JP2010014514A - Optical tomographic imaging apparatus and coherent signal processing method in optical tomographic imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently improve the image quality of a tomographic image without lowering its effect by phase shift when processing using a plurality of coherence signal data obtained by OCT measurement in SS-OCT. <P>SOLUTION: The coherence signal processing method in an optical tomographic image apparatus using an SS-OCT measuring method is characterized by performing phase correcting processing for correcting the phase shift of a plurality of coherence signals obtained by measuring the same measuring region of a measuring target a plurality of times, further characterized by performing averaging processing before Fourier transform after the phase correcting processing is performed, and furthermore characterized by adapting a Doppler system after the phase correcting processing is performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical tomographic imaging apparatus and an interference signal processing method in the optical tomographic imaging apparatus, and more particularly to an applied technique of interference signal phase correction processing in SS-OCT using a wavelength swept light source.

  Conventionally, an optical tomographic imaging apparatus using an optical coherence tomography (OCT) measurement method is known as a method for acquiring a cross-sectional image without cutting a measurement target such as a living tissue. The OCT measurement method divides light emitted from a light source into measurement light and reference light, irradiates the measurement light to the measurement object, and combines the reflected light reflected from the measurement object and the reference light to obtain interference light. This is a kind of optical interferometry that generates tomographic images from images. OCT is roughly classified into TD-OCT (Time Domain OCT) and FD-OCT (Fourier Domain OCT). FD-OCT is further divided into SD-OCT (Spectral Domain OCT) and SS-OCT (Swept Source OCT).

  In TD-OCT, light emitted from a light source is divided into measurement light and reference light, and the measurement light is irradiated onto the measurement object, and the reflected light reflected from the measurement object and the reference light are combined to obtain interference light. However, it is a measurement method that utilizes the fact that the interference light is detected when the optical path lengths of the measurement light and the reference light coincide with each other. By changing the optical path length of the reference light, the measurement position relative to the measurement object (measurement (Depth) can be changed.

  SD-OCT divides broadband low-coherence light into measurement light and reference light, then irradiates the measurement light with the measurement light, causes the reflected light from the measurement light to interfere with the reference light, An optical tomographic image is constructed without performing scanning in the depth direction by Fourier transforming the channeled spectrum decomposed into frequency components.

  In SS-OCT, the frequency of the laser light emitted from the light source is swept to cause the reflected light and the reference light to interfere with each other at each wavelength, and the interference signal for a series of wavelengths is Fourier transformed to measure the depth of the measurement target. The reflected light intensity at the position is detected, and this is used to construct an optical tomographic image.

  At this time, various methods for improving the image quality of a tomographic image by signal processing from OCT data obtained by OCT measurement are considered.

  For example, in order to improve the image quality, a plurality of OCT images are averaged to emphasize image characteristics (see, for example, Patent Document 1), or ACT (depth direction) OCT data is converted to discrete Fourier transform (DFT). The phase difference is calculated by calculating the phase difference from the difference between the adjacent angles in the A direction (see, for example, Patent Document 2). Alternatively, an apparatus that performs OCT measurement for each angle component of reflected light and performs an averaging process to remove speckles and improve the resolution of the image (for example, see Non-patent Document 1). Are known.

In addition, although the above-mentioned patent document 2 mentions Doppler OCT, this utilizes the fact that the amount of phase change obtained by Fourier transforming spectral interference information corresponds to the moving speed of the measurement object as a Doppler signal. This is a method for obtaining the velocity of blood flow or the like.
US Patent Application Publication No. 2006/0109423 US Patent Application Publication No. 2006/0279742 AEDesjardins, et al., "Angle-resolved Optical Coherence Tomography with sequential angular selectivity for speckle reduction", Vol. 15, No. 10, OPTICS EXPRESS 6200

  However, in the above prior art, for example, various processes such as an averaging process and a Doppler OCT process are performed to improve the image quality of a tomographic image, but when processing using a plurality of interference signal data, There exists a problem that the effect falls by phase shift.

  For example, in the case of the above-mentioned patent document 1, characteristic structure information can be enhanced by averaging the noise on the image and enhancing the signal, so that the resolution can be enhanced, but the sensitivity itself does not increase. Therefore, the S / N at the signal level cannot be improved. Further, the Doppler OCT described in Patent Document 2 has a slow calculation speed, and there is a problem in that both phase correction and calculation speed are compatible.

The present invention has been made in view of such circumstances, and when processing using a plurality of interference signal data obtained by OCT measurement in SS-OCT, the efficiency is not reduced due to a phase shift. In particular, it is an object of the present invention to provide an optical tomographic imaging apparatus capable of improving the image quality of a tomographic image and an interference signal processing method in the optical tomographic imaging apparatus.

  In order to achieve the above object, the invention according to claim 1 is an interference signal processing method in an optical tomographic imaging apparatus using an SS-OCT measurement method, and measures the same measurement site of a measurement object a plurality of times. An interference signal processing method in an optical tomographic imaging apparatus is provided that performs phase correction processing for correcting a phase shift of a plurality of interference signals obtained in this way.

  According to this, when processing using a plurality of interference signals, it is possible to improve the image quality of the tomographic image without reducing the image quality improvement effect due to the phase shift.

  Similarly, in order to achieve the object, the invention according to claim 2 is an interference signal processing method in an optical tomographic imaging apparatus using an SS-OCT measurement method, wherein the same measurement site of a measurement object Of the interference signal in the optical tomographic imaging apparatus, wherein the phase correction processing for correcting the phase shift of the plurality of interference signals obtained by measuring the plurality of interference signals is performed, and then the averaging processing is performed before Fourier transform. A processing method is provided.

  Thereby, S / N at the signal level in the averaging process can be improved in the signal processing from the OCT measurement data in SS-OCT.

  Similarly, in order to achieve the above object, the invention according to claim 3 is an interference signal processing method in an optical tomographic imaging apparatus using an SS-OCT measurement method, wherein the same measurement site of a measurement object A method of processing an interference signal in an optical tomographic imaging apparatus, wherein a Doppler method is applied after performing a phase correction process for correcting a phase shift of a plurality of interference signals obtained by measuring a plurality of times To do.

    This makes it possible to achieve both phase correction and calculation speed, improve the S / N of the phase shift amount between data in Doppler OCT, and improve the image quality efficiently.

  According to a fourth aspect of the present invention, the phase correction process uses a value calculated based on a voltage signal of the interference signal.

  Similarly, in order to achieve the above object, the invention according to claim 5 is an optical tomographic imaging apparatus using the SS-OCT measurement method, and measures the same measurement site of the measurement object a plurality of times. There is provided an optical tomographic imaging apparatus comprising phase correction means for performing phase correction processing for correcting a phase shift of a plurality of obtained interference signals.

  According to this, when processing using a plurality of interference signals, it is possible to improve the image quality of the tomographic image without reducing the image quality improvement effect due to the phase shift.

  Similarly, in order to achieve the above object, the invention according to claim 6 is an optical tomographic imaging apparatus using an SS-OCT measurement method, and measures the same measurement site of a measurement object a plurality of times. A phase correction unit that performs a phase correction process for correcting the phase shift of the plurality of interference signals obtained, and an averaging unit that performs an averaging process on the interference signal after the phase correction process before Fourier transform. An optical tomographic imaging apparatus is provided.

  Thereby, S / N at the signal level in the averaging process can be improved in the signal processing from the OCT measurement data in SS-OCT.

  Similarly, in order to achieve the above object, the invention according to claim 7 is an optical tomographic imaging apparatus using an SS-OCT measurement method, and measures the same measurement site of a measurement object a plurality of times. Light comprising: phase correction means for performing phase correction processing for correcting phase shifts of a plurality of obtained interference signals; and means for applying a Doppler method to the interference signals after the phase correction processing. A tomographic imaging apparatus is provided.

  This makes it possible to achieve both phase correction and calculation speed, improve the S / N of the phase shift amount between data in Doppler OCT, and improve the image quality efficiently.

  The phase correction unit may use a value calculated based on a voltage signal of the interference signal.

  As described above, according to the present invention, in the signal processing from the OCT measurement data in SS-OCT, when processing using a plurality of interference signals, the image quality improvement effect is not deteriorated due to the phase shift. Image quality can be improved.

  Further, it is possible to achieve both phase correction and calculation speed in Doppler OCT, improve S / N of the amount of phase shift between data in Doppler OCT, and efficiently improve image quality.

  Hereinafter, an optical tomographic imaging apparatus and an interference signal processing method in the optical tomographic imaging apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an embodiment of an optical tomographic imaging apparatus according to the present invention. The optical tomographic imaging apparatus of the present embodiment uses an SS-OCT (Swept Source OCT) measurement method, and reads the jitter amount with respect to the A trigger which is a trigger signal of one sweep (one pulse) of the wavelength-swept light. Thus, the phase shift of the interference signal is corrected, and the correction result is applied to the averaging process or the Doppler method.

  As shown in FIG. 1, the optical tomographic imaging apparatus 1 according to this embodiment includes a light source unit 10 and light splitting that divides the light emitted from the light source unit 10 into two light, a measurement light and a phase matching light. Means 3, a first interference system I1 that generates a first interference signal from the measurement light, a first detector D1 that detects the first interference signal, and a second interference from the phase matching light A second interference system I2 that generates a signal, a second detector D2 that detects the second interference signal, an AD board 44 that converts the first interference signal and the second interference signal into digital signals, and AD It comprises a processing system 55 for processing the output signal from the board 44 and forming a tomographic image.

  The light source unit 10 emits light while sweeping the frequency at a constant period. The first interference system I1 is for obtaining an interference signal (herein referred to as a first interference signal) for performing normal OCT measurement, and the second interference system I2 is an interference signal for phase matching (here. Then, it is called a second interference signal). The light emitted from the light source unit 10 is divided into light for measurement sent to the first interference system I1 and light for phase matching sent to the second interference system I2 by the light splitting means 3. At this time, the power of the light is divided. As for measurement, the ratio for phase measurement may be about 1 with respect to 99 for measurement, and the power of light for phase matching may be very small.

  The AD board 44 performs AD (Analog-digital) conversion on the first interference signal and the second interference signal to form a digital signal. The AD board 44 receives the A trigger from the light source unit 10, and the AD board 44 takes the first interference signal and the second interference signal based on the A trigger and converts them into digital signals. The data is transferred to the processing unit 55.

  The processing unit 50 performs various processes on the interference signal converted into a digital signal. As will be described in detail later, the processing unit 50 functions as a phase correction unit, an averaging unit, a unit applying a Doppler system, and the like. Is.

  FIG. 2 shows a more detailed configuration of the optical tomographic imaging apparatus 1 of the present embodiment.

  As shown in FIG. 2, the light source unit 10 emits laser light La while sweeping the frequency at a constant period. The light source 11 emits light having a constant wavelength band, and is emitted from the light source 11. Wavelength selecting means 12 for selecting a wavelength to be transmitted. The light source 11 includes a semiconductor optical amplifier (semiconductor gain medium) 13 that is connected to the optical fiber FB10 in a loop and emits spontaneously emitted light and amplifies the spontaneously emitted light guided from the optical fiber FB10. The light source 11 has a function of emitting weak spontaneous emission light to one end side of the optical fiber FB10 by a drive current injection and amplifying light incident from the other end side of the optical fiber FB10. When a driving current is supplied to the semiconductor optical amplifier 13, the pulsed laser light La is emitted to the optical fiber FB11 by the laser light source resonator formed by the semiconductor optical amplifier 13 and the optical fiber FB10. Yes.

  The wavelength selection unit 12 selects a wavelength of spontaneous emission light guided from the optical fiber FB10 as a filter for a wavelength swept light source, and transmits light from an optical branching unit (circulator) 14 coupled to the optical fiber FB10. Spontaneous emission light is made incident through the fiber FB11. The wavelength selection unit 12 includes a collimator lens 15, a diffraction grating element 16, an optical system (surface tilt correction lens) 17, a rotary polygon mirror (polygon mirror) 18, and the like.

  Light incident from the optical fiber FB11 is reflected by a rotary polygon mirror (polygon mirror) 18 via a collimator lens 15, a diffraction grating element 16, and an optical system 17. The reflected light is incident on the optical fiber FB11 again via the optical system 17, the diffraction grating element 16, and the collimator lens 15.

  The rotary polygon mirror 18 rotates in the direction of the arrow R <b> 1 so that the angle of each reflecting surface changes with respect to the optical axis of the optical system 17. Thereby, only the light which consists of a specific frequency area among the lights disperse | distributed in the diffraction grating element 16 returns to the optical fiber FB11 again.

  The frequency of light returning to the optical fiber FB11 is determined by the angle between the optical axis of the optical system 17 and the reflecting surface. The light having a specific frequency range incident on the optical fiber FB11 is incident on the optical fiber FB10 from the optical splitter 14, and as a result, the laser beam La having the specific frequency range is emitted from the optical fiber coupler 6 to the optical fiber FB8 side. It has become so.

  Therefore, when the rotary polygon mirror 18 rotates at a constant speed in the direction of the arrow R1, the wavelength of the light incident on the optical fiber FB11 is swept at a constant period. That is, the laser light La whose wavelength is swept from the light source unit 10 at a constant period, for example, the wavelength is changed from 1.25 μm to 1.35 μm by one sweep, is emitted to the optical fiber FB 8 side through the optical fiber coupler 6. Will be.

  The optical fiber FB8 is connected to the light dividing means 3. The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler. The laser light La guided through the optical fiber FB8 is split into light for measurement and light for phase matching by the light splitting means 3, and the light for measurement is sent to the first interference system I1 by the optical fiber FB3. The phase matching light is guided to the second interference system I2 by the optical fiber FB9.

  The first interference system I1 irradiates the measuring object S with the light splitting means 2 that splits the laser light La guided through the optical fiber FB3 into the measuring light L1 and the reference light L2. In order to adjust the position of the probe 30 for obtaining the tomographic image and the optical path length adjusting means 20 for changing the optical path length of the reference light L2.

  The light splitting means 2 is composed of an optical fiber coupler in the same manner as the light splitting means 3 described above, and two optical fibers FB2 and FB4 are further connected to the light splitting means 2. The measurement light L1 split by the light splitting means 2 is guided to the probe 30 side by the optical fiber FB2, and the reference light L2 is guided to the optical path length adjusting means 20 side by the optical fiber FB4.

  One end of the optical fiber FB4 is connected to an optical branching unit (circulator) 32, and an optical fiber FB5 and an optical fiber FB7 are further connected to the optical branching unit 32. The reference light L2 guided from the optical fiber FB4 is guided from the optical branching device 32 to the optical fiber L5. An optical path length adjusting means 20 is disposed at the tip of the optical fiber FB5.

  The optical path length adjusting means 20 includes a reflection mirror 22 that reflects the reference light L2 emitted from the optical fiber FB5, a first optical lens 21a that is disposed between the reflection mirror 22 and the optical fiber FB5, and a first optical lens. And a second optical lens 21b disposed between the reflecting mirror 22a and the reflecting mirror 22.

  The first optical lens 21a has a function of converting the reference light L2 emitted from the optical fiber FB5 into parallel light and condensing the reference light L2 reflected by the reflection mirror 22 onto the core of the optical fiber FB5. . Further, the second optical lens 21b condenses the reference light L2 converted into parallel light by the first optical lens 21a on the reflection mirror 22, and makes the reference light L2 reflected by the reflection mirror 22 into parallel light. have.

  Thereby, the reference light L2 emitted from the optical fiber FB5 is converted into parallel light by the first optical lens 21a, and is condensed on the reflection mirror 22 by the second optical lens 21b. Thereafter, the reference light L2 reflected by the reflection mirror 22 becomes parallel light by the second optical lens 21b, and is condensed on the core of the optical fiber FB5 by the first optical lens 21a.

  Further, the optical path length adjusting means 20 includes a movable stage 23 in which the second optical lens 21b and the reflection mirror 22 are fixed, and a mirror moving mechanism 24 that moves the movable stage 23 in the optical axis direction of the first optical lens 21a. Have. When the movable stage 23 moves in the arrow H direction, the optical path length of the reference light L2 is changed.

  The light whose optical path length has been changed by the optical path length adjusting means 20 is incident on the optical fiber FB5 again, and is further guided to the optical fiber FB7 side through the optical branching device 32.

  On the other hand, an optical branching unit (circulator) 34 is connected to the tip of the optical fiber FB2 that guides the measurement light L1, and an optical fiber FB1 and an optical fiber FB6 are further connected to the optical branching unit 34. The light L1 is guided from the optical splitter 34 to the optical fiber FB1 side.

  The probe 30 is optically connected to one end of the optical fiber FB1, and the measurement light L1 is guided from the optical fiber FB1 to the optical fiber FB0 in the probe 30. The probe 30 is inserted into a body cavity from a forceps opening through a forceps channel, for example, and is detachably attached to the optical fiber FB1 by an optical connector OC.

  The probe 30 is connected to the optical fiber FB1 via the optical connector OC, and the measurement light L1 guided by the optical fiber FB1 is incident on the optical fiber FB0 in the probe 30. The incident measurement light L1 is transmitted through the optical fiber FB0 and irradiated onto the measurement object S. Then, the return light (reflected light) L3 reflected by the measuring object S enters the optical fiber FB0, whereby the OCT imaging of the measuring object S is performed.

  The reflected light L3 incident on the optical fiber FB0 is emitted from the optical fiber FB0 to the optical fiber FB1 via the optical connector OC.

  The reflected light L3 incident on the optical fiber FB1 is guided to the optical fiber FB6 side via the optical splitter 34. On the other hand, the reference light L2 whose optical path length has been changed by the optical path length adjusting means 20 is guided to the optical fiber FB7 side via the optical fiber FB5 and the optical branching device 32.

  The reflected light L3 guided by the optical fiber FB6 and the reference light L2 guided by the optical fiber FB7 are combined by the combining unit 4 and output as interference light L4 and L5.

  The interference lights L4 and L5 are detected by the first detector D1. The first detector D1 includes detectors 40a and 40b and an interference light detector 40.

  The interference light L4 is incident on the detector 40a, and the interference light L5 is incident on the detector 40b.

  The interference light detection unit 40 detects interference light L4 and L5 generated by combining the reflected light L3 and the reference light L2 as interference signals. The interference light detection unit 40 has a function of adjusting the balance of the intensity of the interference light L4 and L5 output from the multiplexing unit 4 based on the detection results of the detectors 40a and 40b. The interference signal detected by the interference light detection unit 40 is output to the AD board 44 as a first interference signal.

  Further, the phase matching light split by the light splitting means 3 and guided by the optical fiber FB9 is guided to the second interference system I2.

  The second interference system I2 includes a light dividing unit 5, a combining unit 7, and two optical fibers FB12 and FB13 having different lengths.

  Each of the light dividing means 5 and the combining means 7 is composed of the same optical fiber coupler as the light dividing means 3 and the like. Further, if the optical path length difference between the optical fiber FB12 and the optical fiber FB13 is Δl, Δl is normally used within a range of 2 mm or less. Here, the length of Δl has an optimum value corresponding to the amount of variation in phase shift, and this optimization method will be described later. The light split into two by the light splitting means 5 passes through the optical fiber FB12 and the optical fiber FB13, respectively, and then multiplexed by the multiplexing means 7 to generate an interference signal.

  The interference signal is input to the interference light detection unit 42 via the detectors 42a and 42b, and is output from the interference light detection unit 42 to the AD board 44 as a second interference signal.

  The AD board 44 AD-converts each of the first interference signal and the second interference signal and outputs the digital signal to the processing system 55.

  The processing system 55 includes a processing unit 50, a display unit 52, and a control operation unit 54.

  The processing unit 50 is a region where the probe 30 and the measurement target S are in contact with each other at the measurement site, more precisely, a region where the surface of the probe outer cylinder of the probe 30 and the surface of the measurement target S can be considered to be in contact with each other. Based on the first interference signal and the second interference signal detected and input from the AD board 44, various processes such as a phase correction process, an averaging process, or a Doppler process are performed to form a tomographic image.

  The display unit 52 includes a CRT or a liquid crystal display device, and displays the tomographic image acquired by the processing unit 50.

  The control operation unit 54 includes input means such as a keyboard and a mouse, and control means for managing various conditions based on the input information, and is connected to the processing unit 50 and the display unit 52. The control operation unit 54 inputs, sets, and changes various processing conditions in the processing unit 50 and performs display setting and change of the display unit 52 based on an operator instruction input from the input unit.

  Next, the averaging process will be described.

  FIG. 3 shows the flow of the averaging process.

  The averaging process here is performed on the first interference signal obtained from the measurement light. A light La whose wavelength changes in a constant wavelength band with a constant period is emitted from the light source unit 10, and at that time, an A trigger indicating a certain timing in one sweep of the wavelength is input from the light source unit 10 to the AD board 44. . Based on the A trigger, the AD board 44 receives the interference light L4 (first interference light) from the interference light detection unit 40, converts it into a digital signal, and delivers it to the processing unit 50.

  In this way, in step S101 of FIG. 3, the processing unit 50 acquires the interference signal (first interference signal).

  Next, in step S102, the processing unit 50 performs a rescaling process on the received interference signal. This is a process of converting the interference signal into a wave number linear. The rescaled data is stored in the memory.

  Next, in step S <b> 111, the processing unit 50 acquires an interference signal based on the next A trigger reference from the AD board 44. In step S112, the interference signal is also rescaled, and the processed data is stored in the memory.

  In this way, when a plurality of data obtained by performing a rescale process on a plurality of interference signals obtained by performing the OCT measurement on the same measurement site of the measurement object S a plurality of times, next, in step S103, these data are obtained. An averaging process is performed on a plurality of data obtained from a plurality of interference signals. This average is a simple average.

  Next, in step S104, Fourier transform is performed on the averaged data. By the Fourier transform, a reflection intensity distribution in the depth direction at the measurement site of the measurement object S is obtained.

  In the next step S105, an image forming process is performed based on the Fourier transformed data to form a tomographic image.

  Next, a process for performing the averaging process after correcting the phase shift for the interference signal will be described.

  FIG. 4 shows a flow of processing for averaging the result of the phase correction of the interference signal.

  First, in step S201 of FIG. 4, the processing unit 50 acquires a first interference signal for measurement and a second interference signal for phase matching.

  Here, the first interference signal is sampled on the basis of the A trigger as in the case of the averaging process shown in FIG. 3, but the second interference signal obtains a value after t0 seconds from the A trigger. To do.

  This will be described with reference to FIGS.

  FIG. 5 shows an example of the waveform of the interference signal. 5A shows the first interference signal, FIG. 5B shows the A trigger signal, and FIG. 5C shows the second interference signal. FIG. 6 is an enlarged view of a region R surrounded by a broken line in FIG. 5C, where the horizontal axis is time t and the vertical axis is voltage V.

  The signal is always read into the memory, and the first interference signal is acquired from the memory in a predetermined data acquisition range from the data at the point before the post-trigger from the point when the A trigger is detected. .

  Further, as the second interference signal, data after time t0 seconds from the A trigger is acquired. This time t0 is a time set by measurement in advance. As described below, t0 is preferably set to a value that becomes 0 V near the maximum amplitude of the second interference signal and at the center of the A trigger jitter variation.

  That is, there is A trigger jitter variation (jitter amount) as indicated by the arrow in the time axis t direction of FIG. 6, and the fluctuation range of the output voltage V is present only by the output fluctuation range indicated by the arrow in the vertical axis direction. At this time, the position where the center of the output fluctuation width becomes 0V is set as t = t0.

  As shown in FIG. 6, by setting t = t0 where V = 0, the linear portion of the sine wave of the second interference signal can be used most widely.

  As described above, the acquisition timing (delay amount t0) of the second interference signal is determined in accordance with the A trigger jitter amount.

  Thus, once t0 is set, the value is used all the time. Thereafter, every time the second interference signal is acquired, the output power V fluctuates within the output fluctuation range of FIG. At this time, even if t0 is determined so that V = 0, the center may deviate from V = 0 due to, for example, subsequent temperature fluctuations.

  Next, correction processing is performed in step S202 of FIG.

  FIG. 7 shows a method for correcting the phase shift.

As shown in FIG. 7, the first interference signal, from 1 to n, the sequence of the output voltage value corresponding thereto is assumed to be v _n from v _1. Further, it is assumed that the output voltage value of the second interference signal is V, and the deviation amount (V−V0) from the reference voltage V0 that is the center of the output fluctuation range is calculated from the following equation (1) as the phase shift amount Δpx. Convert to (number of pixels, pixel shift).

Δpx = α · (V−V0) (1)
Here, the reference voltage V0 is set by measuring the center value of V at t = 0 at the time of maintenance as V0. Further, the coefficient α is an inclination at t = t0 in the graph of the second interference signal in FIG. 6, and is determined in advance by actual measurement. Further, the relationship between the voltage value and the number of pixels is also obtained in advance by actual measurement. According to actual measurements, the amount of shift of this pixel is usually 4 pixels or less.

  For example, when actually measured with a sweep frequency of 20 kHz and an AD sampling frequency of 80 MHz, 4 pixels = 50 nsec.

  When the jitter amount is small, it is desirable to set α large so that the maximum range can be used in a region where the relationship between the jitter and the voltage is substantially a straight line. Here, in order to increase α, the optical path length difference Δl may be shortened. Further, Δl can be adjusted by inserting a delay device or adjusting stress on the fiber.

  Next, the phase shift amount Δpx expressed as the number of pixels is divided into an integer part a and a decimal part b. Using the integer part value a, the array element number is shifted from 1,..., N to 1 + a,.

Next, the array values v ₁ ,..., V _n are corrected so as to internally divide each two adjacent values into b: 1−b. That is, v _i ′ = (1−b) · v _i + b · v _{i + 1} (i = 1,..., N−1).

  Next, in step S203 of FIG. 4, a rescale process is performed on the first interference signal that has been subjected to the correction process. The data that has been rescaled is stored in the memory.

  Next, in step S211, the first interference signal sampled with the next A trigger reference and the value of the second interference signal after t0 seconds from the A trigger signal are obtained. In step S212, the same as above. Then, a correction process is performed on the first interference signal using the second interference signal. Thereafter, in step S213, the rescaling process is performed and similarly stored in the memory.

  Thus, after performing the said correction process with respect to the some interference signal obtained by performing OCT measurement in multiple times with respect to the same site | part of the measuring object S, these correction processes are performed in step S204. An averaging process is performed on the plurality of interference signals. The averaging process is performed by taking a simple average of a plurality of data.

  Next, in step S205, Fourier transform is performed on the averaged data, and in step S206, an image forming process is performed to obtain a tomographic image.

  FIG. 8 is a graph showing the results when only the averaging process is performed and when the averaging process is performed after the correction process. The horizontal axis is px, the vertical axis is dB, and the data is an average of 10 lines without scanning the galvanometer mirror (0 Hz).

  In FIG. 8, S0 is the original data of the signal, S1 is the result of the simple average of the signal, S2 is the simple average of the signal and further phase-adjusted (corrected), N0 is the original data of the noise, N1 is the simple noise As a result of averaging, N2 represents a simple average of noise and further phase adjustment (correction).

  As indicated by the symbol P in FIG. 8, the signal is about 2 dB down due to the influence of the A trigger jitter when only the simple average is present, but there is almost no influence of the A trigger jitter when the phase adjustment is performed.

  Further, as indicated by the symbol Q, noise can be reduced even with a simple average alone. Since it is an average of 10 lines now, it can be seen from FIG. 8 that the value is reduced by the same amount as about 5 dB obtained by theoretical calculation as 10 × log√ (10).

  As described above, in the embodiment described above, the averaging process is performed on the result of the phase correction process, so that the signal is not affected by the jitter, while the noise is reduced, and the OCT in SS-OCT. In the signal processing from the measurement data, the S / N at the signal level in the averaging process can be improved, and the image quality of the tomographic image can be improved without reducing the image quality improvement effect due to the phase shift.

  Next, as another embodiment, the result of performing the phase correction processing may be applied to Doppler processing (Doppler OCT).

  Doppler OCT detects a Doppler signal as a phase change amount obtained by Fourier transform of interference information in order to correct distortion of a tomographic image derived from the movement of the measuring object S itself, and detects the movement using the detected signal. Therefore, the positional relationship is corrected using the measurement data information.

  Specifically, phase shifts in a plurality of tomographic images in the A direction due to movement blur of the measurement target S in the A direction (depth direction) are detected using Doppler signal information, and A based on the detection result. The speed information of the tomographic image in the direction is displayed and reconstructed with different color distributions.

  Thus, by applying the result of the phase correction process to the Doppler process (Doppler OCT), it is possible to correct the distortion of the tomographic image due to the movement of the measurement target S, and the amount of phase shift between the data in the Doppler OCT. The S / N ratio of the tomographic image can be improved. It is also possible to determine the speed of blood flow that flows through the blood vessel.

  The optical tomographic imaging apparatus and the interference signal processing method in the optical tomographic imaging apparatus of the present invention have been described in detail above, but the present invention is not limited to the above examples and does not depart from the spirit of the present invention. Of course, various improvements and modifications may be made.

1 is a block diagram showing a schematic configuration of an embodiment of an optical tomographic imaging apparatus according to the present invention. It is a block diagram which shows the more detailed structure of the optical tomographic imaging apparatus of this embodiment. It is a flowchart which shows the flow of an averaging process. It is a flowchart which shows the flow of the process which averages with respect to the result of having performed phase correction to the interference signal. It is a graph which shows the example of the waveform of an interference signal, (a) shows a 1st interference signal, (b) shows A trigger, (c) shows a 2nd interference signal. It is an enlarged view of the area | region R enclosed with the broken line of FIG.5 (c). It is explanatory drawing which shows the correction method of a phase shift. It is a diagram which shows the result by an averaging process and a correction process.

Explanation of symbols

      DESCRIPTION OF SYMBOLS 1 ... Optical tomography apparatus, 10 ... Light source unit, 11 ... Light source, 12 ... Wavelength selection means, 14 ... Optical splitter (circulator), 15 ... Collimator lens, 16 ... Diffraction grating element, 17 ... Optical system, 18 ... Rotating polygonal mirror (polygon mirror), 20 ... optical path length adjusting means, 22 ... reflecting mirror, 23 ... movable stage, 24 ... mirror moving mechanism, 30 ... probe, 32, 34 ... optical splitter, 40, 42 ... interference light detection , 44 ... AD board, 50 ... processing unit, 52 ... display unit, 54 ... control operation unit, 55 ... processing system, I1 ... first interference system, I2 ... second interference system, D1 ... first detector , D2 ... second detector

Claims (8)

  An interference signal processing method in an optical tomographic imaging apparatus using an SS-OCT measurement method, which corrects a phase shift of a plurality of interference signals obtained by measuring the same measurement site to be measured a plurality of times An interference signal processing method in an optical tomographic imaging apparatus characterized by performing processing.   An interference signal processing method in an optical tomographic imaging apparatus using an SS-OCT measurement method, which corrects a phase shift of a plurality of interference signals obtained by measuring the same measurement site to be measured a plurality of times An interference signal processing method in an optical tomographic imaging apparatus, wherein an averaging process is performed after the processing and before Fourier transform.   An interference signal processing method in an optical tomographic imaging apparatus using an SS-OCT measurement method, which corrects a phase shift of a plurality of interference signals obtained by measuring the same measurement site to be measured a plurality of times An interference signal processing method in an optical tomographic imaging apparatus, wherein a Doppler method is applied after processing.   The method for processing an interference signal in an optical tomographic imaging apparatus according to claim 1, wherein the phase correction process uses a value calculated based on a voltage signal of the interference signal. An optical tomographic imaging apparatus using an SS-OCT measurement method,
An optical tomographic imaging apparatus comprising phase correction means for performing phase correction processing for correcting a phase shift of a plurality of interference signals obtained by measuring the same measurement site to be measured a plurality of times. An optical tomographic imaging apparatus using an SS-OCT measurement method,
Phase correction means for performing phase correction processing for correcting phase shifts of a plurality of interference signals obtained by measuring the same measurement site to be measured multiple times;
Averaging means for performing an averaging process on the interference signal after the phase correction process before Fourier transform;
An optical tomographic imaging apparatus comprising: An optical tomographic imaging apparatus using an SS-OCT measurement method,
Phase correction means for performing phase correction processing for correcting phase shifts of a plurality of interference signals obtained by measuring the same measurement site to be measured a plurality of times;
Means for applying a Doppler method to the interference signal after the phase correction processing;
An optical tomographic imaging apparatus comprising:   The optical tomographic imaging apparatus according to claim 5, wherein the phase correction unit uses a value calculated based on a voltage signal of the interference signal.

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