JP2015179053A - Tomographic imaging device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a rotation velocity of an imaging core to be increased without deteriorating resolution.SOLUTION: A tomographic imaging device acquiring a cross sectional image by generating interference light between reflection light and reference light by use of light output from a light source repeating wavelength sweep has a FIFO memory that stores interference light data to be obtained based on the interference light in plurality of lines, and destroys the oldest interference light data in accordance with writing of new interference light data. The tomographic imaging device is configured to: write interference light data obtained from the interference light in synchronization with repetition of the wavelength sweep in the FIFO memory as non-used interference light data; read the oldest non-used interference light data of pieces of interference data stored in the FIFO memory for each rotation of an imaging core at a prescribed angle; generate line data; and control a rotating velocity of the imaging core or cycle of the wavelength sweep on the basis of the number of pieces of non-used interference light data stored in the FIFO memory.

Description

  The present invention relates to a tomographic imaging apparatus that performs tomographic imaging by optical frequency domain imaging (OFDI) and a control method thereof.

  In a tomography apparatus using OFDI, an optical transmission / reception unit (imaging core) having an optical lens and an optical mirror, and a drive shaft with the optical transmission / reception unit attached to the distal end are built in, and at least the distal end is transparent catheter sheath A catheter is used. In blood vessel tomography, the catheter is guided into the patient's blood vessel. Then, while rotating the imaging core, light is applied to the blood vessel wall through the optical mirror, and the reflected light from the blood vessel wall is received again through the optical mirror to perform radial scanning, and the obtained reflection is obtained. A cross-sectional image of the blood vessel is constructed based on the interference light generated by the light and the reference light. Also, a three-dimensional image of the lumen surface in the longitudinal direction of the blood vessel is formed by performing an operation of pulling at a predetermined speed (generally called pullback) while rotating the drive shaft.

  As a specific example, in radial scanning, 512 radial line data are acquired during one rotation of the drive shaft, and a tomographic image is generated. Each line data is interference light data acquired during one sweep of wavelength. That is, it is preferable to synchronize the two so that the wavelength sweep is performed once every time the drive shaft rotates 360/512 degrees. In other words, it is preferable to accurately synchronize the rotation of the drive shaft and the wavelength sweep, but such synchronization is technically difficult.

  In general, the tomographic imaging apparatus creates one-dimensional line data using interference light data acquired in synchronization with the latest sweep at every predetermined rotation angle (for example, 1/512 rotation) of the drive shaft. That is, the buffer memory is overwritten with a new line of interference light data for each sweep, and one line of interference light data is read from the buffer at every predetermined rotation angle. Here, if the wavelength sweep cycle and the rotation time of the predetermined rotation angle of the drive shaft are substantially the same, writing one line of interference light data to the buffer and reading one line of interference light data from the buffer are alternately performed. To be done.

  However, when the rotational speed of the drive shaft is relatively slow with respect to the wavelength sweep period, the interference light data acquired in some sweeps is skipped. On the other hand, when the rotational speed of the drive shaft becomes relatively faster with respect to the wavelength sweeping cycle, a plurality of readings are executed before a new line of interference light data is written to the buffer. For this reason, redundant reading occurs in which data acquired by one sweep is used a plurality of times. When overlapping reading like the latter occurs, since the contents of a plurality of line data are the same among the tomographic images constructed by a fixed number of line data such as 512, the resolution is lowered. In order to avoid the occurrence of duplicate readings more reliably, it is proposed to reduce the rotation speed of the drive shaft with respect to the wavelength sweep period so that the rotation time of the predetermined angle of the drive shaft does not become shorter than the wavelength sweep period. (Patent Document 1).

JP 2007-268132 A

  However, if the rotational speed of the drive shaft is slowed down, the construction time of one tomographic image becomes slower than the theoretical value determined from the light sweep cycle. Therefore, the resolution in the sweep direction of the longitudinal section image obtained when the optical transmission / reception unit is pulled inside the catheter becomes rough.

  The present invention has been made in view of the above problems, and an object thereof is to realize tomographic imaging by high-speed imaging core rotation while suppressing deterioration in resolution.

In order to achieve the above object, a tomographic imaging apparatus according to one aspect of the present invention comprises the following arrangement. That is,
A cross-section by generating measurement light and reference light using light output from a light source that repeats wavelength sweep, and detecting interference light between the reflected light of the measurement light and the reference light acquired via an imaging core A tomography apparatus for acquiring an image,
A FIFO memory that stores a plurality of lines of interference light data obtained based on the interference light, and discards the oldest interference light data in response to writing of new interference light data;
Writing means for writing interference light data obtained from the interference light into the FIFO memory as unused interference light data in synchronization with repetition of wavelength sweep of the light source;
Generation means for generating line data using the oldest unused interference light data stored in the FIFO memory every rotation of the imaging core by a predetermined angle, and the interference used for generating the line data here Optical data is treated as used,
First control means for controlling the rotation speed of the imaging core or the period of the wavelength sweep based on the number of unused interference light data stored in the FIFO memory.

  According to the present invention, it is possible to realize tomographic imaging by high-speed imaging core rotation while suppressing resolution degradation.

The figure which shows the external appearance of the tomography apparatus by embodiment. 1 is a block configuration diagram of a tomography apparatus 100 according to an embodiment. The figure for demonstrating the outline | summary of the reconstruction process of a cross-sectional image. The figure explaining the structure for acquiring the interference light data and line data by embodiment. The figure explaining a wavelength sweep synchronous pulse and an encoder pulse. The block diagram explaining the structure of an interference light data holding part and an interference light data reading part. The figure explaining the selection operation | movement of the interference light data by a selector control part. The figure explaining the rotational speed control structure at the time of starting of a radial scanning motor. 6 is a flowchart for explaining the operation of the tomography apparatus according to the embodiment. 6 is a flowchart for explaining the operation of the tomography apparatus according to the embodiment.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a diagram showing an example of the overall configuration of a tomographic imaging apparatus 100 using OFDI that uses a wavelength swept light source according to an embodiment of the present invention. The tomographic imaging apparatus 100 includes an optical probe unit 101, a pull back unit 102, and an operation control device 103. The pull back unit 102 and the operation control device 103 are connected by a cable 104 via a connector 105. The cable 104 accommodates an optical fiber and various signal lines.

  The optical probe unit 101 accommodates an optical fiber rotatably. At the tip of this optical fiber, light (measurement light) transmitted from the operation control device 103 via the pullback unit 102 is transmitted in a direction substantially perpendicular to the central axis of the optical fiber, and the transmitted light An imaging core 250 (FIG. 2) having an optical transmission / reception unit for receiving reflected light from outside is provided.

  The pullback unit 102 holds the optical fiber in the optical probe unit 101 via an adapter provided in the optical probe unit 101. The imaging core 250 provided at the tip can be rotated by rotating the optical fiber in the optical probe unit 101 by driving a motor built in the pullback unit 102. The pullback unit 102 also drives a motor provided in the built-in linear drive unit and pulls the optical fiber in the optical probe unit 101 at a predetermined speed (this is the reason called the pullback unit).

  With the above configuration, the optical probe unit 101 is guided into the blood vessel of the patient, the radial scanning motor 241 (FIG. 2) built in the pullback unit 102 is driven, and the optical fiber in the optical probe 101 is rotated, whereby the blood vessel It is possible to scan the wall and lumen surface over 360 degrees. Further, the pullback unit 102 pulls the optical fiber in the optical probe unit 101 at a predetermined speed by the linear drive unit 243 (FIG. 2), so that scanning along the blood vessel axis is performed. It is possible to construct a tomographic image as seen from above.

  The operation control apparatus 103 has a function for overall control of the operation of the tomography apparatus 100, a function for inputting various setting values based on user instructions into the apparatus, and processing data obtained by the measurement as a tomographic image in the body cavity. It has a function to display. The operation control device 103 includes a main body control unit 111, a printer / DVD drive 115, an operation panel 112, an LCD monitor 113, and the like.

  The main body control unit 111 generates an optical tomographic image. The optical tomographic image generates interference light data by causing interference between reflected light obtained by measurement and reference light obtained by separating light from the light source, and is generated based on the interference light data. It is generated by processing the line data. The printer / DVD drive 115 prints the processing result in the main body control unit 111 or stores it as data. The operation panel 112 is a user interface through which a user inputs various setting values and instructions. The LCD monitor 113 functions as a display device and displays, for example, a tomographic image generated by the main body control unit 111. Reference numeral 114 denotes a mouse as a pointing device (coordinate input device).

  Next, the functional configuration of the tomography apparatus 100 will be described. FIG. 2 is a block configuration diagram of the tomographic imaging apparatus 100. Hereinafter, the functional configuration of the wavelength sweep type OCT (OFDI) will be described with reference to FIG.

  In FIG. 2, reference numeral 201 denotes a signal processing unit that controls the entire tomographic imaging apparatus, and includes a microprocessor and several circuits. Reference numeral 210 denotes a non-volatile storage device represented by a hard disk, which stores various programs executed by the signal processing unit 201, data files, and the like. Reference numeral 202 denotes a memory (RAM) provided in the signal processing unit 201. A wavelength swept light source 203 is a light source that repeatedly generates light having a wavelength that changes within a preset range along the time axis.

  The light output from the wavelength swept light source 203 is incident on one end of the first single mode fiber 271 and transmitted toward the distal end side. The first single mode fiber 271 is optically coupled to the fourth single mode fiber 275 at an intermediate optical fiber coupler 272. By the optical fiber coupler 272, the light from the wavelength swept light source 203 is branched into reference light traveling toward the fourth single mode fiber 275 and measurement light traveling toward the distal end side of the first single mode fiber 271.

  Light (measurement light) emitted from the front end side of the optical fiber coupler 272 in the first single mode fiber 271 is guided to the second single mode fiber 273 in the cable 104 via the connector 105. The other end of the second single mode fiber 273 is connected to the optical rotary joint 230 in the pullback unit 102.

  On the other hand, the optical probe unit 101 has an adapter 101 a for connecting to the pullback unit 102. Then, the optical probe unit 101 is stably held by the pullback unit 102 by connecting the optical probe unit 101 to the pullback unit 102 by the adapter 101a. Further, the end of the third single mode fiber 274 rotatably accommodated in the optical probe unit 101 is connected to the optical rotary joint 230. As a result, the second single mode fiber 273 and the third single mode fiber 274 are optically coupled. At the other end of the third single-mode fiber 274 (on the leading portion side of the optical probe unit 101), an imaging core 250 is provided that mounts a mirror and a lens that emits light in a direction substantially perpendicular to the rotation axis. Yes.

  As a result, the light emitted from the wavelength swept light source 203 passes through the first single mode fiber 271, the second single mode fiber 273, and the third single mode fiber 274 to the end of the third single mode fiber 274. Guided to an imaging core 250 provided in the section. The imaging core 250 emits this light in a direction orthogonal to the axis of the fiber, receives the reflected light, and the received reflected light is led backwards this time and returned to the operation control device 103.

  On the other hand, an optical path length adjustment mechanism 220 for finely adjusting the optical path length of the reference light is provided at the opposite end of the fourth single mode fiber 275 coupled to the optical fiber coupler 272. The optical path length adjustment mechanism 220 changes the optical path length to change the optical path length corresponding to the variation in length so that the variation in length of each optical probe unit 101 can be absorbed, such as when the optical probe unit 101 is replaced. Functions as a means. Therefore, a collimating lens 225 located at the end of the fourth single mode fiber 275 is provided on a movable uniaxial stage 224 as indicated by an arrow 226 in the optical axis direction.

  Specifically, when the optical probe unit 101 is replaced, the uniaxial stage 224 functions as an optical path length changing unit having a variable range of optical path length that can absorb variations in the optical path length of the optical probe unit 101. Further, the uniaxial stage 224 also has a function as an adjusting means for adjusting the offset. For example, even when the tip of the optical probe unit 101 is not in close contact with the surface of the living tissue, the optical path length is minutely changed by the uniaxial stage, thereby setting the state to interfere with reflected light from the surface position of the living tissue. It is possible.

  The optical path length is finely adjusted by the uniaxial stage 224, and the reference light reflected by the mirror 223 via the grating 221 and the lens 222 is guided again to the fourth single mode fiber 275. The reference light is mixed with the measurement light obtained from the first single mode fiber 271 side by the optical fiber coupler 272 and received by the photodiode 204 as interference light.

  The interference light received by the photodiode 204 in this manner is photoelectrically converted, amplified by the amplifier 205, and then input to the demodulator 206. The demodulator 206 performs demodulation processing for extracting only the signal portion of the interfered light, and its output is input to the A / D converter 207 as an interference light signal.

  The A / D converter 207 samples the interference light signal for 2048 points at 90 MHz, for example, in order to generate one line of digital data (interference light data). The sampling frequency of 90 MHz is based on the assumption that about 90% of the wavelength sweep cycle (25 μsec) is extracted as 2048 digital data when the wavelength sweep repetition frequency is 40 kHz. There is no particular limitation. For example, in order to obtain a higher-speed image, an interference light signal sampling frequency of 176 MHz and a wavelength repetition frequency of 81 kHz has been commercialized.

  The digital signal of the interference light signal generated by the A / D converter 207 is interference light intensity data, which is input to the signal processing unit 201 and processed for each digital signal (interference light data) in units of lines. In the signal processing unit 201, the interference light data is frequency-resolved by FFT (Fast Fourier Transform) to generate line-shaped image data (line data) in the depth direction. Then, the signal processing unit 201 performs coordinate conversion on the line data to construct an optical cross-sectional image at each position in the blood vessel, and outputs it to the LCD monitor 113 at a predetermined frame rate. The signal processing unit 201 is further connected to an optical path length adjustment driving unit 209 and a communication unit 208. The signal processing unit 201 controls the position of the uniaxial stage 224 (optical path length control) via the optical path length adjustment driving unit 209.

  The communication unit 208 incorporates several types of drive circuits and communicates with the rotation drive device 240 in the pullback unit 102 under the control of the signal processing unit 201. Specifically, a drive signal is supplied to the radial scanning motor 241 for rotating the third single-mode fiber 274 by the optical rotary joint 230 in the pullback unit 102, and the rotational position of the radial scanning motor 241 is detected. Signal from the encoder unit 242 and supply of a drive signal to the linear drive unit 243 for pulling the third single mode fiber 274 at a predetermined speed.

  Note that the above processing in the signal processing unit 201 is also realized by a predetermined program being executed by a computer.

  In the above configuration, the user positions the optical probe unit 101 (imaging core 250) at the blood vessel position (coronary artery or the like) of the patient's diagnosis target, and a transparent flush liquid (usually physiological saline or (Contrast agent) is released into the blood vessel. This is to exclude the influence of blood at the time of photographing. When the user inputs an instruction to start scanning, the signal processing unit 201 drives the wavelength swept light source 203 to drive the radial scanning motor 241 and the linear driving unit 243 (hereinafter, the radial scanning motor 241 and the linear driving unit). (Light irradiation and light reception processing by driving 243 is called scanning). As a result, the wavelength swept light is supplied from the wavelength swept light source 203 to the imaging core 250 through the path as described above. At this time, the imaging core 250 at the tip position of the optical probe unit 101 moves along the rotation axis while rotating, so the imaging core 250 moves along the blood vessel axis while rotating. However, light is emitted to the blood vessel lumen surface and the reflected light is received.

  Here, a process for generating one optical cross-sectional image will be briefly described with reference to FIG. FIG. 3 is a view for explaining the reconstruction processing of the cross-sectional image of the lumen surface 301 of the blood vessel in which the imaging core 250 is located. During one rotation (360 degrees) of the imaging core 250, the measurement light is transmitted and received a plurality of times. By transmitting and receiving light during one wavelength sweep, it is possible to obtain one line of data in the direction of irradiation with the light. Therefore, 512 line data extending radially from the rotation center 302 can be obtained by transmitting and receiving, for example, 512 times wavelength-swept light during one rotation. By performing a known calculation for the data of this line, 3D model data is generated from the rotation center position in the radial direction (r direction). One line in the model data is line data 350 composed of 1024 luminance values I0 to I1023. I0 is at the rotation center position, and I1023 is a luminance value at a position farthest from the rotation center position.

  The 512 line data obtained in this way are dense in the vicinity of the rotation center position, and become sparse with each other as the distance from the rotation center position increases. Therefore, the pixels in the empty space of each line are generated by performing a known interpolation process, and a two-dimensional cross-sectional image that can be seen by humans is generated. A three-dimensional blood vessel image can be obtained by connecting the generated two-dimensional cross-sectional images to each other along the blood vessel axis. It should be noted that the center position of the two-dimensional cross-sectional image coincides with the rotation center position of the imaging core 250, but is not the center position of the blood vessel cross section.

In the tomographic imaging apparatus using the wavelength sweep, the wavelength sweep light source 203 emits light by gradually changing the wavelength of the output light with respect to the time axis during a period of light output and reception for a certain line in FIG. To do. The wavelength swept light source 203 has a known configuration and will not be described in particular. However, rotation of the polygon scanner generates light whose wavelength continuously changes from λ _min to λ _max per sweep (FIG. 5A). See). For example, 90% of the one sweep period (λ _S to λ _E ) is used to generate interference light data for one line. In the present embodiment, a pulse signal (hereinafter, wavelength sweep synchronization pulse 411) is output every time the wavelength becomes λ _S. In other words, a period from when the wavelength sweep synchronization pulse 411 is output until the next wavelength sweep synchronization pulse 411 is output is a period for obtaining data for one line in FIG.

  When light is transmitted and received, since there is also reflection from the catheter sheath itself of the optical probe unit 101, a catheter sheath shadow 303 is formed in the cross-sectional image as shown in FIG. Reference numeral 304 shown in the figure is a shadow of a guide wire that guides the optical probe unit 101 to the affected part. The guide wire is made of metal and does not transmit light. Therefore, it is not possible to obtain an image of the back side portion of the guide wire as viewed from the rotation center 302. It should be recognized that the illustration is only a conceptual diagram.

  Next, in the tomographic imaging apparatus 100 of the present embodiment having the above-described configuration, acquisition / holding of interference light data synchronized with wavelength sweep and acquisition of line data synchronized with the rotation of the imaging core are performed. The configuration will be described.

FIG. 4 is a block diagram illustrating a functional configuration for acquiring interference light data and line data in the tomographic imaging apparatus 100 of the present embodiment. The wavelength sweep light source 203 is a light source 401 and a wavelength sweep unit 402 that sweeps the wavelength of light output from the light source 401. FIGS. 5A to 5C are diagrams illustrating the operation of the wavelength sweep unit 402 and the operation timing of acquiring interference light data. As shown in FIG. 5A, the wavelength sweep unit 402 outputs light that has been wavelength swept from λ _min to λ _max by rotation of a polygon scanner (not shown) (hereinafter, wavelength swept light 421). Further, in the wavelength sweep unit 402, a sweep trigger detection unit (not shown) detects a predetermined wavelength (λ _S ) of the output light, and outputs a wavelength sweep synchronization pulse 411 as shown in FIG. As shown in FIG. 4, the wavelength sweep synchronization pulse 411 is input to the interference light data holding unit 405 and the motor drive signal generation unit 408.

  The wavelength sweep light 421 is branched into the reference light 422 and the measurement light 423 in the optical fiber coupler 272 described above. The measurement light 423 is irradiated onto the subject through the third single mode fiber 274 and the imaging core 250 constituting the optical probe unit 101, and the reflected light 424 passes through the imaging core 250 and the third single mode fiber 274. It is supplied to the interference unit 404. The reference light 422 is supplied to the light interference unit 404 after being reflected by the mirror 223 described above. The optical interference unit 404 includes the optical fiber coupler 272, the photodiode 204, the amplifier 205, and the demodulator 206 described in FIG. 2, and the interference light signal of the reflected light 424 and the reference light 422 is sent to the A / D converter 207. Output. The A / D converter 207 performs A / D conversion on the interference light signal and outputs it to the signal processing unit 201.

  On the other hand, the rotary shaft of the radial scanning motor 241 that rotates the imaging core (drive shaft) in the optical probe unit 101 is connected to the encoder unit 242. The encoder unit 242 outputs an encoder pulse at every predetermined rotation angle of the radial scanning motor 241 (accordingly, every predetermined rotation angle of the imaging core). This is shown in FIGS. 5 (d) and 5 (e). As described with reference to FIG. 3, in this embodiment, in order to obtain 512 line data 350 per rotation, a pulse signal (hereinafter referred to as “pulse signal”) is transmitted from the encoder unit 242 at every rotation of a predetermined angle (360/512 degrees in this embodiment). Encoder pulse 412) is output. The encoder pulse 412 is input to the motor drive signal generation unit 408 and the interference light data reading unit 406.

  The interference light data holding unit 405 of the signal processing unit 201 obtains and holds interference light data for one line from the A / D converted interference light signal based on the wavelength sweep synchronization pulse 411. As shown in FIG. 5C, the interference light data is composed of digital data of 2048 interference light signals from the reception of the wavelength sweep synchronization pulse 411, and this is held in the line memory. As will be described later with reference to FIG. 6, the interference light data holding unit 405 has a plurality of line memories, stores a plurality of lines of interference light data, and discards the oldest interference light data in response to writing of new interference light data. A memory 601 is configured.

  The interference light data reading unit 406 of the signal processing unit 201 selects and outputs the interference light data used by the signal processing circuit 407 to generate line data from the plurality of lines of interference light data held in the FIFO memory 601. The interference light data reading unit 406 controls the selection of interference light data in accordance with the execution of holding new interference light data by the interference light data holding unit 405 and the input of the encoder pulse 412. The signal processing circuit 407 generates line data 350 as described with reference to FIG. 3 using the interference light data selected by the interference light data reading unit 406 according to the encoder pulse 412, and forms a tomographic image.

  Further, the interference light data reading unit 406 generates a motor drive signal by calculating the number of lines of interference light data (hereinafter, unused interference light data) stored in the FIFO memory 601 and not yet used for generating line data. Output to the unit 408. The motor drive signal generation unit 408 controls the radial scanning motor 241 based on the number of unused interference light data lines held in the FIFO memory 601 to control the rotation speed of the imaging core.

  FIG. 6 is a block diagram for explaining detailed configurations and operations of the interference light data holding unit 405 and the interference light data reading unit 406 of the signal processing unit 201.

  In the interference light data holding unit 405, the write controller 611 accumulates 2048 points of A / D converted interference signals in the buffer memory 612 in synchronization with the wavelength sweep synchronization pulse 411. When 2048 points of interference signals are accumulated, the buffer memory 612 holds interference light data for one line. When the write controller 611 accumulates 2048 points of interference signals, the write controller 611 first sequentially shifts the interference light data held in the plurality of line memories 613 in the FIFO memory 601. Thereafter, the write controller 611 transfers the interference light data for one line held in the buffer memory 612 to the # 0 line memory 613. Thus, the interference light data held in the # 7 line memory 613 is discarded, and the interference light data held in the # 0 to # 6 line memory 613 is moved to the # 1 to # 7 line memory 613, respectively. Then, new interference light data is written into the # 0 line memory. At this time, the write controller 611 outputs a write signal indicating that new interference light data has been written to the FIFO memory 601 to the selector control unit 621.

  In this embodiment, the FIFO memory 601 has a configuration including eight line memories 613, but the number of line memories is not limited to this. However, if the number of line memories 613 is too large, the image may be rotated when the difference between the encoder pulse 412 and the wavelength sweep synchronization pulse 411 increases. This is because when the encoder pulse 412 is generated, the difference between the direction in which the imaging core 250 faces and the position of the line of the interference light data to be read out increases. If the number of line memories is too small, the allowable range with respect to the variation in the difference between the encoder pulse 412 and the wavelength sweep synchronization pulse 411 is narrowed, and interfering light data is likely to be skipped or duplicated.

  In the interference light data reading unit 406, the selector control unit 621 controls the selection of interference light data by the selector 622. The line memories 613 of # 0 to # 7 are connected to the input ports (IN) of # 0 to # 7 of the selector 622, respectively. The selector 622 outputs the interference light data of the selected input port from the output port (OUT) in response to the selection instruction from the selector control unit 621. The interference light data output from the selector 622 is input to the signal processing circuit 407. The signal processing circuit 407 generates line data 350 for one line using the interference light data input from the selector 622.

  FIG. 7 is a diagram illustrating input port (line memory) selection control by the selector control unit 621. The selector control unit 621 performs a selection operation by the selector 622 by controlling the pointer 701 indicating the input port to be selected based on the write signal from the write controller 611 and the encoder pulse 412 from the encoder unit 242 described above. To control. For example, when interference light data is first written into the FIFO memory 601 by the writing controller 611, unused interference light data is held in the # 0 line memory 613, and interference light data is stored in other line memories. not exist. In this state, the selector control unit 621 controls the pointer 701 to indicate the input port of # 0 as shown in FIG. As a result, the interference light data held in the # 0 line memory 613 is output from the output port of the selector. In FIG. 7, the line memory described as “read data” is in a state in which interference light data that has been read for generating line data is held, or in which no interference light data exists.

  For example, from the state shown in FIG. 7A, when reading for line data generation is not performed and three pieces of interference light data are accumulated, four unused interference lights are used as shown in FIG. 7B. Data is accumulated. As described above, every time new interference light data is held in the FIFO memory 601, the data is transferred in the line memories 613 # 0 to # 7. Therefore, in FIG. 7B, the interference light data held in the # 3 line memory 613 is the oldest unused interference light data (data held in # 0 in FIG. 7A). . As described above, the selector control unit 621 advances the pointer 701 by one in accordance with the write signal from the write controller 611 so that it points to the line memory storing the oldest unused interference light data. The pointer 701 is controlled.

  On the other hand, when the signal processing circuit 407 processes the interference light data output from the output port of the selector 622 according to the encoder pulse 412 from the encoder unit 242, the interference light data is processed data, that is, read data. It becomes. Therefore, the selector control unit 621 restores the pointer 701 to one by the generation of line data by the signal processing circuit 407 corresponding to the encoder pulse 412. For example, when the signal processing circuit 407 generates one line of data in response to the encoder pulse 412 in the state of FIG. 7B, the interference light data held in the # 3 line memory 613 becomes the read data. . Therefore, as shown in FIG. 7C, the pointer 701 is updated to indicate the input port of # 2 (# 2 line memory 613).

  As described above, under the control of the pointer 701 by the selector control unit 621, the oldest unused interference light data among the unused interference light data held in the FIFO memory 601 is output to the output port of the selector 622. Will be output. Note that the selector control unit 621 updates the pointer 701 after a predetermined time has elapsed since the detection of the encoder pulse 412. This is because the time required for the signal processing circuit 407 to read the interference light data currently output from the selector 622 is secured. Alternatively, when the signal processing circuit 407 finishes reading the interference light data to generate line data, the signal processing circuit 407 transmits a signal for updating the pointer 701 to the selector control unit 621, and the selector control unit 621 receives this signal. Therefore, the pointer 701 may be updated.

  If the wavelength sweep synchronization pulse 411 is input before the next encoder pulse 412 is input after the state shown in FIG. 7C, the state returns to the state of FIG. 7B. However, if the period of the wavelength sweep synchronization pulse 411 is longer than the period of the encoder pulse 412 and the encoder pulse 412 is input before the wavelength sweep synchronization pulse 411 is input, the FIFO as shown in FIG. Unused interference light data in the memory 601 decreases, and the pointer 701 indicates the input port of # 1. Conversely, when the period of the wavelength sweep synchronization pulse 411 is shorter than the period of the encoder pulse 412, unused interference light data in the FIFO memory 601 increases, and for example, a pointer as shown in FIG. 701 moves.

  From the above, it can be seen that whether the rotational speed of the radial scanning motor 241 is excessive or insufficient can be determined from the number of unused interference light data stored in the FIFO memory 601, that is, the position of the pointer 701. Therefore, in the present embodiment, the motor drive signal generation unit 408 acquires information related to the position of the pointer 701 from the selector control unit 621, and controls the rotational speed of the radial scanning motor 241 based on the information. For example, the motor drive signal generation unit 408 reduces the rotational speed of the radial scanning motor 241 when the number of unused interference light data stored in the FIFO memory 601 is smaller than a predetermined number (4 in this embodiment). A drive signal is generated. When the number of unused interference light data stored in the FIFO memory 601 is larger than a predetermined number (4 in this embodiment), the motor drive signal generation unit 408 determines the rotational speed of the radial scanning motor 241. A drive signal is generated to accelerate.

  Note that the rotation control of the radial scanning motor 241 based on the number of unused interference light data in the FIFO memory 601 as described above can be performed after adjusting the periods of the encoder pulse 412 and the wavelength sweep synchronization pulse 411 to some extent. desirable. Therefore, in this embodiment, when the rotation of the radial scanning motor 241 and the polygon scanner of the wavelength sweep unit 402 is started, speed adjustment is performed with the configuration shown in FIG. In FIG. 8, the motor drive signal generation unit 408 includes an up / down counter 801 and a drive control unit 802. The wavelength sweep synchronization pulse 411 from the wavelength sweep unit 402 is input to the addition input of the up / down counter 801, and the encoder pulse 412 from the encoder unit 242 is input to the subtraction input. Therefore, the output value of the up / down counter 801 is the difference between the count value of the wavelength sweep synchronization pulse 411 and the count value of the encoder pulse 412.

  The drive control unit 802 continues to reset the up / down counter 801 while the radial scanning motor 241 is stopped, and cancels the reset when the radial scanning motor 241 is started and starts counting. When the output value of the up / down counter 801 increases, the radial scanning motor 241 is accelerated, and when the output value of the up / down counter 801 decreases, the radial scanning motor 241 is decelerated. Note that acceleration and deceleration of the radial scanning motor 241 are controlled so as to be proportional to the count value of the up / down counter 801. According to the above control, when the radial scanning motor 241 is started, the radial scanning motor 241 accelerates at an increasing pace of the wavelength sweep synchronization pulse 411 from the polygon scanner. After that, when the number of pulses approaches, the pace of increase in the count value decreases, and the count value of the up / down counter 801 is stabilized when the speed becomes the same. Thus, when the count value by the up / down counter 801 falls within the predetermined range, it is determined that the periods of the wavelength sweep synchronization pulse 411 and the encoder pulse 412 coincide.

  When the drive control unit 802 determines that the periods of the wavelength sweep synchronization pulse 411 and the encoder pulse 412 coincide, the rotational speed control of the radial scanning motor 241 is changed from the control using the up / down counter 801 to the selector control unit 621. Switch to control. The drive control using the selector control unit 621 is as described above.

  The operation of the tomographic imaging apparatus 100 of the present embodiment having the above configuration will be further described with reference to the flowcharts of FIGS.

  When the start of tomographic imaging is instructed via the operation panel 112, the processing shown in FIG. 9 starts. First, in step S901, in response to an instruction from the signal processing unit 201, the wavelength sweep unit 402 of the wavelength sweep light source 203 starts to rotate the polygon scanner. Subsequently, in step S <b> 902, the radial scanning motor 241 starts rotating according to an instruction from the motor drive signal generation unit 408 of the signal processing unit 201. As described above, the motor drive signal generation unit 408 performs drive control using the output of the up / down counter 801 at the start of rotation of the radial scanning motor 241. In step S903, the motor drive signal generation unit 408 acquires the count value (output value) of the up / down counter 801 as described above, and controls the rotation of the radial scanning motor 241 so that the fluctuation of the count value falls within a predetermined range. To do. If the count value of the up / down counter 801 is stabilized, the process proceeds from step S904 to step S905, and the motor drive signal generation unit 408 uses the selector control unit 621 from the control using the up / down counter 801 to control the rotation speed. Switch to the previous control.

  In step S <b> 905, the write controller 611 acquires interference light data according to the wavelength sweep synchronization pulse 411 from the wavelength sweep unit 402, and starts a process of writing the interference light data to the FIFO memory 601. The writing process of the interference light data by the writing controller 611 will be described later with reference to the flowchart of FIG. Based on the position of the pointer 701, the selector control unit 621 has a line number of unused interference light data accumulated in the FIFO memory 601 that is half of the total number n of line memories included in the FIFO memory 601 (n / 2). It is determined whether or not. In this embodiment, since n = 8, it is determined whether unused interference light data for four lines has been accumulated. When four lines of unused interference light data are accumulated in the FIFO memory 601, the process proceeds from step S906 to step S907, and the selector control unit 621 and the signal processing circuit 407 generate line data in synchronization with the encoder pulse 412. Start. That is, reading of the interference light data from the FIFO memory 601 using the pointer 701 described above is started.

  Next, in step S908, the motor drive signal generation unit 408 acquires the number N of unused interference light data lines in the FIFO memory 601. The number N of lines is acquired from the position of the pointer 701 notified from the selector control unit 621 as described above. Then, the motor drive signal generation unit 408 compares the number of lines N with half the number of lines n of the line memory included in the FIFO memory 601. As described above, since n = 8 in the present embodiment, the number N of lines of unused interference light data accumulated and 4 (= n / 2) are compared.

  When the number of lines N> 4, it means that the period of the encoder pulse 412 is long with respect to the wavelength sweep synchronization pulse 411 and unused interference light data tends to increase. Therefore, the process proceeds from step S909 to step S910, and the motor drive signal generation unit 408 accelerates the rotation of the radial scanning motor 241. On the other hand, when the number of lines N <4, it means that the period of the encoder pulse 412 is short with respect to the wavelength sweep synchronization pulse 411 and unused interference light data tends to decrease. Accordingly, the process proceeds from step S911 to step S912, and the motor drive signal generation unit 408 decelerates the rotation of the radial scanning motor 241. When N = 4, it is determined that the relationship between the periods of the wavelength sweep synchronization pulse 411 and the encoder pulse 412 is appropriate, and the rotational speed of the radial scanning motor 241 is maintained as it is. The degree of acceleration / deceleration may be set according to the magnitude of the difference between the number of unused interference light data lines N and n / 2, or may be constant regardless of the magnitude of the difference.

  FIG. 10A is a flowchart for explaining the control of writing interference light data to the FIFO memory 601 by the write controller 611. The write controller 611 waits for the generation of the wavelength sweep synchronization pulse 411 in step S1001, and when detecting the wavelength sweep synchronization pulse 411, the writing controller 611 starts accumulation of the interference light signal using the buffer memory 612 in step S1002. Thereafter, when the interference light signals for one line (2048 interference light signals) are accumulated, the writing controller 611 advances the processing from step S1003 to step S1004. In step S1004, the write controller 611 moves the respective interference light data stored in the # 0 to # 6 line memories 613 of the FIFO memory 601 to the # 1 to # 7 line memories 613. In step S1005, the write controller 611 writes new one-line interference light data to the FIFO memory 601. That is, the write controller 611 writes the interference light data held in the buffer memory 612 into the # 0 line memory 613.

  In step S1006, the write controller 611 outputs a write signal to the selector control unit 621 to advance the position of the pointer 701 of the selector control unit 621 as described above with reference to FIG. The selector control unit 621 advances the pointer 701 by one according to the write signal. As a result, the pointer 701 is controlled so as to continue pointing to the unused interference light data that has been pointed to. And a process returns to step S1001 and the above-mentioned process is repeated.

  FIG. 10B is a flowchart for explaining the operation of reading the interference light data by the selector control unit 621 and the signal processing circuit 407. In step S1021, the selector control unit 621 and the signal processing circuit 407 wait for the generation of the encoder pulse 412. When detecting the encoder pulse 412, the signal processing circuit 407 reads the interference light data output from the selector control unit 621 in step S1022, and generates line data. That is, the selector control unit 621 and the signal processing circuit 407 generate line data using the oldest unused interference light data stored in the FIFO memory 601 every rotation of the imaging core (drive shaft) by a predetermined angle. The interference light data used to generate the line data becomes used. In step S1023, the selector control unit 621 performs a delay that allows the signal processing circuit 407 to read the interference light data, and then returns the position of the pointer 701 by one as described with reference to FIG. . And a process returns to step S1021 and the above-mentioned process is repeated.

  As described above, according to the present embodiment, writing and reading of interference light data (line data) while finely adjusting the rotational speed of the radial scanning motor 241 according to the number of unused interference light data lines in the FIFO memory 601. Generation). For this reason, the writing period and the reading period of the interference light data are appropriately maintained, and even when the imaging core is rotated at a higher rotational speed, resolution deterioration due to duplicate reading or the like is less likely to occur.

  In the above embodiment, the configuration for controlling the rotational speed of the radial scanning motor 241 has been described. However, the sweep period of the wavelength sweep unit 402 (that is, the rotational speed of the polygon scanner) may be controlled. In that case, for example, in step S910, the rotational speed of the polygon scanner is decelerated (the sweep cycle is lengthened), and in step S912, the rotational speed of the polygon scanner is accelerated (the sweep cycle is shortened). That is, the rotational speed of the radial scanning motor 241 may be controlled so as to accelerate and decelerate relatively with respect to the wavelength sweep cycle.

  In the above embodiment, the rotational speed of the radial scanning motor 241 is accelerated or decelerated depending on whether the number of lines of unused interference light data exceeds or falls below half of the number of lines of the line memory included in the FIFO memory. It is not essential. That is, the rotational speed may be controlled according to whether the number of unused interference light data lines exceeds or falls below a predetermined number. Therefore, in step S906, it waits until unused interference light data is accumulated up to a predetermined number used for switching acceleration / deceleration of the radial scanning motor 241. In addition, since the rotational speed of the radial scanning motor 241 is controlled so that a predetermined number of unused interference light data is accumulated in the FIFO memory 601, it waited for a predetermined number of unused interference light data to be accumulated. Alternatively, the reading of interference light data (generation of line data) may be started. Further, the reading of interference light data (generation of line data) may be started after the accumulation of unused interference light data having a line number smaller than a predetermined number or a line number larger than the predetermined number.

DESCRIPTION OF SYMBOLS 100: Tomography apparatus 101: Optical probe part 102: Pull back part 201: Signal processing part 203: Wavelength sweep light source 240: Rotation drive device 241: Radial scanning motor 242: Encoder part 401: Light source 402: Wavelength sweep part 405: Interference Optical data holding unit 406: Interference light data reading unit 407: Signal processing circuit 408: Motor drive signal generation unit

Claims (10)

A cross-section by generating measurement light and reference light using light output from a light source that repeats wavelength sweep, and detecting interference light between the reflected light of the measurement light and the reference light acquired via an imaging core A tomography apparatus for acquiring an image,
A FIFO memory that stores a plurality of lines of interference light data obtained based on the interference light, and discards the oldest interference light data in response to writing of new interference light data;
Writing means for writing interference light data obtained from the interference light into the FIFO memory as unused interference light data in synchronization with repetition of wavelength sweep of the light source;
Generation means for generating line data using the oldest unused interference light data stored in the FIFO memory every rotation of the imaging core by a predetermined angle, and the interference used for generating the line data here Optical data is treated as used,
A tomographic imaging apparatus comprising: first control means for controlling a rotation speed of the imaging core or a period of the wavelength sweep based on the number of unused interference light data stored in the FIFO memory. .   The tomography apparatus according to claim 1, wherein the interference light data is interference light intensity data obtained during one wavelength sweep of the light source.   The first control means decelerates the rotation speed when the number of unused interference light data stored in the FIFO memory is smaller than a predetermined number, and unused interference light stored in the FIFO memory. The tomography apparatus according to claim 1, wherein the rotation speed is accelerated when the number of data is larger than the predetermined number.   4. The tomography according to claim 3, wherein the generation unit starts generating line data for each rotation of the predetermined angle after the predetermined number of unused interference light data is accumulated in the FIFO memory. 5. Image taking device.   The tomography apparatus according to claim 3 or 4, wherein the predetermined number is half of the total number of interference light data stored in the FIFO memory. Second control means for controlling the rotational speed based on a difference between a period of a pulse signal synchronized with the wavelength sweep in the light source and a period of a pulse signal generated every rotation of the predetermined angle of the imaging core;
The apparatus further comprises switching means for controlling the rotation speed by the second control means at the start of rotation of the imaging core and then switching the rotation speed to be controlled by the first control means. The tomography apparatus according to any one of 1 to 5.   The second control means controls the rotation speed based on a difference between a count value of a pulse signal synchronized with the wavelength sweep and a count value of a pulse signal generated every rotation of the imaging core at the predetermined angle. The tomographic imaging apparatus according to claim 6, wherein   The switching means switches from the control of the rotational speed by the second control means to the control of the rotational speed by the first control means when the variation of the difference falls within a predetermined range. Item 8. The tomographic imaging apparatus according to Item 6 or 7. A cross-section by generating measurement light and reference light using light output from a light source that repeats wavelength sweep, and detecting interference light between the reflected light of the measurement light and the reference light acquired via an imaging core A method for controlling a tomographic imaging apparatus for acquiring an image, comprising:
A writing step of writing the interference light data obtained from the interference light into the FIFO memory as unused interference light data in synchronization with the repetition of the wavelength sweep of the light source, and the FIFO memory based on the interference light Store multiple lines of the obtained interference light data, discard the oldest interference light data according to the writing of new interference light data,
A generation step of generating line data using the oldest unused interference light data stored in the FIFO memory every rotation of the imaging core by a predetermined angle, and the interference used for generating the line data here Optical data is treated as used,
And a control step of controlling the rotational speed of the imaging core or the period of the wavelength sweep based on the number of unused interference light data stored in the FIFO memory. Method.   The program for making a computer perform each process of the control method described in Claim 9.

Images