JP5451485B2 - Optical coherence tomography apparatus and method for operating the same - Google Patents

Description

  The present invention relates to an optical coherence tomographic image forming apparatus and a control method therefor.

  Conventionally, optical coherent tomography (OCT) for diagnosis of arteriosclerosis, preoperative diagnosis during endovascular treatment with high-function catheters such as balloon catheters and stents, and confirmation of postoperative results Is used.

  In an optical coherence tomography device, a catheter containing an optical lens and optical fiber with an optical mirror attached at the tip is inserted into a blood vessel, light is irradiated into the blood vessel while rotating the optical mirror, and reflection from living tissue is performed. Radial scanning is performed to receive light. A cross-sectional image of the blood vessel is drawn based on the reflected light obtained by the radial scanning. More specifically, the optical coherence tomographic image forming apparatus divides light output from the light source inside the apparatus into measurement light and reference light. The measurement light is emitted in the body cavity through the optical fiber, and scattered light (reflected light) reflected from the living tissue is received through the same optical fiber. By making this reflected light interfere with the reference light inside the apparatus, the intensity of the measuring light from the same optical path length as the reference light, that is, the intensity of the reflected light can be obtained. Here, the optical path length of the reference light is scanned by moving the position of the mirror that reflects the reference light by the mirror in the apparatus back and forth, and the interference light is obtained in synchronization therewith, so that the reflection intensity in the depth direction is increased. Distribution can be obtained. Furthermore, a blood vessel cross-sectional image can be drawn by the radial scanning.

  On the other hand, an optical coherence tomographic image forming apparatus using wavelength sweeping has been developed as an improved type of the optical coherent tomographic image forming apparatus. The optical coherence tomographic image forming device using the wavelength sweep repeatedly sweeps the wavelength of the emitted light, so that the measurement light and the reference can be obtained from the frequency distribution of the obtained interference light without scanning the optical path length of the reference light. A reflection intensity distribution in the depth direction is obtained with respect to a point having the same optical path difference.

JP 2009-128074 A

  As described above, the optical coherence tomographic image forming apparatus renders a cross-sectional image of a blood vessel obtained by receiving backscattered light from a living tissue. At this time, the scattered light from the living body is very weak light of about −80 dB with respect to the emitted light. Therefore, a sensitive detection circuit having a sensitivity of 90 dB to 110 dB is configured using an optical interference technique, and an image is drawn. Considering the appearance in 256 gradation display on the screen, it is considered that the signal dynamic range is about 30 to 60 dB. If the observation target is only a living body, there is no problem if the optical coherence tomographic image forming apparatus is configured under the above conditions.

  However, for example, when a coronary artery in which a net-like metal tube called a stent is indwelled for treatment is set as an object to be imaged by an optical coherence tomography apparatus, the following problems arise. In other words, in this case, when light is irradiated obliquely on the metal (stent), a signal having a strength not much different from that of the living body is reflected by the roughness of the metal surface and the scattered light from the protein attached to the surface. . However, if the metal is irradiated with light at substantially right angles, extremely large light is reflected as compared with the reflected light from the living body. The difference in magnitude between such reflected light and scattered light from the living body actually reaches 100,000 to 1 million times. In an optical coherent tomographic image forming apparatus using wavelength sweep, in the process of obtaining a vascular tomographic image from interfering light, the interference signal converted into an electric signal is sampled and AD converted, and calculation to a frequency domain such as FFT is performed. There is a need. Since the width of the input voltage is limited at the time of sampling, (1) a method of determining the width of amplification in the photoelectric conversion unit (optical detector) according to the largest signal, or (2) on the premise that the large signal is shaken off, One of the methods for setting the optimum sensitivity for the signal level to be observed is used.

  Since the signal intensity of the stent is not important information, it is desired to determine the input width in sampling so that a biological signal can be detected with high sensitivity. However, in the case of a wavelength swept light source, a discontinuous point occurs when a large signal sways out of the input width, so that the noise level of line data after FFT is greatly increased. As a result, the vascular tomographic image drawn by the optical coherence tomographic image forming apparatus using the wavelength swept light source is observed as radial noise as shown in FIG. Such radiation noise may interfere with diagnosis. On the other hand, if the width of the input voltage in sampling is increased in order to eliminate this, the signal of the blood vessel tissue that is originally desired to be accurately drawn becomes only 1 / 100,000 to 1 / 1,000,000 of the input voltage width. There is a problem that a large signal is buried in noise.

  The present invention has been made in view of the above problems, and in a wavelength-sweep optical coherence tomographic image forming apparatus, the appearance of radial noise due to a stent or the like in an image is suppressed, and a weak biological signal is highly sensitive. It aims to make it possible to detect.

In order to achieve the above object, an optical coherence tomographic image forming apparatus according to an aspect of the present invention comprises the following arrangement. That is,
The light output from the wavelength swept light source inside the device is divided into measurement light and reference light, and the measurement light is emitted into the body cavity while rotating the irradiation direction through the probe inserted into the body, and the reflected light and the above-mentioned light An optical coherence tomographic image forming apparatus for generating a cross-sectional image in the body cavity based on the light intensity of interference light obtained from reference light,
Photoelectric conversion means for converting the light intensity of the interference light into an electrical signal;
Logarithmic amplification means for logarithmically amplifying the output signal of the photoelectric conversion means;
AD conversion means for discretely sampling the output signal of the logarithmic amplification means and converting it into digital interference data;
The digital interference data obtained by the AD conversion means is divided into irradiation directions for each line direction, and the line interference data is demodulated by performing inverse logarithmic conversion at a magnification according to the signal intensity for each line interference data. Demodulating means,
Constructing means for constructing a tomographic image by converting the line interference data demodulated by the demodulating means into frequency domain data.

  According to the present invention, in the optical coherence tomographic image forming apparatus, it is possible to suppress the appearance of radial noise due to a stent or the like, and it is possible to detect a very weak biological signal with high sensitivity.

The figure which shows the external appearance structure of the diagnostic imaging apparatus concerning embodiment. FIG. 2 is a block diagram showing a functional configuration of the diagnostic imaging apparatus 100. The block diagram which shows the function structure of a signal processing part. The figure explaining irradiation of measurement light and taking in reflected light about rotation scanning and axial movement by an optical probe in a blood vessel. The schematic diagram for demonstrating operation | movement of the optical probe in the blood vessel. The figure which shows an example of the relationship between the input value of a logarithmic amplifier, and an output error. The figure explaining the process to FFT of the electrical signal obtained by photoelectrically converting interference light by embodiment. The flowchart explaining a linear demodulation process. The figure which shows the example of the image which radial noise generate | occur | produced.

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

[First Embodiment]
FIG. 1 is a diagram showing a system configuration and an external configuration of a wavelength-swept optical coherence tomographic image forming apparatus (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 body cavity such as a blood vessel, and measures the state inside the body cavity using an imaging core. The scanner / pullback unit 102 is configured to be detachable from the optical probe unit 101, and is driven by a built-in motor to perform a radial operation of the imaging core in the optical probe unit 101 (described in detail with reference to FIGS. 4 and 5). ).

  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-body 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 block diagram illustrating a functional configuration of the diagnostic imaging apparatus 100 which is an optical coherence tomographic image forming apparatus using wavelength sweeping.

  208 is a light source, and Swept Laser is used. The light source 208 is a type of extended-cavity laser that includes a light source unit (208a) having an optical fiber 217 coupled to an SOA 216 (semiconductor optical amplifier) and a ring 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. The light whose wavelength is selected here 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 light source 208 output from the coupler 214 is incident on one end of the single mode fiber 230 and transmitted to the tip surface side. The single mode fiber 230 is optically coupled to the single mode fiber 231 at an intermediate optical coupler unit 226. Accordingly, the light from the light source 208 is split into two by the optical coupler unit 226, one being transmitted to the single mode fiber 230 as measurement light and the other being transmitted to the single mode fiber 231 as reference light.

  A scanner / pullback unit 102 is provided on the tip side of the optical coupler unit 226 of the 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 single mode fiber 235 in the optical rotary joint 203 is detachably connected to the single mode fiber 236 of the optical probe unit 101 via the adapter 202. As a result, the light (measurement light) from the light source 208 is transmitted to the 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 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 captured by the imaging core 201, returns to the single mode fiber 230 side through the reverse optical path, and a part of the reflected light is single mode fiber 237 by the optical coupler unit 226. Move to the side. In the single mode fiber 237, the reflected light is mixed with reference light (described later) that travels through the single mode fiber 231, and emitted from one end of the single mode fiber 229 as interference light. This interference light is received by a photodetector 219 (for example, a photodiode).

  Note that the rotating portion side of the optical rotary joint 203 is rotationally driven by a radial scanning motor 205 of the 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.

  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 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 single mode fiber 231 and the collimator lens 234 are provided on a uniaxial stage 232 that is movable as indicated by an arrow 233 in the optical axis direction, and form an 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 by the uniaxial stage 232. .

  The reflected light is input to the 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 mixed with the light (reflected light) from the single mode fiber 230 side by the optical coupler unit 226 provided in the middle of the single mode fiber 231. Thus, it becomes interference light and is received by the photodetector 219. The light received by the photodetector 219 is photoelectrically converted, amplified by the amplifier 220a, and then input to the logarithmic amplifier 220b. The logarithmic amplifier 220b amplifies the electric signal obtained by photoelectrically converting the interference light and amplified by the amplifier 220 logarithmically. The output of the logarithmic amplifier 220b 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 a cross-sectional image 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 218. The signal processing unit 223 controls the position of the uniaxial stage 232 via the optical path length adjusting unit control unit 218. 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.

  FIG. 4A is a diagram illustrating a state in which the image core 201 of the optical fiber unit 101 is inserted into a body cavity (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 light source 208 is irradiated to the body cavity by the optical mirror 401 through the optical fiber 236. 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 405 direction by the radial scanning motor 205.

  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, transmission of the measurement light / reception of the reflected light by the imaging core 201 is performed while the imaging core 201 proceeds in the direction of the arrow 406 in the blood vessel.

  Next, the signal processing unit 223 will be described. FIG. 3 is a block diagram illustrating a configuration example of the signal processing unit 223.

  As described above, the reflected light input through the optical fiber 230 is combined with the reference light by the optical coupler unit 226 to generate interference light. The photodetector 219 converts the intensity of the interference light (interference intensity) into an electrical signal and outputs it to the subsequent amplifier 220a. The amplifier 220a amplifies the electrical signal output from the photodetector 219 and outputs it to the logarithmic amplifier 220b. The logarithmic amplifier 220b amplifies the electrical signal amplified by the amplifier 220a logarithmically and outputs the obtained signal to the demodulator 221. The output of the demodulator 221 is input to the A / D converter 222. The A / D conversion unit 222 samples the input signal for 2048 points, 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 a series of operations of each unit described above.

  FIG. 7 is a diagram showing a functional configuration related to processing from conversion of interference light into an electrical signal to generation of line data by FFT according to the present embodiment. In this embodiment, a logarithmic amplifier 220b is provided that logarithmically amplifies the output signal of the photodetector 219 that performs photoelectric conversion to convert interference light into an electrical signal. Such logarithmic amplifiers are often used to amplify signals with a strong and weak range, but care must be taken because the accuracy may deteriorate depending on the amplification range. FIG. 6 shows the input / output characteristics of a typical logarithmic amplifier. From this input / output characteristic, it can be seen that when the input current is 10 nA or less and 1 mA or more, the output error increases and the characteristics are greatly deteriorated. Therefore, when logarithmic amplification is performed in optical coherence tomographic image formation, the sensitivity (amplification characteristic) of the amplifier 220a is set so that a signal by reflected light from the living body (hereinafter referred to as a biological signal) is in an accurate region. . In the case of FIG. 6, the sensitivity of the amplifier 220 a is set so that the biological signal enters the range of the input range 610. In that case, the accuracy of reproduction of the amplitude is poor for reflection from a stent that is 100,000 times or more larger than the biological signal. However, since the existence of the stent signal only needs to be confirmed, there is no problem even if the error is large.

  That is, an electrical signal corresponding to the light intensity of the interference light corresponding to the reflected light from the living body is in an input range (input range 610 in the input / output characteristic 720) in which the output error in the logarithmic amplifier 220b is within a predetermined range. An amplification characteristic 710 (sensitivity) of the amplifier 220a is set. The amplifier 220a linearly amplifies the output signal of the photodetector 219 based on this amplification characteristic and provides it to the logarithmic amplifier 220b. For example, when the error characteristic of the logarithmic amplifier 220b is as shown in FIG. 6, the amplifier 220a amplifies the light intensity signal of the interference light corresponding to the reflected light from the living body within the input range 610 of 10 nA to 1 mA. .

  The signal logarithmically amplified by the logarithmic amplifier 220 b is converted into digital data by the AD converter 222 and supplied to the signal processing unit 223. Due to logarithmic amplification by the logarithmic amplifier 220b, the entire range of the interference data of the line where the metal such as the stent is present becomes the input level range of the AD converter 222, and the continuity of the interference data is maintained. The line memory unit 301 divides the digital data obtained by the A / D converter 222 for each irradiation direction and provides it to the line data generation unit 302 as digital data for each line. In the line data generation unit 302, since the signal is logarithmically amplified in the logarithmic amplifier 220b, it is necessary to demodulate to a linear signal before performing FFT. The linear demodulator 701 eliminates the modulation by the logarithmic amplifier from the digital data by performing inverse logarithmic conversion on the digital data for each line at a magnification according to the signal strength, and demodulates the digital data. Hereinafter, the linear demodulation processing by the linear demodulation unit 701 will be described with reference to the flowchart of FIG.

  The linear demodulator 701 acquires one line of digital data (line data before demodulation and FFT processing) from the line memory unit 301 (S801), and data exceeding a predetermined signal range is included in the acquired interference data of one line. It is determined whether or not it exists (S802). Here, the data exceeding the predetermined signal range is data that exceeds the predetermined signal range when such data is demodulated (when inverse logarithmic conversion is performed). If such data exists, discontinuous points occur in the demodulated data, and the image deteriorates. Therefore, for interference data that has data that spills out of the signal range, it is determined that there is direct reflection from the metal such as a stent in that line, and the level of interference data in that line is not swayed even if demodulated. And then demodulate (S804, S805, S806). For example, the attenuation rate is set so that the maximum value of interference data for one line falls within a predetermined signal range after demodulation, the attenuation rate set for the entire interference data for the line is applied, and interference data for the line is applied. Even if the signal is demodulated, it falls within a predetermined signal range. For example, when the maximum value in one line of interference data is Smax and the predetermined signal range is 0 to R, the attenuation rate is calculated as R / Smax. The attenuation rate can be arbitrarily set as long as it is larger than this value (R / Smax). On the other hand, if there is no data that can swing the signal range, demodulation is performed using the interference data of the line as it is (S803: NO → S806). The above processing is executed until there is no interference data of unprocessed lines (S807).

  In the above processing, signals of a certain level or higher are demodulated with the same intensity through S803 to S805. However, although it is the same here, a demodulation method such as decreasing the magnification stepwise at the time of demodulation is also conceivable. That is, the attenuation rate at the time of demodulation is set so that the demodulated signal level falls within a predetermined level according to the signal strength of the interference data of each line. As a result, the line data having a signal that diverges the input range is attenuated below the input range and demodulated, and the signal having a small amplitude level is demodulated as it is. In the line data generation unit 302, the above-described FFT is performed on the data of each line thus obtained, and data in the depth direction is generated.

  As described above, according to the first embodiment, by performing logarithmic amplification on a signal having interference intensity, even when a signal having an extremely large interference intensity compared to a biological signal is input, While a biological signal is amplified, the level of an extremely large interference signal can be suppressed. Therefore, AD conversion can be performed while maintaining the continuity of the signal. Also, when demodulating the logarithmically modulated state into a linear state, for the line where the demodulated signal level exceeds a predetermined value, the signal level after demodulation is predetermined by attenuating the entire line. It is kept within the value. Through the above processing, even if interference light is extremely generated by reflected light from a metal such as a stent, the signal is converted to the frequency domain while maintaining the continuity of the signal without damaging the biological signal. be able to. Therefore, in the wavelength-swept optical coherence tomographic image forming apparatus, it is possible to suppress the appearance of radial noise due to a stent or the like in the image. It is also possible to detect a weak biological signal with high sensitivity.

[Second Embodiment]
The logarithmic amplifier 220b generally has a temperature-sensitive characteristic, and is assumed to be affected by heat generated from various components inside the apparatus. Therefore, in the second embodiment, the temperature inside the optical coherence tomographic image forming apparatus is monitored and the accuracy of the logarithmic amplifier 220b is corrected. Specifically, a temperature measurement unit (not shown) is provided in the apparatus, and the line data generation unit 302 monitors the apparatus temperature from the temperature measurement unit. In addition, the line data generation unit 302 has a correction table in which correction coefficients set so that the amplification factor is constant regardless of the temperature are registered in association with the temperature based on the relationship between the temperature and the amplification factor in the logarithmic amplifier 220b. Are prepared in advance. Then, a correction coefficient corresponding to the apparatus temperature is acquired from this correction table, and the correction of the logarithmic amplifier is performed by correcting the entire line data before demodulation with the correction coefficient. Other points are the same as in the first embodiment.

  According to the second embodiment as described above, it is possible to reduce the influence of the characteristic variation due to the temperature of the logarithmic amplifier 220b, and to always obtain a high-accuracy and high-quality tomographic image.

[Third Embodiment]
In the second embodiment, the influence on the temperature of the logarithmic amplifier 220b is reduced by monitoring the temperature of the apparatus and selecting a correction coefficient. In the third embodiment, the characteristic variation (amplification) of the logarithmic amplifier 220b using the fluctuation of the reference signal obtained by amplifying the electric signal obtained by inputting only the reference light to the photodetector 219 by the logarithmic amplifier 220b. Rate fluctuation).

  More specifically, the amplitude of the reference signal is recorded during manufacturing or maintenance, and this is used as a reference. Then, the reference signal amplitude measured during tomographic image measurement is compared with the reference to determine a correction coefficient. Correction is performed on the line data before demodulation using the correction coefficient thus determined. That is, in the second embodiment, the amplification factor of the logarithmic amplifier 220b is estimated from the temperature, whereas in the third embodiment, the amplification factor of the logarithmic amplifier 220b is estimated from the amplitude of the reference signal. For example, it is assumed that the relationship that the amplitude of the reference signal becomes 1 Vp-p when the amplification factor of the logarithmic amplifier 220b is 1000 times is obtained from the measurement of the reference signal at the time of manufacture or maintenance. Then, when the amplitude of the reference signal measured at the time of tomographic image formation is, for example, 0.9 Vp-p, the line data generation unit 302 estimates that the amplification factor fluctuates 900 times, and copes with this. Line data is corrected by setting a correction coefficient.

  According to the third embodiment as described above, it is not necessary to provide a temperature measurement unit or a correction table, so that temperature correction can be performed more easily than in the second embodiment. Further, when the amplification factor of the logarithmic amplifier 220b fluctuates due to factors other than temperature, correction corresponding to this can be performed.

Claims (6)

The light output from the wavelength swept light source inside the device is divided into measurement light and reference light, and the measurement light is emitted into the body cavity while rotating the irradiation direction through the probe inserted into the body, and the reflected light and the above-mentioned light An optical coherence tomographic image forming apparatus for generating a cross-sectional image in the body cavity based on the light intensity of interference light obtained from reference light,
Photoelectric conversion means for converting the light intensity of the interference light into an electrical signal;
Logarithmic amplification means for logarithmically amplifying the output signal of the photoelectric conversion means;
AD conversion means for discretely sampling the output signal of the logarithmic amplification means and converting it into digital interference data;
The digital interference data obtained by the AD conversion means is divided into irradiation directions for each line direction, and the line interference data is demodulated by performing inverse logarithmic conversion at a magnification according to the signal intensity for each line interference data. Demodulating means,
An optical coherence tomographic image forming apparatus comprising: construction means for constructing a tomographic image by converting line interference data demodulated by the demodulating means into frequency domain data. The demodulating means includes
Detecting means for detecting line interference data in which data exceeding a predetermined signal level exists by the demodulation;
Attenuating means for attenuating the entire line interference data with respect to the line interference data detected by the detecting means so that all data after demodulation falls within the predetermined signal level,
Said for the detected line interference data detecting means the result of the attenuated inverse logarithmic transformation by the attenuating means, wherein the line interference data that was not detected by the detecting means for inverse logarithmically converting the line interference data The optical coherence tomographic image forming apparatus according to claim 1.   The output signal of the photoelectric conversion means is linearly amplified so that an electric signal corresponding to the light intensity of the interference light corresponding to the reflected light from the living body becomes an input range in which the output error is a predetermined range in the logarithmic amplification means. The optical coherence tomographic image forming apparatus according to claim 1, further comprising: linear amplification means provided to the logarithmic amplification means. A correction table that registers the relationship between temperature and the correction coefficient of the logarithmic amplification means;
A temperature measuring means for measuring the temperature inside the apparatus;
The demodulating means acquires a correction coefficient from the correction table based on the temperature measured by the temperature measuring means, and corrects the line interference data before performing the inverse logarithmic conversion using the correction coefficient. The optical coherence tomographic image forming apparatus according to claim 1, wherein the optical coherence tomographic image forming apparatus is characterized. The demodulating means includes
By monitoring the fluctuation of the reference signal obtained from the logarithmic amplification means by supplying only the reference light to the photoelectric conversion means, the error of the logarithmic amplification in the logarithmic amplification means is estimated from the fluctuation, and the estimation result of the error The optical coherence tomographic image forming apparatus according to claim 1, further comprising: a correcting unit that corrects the line interference data before the inverse logarithmic transformation is performed based on the above. The light output from the wavelength swept light source inside the device is divided into measurement light and reference light, and the measurement light is emitted into the body cavity while rotating the irradiation direction via a probe for insertion into the body, and the reflected light and An operation method of an optical coherence tomographic image forming apparatus that generates a cross-sectional image in the body cavity based on light intensity of interference light obtained from the reference light,
A photoelectric conversion step in which the photoelectric conversion means of the optical coherence tomographic image forming apparatus converts the light intensity of the interference light into an electrical signal;
A logarithmic amplification step in which the logarithmic amplification means of the optical coherence tomographic image forming apparatus logarithmically amplifies the output signal obtained by the photoelectric conversion step;
An AD conversion step in which the AD conversion means of the optical coherence tomographic image forming apparatus discretely samples the output signal obtained by the logarithmic amplification step and converts it into digital interference data;
The demodulating means of the optical coherence tomographic image forming apparatus divides the digital interference data obtained in the AD conversion process into line interference data for each irradiation direction, and the line interference data is multiplied by a magnification corresponding to the signal intensity. A demodulation step of demodulating the line interference data by performing inverse logarithmic transformation;
The optical coherence tomographic image forming apparatus has a construction step of constructing a tomographic image by converting the line interference data demodulated in the demodulation step into frequency domain data. Method of operating the forming device.