JP2012200283A - Optical coherence tomographic imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical coherence tomographic imaging apparatus capable of reconstructing an image of higher resolution by utilizing a signal obtained by detecting a light of a given wavelength previously set due to sweeping of wavelength of interest, for not a trigger signal for sampling of an interference light in subsequent wavelength sweeping but for sampling of the interference light of the sweeping of the wavelength of interest.SOLUTION: A light of a predetermined wavelength in one-time wavelength sweeping is reflected by an FBG (fiber bragg grating) 241, and the reflected light is detected by a photodetector 242. When a time from the start of wavelength sweeping in this case to the emission of the light of the predetermined wavelength is ΔT, an interference light generated by a photocoupler 226 is delayed by ΔT before arriving at a photodetector 219. To avoid the delay, an optical fiber bundle 237a having a length equivalent to the delay is intervened. When a detection signal is input from the photodetector 242, a signal processing section 223 starts sampling as effective data of the interference light by the photodetector 219.

Description

  The present invention relates to an optical coherence tomographic image forming apparatus.

  There are intravascular treatments using highly functional catheters such as balloon catheters and stents. For the diagnosis before the medical treatment or the progress confirmation after the operation, an image diagnostic device such as an optical coherence tomography (OCT: Optical Coherence Tomography) has been generally used.

  This diagnostic imaging apparatus has a catheter with an optical lens at the tip and a built-in optical fiber with an optical mirror attached. Then, the catheter is inserted into the blood vessel of the patient, and while rotating the optical mirror, light is irradiated into the blood vessel through the optical mirror, and reflected light from the living tissue is received again through the optical mirror. Thus, radial scanning is performed, and a cross-sectional image of the blood vessel is reconstructed based on the obtained reflected light. As an improved type of OCT, an optical coherence tomography (SS-OCT) using wavelength sweep has been developed.

  The basic principle of the optical coherence tomography diagnosis apparatus is that light output from a light source inside the apparatus is divided into measurement light and reference light, and the measurement light is emitted toward the optical fiber mirror inside the catheter. Then, the scattered light reflected by the living tissue is received through the same optical fiber, and interference light with the reference light reflected through a known distance is obtained, and a tomographic image of the living body (blood vessel) near the catheter is obtained from its intensity. (For example, Patent Document 1).

  In particular, in the case of an optical coherence tomography diagnostic apparatus using wavelength sweep, the interference light obtained without repeating the optical path length of the reference light by repeatedly sweeping the wavelength of the emitted light within a predetermined range. From this frequency distribution, it is possible to obtain a reflection intensity distribution in the depth direction based on the same point of the measurement light and the reference light.

  In the case of an optical coherence tomography diagnostic apparatus using wavelength sweep, a straight line extending from the center part (mirror part) of the tomographic image onto the radiation is called a line, and the values of a plurality of pixels on the line are determined by the obtained wavelength sweep. The calculation is performed according to the intensity of the interference light. A pixel group on a line (several hundred lines) for one rotation of the mirror is calculated in the same manner. Naturally, as the distance from the central portion increases, the distance between adjacent lines also increases, so that the process of interpolating the pixels between them is also performed. Such processing is performed to generate a two-dimensional image. Further, by moving the catheter along the blood vessel axis, it is possible to obtain three-dimensional image information along the axial direction of the blood vessel.

JP 2007-267867 A

  In order to obtain the interference light for one line, light between wavelengths [lambda] s to [lambda] e is generated between them. Then, as a result of the generation of the light, the obtained interference light is sampled, and how to start the sampling for this wavelength sweep is important.

  Until now, only light having a preset wavelength is reflected by FBG (Fiber Bragg Grating) while being emitted by wavelength sweeping. Then, it is detected by a photodetector (photo detector) to generate an electric signal. Then, the electrical signal is used as a reference, and a predetermined time after that is set as the start timing of interference light sampling at the next wavelength sweep.

  The above will be described in more detail with reference to FIG. In FIG. 6A at the top of the figure, the vertical axis indicates the intensity of the measurement light. The horizontal axis indicates the time axis, and shows how the measurement light during the wavelength sweep for one line changes from the wavelength λs to λe. In order to increase the accuracy of the photodetector, the wavelength reflected by the FBG is set to the maximum light intensity, and when the reflected light is detected, a signal as shown in FIG. Then, a signal for starting sampling of interference light is generated, for example, after T3 time from the time of the light detection ((c) in the figure). Then, the period T1 is determined as an effective sampling range from this signal ((d) in the figure).

  However, according to the present inventor, the relationship between the light intensities between the wavelengths λs and λe in the wavelength sweep is shown in FIG. The valley distance (time) varies and is difficult to keep constant. Therefore, it is difficult to define a sampling effective range of the same phase for each line in the conventional methods of generating a trigger signal for starting sampling for the wavelength sweep of the next line from the wavelength sweep of the line of interest. FIG. 6 (e) is the same as FIG. 6 (a), and is arranged immediately below FIG. 6 (d) in order to clarify that the sampling effective range is shifted with respect to the wavelength sweep period. It is. For the above reasons, there is a slight difference in the sampling effective period for each line, which is a factor in image quality degradation.

  The present invention has been made in view of such a point, and a signal obtained by detecting light of a predetermined wavelength set in advance by wavelength scanning of interest is used as a trigger signal for sampling interference light in subsequent wavelength sweeping. It is intended to provide a technique that makes it possible to reconstruct a tomographic image with higher accuracy by using it for sampling of interference light of a wavelength of interest sweep instead of using it.

In order to solve the above problems, for example, an optical coherence tomographic image forming apparatus of the present invention has the following configuration. That is,
The light output from the light source by wavelength sweep is divided into measurement light and reference light by a light splitting mechanism, and the measurement light is emitted into the living body lumen while rotating the irradiation direction through a probe inserted into the body, An optical coherence tomographic image forming apparatus that generates a cross-sectional image in the living body lumen based on the light intensity of interference light obtained from the obtained reflected light and the reference light,
A detecting unit that is interposed between the light source and the light splitting mechanism and generates a trigger signal for sampling the interference light by detecting light of a predetermined wavelength set by a single wavelength sweep; ,
Optical detection for converting the interference light from the light splitting mechanism into an electrical signal, where ΔT is the time from the start of the one wavelength sweep until the light of the predetermined wavelength is generated Delay means for delaying by ΔT to the device,
The trigger signal detected for the target wavelength sweep from the detection means is used as a start signal for sampling the interference light of the target wavelength sweep by the photodetector.

  According to the configuration of the present invention, the signal obtained by detecting light of a predetermined wavelength set in advance by the wavelength sweep of interest is not used as a trigger signal for sampling the interference light in the subsequent wavelength sweep, Since it can be used for sampling the interference light of the wavelength sweep, it becomes possible to reconstruct a tomogram with higher accuracy.

It is a figure which shows the external appearance structure of the diagnostic imaging apparatus concerning embodiment. 2 is a block diagram illustrating a functional configuration of the diagnostic imaging apparatus 100. FIG. It is a block diagram which shows the function structure of a signal processing part. It is a figure explaining irradiation of measurement light and taking-in of reflected light about rotation scanning and axial movement by an optical probe in a blood vessel. It is a schematic diagram for demonstrating operation | movement of the optical probe in the blood vessel. It is a figure for demonstrating the principle of the sampling of the conventional interference light. It is a figure for demonstrating the principle of the sampling of the interference light in embodiment.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a system configuration and an external configuration of a wavelength sweep type optical coherence tomographic image forming apparatus (SS-OCT apparatus) (hereinafter referred to as an image diagnostic apparatus) having the present invention. As shown in FIG. 1, the diagnostic imaging apparatus 100 includes an optical probe unit 101, a scanner / pullback unit 102, and an operation control device 103. The scanner / pullback unit 102 and the operation control device 103 are connected by a signal line / optical fiber 104. The optical probe unit 101 is directly inserted into a living body lumen such as a blood vessel, and measures the state inside the living body lumen using an imaging core. The scanner / pullback unit 102 is configured to be detachable from the optical probe unit 101, and regulates the radial operation of the imaging core in the optical probe unit 101 when driven by a built-in motor.

  The operation control apparatus 103 has a function for inputting various setting values and a function for processing data obtained by measurement and displaying it as a tomographic image when performing intra-luminal optical coherence tomographic image formation. . In the operation control device 103, reference numeral 111 denotes a main body control unit that processes data obtained by measurement and outputs a processing result. Reference numeral 111-1 denotes a printer / DVD recorder, which prints a processing result in the main body control unit 111 or stores it as data. Reference numeral 112 denotes an operation panel, and the user inputs various setting values and instructions via the operation panel 112. Reference numeral 113 denotes an LCD monitor as a display device, which displays a processing result in the main body control unit 111.

  FIG. 2 is a functional configuration diagram of the diagnostic imaging apparatus 100 shown in FIG. In the figure, reference numeral 208 denotes a wavelength sweep light source, and Swept Laser is used. The wavelength swept light source 208 is a kind of extended-cavity laser including a light source unit (208a) having an optical fiber 217 coupled to a SOA 216 (semiconductor optical amplifier) and a ring shape, and a polygon scanning filter (208b). The light output from the SOA 216 travels through the optical fiber 217 and enters the polygon scanning filter 208b, where the wavelength-selected light is amplified by the SOA 216 and finally output from the coupler 214. The polygon scanning filter 208b selects a wavelength by a combination of the diffraction grating 212 that separates light and the polygon mirror 209. The light split by the diffraction grating 212 is condensed on the surface of the polygon mirror 209 by two lenses (210, 211). As a result, only light having a wavelength orthogonal to the polygon mirror 209 returns on the same optical path and is output from the polygon scanning filter 208b, so that the time sweep of the wavelength is performed by rotating the mirror. As the polygon mirror 209, for example, a 32-hedron mirror is used, and the rotation speed is about 50000 rpm. High speed and high output wavelength sweeping is possible by a unique wavelength sweeping system combining the polygon mirror 209 and the diffraction grating 212.

  The light from the wavelength swept light source 208 output from the coupler 214 is incident on one end of the first single mode fiber 230. The first single mode fiber 230 is branched into two at the optical coupler section 240, and one is guided to an FBG (Fiber Bragg Grating) 241. It is assumed that the FBG 241 in the embodiment reflects only a wavelength having the maximum intensity when light having a wavelength from the wavelength λs to λe is emitted from the wavelength swept light source 208. This reflected light is supplied to a photodetector (for example, a photodiode) 242 via an optical coupler 240, where a trigger signal for starting sampling of interference light is generated and supplied to a signal processing unit 223 described later.

  Further, the light branched by the optical coupler 240 from the wavelength swept light source 208 is guided to the optical coupler 226 optically coupled to the second single mode fiber 231, where it is branched into two and transmitted. The

  A scanner / pullback unit 102 is provided on the distal end side of the optical coupler unit 226 of the first single mode fiber 230. In the rotation drive device 204 of the scanner / pullback unit 102, an optical rotary joint (optical coupling unit) 203 that couples a non-rotating unit (fixed unit) and a rotating unit (rotary driving unit) and transmits light. Is provided. Further, the distal end side of the fourth single mode fiber 235 in the optical rotary joint 203 is detachably connected to the fifth single mode fiber 236 of the optical probe unit 101 via the adapter 202. As a result, the light from the wavelength swept light source 208 is transmitted to the fifth single mode fiber 236 that is inserted into the imaging core 201 that repeatedly transmits and receives light and can be driven to rotate.

  The light transmitted to the fifth single mode fiber 236 is irradiated from the distal end side of the imaging core 201 to the living tissue in the blood vessel while performing a radial operation. Then, a part of the reflected light scattered on the surface or inside of the living tissue is taken in by the imaging core 201, returns to the first single mode fiber 230 side through the reverse optical path, and a part of the reflected light is first reflected by the optical coupler unit 226. 2 moves to the single mode fiber 237 side. In the second single mode fiber 237, the reflected light is mixed with reference light described later, and is received by a photodetector 219 (for example, a photodiode) as interference light. Although details will be described later, in the embodiment, the fiber bundle 237a of the second single mode fiber 237 is provided in order to delay the interference light reaching the photodetector 219 from the optical coupler unit 226 in terms of time.

  The rotating part side of the optical rotary joint 203 is rotationally driven by a radial scanning motor 205 of a rotational driving device 204. The rotation angle of the radial scanning motor 205 is detected by the encoder unit 206. Furthermore, the optical rotary joint 203 includes a linear drive device 207 and regulates the operation in the insertion direction (axial direction) of the catheter unit 101 based on an instruction from the signal processing unit 223. The axial movement is realized by operating a linear drive motor in the linear drive device 207 based on a control signal from the signal processing unit 223.

  Further, an optical path length variable mechanism 225 for finely adjusting the optical path length of the reference light is provided on the tip side of the optical coupler section 226 of the second single mode fiber 231. The optical path length variable mechanism 225 changes the optical path length that changes the optical path length corresponding to the variation in length so that the variation in length of each optical probe when the optical probe is replaced and used can be absorbed. It has. The second single mode fiber 231 and the collimating lens 234 are provided on a uniaxial stage 232 that is movable as indicated by an arrow 233 in the direction of the optical axis, and form optical path length adjusting means.

  Specifically, when the optical probe unit 101 is replaced, the uniaxial stage 232 forms an optical path length changing unit having a variable range of the optical path length that can absorb variations in the optical path length of the optical probe. Further, the uniaxial stage 232 also has a function as an adjusting means for adjusting the offset. For example, even when the tip of the optical probe is not in close contact with the surface of the living tissue, it is possible to set the state of interference from the surface position of the living tissue by minutely changing the optical path length using the single axis stage.

  The reflected light is input to the second single mode fiber 231 as reference light through the mirrors 227 and 229 and the lens 228. The light (reference light) whose optical path length is finely adjusted by the optical path length variable mechanism 225 is transmitted from the first single mode fiber 230 side by the optical coupler unit 226 provided in the middle of the second single mode fiber 231 ( Mixed with (reflected light) to form interference light, which is received by the photodetector 219. Light received by a photodetector 219 (details will be described later) is subjected to photoelectric conversion and amplification and input to the logarithmic amplifier 220. The logarithmic amplifier 220 logarithmically amplifies the electric signal obtained by photoelectrically converting the interference light and amplified in the photodetector 219. The output of the logarithmic amplifier 220 is supplied to the demodulator 221. The demodulator 221 performs demodulation processing for extracting only the signal portion of the interfered light, and its output is input to the A / D converter 222.

  The A / D converter 222 samples the interference light signal for 2048 points at 180 MHz to generate one line of digital data (interference light data). The sampling frequency of 180 MHz is based on the premise that about 90% of the wavelength sweep period (12.5 μsec) is extracted as 2048 digital data when the wavelength sweep repetition frequency is 80 kHz. However, the present invention is not limited to this.

  The line-by-line interference light data generated by the A / D converter 222 is input to the signal processing unit 223. In this signal processing unit 223, the interference light data is subjected to frequency decomposition by FFT (Fast Fourier Transform) to generate data in the depth direction, and this is subjected to coordinate conversion to form cross-sectional images at each position in the blood vessel. The data is output to the LCD monitor 113 at a predetermined frame rate.

  The signal processing unit 223 is connected to the optical path length adjusting unit control unit 224. The signal processing unit 223 controls the position of the uniaxial stage 232 via the optical path length adjusting unit control unit 224. The signal processing unit 223 is connected to the motor control circuit 224, and stores the cross-sectional image in an internal memory in synchronization with a video synchronization signal when forming the cross-sectional image. The video synchronization signal of the motor control circuit 224 is also sent to the rotation drive device 204, and the rotation drive device 204 outputs a drive signal synchronized with the video synchronization signal. Further, the signal processing unit 223 uses the signal indicating the predetermined wavelength detection for the wavelength sweep from the light detector 242 as a trigger, and executes sampling of the interference light by the light detector 219 to the A / D converter 222 described above. become.

  FIG. 4A is a diagram illustrating a state in which the image core 201 of the optical probe unit 101 is inserted into a living body lumen (blood vessel lumen) and radial scanning is performed. A catheter sheath 403 containing an imaging core 201 composed of an optical fiber 236 having an optical mirror 401 and an optical lens 402 at the tip is inserted into, for example, a blood vessel lumen. The rotation driving device 204 rotates the imaging core 201 in the direction of the arrow 405 in the catheter sheath 403, and the linear driving device 207 moves in the direction of the arrow 406. At this time, as shown in FIG. 4B, the measurement light from the wavelength swept light source 208 passes through the optical fiber 236 and is irradiated to the living body lumen by the optical mirror 401. The reflected light of the irradiated light is returned to the apparatus through the optical fiber 236 by the optical mirror 401.

  FIG. 5 is a schematic diagram for explaining the operation of the optical probe unit 101 during intravascular tomography. 5A and 5B are a perspective view and a cross-sectional view of a blood vessel in a state where the optical probe unit 101 is inserted, respectively. In FIG. 5A, reference numeral 501 denotes a blood vessel cross section in which the optical probe unit 101 is inserted. As described above, the imaging lens 201 of the optical probe unit 101 has the optical lens 402 and the optical mirror 401 attached to the tip thereof, and is rotated in the direction indicated by reference numeral 405 in FIG. To do.

  From the optical lens 402, measurement light is transmitted / received at each rotation angle. Lines 1, 2,..., 512 indicate the irradiation direction of the measurement light at each rotation angle. In the present embodiment, while the imaging core 201 including the optical mirror 401 and the optical lens 402 is rotated 360 degrees at the position of the predetermined blood vessel cross section 501, 512 transmissions of measurement light / reception of reflected light are intermittently performed. Done. Note that the number of transmission / reception times of the measurement light during 360 ° rotation is not limited to this, and can be arbitrarily set. In this way, scanning (scanning) in which signal transmission / reception is repeated while rotating the imaging core 201 is generally referred to as “radial scanning (radial scanning, rotational scanning)”. Further, such transmission of the measurement light / reception of the reflected light by the imaging core 201 is performed while the imaging core 201 advances in the blood vessel in the direction of the arrow 406 (see FIG. 4A).

  Next, the method for determining the interference light sampling start timing in the embodiment will be described in more detail with reference to FIG.

  FIG. 7A at the top of FIG. 7 shows the intensity of light emitted by the wavelength sweep of the wavelength sweep light source 208. The horizontal axis indicates the time axis, and shows how the measurement light during the wavelength sweep for one line changes from the wavelength λs to λe. The wavelength of the light reflected by the FBG 241 in the embodiment may be in the range of λs to λe. However, in order for the photodetector 242 to reliably detect light, a certain level of light is required. Therefore, the wavelength of the light reflected by the FBG 241 in the embodiment is the wavelength of the maximum intensity of the emitted light. Therefore, the photodetector 242 generates a detection signal at the timing as shown in FIG. 7B for each line.

  As described above, FIG. 7A is exaggerated to some extent for easy understanding, but the shape of the convex crest of each line is not different between the lines, or Although the difference is negligible, the length (time) of the valley between the mountains is not constant but rather is indefinite. Accordingly, now focusing on one detection signal in FIG. 7B, if the interference light obtained between λs and λe in the wavelength sweep including this detection signal can be sampled, the shift in each line The problem can be solved. However, the start timing of the wavelength sweep with respect to the signals detected by the FBG 241 and the photodetector 242 is retroactive by a period T3 as shown in FIG. It is impossible to generate the signal shown in FIG. 7C by going back to the past by the period T3 without needing to discuss it. However, in other words, if the interference light can be delayed by the time T3, a sampling period as shown in FIG. 7D can be defined, and as shown in FIG. The period can be matched.

In the wavelength sweep type optical coherence tomographic image forming apparatus (SS-OCT apparatus) in this embodiment, the rotation speed of the mirror in the catheter is 9600 rpm, and the wavelength sweep is performed 512 times (line) by one rotation. When calculated under such conditions, the time T3 in FIG. 7C is about 6 μs (of course, this value is determined depending on the configuration of the apparatus, and is not limited to this). The refractive index n of a general optical fiber is about 1.5, and the fiber used in this embodiment is also made of the same material. In this case, the propagation speed c ′ of light in the fiber is obtained by the following equation (the speed of light in vacuum is c).
c ′ = c / n≈3 × 10 ⁸ (m) /1.5=2×10 ⁸ (m)
Since the target delay time is 6 μs, the fiber length L required for the delay is
L = 2 × 10 ⁸ × 6 × 10 ⁻⁶ = 1.2 × 10 ³
Therefore, it is sufficient to prepare a fiber having a length of about 1.2 km.

  The fiber bundle 237a in the present embodiment is composed of this 1.2 km long fiber. In general, the loss of light propagating in the optical fiber is several percent per km, and the influence on the tomographic image due to the attenuation of the interference light caused by the fiber bundle 237a can be ignored. In addition, in the case of the apparatus of the embodiment, fibers are used everywhere other than the fiber bundle 237a. However, since these are sufficiently shorter than the fiber bundle 237a, their influence can be ignored. Incidentally, the volume of the fiber bundle 237a represented by the optical fiber having a length of 1.2 km is small enough to be held by a human hand and can be easily stored in the housing of the main body control unit 111. It is as much as possible.

  As described above, when the light detection signal having a preset wavelength is input from the light detector 242 to the signal processing unit 223, the signal processing unit 223 uses the signal as a sampling start signal for interference light, and the A / D converter It suffices to repeat the sampling by 222 only for the period corresponding to one period of wavelength transmission (period T1 in FIG. 7). The specific processing of the signal processing unit 223 will be described with reference to FIG.

  As described above, the measurement light from the optical probe unit 101 and the reference light from the optical path length variable mechanism 225 are combined by the optical coupler unit 226 to become interference light. In this process, the photodetector 242 supplies a signal obtained by detecting light having a preset wavelength to the signal processing unit 223. When the signal processing unit 223 receives the signal from the photodetector 242, it is considered that the interference light at the initial wavelength λs of the wavelength sweep is incident on the photodetector 219 through the fiber bundle 237 a serving as a delay unit. . That is, at this timing, the signals obtained by the photodetector 219, the logarithmic amplifier 220, the demodulator 221, and the A / D converter 222 are used as effective signals, and sampling is repeated for a time T1 related to one wavelength sweep. . The A / D conversion unit 222 samples 2048 points by one wavelength sweep and outputs it as digital data to the line memory unit 301 at the subsequent stage.

  In the optical coherence tomographic image forming apparatus using the wavelength sweep, the reflection intensity distribution in the depth direction can be obtained by Fourier transforming the data obtained here. That is, since data in the depth direction can be acquired without scanning the optical path length, high-speed data acquisition is possible. The line memory unit 301 in FIG. 3 selects and groups signals so that the number of lines per motor rotation is 512 based on the motor encoder signal output from the motor control circuit 224. That is, 512 pieces of interference data for each line are output to the line data generation unit 302 by 512 per rotation of the motor.

  The line data generation unit 302 generates line data by performing FFT (Fast Fourier Transform Processing), and performs line addition averaging processing, filter processing, logarithmic conversion, and the like, and post-processes the obtained line data. To the output.

  The post-processing unit 303 performs contrast adjustment, luminance adjustment, gamma correction, frame correlation, sharpness processing, and the like on the line data received from the line data generation unit 302 and outputs the processing result to the image construction unit 304. The image construction unit 304 converts a polar coordinate line data string into a video signal and displays it on the LCD monitor 113 as a blood vessel cross-sectional image. Here, as an example, an example in which an image is constructed from 512 lines is shown, but the number of lines is not limited thereto. The control unit 305 controls the series of operations of each unit described above, and the calculation contents until obtaining the vascular tomographic image and the display processing part are not directly related to the present invention. Further explanation is omitted.

  As described above, according to the present embodiment, in the optical coherence tomographic image forming apparatus using the wavelength sweep, the signal for starting sampling the light of the preset wavelength in the wavelength sweep for the line of interest is used as the interference of the next line. Interfering light at the start of the sub-wavelength sweep for the line of interest can be used for sampling instead of optical sampling. An image can be reconstructed.

  In this embodiment, an optical system using an optical passive element such as an optical fiber, an optical coupler, or an optical circulator is used. However, in the free space, an optical element such as a beam splitter or a half mirror is used. It is also possible to do.

Claims (4)

The light output from the light source by wavelength sweep is divided into measurement light and reference light by a light splitting mechanism, and the measurement light is emitted into the living body lumen while rotating the irradiation direction through a probe inserted into the body, An optical coherence tomographic image forming apparatus that generates a cross-sectional image in the living body lumen based on the light intensity of interference light obtained from the obtained reflected light and the reference light,
A detecting unit that is interposed between the light source and the light splitting mechanism and generates a trigger signal for sampling the interference light by detecting light of a predetermined wavelength set by a single wavelength sweep; ,
Optical detection for converting the interference light from the light splitting mechanism into an electrical signal, where ΔT is the time from the start of the one wavelength sweep until the light of the predetermined wavelength is generated Delay means for delaying by ΔT to the device,
The optical coherence tomographic image forming apparatus, wherein the trigger signal detected with respect to the target wavelength sweep from the detection means is used as a start signal for sampling the interference light of the target wavelength sweep by the photodetector.   The detection means includes an optical coupler that splits the light from the light source into two, an FBG (fiber Bragg Grating) that is connected to one branch destination of the optical coupler and reflects the light of the predetermined wavelength, and its reflection The optical coherence tomographic image forming apparatus according to claim 1, wherein the optical coherence tomographic image forming apparatus comprises a photodiode for detecting light.   The delay means is constituted by an optical transmission line having a length of (c / n) × ΔT, where n is the refractive index of light in the optical transmission line and c is the speed of light in vacuum. The optical coherence tomographic image forming apparatus according to claim 1.   4. The optical coherence tomographic image forming apparatus according to claim 3, wherein the optical transmission path is a bundle of optical fibers.

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