JP2015117978A - Optical interference tomography device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OCT capable of acquiring information of a deep site of an object without requiring a high-speed and expensive AD conversion mechanism.SOLUTION: An optical interference tomography device has: a light source section changing the wavelength of emitted light; an interference optical system splitting light from the light source section into irradiation light for irradiating an object and reference light, and generating interference light of reflected light obtained by irradiating the object and the reference light; an optical detection section receiving the interference light; a clock generation section, based on the light emitted from the light source section, generating a plurality of clock signals that have different phases from each other and have the same wave number interval with each other; and an information acquisition section acquiring a plurality of interference signals on the same position on the object, sampling each of the plurality of interference signals on the basis of the plurality of clock signals, and acquiring information of the object on the basis of the sampled interference signals.

Description

  The present invention relates to an optical coherence tomography used for medical diagnosis and the like.

  In optical coherence tomography (hereinafter abbreviated as OCT) using a wavelength tunable light source, the object is irradiated with light, the wavelength of the irradiated light is changed, and reflected light returning from different depths of the reference light and the object To interfere with. Then, by analyzing the frequency component included in the temporal waveform (interference signal) of the intensity of the interference light, information relating to the tomography of the object, for example, a tomographic image is obtained. Hereinafter, OCT using a wavelength tunable light source may be abbreviated as SS-OCT.

  Here, in SS-OCT, in order to acquire information on a fault in a deeper part, it is necessary to shorten the sampling interval when sampling the data of the interference signal at an equal wave number (equal frequency) interval ( Patent Document 1).

  Patent Document 2 discloses a method for correcting signal blurring when photographing the same point on an observation target object a plurality of times.

JP 2013-181790 A JP 2010-14514 A

  By the way, the technique disclosed in Patent Document 1 discloses a technique for correcting the fluctuation of the phase of the interference signal when the interference signal is acquired a plurality of times for the same point on the observation object. However, the sampling interval for correcting the phase fluctuation of the interference signal acquired a plurality of times does not change, and it is not possible to acquire information on a fault in a deeper part. Further, in order to shorten the sampling interval, it is necessary to use a high-speed AD conversion mechanism, but it is expensive and there is a limit to speeding up.

  An object of the present invention is to provide an OCT capable of acquiring information on a deep part of an object without using a high-speed and expensive AD conversion mechanism.

According to the optical coherence tomometer according to the present invention, a light source unit that changes the wavelength of the emitted light,
An interference optical system that demultiplexes the light from the light source unit onto the object and the reference light and generates reflected light of the light irradiated on the object and interference light by the reference light; and the interference An optical coherence tomography comprising: a light detection unit that receives light; and a clock generation unit that generates a plurality of clock signals having mutually different phases and the same wave number intervals based on the light emitted from the light source unit A plurality of interference signals at the same position on the object, each of the plurality of interference signals is sampled based on the plurality of clock signals, and based on the sampled interference signals, the An optical coherence tomometer, comprising: an information acquisition unit that acquires information on an object.

  According to the OCT according to the present invention, a high-speed and expensive AD conversion mechanism is used by sampling time waveforms of a plurality of interference lights based on a plurality of clock signals having mutually different phases and the same wave number interval. It is possible to acquire information on a deep part of the object without the need.

It is a schematic diagram which shows the structure of OCT which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the sampling method in Embodiment 1 of this invention. In embodiment of this invention, it is a figure which shows the irradiation position of the irradiation light to the measurement object. It is a schematic diagram which shows the structure of OCT which concerns on Example 1 of this invention. It is a figure which shows the time change of the frequency of the light emitted from the wavelength sweep light source in Example 1 of this invention. It is a figure for demonstrating the sampling method in Example 1 and 2 of this invention. It is a figure for demonstrating the k clock signal which the clock generation part in Example 1 of this invention generates. It is a schematic diagram which shows a structure in OCT which concerns on Example 3 of this invention. In an embodiment of the present invention, it is a figure for explaining an AD conversion element.

  Hereinafter, although OCT which concerns on embodiment of this invention is demonstrated, this invention is not limited to these.

(Embodiment 1)
FIG. 1 is a schematic diagram showing an OCT apparatus configuration according to this embodiment.

  The OCT according to the first embodiment of the present invention includes a wavelength swept light source 101 as a light source unit, a k-clock system 102 as a clock generation unit, an interference optical system 103, a light detection unit 104, and an information acquisition unit 105. Have.

  In the OCT according to the present embodiment, the interference optical system 103 includes a reference mirror 107, an optical waveguide 109, an optical coupler 110, and a scanning mirror 111. Reference numeral 108 denotes a subject (object). Next, a method for acquiring object information using the OCT according to the present embodiment will be described.

  First, the interference optical system 103 demultiplexes the light emitted from the wavelength swept light source 101 that changes the wavelength of the emitted light into irradiation light and reference light that are applied to the subject 108, and is applied to the subject 108. Interference light caused by reflected light and the reference light is generated. The light detection unit 104 receives the interference light generated by the interference optical system 103. Further, the k-clock system 102 generates a clock signal (k trigger signal) at equal wave number intervals and transmits it to the information acquisition unit 105 in accordance with the wavelength change of the light emitted from the wavelength swept light source 101.

  The k-clock system 102 can be configured by a wavelength selection unit 106 that transmits or reflects light at equal wavenumber intervals. For example, the wavelength selection unit 106 includes an interferometer including two optical paths having different lengths. Then, the k-clock system 102 can be constructed by detecting the light interfering in this optical path with a differential photodetector or a normal photodetector.

  When the light emitted from the wavelength swept light source 101 is guided to the k-clock system 102, a k trigger signal is generated from the k-clock system at every certain light wave number unique to the k-clock system with the wavelength sweep of the wavelength swept light source 101. Generated. By sampling the interference signal from the interference optical system 103 based on this k trigger signal, it is possible to acquire the interference signal at equal wave number intervals.

  The information acquisition unit 105 samples an interference signal (a temporal waveform of the intensity of interference light) based on the received k trigger signal, and performs Fourier transform on the sampled data to acquire information on the tomographic object. Here, the object information is typically a tomographic image, but may be an absolute value of a value of reflected light intensity from each tomogram, or may be a normalized value, and is particularly limited. Not. Hereinafter, the object information will be described as a tomographic image of the object.

  The optical coherence tomometer according to the present embodiment generates a plurality of interference lights by sweeping the wavelength using the wavelength swept light source 101 a plurality of times at the same position on the subject.

  The information acquisition unit 105 samples a plurality of acquired interference signals at different phases (timing) and at the same frequency. Sampling of the interference signal is performed based on a plurality of clock signals generated by the clock generation unit and having different phases and the same wave number interval. For example, when n is a natural number and the wave number of light is Δk, a clock signal is generated at a wave number interval of n × Δk, and the information acquisition unit is based on this clock signal at the same position on the subject at the number n. Acquire the interference signal. Then, the sampling frequencies of the acquired n interference signals are set to be different from each other by Δk.

  As described above, when the wave number interval for sampling is shorter, information on a deeper position of the object can be obtained when the object information is acquired. As in the present embodiment, by obtaining a plurality of interference signals and sampling at different timings and at the same wave number interval, the same effect as in the case of shortening the sampling wave number interval can be obtained.

  That is, a plurality of sampling data of interference signals at the same position of the subject 108 is acquired, a tomographic image is acquired based on each data, and these tomographic images are synthesized. As a result, information on a deeper position of the object can be obtained.

  In addition, a plurality of sampling data of the interference signal at the same position of the subject 108 is acquired, and by synthesizing the plurality of data, the same meaning as that the wave number interval of the sampling data is shortened is obtained, and the object is deeper. Location information is obtained.

  Further, the OCT according to the present embodiment can acquire information on a tomographic plane where an object is present by changing the irradiation position of the irradiation light by the scanning mirror 111 that changes the irradiation position of the irradiation light to the subject 108. . Scanning for acquiring information on one tomographic plane is called B scan. On the other hand, a wavelength sweep operation for acquiring information on a tomogram at a position where an object is present is called A scan.

  The control of the scanning mirror 111 may be performed by a control unit (not shown) or the information acquisition unit 105. In order to acquire a plurality of interference signals at the same position on the object, after acquiring a plurality of pieces of object information at the same position on the object, the irradiation position of the irradiation light can be changed using the scanning mirror 111. Good. In addition, after acquiring the object information once at the same position of the object, the scanning mirror 111 is used to change the irradiation position of the irradiation light, and the same scanning process is repeated a plurality of times, so that a plurality of interference signals are obtained. You may get it.

  Hereinafter, the OCT according to the present embodiment will be described in detail with reference to FIGS. FIG. 2A illustrates an example of a k clock (k-clock) signal and a clock signal (k trigger signal). The k clock signal is an interference signal having a peak at an equal wave number interval, which is generated by an interferometer in the k-clock system. The k trigger signal is a clock signal having an equal wave number interval generated from the k clock signal.

  FIG. 2B is a graph obtained by differentiating the graph of FIG. FIG. 2C is a diagram showing an example of the acquired interference signal 210 and sampling points of the interference signal. FIG. 3 is a view of the subject 108 in FIG. 1 as viewed from the direction of light irradiation.

  In the present embodiment, when acquiring a plurality of tomographic images, the wave number of the light source when acquiring the interference signal from the interference optical system 103 in each tomographic image is set to a different value for each of the plurality of imaging operations. Is a feature.

  For example, as shown in FIG. 2, it is assumed that a k trigger signal is generated at a point (zero cross point) 202 that intersects the horizontal axis with an ascending slope of a signal 201 that can be generated by the k clock 102. In FIG. 2, the vertical axis indicates the output from the differential photodetector of the k-clock system 102, and the horizontal axis indicates the wave number of light.

  The k trigger signal may be generated at equal wave number intervals, and the generation point of the k trigger signal is not limited to the zero-cross point of the upward gradient. The points of the peaks and valleys of the k-clock signal, and the points of the zero-gradient zero crossing also have equal wave number intervals, and these may be used. The zero-cross point of the upward gradient and the zero-cross point of the downward gradient are a positive point and a negative point, respectively, in the curve of FIG.

  There are other points of the zero-crossing of the up-gradient of the k-clock signal, such as point 203 and point 204, and the wave numbers of the light sources corresponding to these points are spaced apart from each other at equal intervals. It is possible to generate a k trigger signal at wave number intervals.

  Wavelength sweep is performed by irradiating the measurement target region 302 on the subject 108 with light from the wavelength sweep light source 101, and based on the k trigger signal at the zero-cross point of the upward slope of the k-clock signal as described above. Sampling the interference signal. As a result, points 211, 212, 213... On the interference signal 210 are acquired.

  Next, a k-trigger is generated at the peak of the k-clock signal for the measurement target region 201, and an interference signal is acquired based on this. This is equivalent to generating a k-trigger and sampling data with a wave number shifted by ¼ period of the k-clock signal as compared with the sampling at the previous points 202, 203 and 204.

  In order to generate such a k trigger signal, for example, an electric circuit for detecting a peak point of the k-clock signal may be used. Alternatively, by using an electrical differentiating circuit, the k-clock signal 201 is differentiated and converted into the k-clock signal 230, and the zero-crossing points 231, 232, and 233 of the rising slope of this signal may be detected. It is possible (FIG. 2 (b)).

  By this operation, points 214, 215, 216,... On the interference signal 210 are acquired.

  The same operation is repeated, and points 217, 218, 219... On the interference signal 210 are acquired, and further points 220, 221, 222,.

  By the above-described operation, the interference signal 210 can be sampled with high density at equal wave number intervals at a density four times that of the single wavelength sweep operation using a total of four interference signal acquisition results.

  The fact that the wave number interval for acquiring the interference signal is reduced to a quarter means that a tomographic image acquired by using OCT (hereinafter abbreviated as an OCT image) can be imaged up to a site four times deeper. Correspondingly, a deep OCT image can be obtained.

  In addition, in order to obtain a high-depth tomogram, in this embodiment, a high-depth image can be obtained while using a high-speed and expensive AD conversion element, but using the same speed AD conversion element. This is preferable from the viewpoint of apparatus cost.

  The OCT according to the present embodiment has the following two features. One is to vary the generated wave number of the k trigger signal in a plurality of image acquisitions so that it can be reconstructed as data acquired at higher density and equal wave number intervals in post-processing. The second setting is such that the k-trigger generated wave numbers at the time of the plurality of image acquisitions are finally separated from each other by equal wave number intervals.

  Consider that interference signals are acquired at a plurality of points on a certain straight line 310 on the subject, and a tomographic image of a part of the straight line 310 is acquired.

The process of acquiring a tomographic image includes the following processes in normal OCT.
(1) An interference signal is acquired once at a position of the subject.
(2) While changing the signal acquisition site of (1) on the straight line 310, an interference signal is acquired at each point, and one tomographic image is acquired.

further,
(3) The process of (2) may be repeated to acquire a large number of images, and a process of removing overlay noise by image processing later may be added.

  In order to acquire a tomographic image corresponding to the straight line 310, the points to be irradiated with light are changed to points 302, 303, and 304, and wavelength sweeping is performed at each point to acquire an interference signal at each point. A tomographic image at each point is acquired by Fourier transforming this. A tomographic image corresponding to the straight line 310 can be created by arranging the tomographic images at each point into one image.

  In the conventional OCT, in all of these four images, the wave numbers for generating the k trigger signal have the same phase. At this time, the wave number interval for generating the k trigger signal is 4 × Δk. That is, the wave number of the light source when acquiring the interference signal is separated by an equal wave number interval of 4 × Δk. When tomographic images are acquired from a plurality of interference signals obtained in this way and synthesized, the image quality is improved, but images at deeper parts of the subject cannot be acquired.

  On the other hand, in the OCT according to the present embodiment, when a plurality of interference signals are acquired for the same measurement site and an image of the affected area is captured, the respective phases are different from each other when acquiring each interference signal. Generate trigger signal and acquire data.

  When signals are acquired four times for the tomographic structure of the same measurement site, the data sampling wave number interval is 4 × Δk, as described above, for each signal acquisition.

  In the present embodiment, the wave number of data sampling is set to be different by Δk for each of the above four signal acquisitions.

  As a result, the obtained interference signals are combined to create one interference signal whose data sampling wave number interval is Δk.

  As described above, there are several methods for acquiring the interference signal at each point on the straight line 310 a plurality of times, acquiring the interference signal a plurality of times, and setting the wave number interval of the data sampling to Δk.

  For example, for each point of the measurement target region, the interference signal is acquired four times continuously while shifting the wave number of data sampling in the k-clock signal by Δk corresponding to ¼ of the period of the k-clock signal. Then, in the step (2), the process moves to an adjacent point on the straight line 310 on the measurement target portion, and data sampling is performed again four times in succession. This process is repeated. By repeating this process, an interference signal corresponding to a point on a certain straight line 310 is obtained, and a plurality of interference signals having different wave numbers by Δk can be obtained at each point.

  The order of finally acquiring four signals with different wave numbers sampled by Δk is not limited to the acquisition method of sequentially shifting by Δk as described above. First, data sets whose sampling wave numbers are different by 2Δk may be acquired.

(Light source)
In the present embodiment, the light source unit is not particularly limited as long as it is a light source that changes the wavelength of light. In order to obtain object information using the OCT according to the present embodiment, it is necessary to sweep the wavelength of light emitted from the light source unit within a desired wavelength range with time.

  As the light source unit in the present embodiment, for example, a surface emitting laser, an external resonator type wavelength swept light source using a diffraction grating or a prism, and various external resonator type light sources using a Fabry-Perot tunable filter with a variable resonator length are used. Can be. Or SSG-DBR which changes a wavelength using a sampled grating, MEMS-VCSEL of wavelength variable, etc. can also be used. A fiber laser can also be used. The fiber laser may be a dispersion tuning method or a Fourier domain mode lock method.

  As an external resonator type wavelength sweep light source using a diffraction grating, a prism, etc., a resonator is provided with a diffraction grating to disperse light, and a polygon mirror or a striped reflection mirror is provided on a rotating disk. A wavelength swept light source or the like may be used by continuously changing the wavelength of light emitted by using.

(Light detector)
In the light detection part in this embodiment, if the intensity | strength of interference light is converted into the intensity | strength of electricity, such as a voltage, it will not specifically limit. The information of the interference signal is converted into information of the time waveform of the received light voltage by this light detection unit.

(object)
In the present embodiment, the object is a measurement target by OCT according to the present embodiment, and the type is not particularly limited. Examples include living bodies such as eyeballs, skin, blood vessels, and teeth.

(Display section)
In the OCT according to the present embodiment, the object information acquired by the information acquisition unit is a tomographic image, and may include a display unit that displays the acquired tomographic image.

(Use)
The OCT according to the present embodiment can be used for medical diagnosis such as ophthalmic imaging, skin imaging, angiography, and dental imaging for obtaining a tomographic image of the fundus.

(Embodiment 2)
Next, OCT according to Embodiment 2 of the present invention will be described. Here, differences from the first embodiment will be described, and description of common matters will be omitted.

  In the step (1) described in the first embodiment, the k trigger signal is fixed, and an interference signal is acquired at the point 302 on the measurement target region. In step (2), the site to be measured is changed to the adjacent point 303 on the straight line 310, and the interference signal is acquired once while the wave number of data sampling is fixed to the same value as in step (1). This operation is repeated to acquire an interference signal for each point on the straight line 310.

  Next, the wave number of data sampling with respect to the k-clock signal is shifted from the aforementioned wave number by Δk which is ¼ of the period of the k-clock signal, and the points 302, 303,. To obtain an interference signal.

  The interference signal acquisition with the wave number shifted by Δk is performed a total of four times, so that a plurality of interference signals having different phases of the k trigger signal at each point with respect to the straight line 310 are finally obtained.

  Next, signal processing after a plurality of interference signals having different phases of the k trigger signal are obtained for each point on the measurement target object will be described below. In order to generate a high-depth OCT image, it is only necessary to synthesize one interference signal having a wave number interval Δk from four pieces of interference signal data having a wave number interval of 4 × Δk and Fourier-transform this.

  The order of finally acquiring four signals having different sampling wavenumbers by Δk is not limited to the acquisition method of sequentially shifting by Δk as described above. First, a data set whose timing is shifted by 2 × Δk may be acquired.

  This is because, before finally acquiring the data of the wave number interval of 1/4 of the wave number interval of the original data, the data of the half acquisition interval is obtained on the way, and the image is deepened from the sequentially obtained data. It is preferable because it is easy to confirm the situation.

  As described above, when the data of the wave number interval of Δk is finally obtained, the measurement is performed in the order of obtaining the data set of the interference signal that becomes the wave number interval of m × Δk (where n ≠ m) during the acquisition. can do. This is because even in the middle stage where the final stage of measurement is not reached, it is possible to sequentially acquire images with a somewhat increased imaging area in the depth direction. Further, as described above, each of the interference signals acquired four times may be Fourier-transformed using k trigger signals having different phases, and an OCT image may be formed one by one from each interference signal. In this case, four pictures having the same depth with a data sampling wave number interval of 4 × Δk can be formed, and therefore, four pictures having the same depth can be overlapped and used for image quality improvement as in the prior art.

  In other words, in the OCT according to the present embodiment, the interference signals sampled at higher density wave number intervals can be reconfigured by differentiating the sampling wave numbers used when acquiring the interference signals multiple times, and the depth of the signals is increased. An OCT image can be obtained. Alternatively, in addition to the above, it is also possible to construct an OCT image from each of a plurality of interference signal data and superimpose these pictures to improve the image quality, as in the past.

  Therefore, as compared with the conventional OCT, a high-speed AD conversion element is not required for increasing the depth, and the cost can be reduced. In addition, there is an advantage that the choice of data processing methods after data acquisition is increased.

  Furthermore, both of these operations can be incorporated to achieve both high depth of image and high image quality.

  In other words, when 40 images of the same part are captured and image processing is performed by superimposing these images, it is possible to simply obtain 40 images with the same data sampling wavenumber to improve the image quality, that is, to increase the SN ratio. Is possible. However, in the present embodiment, 40 images of a certain part are acquired at the same data acquisition time, and the 40 images are in a group of 4 images whose data sampling timings are shifted from each other by Δk.

  Therefore, this 40 images can be simply overlapped to increase the SN as in the prior art, and it is also possible to synthesize one high depth image that can be seen up to 4 times deep from the data for 4 images. . In other words, ten images that are four times deeper can be generated from 40 pieces of data. By performing image processing to superimpose these 10 sheets, the SN ratio can be increased.

  In the present embodiment, since it is assumed that an image is finally formed up to a deep part, it is preferable that the instantaneous line width of the light source included in the SS-OCT apparatus is sufficiently narrow. In other words, it is preferable that the light source has a coherence length that has coherence with respect to the reflected light from the part of the depth to be finally imaged.

  In the present embodiment, the original wave number interval at the time of sampling is 4 × Δk, and four pieces of data are combined into one wave number interval data of Δk.

  There are several types of AD conversion elements, and one of them is a type having a sampling and holding circuit therein. In this type of element, an analog signal which is an input value from the outside is taken as a voltage into a certain capacitor. Once the capacitor is charged, the analog value is converted to a digital value based on the voltage of the capacitor and then output.

  The total time from acquiring the analog value to outputting the digital value is T, of which t1 is the time until the capacitor is charged and t2 is the time until the digital value is output after reading the capacitor voltage. To do. In this case, T = t1 + t2 as shown in FIG. By repeating such a process, analog data is converted into digital data one after another and output.

  As can be seen from FIG. 9, the time for the AD conversion element to read the analog input value is only t1, and the analog input value for the remaining time t2 is not acquired by the AD conversion element.

  Therefore, in order to perform high-density sampling by shifting the phase of the k trigger signal as in the present embodiment, it is only necessary to sample one after another at time intervals shifted by t1 as shown in FIG. 9B. As a result, the data acquisition interval can be increased to a high density of about T / t1, which is preferable. In an AD conversion element having a sampling and holding circuit, t1 is often about 10% to 20% of T. In this case, when data sampling is finally performed with a small wave number interval by the OCT according to the present embodiment, it is considered preferable to set the wave number interval to about 1/4 to 1/5 of the original data sampling wave interval. It is done.

  Furthermore, the OCT according to the present embodiment may be provided with a measurement unit 112 for assigning, that is, measuring, absolute values of wavelengths and wave numbers to k-clock signals or k trigger signals. As the measurement unit 112, it is preferable to use a wavelength selection element having one or two selected wavelengths in the emission wavelength band of the wavelength swept light source. For example, it is possible to use a Fabry-Perot filter that has a large free spectral range (FSR) and one selected wavelength near the upper limit and lower limit of the wavelength sweep band of the wavelength swept light source.

  These selected wavelengths are known in advance from the gap length of the Fabry-Perot filter.

  Alternatively, a bandpass filter that transmits only a specific wavelength can be used.

  For example, when the transmitted light intensity from the wavelength swept light source is monitored by the wavelength selection element and the k-clock signal is simultaneously monitored when light is selected, each k trigger signal generated from the k-clock signal is monitored. The wavelength (wave number) of light can be assigned.

  If the wave number of light can be assigned to the k-clock signal in this way, it is possible to confirm the wavelength sweep start timing or end timing of the light source. Alternatively, when there are upper and lower limits on the optical frequency of the data used to output the OCT image, the transmission light intensity of the wavelength selection element is set to increase at those optical frequencies, and the light source wavelength may be monitored. it can. Furthermore, it can also be used to check the state of the light source, such as whether the wavelength swept light source can operate in a desired wavelength sweep range at a desired wavelength sweep speed.

Example 1
Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  FIG. 4 is a configuration diagram showing the configuration of the OCT according to the present embodiment. In this embodiment, it is assumed that the subject is the fundus. A wavelength swept light source unit 401 as a light source unit, a reference light optical path fiber 402 constituting a reference unit, a fiber coupler 403 constituting an interference unit, and a reflection mirror 404 are arranged.

  Further, the inspection light optical path fiber 405, the irradiation condensing optical system 406, and the scanning mirror 407 constituting the specimen measurement unit are connected.

  In addition, a light receiving fiber 408, a photodetector 409 as a light detection unit, an irradiation fiber 410, a signal processing unit 411 as an information acquisition unit, and an image output monitor 413 as a display unit are connected. Further, the signal processing unit 411 includes a differentiation circuit 430 that performs a differentiation process on the k-clock signal, a switch 431, an analog / digital conversion element 432, and a calculation unit 433.

  And an OCT apparatus can be comprised by the structure which connected the light source control part 412. FIG. Reference numeral 414 denotes an inspection object (object). Reference numerals 420 and 421 denote collimators for coupling light to the fiber and collimating light from the fiber.

  Although the fiber constituting the interference optical system is a single mode fiber in this embodiment, this is not restrictive. The wavelength sweep light source unit 401 includes a wavelength sweep light source 415, a k-clock system 417, and a band pass filter 418, as shown in FIG.

  In this embodiment, a system that introduces light from a Michelson interferometer in which the optical path length difference between both arms of the interferometer is 8 mm into the differential photodetector is used as the k-clock system. The interference signal output from the interferometer generates a k-trigger signal every light frequency of 18.737 GHz. The wavelength sweep light source 415 has a wavelength sweep frequency of 50 kHz (with a wavelength sweep period of 20 us), and a wavelength sweep range of 1000 nm to 1090 nm. Therefore, the number of generations of the k trigger signal per wavelength sweep of the wavelength sweep light source 415 is 1321 times. The sweep speed of the light source is controlled to be constant, as shown in FIG. At this time, the generation frequency of the k trigger signal while sweeping the wavelength of the light emitted from the light source is 66 MHz. Therefore, each element in the signal processing unit uses an element that can cope with a signal frequency of 66 MHz or more.

  The band pass filter 418 transmits light having a wavelength of 1000 nm whose transmission wavelength is close to the short wavelength end of the emission spectrum of the light source.

  A control signal is input from the light source control unit 412 to the wavelength swept light source 415.

  The wavelength swept light source 415 controls its oscillation wavelength and intensity and its time change by the light source control unit.

  The light emitted from the wavelength swept light source 415 is split and introduced into a reference light optical path fiber 402 and an inspection light optical path fiber 405 in a fiber coupler.

  Furthermore, a collimator 421 is attached to the tip of the reference light path optical fiber, and parallel light is irradiated onto the reflection mirror 404. Then, the light is reflected by the reflection mirror 404 and introduced into the light receiving fiber to reach the photodetector 409.

  At the same time, the light introduced into the inspection light optical path fiber 405 by the fiber coupler 403 is irradiated onto the inspection object 414, and backscattered light is generated from the inside and the surface of the test object.

  The backscattered light is condensed from the fiber coupler to the photodetector 409 through the irradiation condensing optical system 406.

  The light received by the photodetector 409 is converted into a spectrum signal by the signal processing unit 411, and further subjected to Fourier transform to acquire tomographic information of the test object.

  In this embodiment, an OCT image is formed as follows.

  The point 302 on the observation target object is irradiated with light.

  The k-clock system 417 generates a k-trigger signal at a zero-cross point of the upward gradient of the k-clock signal 601, for example, the point 602, the point 603, and the point 604. The wavelength swept light source 415 is wavelength swept to obtain points 611, 612, and 613 on the interference signal based on the k trigger signal. The horizontal axis of FIG. 6 is the wave number of light, and the light wave number can be obtained by multiplying the frequency of light by 2π divided by the speed of light.

  In FIG. 7, the horizontal axis is time, and the k-clock signal 701 is illustrated. Here, the signal 710 is the intensity of light transmitted through the band-pass filter 418, and the emission wavelength at time 711 is 1000 nm.

  In addition, the k trigger generated at the point 702 advanced by 3/4 period by the k-clock signal from the time 711 is that the frequency of light with a wavelength of 1000 nm is 299.79 THz and the k-clock is 18.7 GHz period. To 299.77 THz. Similarly, the optical frequencies of the points 703 and 704 can be calculated.

  Next, the switch 430 passes the k-clock signal 601 through the differentiating circuit 431 to generate the differentiated k-clock signal 630. Similarly, a k-trigger signal is generated at the zero-crossing points of the upward gradient of the k-clock signal 630, for example, the points 631, 632, and 633, and the points 614, 615, and 616 on the interference signal are obtained.

  Further, the switch 430 passes the k-clock signal to the differentiating circuit 431 to generate the k-clock signal 650. Similarly, a k-trigger signal is generated at points of the zero crossing of the k-clock signal 650, for example, points 651, 652, and 653, and points 617, 618, and 619 on the interference signal are acquired.

  Then, the switch 430 passes the k-clock signal through the differentiating circuit 431 to generate the k-clock signal 670. Similarly, a k-trigger signal is generated at points of the zero crossing of the k-clock signal 670, for example, points 671, 672, and 673, and points 620, 621, and 622 on the interference signal are acquired.

  The data of the points 611, 612,..., 621, 622 on the obtained interference signal are combined to generate an interference signal 610. The acquisition wave number interval of this interference signal data is 4.684 GHz, which is 1/4 of 18.737 GHz.

  Then, the tomographic information of the object at a certain point is obtained by Fourier transforming this interference signal.

  Next, the irradiation position on the object is displaced by 10 μm, and the point 303 is irradiated. Then, the interference signal is acquired four times in the same manner as described above, and similarly, the tomographic information based on the data having the wave number interval of 4.684 GHz at this point is acquired. By these series of operations, tomographic information on the tomographic plane 310 can be obtained.

  According to the OCT according to the present embodiment, four signals with different data acquisition wave numbers for k-clock are continuously acquired at each point of the observation target region. For this reason, it is suitable for a case where it is desired to acquire a deeper depth image of a certain point or a narrow area on the observation target object at high speed, such as when the observation target object may move.

(Example 2)
Examples of the present invention will be described below, but descriptions of matters common to Example 1 will be omitted. The apparatus configuration of the OCT according to the present embodiment is the same as that shown in FIG.

  In this embodiment, an OCT image is formed as follows.

  The k-clock system 417 generates a k trigger signal at the point 602, point 603, point 604,... of the zero cross of the k-clock signal 601.

  First, the irradiation position is set to the point 302, the light from the wavelength swept light source 415 is irradiated, and the points 611, 612, and 613 of the interference signal are acquired based on the k trigger signal. Next, the irradiation position is moved to a point 303, and an interference signal is acquired in the same manner.

  Also at this time, the k trigger for acquiring the interference signal is the point 602, the point 603, the point 604, etc., which is the point of the zero crossing on the k-clock signal. In this way, an interference signal is acquired while sequentially moving the irradiation position to point 302, point 303, point 304,... On the tomographic plane 310 while the k trigger generation wave number on the k-clock is fixed.

  As a result, for all points on the tomographic plane 310, interference signals are acquired with the same k-trigger generated wave number with respect to k-clock.

  If these signals are Fourier-transformed in this state, it is the same as the method of acquiring an image of the tomographic plane 310 by normal OCT. However, in the present invention, the k-trigger generation wave number is further set to a different value and continued. Acquire the interference signal. The k-clock signal 601 is passed through the differentiating circuit 431 by the switch 430 to generate the k-clock signal 630. Similarly, a k-trigger signal is generated at the zero-crossing point, point 631, point 632, and point 633 of the k-clock signal 630, and the point 614, point 615, point on the interference signal at point 302 on the tomographic plane 310 616 is acquired. Next, the irradiation position is moved to a point 303, and an interference signal is acquired in the same manner. In this way, while the trigger signal generation timing on the k-clock is fixed, the interference signal is acquired while sequentially shifting the irradiation position to the points 304 on the tomographic plane 310.

  Further, the switch 430 passes the k-clock signal 630 through the differentiating circuit 431 to generate the k-clock signal 650. Similarly, a k-trigger signal is generated at the point of the rising zero cross of the k-clock signal, point 651, point 652, point 653,..., Point 617, point 618 on the interference signal at point 302 on the tomographic plane 310, Points 619,... Are acquired. Next, the irradiation position is moved to a point 303, and an interference signal is acquired in the same manner. In this way, while the trigger signal generation timing on the k-clock is fixed, the interference signal is acquired while sequentially shifting the irradiation position to the points 304 on the tomographic plane 310.

  Finally, the switch 430 passes the k-clock signal 650 through the differentiating circuit 431 to generate the k-clock signal 670. Similarly, a trigger signal is generated at the point of the zero crossing of the k-clock signal 670, the point 671, the point 672, the point 673,..., And the point 620, the point 621 on the interference signal at the point 302 on the tomographic plane 310, Points 622, ... are acquired. Next, the irradiation position is moved to a point 303, and an interference signal is acquired in the same manner. In this way, while the trigger signal generation timing on the k-clock is fixed, the interference signal is acquired while sequentially shifting the irradiation position to the points 304 on the tomographic plane 310.

  By these operations, four interference signals having different trigger generation wave numbers for the k-clock signal can be acquired for all points 302, 303, 304,... On the tomographic plane 310.

  Finally, for example, at a point 302, points 611, 612, ..., 621, 622 on the interference signal are obtained.

  From these points, one interference signal is combined to generate an interference signal 610.

  The interference signal 610 is Fourier transformed to obtain an OCT image. This OCT image is imaged to a depth four times that of the tomographic image in a state before the above-described interference signal is synthesized.

  According to the apparatus of the present embodiment, an image of a shallow range is sequentially obtained in the middle stage before an image having a quadruple tomogram is obtained based on the interference signal to be finally synthesized. This is suitable when the user wants to check the state of the camera, the shooting location, etc. at any time.

(Example 3)
Examples of the present invention will be described below, but descriptions of matters common to Examples 1 and 2 will be omitted.

  In this embodiment, as shown in FIG. 8, the interference signal is acquired using a differential detector.

  In FIG. 8, a light source unit 801, an isolator 802, a reference light path optical fiber 806 constituting a reference unit, a polarization controller 818, a fiber coupler 805 constituting an interference unit, and a reflection mirror 807 are arranged. A collimator 820 and a collimator 821 are also arranged. As in the system of FIG. 4, the light source unit 801 includes a k-clock system and a wavelength selection element (not shown).

  Further, an inspection light optical path fiber 814, a polarization controller 819, an irradiation condensing optical system 815, and an irradiation position scanning mirror 808 constituting the specimen measurement unit are connected.

  In addition, a fiber coupler 803, a fiber coupler 804, a light receiving fiber 816, a light receiving fiber 817, a balance photodetector 810, a signal processing device 811 forming an image processing unit, and an image output monitor 813 are connected. . As in the system of FIG. 4, the signal processing device 811 includes a differential circuit, a switch, a computing element, etc. (not shown).

  And the optical coherence tomography apparatus can be comprised by the structure which connected the light source control apparatus 812 which comprises a light source part. Reference numeral 809 denotes an inspection object.

101 Light source (wavelength swept light source)
102 Clock generator (k-clock system)
103 Interferometric optical system 104 Photodetector 105 Information processor

Claims (12)

A light source unit for changing the wavelength of the emitted light;
An interference optical system that demultiplexes the light from the light source unit onto the object and the reference light, and generates reflected light of the light applied to the object and interference light from the reference light;
A light detector that receives the interference light;
A clock generation unit that generates a plurality of clock signals having different phases and the same wave number interval from each other based on the light emitted from the light source unit;
An optical coherence tomograph having
A plurality of interference signals are acquired at the same position on the object, each of the plurality of interference signals is sampled based on the plurality of clock signals, and information on the object is acquired based on the sampled interference signals. And an information acquisition unit. The clock generation unit generates the clock signal at a wave number interval of n × Δk, where n is a natural number and the wave number of light is Δk,
The information acquisition unit acquires n interference signals at the same position on the object based on the clock signal,
The optical coherence tomometer according to claim 1, wherein sampling frequencies of the acquired n interference signals are different from each other by Δk.   3. The information acquisition unit according to claim 1, wherein the information acquisition unit acquires a plurality of tomographic images based on the plurality of sampled interference signals, and acquires the tomographic image of the object by combining the acquired plurality of tomographic images. Optical coherence tomography.   4. The optical coherence tomography device according to claim 1, wherein the information acquisition unit combines the plurality of sampled interference signals and acquires a tomographic image of the object based on the combined data. 5.   The optical coherence tomography further includes a scanning mirror that changes an irradiation position of the irradiation light on the object, and acquires information on a tomographic plane of the object by changing the irradiation position of the irradiation light by the scanning mirror. The optical coherence tomometer according to claim 1, comprising a configuration for   The optical coherence tomometer according to claim 5, wherein after the plurality of pieces of information on the object are acquired at the same position on the object, the irradiation position of the irradiation light is changed using the scanning mirror.   The information of the object is acquired once at the same position of the object, and then scanning is performed by changing the irradiation position of the irradiation light using the scanning mirror, and the same scanning process is repeated a plurality of times. Optical coherence tomography.   The optical coherence tomography device according to any one of claims 1 to 7, further comprising a measurement unit that measures a wave number or a wavelength of the clock signal.   The optical coherence tomography device according to any one of claims 1 to 8, wherein the object is a living body.   The optical coherence tomography device according to claim 9, wherein the living body is an eyeball.   The optical coherence tomometer according to claim 9, wherein the living body is a blood vessel.   The optical coherence tomometer according to claim 1, wherein the light source unit is a surface emitting laser.

Images