WO2010137373A1 - Light interference tomogram acquiring device, probe used for light interference tomogram acquiring device, and light interference tomogram acquiring method - Google Patents

Abstract

Disclosed is a light interference tomogram acquiring device enabling formation of a light interference tomogram with a high image quality by effectively eliminating the influence of reflection of the measurement light from a reflective surface of a focusing optical system from the light interference tomogram even though the light interference tomogram acquiring device has a simple configuration. A probe used for light interference tomogram acquiring devices and a light interference tomogram acquiring method are also disclosed. The reference optical path length from a coupler (BS)to a reference mirror (RM) is longer than the measurement optical path length from the coupler (BS) to the focus position (FP) of the subject (S). With this, even if pulse-shape waveforms (WS1, WS2) are produced by the interference between the reflected light from both surfaces of a parallel plate (PP) and the reference light, a waveform (WS3) representing a tissue of the subject (S) and a signal can be separated, the coherence of the waveform (WS3) acquired in a position near the origin is good, and the SN ratio of the signal is high. Therefore, a tomogram with high accuracy can be formed on the basis thereof.

Description

Optical coherence tomographic image acquisition apparatus, probe used in optical coherence tomographic image acquisition apparatus, and optical coherent tomographic image acquisition method

The present invention includes SS-OCT (Swept Source Optical Coherence Tomography), SD-OCT (Special Domain Optical Coherence Tomography), and FD-OCT (FourierTormoD). The present invention relates to a probe used in a tomographic image acquisition apparatus, an optical coherence tomographic image acquisition apparatus, and an optical coherent tomographic image acquisition method.

2. Description of the Related Art In recent years, electronic endoscope apparatuses that take an image of a living body using reflected light reflected from a living body irradiated with illumination light and display it on a monitor or the like are widely used as endoscope apparatuses for observing the inside of a body cavity of a living body. It is used in various fields. Many endoscopes are provided with forceps openings, and biopsy and treatment of tissues in the body cavities can be performed with probes introduced into the body cavities from the forceps openings through the forceps channels.

An ultrasonic tomographic image acquisition apparatus using ultrasonic waves is known as the above-described endoscope apparatus, but an optical tomographic imaging apparatus using OCT measurement may also be used (see Patent Document 1). . In order to introduce the probe into the body cavity, a probe having a thin outer shape is used (see Patent Document 2).
This OCT measurement is a kind of optical interferometry, which divides low-coherent light emitted from a light source into measurement light and reference light, irradiates the object with the measurement light, and reflects or backscattered light. And the reference light reflected by the reference mirror are combined, and a tomographic image is acquired based on the intensity of the interference light between the reflected light and the reference light.

The OCT measurement is roughly divided into two types: TD (Time domain) -OCT measurement and FD (Fourier Domain) -OCT measurement. In the TD-OCT measurement, the reflected light intensity distribution corresponding to the position in the depth direction of the measurement target (hereinafter referred to as the depth position) is obtained by measuring the interference light intensity while changing the optical path length of the reference light. Is the method.

On the other hand, in the FD-OCT measurement, the interference light intensity is measured for each spectral component of the light without changing the optical path lengths of the reference light and the signal light, and the obtained spectral interference intensity signal is Fourier transformed by a computer. This is a method of obtaining a reflected light intensity distribution corresponding to a depth position by performing a representative frequency analysis. In recent years, FD-OCT measurement has attracted attention as a technique that enables high-speed measurement by eliminating the need for mechanical scanning existing in TD-OCT measurement.

As typical apparatus configurations for performing FD-OCT measurement, there are two types, that is, an SD (Spectral Domain) -OCT apparatus and an SS (Swept source) -OCT apparatus. The SD-OCT apparatus uses broadband low-coherent light, decomposes the interference light into each optical frequency component by a spectroscopic means, and measures the interference light intensity for each optical frequency component with an array-type photodetector. A tomographic image is constructed by performing Fourier transform analysis on the spectrum interference waveform obtained in step 1 by a computer. The SS-OCT apparatus uses a laser or the like that temporally sweeps the optical frequency as a light source, measures the time waveform of the signal corresponding to the temporal change of the optical frequency of the interference light, and obtains the spectral interference intensity signal obtained thereby. A tomographic image is constructed by performing Fourier transform on a computer.

JP 2008-289850 A US Patent No. 6891984

However, since the probe that irradiates the measurement light in the OCT measurement is used by approaching or contacting the human tissue that is the subject, as shown in Patent Document 1, the measurement light is formed by a transparent cylindrical sheath. The condensing optical system is covered. In particular, in the prior art of Patent Document 1, in order to increase the contact area with the subject, the sheath has a triangular cylindrical shape, but this causes a part of the measurement light collected by the condensing optical system to be a side surface of the sheath. When this reflected light is combined with the reference light together with the reflected light from the subject, it becomes manifest as noise on the tomographic image, making it difficult to distinguish it from the subject image. Further, since a certain noise appears even if the reflectance on the side surface of the sheath is low, it can be said that even if an antireflection film is formed on the surface of the sheath, it is not a fundamental measure.

On the other hand, in Patent Document 2, the reflected light of the measurement light on the prism surface is directed in another direction by inclining the prism surface provided at the probe emission tip to a predetermined angle, thereby reflecting from the subject. A configuration in which only light is combined with reference light is disclosed. However, since the prism provided in the probe is small, there is a problem that it is difficult to obtain the accuracy of the surface inclined at a predetermined angle, and the cost increases. Even if the prism surface is tilted at a predetermined angle, it is difficult to completely prevent the reflected light from being combined with the reference light.

The present invention has been made in view of the above-described problems, and has a simple configuration, but effectively removes the influence of the reflection of measurement light from the reflection surface of the condensing optical system from the optical coherence tomographic image. An object of the present invention is to provide an optical coherence tomographic image acquisition apparatus capable of forming a high-quality optical coherence tomographic image, a probe used in the optical coherence tomographic image acquisition apparatus, and an optical coherence tomographic image acquisition method.

The optical coherence tomographic image acquisition apparatus according to claim 1,
A light source that emits light of a broadband wavelength;
Splitting means for splitting light from the light source into reference light and measurement light;
Reference light transmitting means for transmitting the reference light divided by the dividing means;
A reference mirror for reflecting the reference light transmitted through the reference light transmitting means and making it incident on the reference light transmitting means;
Measurement light transmission means for transmitting the measurement light divided by the division means;
The measurement light transmitted through the measurement light transmission means is collected toward the subject, and the measurement light reflected from the subject is received and incident on the measurement light transmission means. A probe including an optical optical system;
Combining means for combining the reference light returned via the reference light transmitting means and the measurement light returned via the measuring light transmitting means to form a combined light;
Interference signal acquiring means for acquiring an interference signal from the combined light formed by the combining means;
Image acquisition means for decomposing the interference signal acquired by the interference signal acquisition means into frequency components and acquiring a tomographic image of the subject accordingly;
The condensing optical system has at least one reflecting surface,
The reference optical path length from the dividing means to the combining means via the reference mirror along the reference light transmitting means is the condensing position of the condensing optical system along the measuring light transmitting means from the dividing means. It is characterized by being longer than the measurement optical path length leading to the synthesizing means.

Generally, in SD-OCT measurement or SS-OCT measurement, if there is a large difference between the reference optical path length from the light source to the reference mirror and the measurement optical path length from the light source to the subject, it is reflected by the reference mirror. The reference light and the measurement light reflected by the subject are less likely to interfere with each other, and an effective optical coherence tomographic image cannot be formed. Therefore, it is desirable to make the reference optical path length from the light source to the reference mirror close to the measurement optical path length from the light source to the subject. However, when the measuring light condensing optical system has a reflecting surface, the reflecting surface is relatively close to the subject, so that the reflected light is picked up to distinguish it from the reflected light from the subject. There is a risk that it will not be possible.

On the other hand, according to the present invention, the reference optical path length from the light source to the reference mirror is longer than the measurement optical path length from the light source to the condensing position of the condensing optical system. Even if reflected light is generated from such a reflective surface, it can be clearly distinguished from the reflected light from the subject, and the reflective surface of the condensing optical system and the reference mirror are separated in the optical path length direction. The coherence is reduced, and the interference signal waveform from the reflecting surface is reduced. In addition, since the coherence with the reflected light from the subject becomes relatively large, a high-quality optical coherence tomographic image with a good SN (Signal to Noise) ratio can be formed. The “condensing optical system” includes not only an optical element having power but also all elements that are arranged between the measurement light transmission means and the subject and transmit or reflect the measurement light. The “reference light transmission means” refers to an optical path through which reference light is transmitted in a reciprocating manner, and includes cases where the forward path and the return path are different. In this case, there is also a reference light transmission means in which the reference light directed to the reference mirror passes but the reference light reflected from the reference mirror does not pass, or the reference light reflected from the reference mirror passes, but the reference directed to the reference mirror There is also a reference light transmission means through which light does not pass. Similarly, “measurement light transmission means” refers to an optical path through which measurement light is transmitted in a reciprocating manner, and includes cases where the forward path and the return path are different. In this case, there is also a measurement light transmitting means that passes measurement light toward the subject but does not pass measurement light reflected from the subject, or measurement light reflected from the subject passes but measurement toward the subject. There is also a measuring light transmission means through which light does not pass.

The optical coherence tomographic image acquisition apparatus according to claim 2 is characterized in that, in the invention according to claim 1, the optical path length difference Δl between the reference optical path length and the measurement optical path length satisfies the following expression. . Thereby, the reference light reflected by the reference mirror and the measurement light reflected by the subject can be easily interfered with each other, and an effective optical coherence tomographic image can be formed. More specifically, when the optical path length difference Δl is less than the lower limit of the expression (1), a signal from the subject can be acquired in a coherent state, but the acquired interference signal has a lower frequency and a direct current component Therefore, an image with a high S / N ratio cannot be obtained. In other words, when the interference signal is Fourier-transformed, the DC component interference signal is generated in the vicinity of the origin position, and it can be said that it is difficult to separate the image from the signal from the subject. On the other hand, if the optical path length difference Δl exceeds the upper limit of the equation (1), the coherence becomes worse and an image with a high SN ratio cannot be obtained. Therefore, it is preferable to satisfy the formula (1).

0.3 / π · (λ / NA ² ) <Δl <3.0 / π · (λ / NA ² ) (1)
Where NA is the numerical aperture NA of 1 / e ² intensity light incident on the subject, and λ is the center wavelength of the light emitted from the light source. The expression (1) is an expression that expresses the degree of possibility of interference based on the Rayleigh length.

The optical coherence tomographic image acquisition device according to claim 3 is the optical acquisition device according to claim 1 or 2, wherein the position of the reflection surface is obtained by obtaining reflected light reflected by the reflection surface as the interference signal. It is in the range. The image acquisition range is a range in the depth direction (δz) that can be measured by the optical coherence tomographic image acquisition apparatus.

According to a fourth aspect of the present invention, there is provided the optical coherence tomographic image acquisition apparatus according to the third aspect of the invention, wherein the image acquisition range is determined by a sampling number of data for detecting the interference signal. Here, the number of sampling points of the object N, [delta] [lambda] the wavelength of the scanning during sampling, when the central wavelength of the measuring light and lambda _C, the image acquiring range [delta] _Z can be expressed by the following equation (26 December 2005 / Vol .13, No. 26 / OPTICS EXPRESS 10652).

^{_{δ Z = Nλ C 2 / 4δλ}} (2)
According to a fifth aspect of the present invention, in the optical coherence tomographic image acquisition apparatus according to the third aspect of the invention, the image acquisition range is determined by a coherence distance of measurement light emitted from the probe. The “coherence distance” refers to a distance at which interference is possible.

The optical coherence tomographic image acquisition apparatus according to claim 6 is the invention according to claim 3, wherein the image acquisition range is 20 mm or less.

The optical coherence tomographic image acquisition apparatus according to claim 7 is the optical interference tomographic image acquisition apparatus according to any one of claims 1 to 6, wherein the reflecting surface of the condensing optical system reflects the incident measurement light to the optical axis. It is characterized by returning along. The reflective surface includes a flat surface, a spherical surface, or an aspheric surface.

The probe used in the optical coherence tomographic image acquisition apparatus according to claim 8 is:
A light source that emits light of a broadband wavelength;
Splitting means for splitting light from the light source into reference light and measurement light;
Reference light transmitting means for transmitting the reference light divided by the dividing means;
A reference mirror for reflecting the reference light transmitted through the reference light transmitting means and making it incident on the reference light transmitting means;
Measurement light transmission means for transmitting the measurement light divided by the division means;
The measurement light transmitted through the measurement light transmission means is collected toward the subject, and the measurement light reflected from the subject is received and incident on the measurement light transmission means. A probe including an optical optical system;
Combining means for combining the reference light returned via the reference light transmitting means and the measurement light returned via the measuring light transmitting means to form a combined light;
Interference signal acquiring means for acquiring an interference signal from the combined light formed by the combining means;
A probe used in an optical coherence tomographic image acquisition apparatus having image acquisition means for decomposing the interference signal acquired by the interference signal acquisition means into frequency components and acquiring a tomographic image of the subject accordingly. ,
The condensing optical system of the probe has at least one reflecting surface, and a reference optical path length from the dividing unit to the combining unit through the reference mirror along the reference light transmitting unit is equal to the dividing unit. The measurement light path length is longer than the measurement light path length from the condensing position of the condensing optical system to the combination means along the measurement light transmission means.

According to the present invention, the reference optical path length from the light source to the reference mirror is longer than the measurement optical path length from the light source to the condensing position of the condensing optical system. Even if reflected light is generated from such a reflective surface, it can be clearly distinguished from the reflected light from the subject, and the reflective surface of the condensing optical system and the reference mirror are separated in the optical path length direction. The waveform of the reflecting surface becomes smaller, so that a high-quality optical coherence tomographic image can be formed.

The optical coherence tomographic image acquisition method according to claim 9,
Splitting light of a broadband wavelength emitted from a light source into reference light and measurement light using a splitting means;
Transmitting the divided reference light through reference light transmission means and reflecting it by a reference mirror;
Condensing the divided measurement light toward the subject via the measurement light transmitting means and a condensing optical system having at least one reflecting surface, and receiving the measurement light reflected from the subject When,
Obtaining an interference signal from the combined light obtained by combining the reflected reference light and the reflected measurement light using a combining unit;
Decomposing the acquired interference signal into frequency components, and obtaining a tomographic image of the subject accordingly,
The reference optical path length from the dividing unit to the combining unit through the reference mirror along the reference light transmitting unit is determined, and the condensing position of the condensing optical system from the dividing unit along the measuring light transmitting unit. It is characterized in that it is longer than the measurement optical path length to reach the synthesis means.

According to the present invention, since the reference optical path length from the light source to the reference mirror is longer than the measurement optical path length from the light source to the condensing position of the condensing optical system, the measurement light is reflected on the condensing optical system. Even if reflected light is generated from such a reflecting surface, it can be clearly distinguished from the reflected light from the subject, and the reflecting surface of the condensing optical system and the reference mirror are separated in the optical path length direction. Thus, the waveform of the reflection surface becomes smaller, so that a high-quality optical coherence tomographic image can be formed.

According to the present invention, it is possible to form a high-quality optical coherence tomographic image by effectively removing the influence of measurement light reflection from the reflecting surface of the condensing optical system from the optical coherence tomographic image while having a simple configuration. It is possible to provide an optical coherence tomographic image acquisition apparatus, a probe used in the optical coherence tomographic image acquisition apparatus, and an optical coherence tomographic image acquisition method.

It is an external appearance perspective view of the optical coherence tomographic image acquisition apparatus concerning this Embodiment. It is a block diagram which shows preferable embodiment of the optical coherence tomographic image acquisition apparatus of this invention. It is sectional drawing which shows the front-end | tip part of the probe PLB concerning 1st Embodiment. FIG. 4A is a diagram illustrating the relationship between the reference mirror according to the first comparative example and the position of the subject, and FIG. 4B illustrates the interference signal acquired from the synthesized light in the first comparative example. It is a figure of the tomographic image obtained by Fourier-transform, a vertical axis | shaft is signal intensity, and a horizontal axis is an optical distance (distance along optical path length). FIG. 4C is a diagram showing the relationship between the reference mirror according to the third comparative example and the position of the subject. FIG. 4D shows the interference signal acquired from the synthesized light in the third comparative example. It is a figure of the tomographic image obtained by Fourier-transform. FIG. 5A is a diagram showing the relationship between the reference mirror and the position of the subject according to the first example, and FIG. 5B shows the interference signal acquired from the synthesized light in the first example. It is a figure of the tomographic image obtained by Fourier-transform, a vertical axis | shaft is signal intensity, and a horizontal axis is an optical distance (distance along optical path length). FIG. 6A is a diagram showing the relationship between the reference mirror according to the second comparative example and the position of the subject, and FIG. 6B shows the interference signal acquired from the synthesized light in the second comparative example. It is a figure of the tomographic image obtained by Fourier-transform, a vertical axis | shaft is signal intensity, and a horizontal axis is an optical distance (distance along optical path length). FIG. 7A is a diagram showing the relationship between the reference mirror according to the second embodiment and the position of the subject. FIG. 7B shows the interference signal acquired from the combined light in the second embodiment. It is a figure of the tomographic image obtained by Fourier-transform, a vertical axis | shaft is signal intensity, and a horizontal axis is an optical distance (distance along optical path length). It is sectional drawing of the probe concerning 2nd Embodiment. It is sectional drawing of the probe concerning 3rd Embodiment. It is sectional drawing of the probe concerning 4th Embodiment. It is a schematic block diagram of the optical coherence tomographic image acquisition apparatus concerning another embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an external perspective view of the optical coherence tomographic image acquisition apparatus according to the present embodiment. The optical coherence tomographic image acquisition apparatus includes a main body MB that acquires a tomographic image of the subject S by OCT measurement, and a probe PLB that is detachably attached to the main body MB and guides measurement light to the measurement target. . The probe PLB can be removed and cleaned and disinfected or replaced with another probe.

FIG. 2 is a schematic configuration diagram of the optical coherence tomographic image acquisition apparatus according to the present embodiment. Here, the SD-OCT configuration is adopted. The main body MB of the optical coherence tomographic image acquisition apparatus is integrated with a light source SLD that emits low-coherent light L with a broadband wavelength, an optical fiber FB1 that transmits low-coherent light L emitted from the light source SLD, and an end of the optical fiber FB1. Optically coupled to the coupler BS, the measurement light L1 split by the coupler BS to the probe PLB side, and the measurement light L1 from the probe PLB side to the coupler BS, and the coupler BS The reference light L2 is guided to the reference mirror RM side, the reference light L2 from the reference mirror RM side is transmitted to the coupler BS, and the reference light L2 emitted from the end of the optical fiber FB3 is converted into parallel light. Reference optical system ROP to convert, reference mirror RM reflecting parallel light from reference optical system ROP, and position of reference mirror RM An adjustment device ADJ for adjustment, a control device CONT for controlling the drive device DR for the probe PLB, a measurement light L1 from the probe PLB side by the coupler BS, and a reference light L2 reflected from the reference mirror RM The optical fiber FB4 that transmits the combined light L5 obtained by combining, the interference signal detection unit ISD that acquires an interference signal from the combined light L5 transmitted by the optical fiber FB4, and the interference signal detection unit ISD An image processing unit IP that performs frequency analysis by Fourier transforming the interference signal and acquires an optical coherence tomographic image, and a monitor MNT that displays the optical coherence tomographic image based on a signal from the image processing unit IP Yes.

Here, the light source SLD is composed of a laser light source that emits low-coherent light having a wide-band wavelength, such as SLD (Super Luminescent Diode) and ASE (Amplified Spontaneous Emission). Since the optical coherent tomographic image acquisition apparatus acquires a tomographic image when the living body is the subject S, the attenuation of light due to scattering and absorption when passing through the subject S is minimized. For example, it is preferable to use an ultrashort pulse laser light source having a wide spectrum band.

The coupler BS integrated with the optical fibers FB1, FB2, FB3, and FB4 is made of, for example, a 2 × 2 optical fiber coupler, and measures the low coherent light L guided from the light source SLD through the optical fiber FB1. The light L1 is divided into the reference light L2, and the returned measurement light L1 and reference light L2 are combined and output to the optical fiber FB4. The measurement light L1 is guided by the optical fiber FB2, the reference light L2 is guided by the optical fiber FB3, and the combined light L5 is guided by the optical fiber FB4. Here, the optical fibers FB1, FB2, FB3, FB4 and the coupler BS constitute an optical transmission means. However, the optical fibers FB1, FB2, FB3, and FB4 and the coupler BS may be composed of separate members and connected. The tip of the optical fiber is provided in a protective cylinder called a ferrule, but is omitted in this specification.

The optical fiber FB2 is connected to the internal optical fiber FB of the probe PLB via an optical coupling CPL, and the measurement light L1 is guided from the optical fiber FB2 to the probe PLB. The optical coupling CPL enables the measurement light L1 to be transmitted even when a relative displacement occurs between the optical fiber FB2 and the internal optical fiber due to driving of the driving device DR described later.

FIG. 3 is a cross-sectional view showing the tip portion of the probe PLB, and the probe PLB will be described with reference to FIGS. The probe PLB is inserted, for example, into a body cavity or disposed close to a living body, and is connected to a connector CN (FIG. 1) provided at a ferrule end surrounding the optical fiber FB2. In FIG. 3, the probe PLB includes a round or square sheath CY, a hollow flexible torque wire TW supported by an annular torque wire guide (bearing) TWG in the sheath CY, and the outside of the sheath CY. And a drive lens DR that rotates and axially displaces the torque wire TW, and a convex lens PL whose outer periphery is fixed to the end of the torque wire TW and is connected to the end of the internal optical fiber FB. The driving device DR and the control device CONT of the main body MB are connected by a wiring H. The sheath CY is formed of, for example, a flexible resin, and a transparent parallel plate PP is fixed to the distal end portion of the sheath CY, while the inside is sealed and the measurement light L1 is transmitted. The torque wire TW is composed of, for example, a double contact coil in which a metal wire is spirally wound, and each of the contact coils is wound so that the winding directions are opposite to each other, and therefore flexible. However, when one end is rotationally displaced / displaced in the axial direction by the driving device DR, the other end is also displaced in the same direction even in a bent state. The parallel plate PP is attached coaxially with the convex lens PL, but may be attached at an angle.

The operation of the optical coherence tomographic image acquisition apparatus (optical coherence tomographic image acquisition method) will be described. First, the control device CONT reads out the unique data of the probe PLB, and adjusts the position of the reference mirror RM by driving the adjustment device ADJ accordingly. Thereby, the reference optical path length from the light source to the reference mirror RM is always longer than the measurement optical path length from the light source to the condensing position FP of the subject S.

In FIG. 2, the low coherent light L emitted from the light source SLD propagates inside the optical fiber FB1, and is split into measuring light L1 and reference light L2 by a coupler BS which is a splitting unit (here, also serves as a combining unit). Divided. The measurement light L1 divided by the coupler BS propagates through the optical fiber FB2 serving as measurement light transmission means, and enters the probe PLB through the optical coupling CPL. In FIG. 3, the measurement light L1 transmitted to the probe PLB side via the optical fiber FB2 is incident on the internal optical fiber FB connected via the optical coupling CPL, and after exiting the internal optical fiber FB, the convex lens PL Thus, the light is converted into convergent light, passes through the parallel plate PP, and is condensed on the tissue of the subject. The reflected light L3 from the subject passes through the parallel plate PP, is condensed on the end surface of the internal optical fiber FB by the convex lens PL, passes through the internal optical fiber FB, and passes through the optical coupling CPL to the optical fiber FB2. To the coupler BS along the optical fiber FB2.

On the other hand, in FIG. 2, the reference light L2 divided by the coupler BS propagates inside the optical fiber FB3 as reference light transmission means, enters the reference optical system ROP from its end face, and travels toward the reference mirror RM. Irradiated. The reference light L2 is reflected by the reference mirror RM, becomes reference light L4 as reflected light, is reflected by the reference mirror RM, enters from the end of the optical fiber FB3, and travels toward the coupler BS along the optical fiber FB3. The reflected light L3 and the reflected light L4 are combined by the coupler BS, and the combined light L5 is transmitted to the interference signal detection unit ISD which is an interference signal acquisition unit, where an interference signal is acquired. The image processing unit IP, which is an image acquisition unit, receives the interference signal, performs frequency analysis by decomposing the interference signal into frequency components, that is, Fourier transform, and acquires an optical coherence tomographic image. If the control device CONT displaces the torque wire TW of the probe PLB via the drive device DR and scans the measurement light L1 on the subject S, the depth of the subject S in each tissue along this scanning direction Since direction information is obtained, a tomographic image of a tomographic plane including this scanning direction can be acquired. The tomographic image acquired in this way is displayed on the monitor MNT.

Here, detection of interference light in the interference signal detection unit ISD and generation of an image in the image processing unit IP will be briefly described. Details of this are described in “Takeda Mitsuo,“ Optical Frequency Scanning Spectrum Interference Microscope ”, Optical Technology Contact, 2003, Vol 41, No7, p426-p432”.

When the measurement light L1 is irradiated onto the subject S, various optical path lengths are obtained in the combined light L5 of the reflected light L3 from the depth of each tissue of the subject S and the reference light L4 reflected by the reference mirror RM. Assuming that the light intensity of the interference fringes for each optical path length difference l when interfering with a difference is S (l), the light intensity I (k) detected by the interference signal detector ISD is
I (k) = ∫ ₀ ^∞ S (l) [1 + cos (kl)] dl (3)
It is represented by Here, k is the wave number, and l is the optical path length difference. Equation (3) can be considered to be given as an interferogram in the optical frequency domain with the wave number k as a variable. Therefore, in the image processing unit IP, the interference light detected by the interference signal detection unit ISD is subjected to frequency analysis by performing Fourier transform, and the light intensity S (l) of the interference light is determined, so that each tissue of the subject S is determined. Reflection information at the depth position can be acquired and a tomographic image can be generated. Then, the tomographic image generated by the image processing unit IP is displayed on the monitor MNT.

Next, consider the position of the reference mirror RM. FIG. 4A is a diagram illustrating the relationship between the reference mirror according to the first comparative example and the position of the subject, and FIG. 4B illustrates the interference signal acquired from the synthesized light in the first comparative example. It is a figure of the tomographic image obtained by Fourier-transform. FIG. 4C is a diagram showing the relationship between the reference mirror according to the third comparative example and the position of the subject. FIG. 4D shows the interference signal acquired from the synthesized light in the third comparative example. It is a figure of the tomographic image obtained by Fourier-transform. FIG. 5A is a diagram showing the relationship between the reference mirror and the position of the subject according to the first example, and FIG. 5B shows the interference signal acquired from the synthesized light in the first example. It is a figure of the tomographic image obtained by Fourier-transform. In the tomographic image, random noise generated in the background due to electrical signals and optical fluctuations is detected, but this is not shown here.

Here, the convex lens PL and the parallel plate PP constitute a condensing optical system. However, since the measurement light L1 passes through the parallel plate PP attached to the end of the sheath CY, both surfaces of the parallel plate PP (condensing optics). A certain amount of reflected light is generated from the surface PP1 on the convex lens PL side and the surface PP2 on the subject S side constituting the reflection surface of the system, and returns along the optical axis. However, in the case of the first comparative example shown in FIGS. 4A and 4B, the reference optical path length RL from the coupler BS to the reference mirror RM (the forward path from the dividing means to the reference mirror RM and the reference mirror RM to the combining means). Is different from the return path + the return path length (hereinafter the same), the measurement optical path length ML from the coupler BS to the collection position FP of the subject S (the forward path from the dividing means to the collection position FP) and the collection path If the return path from the optical position FP to the combining means is different, the return path length is equal to the return path length (the same applies hereinafter). In such a case, the reflected light from both sides of the parallel plate PP interferes with the reference light, and as shown in FIG. 4 (b), the two near the origin (the position of the reference mirror along the optical path length). Large pulse waveforms WS1 and WS2 are generated. On the other hand, the waveform WS3 indicating the tissue of the subject S is generated at a position farther from the origin than the pulsed waveforms WS1 and WS2. When the interference light is Fourier-transformed, a mirror image waveform is generated with the origin at the center as shown in the figure.

In general, in the OCT measurement, when the difference Δl between the reference optical path length RL and the measurement optical path length ML is large, the coherence is deteriorated and the signal-to-noise ratio of the signal is reduced, and noise is identified when a tomographic image is formed. Becomes difficult. Therefore, in the case of the comparative example in FIG. 4, the waveform of the waveform WS3 is small, the SN ratio is bad, and a high-quality image cannot be acquired.

On the other hand, in the case of the third comparative example shown in FIGS. 4C and 4D, the position of the reference mirror RM is set to the subject S so that the signal W3 from the subject S can be acquired in a state with good coherence. Shown close-up. Here, the position of the reference mirror RM is such that the reference optical path length RL is shorter than the measurement optical path length ML and longer than the optical path length of the reflected light reflected from both surfaces of the parallel plate PP (that is, the reference mirror RM is longer than the parallel plate PP from the light source). It is set to be located far away). In such a case, the reflected light from both surfaces of the parallel plate PP interferes with the reference light, so that the waveforms WS1 and WS2 indicate the tissue of the subject S at positions close to the origin as shown in FIG. The waveform WS3 overlaps and an accurate tomographic image cannot be obtained. Thus, it is difficult to obtain a high-quality image with a measurement probe that has a reflecting surface due to its configuration.

On the other hand, in the case of the first embodiment shown in FIG. 5, the reference optical path length RL from the coupler BS to the reference mirror RM is made longer than the measurement optical path length ML from the coupler BS to the condensing position FP of the subject S. Yes. As a result, the reflected light from both surfaces of the parallel plate PP interferes with the reference light, thereby generating pulsed waveforms WS1 and WS2, which are unnecessary signals generated after Fourier transform, as shown in FIG. 5B. Even so, the waveform WS3 indicating the tissue of the subject S can be separated from the signal, and the waveform WS3 acquired at a position close to the origin has a good coherence and a high signal-to-noise ratio. An image can be formed. If the reference mirror position is set as in this configuration, it is not necessary to incline the parallel plate PP or to apply an AR coat to prevent reflection from the parallel plate PP as a reflection surface, while the signal of the parallel plate PP is transmitted. Since it is separated from the waveform WS3, the signals WS1 and WS2 which are signals from the parallel plate PP can be completely removed, and a high-quality tomographic image can be acquired. Although not shown here, the reflection surface is considered not only the parallel plate PP but also the emission end surface SS (see FIG. 6) of the internal optical fiber FB. In Example 1, for example, a convex lens PL with NA = 0.02 and a light source that emits a light beam with a center wavelength of 1.3 μm can be used. In this case, Δl may be set from 0.3 mm to 3.1 mm.

FIG. 6A is a diagram showing the relationship between the reference mirror according to the second comparative example and the position of the subject, and FIG. 6B shows the interference signal acquired from the synthesized light in the second comparative example. It is a figure of the tomographic image obtained by Fourier-transform. FIG. 7A is a diagram showing the relationship between the reference mirror according to the second embodiment and the position of the subject. FIG. 7B shows the interference signal acquired from the combined light in the second embodiment. It is a figure of the tomographic image obtained by Fourier-transform.

In the second comparative example shown in FIG. 6, unlike the first comparative example described above, a convex lens PL having a plane PL1 on the internal optical fiber FB side is used. Accordingly, the reflecting surfaces of the condensing optical system are the surface PL1 of the convex lens PL and both surfaces PP1 and PP2 of the parallel plate PP. Similarly, the reference optical path length RL from the coupler BS to the reference mirror RM is shorter than the measurement optical path length ML from the coupler BS to the condensing position FP of the subject S. Accordingly, three large pulse waveforms WS1, WS2, and WS4 are generated at positions close to the origin in accordance with the reflected light from the reflecting surface of the condensing optical system. On the other hand, the waveform WS3 indicating the tissue of the subject S is generated at a position farther from the origin than the pulse-like waveforms WS1, WS2, and WS4, and is acquired as a signal having poor coherence, so the SN ratio is poor.

On the other hand, in the case of the second embodiment shown in FIG. 7, the reference optical path length RL from the coupler BS to the reference mirror RM is made longer than the measurement optical path length ML from the coupler BS to the condensing position FP of the subject S. Yes. As a result, the reflected light from both surfaces of the parallel plate PP and the surface PL1 of the convex lens PL interferes with the reference light, thereby generating pulsed waveforms WS1, WS2, WS4, WS5 as shown in FIG. 7B. Even so, the waveform WS3 indicating the tissue of the subject S can be separated from the signal, and the waveform WS3 acquired at a position close to the origin has good coherence and the signal SN ratio becomes large. A high-quality tomographic image can be formed. The waveform WS5 is a waveform based on the reflected light from the emission end face SS of the internal optical fiber FB. If the reference mirror position is set as in this configuration, it is not necessary to incline the parallel plate PP and the surface PL1 or to apply an AR coating in order to prevent reflection from the parallel plate PP and the surface PL1, which are reflection surfaces. Since the signals of the parallel plate PP and the surface PL1 are separated from the waveform WS3, the signals WS1, WS2, WS4 and WS5 that are signals from the parallel plate PP and the surface PL1 can be completely removed, and the image quality is high. Tomographic images can be acquired.

FIG. 8 is a cross-sectional view of the probe according to the second embodiment. The probe PLB includes a cylindrical sheath CY, a hollow flexible torque wire TW supported by an annular torque wire guide (bearing) TWG in the sheath CY, and a torque provided outside the sheath CY. A driving device DR that rotationally and axially displaces the wire TW, a GRIN lens (Gradient Index Lens) GL whose outer periphery is fixed to the end of the torque wire TW and connected to the end of the internal optical fiber FB, and a GRIN lens GL And a cap CP fixed to the tip of the sheath CY. In the present embodiment, the sheath CY constitutes a part of the condensing optical system, and thus both sides of the side wall of the sheath CY constitute a reflecting surface.

The measurement light L1 transmitted to the probe PLB side via the optical fiber FB2 enters the internal optical fiber FB connected via the optical coupling CPL, is condensed by the GL on the GRIN lens, and is reflected by the prism PR. Thus, the light is condensed on the tissue of the subject S. The reflected light L3 from the subject S is reflected by the prism PR, enters the GRIN lens GL, passes through the internal optical fiber FB, and returns to the optical fiber FB2 through the optical coupling CPL. Other configurations are the same as those of the embodiment shown in FIG.

FIG. 9 is a cross-sectional view of a probe according to the third embodiment. The probe PLB includes a cylindrical sheath CY, a hollow flexible torque wire TW supported by an annular torque wire guide (bearing) TWG in the sheath CY, and a torque provided outside the sheath CY. A driving device DR that rotationally and axially displaces the wire TW, a GRIN lens (Gradient Index Lens) GL whose outer periphery is fixed to the end of the torque wire TW and connected to the end of the internal optical fiber FB, and a GRIN lens GL And a cap CP fixed to the tip of the sheath CY. Also in the present embodiment, the sheath CY constitutes a part of the condensing optical system, and thus both sides of the side wall of the sheath CY constitute a reflecting surface.

The measurement light L1 transmitted to the probe PLB side through the optical fiber FB2 is incident on the internal optical fiber FB connected through the optical coupling CPL, is condensed by the GL on the GRIN lens, and is reflected by the reflection mirror MR. The light is reflected and collected on the tissue of the subject S. The reflected light L3 from the subject S is reflected by the reflecting mirror MR, enters the GRIN lens GL, passes through the internal optical fiber FB, and returns to the optical fiber FB2 through the optical coupling CPL. Other configurations are the same as those of the embodiment shown in FIG.

FIG. 10 is a cross-sectional view of a probe according to the fourth embodiment. The probe PLB includes a cylindrical sheath CY, a hollow flexible torque wire TW supported by an annular torque wire guide (bearing) TWG in the sheath CY, and a torque provided outside the sheath CY. A driving device DR for rotating and axially displacing the wire TW, a prism PR whose outer periphery is fixed to the end of the torque wire TW and connected to the end of the internal optical fiber FB, and an output surface of the prism PR It has a convex lens PL and a cap CP fixed to the tip of the sheath CY. Also in the present embodiment, the sheath CY constitutes a part of the condensing optical system, and thus both sides of the side wall of the sheath CY constitute a reflecting surface.

The measurement light L1 transmitted to the probe PLB side through the optical fiber FB2 is incident on the internal optical fiber FB connected through the optical coupling CPL, is further reflected by the prism PR, and is received through the convex lens PL. It is focused on the tissue of the sample S. The reflected light L3 from the subject S passes through the convex lens PL, is reflected by the prism PR, passes through the internal optical fiber FB, and returns to the optical fiber FB2 through the optical coupling CPL. Other configurations are the same as those of the embodiment shown in FIG.

FIG. 11 is a schematic configuration diagram of an optical coherence tomographic image acquisition apparatus according to another embodiment. In the present embodiment, the coupler BS of the embodiment shown in FIG. 2 is replaced with a dividing coupler DV as a dividing means, a combining coupler CMP as a combining means, a first circulator C1, and a second circulator C2. Is different. The optical coupling CPL includes lenses LS1 and LS2. Other configurations are the same as those in the above-described embodiment, including those omitted. The optical fiber FB22 connecting the first circulator C1 and the optical coupling CPL constitutes the measurement light transmission means, and the optical fiber FB32 extending from the second circulator C2 to the reference mirror RM side constitutes the reference light transmission means. To do. The measurement optical path length is the total optical path length up to the splitting coupler DV-condensing position of the subject-optical coupling CPL, and the reference optical path length is up to the splitting coupler DV-reference mirror RM-optical coupling CPL. Is the total optical path length. The measurement light transmission means for transmitting the measurement light L1 and the reflected light L3 may be common or independent. Further, the reference light transmission means for transmitting the reference light L2 and the reflected light L4 may be common or may be independent.

In FIG. 11, the low coherent light L emitted from the light source SLD propagates in the optical fiber FB1 integrated with the splitting coupler DV, and is split into the measuring light L1 and the reference light L2 by the splitting coupler DV. The measurement light L1 split by the splitting coupler DV propagates in the optical fiber FB21, passes through the first circulator C1, propagates in the optical fiber FB22, and enters the optical coupling CPL. Here, the measurement light L1 emitted from the end of the optical fiber FB22 is converted into parallel light by the lens LS1, and condensed by the lens LS2 on the end of the internal optical fiber FB of the probe PLB. Obviously, even if a relative rotational displacement occurs between the optical fiber FB22 and the internal optical fiber FB, the amount of light transmitted by the optical coupling CPL does not change. Further, the relative displacement of the internal optical fiber FB in the optical axis direction can be realized by stretching the internal optical fiber FB in a bent state.

The measurement light L1 transmitted to the probe PLB side through the optical coupling CPL passes through the internal optical fiber FB, is converted into convergent light by the GRIN lens, is reflected by the prism PR, and is condensed on the tissue of the subject. It has come to be. The reflected light L3 from the subject is reflected by the prism PR, collected on the end surface of the internal optical fiber FB by the GRIN lens, passes through the internal optical fiber FB, and returns to the optical fiber FB22 through the optical coupling CPL. Then, it goes to the first circulator C1 along the optical fiber FB22. The reflected light L3 is directed to the synthesis coupler CMP along the optical fiber FB23 by the first circulator C1.

On the other hand, in FIG. 11, the reference light L2 split by the splitting coupler DV propagates in the optical fiber FB31, passes through the second circulator C2, propagates in the optical fiber FB32, and the reference optical from its end face. The light enters the system ROP and is irradiated toward the reference mirror RM. The reference light L2 is reflected by the reference mirror RM, becomes reference light L4 as reflected light, enters from the end of the optical fiber FB32, and travels along the optical fiber FB32 toward the second circulator C2. The reflected light L4 is directed to the synthesizing coupler CMP along the optical fiber FB33 by the second circulator C2. The reflected light L3 and the reflected light L4 are combined by the combining coupler CMP, and the combined light L5 is transmitted to the interference signal detection unit ISD which is an interference signal acquisition unit, where an interference signal is acquired. The image processing unit IP, which is an image acquisition means, can input this interference signal and perform Fourier transform to perform frequency analysis and acquire an optical coherence tomographic image.

Note that the present invention can be applied to both SD-OCT measurement and SS-OCT measurement, and the configuration of the condensing optical system may not be the configuration of the embodiment.

ADJ adjustment device BS coupler CONT control device CN connector CY sheath DR drive device FB internal optical fiber FB1 optical fiber FB2 optical fiber FB3 optical fiber FB4 optical fiber FP condensing position GL GRIN lens H wiring IP image processing unit ISD interference signal detection unit L Low coherent light L1 Measurement light L2 Reference light L3 Reflected measurement light L4 Reflected reference light L5 Composite light MB Body MNT monitor MR Reflective mirror PL Convex lens PL1 surface PLB probe PP Parallel plate PP1 surface PP2 surface PR prism RM Reference mirror ROP Reference optics System SLD Light source TW Torque wire WS1 to WS4 Waveform

Claims (9)

1. A light source that emits light of a broadband wavelength;
   Splitting means for splitting light from the light source into reference light and measurement light;
   Reference light transmitting means for transmitting the reference light divided by the dividing means;
   A reference mirror for reflecting the reference light transmitted through the reference light transmitting means and making it incident on the reference light transmitting means;
   Measurement light transmission means for transmitting the measurement light divided by the division means;
   The measurement light transmitted through the measurement light transmission means is collected toward the subject, and the measurement light reflected from the subject is received and incident on the measurement light transmission means. A probe including an optical optical system;
   Combining means for combining the reference light returned via the reference light transmitting means and the measurement light returned via the measuring light transmitting means to form a combined light;
   Interference signal acquiring means for acquiring an interference signal from the combined light formed by the combining means;
   Image acquisition means for decomposing the interference signal acquired by the interference signal acquisition means into frequency components and acquiring a tomographic image of the subject accordingly;
   The condensing optical system has at least one reflecting surface,
   The reference optical path length from the dividing means to the combining means via the reference mirror along the reference light transmitting means is the condensing position of the condensing optical system along the measuring light transmitting means from the dividing means. An optical coherence tomographic image acquisition apparatus characterized in that it is longer than the measurement optical path length from the first through the synthesis means.
2. The optical coherence tomographic image acquisition apparatus according to claim 1, wherein an optical path length difference Δl between the reference optical path length and the measurement optical path length satisfies the following expression.
   0.3 / π · (λ / NA ² ) <Δl <3.0 / π · (λ / NA ² ) (1)
   Where NA is the numerical aperture NA of 1 / e ² intensity light incident on the subject, and λ is the center wavelength of the light emitted from the light source.
3. The optical coherence tomographic image acquisition apparatus according to claim 1 or 2, wherein the position of the reflection surface is within an image acquisition range in which reflected light reflected by the reflection surface is acquired as the interference signal.
4. 4. The optical coherence tomographic image acquisition apparatus according to claim 3, wherein the image acquisition range is determined by a sampling number of data for detecting the interference signal.
5. The optical coherence tomographic image acquisition apparatus according to claim 3, wherein the image acquisition range is determined by a coherence distance of measurement light emitted from the probe.
6. 4. The optical coherence tomographic image acquisition apparatus according to claim 3, wherein the image acquisition range is 20 mm or less.
7. The optical coherence tomographic image acquisition apparatus according to any one of claims 1 to 6, wherein the reflecting surface of the condensing optical system reflects the incident measurement light and returns it along the optical axis.
8. A light source that emits light of a broadband wavelength;
   Splitting means for splitting light from the light source into reference light and measurement light;
   Reference light transmitting means for transmitting the reference light divided by the dividing means;
   A reference mirror for reflecting the reference light transmitted through the reference light transmission means and making it incident on the reference light transmission means;
   Measurement light transmission means for transmitting the measurement light divided by the division means;
   The measurement light transmitted through the measurement light transmission means is collected toward the subject, and the measurement light reflected from the subject is received and incident on the measurement light transmission means. A probe including an optical optical system;
   Combining means for combining the reference light returned via the reference light transmitting means and the measurement light returned via the measuring light transmitting means to form a combined light;
   Interference signal acquiring means for acquiring an interference signal from the combined light formed by the combining means;
   A probe used in an optical coherence tomographic image acquisition apparatus having image acquisition means for decomposing the interference signal acquired by the interference signal acquisition means into frequency components and acquiring a tomographic image of the subject accordingly. ,
   The condensing optical system of the probe has at least one reflecting surface, and a reference optical path length from the dividing unit to the combining unit through the reference mirror along the reference light transmitting unit is equal to the dividing unit. A probe having a length longer than the measurement optical path length from the converging position of the condensing optical system to the synthesizing means along the measuring light transmitting means.
9. Splitting light of a broadband wavelength emitted from a light source into reference light and measurement light using a splitting means;
   Transmitting the divided reference light through reference light transmission means and reflecting it by a reference mirror;
   Condensing the divided measurement light toward the subject via the measurement light transmitting means and a condensing optical system having at least one reflecting surface, and receiving the measurement light reflected from the subject When,
   Obtaining an interference signal from the combined light obtained by combining the reflected reference light and the reflected measurement light using a combining unit;
   Decomposing the acquired interference signal into frequency components, and obtaining a tomographic image of the subject accordingly,
   The reference optical path length from the dividing unit to the combining unit through the reference mirror along the reference light transmitting unit is determined, and the condensing position of the condensing optical system from the dividing unit along the measuring light transmitting unit. An optical coherence tomographic image acquisition method characterized in that it is longer than the measurement optical path length up to the synthesis means.

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