CN115715668A - Method and device for detecting lipid plaque by combining OCT imaging and absorption spectrum - Google Patents
Method and device for detecting lipid plaque by combining OCT imaging and absorption spectrum Download PDFInfo
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Abstract
The invention discloses a lipid plaque detection method and a device combining OCT imaging and absorption spectrum. Scanning the lumen of the blood vessel by OCT, collecting the interference spectrum signal of the two-dimensional/three-dimensional space under the surface, the central wavelength of the OCT working wave band is 1200-1350 nm; dividing the interference spectrum signal into N wave bands, respectively calculating the absorption (or attenuation) coefficient of each spectrum wave band, wherein N is an integer greater than 1, and obtaining N frames of absorption (or attenuation) coefficient images; the characteristic identification and detection of the lipid plaque are carried out by utilizing the characteristic that cholesterol in the lipid plaque has strong short-wave band absorption and weak long-wave band absorption near the wavelength 1310 nm. The invention can realize the high-sensitivity extraction of lipid plaques in blood vessels and effectively improve the discrimination of the lipid plaques.
Description
Technical Field
The invention relates to a lipid plaque detection method and a device in the field of biomedical imaging, in particular to a lipid plaque detection method and a device combining Optical Coherence Tomography (OCT) imaging and absorption spectrum.
Background
Vulnerable plaques (Vulnerable Plaque) refer to those plaques that are unstable and thrombophilitic. Vulnerable plaques are prone to rupture, bleeding, calcification, or thrombosis due to their very thin surface envelope, high internal lipid content, and high levels of inflammatory material. Research shows that vulnerable plaque is closely related to occurrence of cardiovascular diseases, and is a main reason for inducing diseases such as thrombus, acute coronary syndrome, coronary heart disease and the like. Among these, the presence of lipid components is an important indicator of plaque vulnerability, and it is therefore important to accurately determine cardiovascular lipid plaques.
Coronary angiography is commonly used to detect the location and extent of stenosis of coronary arteries. However, angiography "sees" only the blood, and not the vascular structure and plaque composition. Near-infrared spectroscopy (NIRS) is based on the absorption of Near-infrared light by organic molecules, and the results of NIRS are shown in the form of "chemical diagrams" and color-coded maps, indicating the possibility of the presence of a lipid core at a given site, but it can only provide compositional data, and cannot show plaque features. Intravascular ultrasound (IVUS) is an invasive imaging technique that uses ultrasound to visualize the inside of the coronary wall, where predicting plaque progression is challenging due to the limited resolution of IVUS images (about 150-200 μm).
OCT is a low coherence interference imaging technology invented in the nineties of the last century, and has the advantages of non-contact, non-invasive, no mark, high sensitivity, high resolution and the like. Since the first development of OCT and endoscopic probe combination in 1996, endoscopic OCT technology has been widely used in the diagnosis and study of diseases in internal organs such as gastrointestinal tract, airway, ovary, urethra, and cardiovascular system. Among them, intravascular OCT (Intravascular Optical Coherence Tomography, IV-OCT) has become a commonly used imaging technique in Percutaneous Coronary Intervention (PCI) surgery.
However, the existing OCT technology uses the characteristic of high absorption coefficient (or attenuation coefficient) of lipid plaque in the full-wave range to distinguish from other tissue components, and the method specificity and distinguishing degree of the full-wave range are limited; there are also OCT techniques that use multiple (N = 16) short-time fourier transforms to construct wavelength-resolved absorption coefficient (or attenuation coefficient) curves for principal component analysis to extract lipid plaques, but such multi-band methods have low signal-to-noise ratios. Therefore, how to improve the discrimination and the signal-to-noise ratio of the lipid plaque detection method in the OCT image is a problem that needs to be solved urgently at present.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a lipid plaque detection method and a device combining OCT imaging and absorption spectrum, which can realize the extraction of a vascular wall spectrum signal by using an endoscopic micro probe, calculate the light absorption coefficient (or attenuation coefficient) by dividing into two wave bands (N = 2), and classify the lipid plaque based on the two wave bands (N = 2) by using the difference of the light absorption coefficient (or attenuation coefficient) caused by the absorption characteristics of the lipid plaque in the wave bands before and after 1310nm, wherein the absorption coefficient (or attenuation coefficient) is large in the short wave band and the absorption coefficient (or attenuation coefficient) in the long wave band.
The purpose of the invention is realized by the following technical scheme:
1. lipid plaque detection method combining OCT imaging and absorption spectrum
A weak coherent optical imaging method, utilize OCT to scan the lumen of blood vessel, gather the interference spectral signal of the two-dimentional/three-dimensional space under the surface;
a spectral calculation method of absorption coefficient divides interference spectral signals into N spectral bands, calculates the absorption coefficient of each spectral band respectively, N is an integer larger than 1, and obtains N frames of absorption coefficient images of vascular lumen tissues;
a lipid plaque detection method based on spectral absorption carries out feature identification and detection on lipid plaques according to the central wavelength of an OCT working waveband and N frames of absorption coefficient images of blood vessel lumen tissues.
In the weak coherent optical imaging method, the OCT imaging is one of the following methods:
a time domain OCT imaging method by changing the optical path of the reference arm;
or a spectral domain OCT imaging method for recording spectral interference signals by a spectrometer;
or a swept frequency OCT imaging method that records spectral interference signals with a detector.
The central wavelength of the OCT working wave band is 1200-1350 nanometers.
The calculating of the absorption coefficient of each spectrum band signal specifically includes:
and for each spectral band signal, obtaining an OCT intensity signal with distinguishable wave number by a short-time Fourier transform algorithm, and calculating an optical absorption coefficient according to the OCT intensity signal in the depth direction to obtain a current frame absorption coefficient image of the blood vessel lumen tissue.
The calculating of the light absorption coefficient according to the OCT intensity signal in the depth direction specifically includes:
removing average system noise from the OCT intensity signal along the depth direction to obtain a denoised OCT intensity signal;
performing linear fitting on the denoised OCT intensity signal in the depth direction to obtain an intensity depth curve, wherein the slope of each position on the intensity depth curve is used as the light absorption coefficient of the current position to obtain the light absorption coefficient of the target tissue area;
or the light absorption coefficient of the target tissue area is calculated by the following formula:
wherein x is a coordinate value in a fast scanning direction in the OCT probe scan, y is a coordinate value in a slow scanning direction in the OCT probe scan, z is a coordinate value in a depth direction, the depth direction is a direction perpendicular to a plane formed by the fast scanning direction and the slow scanning direction, i.e., an optical axis direction, μ (k, x, y, z) is a light absorption coefficient at a current position (x, y, z) of a current waveband k, S' (k, x, y, z) is an intensity of the denoised OCT signal at the current position (x, y, z) of the current waveband k, σ is a physical size in air corresponding to each pixel in the depth direction, and n is a refractive index of a target tissue region.
The lipid plaque detection method based on spectral absorption performs feature identification and detection of the lipid plaque according to the central wavelength of an OCT working waveband and N frames of absorption coefficient images of a blood vessel lumen tissue, and specifically comprises the following steps:
and dividing the N frames of absorption coefficient images of the vascular lumen tissue into short-wave-band absorption coefficient images and long-wave-band absorption coefficient images according to the central wavelength of the OCT working wave band, and performing characteristic identification on the short-wave-band absorption coefficient images and the long-wave-band absorption coefficient images by using a lipid plaque analysis method to realize the detection of the lipid plaque.
The lipid plaque analysis method comprises the following steps:
directly subtracting the short-wave-band absorption coefficient image and the long-wave-band absorption coefficient image to calculate an absorption coefficient difference value, and when the absorption coefficient difference value is larger than a preset threshold value, determining the difference value as a lipid plaque;
or processing the absorption coefficient image by using an averaging method according to the short-wave-band absorption coefficient image and the long-wave-band absorption coefficient image to obtain attenuation coefficient curves under different wavelengths, respectively performing principal component analysis on the short-wave-band attenuation coefficient curve and the long-wave-band attenuation coefficient curve to obtain corresponding characteristic values, forming a principal component characteristic value space by all the obtained characteristic values, and finally clustering the principal component characteristic value space to realize the detection of the lipid plaque;
or constructing a short-long wave band absorption coefficient space according to the short-long wave band absorption coefficient image and the long-long wave band absorption coefficient image, and clustering the short-long wave band absorption coefficient space to realize the detection of the lipid plaque;
or constructing a short-long wave band absorption coefficient space according to the short-long wave band absorption coefficient image and the long-long wave band absorption coefficient image, and classifying the short-long wave band absorption coefficient space by using a multiple linear regression model to obtain a classification curve so as to realize the detection of the lipid plaque.
The clustering includes clustering based on Euclidean distance, cosine distance, mahalanobis distance, or Manhattan distance.
2. Lipid plaque detection device combining OCT imaging and absorption spectrum
A scanning device, including endoscopic scanning, for scanning the blood vessel lumen multiple times;
the OCT optical coherence tomography device is used for carrying out OCT detection and imaging on the vessel wall;
one or more signal processors for performing spectral calculation of absorption coefficients and lipid plaque detection based on spectral absorption on the acquired OCT signals.
The OCT optical coherence tomography device adopts one of the following methods:
the system comprises a low-coherence light source, an interferometer and a detector;
or include low coherence light sources, interferometers and spectrometers;
or a swept-bandwidth spectral light source, an interferometer and a detector.
The invention has the following beneficial effects and innovation points:
compared with the prior art, the invention breaks through the limitation of the existing OCT lipid plaque differentiation, utilizes the endoscopic micro scanning probe to collect spectral signals of the vascular wall of a human body, carries out segmented spectral space analysis based on short-time Fourier transform (STFT), calculates the light absorption coefficients (or attenuation coefficients) of different wave bands, and finally successfully realizes lipid plaque classification by utilizing the difference of the light absorption coefficients (or attenuation coefficients) caused by the absorption characteristics of the lipid plaque of wave bands before and after 1310 nanometers.
The method and the device can realize the high-sensitivity extraction of the lipid plaque in the blood vessel and effectively improve the discrimination of the lipid plaque and other tissue components.
Drawings
FIG. 1 is a schematic diagram of the process of the present invention;
FIG. 2 is a schematic view of the apparatus of the present invention;
FIG. 3 is a schematic diagram of an apparatus according to an exemplary embodiment of the present invention;
FIG. 4 is a graph of simulated experimental results of an exemplary embodiment of the present invention;
in the figure: 1-a weak coherent optical imaging method; 2-a method for calculating the spectral absorption coefficient; 3-a method for lipid plaque detection based on spectral absorption; 5-a light source; 6-fiber coupler; 7-a polarization controller; 8-reference arm collimating mirror; 9-a plane mirror; 11-scanning the imaging device; 12-a sample to be tested; 13-point detector; 14-a signal processor; 15-swept light source; 16-90; 17-a first optical circulator; 18-reference arm collimator lens; 19-reference arm focusing lens; 20-a reference arm plane mirror; 21-a polarization controller; 22-a second optical circulator; 24-a fiber optic connector; 25-a rotating electrical machine; 26-a linear motor; 27-an endoscopic probe; 28-sample to be tested; 29-50 optical fiber coupler; 30-a balanced detector; 31-signal processor.
Detailed Description
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings, which form a part hereof. It should be noted that the description and illustrations are exemplary only and should not be construed as limiting the scope of the invention, which is defined by the appended claims, as any variation based on the claims is intended to be within the scope of the invention.
To facilitate an understanding of embodiments of the invention, operations are described as multiple discrete operations, however, the order of description does not represent the order in which the operations are performed.
The present description uses three-dimensional spatial directions x-y-z coordinates to represent the sample measurement space. This description is merely intended to facilitate discussion and is not intended to limit application of embodiments of the present invention. Wherein, x, y and z are orthogonal pairwise, and the z direction represents the depth direction, namely the incident optical axis direction; the x-direction is the OCT fast scan direction, the y-direction is the OCT slow scan direction, and the x-y plane forms a plane perpendicular to the optical axis.
T represents a variable, used merely to facilitate discussion and is not intended to limit the application of embodiments of the present invention, and may be any value, such as 1,2,3, etc.
As shown in figure 1, the method of the invention is a weak coherent optical imaging method 1, the central wavelength of the OCT working band is 1210-1410 nm, in the concrete implementation, the central wavelength of the OCT working band is 1310nm, and an OCT system based on the central wavelength 1310nm scans and collects the interference spectrum signal of the three-dimensional space of the vascular lumen tissue. A spectral calculation method 2 for absorption coefficient divides interference spectrum signals into N spectral bands (N = 2), performs segmented spectral space analysis by using STFT, and calculates light absorption coefficients (or attenuation coefficients) of different spectral bands. A lipid plaque detection method 3 based on spectral absorption is disclosed, wherein the short wave band is a wave band smaller than the central wavelength of an OCT working wave band, and the long wave band is a wave band larger than the central wavelength of the OCT working wave band. The lipid plaque feature identification and detection are carried out by utilizing the characteristics that cholesterol in the lipid plaque has strong short-wave band absorption and weak long-wave band absorption near 1310nm, and according to the central wavelength of OCT working wave band and N (N = 2) frame absorption (or attenuation) coefficient images of blood vessel lumen tissue.
Wherein, the scanning mode that adopts includes:
the endoscope type light beam scanning device is positioned in a near end scanning method that the scanning driving device is positioned outside a human body and a far end scanning method that the scanning driving device is positioned inside the human body. The near-end scanning method is mainly based on a light ray torque scanning method, a layer of torque coil is coated outside an optical fiber, and an external motor is used for driving the coil to rotate, so that detection light beams emitted from the tail end of the optical fiber synchronously rotate, and the cost is low. The far-end scanning method is mainly characterized in that a micro motor and a micro reflector are arranged at the tail end of a probe, the micro motor is used for driving the reflector to rotate so as to scan a sample, the sample is scanned, the rotating speed is relatively high, and the cost is relatively high.
A spectral calculation method 2 of an absorption coefficient.
First, STFT, i.e. short-time fourier transform, is performed on the spectral signal to obtain an axial OCT intensity signal S (k, z) resolvable along the depth z wavenumber k:
wherein, I int (k) For an interference spectral signal with a wavenumber k, w (k) is a window function with a spectral bandwidth Δ k, the fixed window function performs a fourier transform on the spectral interference signal in a sliding manner, the type of window function here we choose a Hanning window, and other windows such as Gaussian windows can also be used.
Then, calculating the light absorption coefficients (or attenuation coefficients) of different wavebands according to the OCT intensity signal characteristics which can be resolved by the wavenumber in the depth direction, and comprising the following steps:
removing average system noise from the OCT intensity signal along the depth direction to obtain a denoised OCT intensity signal; the setting is made by the following formula:
S′(k,z)＝S 0 (k,z)-N(k,z)
wherein S' (k, z) represents the corresponding denoised OCT intensity signal for the current depth and the band coordinate value z, S 0 (k, z) is the OCT intensity signal corresponding to the current depth coordinate z and the current band k, and N (k, z) is the average system noise corresponding to the coordinate value z in the current depth direction. The average system noise is specifically: and obtaining system noise without placing a sample for empty scanning, and averaging the system noise of each X-Y plane along the depth direction, namely averaging the system noise values in the Y direction and the X direction in sequence to obtain a one-dimensional average system noise distributed along the depth direction.
Calculating the light absorption coefficient (or attenuation coefficient) of the target tissue region according to the depth direction characteristic of the denoised OCT signal, specifically:
performing linear fitting on the depth direction characteristics of the denoised OCT signal in the depth direction to obtain an intensity depth curve, wherein the slope of each position on the intensity depth curve is used as the light absorption coefficient (or attenuation coefficient) of the current position to obtain the light absorption coefficient (or attenuation coefficient) of the target tissue area;
or the optical absorption coefficient (or attenuation coefficient) of the target tissue region is set by the following formula:
wherein x is a coordinate value in a fast scanning direction in the OCT probe scan, y is a coordinate value in a slow scanning direction in the OCT probe scan, z is a coordinate value in a depth direction, the depth direction is a direction perpendicular to a plane formed by the fast scanning direction and the slow scanning direction, i.e., an optical axis direction, μ (k, x, y, z) is a light absorption coefficient (or an attenuation coefficient) at a current position (x, y, z) of a current waveband k, S' (k, x, y, z) is an intensity of the denoised OCT signal at the current position (x, y, z) of the current waveband k, σ is a physical size in air corresponding to each pixel in the depth direction, and n is a refractive index of a target tissue region.
A lipid plaque detection method 3 based on spectral absorption.
In the 1310nm band, fibrous or normal tissue exhibits flat absorption characteristics. While lipids containing cholesterol have higher absorption properties in the lower bands, and the absorption in the lower bands predominates compared to the higher bands. The spectral differences between such substances can be used to distinguish lipid rich plaques from other tissues. Among them, lipid plaques show a large difference in light absorption coefficient (or attenuation coefficient) in a wavelength band lower than 1310nm and a small difference in light absorption coefficient (or attenuation coefficient) in a wavelength band higher than 1310 nm. The specific classification method can adopt direct subtraction of absorption (or attenuation) coefficient images of front and back wave bands to classify according to the difference value, or Euclidean distance measurement, least square method, multiple linear regression and principal component analysis. The embodiment herein uses Principal Component Analysis (PCA) to classify lipid plaques, PCA to classify spectral absorption (or attenuation) coefficients μ (k, x, y, z), and finds a principal component score for each sample point, clustering into lipid plaques and other tissues in principal component space.
The method specifically comprises the following steps:
according to the central wavelength of an OCT working waveband, dividing an N (N = 2) frame absorption (or attenuation) coefficient image of the vascular lumen tissue into a short-waveband absorption coefficient image and a long-waveband absorption coefficient image, and according to the difference of the absorption (or attenuation) coefficients of the lipid plaque in the short-waveband and the long-waveband, performing feature identification on the short-waveband absorption coefficient image and the long-waveband absorption coefficient image by using a lipid plaque analysis method to realize the detection of the lipid plaque.
A method of lipid plaque analysis comprising:
directly subtracting the short-wavelength band absorption coefficient image from the long-wavelength band absorption coefficient image (namely directly subtracting the absorption coefficients of the short-wavelength band from the absorption coefficients of the long-wavelength band) to calculate an absorption coefficient difference, wherein the coefficient difference of the lipid plaque is larger than other components, the other components refer to all tissues except the lipid plaque in the blood vessel lumen tissue, such as normal blood vessel wall tissue, fibrous plaque, calcified plaque and fibrocalcified mixed plaque, and when the absorption coefficient difference is larger than a preset threshold, the lipid plaque is obtained;
or processing the absorption coefficient image by using an averaging method according to the short-wave-band absorption coefficient image and the long-wave-band absorption coefficient image to obtain attenuation coefficient curves under different wavelengths, respectively performing principal component analysis on the short-wave-band attenuation coefficient curve and the long-wave-band attenuation coefficient curve to obtain corresponding characteristic values, forming a principal component characteristic value space by all the obtained characteristic values, finally clustering the principal component characteristic value space, and realizing the detection of lipid plaques according to the high attenuation characteristic of lipid compared with other components;
or constructing a short-long wave band absorption coefficient space according to the short-long wave band absorption coefficient image and the long-long wave band absorption coefficient image, and clustering the short-long wave band absorption (or attenuation) coefficient space to realize the detection of the lipid plaque; in the short-and-long-band absorption (or attenuation) coefficient space, the absorption (or attenuation) coefficient of the short band is represented by the abscissa and the absorption (or attenuation) coefficient of the long band is represented by the ordinate, or the absorption (or attenuation) coefficient of the long band is represented by the abscissa and the absorption (or attenuation) coefficient of the short band is represented by the ordinate, in a two-dimensional coordinate system.
Or constructing a short-long wave band absorption coefficient space according to the short-long wave band absorption coefficient image and the long-long wave band absorption coefficient image, and classifying the short-long wave band absorption coefficient space by using a multiple linear regression model to obtain a classification curve so as to realize the detection of the lipid plaque.
Fig. 2 shows an optical coherence tomography apparatus for distinguishing lipid plaques based on the absorption (or attenuation) coefficient of the present invention.
The main structure of the low coherence interferometry part of the device is a Michelson interferometer which is composed of 5-14 parts. After being transmitted to the optical fiber coupler 6, the light emitted from the light source 5 is divided into two light beams: one beam of light enters a reference arm part of the Michelson interferometer, passes through a polarization controller 7, reaches a reference arm collimating mirror 8, becomes parallel light beams through the collimating mirror and then irradiates a plane reflecting mirror 9; the other beam of light enters the sample arm part of the michelson interferometer and passes through the scanning imaging device 11 to focus the probe beam on the sample 12 to be measured. Then the light reflected back by the reference arm and the light reflected back by the sample arm interfere with each other, and are transmitted to the signal detector 13 through the optical fiber coupler 6, received by the signal detector and further transmitted to the signal processor 14.
According to different modes of low coherence interference detection signals, the optical coherence tomography device for distinguishing lipid plaques based on absorption (or attenuation) coefficients shown in fig. 2 specifically comprises:
1) Time domain detection means. The light source 5 adopts broadband low coherent light, the plane reflector 9 can move back and forth along the direction of the optical axis of the reference arm, and the signal detector 13 is a point detector. The change of the optical path of the reference arm is realized by translating the position of the plane mirror 9, and interference signals generated by the two arms are collected by the point detector 13, so that the low coherence interference detection of scattered signals in the z direction of a certain space depth is realized, and a depth-resolved sampling body is obtained.
2) A spectral domain detection device. The light source 5 adopts broadband low coherent light, the plane reflector 9 is fixed, and the signal detector 13 is a spectrometer. Interference signals generated by the two arms record interference spectra through a linear array camera in the spectrometer 13, the interference spectrum signals are decoded by adopting a Fourier transform analysis method, and depth z-direction information is parallelly acquired, so that a depth-resolved sampling body is obtained.
3) Provided is a sweep frequency detection device. The light source 5 adopts a sweep frequency light source, the plane reflector 9 is fixed, and the signal detector 13 is a point detector. The low coherence interference spectrum emitted by the sweep frequency light source is recorded in a time-sharing mode through the point detector 13, interference spectrum signals are decoded by adopting a Fourier transform analysis method, and depth z-direction information is parallelly acquired, so that a depth-resolved sampling body is obtained.
For the above measurement device, the absorption (or attenuation) coefficient calculation method can be combined with the spectrum in fig. 1, and a classification algorithm is used to realize high-sensitivity extraction of lipid plaques based on the absorption characteristic difference of 1310nm front and back wave bands.
Fig. 3 is an exemplary embodiment utilizing the present invention. The interference signal detection device adopts a sweep frequency OCT system, and the endoscopic micro probe adopts a lateral probe based on a light torque type. The whole device comprises a swept-frequency light source 15, a 90 optical fiber coupler 16, a 10 optical circulator 22, a reference arm collimating mirror 18, a reference arm focusing lens 19, a reference arm flat mirror 20, a polarization controller 21, a 50 optical fiber coupler 29, a balance detector 30, a signal processor 31, an optical fiber connector 24, a rotating motor 25, a linear motor 26, an endoscopic probe 27 and a sample 28 to be measured. The fiber connector 24, the rotating motor 25, the linear motor 26 and the endoscopic probe 27 form an endoscopic OCT probe scanning device, and the remaining swept-frequency light sources 15, 90.
The sweep frequency light source 15 adopts a wavelength tunable vertical cavity surface emitting laser with the center wavelength of 1310nm and the bandwidth of 100nm, the working frequency is 100kHz, and the endoscopic probe 27 adopts a probe with the working distance of 1.5 mm; the light emitted by the sweep light source 15 used in the device of the present invention is divided into two sub-beams after passing through the 90. One end of the first optical circulator 17 is connected with the incident end of the reference arm collimating mirror 18, and the light beam is emitted by the reference arm collimating mirror 18 and then focused on the reference arm plane mirror 20 through the reference arm focusing lens 19. In the sample arm endoscopic probe scanning device, the rotating motor 25 drives the optical fiber connector 24 to control the probe 27 to realize rotary scanning, the optical fiber connector 24 and the rotating motor 25 are placed on a guide rail of the linear motor 26 through a bracket, the linear motor 26 controls the endoscopic probe 27 to realize linear retraction scanning, and the sample 28 to be measured is positioned in the focal depth range of the endoscopic probe 27. The computer collects a trigger signal and a clock signal sent by a sweep frequency light source 15, and after frequency-variable light sent by the sweep frequency light source passes through a 90; the 90. The rotating motor 25 applies torque to the probe 27 through the optical fiber connector 24 to realize the rotation of the emergent light beam in the sample arm, and the linear motor 26 drives the rotating motor 25 and the optical fiber connector 24 which are arranged on the linear motor through the guide rail to realize the retraction scanning of the endoscopic probe 27, thereby realizing the acquisition of two-dimensional and three-dimensional OCT signals. After the back scattering light on the sample 28 to be measured returns back, the back scattering light enters the 50.
FIG. 4 shows the results of the mock experiments obtained in this example. Scanning the fault plane of the same position of the uniform imitation body by adopting the sweep frequency OCT device based on the endoscope type scanning probe shown in figure 3 to obtain a corresponding OCT interference spectrum signal, and obtaining the lipid plaque information by applying the spectral absorption coefficient (or attenuation coefficient) algorithm shown in the invention. Fig. 4 (a) is an OCT structural image corresponding to a cross section of a homogenate, with gel simulating other tissues on the left and mayonnaise simulating lipid plaques on the right. Fig. 4 (b) is a light absorption coefficient (or attenuation coefficient) image obtained in the full wavelength band, and it can be seen that the lipid component is different from other components. After calculating the absorption (or attenuation) coefficient by using the spectrum proposed in the present invention, the wavelength-resolved optical absorption coefficient (or attenuation coefficient) results are shown in fig. 4 (c), where the lipid component has a large absorption (or attenuation) coefficient in the short wavelength band and a small absorption (or attenuation) coefficient in the long wavelength band, and the other components show a small difference in the short/long wavelength bands. The clustering result is shown in fig. 4 (d), and the lipid component and other components show different absorption (or attenuation) coefficient distributions in the short-wavelength band space and the long-wavelength band space, and the lipid plaque can be better distinguished by using the absorption characteristics.
The above experimental comparison results fully illustrate that: the lipid plaque detection method combining OCT imaging and absorption spectrum can effectively extract lipid plaque information, improve classification sensitivity and has remarkable technical effect.
Claims (10)
1. A method for lipid plaque detection combining OCT imaging and absorption spectroscopy, comprising:
a weak coherent optical imaging method (1) scans a blood vessel lumen by OCT (optical coherence tomography), and acquires an interference spectrum signal of a two-dimensional/three-dimensional space below the surface;
a spectral calculation method (2) of absorption coefficient divides interference spectrum signals into N spectral bands, and respectively calculates the absorption coefficient of each spectral band, wherein N is an integer larger than 1, and N frames of absorption coefficient images of vascular lumen tissues are obtained;
a lipid plaque detection method (3) based on spectral absorption carries out feature recognition and detection on a lipid plaque according to the central wavelength of an OCT working waveband and N frames of absorption coefficient images of a blood vessel lumen tissue.
2. A method for lipid plaque detection combining OCT imaging and absorption spectroscopy according to claim 1, characterized by a weak coherent optical imaging method (1), OCT imaging being one of the following methods:
a time domain OCT imaging method by changing the optical path of the reference arm;
or a spectral domain OCT imaging method for recording spectral interference signals by a spectrometer;
or a swept frequency OCT imaging method that records spectral interference signals with a detector.
3. The method of claim 1, wherein the central wavelength of the OCT operating band is between 1200 and 1350 nanometers.
4. The method for detecting lipid plaques by combining OCT imaging and absorption spectroscopy as claimed in claim 1, wherein said calculating the absorption coefficient of each spectral band signal specifically comprises:
and for each spectral band signal, obtaining an OCT intensity signal with distinguishable wave number by a short-time Fourier transform algorithm, and calculating an optical absorption coefficient according to the OCT intensity signal in the depth direction to obtain a current frame absorption coefficient image of the blood vessel lumen tissue.
5. The method for detecting lipid plaque combining OCT imaging and absorption spectroscopy of claim 1, wherein the calculating of the light absorption coefficient from the OCT intensity signal in the depth direction specifically comprises:
removing average system noise from the OCT intensity signal along the depth direction to obtain a denoised OCT intensity signal;
performing linear fitting on the denoised OCT intensity signal in the depth direction to obtain an intensity depth curve, wherein the slope of each position on the intensity depth curve is used as the light absorption coefficient of the current position to obtain the light absorption coefficient of the target tissue area;
or the optical absorption coefficient of the target tissue region is calculated by the following formula:
wherein x is a coordinate value in a fast scanning direction in the OCT probe scan, y is a coordinate value in a slow scanning direction in the OCT probe scan, z is a coordinate value in a depth direction, the depth direction is a direction perpendicular to a plane formed by the fast scanning direction and the slow scanning direction, i.e., an optical axis direction, μ (k, x, y, z) is a light absorption coefficient at a current position (x, y, z) of a current waveband k, S' (k, x, y, z) is an intensity of the denoised OCT signal at the current position (x, y, z) of the current waveband k, σ is a physical size in air corresponding to each pixel in the depth direction, and n is a refractive index of a target tissue region.
6. The method for detecting lipid plaque according to claim 1 in combination with OCT imaging and absorption spectroscopy, wherein the method (3) for detecting lipid plaque based on spectral absorption performs feature identification and detection of lipid plaque according to the central wavelength of OCT operating band and N frames of absorption coefficient images of vascular lumen tissue, and specifically comprises:
and dividing the N frames of absorption coefficient images of the vascular lumen tissue into short-wave-band absorption coefficient images and long-wave-band absorption coefficient images according to the central wavelength of the OCT working wave band, and performing characteristic identification on the short-wave-band absorption coefficient images and the long-wave-band absorption coefficient images by using a lipid plaque analysis method to realize the detection of the lipid plaque.
7. The method for lipid plaque detection combining OCT imaging and absorption spectroscopy of claim 6, wherein said method for lipid plaque analysis comprises:
directly subtracting the short-wave-band absorption coefficient image and the long-wave-band absorption coefficient image to calculate an absorption coefficient difference value, and when the absorption coefficient difference value is larger than a preset threshold value, determining the difference value as a lipid plaque;
or processing the absorption coefficient image by using an averaging method according to the short-wave-band absorption coefficient image and the long-wave-band absorption coefficient image to obtain attenuation coefficient curves under different wavelengths, respectively performing principal component analysis on the short-wave-band attenuation coefficient curve and the long-wave-band attenuation coefficient curve to obtain corresponding characteristic values, forming a principal component characteristic value space by all the obtained characteristic values, and finally clustering the principal component characteristic value space to realize the detection of the lipid plaque;
or constructing a short-long wave band absorption coefficient space according to the short-long wave band absorption coefficient image and the long-long wave band absorption coefficient image, and clustering the short-long wave band absorption coefficient space to realize the detection of the lipid plaque;
or constructing a short-long wave band absorption coefficient space according to the short-long wave band absorption coefficient image and the long-long wave band absorption coefficient image, and classifying the short-long wave band absorption coefficient space by using a multiple linear regression model to obtain a classification curve so as to realize the detection of the lipid plaque.
8. The method of claim 7, wherein the clustering comprises Euclidean distance, cosine distance, mahalanobis distance, or Manhattan distance based clustering.
9. A combined OCT imaging and absorption spectroscopy lipid plaque detection device for performing the method of any one of claims 1 to 8, comprising:
a scanning device, including endoscopic scanning, for scanning the blood vessel lumen multiple times;
the OCT optical coherence tomography device is used for carrying out OCT detection and imaging on the vessel wall;
one or more signal processors for performing spectral calculation of absorption coefficients and lipid plaque detection based on spectral absorption on the acquired OCT signals.
10. A combined OCT imaging and absorption spectroscopy lipid plaque detection device of claim 9, wherein said OCT optical coherence tomography device employs one of the following:
the system comprises a low-coherence light source, an interferometer and a detector;
or a low coherence light source, an interferometer and a spectrometer;
or a swept-bandwidth spectral light source, an interferometer and a detector.
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