CN103190887A - Scattered chaotic light tomography method - Google Patents

Abstract

A scattering chaotic optical tomography method, the method is to realize the signal of 1 μm ytterbium-doped chaotic fiber laser; realize the transmission of the reference light of the chaotic optical signal; realize the transmission of the scattered light of the chaotic optical signal; realize the chaotic light of two paths Correlation of signals; acquisition of point spread function; acquisition of tissue optical information; reconstruction of tissue parameters and graphics. The invention applies the chaotic light signal to the device of scattered light tomography, solves the problems of low precision, low spatial resolution and quantization performance of the pseudo-random signal, and realizes the detection of the parameter characteristics of biological tissues, which will promote chaos Research work on the originality of scientific research of laser in biomedical imaging and biological tissue health detection and other related disciplines.

Description

Scattering chaos optical tomography method

technical field

The invention relates to a tomographic imaging method, in particular to a method of applying chaotic signals to an optical tomographic imaging system to realize biomedical imaging and biological tissue health detection.

Background technique

The existing scattered optical tomography technology utilizes the relative penetration depth of scattered light in tissues to achieve clinical diagnosis at the organ level of 5-10 cm, uses near-infrared light to determine the three-dimensional distribution of optical parameters in biological tissues in a non-invasive manner, and provides tissue-based Noninvasive functional assay modality for important biochemical components of body weight. Due to its advantages of non-destructive, non-radiation, and continuous monitoring, it plays an important role in clinical medical diagnosis and has become the research focus of medical imaging modalities.

Ultrasound-guided light-scattering imaging system is currently a relatively mature monitoring technology for scattered light tomography, which has been used in clinical trials at home and abroad (Xu Zhenhua, Wu Chen, Mao Ling, Bai Jin, Huang Xuandong. Screening of ultrasonic light-scattering imaging system Investigation of early breast cancer, Chinese Oncology, 20(12): 932-936, 2011). With the continuous development of scattered light tomography, new scattering imaging techniques applied to biological tissues are also continuously researched and presented. The Sergio Fantini research group of Tufts University in the United States proposed hyperspectral-based light scattering tomography (Fridrik Larusson, Sergio Fantini and Eric L. Miller. Parametric level set reconstruction methods for hyperspectral diffuse optical tomography. Biomed Optics Express, 3(5) : 1006–1024. 2012.). The Yves Bérubé-Lauzière research group of the University of Sherbrooke, Canada proposed fluorescence light scattering chromatography (Yves Bérubé-Lauzière and Eric Lapointe. A time-domain non-contact fluorescence diffuse optical tomography scanner for small animal imaging. OSA Biomed. BTuD76 .2010. ). A self-normalized, full time-resolved scheme for fluorescence diffuse optical tomography proposed by Feng Gao, Limin Zhang, Huiyuan He et al. A self-normalized, full time-resolved scheme for fluorescence diffuse optical tomography .Proc. of SPIE Vol. , 68500N, 1-12, 2008.). However, these light scattering techniques based on different principles use ultrashort pulses as the detection light source.

With the development of biomedical imaging, scattered light tomography has also been continuously developed. However, due to the existence of ultrashort pulse light source, the scattered light tomography based on near-infrared ultrashort pulse has a complex structure in terms of measurement and imaging using point spread function. Since the pulse width of the ultrashort pulse is usually on the order of ps (10 ^-12 seconds), and the bandwidth of the current photoelectric detection and oscilloscope cannot meet the needs of the pulse response, the application is greatly limited.

The use of near-infrared continuous light as a light source to realize scattered light tomography provides a way to solve the problem of scattered light tomography. In 1999, J. J. A. Marota realized light scattering tomography using 32 continuous light sources of different wavelengths, and successfully detected the concentration of hemoglobin and deoxyhemoglobin in biological tissues (A. M. Siegel J. J. A. Marota and D. A. BoasDesign and evaluation of a continuous-wave diffuse optical tomography system. Optics Express.4 (8): 287-298, 1999.), since then the scattered light tomography based on continuous light has been widely studied. In 2003, Hamid Dehghani used a multi-wavelength light source for light-scattering tomography measurements compared with usual ultrasonic testing (Hamid Dehghani, Brian W. Pogue, Steven P. Poplack, and Keith D. Paulsen. Multiwavelength three-dimensional near-infrared tomography of the breast: initial simulation, phantom, and clinical results. Applied Optics, 42 (1): 135-145, 2003.), J. P. Culver realized three-dimensional light scattering tomography using continuous light (J . P. Culver, R. Choe, M. J. Holboke, L. Zubkov, T. Durduran, and A. Slemp V. Ntziachristos, B. Chance A. G. Yodh Three-dimensional diffuse optical tomography in the parallel plane transmission geometry: Evaluation of a hybrid frequency domain continuous wave clinical system for breast imaging. Medical. Physics. 30 (2): 235-246, 2003.). However, compared with light scattering tomography based on ultrashort pulses, light scattering imaging using continuous wavelengths has a lower signal-to-noise ratio, poor imaging quality, and limited detection accuracy.

Biological tissue imaging is playing an increasingly important role in medical health detection. Near-infrared light is used to detect the oxidation level of hemoglobin in tissues, and it is used in the human body without damage, radiation, and safety. High-definition imaging technology is urgently needed Realize human health monitoring such as early tumors.

However, the traditional measurement method has flaws in the measurement accuracy and measurement application principle, and there is a contradiction between the measurement clarity and the pulse width of the light source: to improve the measurement accuracy, it is necessary to use ultrashort pulses. The narrower the ultrashort pulse, the higher the detection accuracy and the more complex the system. If the ultrashort pulse is used to improve the accuracy, the ultrashort pulse generation technology and the weak optical signal detection technology will greatly increase the complexity of the system, the difficulty of operation and cost, and it is difficult to be practical and miniaturized.

  The pseudo-random code correlation method can solve the problem of limited measurement accuracy and detection in continuous light scattering imaging. In 2003, Nan Guang Chen's research group achieved a resolution of 0.6 ns for the point spread function by using pseudo-random code acousto-optic modulation semiconductor lasers to output pseudo-random pulse sequences and using them in scattered light tomography research (9. Nan Guang Chen and Quing Zhu Time-resolved diffusive optical imaging using

pseudo-random bit sequences. Optics Express. 11(25); 3445-3544, 2003.), through the efforts of the research group, a resolution of 200ps was achieved in 2009 by using 10GHz pseudo-random code modulation (10. Qiang Zhang and Nan Guang Chen. Pseudo-random single photon counting: the principle, simulation, and experimental results .Proc. of SPIE Vol. 7170 71700L-1, 2009.). In 2010, Weirong Mo proposed an improved scattered light tomography based on pseudo-random codes (11. Weirong Mo, and Nanguang Chen. Design of an Advanced Time-Domain Diffuse Optical Tomography System. IEEE Journal of Selected Topics In Quantum Electronics , 16(3):581-587, 2010.).相应已经发表的专利有DIFFUSE OPTICAL TOMOGRAPHY(US20080528146), SCATTER ATTENUATION TOMOGRAPHY(WO2007US76497), IMAGE RECONSTRUCTION METHOD FOR DIFFUSE OPTICAL TOMOGRAPHY, DIFFUSE OPTICAL TOMOGRAPHY SYSTEM, AND COMPUTER PROGEAM(US20100755965), DIFFUSE OPTICAL TOMOGRAPHY SYSTEM AND METHOD FOR USE(US20080050733 ), DETECTION OF STROKE EVENTS USING DIFFUSE OPTICAL TOMOGRAPHY (US2000491595). However, the current research on scattered optical tomography based on pseudo-random signals mainly has the following problems:

(1) Failure to use effective verification standards to verify the accuracy of the constructed forward model based on radiation and transmission equations in pseudo-random signals;

(2) The treatment of photon scattering in the two-dimensional radiative transfer equation violates the physical law of photon propagation;

(3) Failure to solve the problem of inaccurate forward models caused by the difference between the ideal boundary conditions used in solving the radiation transfer equation and the actual physical conditions;

(4) The data used to verify the algorithm of the inverse problem is the data generated by its own forward model,

That is to say, the solution to the inverse problem is a "deceitful problem".

And for the pseudo-random pulse sequence, the resolution of the measurement system can be improved by increasing the code length, but the generation of the pseudo-random optical pulse sequence needs to modulate the laser with an electrical random code. Limited by the bandwidth bottleneck of electronic devices, the phenomenon of low spatial resolution and low quantification performance of the scattered light tomography system based on pseudo-random signals has not been significantly improved.

Contents of the invention

The specific technical problem to be solved by the present invention is based on the accuracy problem existing in the radiation and transmission equation of the pseudo-random signal, and realizes the research of the scattering tomography method with high precision and high spatial resolution. Aiming at the deficiencies in the above-mentioned prior art, the present invention provides a scattering chaotic optical tomography method, and its specific technical scheme is as follows:

Realize 1μm ytterbium-doped chaotic fiber laser signal;

Realize the transmission of the reference light of the chaotic optical signal;

Realize the transmission of scattered light of chaotic optical signal;

Realize the correlation of chaotic optical signals in two paths;

Realize the acquisition of point extension function;

Realize the acquisition of tissue optical information;

Realize the reconstruction of tissue parameters and graphics.

In the above technical solution, further, the additional technical features are:

The reference light enters the imaging system after the signal generated by the 1 μm ytterbium-doped chaotic fiber laser passes through the variable retarder, the photodetector and the correlator to correlate with the scattered light in sequence.

The scattered light is a signal generated by a 1 μm ytterbium-doped chaotic fiber laser, which penetrates the measured object and then correlates with the reference light through a photodetector, an amplifier and a correlator, and then enters the imaging system.

The 1 μm ytterbium-doped chaotic fiber laser outputs a chaotic optical signal through a 980nm pump source sequentially through a wavelength division multiplexer, ytterbium-doped fiber, high nonlinear fiber, optical isolator, fiber grating, polarization controller and output coupler.

The tomographic imaging device divides the chaotic optical signal generated by the 1 μm ytterbium-doped chaotic fiber laser into two paths, one of which is used as a reference light, and the reference light is the chaotic optical signal generated by the 1 μm ytterbium-doped chaotic fiber laser through a variable delay device , photodetector and correlator correlate with the scattered light, and input the data collector and imaging system; the other is used as scattered light, and the scattered light is the chaotic light signal generated by the 1μm ytterbium-doped chaotic fiber laser through the intensity modulator and the sample module , photodetectors, amplifiers and correlators are correlated with the reference light and then input into the data collector and imaging system.

The 1 μm chaotic optical signal generated by the ytterbium-doped chaotic fiber laser proposed above in the present invention is applied to the scheme of scattered light tomography. This scheme adopts fiber grating and utilizes the nonlinear effect of fiber to realize a near-infrared wavelength broadband chaotic fiber laser source with a wavelength of 1 μm in an erbium-doped fiber laser. The optical fiber has a good beam quality and can be divided into different measurement channels according to the needs. The 1 μm chaotic optical signal is used as the probe light and input into the biological tissue to realize the detection of the parameter characteristics of the biological tissue.

For the detection of scattered light tomography, the correlation using chaotic signals has very good characteristics of delta-type pulses. Its characteristics are related to the bandwidth of chaos. The wider the bandwidth, the narrower the δ-type pulse, and its shape is similar to that of an ultrashort pulse. By measuring the amount of light information at each position in the point spread function curve of the δ-type correlation function through the tissue , the parameter characteristic distribution of the biological tissue can be obtained, and the detection of the hemoglobin oxidation level of the tissue can be realized, thereby judging the health status of the biological tissue. The invention utilizes the characteristics of the chaotic δ-type correlation function to solve the contradiction between ultrashort pulse detection complexity and measurement accuracy in time, and realizes scattered light tomography with high measurement accuracy through the good correlation of broadband chaos. the

Compared with the prior art, the present invention provides a device for applying chaotic light signals to scattered light tomography and its tomography method. Compared with the prior art, it has the following advantages and positive effects:

The invention proposes a device that applies chaotic light signals to scattered light tomography, solves the problems of low precision, low spatial resolution and quantization performance of pseudo-random signals, and realizes the monitoring scheme and detection of scattered light tomography method.

The present invention utilizes the excellent δ-type pulse correlation characteristics of the chaotic optical signal to realize the acquisition of the point spread function with small errors, especially the acquisition of the small error of the full width at half maximum of the point spread function and the full width at half maximum of the ideal point spread function, and improves the measurement precision.

The present invention utilizes the high sensitivity to boundary conditions and the disorder of the chaotic optical signal when reconstructing the chaotic optical signal to realize the collection of optical information with low bit error rate at different positions, thereby realizing an image with high measurement accuracy and quantization performance reconstruction.

The invention uses the chaotic light signal for the detection of the scattered light tomography imaging device, adopts the chaotic correlation method, and can obtain abundant optical information parameters in the autocorrelation function. The implementation of this technical solution will promote the original research work of chaotic laser in biomedical imaging and biological tissue health detection and other related disciplines in scientific research.

Description of drawings

Fig. 1 is a block diagram of the tomographic imaging method of the present invention.

Fig. 2 is a structural schematic diagram of the chaotic signal generating device of the present invention.

Fig. 3 is a schematic structural diagram of the present invention applied to the tomographic imaging device of Fig. 1 .

the

In the figure: 1: 1μm ytterbium-doped chaotic fiber laser; 2: variable retarder; 3: photodetector; 4: amplifier; 5: correlator; 6: imaging system.

In the figure: 7: 980nm pump source; 8: wavelength division multiplexer; 9: ytterbium-doped fiber; 10: high nonlinear fiber; 11: optical isolator; 12: fiber grating; 13: polarization controller; 14: output coupler.

In the figure: 1: 1 μm ytterbium-doped chaotic fiber laser; 15: intensity modulator; 2: variable retarder; 5: correlator; 3: photodetector; 16: sample module; 4: amplifier; 17: data acquisition device; 6: imaging system.

Detailed ways

The specific implementation manners of the present invention will be further described below.

As shown in Figure 1, a scattering chaotic optical tomography device provided by the present invention is implemented. The device is to apply the chaotic optical signal to the generation device of the chaotic optical signal in the scattered optical tomography, including a 980nm pump source 7, wavelength division multiplexer 8 , ytterbium-doped fiber 9 , high nonlinear fiber 10 , optical isolator 11 , fiber grating 12 , polarization controller 13 and output coupler 14 .

the

The chaotic optical signal described in the technical solution of the above generating method of the present invention is realized by using the nonlinear effect of optical fiber. The 980nm laser is used as the pump source of the ytterbium-doped fiber, the high nonlinear fiber is used to realize the generation of broadband chaos through the nonlinear effect of the fiber, the optical isolator ensures the one-way operation of the fiber ring, and the fiber grating is used to realize the adjustment and stability of the wavelength . A polarization controller, an optical isolator and a transmission fiber form a ring cavity. A 980nm/1000nm wavelength division multiplexer is used to pump the 980nm laser into the ytterbium-doped fiber laser. By adjusting the polarization controller and the pumping current, the ytterbium-doped fiber laser is realized chaotic laser output.

The invention relates to the application of chaotic optical signals to a scattered light tomography device, including a 1 μm ytterbium-doped chaotic fiber laser, an intensity modulator, a variable delay device, a correlator, a photodetector, a tissue module, a data collector and an imaging system .

The chaotic light signal applied to the optical fiber laser chaotic source of the scattered light tomography device described in the technical solution of the above-mentioned generation method of the present invention satisfies the medical treatment window of 600nm-1300nm wave band to realize deep penetration detection. The intensity modulator modulates the chaotic signal to a controllable intensity. The sample module is simulated according to various parameters of human skin tissue and tumor, and fat emulsion and plastic absorber can generally be used. The detection signal is a chaotic light signal passing through the sample module. The photodetector realizes the conversion of photoelectric signal and is used for the measurement of the tumor position. The correlator realizes the cross-correlation between the reference signal and the detection signal, and obtains the autocorrelation function and the optical information of each position, so as to reconstruct the tumor position.

The chaotic optical signal is applied to the scattered light tomography detection device and its method. Its composition is that the chaotic optical signal generated by the 1 μm ytterbium-doped chaotic fiber laser 1 is modulated and controllable by the intensity modulator 15, and enters the sample module 16 to realize optical detection. The attenuated optical signal undergoes photoelectric conversion in the photodetector 3 and saves the collected data. After the collected detection signal is amplified by the amplifier 4, the reference signal delayed by the chaotic optical signal through the variable delayer 2 is carried out in the correlator 5. Cross-correlation, the correlation signal is collected by the data collector 17 and superimposed into a point spread function curve, and the data of each position on the collected point spread function curve is input into the imaging system 6 to realize the inverse problem algorithm inversion, and realize the reconstruction of the absorption coefficient distribution of the tissue module Acquire, thereby simulating the tumor position image.

。基于此原理，通过数据采集器17采集到不同延迟时段互相关信号叠加成点扩展函数。Klose等采用离散纵标方法和有限差分方法对辐射传输方程进行求解，并在稳态模式下采用梯度方法对图像进行了重建，Jing Meng等在此基础上采用梯度树的方法对图像进行了重建，Kui Ren等在频率模式下对辐射传输方程采用了有限元方法求解，并采用Gauss-Newton方法进行了图像重建。O.Balima等采用最小方差有限元方法求解了频域辐射传输方程。Hyun Keol Kim发展了采用无需进行线性搜索的梯度方法在频域模式下进行图像重建的算法。Tanja Tarvainen等建立了联合辐射传输方程和扩散方程的正向模型。E.D.Aydin采用有限元-球谐波方法求解辐射传输方程。由此，基于扩散方程及边界条件情况下，利用MATLAB程序，可以实现女性乳腺肿瘤位置的检测。 The measurement principle of this experiment: This experiment establishes a mathematical model that simulates the propagation of light in the tissue body, so as to obtain the estimated value of the surface measurement, that is, the forward model; then, according to the forward model and the measurement obtained by the actual measurement system, the tissue The optical parameters inside the body are fitted to obtain the topological image of the internal optical parameters, that is, the inverse problem. This experiment is based on the diffusion equation in the radiation transfer theory, using the boundary element method to establish the corresponding forward mathematical model, and realize the algorithm for scattering optical tomography. The chaotic signal generated by the 1μm ytterbium-doped chaotic fiber laser 1 is divided into two transmission paths, one path is used as a reference signal and transmitted through the variable delay device 2, assuming that its output satisfies the functional relationship h(t); the other path is used as a detection signal and passed through the sample The module 16 uses the photodetector 3 to convert it into an electrical signal for transmission, assuming that its output satisfies the functional relational expression f(t). Then its cross-correlation function

. Based on this principle, the cross-correlation signals collected by the data collector 17 at different delay periods are superimposed into a point spread function. Klose et al. used the discrete ordinate method and the finite difference method to solve the radiative transfer equation, and used the gradient method to reconstruct the image in the steady state mode. Jing Meng et al. used the gradient tree method to reconstruct the image on this basis , Kui Ren et al. used the finite element method to solve the radiative transfer equation in the frequency mode, and used the Gauss-Newton method for image reconstruction. O.Balima et al. used the minimum variance finite element method to solve the frequency-domain radiative transfer equation. Hyun Keol Kim developed algorithms for image reconstruction in frequency domain mode using gradient methods without linear search. Tanja Tarvainen et al established a forward model that combines the radiative transfer equation and the diffusion equation. EDAydin uses the finite element-spherical harmonic method to solve the radiative transfer equation. Therefore, based on the diffusion equation and the boundary conditions, the detection of the position of the female mammary gland tumor can be realized by using the MATLAB program.

Claims (5)

1. a scattering chaotic light tomography method, comprising chaos correlation method; The realization method of its described tomography is as follows: Realize 1μm ytterbium-doped chaotic fiber laser signal; Realize the transmission of the reference light of the chaotic optical signal; Realize the transmission of scattered light of chaotic optical signal; Realize the correlation of chaotic optical signals in two paths; Realize the acquisition of point extension function; Realize the acquisition of tissue optical information; Realize the reconstruction of tissue parameters and graphics. 2. The scattering chaotic optical tomography method according to claim 1, wherein the reference light is to pass the signal generated by the 1 μm ytterbium-doped chaotic fiber laser (1) through the variable retarder (2) and the photodetector (3) in sequence. ) and the correlator (5) correlate the scattered light, and enter the imaging system (6). 3. The scattered chaotic optical tomography method according to claim 1, wherein the scattered light is generated by a 1 μm ytterbium-doped chaotic fiber laser (1) and passes through the measured object (16) through the photodetector (3) in turn. , the amplifier (4) and the correlator (5) enter into the imaging system (6) after correlating with the reference light. 4. The scattering chaotic optical tomography method according to claim 1, wherein the 1 μm ytterbium-doped chaotic fiber laser (1) passes the 980nm pump source (7) sequentially through a wavelength division multiplexer (8), doped An ytterbium optical fiber (9), a highly nonlinear optical fiber (10), an optical isolator (11), a fiber grating (12), a polarization controller (13) and an output coupler (14) output chaotic optical signals. 5. scattering chaotic light tomography method as claimed in claim 1, the device of its described tomography is that the chaotic light signal that 1 μm doped ytterbium chaotic fiber laser (1) produces is divided into two paths, one path is used as reference light , whose reference light is the chaotic optical signal generated by 1μm ytterbium-doped chaotic fiber laser (1), after being correlated with the scattered light by variable retarder (2), photodetector (3) and correlator (5), it is input into the data collector (17) and imaging system (6); the other way is used as scattered light, and the scattered light is the chaotic light signal generated by the 1 μm ytterbium-doped chaotic fiber laser (1) passing through the intensity modulator (15), sample module (16), photoelectric After the detector (3), the amplifier (4) and the correlator (5) correlate with the reference light, it is input into the data collector (17) and the imaging system (6).

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