CN109164048B - Polarization demodulation method for polarization-sensitive optical coherence tomography of catheter - Google Patents

Abstract

A polarization demodulation method for catheter polarization-sensitive optical coherence tomography, comprising: setting the polarization state of input light of a catheter polarization-sensitive optical coherence tomography system; setting the reference light on H and V paths in the system as Equal light intensity; perform dispersion compensation, interpolation Fourier transform, and image segmentation on the electrical signal measured at the polarization diversity; convert the Jones matrix at the sample depth and the reference surface position to the Mueller matrix; convert the sample depth at the The Mueller matrix is multiplied by the inverse of the Mueller matrix at the reference surface position to obtain the measured Mueller matrix of the sample; the debiasing and double attenuation effects are eliminated; the measured Mueller matrix is used to obtain the phase retardation in polar coordinates; The phase retardation is converted from polar coordinates to Cartesian coordinates, and finally the birefringence image of the sample of the catheter polarization-sensitive optical coherence tomography system is obtained. The invention can eliminate the problem that the guide tube cannot demodulate the birefringence information of the sample in the state of high-speed rotation.

Description

A polarization demodulation method for catheter polarization-sensitive optical coherence tomography

technical field

The invention relates to a catheter optical coherence tomography method. In particular, it relates to a polarization demodulation method for catheter polarization-sensitive optical coherence tomography.

Background technique

Catheter OCT imaging technology is the vascular imaging method with the highest image resolution at present, especially the catheter PS-OCT imaging technology, which can solve the medical problem that the stability of atherosclerotic plaque is difficult to judge in vivo, real-time and quickly, and can improve the arterial stability. Prevention and treatment of atherosclerotic diseases. However, the resolution of the existing OCT system has reached the level that it is possible to judge the nature of tissue plaques, but it is still insufficient in terms of tissue penetration ability, image clarity and the accuracy of tissue plaque type judgment. PS-OCT technology is used. , improving the performance of related technologies is the key direction of OCT system development, and it is also the only way to solve the above-mentioned key scientific problems.

In catheter OCT, catheter PS-OCT is an extension of catheter OCT technology that provides a quantitative measure of tissue birefringence properties. Birefringence of light changes the polarization state of light and can be associated with proteins and biological macromolecules with directional structures such as collagen, actin, and the like. The enhanced birefringence of ductal PS-OCT is closely related to the presence of abundant thick collagen fibers or intimal smooth muscle cells, so the high-resolution detection of ductal PS-OCT imaging can be applied for plaque stability measurements after enhancement. In addition, the catheter PS-OCT system has the potential to assess plaque collagen and differentiate between normal intima, fibrous plaques, lipid plaques, and calcified plaques. Existing polarization demodulation methods utilize Jones matrices to characterize the polarization characteristics of systems and samples. However, in catheter PS-OCT, the fiber in the catheter needs to rotate at high speed, which makes the system have strong depolarization and double attenuation effects.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a polarization demodulation method capable of realizing polarization demodulation of the PS-OCT image of the catheter.

The technical scheme adopted by the present invention is: a polarization-demodulation method for catheter polarization-sensitive optical coherence tomography imaging, which is used in a catheter polarization-sensitive optical coherence tomography imaging system, comprising the following steps:

1) The polarization state of the input light of the catheter polarization-sensitive optical coherence tomography system is set to be E _in ; the reference light on the H and V paths in the system is set to equal light intensity; The signal is subjected to dispersion compensation, interpolation Fourier transform, and then image segmentation; the Jones matrix at the sample depth position and the selected reference surface position are converted into Mueller matrices respectively; the Mueller matrix at the sample depth position is multiplied by The inverse of the Mueller matrix at the selected reference plane position yields the measured Mueller matrix of the sample;

2) Eliminate depolarization and double attenuation effects by matrix decomposition;

3) The phase delay amount R under polar coordinates is obtained by calculating the measured Mueller matrix M(z _ref , z);

4) Perform coordinate interpolation transformation on the phase retardation in polar coordinates, convert polar coordinates into Cartesian coordinates, and finally obtain the birefringence image of the catheter polarization-sensitive optical coherence tomography system sample.

The polarization state E _in described in step 1) is expressed as:

是输入光在H和V路上两个偏振态的相位差。where H _in1 is the light intensity of the input polarization state 1 in the H channel, H _in2 is the light intensity of the input polarization state 2 in the H channel, _Vin1 is the light intensity of the input polarization state 1 in the V channel, and _Vin2 is the input polarization state 2 light intensity in the The light intensity of the V channel, where the input polarization states 1 and 2 are the same light intensity in the H and V channels,

is the phase difference between the two polarization states of the input light on the H and V paths.

In the system described in step 1), the reference light that is set to equal intensity on the H and V paths is expressed as:

where H _ref and V _ref are the quadrature components of the reference light on the H and V channels, respectively, and ψ is the phase difference of the polarization states of the reference light on the H and V paths.

The conversion method described in step 1) that respectively converts the Jones matrix at the sample depth position and the selected reference surface position into the Mueller matrix includes:

The Jones matrix is expressed as:

where a, b, c, d are any four elements of the Jones matrix,

The conversion relationship between Jones matrix and Mueller matrix is:

表示Kronecker积，U表示变换矩阵：in

represents the Kronecker product, and U represents the transformation matrix:

According to the conversion relationship between Jones matrix and Mueller matrix, the Jones matrix Q(z) at the sample depth position and the Jones matrix Q(z _ref ) at the selected reference surface position are respectively converted into Mueller matrix

Let M _ST be the sample round-trip matrix, M _in , M _out represent the Mueller matrix of the optical path of the system, and the Mueller matrix S(z _ref ) at the position of the sample reference plane measured at the polarization diversity is expressed as:

The Mueller matrix S(z) at the z position of the sample measured at polarization diversity, expressed as:

The measurement matrix M(z _ref ,z) of the sample at z is obtained by operating S(z _ref ) and S(z):

In step 2), the depolarization and double attenuation effects are eliminated by matrix decomposition, including:

Decompose the 4*4 Mueller matrix M:

M=M _Δ M _R M _D (11)

_{M Δ} is the depolarization matrix, MR is the birefringence matrix, and _MD is the double attenuation matrix. The ultimate purpose of this method is to eliminate the depolarization and double attenuation effects in the Mueller matrix, and then obtain the birefringence matrix _MR .

Perform matrix decomposition on the measurement matrix M(z _ref ,z) to eliminate the depolarization and double attenuation effects to obtain a Mueller matrix containing only birefringence:

和

是只包含双折射成分的穆勒矩阵，此时

为酉矩阵，M^R(z_ref,z)与

为相似矩阵。where M ^R (z _ref ,z),

and

is the Mueller matrix containing only birefringent components, then

is a unitary matrix, M ^R (z _ref ,z) is the same as

is a similarity matrix.

The phase delay amount R under the polar coordinates described in step 3) is obtained by the following formula:

是探测到样品在z位置处的只包含双折射成分的穆勒矩阵，tr是矩阵的迹。In the formula,

is the Mueller matrix containing only the birefringent component of the detected sample at the z position, and tr is the trace of the matrix.

A polarization demodulation method for catheter polarization-sensitive optical coherence tomography of the present invention relates to how to demodulate birefringence information of a sample in a catheter polarization-sensitive optical coherence tomography (Polarization-sensitive OCT), namely PS-OCT image, and simultaneously It can eliminate the problem that the catheter cannot demodulate the birefringence information of the sample under high-speed rotation. The invention enables the PS-OCT system to fully express the birefringence information of the sample, improves the analysis ability of microscopic lesions in blood vessels, and obtains more characteristic information of atherosclerotic plaque than the traditional OCT intensity image. Interpretation, the ability to gain additional intravascular microscopic lesion analysis. The invention utilizes the Mueller matrix to characterize the polarization characteristics of the system and the sample, and eliminates the depolarization and double attenuation effects of the system and the sample through matrix decomposition. By deriving the intrinsic relationship between the sample transmission matrix and the PS-OCT signal matrix, that is, the two matrices are similar and the traces of the similar matrices are equal, the birefringence phase delay of the sample is obtained, and the polarization demodulation of the PS-OCT image of the catheter is realized. .

Description of drawings

1 is a schematic structural diagram of a catheter polarization-sensitive optical coherence tomography imaging system in the present invention;

FIG. 2 is a flow chart of a polarization demodulation method for catheter polarization-sensitive optical coherence tomography according to the present invention.

Detailed ways

The following describes a polarization demodulation method for catheter polarization-sensitive optical coherence tomography of the present invention in detail with reference to the embodiments and the accompanying drawings.

The invention provides a polarization demodulation method for catheter polarization-sensitive optical coherence tomography, which utilizes the Mueller matrix to characterize the polarization characteristics of the system and the sample, and eliminates the depolarization and double attenuation effects of the system and the sample through matrix decomposition. By deriving the intrinsic relationship between the sample transmission matrix and the PS-OCT signal matrix, that is, the two matrices are similar and the traces of the similar matrices are equal, the birefringence phase delay of the sample is obtained, and the polarization demodulation of the PS-OCT image of the catheter is realized.

The present invention is a polarization demodulation method for catheter polarization-sensitive optical coherence tomography, which deduces the PS-OCT signal matrix of the catheter and the sample Jones matrix by performing a series of calculations and transformations on the time domain data collected by the balance detector. By eliminating the interference of the external environment and the transmission matrix of the optical fiber path on the sample phase delay, and then through the transformation of the Jones matrix to the Mueller matrix and the Mueller decomposition, the PS-OCT image polarization demodulation method in the catheter is proposed. In the catheter PS-OCT system, the birefringence information of the sample can be accurately demodulated when the catheter is rotated at a high speed.

A polarization demodulation method for catheter polarization-sensitive optical coherence tomography of the present invention is used for the catheter polarization-sensitive optical coherence tomography (PS-OCT) system as shown in Figure 1, and its working principle is:

The outgoing light of the scanning light source 1 of the catheter PS-OCT system enters through the first port 21 of the 1:99 fiber coupler 2, and is respectively transmitted from the second port 22 and the third port of the first fiber coupler 2 in a ratio of 1:99. Port 23 is assigned to the sample arm and reference arm. The outgoing light from the second port 22 of the first fiber coupler 2 at 1:99 enters the sample arm, and the light beam entering the sample arm enters the first three-ring polarization controller 3 and then enters the polarization maintaining fiber 4 with a length of 18.5 meters. Entering the first port 24 of the first circulator 6, the light exits from the second port 25 of the first circulator 6, the outgoing light enters the imaging catheter 11 through the rotating mechanism 8, and the light reflected by the sample returns from the imaging catheter 11 into the first circulator 6 and exit through the third port 26 of the first circulator 6 . 1:99 The outgoing light of the third port 23 of the fiber coupler 2 enters the reference arm, the light entering the reference arm is incident on the single-mode fiber 5 with a length of 18.5 meters, and the outgoing light enters the first port 27 of the second circulator 7, The reflected light enters the reflective fiber delay line 10 from the second port 28 of the second circulator 7 , the reflected light is incident through the second port 28 of the second circulator 7 , and exits from the third port 29 to the second three-ring polarization controller 9 . The outgoing light of the sample arm passing through the third port 26 of the circulator 6 and the outgoing light of the reference arm passing through the three-ring polarization controller 9 are respectively incident at 50:50 from the first port 30 and the second port 31 of the second fiber coupler 12 The interference occurs in the second fiber coupler 12, and enters the third three-ring polarization controller 13 and the fourth three-ring polarization controller 14 from the third port 32 and the fourth port 33 in a ratio of 50:50, and exits The outgoing light is incident on the first polarizing beam splitter 15 and the second polarizing beam splitter 16 respectively, and the outgoing light from the first polarizing beam splitter 15 is incident from the first port 34 and the second port 35 of the first polarizing beam splitter 15 respectively. To the balanced detectors 17 and 18, the outgoing light of the second polarization beam splitter 16 enters the first balanced detector 17 and the second balanced detector from the first port 36 and the second port 37 of the second polarization beam splitter 16, respectively. The electrical signals of the first balance detector 17 and the second balance detector 18 are received by the acquisition card 19 and transmitted to the computer 20 .

The light source adopts a fast scanning light source. The polarization maintaining fiber is used in the system to generate the retardation of the orthogonal polarization state, and the polarization diversity acquisition is performed through a polarization beam splitter. The length of the polarization maintaining fiber depends on its birefringence to generate a phase delay equal to half of the ordinary OCT imaging depth. This method ensures that the system can simultaneously present a polarization-divided integrated image of two orthogonal input polarization states in one image, which makes it possible to eliminate the birefringence change of the system caused by the rotation of the catheter subsequently.

As shown in Figure 2, a polarization demodulation method for catheter polarization-sensitive optical coherence tomography of the present invention includes the following steps:

1) Set the polarization state of the input light of the catheter polarization-sensitive optical coherence tomography (PS-OCT) system as E _in ; set the reference light on the H and V paths in the system as equal light intensity; The measured electrical signal is subjected to dispersion compensation, interpolation Fourier transform, and then image segmentation; the Jones matrices at the detected sample depth position and the selected reference surface position are converted into Mueller matrices respectively; Multiplying the Mueller matrix by the inverse of the Mueller matrix at the selected reference plane position yields the measurement matrix of the sample; where,

The polarization state E _in described in (1) is expressed as:

是输入光在H和V路上两个偏振态的相位差。where H _in1 is the light intensity of the input polarization state 1 in the H channel, H _in2 is the light intensity of the input polarization state 2 in the H channel, _Vin1 is the light intensity of the input polarization state 1 in the V channel, and _Vin2 is the input polarization state 2 light intensity in the The light intensity of the V channel, where the input polarization states 1 and 2 are the same light intensity in the H and V channels,

is the phase difference between the two polarization states of the input light on the H and V paths.

(2) The reference light set as equal light intensity on the H and V paths in the described system is expressed as:

where H _ref and V _ref are the quadrature components of the reference light on the H and V channels, respectively, and ψ is the phase difference of the polarization states of the reference light on the H and V paths.

(3) The described conversion method for respectively converting the Jones matrix at the detected sample depth position and the selected reference surface position into the Mueller matrix includes:

The Jones matrix is expressed as:

where a, b, c, d are any four elements of the Jones matrix,

The conversion relationship between Jones matrix and Mueller matrix is:

表示Kronecker积，U表示变换矩阵：in

represents the Kronecker product, and U represents the transformation matrix:

According to the conversion relationship between Jones matrix and Mueller matrix, the Jones matrix Q(z) at the depth position of the detected sample and the Jones matrix Q(z _ref ) at the selected reference surface position are respectively converted into Mueller matrix

The electrical signals directly collected in the H and V channels measured at the polarization diversity are respectively subjected to dispersion compensation and interpolation Fourier transform to obtain two-channel signals H ₁ +H ₂ , V ₁ +V ₂ , and H ₁ is obtained after image segmentation, Four images of H ₂ , V ₁ , V ₂ . Taking an A-line as an example, construct the Jones matrix J(z)=[H ₁ (z) H ₂ (z); V ₁ (z) V ₂ (z)] and Jones matrix J(z _ref )=[H ₁ (z _ref ) H ₂ (z _ref ); V ₁ (z _ref ) V ₂ ( _{z ref )} ], the reference plane can be selected The outer surface of the catheter or the surface of the sample, converted to S(z) and S(z _ref ) of the Mueller matrix using equations (4) and (5).

Let M _ST be the sample round-trip matrix, M _in , M _out represent the Mueller matrix of the optical path of the system, and the Mueller matrix S(z _ref ) at the position of the sample reference plane measured at the polarization diversity is expressed as:

The Mueller matrix S(z) at the z position of the sample measured at polarization diversity, expressed as:

The measurement matrix M(z _ref ,z) of the sample at z is obtained by operating S(z _ref ) and S(z):

2) In order to construct M(z _ref ,z) and M _S,T (z) as similarity matrices, Q _Zref M _out is required to be a unitary matrix, but if Q _Zref M _out contains depolarization and double attenuation effects, the similarity matrix condition invalid. Q _Zref is a unitary matrix, but in the catheter PS-OCT system, the high-speed rotation of the fiber in the catheter will inevitably bring strong depolarization and double attenuation effects. Therefore, M _out contains depolarization and double attenuation effects, which need to be eliminated by matrix decomposition. Bias and double decay effects. Elimination of depolarization and double decay effects by matrix factorization includes:

Decompose the 4*4 Mueller matrix M:

M=M _Δ M _R M _D (11)

where _MΔ is the depolarization matrix, MR is the birefringence matrix, and _{M D} is the double attenuation matrix. The ultimate purpose of the method of the present invention is to eliminate the depolarization and double attenuation effects in the Mueller matrix, and then obtain the birefringence matrix M _R.

Perform matrix decomposition on the measurement matrix M(z _ref ,z) to eliminate the depolarization and double attenuation effects to obtain a Mueller matrix containing only birefringence:

和

是只包含双折射成分的穆勒矩阵，此时

为酉矩阵，M^R(z_ref,z)与

为相似矩阵。where M ^R (z _ref ,z),

and

is the Mueller matrix containing only birefringent components, then

is a unitary matrix, M ^R (z _ref ,z) and

is a similarity matrix.

3) The measurement matrix M(z _ref , z) is calculated to obtain the phase delay R under polar coordinates; the phase delay R under the polar coordinates is obtained by the following formula:

是探测到样品在z位置处的只包含双折射成分的穆勒矩阵，tr是矩阵的迹。In the formula,

is the Mueller matrix containing only the birefringent component of the detected sample at the z position, and tr is the trace of the matrix.

4) Perform coordinate interpolation transformation on the phase retardation in polar coordinates, convert polar coordinates into Cartesian coordinates, and finally obtain the birefringence image of the catheter polarization-sensitive optical coherence tomography system sample.

The coordinate interpolation transformation described is because in the data acquisition process of the PS-OCT system, the depth information A-Scan and the lateral information B-Scan are imaged, and the final imaging result outputs a polar coordinate image, but the actual demand is to Therefore, the processed polar coordinate image needs to be processed into a PS-OCT image in Cartesian coordinates.

Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative rather than restrictive. Under the inspiration of the present invention, many modifications can be made without departing from the spirit of the present invention, which all belong to the protection of the present invention.

Claims (6)

1. a kind of polarization demodulation method to conduit polarization-sensitive optical coherence tomography, for conduit polarization-sensitive optical coherence tomography imaging system, is characterized in that, comprises the steps: 1) The polarization state of the input light of the catheter polarization-sensitive optical coherence tomography imaging system is set to be E _in ; the reference light on the H and V roads in the system is set to equal light intensity; The signal is subjected to dispersion compensation, interpolation Fourier transform, and then image segmentation; the Jones matrix at the sample depth position and the selected reference surface position are converted into Mueller matrices respectively; the Mueller matrix at the sample depth position is multiplied by The inverse of the Mueller matrix at the selected reference plane position yields the measured Mueller matrix of the sample; 2) Eliminate depolarization and double attenuation effects by matrix decomposition; 3) The phase delay amount R under polar coordinates is obtained by calculating the measured Mueller matrix M(z _ref , z); 4) Perform coordinate interpolation transformation on the phase retardation in polar coordinates, convert polar coordinates into Cartesian coordinates, and finally obtain the birefringence image of the catheter polarization-sensitive optical coherence tomography system sample. 2. the polarization-sensitive optical coherence tomography polarization demodulation method according to claim 1, is characterized in that, the described polarization state E _in of step 1) is expressed as:

where H _in1 is the light intensity of the input polarization state 1 in the H channel, H _in2 is the light intensity of the input polarization state 2 in the H channel, _Vin1 is the light intensity of the input polarization state 1 in the V channel, and _Vin2 is the input polarization state 2 light intensity in the The light intensity of the V channel, where the input polarization states 1 and 2 are the same light intensity in the H and V channels,

is the phase difference between the two polarization states of the input light on the H and V paths. 3. The polarization-sensitive optical coherence tomography polarization demodulation method for catheter according to claim 1, characterized in that, in the system described in step 1), the reference light representation of equal light intensity is set on the H and V roads. for:

where H _ref and V _ref are the quadrature components of the reference light on the H and V channels, respectively, and ψ is the phase difference of the polarization states of the reference light on the H and V paths. 4. The polarization-sensitive optical coherence tomography polarization demodulation method according to claim 1, wherein the Jones matrix at the sample depth position and the selected reference plane position in step 1) are respectively Transformation methods to convert to a Mueller matrix include: The Jones matrix is expressed as:

where a, b, c, d are any four elements of the Jones matrix, The conversion relationship between Jones matrix and Mueller matrix is:

in

represents the Kronecker product, and U represents the transformation matrix:

According to the conversion relationship between Jones matrix and Mueller matrix, the Jones matrix Q(z) at the sample depth position and the Jones matrix Q(z _ref ) at the selected reference surface position are respectively converted into Mueller matrix

Let M _ST be the sample round-trip matrix, M _in , M _out represent the Mueller matrix of the optical path of the system, and the Mueller matrix S(z _ref ) at the position of the sample reference plane measured at the polarization diversity is expressed as:

The Mueller matrix S(z) at the z position of the sample measured at polarization diversity, expressed as:

The measurement matrix M(z _ref ,z) of the sample at z is obtained by operating S(z _ref ) and S(z):

. 5. the polarization-sensitive optical coherence tomography polarization demodulation method for catheter according to claim 1, is characterized in that, the described elimination of depolarization and double attenuation effect by matrix decomposition in step 2), comprises: Decompose the 4*4 Mueller matrix M: M=M _Δ M _R M _D (11) where _{M Δ} is the depolarization matrix, MR is the birefringence matrix, and _MD is the double attenuation matrix. The ultimate purpose of this method is to eliminate the depolarization and double attenuation effects in the Mueller matrix, and then obtain the birefringence matrix M _R ; Perform matrix decomposition on the measurement matrix M(z _ref ,z) to eliminate the depolarization and double attenuation effects to obtain a Mueller matrix containing only birefringence:

where M ^R (z _ref ,z),

and

is the Mueller matrix containing only birefringent components, then

is a unitary matrix, M ^R (z _ref ,z) and

is a similarity matrix. 6. the polarization-sensitive optical coherence tomography polarization demodulation method according to claim 1, is characterized in that, the phase retardation R under the described polar coordinates of step 3) is obtained by following formula:

In the formula,

is the Mueller matrix containing only the birefringent component of the detected sample at the z position, and tr is the trace of the matrix.

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