CN102628799A - Method and system of time-domain optical coherence tomography without depth scan - Google Patents

Abstract

The invention provides a method and a system of time-domain optical coherence tomography without depth scan. On the basis of a time-domain optical coherence tomography method, the method of the invention comprises substituting convex lens with cylindrical surface for focusing lens interfering with a reference arm to form linear reference light, introducing continuous light path difference in a linear length direction of the reference light through tilting a reference planar mirror of the reference arm, substituting a one-dimensional detector array for a point photoelectric detector, acquiring interference signals of a sample to be measured at continuous different depth of a same detecting point, carrying out a Hilbert transformation analysis on the interference signals in the linear length direction of the reference light after removing direct current background, and finally obtaining a tomographic profile of the sample to be measured. The method and the system of the invention can realize one-dimensional optical coherence tomography with single exposure, and have the advantages of a simple structure, a high imaging speed, no parasitic image, and insensitivity to motion blur. In a situation of not sacrificing a system signal-to-noise ratio, time-domain optical coherence tomography without depth scan can be realized.

Description

Need not the time domain optical coherence chromatography imaging method and the system of depth scan

Technical field

The present invention relates to optical coherent chromatographic imaging (Optical Coherence Tomography; Be called for short OCT); Relate in particular to a kind of time domain optical coherent chromatographic imaging (Time-domain Optical Coherence Tomography is called for short TD-OCT) method and system that need not depth scan.

Background technology

Optical coherent chromatographic imaging (OCT) is a kind of optical tomography technology that development in recent years is got up; It can carry out the imaging of high resolving power non-intruding to the micro-structure in the several mm depth scopes of high scattering medium such as biological tissue inside, is with a wide range of applications in fields such as biological tissue's living imaging and imaging of medical diagnosis.

OCT system the earliest be time domain optical coherence tomography system (TD-OCT) (referring to formerly the technology [1], D.Huang, E.A.Swanson, C.P.Lin; J.S.Schuman, W.G.St inson, W.Chang, M.R.Hee; T.Flotte, K.Gregory, C.A.Puliafito and J.G.Fujimoto, " Optical coherence tomography "; Science, Vol.254, pp.1178-1181,1991).The one dimension tomographic map (A-line) that its axial depth scanning and interference signal intensity of writing down corresponding different depth place through the optical reference arm obtains sample.The speed of detection of TD-OCT is lower, if sample has motion in the detection process, will be easy to generate motion blur.If the axial depth sweep velocity of forcing to improve TD-OCT is to increase the decline that speed of detection can cause system sensitivity.

Domain optical coherence tomography system (Fourier-domain Optical Coherence Tomography, be called for short FD-OCT) be a kind of New O CT system (referring to technology [2] formerly, N.Nassif; B.Cense, B.H.Park, S.H.Yun; T.C.Chen, B.E.Bouma, G.J.Tearney and J.F.de Boer; " In vivo human retinal imaging by ultrahigh-speed spectral domain optical coherence tomography "; Optics Letter, Vol.29, pp.480-482; 2004); It is through surveying interference spectum and it is obtained the one dimension tomographic map (A-line) of sample do inverse Fourier transform, has with respect to previous time domain optical coherence tomography system (TD-OCT) to need not depth direction scanning, image taking speed is fast and detection sensitivity is high advantage, can satisfy the real-time requirement of biological tissue's living imaging and imaging of medical diagnosis better.But, comprising some parasitic images in the tomographic map that FD-OCT obtains, limited the application of FD-OCT.These parasitic images are respectively: the direct current background, and from coherent noise and complex conjugate mirror image.Wherein, direct current background and reduced the signal to noise ratio (S/N ratio) of FD-OCT from the existence of coherent noise has influenced image quality; And the existence of complex conjugate mirror image makes FD-OCT can't distinguish positive and negative optical path difference (surveying the optical path difference of light path relative reference light path), and testing sample can only place a side of zero optical path difference position during measurement, and it is half the to cause effective investigation depth scope to reduce.In addition, the signal to noise ratio (S/N ratio) of FD-OCT is along with the increase of optical path difference also can sharply descend.

Parallel FD-OCT is that with the key distinction of tradition based on the FD-OCT of single-point illumination it realizes the parallel detecting of FD-OCT two dimension tomographic map (B-scan) through adopting Line of light illumination testing sample.(referring to formerly the technology [3], Branislay Grajciar, Michael Pircher; Adolf F.Fercher and Rainer A.Leitgeb; " Parallel Fourier domain optical coherence tomography in vivo measurement of the human eye ", Optics Express, Vol.13; Pp.1131-1137,2005).This method generally realizes the Line of light illumination to testing sample through in light path, adding cylindrical convex mirror, and utilizes 2 D photoelectric detection array and line item frequency domain interference fringe, rebuilds the two-dimentional tomographic map (B-scan) that obtains a width of cloth testing sample.Parallel FD-OCT is owing to avoided the horizontal mechanical scan to testing sample, and image taking speed is faster, and is insensitive to motion blur.But the same with traditional FD-OCT, still there are problems such as complex conjugate mirror image parasitic image in parallel FD-OCT.

Summary of the invention

The objective of the invention is provides a kind of method and system that need not the time domain optical coherent chromatographic imaging of depth scan in order to overcome the above-mentioned deficiency of technology formerly.The present invention only needs single exposure can realize the one dimensional optical coherence chromatographic imaging, have that simple in structure, image taking speed is fast, no parasitic image, to the insensitive characteristics of motion blur.

Technical solution of the present invention is following:

A kind of method that need not the time domain optical coherent chromatographic imaging of depth scan; This method is on the basis of time domain optical coherence chromatography imaging method; Replace interfering the condenser lens of reference arm to form the wire reference light with cylindrical convex mirror; And the reference planes catoptron through the tilt reference arm introduces continuous optical path difference on reference light wire length direction, replaces putting a photodetector with the one dimension photodetector array, the interference signal at the continuous different depth of the acquisition same sensing point of testing sample place; Through going this interference signal to be made the tomographic map that Hilbert transform can obtain testing sample along reference light wire length direction after the direct current background.

The concrete steps of method of time domain optical coherent chromatographic imaging that the present invention need not depth scan are following:

1. on the basis of time domain optical coherence chromatography imaging method, replace interfering the condenser lens of reference arm to form the wire reference light with cylindrical convex mirror;

2. the reference planes catoptron that makes reference arm is introduced continuous optical path difference in the plane tilt of being made up of wire reference light length direction and reference light illumination direction on wire reference ray shape length direction; The incident angle that reference light incides on the clinoplane catoptron is θ, and wherein the θ span is-60 °≤θ≤60 °;

3. replace the some photodetector with the one dimension photodetector array, obtain the interference signal at the continuous different depth of the same sensing point of testing sample place; After the system works, the interference signal of described one dimension photodetector array record is suc as formula shown in (1):

Wherein: m is the probe unit sequence number of said one dimension photodetector array, and I (m) is the interference signal intensity that m probe unit of said one dimension photodetector array detects; I _Sig, I _Ref, I _InBe respectively reference optical signal intensity, sample light signal strength and incident optical signal intensity; Z is the relatively vertically depth location of testing sample,

P represents the single probe unit width of said one dimension photodetector array, and σ represents the imaging magnification of sample to said one dimension photodetector array, z ₀It is a constant; R (z) is the relatively vertically reflectivity or the backscattering rate at depth location z place of testing sample; γ (m) is the spatial coherence function of low-coherence light source, and c is the light velocity,

Be a phase constant, * representes convolution algorithm;

4. described interference signal is averaged processing, obtains the direct current background suc as formula shown in (2):

$I_{\mathrm{dc}}=\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{I}_m,---\left(2\right)$

Wherein: M is the probe unit sum of said one dimension photodetector array; Formula (1) is deducted formula (2), tentatively removed the interference signal of direct current background, shown in (3):

I _nodc(m)＝I(m)-I _dc； (3)

5. to step 4. the formula of gained (3) to do with m be that the Fourier transform of variable obtains formula (4):

Wherein: f _mRepresent the Fourier transform frequency spectrum of corresponding m,

Representative is the Fourier transform of variable with m; With formula (4) the signal rectangular window function that to be multiplied by an interval size earlier be 2 π $W\left(f_m\right)=\left\{\begin{array}{c}0,\left|f_m\right|\≤\mathrm{\π}\\ 1,\left|f_m\right|>\mathrm{\π}\end{array}\right.$ Carry out high-pass filtering, obtain formula (5):

E′ _nodc(f _m)＝E _nodc(f _m)·W(f _m)； (5)

Again formula (5) signal is done with f _mFor the interference signal of direct current background is removed in the inverse Fourier transform of variable fully, shown in (6):

Wherein

Representative is with f _mInverse Fourier transform for variable;

6. to step 5. the Hilbert transform of removing background interference signal (6) to do to be variable of gained with m obtain formula (7):

Wherein

representative is the Hilbert transform of variable with m; With signal formula (6) and the synthetic formula (8) that obtains of formula (7),

$I_0\left(m\right)={\left|I_{\mathrm{Hilbert}}\left(m\right)\right|}^2+{\left|I_{\mathrm{nodc}}^{\′}\left(m\right)\right|}^2=4I_{\mathrm{ref}}{I}_{\mathrm{in}}R\left(z\right)*\left|\mathrm{\γ}\left(m\right)\right|;---\left(8\right)$

7. with step 6. the independent variable m of gained signal formula (8) convert independent variable z into, promptly obtain the one dimension tomographic map of testing sample, shown in (9):

I ₀(z)＝4I _refI _inR(z)*|γ(z)|。(9)

8. through accurate translation stage two-dimensional scan is done on the plane vertical with the illumination light optical axis direction, testing sample edge, repeated the three-dimensional tomographic map that 2.～7. above step obtains testing sample.

A kind of time domain optical coherence tomography system that need not depth scan of realizing said method; Comprise low-coherence light source; Order is placed collimator and extender device and Michelson interferometer on the illumination direction of low-coherence light source; The optical splitter of this Michelson interferometer is divided into transmitted light beam and folded light beam with incident light; Its characteristics are: set gradually cylindrical lens in described transmitted light beam direction and constitute the reference arm light path with the plane mirror that tilts to put, set gradually first condenser lens and testing sample formation feeler arm light path in described folded light beam direction, described testing sample is placed on the precise mobile platform; Place second condenser lens and one dimension photodetector array in proper order at described Michelson interferometer output terminal; This one dimension photodetector array is connected with computing machine through the image data acquiring card; Described cylindrical lens assembles the incident directional light for Line of light, produces a wire reference light; Described plane mirror tilts to put, and on reference light wire length direction, introduces continuous optical path difference; The focal length of described cylindrical lens is identical with the focal length of described first condenser lens; Described testing sample and plane mirror constitute the object-image conjugate relation with described one dimension photodetector array respectively; Wire illumination light length direction in the probe unit array direction of described one dimension photodetector array and the described reference arm light path is in same plane.

Described low-coherence light source is a wideband light source, and its spectrum typical case full width at half maximum is that tens nanometers are to the hundreds of nanometer, like light emitting diode or super-radiance light emitting diode or femto-second laser or super continuum source etc.

Described collimator and extender device is made up of object lens and some lens.

Described one dimension photodetector array is that line array CCD or linear array CMOS or linear array InGaAs or other have the one dimension detector array of photosignal translation function.

Described precise mobile platform can be done the translation of micron order precision along three orthogonal directions.

The working condition of this system is following:

The light that low-coherence light source sends is after collimating apparatus expands bundle; In Michelson interferometer, wait to be divided into two bundles, a branch of light is through reference arm, the inner focusing on the converging action plane of cylindrical convex mirror; Produce a wire illumination light; Incide on the plane inclined catoptron, another Shu Guangjing feeler arm incides in the testing sample, and reflected light of returning from plane mirror and the sample light that different depth reflection or backscattering are returned in the testing sample return along reference arm and feeler arm respectively; In Michelson interferometer, join and interfere; Interference signal focuses on the back by one dimension photodetector array record through condenser lens, after the digital-to-analog conversion of image data acquiring card, sends into computing machine and carries out data processing, obtains the one dimension tomographic map of testing sample along the illumination light optical axis direction.Through accurate translation stage two-dimensional scan is done on the plane vertical with the illumination light optical axis direction, testing sample edge, obtained the three-dimensional tomographic map of testing sample.

Compared with prior art, the invention has the beneficial effects as follows:

The characteristics of method that the present invention need not the time domain optical coherent chromatographic imaging of depth scan are to utilize wire reference light and tilted-putted plane reference mirror on wire reference light length direction, to introduce continuous optical path difference; The one dimension chromatography information of usage space filtering and the disposable acquisition testing sample of Hilbert transform analytical approach; Under the situation of sacrificial system signal to noise ratio (S/N ratio) not; Improve image taking speed, realize need not the time domain optical coherent chromatographic imaging of depth scan.

1 compare with technology formerly, the present invention need not axial depth scanning, and image taking speed is fast, and is insensitive to motion blur, less demanding to interferometer and stability of sample.

Compare with 3 with technology 2 formerly, system architecture of the present invention is simple, does not have the puzzlement of parasitic image problem, and signal noise ratio (snr) of image does not descend with the increase of optical path difference.

Description of drawings

Fig. 1 need not the light path and the structural representation of the time domain optical coherence tomography system of depth scan for the present invention.

Embodiment

Below in conjunction with embodiment and accompanying drawing the present invention is described further, but should limit protection scope of the present invention with this.

See also Fig. 1.Fig. 1 need not the light path and the structural representation of the time domain optical coherence tomography system of depth scan for the present invention.Visible by Fig. 1; The time domain optical coherence tomography system that the present invention need not depth scan comprises low-coherence light source 1; Order is placed collimator and extender device 2, Michelson interferometer 3 on the illumination direction of this low-coherence light source 1; The Amici prism 31 of this Michelson interferometer 3 is divided into feeler arm light path 34 and reference arm light path 32 with incident light; The end of reference arm light path 32 is a cylindrical convex mirror 36 and the plane mirror 33 that tilts to put, and the end of feeler arm light path 34 is a condenser lens 37 and testing sample 35, and testing sample 35 is placed on the precise mobile platform (not shown); Michelson interferometer 3 output terminals are placed condenser lens 4 and line array CCD detector 5 in proper order; Line array CCD detector 5 is connected with computing machine 7 through image data acquiring card 6.The characteristics of this system are that said reference arm light path 32 terminal cylindrical convex mirrors 36 assemble the incident directional light for Line of light, produce a wire reference light; Said reference arm light path 32 terminal clinoplane catoptrons 33 are introduced continuous optical path difference on reference light wire length direction.

The focal length of the condenser lens 37 before the cylindrical convex mirror 36 in the described Michelson interferometer 3 before plane mirror 33 and the testing sample 35 is identical; Described testing sample 35 is the object-image conjugate relation on system light path with line array CCD detector 5 respectively with plane mirror 33; Wire illumination light length direction in the probe unit array direction of described line array CCD detector 5 and the described reference arm light path 32 is in same plane.

The wide spectral light that low-coherence light source 1 sends is after collimating apparatus 2 expands bundle; In Michelson interferometer 3, be divided into two bundles by Amici prism 31; A branch of transmitted light produces a wire illumination light through cylindrical convex mirror 36 in reference arm light path 32, reverse the returning of plane mirror 33 reflections that is tilted again; Another bundle reflected light is in feeler arm light path 34 incides the testing sample 35 that is placed on the accurate translation stage (not shown); Light that reflects from plane mirror 33 and the light that different depth reflection or backscattering are returned in the testing sample 35 return along reference arm light path 32 and feeler arm light path 34 respectively; In Michelson interferometer 3, converge and interfere; Line focus lens 4 focus on again, are imaged on the line array CCD detector 5, convert electric signal to after; After 6 digital-to-analog conversions of image data acquiring card, send into computing machine 7 and carry out data processing, obtain the one dimension tomographic map of testing sample 35 along the illumination light optical axis direction.

Reference planes catoptron 33 in the described reference arm light path 32 is in the plane tilt of being made up of wire reference light length direction and reference light illumination direction, and the incident angle that reference light incides on the clinoplane catoptron 33 is θ.

The interference signal that described line array CCD detector 5 records the continuous different depth of described testing sample 35 same sensing points place is:

Wherein: m is the probe unit sequence number of described line array CCD detector 5, and I (m) is the interference signal intensity that line array CCD detector 5 a m probe unit detect; I _Sig, I _Ref, I _InBe respectively reference optical signal intensity, sample light signal strength and incident optical signal intensity; Z is the relatively vertically depth location of testing sample 35,

P represents the single probe unit width of line array CCD detector 5, σ=F ₂/ F ₁Represent the lateral magnification of one-dimensional image system, F ₁Represent the focal length of condenser lens 37 and cylindrical convex mirror 36, F ₂Represent the focal length of condenser lens 4, z ₀It is a constant; R (z) is the relatively vertically reflectivity or the backscattering rate at depth location z place of testing sample 35; γ (m) is the spatial coherence function of said low-coherence light source 1, and c is the light velocity, Be a phase constant, * representes convolution algorithm.

At first, interference signal formula (10) is averaged processing, obtains the direct current background suc as formula shown in (11):

$I_{\mathrm{dc}}=\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{I}_m,---\left(11\right)$

Wherein: M is the probe unit sum of line array CCD detector 5; Formula (10) is deducted formula (11), tentatively removed the interference signal of direct current background, shown in (12):

I _nodc(m)＝I(m)-I _dc； (12)

Then signal formula (12) being done with m is that the Fourier transform of variable obtains formula (13):

Wherein: f _mRepresent the Fourier transform frequency spectrum of corresponding m, Representative is the Fourier transform of variable with m; With signal formula (13) rectangular window function that to be multiplied by an interval size earlier be 2 π $W\left(f_m\right)=\left\{\begin{array}{c}0,\left|f_m\right|\≤\mathrm{\π}\\ 1,\left|f_m\right|>\mathrm{\π}\end{array}\right.$ Carry out high-pass filtering, obtain formula (14):

E′ _nodc(f _m)＝E _nodc(f _m)·W(f _m)； (14)

Again signal formula (14) is done with f _mFor the interference signal of direct current background is removed in the inverse Fourier transform of variable fully, shown in (15):

Wherein

Representative is with f _mInverse Fourier transform for variable.

It is that the Hilbert transform of variable obtains formula (16) that the interference signal (15) of removing background information is done with m:

Wherein

representative is the Hilbert transform of variable with m; With signal formula (15) and the synthetic formula (17) that obtains of formula (16),

I ₀(m)＝|I _Hilbert(m)| ²+|I′ _nodc(m)| ²＝4I _refI _inR(z)*|γ(m)|； (17)

At last, convert the independent variable m of signal formula (18) into independent variable z, promptly obtain the one dimension tomographic map of testing sample 35, shown in (18):

I ₀(z)＝4I _refI _inR(z)*|γ(z)|。(18)

Through accurate translation stage (not shown) two-dimensional scan is done on the plane vertical with the illumination light optical axis direction, testing sample 35 edges, repeated the three-dimensional tomographic map that above process obtains testing sample 35.

Claims (4)

1. method that need not the time domain optical coherent chromatographic imaging of depth scan; It is characterized in that this method is on the basis of time domain optical coherence chromatography imaging method; Replace interfering the condenser lens of reference arm to form the wire reference light with cylindrical convex mirror; And the reference planes catoptron through the tilt reference arm introduces continuous optical path difference on reference light wire length direction, replaces putting a photodetector with the one dimension photodetector array, the interference signal at the continuous different depth of the acquisition same sensing point of testing sample place; Through going this interference signal to be made the tomographic map that Hilbert transform can obtain testing sample along reference light wire length direction after the direct current background.

2. the method that need not the time domain optical coherent chromatographic imaging of depth scan according to claim 1 is characterized in that the concrete steps of this method are following:

1. on the basis of time domain optical coherence chromatography imaging method, replace interfering the condenser lens of reference arm to form the wire reference light with cylindrical convex mirror;

2. the reference planes catoptron that makes reference arm is introduced continuous optical path difference in the plane tilt of being made up of wire reference light length direction and reference light illumination direction on wire reference ray shape length direction; The incident angle that reference light incides on the clinoplane catoptron is θ, and wherein the θ span is-60 °≤θ≤60 °;

3. replace the some photodetector with the one dimension photodetector array, obtain the interference signal at the continuous different depth of the same sensing point of testing sample place:

Wherein: m is the probe unit sequence number of said one dimension photodetector array, and I (m) is the interference signal intensity that m probe unit of said one dimension photodetector array detects; I _Sig, I _Ref, I _InBe respectively reference optical signal intensity, sample light signal strength and incident optical signal intensity; Z is the relatively vertically depth location of testing sample,

P represents the single probe unit width of said one dimension photodetector array, and σ represents the imaging magnification of sample to said one dimension photodetector array, z ₀It is a constant; R (z) is the relatively vertically reflectivity or the backscattering rate at depth location z place of testing sample; γ (m) is the spatial coherence function of low-coherence light source, and c is the light velocity,

Be a phase constant, * representes convolution algorithm;

4. described interference signal I (m) is averaged processing, obtains the direct current background:

$I_{\mathrm{dc}}=\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{I}_m,$

Wherein: M is the probe unit sum of said one dimension photodetector array; Described interference signal I (m) is deducted described direct current background I _Dc, tentatively removed the interference signal I of direct current background _Nodc(m) be:

I _nodc(m)＝I(m)-I _dc；

5. to the interference signal I of described preliminary removal direct current background _Nodc(m) doing with m is that the Fourier transform of variable obtains:

Wherein: f _mRepresent the Fourier transform frequency spectrum of corresponding m,

Representative is the Fourier transform of variable with m; With E _Nodc(f _m) rectangular window function that to be multiplied by an interval size earlier be 2 π carries out high-pass filtering, obtain:

E′ _nodc(f _m)＝E _nodc(f _m)·W(f _m)，

Wherein, rectangular window function does $W\left(f_m\right)=\left\{\begin{array}{c}0,\left|f_m\right|\≤\mathrm{\π}\\ 1,\left|f_m\right|>\mathrm{\π}\end{array}\right.;$ Again with E ' _Nodc(f _m) do with f _mRemoved the interference signal I ' of direct current background fully for the inverse Fourier transform of variable _Nodc(m):

Wherein Representative is with f _mInverse Fourier transform for variable;

6. to the described interference signal I ' that removes background fully _Nodc(m) doing with m is that the Hilbert transform of variable obtains:

Wherein, Representative is the Hilbert transform of variable with m; With signal I ' _Nodc(m) and I _Hilbert(m) synthetic obtaining:

I ₀(m)＝|I _Hilbert(m)| ²+|I′ _nodc(m)| ²＝4I _refI _inR(z)*|γ(m)|；

7. with 6. gained signal I of step ₀(m) independent variable m converts independent variable z into, promptly obtains the one dimension tomographic map of testing sample:

I ₀(z)＝4I _refI _inR(z)*|γ(z)|。

3. method according to claim 2 is characterized in that also comprising the following steps:

8. make the plane vertical, described testing sample (35) edge do two-dimensional scan through accurate translation stage, repeat above-mentioned steps 2.～7., obtain the three-dimensional tomographic map of testing sample (35) with the illumination light optical axis direction.

4. time domain optical coherence tomography system that need not depth scan of realizing each said method of claim 1 to 3; Comprise low-coherence light source (1); Order is placed collimator and extender device (2) and Michelson interferometer (3) on the illumination direction of low-coherence light source (1); The optical splitter of this Michelson interferometer (31) is divided into transmitted light beam and folded light beam with incident light; It is characterized in that: set gradually cylindrical lens (36) and the plane mirror (33) put that tilts constitutes reference arm light path (32) in described transmitted light beam direction; Set gradually first condenser lens (37) and testing sample (35) formation feeler arm light path (34) in described folded light beam direction, described testing sample (35) is placed on the precise mobile platform; Place second condenser lens (4) and one dimension photodetector array (5) in proper order at described Michelson interferometer (3) output terminal; This one dimension photodetector array (5) is connected (7) through image data acquiring card (6) with computing machine; Described cylindrical lens (36) assembles the incident directional light for Line of light, produces a wire reference light; Described plane mirror (33) tilts to put, and on reference light wire length direction, introduces continuous optical path difference; The focal length of described cylindrical lens (36) is identical with the focal length of described first condenser lens (37); Described testing sample (35) and plane mirror (33) constitute the object-image conjugate relation with described one dimension photodetector array (5) respectively; Wire illumination light length direction in the probe unit array direction of described one dimension photodetector array (5) and the described reference arm light path (32) is in same plane.

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