of an exponential decay signal, a sensitivity roll-off signal, a proportionality constant, copolymerization Jiao Hanshu and multiplicative and additive noise, and the Fourier domain OCT signal at a physical depth z in a sample is expressed as:
I(z)＝h(z)Cαe-2μzS(z)+N(z)
Wherein h (z) is an axial point spread function based on a single-mode fiber, C represents a scale factor, alpha represents a backscattering coefficient, mu represents an attenuation coefficient, and roll-off Σ represents measurement sensitivity, and N (z) represents noise floor.
3. The method for extracting a confocal curved surface for attenuation coefficient imaging by using a beam matching method as claimed in claim 2, wherein the method comprises the following steps of: the simulation modeling based on the confocal OCT signal further comprises adding additive noise and multiplicative noise with SNR of 10, and fitting the focal position and the Rayleigh range as free parameters by comparing the two signals, wherein a fitting model is expressed as:
where b is the diameter ratio of the two beams, z 0 represents the focal plane depth position, and z R represents the apparent rayleigh range.
4. The method for extracting confocal curved surfaces for attenuation coefficient imaging according to the beam matching method of claim 3, wherein the method comprises the following steps: the method comprises the steps of changing the Rayleigh range in the confocal effect of a system by changing the diameter of an incident beam, diluting 20% Intralipid solution by distilled water, filling in a cuvette, imaging by placing in a sample arm at an inclined angle of 10 degrees, adjusting the position of a focal plane from the surface of the sample by the sample arm, acquiring different NA at the same focal depth twice, acquiring OCT signals of different confocal functions by changing NA, acquiring 1024B scans of 512×1024 each time, and averaging the middle 120B scans.
5. The method for extracting confocal curved surfaces for attenuation coefficient imaging according to the beam matching method of claim 4, wherein the method comprises the following steps: the changing the rayleigh range in the confocal effect of the system by changing the diameter of the incident beam further comprises changing NA by using a beam expanding method, expanding a Gaussian beam with the diameter of 2.8mm to 5.6mm, and under the condition that the focal length of a 1310 nanometer light source and a focusing lens is 30mm, the focusing spot size of the beam with the diameter of 2.8mm is 17.9 micrometers, and expanding the diameter of the beam reduces the focusing spot to improve the transverse resolution to two times, which is expressed as:
Wherein Δd is the focal spot diameter, λ 0 is the light source center wavelength 1310nm, f is the focal length of the focusing lens 30mm, d is the beam diameter on the focusing lens, the beam diameter is changed from 2.8mm to 5.6mm, and the rayleigh range is changed, expressed as:
The change of the Rayleigh range is carried out while the confocal function is changed, the apparent Rayleigh range of B scanning with 2 times of difference between NA is 4 times, the larger the beam diameter is, the smaller the Rayleigh range is, the larger the influence of copolymerization Jiao Hanshu on the intensity distribution of OCT signals is, the full width at half maximum of the confocal function is narrowed, and the known Rayleigh range ratio is obtained by acquiring OCT signals with different beam diameters to meet the change of the Rayleigh range in a fitting model.
6. The method for extracting confocal curved surfaces for attenuation coefficient imaging according to the beam matching method of claim 5, wherein the method comprises the following steps: the confocal parameter extraction through the confocal effect of different Rayleigh ranges is carried out on an SS-OCT system, the central wavelength of a sweep laser light source is 1310 nanometers, a data acquisition card carries out analog-to-digital conversion on the acquired signals at the sampling rate of 100MS/s, and a digitized interference spectrum is temporarily stored in a memory of the data acquisition card board;
The data acquisition card is driven by an external k clock provided by a laser source, and spectrum is sampled to a linear wave number space through the k clock;
The data acquisition program is established on the visual studio platform and is used for acquiring data and storing spectrum signals, and the data processing of B scanning and C scanning comprises the steps of shaping, fourier transformation, fixed mode noise removal, depth-related background noise subtraction and sensitivity roll-off removal of the acquired spectrum signals.
7. The method for extracting confocal curved surfaces for attenuation coefficient imaging according to the beam matching method of claim 6, wherein the method comprises the following steps: the confocal correction of the acquired OCT data comprises fitting the focal plane position z 0 and the apparent Rayleigh range z R of I 1, so that copolymerization Jiao Hanshu h (z) of I 1 is obtained, the original OCT signal without the influence of a confocal function is obtained by dividing I 1 (z) by h (z), and then the attenuation coefficient is calculated by a depth resolution method and is expressed as:
Where μz is the attenuation coefficient of z depth, iz is the OCT signal of z depth, iz at the current time has subtracted the depth dependent background noise N (z), the confocal function h (z) and roll-off S (z) are excluded, and is achieved by dividing the acquired h (z) and S (z) in the Fourier domain OCT signal, and δ is the axial size of the pixel. This is done for each column of OCT signals to obtain the final attenuation coefficient image.
8. A system for performing an attenuation coefficient imaging method by extracting a confocal curved surface by using the beam matching method as defined in any one of claims 1 to 7, wherein: the system comprises a simulation modeling module, a Rayleigh range changing module, a confocal parameter extracting module and a copolymerization Jiao Jiaozheng module;
the simulation modeling module is used for performing simulation modeling based on the confocal OCT signal;
The Rayleigh range changing module is used for changing the Rayleigh range in the confocal effect of the system by changing the diameter of an incident beam;
the confocal parameter extraction module is used for extracting the confocal parameters through the confocal effects of different Rayleigh ranges;
the confocal correction module is used for carrying out confocal correction on the acquired OCT data.
9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the beam matching method of any one of claims 1 to 7 for extracting a confocal curved surface for an attenuation coefficient imaging method.
10. A computer readable storage medium having stored thereon a computer program, wherein the computer program when executed by a processor performs the steps of the beam matching method of any of claims 1 to 7 for extracting a confocal curved surface for an attenuation coefficient imaging method.
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