JP5289220B2 - Imaging apparatus using optical coherence tomography, control method, and program - Google Patents

Description

  The present invention relates to an imaging apparatus using optical coherence tomography, a control method, a program, and a storage medium, and in particular, an imaging apparatus using optical coherence tomography using an interference optical system used in the medical field, a control method, a program, And a storage medium.

Currently, there are various ophthalmic devices using optical devices. For example, an anterior ocular segment photographing machine, a fundus camera, a confocal laser scanning ophthalmoscope (SLO), or the like. Among them, an imaging apparatus using optical coherence tomography (OCT) (hereinafter also referred to as an OCT apparatus) can obtain a tomographic image (tomographic image) of an inspection object with high resolution. It is becoming an indispensable device for specialized outpatients.

  In the OCT apparatus, a low coherent light source is used as a light source. Light from the light source is divided into measurement light and reference light via a split optical path such as a beam splitter. The measurement light is irradiated onto an object such as an eye through the measurement optical path, and the return light is guided to the detection position through the detection optical path. The return light is reflected light or scattered light including information on the interface with respect to the light irradiation direction of the inspection object. The reference light is guided to the detection position via the reference light path. Interference light obtained by interference between the return light and the reference light is input to the detection position. Specifically, the interference light is decomposed into wavelength units via an optical element such as a spectroscope (after obtaining the wavelength spectrum of the interference light in a lump), and then a photoelectric sensor such as a CCD line sensor or a CMOS line sensor. Guided to the conversion element. And the intensity | strength of interference light is converted into an analog electric signal for every wavelength by a photoelectric conversion element. Further, the converted analog electric signal is converted into a digital electric signal by an A / D converter. The converted digital electrical signal is subjected to Fourier transform processing or the like. Thereby, a tomographic image of the inspection object is obtained. In general, an OCT apparatus that obtains a tomographic image of an object to be inspected from wavelength spectra obtained collectively is called an SD-OCT (Spectral Domain OCT) apparatus.

In the OCT apparatus, the intensity of the interference component of the interference light is significantly smaller than the intensity of the entire interference light. Specifically, when an interference light intensity (analog electric signal; photoelectric conversion signal) is converted into a digital electric signal using an A / D converter having a dynamic range of 10 bits (1024 gradations), an interference component in the interference light The intensity is about 100 tones. That is, the size is about 10% of the dynamic range of the A / D converter. Therefore, if the photoelectric conversion signal of the interference light is A / D converted as it is, the digital signal level (the level of the digital electrical signal) of the interference component necessary for obtaining the tomographic image is remarkably reduced, and the obtained tomographic image is The image will have poor tonality.
As a conventional technique in view of such a problem, there is a technique in which the power spectrum of interference light is integrated over the entire frequency band, and the measurement range of the A / D converter is set according to the integrated value (Patent Document 1).

  By the way, in the SD-OCT apparatus for observing the state of the fundus, in view of the absorption characteristics and reflection characteristics of the eye tissue and the resolution for acquiring tomographic information of the fundus such as the retina, 815 to 865 nm It is preferable to use light in the wavelength range. In light sources that are currently available on the market, the light in such a wavelength region has a wavelength characteristic with different intensities for each wavelength, as shown by a waveform 1301 in FIG. Then, the waveform of the interference light obtained using such light is as shown by a waveform 1302 in FIG. In FIG. 4A, in order to easily understand the state of the interference light, the light intensity of the interference component is increased and the wave number is decreased.

If the measurement range of the A / D converter is set by the method disclosed in Patent Document 1 based on the interference light as shown by the waveform 1302, the above-described intensity variation for each wavelength is not taken into consideration. In some cases, the dynamic range cannot be used effectively. This makes it difficult to obtain a good fundus tomographic image.

Japanese Patent Laid-Open No. 5-60615

  Therefore, an object of the present invention is to provide a technique that can effectively use the dynamic range of an A / D converter and can obtain a good tomographic image.

The imaging apparatus of the present invention divides light from a light source into measurement light and reference light, and generates interference light caused by reference light and return light returned from the inspection object when the measurement light is irradiated onto the inspection object. An object to be inspected based on a digital electric signal obtained by converting the intensity for each wavelength of the interference light into an analog electric signal by the photoelectric conversion means that has acquired the intensity for each wavelength, and converting the analog electric signal by the A / D conversion means. of a to that imaging device acquires a tomographic image, an acquisition unit for acquiring the intensity of each wavelength of the reference light to the photoelectric conversion means, analog electrical signals by the photoelectric conversion means is converted from the intensity of each wavelength of the reference beam the value of each wavelength of the reference optical signal is the digital electrical signals obtained by the a / D conversion means, so that a central portion of the input range of the a / D converting means, output from the photoelectric conversion means For each wavelength of analog electrical signal Or has a adjusting means for adjusting the input range of each wavelength of the A / D converting means.

The control method of the present invention divides the light from the light source into measurement light and reference light, and the interference light caused by the return light returned from the inspection object and the reference light when the measurement light is irradiated onto the inspection object. An object to be inspected based on a digital electric signal obtained by converting the intensity for each wavelength of the interference light into an analog electric signal by the photoelectric conversion means that has acquired the intensity for each wavelength, and converting the analog electric signal by the A / D conversion means. analog a method of controlling to that imaging device acquires a tomographic image, which has been converted and the step for obtaining the intensity of each wavelength of the reference light to the photoelectric conversion means, from the intensity of each wavelength of the reference light by the photoelectric conversion means Output from the photoelectric conversion means so that the value for each wavelength of the reference light signal, which is a digital electric signal obtained by converting the electric signal by the A / D conversion means, is at the center of the input range of the A / D conversion means. Analog electrical signal It has a step of adjusting the input range of each wavelength value of each wavelength or A / D conversion means, and.

The program of the present invention divides the light from the light source into measurement light and reference light, and the wavelength of interference light due to the return light returned from the inspection object when the measurement light is irradiated onto the inspection object and the reference light The photoelectric conversion means that has acquired the intensity for each wavelength converts the intensity for each wavelength of the interference light into an analog electric signal, and the analog electric signal is converted by the A / D conversion means based on the digital electric signal obtained from the test object. to be that an imaging device acquiring a tomographic image, the photoelectric conversion means to acquire the intensity of each wavelength of the reference light, the analog electric signals are converted from the intensity of each wavelength of the reference light by the photoelectric conversion means a / D conversion means For each wavelength of the analog electrical signal output from the photoelectric conversion means so that the value for each wavelength of the reference optical signal, which is a digital electrical signal obtained by conversion by the above, becomes the center of the input range of the A / D conversion means Value or A / Thereby adjusting the input range of each wavelength converting means.

  ADVANTAGE OF THE INVENTION According to this invention, the technique which can utilize the dynamic range of an A / D converter effectively and can acquire a favorable tomographic image by extension can be provided.

1 is a diagram illustrating an example of a configuration of an imaging apparatus according to an embodiment. The figure which shows an example of the flow of a process at the time of setting the input range of an A / D converter. The figure which shows an example of the function and structure of the image information processing part which concerns on this embodiment. The figure which shows an example of a reference light signal, an interference light signal, and a reference signal. The figure which shows an example of an interference optical signal. The figure which shows an example of an interference optical signal. The figure which shows an example of the flow of a process at the time of imaging | photography a tomogram. The figure which shows an example of the flow of a process at the time of imaging | photography a tomogram. The figure which shows an example of a reference light signal, an offset adjustment table, and an amplification table.

<Example 1>
FIG. 1 is a diagram illustrating an imaging apparatus (an imaging apparatus using an optical coherence tomography) according to Example 1 of the present invention and an OCT apparatus for ophthalmology and an imaging method using the apparatus (an imaging method using an optical coherence tomography) as a control method thereof. It explains using.
(Constitution)
First, the configuration of the SD-OCT apparatus according to the present embodiment will be described. FIG. 1A is a diagram illustrating a configuration of the SD-OCT apparatus according to the present embodiment. The light emitted from the light source 101 is split into reference light 112 and measurement light 111 by the beam splitter 102. When the measurement light 111 is irradiated on the observation target (inspection object; eye 105), the measurement light 111 is returned as the return light 113 by reflection or scattering. The return light 113 and the reference light 112 are combined by the beam splitter 102 to become interference light 114. The interference light 114 is split by the diffraction grating 107 and is irradiated to the line sensor 109 through the lens 108. The line sensor 109 converts the intensity of the interference light into an analog electric signal for each wavelength (photoelectric conversion), and outputs the analog electric signal to the image information processing unit 110. The image information processing unit 110 converts the input analog electric signal into a digital electric signal (A / D conversion), and acquires a tomographic image (tomographic image) of the inspection object based on the digital electric signal for each wavelength. Specifically, the image information processing unit 110 obtains a tomographic image of the eye 105 by performing processing such as Fourier transform processing on the digital electrical signal for each wavelength.

The function of the image information processing unit 110 will be described in more detail with reference to the block diagram of FIG. The image information processing unit 110 includes an A / D converter 301, a D / A converter 302, an FFT (Fast Fourier Transform) processing unit 303, and a memory 304. The A / D converter 301 converts the analog electric signal into a digital electric signal of 1024 gradations (10 bits) using the Top_ref signal 305 output from the D / A converter 302 as the upper limit of the input range and the Bottom_ref signal 306 as the lower limit. To do. The output (digital electric signal) of the A / D converter 301 is recorded in the memory 304. In addition, a reference table of an A / D converter 301 described later is recorded in the memory 304. The FFT processing unit 303 performs FFT conversion on the digital electrical signal recorded in the memory 304. The FFT-converted signal is subjected to predetermined processing by a calculation means such as a PC (not shown) and converted to a tomographic image (of the fundus).

The light source 101 will be described in more detail. The light emitted from the light source 101 is preferably near-infrared light in view of measuring the eye. The wavelength affects the resolution in the lateral direction (direction perpendicular to the optical axis) of the obtained tomographic image, and is preferably a short wavelength. The bandwidth (wavelength width) is an important parameter because it affects the resolution in the optical axis direction of the obtained tomographic image. In this embodiment, an SLD (Super Luminescent Diode) which is a typical low-coherent light source is used as the light source 101. The wavelength (center) of the light emitted from the light source 101 is 84.
The width is 0 nm and the bandwidth is 50 nm.
FIG. 4A shows the wavelength characteristic (frequency characteristic) of light from the light source 101. Ideally, the wavelength characteristic matches the Gaussian curve. However, at present, the wavelength characteristic is the waveform 13
It becomes like 01. Specifically, in order to realize light in the wavelength region of 815 to 865 nm (bandwidth of 50 nm), two light sources (for example, LEDs) that emit light having different center wavelengths are used. Therefore, the waveform 1301 has two peaks.
The light source only needs to emit low-coherent light, and may be ASE (Amplified Spontaneous Emission) or the like. In addition, a light source may be selected according to an object to be inspected (a type of measurement site) (for example, a wavelength range of light to be used may be selected and a light source may be determined accordingly).

  The optical path of the reference light 112 will be described in more detail. The reference light 112 split by the beam splitter 102 is reflected by the mirror 106 and returns to the beam splitter 102. The optical path length of the reference light 112 from the split by the beam splitter 102 to the return to the beam splitter 102 is the optical path length of the measurement light 111 from the split by the beam splitter 102 to the return light 113 before returning to the beam splitter 102. Is equal to Thereby, the reference light 112 and the measurement light 111 (return light 113) can be made to interfere with each other.

The optical path of the measurement light 111 will be described in more detail. The measurement light 111 split by the beam splitter 102 is incident on the mirror of the XY scanner 103 and reflected. The measurement light 111 reflected by the XY scanner 103 is condensed on the retina via the lens 104. Then, the measurement light 111 is reflected or scattered by the retina and returned as return light 113. The return light 113 is incident on the beam splitter 102 via the lens 104 and the mirror of the XY scanner 103. The XY scanner 103 is for performing a raster scan on the retina of the eye 105 in a direction perpendicular to the optical axis. The center of the measurement light 111 is adjusted to coincide with the rotation center of the mirror of the XY scanner 103.
In FIG. 1A, the XY scanner 103 is shown as a single mirror, but in reality, two mirrors of an X scan mirror and a Y scan mirror are arranged close to each other.

Next, the spectroscopic system will be described in more detail. The interference light 114 is split by the diffraction grating 107 under the same wavelength condition as the (center) wavelength and bandwidth of the light emitted from the light source 101. That is, light having a wavelength characteristic as shown in FIG. 4A is irradiated to the entire length of the line sensor 109 via the diffraction grating 107 and the lens 108. As a result, as shown in FIG. 4B, the wavelength (light wavelength) on the horizontal axis of FIG. 4A becomes the pixel position as it is.
Further, in this embodiment, control is performed to irradiate the line sensor 109 only with the reference light 112 by blocking the return light 113 (return light in the interference light 114) guided to the line sensor 109. Specifically, the measurement light 111 is removed from the lens 104 by largely moving the mirror of the XY scanner 103. As a result, only the reference light is incident on the line sensor 109.
In this embodiment, a CCD line sensor having 1024 pixels (pixel positions 0 to 1023) is used as the line sensor 109. However, the line sensor 109 may be a CMOS line sensor. .
Each unit (function) is controlled by the control unit 120 executing a program. For example, the program is stored in a computer-readable storage medium, and the computer (control unit 120) controls each unit by reading the program from the storage medium and executing it. Examples of the storage medium include a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, an EEPROM, and a Blu-ray disk.

(Operation)
Next, the operation of the SD-OCT apparatus according to the present embodiment will be described.
The flow of processing when setting the input range of the A / D converter 301 (specifically, the reference signal (reference voltage)) will be described with reference to FIG. In this embodiment, the value for each wavelength of the digital electrical signal (reference light signal) obtained by the A / D converter 301 in a state where the return light 113 is blocked is the central portion of the input range of the A / D converter 301. Thus, the input range for each wavelength of the A / D converter 301 is adjusted. The central portion is preferably an intermediate value (or a half value) of the input range of the A / D converter 301, but is not necessarily limited thereto. The central portion may be a value within the range including the upper and lower vicinity of the intermediate value (that is, the value for each wavelength of the reference light signal is the upper and lower vicinity of the intermediate value of the input range of the A / D converter 301. The input range for each wavelength of the A / D converter 301 may be adjusted so that the value is within the range to be included). The range including the upper and lower vicinity of the intermediate value is a range in which the effect of the present invention can be obtained (the dynamic range of the A / D converter can be effectively used).

First, the control unit 120 sets the upper limit of the input range of the A / D converter 301 (the value of the Top_ref signal).
And the initial value is set to the lower limit (value of Bottom_ref signal) (S201). The initial value may be, for example, a different value for each wavelength (each pixel position) or the same value.
Next, the control unit 120 moves (controls) the mirror of the XY scanner 103 so that the measurement light 111 is deviated from the lens 104 (that is, only the reference light 112 is incident on the line sensor 109). In this state, the digital electric signal obtained by the A / D converter 301 is recorded in the memory 304 as a reference light signal (S202).

Next, the control unit 120 detects the peak of the value for each wavelength of the reference light signal (in this embodiment, the larger of the two peaks), and determines whether the peak value (peak value) is 800 or more. (S203). When the peak value is 800 or more (S203: YES), the value of the Top_ref signal is increased by 3% (S204), and the process returns to S202. The value of the reference light signal is calculated with the Top_ref signal value set to 1023 and the Bottom_ref signal value set to 0. Therefore, if the value of the Top_ref signal is increased, the value of the reference light signal is decreased. The processes in S202 to S204 are repeated until the peak value is less than 800. When the peak value is less than 800 (S203: NO), the process proceeds to S205.

In S205, the control unit 120 determines whether the peak value is 600 or less. When the peak value is 600 or less (S205: NO), the value of the Top_ref signal is decreased by 3% (S206).
, Go to S207. In S207, a reference light signal is acquired and recorded as in S202. The processes of S205 to S207 are repeated until the peak value is greater than 600. If the peak value is greater than 600 (S205: YES), the process proceeds to S208.
In this embodiment, the method of increasing / decreasing the value of the Top_ref signal by ± 3% is used. However, if the peak value falls within a predetermined range (in the present embodiment, a range of 601 to 799), how can the reference voltage be changed? You may adjust it. For example, the ratio of increasing or decreasing the value of the Top_ref signal may be changed (it may not be ± 3%).

Next, the control unit 120 acquires reference light signals for a plurality of lines at the reference voltage (input range) set by obtaining the steps S202 to S207. Then, the acquired reference light signals for a plurality of lines are averaged to remove noise, and are recorded in the memory 304 as reference light signals for one line (S208).
Next, the control unit 120 sets a value obtained by multiplying a value for each wavelength (for each pixel position) of the recorded reference light signal for one line by a first predetermined value and a second predetermined value, for each wavelength. Are set (reset) as the Top_ref signal value and Bottom_ref signal value (S209). Specifically, a value obtained by multiplying the value for each wavelength of the reference light signal (reference numeral 801 in FIG. 4B) by 1.2 is the value of the Top_ref signal for each wavelength (reference numeral 802 in FIG. 4B). And A value obtained by multiplying the value for each wavelength of the reference light signal by 0.8 is set as the value of the Bottom_ref signal (reference numeral 803 in FIG. 4B) for each wavelength. The Top_ref signal value and Bottom_ref signal value for each set wavelength are stored in the memory 30 as a reference table.
4 is recorded.
Through the above processing, the input range for each wavelength of the A / D converter 301 is adjusted.
As described above, in this embodiment, the value obtained by multiplying the value for each wavelength of the reference light signal by the first predetermined value and the second predetermined value are the value of the Top_ref signal and the value of the Bottom_ref signal for each wavelength, respectively. Is done. Thereby, the value of the reference light signal can be made constant (512 in this embodiment) regardless of the wavelength (pixel position).

  Note that the above method is a method in consideration of the characteristics of the light source, the characteristics of the optical system constituting the apparatus, the light absorption characteristics and the reflection characteristics of the inspection object, and depends on the characteristics of the light source and the characteristics of the inspection object. An input range adjustment method may be selected. For example, values such as 1.2 and 0.8 used to set the initial value and ± 3%, 600, 800 used to readjust the input range may be changed.

  With reference to FIG. 7, the flow of processing when capturing a tomographic image of an object to be inspected (eye (fundus) in this embodiment) will be described. The operation until the interference light is applied to the line sensor 109 and the analog electrical signal for each wavelength (for each pixel position) is input to the image information processing unit 110 is the same as described above, and thus description thereof is omitted. Hereinafter, the operation of the image information processing unit 110 will be described in detail.

First, the control unit 120 sets the pixel position n to “0” (S1501). Next, the control unit 120 reads the value of the Top_ref signal and the value of the Bottom_ref signal corresponding to the pixel position n from the reference table recorded in the memory 304, and performs A / D via the D / A converter 302.
The converter 301 is set (S1502).
The A / D converter 301 converts the input analog electric signal (analog electric signal at the pixel position n) into a digital electric signal (interference light signal) based on the set Top_ref signal value and Bottom_ref signal value. (S1503). Then, the interference light signal is recorded in the memory 304 (S1504).
Next, the control unit 120 adds 1 to n (S1505), and determines whether n is 1024 (S1506). If n is less than 1024 (S1506: NO), the process returns to S1502. When n becomes 1024 (S1506: YES), that is, when A / D conversion is performed for all pixel positions on one line, the process proceeds to S1507.
Next, the FFT processing unit 303 performs FFT conversion on the interference light signal for one line recorded in the memory 304 (S1507). The FFT-converted signal is sent to a PC (not shown) and converted into a tomographic image.

FIG. 5A is a diagram illustrating a state of the interference light signal 901 obtained when the values of the Top_ref signal and the Bottom_ref signal are initial values. FIG. 5A also shows a reference light signal 801, a Top_ref signal 802, and a Bottom_ref signal 803. FIG. 5B is a diagram illustrating an interference light signal 902 obtained using the Top_ref signal 802 and the Bottom_ref signal 803. As shown in the figure, the interference light signal 902 is a signal having an interference component around a specific level (512 level).
As described above, according to this embodiment, the input range for each wavelength of the A / D converter is adjusted in consideration of the wavelength characteristics of the light from the light source. As a result, the dynamic range of the A / D converter can be used effectively, and as a result, a good tomographic image can be obtained.

<Example 2>
Next, an optical coherence tomographic imaging apparatus and method according to Embodiment 2 of the present invention will be described with reference to the drawings. In the first embodiment, the input range for each wavelength of the A / D converter is adjusted, but in this embodiment, the value for each wavelength of the analog electric signal output from the line sensor is adjusted.
The A / D converter used in the second embodiment performs A / D conversion according to a ref signal (Top_ref signal, Bottom_ref signal) centered on 0V. That is, in this example, Top_ref
An A / D converter in which the signal is + refV and the Bottom_ref signal is −refV is used. Here, in order to match the description of the first embodiment, it is assumed that 0 is output as a digital signal when the analog input signal level is −refV. When the analog input signal level is 0V, 512 is output as a digital signal. Assume that 1023 is output as a digital signal when the analog input signal level is + refV. In the second embodiment, the Top_ref signal and the Bottom_ref signal, that is, the value of the ref signal is assumed to be the same value regardless of the wavelength value (pixel position).
(Constitution)
First, the configuration of the image information processing unit 110 of the imaging apparatus according to the present embodiment will be described with reference to FIG. The other functions are the same as those in FIG. In FIG. 3B, functions similar to those in the first embodiment (FIG. 3A) are denoted by the same reference numerals, and description thereof is omitted.

The offset adjuster 401 adjusts the analog electrical signal output from the line sensor 109 using the offset signal 403 output from the D / A converter 302. Specifically, the offset adjuster 401 is a circuit that adds and outputs a predetermined offset value (offset level; offset adjustment value) to the value of the analog electrical signal output from the line sensor 109.
The variable amplifier 402 is a circuit that uses the gain signal 404 output from the D / A converter 302 to amplify the analog electric signal value added with the offset value at a predetermined amplification factor and output the amplified signal.

(Operation)
Next, the operation of the image pickup apparatus according to the present embodiment will be described.
The flow of processing when setting (adjusting) the value of the offset signal 403 (offset value) and the value of the gain signal 404 (amplification factor) will be described with reference to FIG.

First, the control unit 120 sets an initial value of offset value (“0” in this embodiment) in the offset adjuster 401 and sets an initial value (predetermined value) of gain in the variable amplifier 402 (S1701). .
Next, the control unit 120 moves (controls) the mirror of the XY scanner 103 so that the measurement light 111 is removed from the lens 104, and acquires reference light signals for a plurality of lines in this state. Then, the acquired reference light signals are averaged and recorded in the memory 304 as a reference light signal for one line (S1702).

Next, the control unit 120 adjusts the offset value for each wavelength based on the value for each wavelength of the recorded reference light signal for one line (S1703). Specifically, in order to match the reference light signal to the 512 level that is the center of 10 bits (1024 gradations), a value obtained by subtracting the value Ca (n) of the reference light signal from 512 for each wavelength (for each pixel position). The offset value is O (n) (Formula 1). Note that n is an integer of 0 to 1023 indicating the pixel position. The adjusted (calculated) offset value for each wavelength is recorded in the memory 304 as an offset level adjustment table. FIG. 9A shows the relationship between the reference light signal 801 and the offset adjustment table 1901.
O (n) = 512-Ca (n) (Formula 1)
Thus, by adjusting the offset value for each wavelength based on the value for each wavelength of the reference light signal, the value of the reference light signal is constant (512 in this embodiment) regardless of the wavelength (pixel position). be able to.

Next, the control unit 120 adjusts the value of the amplification factor for each wavelength based on the value for each wavelength of the recorded reference light signal for one line (S1704). Specifically, for each wavelength (each pixel position), a value obtained by dividing 1024 by the value Ca (n) of the reference light signal is defined as an amplification factor G (n) (Formula 2). The adjusted amplification factor for each wavelength is recorded in the memory 304 as an amplification table. FIG.
b) is a diagram showing the relationship between the reference light signal 801 and the amplification table 2001. FIG.
G (n) = 1024 ÷ Ca (n) (Formula 2)
Through the above processing, the offset value and the amplification factor are set.

Next, the flow of processing when capturing a tomographic image of the inspection object will be described with reference to FIG. Hereinafter, the operation of the image information processing unit 110 will be described in detail.
First, the control unit 120 sets the pixel position n to “0” (S1801). In step S <b> 1802, the control unit 120 reads an offset value O (n) corresponding to the pixel position n from the offset adjustment table recorded in the memory 304, and the offset adjuster 401 via the D / A converter 302. Send to (set). Further, the amplification factor G (n) corresponding to the pixel position n is read from the amplification table, and sent (set) to the variable amplifier 402 via the D / A converter 302.
Then, the value of the analog electric signal of the interference light is adjusted by the offset adjuster 401 and the variable amplifier 402 and converted into a digital electric signal (interference light signal) by the A / D converter 301 (S1803).
The processing of S1804 to S1807 is the same as the processing of S1504 to S1507 in FIG. However, if n is less than 1024 (S1806: NO), the process returns to S1802.

FIG. 6A is a diagram illustrating an interference optical signal 2101 obtained using the adjusted offset value. As shown in the figure, the interference light signal 2101 is a signal having an interference component around a specific level (512 level). FIG. 6B is a diagram illustrating an interference optical signal 2201 obtained using the adjusted offset value and amplification factor.
As described above, according to the present embodiment, the value for each wavelength of the analog electric signal is adjusted in consideration of the wavelength characteristic of the light from the light source. As a result, the dynamic range of the A / D converter can be effectively used, and as a result, a good tomographic image can be obtained.
Note that Example 1 and Example 2 may be combined. For example, the offset component of the interference light is adjusted by the offset adjuster 401, and the value of the Top_ref signal of the A / D converter 301 is adjusted for each pixel based on the reference light information, so that the dynamic range of the A / D converter 301 is adjusted. Can be used effectively.

<Example 3>
In the first and second embodiments, an example in which the present invention is applied to an SD-OCT apparatus has been described. An example applied to OCT) will be described. Note that the description of the same configuration as in the first and second embodiments is omitted.
FIG.1 (b) is a figure which shows the structure of SS-OCT apparatus. In SS-OCT, the wavelength of the light output from the light source 115 is switched instead of separating the interference light with a spectroscope. Specifically, a light source (Swept Source) capable of scanning (changing) the wavelength of light is used as the light source 115, not low-coherent light having a bandwidth. Then, the light receiving element 116 converts the intensity of the interference light into an analog electric signal and transmits it to the image information processing unit 110. By synchronizing the scanning of the wavelength of the light source and the operation of the image information processing unit 110, the same reference light signal and interference light signal as in the first and second embodiments can be obtained.
Then, the dynamic range of the A / D converter can be effectively used by adjusting the value for each wavelength of the analog electric signal and the value for each wavelength of the A / D converter as in the first and second embodiments. As a result, a good tomographic image can be obtained.
The light source 115 can be realized, for example, by inserting a mirror resonator capable of minutely changing the resonator length in a ring type fiber laser resonator. As the light receiving element 116, for example, a PIN photodiode may be applied.

As described above, according to the present embodiment (Examples 1 to 3), the A / D converter is adjusted by adjusting the value for each wavelength of the analog electric signal or the value for each wavelength of the A / D converter. The dynamic range can be effectively used, and as a result, a good tomographic image can be obtained.
In the first to third embodiments, when a three-dimensional tomographic image is acquired, a measurement light condensing position (a position in a two-dimensional direction (a direction perpendicular to the optical axis of the measurement light)) is measured by an XY scanner. Move it. And the process of S1501-S1507 and S1801-S1807 should just be repeated for every condensing position.
In the first to third embodiments, the return light is blocked by largely moving the mirror of the XY scanner. However, any method may be used as long as the return light can be blocked. For example, the measurement light (return light) may be blocked by a shutter or the like.

  DESCRIPTION OF SYMBOLS 101,115 ... Light source 102 ... Beam splitter 105 ... Eye 107 ... Diffraction grating 109 ... Line sensor 110 ... Image information processing part 111 ... Measurement light 112 ... Reference light 113 ... Return light 114 ... Interference light 116 ... Light receiving element 301 ... A / D converter 801 ... Reference light signal

Claims (17)

The intensity of each interference light by the reference light and the return light returned from the inspection object when the light from the light source is divided into measurement light and reference light, and the inspection light is irradiated onto the inspection object The photoelectric conversion means that acquires the intensity of the interference light for each wavelength is converted into an analog electric signal, and the analog electric signal is converted by the A / D conversion means based on the digital electric signal of the object to be inspected. a to that imaging device acquires a tomographic image,
Acquisition means for causing the photoelectric conversion means to acquire the intensity of each wavelength of the reference light;
The value for each wavelength of the reference light signal, which is a digital electric signal obtained by converting the analog electric signal converted from the intensity for each wavelength of the reference light by the photoelectric conversion means by the A / D conversion means, is A. Adjustment means for adjusting the value for each wavelength of the analog electrical signal output from the photoelectric conversion means or the input range for each wavelength of the A / D conversion means so as to be in the center of the input range of the / D conversion means When,
An imaging device comprising: Said adjustment means, the value of each wavelength before hexane illumination signal, such that the central portion of the input range of the A / D converter, the value of each wavelength of the analog electrical signal output from said photoelectric conversion means The imaging apparatus according to claim 1, wherein an input range for each wavelength of the A / D conversion unit is adjusted. The adjustment means sets a value obtained by multiplying a value for each wavelength of the reference light signal by a first predetermined value as an upper limit of an input range for each wavelength, and sets the first value to a value for each wavelength of the reference light signal. the value obtained by multiplying a predetermined value smaller than the second predetermined value, the imaging apparatus according to claim 1 or 2, characterized in that the lower limit of the input range of the previous SL each wavelength.   The adjusting means includes
    The value for each wavelength of the reference light signal is adjusted so that the peak value of the value for each wavelength of the reference light signal is within a predetermined range,
    Multiplying the value for each wavelength of the reference optical signal after the peak value is adjusted to be within a predetermined range by the first predetermined value;
    The second predetermined value is multiplied by the value for each wavelength of the reference light signal after the peak value is adjusted so as to be within a predetermined range.
The imaging apparatus according to claim 3.   After the input range for each wavelength of the A / D converter is adjusted,
  The A / D conversion means converts, for each wavelength, an analog electric signal converted from the intensity for each wavelength of the interference light by the photoelectric conversion means into a digital electric signal based on the adjusted input range.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.   Processing means for performing a Fourier transform process on the digital electrical signal obtained by conversion based on the adjusted input range;
  The tomographic image is acquired by the Fourier transform process.
The imaging apparatus according to claim 5. The photoelectric conversion means converts the acquired intensity for each wavelength of light into an analog electric signal, and then outputs a value for each wavelength of the analog electric signal by adding an offset value for a predetermined wavelength. And
The adjusting means, imaging apparatus according to any one of claims 1 to 6, wherein adjusting the offset value for each said wavelength.   After the offset value for each wavelength is adjusted,
  The photoelectric conversion means outputs the value for each wavelength of the analog electrical signal converted from the intensity for each wavelength of the interference light by adding the offset value for each wavelength after adjustment.
The imaging apparatus according to claim 7. The photoelectric conversion means is a circuit that amplifies and outputs a value for each wavelength of the analog electric signal to which the offset value for each wavelength is added, at a predetermined amplification factor for each wavelength ,
The imaging apparatus according to claim 7 , wherein the adjustment unit adjusts an amplification factor for each wavelength.   After the offset value for each wavelength and the amplification factor for each wavelength are adjusted,
  The photoelectric conversion means amplifies the value for each wavelength of the analog electrical signal converted from the intensity for each wavelength of the interference light by adding the offset value for each wavelength after adjustment, with the amplification factor for each wavelength after adjustment. And output
The imaging apparatus according to claim 9.   The acquisition means includes
  Including a blocking means for blocking the return light guided to the photoelectric conversion means,
  By blocking the return light guided to the photoelectric conversion means, the photoelectric conversion means acquires the intensity for each wavelength of the reference light.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.   The acquisition means includes
  Scanning means for scanning the irradiation position of the measurement light on the inspection object; and control means for controlling the scanning means so that the measurement light is not irradiated on the inspection object.
  By controlling the scanning unit so that the measurement light is not irradiated onto the object to be inspected, the photoelectric conversion unit acquires the intensity of each wavelength of the reference light.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.   The imaging apparatus is an SD-OCT apparatus, and a plurality of light receiving elements that acquire intensities for each wavelength of the interference light by light having a predetermined wavelength range generated from the light source are used as the light source conversion unit.
Have
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.   The imaging apparatus is an SS-OCT apparatus, and includes a light receiving element that acquires the intensity for each wavelength of the interference light by light generated by changing the wavelength from the light source as the photoelectric conversion means.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.   The wavelength of light from the light source is selected according to the type of the object to be inspected.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus. The intensity of each interference light by the reference light and the return light returned from the inspection object when the light from the light source is divided into measurement light and reference light, and the inspection light is irradiated onto the inspection object The photoelectric conversion means that acquires the intensity of the interference light for each wavelength is converted into an analog electric signal, and the analog electric signal is converted by the A / D conversion means based on the digital electric signal of the object to be inspected. a method of controlling to that imaging device acquires a tomographic image,
Causing the photoelectric conversion means to acquire an intensity for each wavelength of the reference light;
The value for each wavelength of the reference light signal, which is a digital electric signal obtained by converting the analog electric signal converted from the intensity for each wavelength of the reference light by the photoelectric conversion means by the A / D conversion means, is A. Adjusting the value for each wavelength of the analog electrical signal output from the photoelectric conversion means or the input range for each wavelength of the A / D conversion means so as to be in the center of the input range of the / D conversion means; ,
A control method characterized by comprising: The intensity of each interference light by the reference light and the return light returned from the inspection object when the light from the light source is divided into measurement light and reference light, and the inspection light is irradiated onto the inspection object The photoelectric conversion means that acquires the intensity of the interference light for each wavelength is converted into an analog electric signal, and the analog electric signal is converted by the A / D conversion means based on the digital electric signal of the object to be inspected. to be that an imaging device acquires a tomographic image,
Causing the photoelectric conversion means to acquire the intensity of each wavelength of the reference light;
The value for each wavelength of the reference light signal, which is a digital electric signal obtained by converting the analog electric signal converted from the intensity for each wavelength of the reference light by the photoelectric conversion means by the A / D conversion means, is A. Adjusting the value for each wavelength of the analog electric signal output from the photoelectric conversion means or the input range for each wavelength of the A / D conversion means so as to be in the center of the input range of the / D conversion means. A featured program.

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