CN101750146B - Adjustable frequency domain optical coherence tomography method and system thereof - Google Patents

Abstract

A frequency domain optical coherence tomography method and a system thereof with adjustable detection depth range and depth resolution are disclosed, wherein a variable period grating is used for frequency domain optical coherence tomography, and the spectral detection width and the spectral detection resolution of a frequency domain interference signal are changed by adjusting the period of the grating and the transverse position of a detector, thereby realizing the frequency domain optical coherence tomography with adjustable detection depth range and depth resolution. The invention can be used with a light source with large spectral width, solves the problem of limited length of a detector pixel array when the spectral width is large, and can meet different imaging requirements of users for obtaining a larger detection depth range or a higher depth resolution ratio.

Description

Adjustable frequency domain optical coherence chromatography imaging method and system thereof

Technical field

The present invention relates to domain optical coherence tomography (Fourier Domain Optical CoherenceTomography, be called for short FDOCT), be a kind of adjustable frequency domain optical coherence chromatography imaging method and system thereof, utilize the variable period grating, realize investigation depth scope and depth resolution adjustable frequency domain optical coherence chromatography imaging.

Background technology

Optical coherent chromatographic imaging (Optical Coherence Tomography is called for short OCT) is a kind of imaging technique that development in recent years is got up.It utilizes the low-coherent light principle of interference, obtains the reflection and the backscatter signals of testee different depth layer, and processing and imaging by to received signal obtain tomographic map.Non-intrusive measurement is an outstanding advantage of this technology, thereby often is used to ophthalmic diagnosis.Now, the OCT technology has been not limited to this, and it is widely used in aspects such as medical science, biology, materialogy.

Domain optical coherence tomography (FDOCT) technology develops on original time domain Optical Coherence Tomography Imaging Technology basis, and its outstanding advantage is the scanning that need not depth direction, can obtain the structural information of testee different depth simultaneously.With respect to the time domain Optical Coherence Tomography Imaging Technology, the FDOCT technology can obtain bigger detection sensitivity and faster speed of detection (referring to technology [1] formerly, R.Leitgeb, C.K.Hitzenberger, Adolf F.Fercher, Performance of fourier domain vs.time domain opticalcoherence tomography, Optics Express, Vol.11, Issue8,2003, pp.889-894).People such as Maciej Wojtkowski use the domain optical coherence tomography technology that people's retina imaging in vivo is studied, the practical value that has shown the domain optical coherence tomography technology is (referring to technology [2] formerly, MaciejWojtkowski, Rainer Leitgeb, Andrzej Kowalczyk, Tomasz Bajraszewski, AdolfF.Fercher, In vivo human retinal imaging by Fourier domain optical coherencetomography, J.Biomed.Opt., Vol.7, No.3,2002, pp.457-463).Also had technical research formerly and eliminated the method for the interference of parasitic image in the FDOCT system (referring to technology [3] formerly, M.Wojtkowski, A.Kowalczyk, R.Leitgeb, A.F.Fercher, Full range complex spectral opticalcoherence tomography technique in eye imaging, Optics Lerrers, Vol.27, No.16,2002, pp.1415-1417; Go on foot roc, complex frequency domain optical coherence tomography imaging Study on Technology (PhD dissertation), Shanghai Optics and Precision Mechanics institute, Chinese Academy of Sciences, 2008).The domain optical coherence tomography system mainly is made up of broad spectrum light source, Michelson interferometer and spectrometer (main element comprises spectro-grating, condenser lens and detector) three parts, obtains tomographic map by the detection to testee.

In the FDOCT system, when

The time (spectral width of Δ λ for surveying, Δ λ _FWHMFull width at half maximum for light source), the depth resolution δ z that the domain optical chromatographic imaging system is surveyed reaches theoretical value, is expressed as

(λ ₀The centre wavelength of the wideband light source of expression FDOCT system, η is the medium refraction index of testee); The depth range z that surveys _MaxBe expressed as

(N represents the pixel count that detector is used to survey).Yet the investigation depth scope and the depth resolution that adopt the FDOCT technology to obtain are fixing value, when measuring when investigation depth scope and depth resolution had a plurality of different the requirement, adopt traditional F DOCT technical method and system to be difficult to meet the demands.Moreover, use along with big spectrum width light source, in order to obtain the result of detection of higher depth resolution, to wish again to reach certain investigation depth scope, becoming is difficult to meet the demands for the pel array length of detector and picture element density (with the unit picture element width means of detector).

Summary of the invention

The objective of the invention is provides a kind of adjustable frequency domain optical coherence chromatography imaging method and system thereof in order to overcome the deficiency of technology formerly.This method and system can either be realized investigation depth scope and depth resolution adjustable frequency domain optical coherence chromatography imaging, thereby obtains the tomographic map of different investigation depth scopes and different depth resolution; Can cooperate the use of big spectrum width light source again, by regulating grating cycle and detector position, the limited problem of detector pixel array length when the solution spectrum width is big.

The variable period grating is the grating that can change according to setting within the specific limits in a kind of cycle, and it is a kind of of tunable gratings.Tunable gratings has been opened brand-new developing direction for optical system, Design for optical system can therefore having more elasticity (sees technology [4] formerly, but little modulation optical grating element, http://www.itrc.org.tw/Research/Product/Nano/grating.php; Yang Yusheng, but the design of cycle and blazing angle modulation optical grating element research and development (PhD dissertation), Power Machinery Engineering system of National Tsing Hua University, 2009, http://ir.lib.nthu.edu.tw/handle/987654321/1776).

Preamble is stated, when

The time, the depth resolution δ z that the domain optical chromatographic imaging system is surveyed reaches theoretical value

But the spectrum width of working as light source is bigger, and system is subjected to the restriction of detector pixel array length and picture element density,

The time, the influence of the spectral width that the depth resolution of detection and depth range are surveyed.Change the spectro-grating in the domain optical chromatographic imaging system into the variable period grating, the angle of establishing incident light and grating normal is θ ₀, be adjusted to d when the grating cycle, detector is moved to position shown in following (1) formula:

$h\left(d\right)=f\tan \left[\arcsin (\frac{p{\mathrm{\λ}}_0}{d}+\sin {\mathrm{\θ}}_0)\right]---\left(1\right)$

H (d) expression detector central point is to the vertical range of spectrometer lens axis, the depth range z of detection _MaxBe respectively with depth resolution δ z:

$z_{\max }=\frac{\mathrm{pf}}{4\mathrm{\η\δL}}\frac{1}{\sqrt{d^2-{({\mathrm{p\λ}}_0+d\sin {\mathrm{\θ}}_0)}^2}[\frac{1}{{\mathrm{\λ}}_0^2}-{(\frac{p}{d}+\frac{{\sin \mathrm{\θ}}_0}{{\mathrm{\λ}}_0})}^2]}---\left(2\right)$

$\mathrm{\δz}=\frac{\mathrm{pf}}{\mathrm{\ηL}}\frac{1}{\sqrt{d^2-{({\mathrm{p\λ}}_0+d\sin {\mathrm{\θ}}_0)}^2}[\frac{1}{{\mathrm{\λ}}_0^2}-{(\frac{p}{d}+\frac{{\sin \mathrm{\θ}}_0}{{\mathrm{\λ}}_0})}^2]}---\left(3\right)$

In the formula: f represents the focal length of spectrometer lens, and p represents the spectral order of the spectro-grating diffraction that is detected, and L represents the pel array length of detector, and δ L represents the unit picture element width of detector.

Thus, can be by regulating the investigation depth scope and the depth resolution of grating cycle regulating system, when the emphasis of surveying when obtaining bigger investigation depth scope, uses the littler grating cycle, depth resolution will decrease at this moment; When the emphasis of surveying when obtaining higher depth resolution, uses the bigger grating cycle, the investigation depth scope will reduce thereupon at this moment.Also can be used in combination, seek interested partial-depth scope with little grating cycle, bigger investigation depth scope earlier, obtain tomographic map more clearly with bigger grating cycle, higher depth resolution again.

Technical solution of the present invention is as follows:

A kind of adjustable frequency domain optical coherence chromatography imaging method, the particularly adjustable method of investigation depth scope and depth resolution, characteristics are that this method comprises the following steps:

1. a domain optical coherence tomography system comprises wideband light source, Michelson interferometer and spectrometer, and described spectrometer comprises spectro-grating, lens and detector, described spectro-grating is changed be made as the variable period mounting for grating;

2. according to the investigation depth scope z that expects _MaxOr depth resolution δ z, determine the cycle d of grating:

Investigation depth scope z according to expectation _MaxOr depth resolution δ z utilizes following formula to calculate and determine the cycle d of grating, or by depth range z _MaxWith the cycle d of depth resolution δ z calculating grating, with the depth range z that obtains to approach to expect most _MaxDetermine the cycle d of grating with depth resolution δ z:

$\mathrm{\&delta;z}=\frac{\mathrm{pf}}{L}\frac{1}{\sqrt{d^2-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="H2009102008435E00011.png"\; state="\{\{state\}\}">p</figure-callout>}}^2{{\mathrm{\&lambda;}}_0}^2}(\frac{1}{{\mathrm{\&lambda;}}_0^2}-\frac{p^2}{d^2})}$

$z_{\max }=\frac{\mathrm{<figure-callout\; id="2"\; label="pf"\; filenames="H2009102008435E00011.png"\; state="\{\{state\}\}">pf</figure-callout>}}{2\mathrm{\&eta;\&delta;L}}\frac{1}{\sqrt{d^2-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="H2009102008435E00011.png"\; state="\{\{state\}\}">p</figure-callout>}}^2{{\mathrm{\&lambda;}}_0}^2}(\frac{1}{{\mathrm{\&lambda;}}_0^2}-\frac{p^2}{d^2})}$

In the formula: f represents the focal length of spectrometer lens, the spectral order of the spectro-grating diffraction that p represents, and L represents the pel array length of detector, and δ L represents the unit picture element width of detector, and η is the medium refraction index of object under test, λ ₀The centre wavelength of the wideband light source of expression domain optical coherence tomography system;

3. the grating cycle of adjusting described variable period mounting for grating is d;

4. utilize the calculating of (1) formula and adjust described position of detector h (d), promptly described detector central point is to the vertical range of spectrometer lens axis;

5. utilize adjusted domain optical coherence tomography system to object image-forming, can obtain the depth range z of user's expectation _MaxWith depth resolution δ z.

Implement the investigation depth scope and the depth resolution adjustable frequency domain optical coherence chromatography imaging system of said method, comprise wideband light source, on the illumination direction of this wideband light source, place collimation lens in turn, Michelson interferometer, the output terminal of Michelson interferometer connects a spectrometer, this spectrometer links to each other with computing machine by image pick-up card, its characteristics are that described spectrometer is by along light beam working direction variable period mounting for grating successively, condenser lens, detector is formed, described variable period mounting for grating is made up of variable period grating and controlling device of grating, described controlling device of grating is the device of the described variable period grating cyclomorphosis of control, described detector is positioned on the slide rail, and the moving direction of described detector on described slide rail is perpendicular to the grating grid line direction of the optical axis and the described variable period grating of the condenser lens of described spectrometer.

Described detector is a photodetector array.

The light that low-coherence light source sends enters Michelson interferometer behind the collimation lens collimator and extender, the interference signal of exporting from Michelson interferometer enters spectrometer; The cycle d of the variable period grating in the spectrometer adjusts according to this method, and according to the different grating cycles, detector is moved to position h (d) along slide rail; After light signal entered spectrometer, by grating beam splitting, the signal of detector after the beam split of position h (d) record sent into computing machine through image pick-up card and handled, and obtains the tomographic map of testee.

Technique effect of the present invention is:

Compare with technology formerly, the present invention utilizes the variable period grating, consider the pel array length of detector and the restriction of picture element density, and tie detector moves to the relevant position along slide rail, can realize the detection of different depth scope and different depth resolution in a domain optical coherence tomography system.The present invention has changed under original technology situation, in the FDOCT system, and the uncontrollable situation of investigation depth scope and depth resolution.The user can select to obtain the bigger still higher depth resolution of investigation depth scope according to different needs; Also can be used in combination, seek interested partial-depth scope with little grating cycle, bigger investigation depth scope earlier, obtain tomographic map more clearly with bigger grating cycle, higher depth resolution again.

Description of drawings

Fig. 1 is the structural representation of adjustable frequency domain optical coherence chromatography imaging of the present invention system.

Embodiment

The invention will be further described below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this.

See also Fig. 1, Fig. 1 is the system architecture synoptic diagram of the embodiment of adjustable frequency domain optical coherence chromatography imaging of the present invention system, adjustable frequency domain optical coherence chromatography imaging of the present invention system, comprise wideband light source 1, on the illumination direction of this wideband light source 1, place collimator and extender device 2 in turn, Michelson interferometer 3, the optical splitter 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 described reference arm light path is a reference mirror 33, the end of described feeler arm light path is an object under test 35, and object under test 35 is placed on the accurate translation stage of three-dimensional; The output terminal of described Michelson interferometer 3 connects a spectrometer 5, this spectrometer 5 links to each other with computing machine 7 by image pick-up card 6, described spectrometer 5 is by along light beam working direction variable period mounting for grating successively, condenser lens 53, detector 54 is formed, described variable period mounting for grating is made up of variable period grating 51 and controlling device of grating 52, described controlling device of grating 52 is devices of described variable period grating 51 cyclomorphosises of control, described detector 54 is positioned on the slide rail 55, and the moving direction of described detector 54 on described slide rail 55 is perpendicular to the grating grid line direction of the optical axis and the described variable period grating 51 of described spectrometer 5.

The light that wideband light source 1 sends enters Michelson interferometer 3 behind collimation lens 2 collimator and extenders, the interference signal of exporting from Michelson interferometer 3 enters spectrometer 5; The cycle d of the variable period grating 51 in the spectrometer 5 adjusts according to this method, and according to the different grating cycles, ccd detector 54 is moved to position h (d) along slide rail 55; After light signal entered spectrometer 5, by 51 beam split of variable period grating, the signal of ccd detector 54 after the beam split of position h (d) record sent into computing machine 7 through image pick-up card 6 and handled, and obtains the tomographic map of testee.

According to method of the present invention, calculate and definite q grating cycle according to formula (2) or (3) earlier, as follows by arranging from big to small:

d(i)＝d(1)，d(2)，d(3)，......，d(q)

d(1)＞d(2)＞d(3)＞......＞d(q) (4)

In the following formula: i is each numbering of surveying the different grating cycles of using.

In the i time was surveyed, the cycle of adjusting the variable period grating was d (i).

In the i time is surveyed, utilize (1) formula to calculate and adjust described position of detector and be (getting the one-level spectrum, p=1, and the angle of establishing incident light and grating normal is zero):

$h\left(d\left(i\right)\right)=f\tan \left[\arcsin \left(\frac{{\mathrm{\&lambda;}}_0}{d\left(i\right)}\right)\right]---\left(5\right)$

Be the vertical range of described detector central point to the spectrometer lens axis.

Utilize adjusted domain optical coherence tomography system to object detection, can obtain the depth range and the depth resolution of user's expectation, survey q time altogether:

z _max| ₁＜z _max| ₂＜z _max| ₃＜......＜z _max| _q (6)

δz| ₁＜δz| ₂＜δz| ₃＜......＜δz| _q (7)

Promptly in this system, along with reducing of grating cycle, the investigation depth scope constantly enlarges, and depth resolution descends; Along with the increase in grating cycle, the investigation depth scope constantly reduces, and depth resolution improves.The user can select to obtain the bigger still higher depth resolution of investigation depth scope according to different needs; Also can be used in combination, seek interested partial-depth scope with little grating cycle, bigger investigation depth scope earlier, obtain tomographic map more clearly with bigger grating cycle, higher depth resolution again.

Claims (3)

1. an adjustable frequency domain optical coherence chromatography imaging method is characterised in that this method comprises the following steps:

1. a domain optical coherence tomography system comprises wideband light source, Michelson interferometer and spectrometer, and described spectrometer comprises spectro-grating, lens and detector, described spectro-grating is changed be made as the variable period mounting for grating;

2. according to the investigation depth scope z that expects _MaxOr depth resolution δ z, determine the cycle d of grating:

Investigation depth scope z according to expectation _MaxOr depth resolution δ z utilizes following formula to calculate and determine the cycle d of grating, or by depth range z _MaxWith the cycle d of depth resolution δ z calculating grating, with the depth range z that obtains to approach to expect most _MaxDetermine the cycle d of grating with depth resolution δ z:

$\mathrm{\&delta;z}=\frac{\mathrm{pf}}{L}\frac{1}{\sqrt{d^2-p^2{\mathrm{\&lambda;}}_0^2}(\frac{1}{{\mathrm{\&lambda;}}_0^2}-\frac{p^2}{d^2})}$

$z_{\max }=\frac{\mathrm{pf}}{2\mathrm{\&eta;\&delta;L}}\frac{1}{\sqrt{d^2-p^2{\mathrm{\&lambda;}}_0^2}(\frac{1}{{\mathrm{\&lambda;}}_0^2}-\frac{p^2}{d^2})}$

In the formula: f represents the focal length of spectrometer lens, the spectral order of the spectro-grating diffraction that p represents, and L represents the pel array length of detector, and δ L represents the unit picture element width of detector, and η is the medium refraction index of object under test, λ ₀The centre wavelength of the wideband light source of expression domain optical coherence tomography system;

3. the grating cycle of adjusting described variable period mounting for grating is d

4. utilize following formula to calculate and adjust described position of detector, promptly described detector central point is to the vertical range of spectrometer lens axis:

$h\left(d\right)=f\tan \left[\arcsin \left(\frac{{\mathrm{p\&lambda;}}_0}{d}\right)\right];$

5. utilize adjusted domain optical coherence tomography system to object image-forming, can obtain the depth range z of user's expectation _MaxWith depth resolution δ z.

2. adjustable frequency domain optical coherence chromatography imaging system that realizes the described method of claim 1, comprise wideband light source (1), on the illumination direction of this wideband light source (1), place collimator and extender device (2) in turn, Michelson interferometer (3), the optical splitter (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 described reference arm light path is reference mirror (33), the end of described feeler arm light path is object under test (35), and object under test (35) is placed on the accurate translation stage of three-dimensional; The output terminal of described Michelson interferometer (3) connects a spectrometer (5), this spectrometer (5) links to each other with computing machine (7) by image pick-up card (6), it is characterized in that described spectrometer (5) is by along light beam working direction variable period mounting for grating successively, condenser lens (53), detector (54) is formed, described variable period mounting for grating is made up of variable period grating (51) and controlling device of grating (52), described controlling device of grating (52) is the device of control described variable period grating (51) cyclomorphosis, described detector (54) is positioned on the slide rail (55), and the moving direction of described detector (54) on described slide rail (55) is perpendicular to the grating grid line direction of the optical axis and the described variable period grating (51) of described spectrometer (5).

3. adjustable frequency domain optical coherence chromatography imaging according to claim 2 system is characterized in that described detector (54) is a photodetector array.

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