JP2022046218A - Optical interference tomographic imaging apparatus and control method of the same - Google Patents

Abstract

To reduce an unnecessary ghost of a tomographic image generated when a time difference (optical path length difference) is generated in each optical path length from a wavelength sweeping light source of an interference signal and a k-clock signal.SOLUTION: An optical interference tomographic imaging apparatus for acquiring a tomographic image of a subject by using light output from a wavelength sweeping light source comprises: clock generation means which generates a clock signal by using the light; light reception means which converts interference light obtained by irradiating the subject with the light into an electric signal; conversion means which converts the electric signal into a data stream by using the clock signal; acquisition means which obtains a strength signal in a depth direction by performing Fourier transformation on the data stream; and adjustment means which adjusts the signal strength of plural peaks included in the strength signal in the depth direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical interference tomographic image apparatus and a control method thereof.

Optical coherence tomography (hereinafter referred to as OCT) has been put into practical use as a method for acquiring a tomographic image of a measurement target such as a living body in a non-destructive and non-invasive manner. OCT acquires tomographic images of the retina in the fundus of the eye to be inspected, especially in the field of ophthalmology, and is widely used in diagnosis of the retina and the like.

OCT obtains a tomographic image by interfering the measurement light reflected by the measurement target with the reference light reflected by the reference mirror and analyzing the time dependence or wave number dependence of the interference signal. As such an optical coherence tomography device, a wavelength sweep light OCT (SS-OCT: Swept Source Optical Coherence Tomography) device using a wavelength sweep light source capable of changing the oscillation wavelength is known.

One of the methods for obtaining a tomographic image by SS-OCT is to generate a signal called a k-lock signal from a part of the light emitted from the wavelength sweep light source and use it as the timing of sampling the interference signal.

The interference signal and the k-clock signal branch off from the output light of the wavelength sweep light source and follow different paths. Therefore, if a large time difference occurs between the paths, the timing of sampling the interference signal shifts, noise occurs, and a desired tomographic image cannot be obtained. An example of noise when there is a time lag between paths is the appearance of unwanted replicas (ghosts) of the retina in a tomographic image.

As a precedent example regarding the timing of sampling of an interference signal, Japanese Patent Application Laid-Open No. 2015-198757 discloses a method of removing fixed pattern noise by adjusting a trigger and a sampling clock generated from the output light of a wavelength sweep light source. ing. Although this method can improve the noise removing effect caused by the unintended scattering of the optical element in the interferometer, the effect of removing the ghost of the tomographic image cannot be expected.

JP-A-2015-19877

As described above, it is an object to reduce unnecessary ghosts of tomographic images generated when a time difference (optical path length difference) occurs in each optical path length from the wavelength sweep light source of the interference signal and the k-clock signal. ..

An object of the present invention is to provide SS-OCT that deletes or reduces ghosts in the obtained tomographic image.

In order to solve the above problems, the optical interference tomographic image apparatus of the present invention is an optical interference tomographic image apparatus that acquires a tomographic image of a subject by using light output from a wavelength sweep light source, and uses the light. Data of the electric signal is obtained by using the lock signal generation means for generating the lock signal, the light receiving means for converting the interference light obtained by irradiating the subject with the light into an electric signal, and the lock signal. A conversion means for converting into a column, an acquisition means for obtaining an intensity signal in the depth direction by Fourier transforming the data string, and an adjusting means for adjusting the signal intensity of a plurality of peaks included in the intensity signal in the depth direction. Have.

According to the present invention, the ghost of the obtained tomographic image can be deleted or reduced.

It is the schematic of the whole composition of the apparatus in 1st Embodiment. It is a figure which shows a part example of the k-clock signal after adjustment. It is a flowchart which shows the processing method of the interference signal of A-scan. It is a figure which shows the A-scan profile. It is a figure which shows the tomographic image. It is a flowchart which shows the embodiment procedure in 1st Embodiment. It is a graph which shows the relationship of four indexes with respect to a delay. It is the schematic of the whole structure of the apparatus in 2nd Embodiment. It is a flowchart which shows the embodiment procedure in 2nd Embodiment. It is a schematic diagram of the whole composition of the apparatus in 3rd Embodiment.

An embodiment of the present invention will be described in detail below with reference to the drawings. The following description is merely explanatory and exemplary in nature and is not intended to limit this disclosure and its uses or uses in any way. The relative configurations of the components shown in the embodiments, as well as the steps, numerical representations and numerical values, do not limit the scope of the present disclosure unless otherwise specified. Techniques, methods and devices well known to those of skill in the art may not be discussed in detail as those of skill in the art do not need to know these details to enable the embodiments discussed below.

[First Embodiment]
What can be imaged by the optical interference tomographic image apparatus of the present embodiment is, for example, a tomographic image of the retina of the fundus of the eye to be inspected.

(Device configuration)
FIG. 1 is a diagram showing an overall configuration of an optical interference tomographic image apparatus according to the first embodiment of the present invention. In FIG. 1, it is composed of an optical interference tomographic image acquisition unit 100 for acquiring an optical interference tomographic signal and a control unit 143. The control unit 143 is composed of a signal processing unit 144, a signal acquisition control unit 145, a display control unit 149, and a display unit 146. Further, the signal processing unit 144 is composed of an image generation unit 147 and a map generation unit 148.

(Optical interference tomographic image acquisition unit 100)
The light source 101 is a wavelength sweep (Swept Source: SS) light source, and emits light in a range centered on 1050 nm having a sweep wavelength of 1000 nm to 1100 nm, for example. The light source 101 has a resonator, and the resonator length has a length of, for example, 50 mm.

The light emitted from the light source 101 is guided to and branched by the optical branching element 151 via the fiber 150, and is guided to the fiber 102 and the fiber 152-1, respectively. The light guided to the fiber 152-1 is guided to the k-clock generation unit 154 via the delay adjusting unit 153 and the fiber 152-2. Details of the delay adjustment unit 153 and the k-clock generation unit 154 will be described later.

The light passing through the fiber 102 is guided to the optical branching element 110 and branched into the measurement light and the reference light. The branching ratio at this time was 30 (measurement light): 70 (reference light). The branched measurement light passes through the fiber 111, is emitted from the end portion 111a of the fiber, and becomes parallel light by the collimator 112. The measured light that has become parallel light is incident on the eye to be inspected 118 via the galvano scanner 114, the scan lens 115, and the focus lens 116 that scan the measured light in the fundus Er of the eye to be inspected 118. Here, the galvano scanner 114 is illustrated as a single mirror, but is actually composed of two galvano scanners (X-axis scanner 114X, Y-axis scanner 114Y) so as to raster scan the fundus Er of the eye 118 to be inspected. ..

Further, the focus lens 116 is fixed on the stage 117, and the focus can be adjusted by moving the stage 117 in the optical axis direction. The galvano scanner 114 and the stage 117 are controlled by the signal acquisition control unit 145, and are measured in a desired range (also referred to as a tomographic image acquisition range, a tomographic image acquisition position, and a measurement light irradiation position) of the fundus Er of the eye to be inspected 118. The light can be scanned.

Although not described in detail in this embodiment, it is desirable that a tracking function for detecting the movement of the fundus Er and scanning the mirror of the galvano scanner 114 while following the movement of the fundus Er is provided. Since the tracking function can be implemented using a general technique, the description thereof will be omitted.

The measurement light is incident on the eye to be inspected 118 by the focus lens 116 mounted on the stage 117, and is focused on the fundus Er. The measurement light irradiating the fundus Er is reflected and scattered in each retinal layer, passes through the above-mentioned optical system path, and returns to the optical branching element 110. The return light of the measurement light incident on the optical branching element 110 passes through the fiber 126 and is incident on the optical branching element 128.

On the other hand, the reference light branched by the optical branching element 110 is emitted from the end portion 119c of the fiber via the fiber 119a, the polarization controller 150, and the fiber 119b, and is converted into parallel light by the collimator 120. The polarization controller 150 can change the polarization of the reference light to a desired polarization state. The reference light is coupled to the fiber end 127a of the fiber 127 via the dispersion compensating glass 122, the ND filter 123, and the collimator 124. One end of the collimator lens 124 and the fiber 127 is fixed on the coherence gate stage 125, and is controlled by the signal acquisition control unit 145 so as to be driven in the optical axis direction in response to a difference in the axial length of the subject. Will be done. In the present embodiment, the optical path length of the reference light is changed, but any configuration may be used as long as the optical path length difference between the optical path of the measurement light and the optical path of the reference light can be changed. Further, although the example in which the fiber 119 and the fiber 127 oppose each other in a straight line has been described, a mirror may be arranged in the optical path to bend the optical path.

The reference light that has passed through the fiber 127 is incident on the optical branching element 128. In the optical branching element 128, the return light of the measurement light and the reference light are combined and branched. The light branched at this time has a relationship in which the phases are inverted from each other. The return light and the reference light of one of the divided measurement lights are incident (received) on one input port of the detector 141 through the fiber 129.

Further, the return light and the reference light of the other divided measurement light pass through the fiber 130 and enter the other input port of the detector 141. At this time, the return light of the measurement light incident on the different input ports of the detector 141 is out of phase with each other. Further, like the return light of the measurement light, the reference light incident (received) on different input ports of the detector 141 also has their phases inverted. As a result, the interference light observed by the detector 141 is received by different input ports, and the phase of the interference fringes (signals in which strength and weakness appear in the signal intensity along the wavelength direction) is inverted. The detector 141 is a differential detector, and when two interference signals having inverted phases are input (received), only the interference component from which the DC component has been removed can be output.

The interference signal, which is an electric signal from which the DC component detected by the detector 141 has been removed, is input to the signal processing unit 144, which is an example of the tomographic image generation unit.

The control unit 143 is composed of a signal processing unit 144, a signal acquisition control unit 145, a display unit 146, and a display control unit 149. Further, the signal processing unit 144 is further configured to have an image generation unit 147 and a map generation unit 148. The image generation unit 147 has a function of generating a luminance image (tomographic image) from the transmitted electric signal, and the map generation unit 148 has a function of generating layer information (segmentation of the retina) from the luminance image.

The signal acquisition control unit 145 controls each unit as described above. The signal processing unit 144 generates a tomographic image, analyzes the generated tomographic image, and generates visible information of the analysis result based on the signal output from the detector 141.

The images and analysis results generated by the signal processing unit 144 are sent to the display control unit 149, and the display control unit 149 displays them on the display screen of the display unit 146. Here, the display unit 146 is, for example, a liquid crystal display. The image data generated by the signal processing unit 144 may be transmitted to the display control unit 149 and then to the display unit 146 by wire or wirelessly.

Further, in the present embodiment, the display unit 146 and the like are included in the control unit 143, but the present invention is not limited to this, and may be provided separately from the control unit 143, for example, an example of a device that can be carried by a user. You may use the tablet which is. In this case, it is preferable to mount a touch panel function on the display unit so that the display position of the image can be moved, enlarged / reduced, and the displayed image can be changed on the touch panel.

The above is the description of the process of acquiring information on the tomography at one point of the eye to be inspected 118. Acquiring information on the tomographic fault in the depth direction of the eye 118 in this way is called A-scan, and the graph of the tomographic fault in the depth direction is called the A-scan profile. Further, the information about the tomographic image of the subject in the direction orthogonal to A-scan, that is, the scanning direction for acquiring the two-dimensional image is called B-scan, and the two-dimensional image obtained by B-scan is called a two-dimensional tomographic image. B-scan is performed by the above-mentioned galvanoscan 114.

(Signal acquisition)
The method of signal acquisition in this embodiment will be described with reference to FIGS. 1 to 3.

The k-clock generation unit 154 generates a k-clock signal based on the light guided through the fiber. In this embodiment, a Mach-Zehnder interferometer was used to generate the k-clock signal. By adjusting the optical path length difference between the two arms of the Mach-Zehnder interferometer, it is possible to adjust the wavenumber interval of the k-clock signal. The larger the optical path length difference, the narrower the wavenumber interval of the k-clock signal, and it is possible to acquire a tomographic image up to a deeper position. The generation of the k-clock signal is not limited to the Mach-Zehnder interferometer, and an interferometer capable of generating an interferometer having equal wave number intervals such as a fabric pero interferometer can also be used.

The signal processing unit 144 receives a delay-adjusted k-clock signal (hereinafter referred to as an adjusted k-clock signal) from the k-clock generation unit 154 via the signal line 160. FIG. 2 shows an example of a part of the adjusted k-clock signal. The signal processing unit 144 samples the interference signal at the points 202-1 to 202-5 where the adjusted k-clock signal 201 crosses upward to zero.

The method of processing the interference signal of A-scan in the present invention will be described with reference to the flowchart shown in FIG.

First, the signal processing unit 144 acquires the interference signal (step S301) and the background signal (step S302). Here, the background signal is a signal acquired in a state where the measurement light does not enter the detector 141. Next, the signal processing unit 144 corrects the fixed noise pattern using the background signal (step S303). The correction of the fixed noise pattern can be performed by using a general technique.

Next, the signal processing unit 144 applies a window function to the interference signal (step S304) and performs a Fourier transform (step S305). The absolute value of the data string obtained as a result of the Fourier transform is calculated (step S306), and the folded image is removed (step S307). By the above processing, an A-scan profile is obtained.

(Delay adjustment)
The light branched by the optical branching element 151 reaches the control unit 143 via different paths. In order to appropriately match the arrival timing of the interference signal and the k-clock signal, the delay adjusting unit 153 adjusts the delay of the k-clock signal. In the present embodiment, the delay adjusting unit 153 has a configuration in which optical fibers having different lengths can be reconnected.

In the delay adjustment, a model eye (not shown) is used as the eye to be inspected 118. In this embodiment, a model eye composed of a composite lens having a focal length of about 17 mm that imitates a cornea and a vitreous body and a reflection mirror that imitates the fundus Er is used. The reflection mirror is placed at the position of the posterior focal point of the composite lens, and imitates the configuration in which the light collected by the fundus is reflected. Further, by inserting a dimming filter between the compound lens and the reflection mirror, the detector 141 was adjusted so that the amount of light was not saturated.

FIG. 4A shows the A-scan profile obtained at this time. The horizontal axis is the distance in the depth direction, and the vertical axis is the signal strength (logarithmic display). The peak 401 is due to the reflection of the mirror (model eye) (hereinafter referred to as the first peak). Further, the thin peak 402 generated by the parasitic oscillation of the SS light source is the largest next to the first peak 401 (hereinafter referred to as the second peak) except for the sidelobes of the first peak 401. In addition, wide peaks 403 and 404 may also be present (hereinafter referred to as Broad Peak).

A general peak detection method can be used for peak detection. Further, the detection of a broad peak can be realized by smoothing the A-scan profile by using a general curve spike detection and outlier detection technique in combination and using a peak detection method.

When searching for the second peak or Broad Peak, it is desirable to exclude the range 423 in order to eliminate the influence of the sidelobes of the first peak. Further, since a large peak often exists in the vicinity of the DC of the depth direction distance shown in FIG. 4A, it is desirable to exclude the range in the vicinity of the DC as well.

When the second peak or Broad Peak is large, it appears as a ghost in the tomographic image of the retina. FIG. 5A schematically shows a tomographic image 501 in which a ghost has occurred. In the retina 511, a ghost 512 at a shallow position and a ghost 513 at a deep position are generated with respect to a retinal layer having a high reflectance (for example, a retinal pigment epithelial layer). For the ghost 513 at the deep position, the fault folds occur due to the sampling theorem in the sampling of A-scan. In particular, when Broad Peak is larger than the other peaks and is the main cause of ghosts, band-shaped ghosts occur.

The signal strength of the first peak and broad peak changes by adjusting the delay. Therefore, by setting an appropriate delay, it is possible to remove ghosts without narrowing the dynamic range of the tomographic image. In the present invention, four indexes based on the signal strength of the peak are set, how the index changes in the adjustment of the device using the model eye, and whether the delay is optimum or not is determined.

These four indexes ((1) to (4)) will be described with reference to FIG. 4 (b). The difference in signal strength between the first peak and the other peaks is called the suppression ratio. For broad peaks, an index (broad peak) based on the signal strength 410 (hereinafter referred to as floor) at the point where the signal strength of the A-scan fault is the lowest (position 405 in FIG. 4B). Height) is provided.
(1) Signal strength of the first peak (431)
(2) Suppression ratio of the second peak (432)
(3) Broad peak suppression ratio (433, 435)
(4) Broad Peak height (434, 436)

The signal strength of the first peak determines whether or not the delay is optimal based on the amount of change in the strength signal that changes due to the delay adjustment. The suppression ratio indicates that the ghost is reduced as the value is larger, and the Broad Peak height indicates that the ghost is reduced as the value is smaller.

The optimum delay setting method based on the above-mentioned four indexes will be described with reference to the flowchart of FIG.

First, the initial delay is set (step 601). In the present embodiment, the delay adjusting unit 153 uses a fiber having a length that substantially matches the length of the path of the k-clock and the interferometer based on the design value of the optical path length traced by the measured light in the optical interference tomographic image acquisition device. Connect at. The fiber may be connected by an operator, or may be switched by the control unit 143 by a device (not shown) configured to be automatically switchable by combining an optical switch and fibers of a plurality of lengths. The standard of the initial delay is not limited to the design value, and any standard may be used as long as a value close to the optimum delay value can be estimated. For example, empirical values from experiments on prototypes with similar interferometers may be used. By using an appropriate initial delay, it is possible to avoid falling into a local optimum delay.

With the initial delay set, the control unit 143 moves the coherence gate stage 125 to adjust the depth position of the first peak 401 (step 602). As shown in FIG. 4A, it is desirable to adjust so that the second peak 402 and the broad peaks 403 and 404 do not overlap with the first peak 401. The position of the second peak 402 does not always appear as shown in FIG. 4A, and may exist in the vicinity of the first peak 401 or may have a plurality of thin peaks similar to the second peak. In some cases (eg, peak 405 in FIG. 4A).

In addition, there are some broad peaks and thin peaks whose degree of reduction by delay adjustment is relatively small compared to other peaks. Therefore, it is desirable to adjust the coherence gate so that the peak that remains as a ghost even after the second peak is reduced by the procedure described later does not overlap with the other peaks. By this method, for example, the suppression ratio can be measured even when the second peak is reduced by adjusting the delay and another thin peak becomes a new second peak. The same is true for Broad Peak. The drive of the coherence gate stage 125 may be configured such that the operator gives an instruction based on the preview of the A-scan profile displayed on the display unit 146.

The signal processing unit 144 acquires the A-scan profile (step 603), calculates and stores the four indexes (step 604). In the delay adjusting unit 153, a plurality of fibers having different lengths are sequentially connected, four indexes obtained from each are obtained, and it is determined whether the calculation and storage of the four indexes are completed (step 605). .. If it is not completed, the next delay is set (the connection is changed to a fiber having a different length) (step 606), and steps 603 and 604 are repeated again.

Based on the four indexes obtained by trying the connection of all the fibers, the signal processing unit 144 calculates and stores the delay for which each index is optimal (step 607). The method will be described with reference to FIG. 7.

FIG. 7 shows a graph in which five fibers having different lengths are prepared as an example, and four indexes obtained by connecting the fibers are plotted.

FIG. 7A is a plot 701 of the signal strength of the first peak with the delay as the horizontal axis. In the present embodiment, since the delay is adjusted by changing the length of the fiber, the horizontal axis may be the length of the fiber. The signal strength of the first peak changes with respect to the delay, and takes the highest value with respect to the delay value 711. This value 711 is the optimum delay for the signal strength of the first peak, and is the value of d1 in the present embodiment.

FIG. 7B is a plot 703 of the second peak suppression ratio with the delay as the horizontal axis. Similar to the signal strength of the first peak, the delay value 712 is the optimum delay d2 of the second peak suppression ratio.

Similarly, FIGS. 7 (c) and 7 (d) are a plot 708 of the Broad Peak suppression ratio and a plot 708 of the Broad Peak height, respectively. Further, the delay values 713 and 714 are the optimum delays d3 and d4, respectively.

The signal processing unit 144 calculates and stores the delay values 711 (d1), 712 (d2), 713 (d3), and 714 (d4) as described above. In the present embodiment, the delay value corresponding to the maximum value or the minimum value of the calculated index is optimized, but the present invention is not limited to this. For example, the graph of the second peak suppression ratio may be approximated by a function, and the delay value corresponding to the maximum value of the approximation function may be calculated. Alternatively, it is also possible to correct the variation by applying a moving average or a median filter and calculate the optimum delay value.

The four delay values corresponding to the four indicators calculated in step 607 may not all match. Therefore, it is necessary to finally calculate an appropriate delay value by weighting and averaging.

In the present embodiment, the weighting is determined based on the change of the index with respect to the delay value. The method will be described below with reference to FIG. 7.

The plot 701 of the signal strength of the first peak shown in FIG. 7A is an amount that can take an absolute value arbitrarily, and what is important is the amount of change with respect to the delay. Therefore, the lower limit 702-2 is set in consideration of the allowable width (allowable width) with the maximum value (upper limit) 702-1 as a reference. The permissible width may be determined, for example, based on the measurement sensitivity of SS-OCT and the permissible width (budget) assigned to the increase / decrease in the measurement sensitivity caused by the change in the delay. In the present embodiment, the allowable width represented by the upper limit 702-1 and the lower limit 702-2 is set to 0.5 dB. In the present embodiment, the measured value of the signal strength of the first peak is within the allowable range for all delays.

The allowable width of the second peak suppression ratio shown in FIG. 7 (b) is determined based on whether or not a ghost is visually recognized in the tomographic image. It depends on the dynamic range required for contrast adjustment when generating tomographic images. In the present embodiment, the lower limit 704 of the second peak suppression ratio is set, and the value thereof is, for example, 30 dB.

The same applies to the Broad Peak suppression ratio and Broad Peak height shown in FIGS. 7 (c) and 7 (d), and the lower limit 706 and the upper limit 708 are set, respectively.

The optimum weighting of the delay value is determined based on the value obtained by taking the reciprocal of the delay width within the allowable range of each index as the sensitivity. Specifically, for the four indicators, the delay widths are indicated by widths 721, 722, 723, and 724, respectively, and the ratio is 5: 4: 4: 4. The ratio of taking the reciprocals of these and normalizing the total to 1. w1: w2: w3: w4 = 0.29: 0.24: 0.24: 0.23
Is used as a weighting coefficient, and an appropriate delay dopt is calculated as follows: dopt = w1 * d1 + w2 * d2 + w3 * d3 + w4 * d4

The same weighting calculation may be performed by considering the amount of change of each index with respect to a predetermined delay width within the search range as the sensitivity.

In the present embodiment, by connecting a fiber having a length corresponding to the dot to the delay adjusting unit 153, a tomographic image 502 with reduced ghost as shown in FIG. 5B can be obtained. It should be noted that instead of using a fiber having a length corresponding to the baptism, the same effect can be obtained by connecting a fiber having a length closest to the calculated baptism from the fiber used when calculating the baptism.

As described above, there are some peaks that cannot be reduced by delay adjustment. FIG. 4B is the initial delay state, and FIG. 4C schematically shows the case where there is a peak that cannot be reduced even after the delay adjustment. Although not shown in order to maintain the clarity of the figure, the peaks in FIGS. 4 (b) and 4 (c) corresponding to the peaks 402 to 405 shown in FIG. 4 (a) are represented by the same symbols.

In FIG. 4 (c), the second peak 402 changes from the suppression ratio 432 to the suppression ratio 442, and the broad peak 403 changes from the suppression ratio 433 to the suppression ratio 443. Broad Peak height also changes from height 434 to height 444. In both cases, the ghost is reduced by adjusting the delay. On the other hand, the peaks 404 and 405 do not depend on the delay adjustment, and the suppression ratio does not change from the initial delay (FIG. 4 (b)) to after the delay adjustment (FIG. 4 (c)).

In such a case, it is desirable to limit the range in which the peak is detected so that the suppression ratio is optimized by adjusting the delay. Explaining with reference to FIG. 4A, when the delay is adjusted and the suppression ratio of the second peak 402 and the suppression ratio and height of the broad peak 403 are measured, the search for the peak is limited to the range 421. This makes it possible to determine an appropriate delay without being affected by the broad peak 404 and the thin peak 405 that do not change due to the delay. When measuring the final suppression ratio, it is desirable to include both the range 421 and the range 422. This makes it possible to determine whether or not the ghost is reduced at an appropriate delay.

As described above, according to the present embodiment, it is possible to set the optimum delay, and it is possible to remove or reduce the ghost appearing in the tomographic image.

In the present embodiment, the delay is adjusted by the delay adjusting unit 153, but the same effect can be obtained by the operator replacing the signal line 160 with a signal line having a different length. Since the optimization procedure for delay adjustment by exchanging signal lines is the same as described above, the description thereof will be omitted.

[Second Embodiment]
In the first embodiment, the delay adjusting unit 153 replaces the fiber to adjust the delay, and the optimum delay value is calculated. However, in the present embodiment, the electronic delay adjustment is used.

A second embodiment of the present invention will be described with reference to FIG. Since the basic configuration is the same as that of the first embodiment, detailed description thereof will be omitted. Further, since the delay electric circuit can be realized by a technique known to those skilled in the art, detailed description thereof will be omitted.

The light emitted from the light source 101 is guided to and branched by the optical branching element 151 via the fiber 150, and is guided to the fiber 102 and the fiber 152, respectively. The light guided to the fiber 152 is guided to the k-clock generation unit 154. The k-clock signal generated by the k-clock generation unit 154 is guided to the delay adjustment unit 156 via the signal line 155.

The delay adjusting unit 156 is configured so that the delay of the k-clock signal can be adjusted by the control unit 143 using an electric circuit. Since an electric circuit is used for delay adjustment, the adjustment time is short, and the delay adjustment interval can be easily set finely. The adjusted k-clock signal is guided to the control unit 143 via the signal line 160.

The optimum delay calculation process in the present embodiment will be described with reference to FIG. 9. Unlike the first embodiment, in the present embodiment, an appropriate delay search range is first determined based on the signal strength of the first peak.

The signal acquisition control unit 145 moves the coherence gate stage 125 and adjusts the depth position of the first peak 401 (step 901). Next, the start range of the delay for searching the signal strength of the first peak is set. As this set value, for example, the lower limit value of the delay that can be adjusted by the electric circuit can be taken.

The signal processing unit 144 acquires the A-scan profile (step 903), calculates and stores the signal strength of the first peak (step 904). It is determined whether to end the measurement (step 906), and if the measurement is to be continued, the next delay is set (step 905), and steps 903 and 904 are repeated.

Based on the signal strength of the first peak stored in the signal processing unit 144, the delay that maximizes the signal strength is calculated, and the delay obtained by subtracting the predetermined delay value is set as the search start (step 907). Here, the predetermined delay value is a predetermined value in order to narrow the search range of the delay and improve the search efficiency within the range of the delay that can be adjusted by the electric circuit. By using the delay that maximizes the signal strength of the first peak as a reference, it is possible to avoid falling into a local optimum delay.

Steps 908 to 911 are the same as in the first embodiment. However, the end of measurement is based on the search start delay, and it is determined whether steps 908 and 909 have been executed with a predetermined delay width. It is desirable to set the delay so that the delay that maximizes the signal strength of the first peak is included in the predetermined delay width.

Steps 912 to 913 are the same as those in the first embodiment.

As described above, since the adjustment is performed by the electric circuit, it is possible to perform the adjustment at fine intervals without preparing unnecessary fibers as compared with the first embodiment.

[Third Embodiment]
In the first and second embodiments, the delay adjustment in the k-clock path is performed, but in the present embodiment, the delay adjustment in the interference signal path is performed.

A third embodiment of the present invention will be described with reference to FIG. Since the basic configuration is the same as that of the first and second embodiments, detailed description thereof will be omitted.

The interference signal, which is an electric signal from which the DC component detected by the detector 141 has been removed, is guided to the delay adjusting unit 157. The delay adjusting unit 157 is configured so that the delay of the interference signal can be adjusted by the control unit 143 using an electric circuit. Since an electric circuit is used for delay adjustment, the adjustment time is short, and the delay adjustment interval can be easily set finely. The delay-adjusted interference signal is guided to the signal processing unit 144 via the signal line 160.

Since the procedure for calculating the optimum delay by adjusting the delay is the same as that in the second embodiment, the description thereof will be omitted.

As described above, according to the present embodiment, an appropriate delay can be set, and ghosts appearing in the tomographic image can be removed or reduced.

[Other embodiments]
In the above-described embodiment, the case where the object to be inspected is an eye is described, but the present invention can also be applied to an object to be inspected such as skin or an organ other than the eye. In this case, the present invention has an aspect as a medical device other than an imaging device, for example, an endoscope. Therefore, it is preferable that the present invention is grasped as an image processing apparatus exemplified by the image pickup apparatus, and the eye to be inspected is grasped as one aspect of the object to be inspected.

The present invention can also be achieved by configuring the device as follows. That is, a recording medium (or storage medium) in which a program code (computer program) of software that realizes the functions of the above-described embodiment is recorded may be supplied to the system or device.

Further, not only the aspect of the recording medium but also a computer-readable recording medium may be used. Then, the computer (or CPU or MPU) of the system or device reads and executes the program code stored in the recording medium. In this case, the program code itself read from the recording medium realizes the function of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present invention. The embodiment can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiment, and various modifications are made within the scope of the gist of the present invention described in the claims.・ Can be changed.

101 Light source 141 Detector 144 Signal processing unit 146 Display unit 147 Image generation unit 148 Map generation unit 153 Delay adjustment unit 154 k-clock generation unit

Claims (12)

An optical interference tomographic image device that acquires a tomographic image of a subject using light output from a wavelength sweep light source.
A clock generation means for generating a clock signal using the light, and
A light receiving means that converts the interference light obtained by irradiating the subject with the light into an electric signal, and the light receiving means.
A conversion means for converting the electric signal into a data string using the clock signal, and
An acquisition means for obtaining an intensity signal in the depth direction by Fourier transforming the data string,
An optical interference tomographic image apparatus comprising an adjusting means for adjusting the signal intensities of a plurality of peaks included in the intensity signal in the depth direction. The optical interference tomographic image apparatus according to claim 1, wherein the adjusting means adjusts the relative signal intensities of the plurality of peaks. The adjusting means is an optical path to the light receiving means in which the light output from the wavelength sweeping light source is input as the interference light, and until the light output from the wavelength sweeping light source is input to the clock generation means. The optical interference tomographic image apparatus according to claim 1 or 2, which adjusts the difference in optical path length from the optical path. The optical interference tomographic image apparatus according to claim 3, wherein the adjusting means changes the optical path length of the light between the wavelength sweeping light source and the clock generating means. The optical interference tomographic image apparatus according to claim 1 or 2, wherein the adjusting means adjusts a delay value of the clock signal input to the converting means. The optical interference tomographic image apparatus according to claim 1 or 2, wherein the adjusting means adjusts a delay value of the electric signal input to the converting means. Further having a detecting means for detecting the signal strength of the plurality of peaks,
The optical interference tomographic image apparatus according to any one of claims 1 to 6, wherein the adjusting means adjusts the signal intensities of the detected plurality of peaks so that the plurality of indexes are appropriate. The optical interference tomographic image apparatus according to claim 7, further comprising a setting means for setting a range for detecting the signal intensities of the plurality of peaks. The optical interference tomographic image apparatus according to claim 8, wherein the setting means sets a range excluding a range in which the signal intensity of the peak does not change even if the adjustment by the adjusting means is performed. It is a control method of an optical interference tomographic image device that acquires a tomographic image of a subject using light output from a wavelength sweep light source.
A clock generation step of generating a clock signal using the light and
A light receiving step of converting the interference light obtained by irradiating the subject with the light into an electric signal, and a light receiving step.
A conversion step of converting the electric signal into a data string using the clock signal, and
The acquisition step of obtaining the intensity signal in the depth direction by Fourier transforming the data string, and
A control method for an optical interference tomographic image apparatus, which comprises an adjusting step for adjusting the signal intensities of a plurality of peaks included in the intensity signal in the depth direction. The control method for an optical interference tomographic image apparatus according to claim 10, wherein in the adjustment step, the relative signal intensities of the plurality of peaks are adjusted. A computer program that causes a computer to function as the optical interference tomographic image apparatus according to any one of claims 1 to 9.

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