JP6798095B2 - Optical coherence tomography equipment and control programs used for it - Google Patents

Description

The present disclosure relates to an optical coherence tomography apparatus that obtains motion contrast data of a subject, and a control program used therein.

In a conventional optical coherence tomography apparatus (also referred to as an OCT apparatus), an apparatus for measuring retinal blood flow is known. This utilizes the fact that the frequency of the measurement light applied to the eye to be inspected changes due to the Doppler shift caused by blood cells flowing through the blood vessels.

International Publication No. 2010/143601

H.C.Hendargo et al. Biomed. Opt. Express, Vol. 4, No.6, p.803 / May 2013 Yonghua Zhao et al. OPTICS LETTERS / Vol. 25, No. 2 / January 15, 2000 Adrian Mariampillai et al. OPTICS LETTERS / Vol. 33, No. 13 / July 1, 2008 Vivek J. Srinivasan et al. OPTICS LETTERS / Vol. 35, No. 1 / January 1, 2010 P. Meemon and J. Rolland, "Swept-source based, single-shot, multi-detectable velocity range Doppler optical coherence tomography," Biomed. Opt. Express, vol. 1, no. 3, pp. 3116 ~ 3121, 2010 ..

The frequency change due to the Doppler shift is slight, and the frequency change of the light wave is detected as the phase change. The detection range of the phase change is often limited to, for example, the range of −π to π. Therefore, when a phase change outside the detection range occurs, the actually generated phase change and the detected phase change may differ, and the waveform of the phase change profile may become discontinuous. Thus, the discontinuous waveform profile was unsuitable for measuring blood flow.

In view of the above problems, it is a technical subject of the present disclosure to provide an optical coherence tomography apparatus capable of suitably obtaining a blood flow velocity of a subject.

In order to solve the above problems, the present invention is characterized by having the following configurations.

(1) An optical coherence tomography apparatus including an OCT optical system for acquiring an OCT signal by a measurement light scanned on a subject by a scanning means and a reference light corresponding to the measurement light. An acquisition means for acquiring motion contrasts of a plurality of OCT signals acquired at time intervals between each B scan by performing B scans that scan light in the transverse direction a plurality of times with respect to the same position on the subject. When the determination means for determining whether or not the profile of the phase difference between the plurality of OCT signals, which is the basis of the motion contrast, is continuous, and when the determination means determines that the profile is discontinuous. The motion contrast between the drive control means that controls the drive of the scanning means and changes the time interval between the B scans and the plurality of OCT signals acquired at the time interval changed by the drive control means. It is characterized by comprising a control means for calculating the blood flow velocity of the subject based on the above.
(2) An optical coherence tomography apparatus including an OCT optical system for acquiring an OCT signal by a measurement light scanned on a subject by a scanning means and a reference light corresponding to the measurement light, wherein the measurement is performed. Acquiring the motion contrast of a plurality of OCT signals acquired with a first time interval between each B scan by performing B scans that scan light in the transverse direction a plurality of times with respect to the same position on the subject. The acquisition means includes means and a vascular information acquisition means for acquiring at least one of the diameter and type of the blood vessel based on the three-dimensional structure of the blood vessel of the subject, and the acquisition means is acquired by the vascular information acquisition means. A second time interval different from the first time interval, which is preset according to the acquired diameter or type of the blood vessel based on the diameter or type of the blood vessel, is provided between each B scan. It is characterized in that the motion contrast of a plurality of acquired OCT signals is acquired.
(3) A control program used in an optical coherence tomography apparatus including an OCT optical system for acquiring an OCT signal by a measurement light scanned on a subject by a scanning means and a reference light corresponding to the measurement light. By being executed by the processor of the optical coherence tomography apparatus, the B scans that scan the measurement light in the transverse direction are performed a plurality of times with respect to the same position on the subject, so that the time interval between each B scan is The acquisition step of acquiring the motion contrasts of the plurality of OCT signals acquired with a space between the two, and the determination of determining whether or not the profile of the phase difference between the plurality of OCT signals which is the basis of the motion contrast is continuous. In the step, the drive control step that controls the drive of the scanning means and changes the time interval between the B scans when the profile is determined to be discontinuous in the determination step, and the drive control step. It is characterized in that the optical coherence tomography apparatus performs a calculation step of calculating the blood flow velocity of the subject based on the motion contrasts of the plurality of OCT signals acquired at the changed time intervals. And.

It is a block diagram explaining the structure of an optical coherence tomography apparatus. It is a figure which shows the outline of an optical system. It is a flowchart for demonstrating the process of this Example. It is an image figure of the fundus for explaining the measurement of this Example. It is an image diagram which shows the tomographic blood vessel image. It is a flowchart explaining control of blood flow measurement of this Example. It is a figure explaining the correspondence of a motion contrast image and an observation image. It is a figure which shows an example of the motion contrast image displayed on the display part. It is a figure explaining how to obtain the blood flow velocity. It is a figure which shows the relationship between time and blood flow velocity. It is a figure for demonstrating the profile of a phase difference.

<Overview>
Hereinafter, the outline of the optical coherence tomography apparatus according to the present disclosure will be described with reference to FIGS. 1 to 11. The optical coherence tomography apparatus of the present disclosure (for example, the optical coherence tomography apparatus 10) acquires motion contrast data of a subject. The motion contrast is, for example, detection information such as a movement of a subject and a change over time. For example, a flow image or the like is also a kind of motion contrast image. The flow image is, for example, an image obtained by detecting the movement of a fluid or the like. Angiographic images and the like obtained by detecting the movement of blood and contrasting the positions of blood vessels can be said to be a kind of motion contrast images.

The optical coherence tomography apparatus of the present disclosure (hereinafter, may be abbreviated as this apparatus) mainly includes, for example, an OCT optical system (for example, OCT optical system 200) and an acquisition unit (for example, a control unit 70). Be prepared. The OCT optical system may acquire an OCT signal (interference signal) by, for example, the measurement light scanned by the scanning unit (for example, the optical scanner 108) on the subject and the reference light corresponding to the measurement light. The acquisition unit acquires, for example, the motion contrasts of a plurality of OCT signals acquired at a first time interval with respect to the same position on the subject. Then, when the profile of the phase difference between the plurality of OCT signals which is the basis of the motion contrast is discontinuous, the acquisition unit is acquired at a second time interval different from the first time interval. The motion contrast of a plurality of OCT signals may be acquired. The acquisition unit may change the time interval so that the phase difference profiles do not become discontinuous. The second time interval may be shorter than the first time interval. By acquiring the motion contrast having a continuous profile in this way, the examiner can easily confirm the distribution of moving objects and the like.

The device may further include a determination unit (for example, a control unit 70). The determination unit may, for example, detect the inclination of the phase difference profile acquired by the acquisition unit and determine whether or not the phase difference profile is continuous based on the detected inclination.

The device may further include a drive control unit (for example, a control unit 70). For example, when the profile of the phase difference is discontinuous, the drive control unit may control the drive of the scanning unit and change the irradiation time interval for the same position. For example, the drive control unit may change the irradiation time interval for the same position to be shorter.

When the acquired phase difference profile is discontinuous, the acquisition unit uses a plurality of OCT signals acquired at intervals of the first time to obtain a second time different from the first time interval. At least one set of OCT signals acquired at intervals may be selected. Then, the acquisition unit may acquire the motion contrast of the selected OCT signal set.

For example, the acquisition unit may select a signal by skipping one of the plurality of OCT signals acquired at the first time interval, and acquire motion contrast based on the selected OCT signal. As a result, the acquisition unit acquires motion contrast based on a plurality of OCT signals acquired at a second time interval, which is twice the first time interval, for example. Similarly, the acquisition unit may select signals by skipping two, three, .... As a result, the calculated time interval T can be changed without having to bother to control the driving of the scanning unit.

In addition, for example, when the profile of the phase difference between a plurality of OCT signals which is the basis of the motion contrast is continuous, the acquisition unit is set from the first time interval in order to increase the signal-to-noise ratio of the motion contrast. The motion contrasts of the plurality of OCT signals acquired at a long second time interval may be acquired.

The device may further include a blood vessel information acquisition unit (for example, a control unit 70). The blood vessel information acquisition unit acquires at least one of the diameter and type of blood vessels based on, for example, the three-dimensional structure of the blood vessels of the subject. Then, the acquisition unit is acquired based on the diameter or type of the blood vessel acquired by the blood vessel information acquisition unit when the profile of the phase difference between the plurality of OCT signals which is the basis of the motion contrast is discontinuous. The motion contrast of a plurality of OCT signals acquired at a second time interval different from the first time interval, which is preset according to the diameter or type of the blood vessel, may be acquired.

The apparatus may include, for example, a processor (for example, a control unit 70) and execute a control program stored in a memory or the like. The control program includes, for example, an acquisition step. In the acquisition step, for example, when the motion contrasts of a plurality of OCT signals acquired at the first time interval with respect to the same position on the subject are acquired and the acquired phase difference profiles are discontinuous. , Is a step of acquiring the phase difference of a plurality of OCT signals acquired at a second time interval different from the first time interval.

<Example>
Hereinafter, one of the typical examples will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an optical coherence tomography apparatus (hereinafter, also referred to as the present apparatus) 10 according to the present embodiment. As an example, this device 10 will be described as a fundus photography device that acquires a tomographic image of the fundus of the eye to be inspected.

The OCT control system 1 processes the detection signal acquired by the OCT optical system 100. The OCT control system 1 has a control unit 70. The OCT optical system 100 captures, for example, a tomographic image of the fundus Ef of the eye E to be inspected. The OCT optical system 100 is connected to, for example, the control unit 70.

The OCT optical system 100 will be described with reference to FIG. The OCT optical system 100 irradiates the fundus with measurement light. The OCT optical system 100 detects an interference state between the measurement light reflected from the fundus and the reference light by the light receiving element (detector 120). In order to change the imaging position on the fundus Ef, the OCT optical system 100 includes an irradiation position changing unit (for example, an optical scanner 108, a fixation target projection unit 300, etc.) that changes the irradiation position of the measurement light on the fundus Ef. The control unit 70 controls the operation of the irradiation position changing unit based on the set imaging position information, and acquires a tomographic image based on the received signal from the detector 120.

<OCT optical system>
The OCT optical system 100 has a device configuration of a so-called optical coherence tomography (OCT) for ophthalmology, and images a tomographic image of the eye E. The OCT optical system 100 divides the light emitted from the measurement light source 102 into the measurement light (sample light) and the reference light by the coupler (optical divider) 104. The OCT optical system 100 guides the measurement light to the fundus Ef of the eye E by the measurement optical system 106, and guides the reference light to the reference optical system 110. The OCT optical system 100 causes the detector (light receiving element) 120 to receive the interference light obtained by combining the measurement light reflected by the fundus Ef and the reference light.

The detector 120 detects the OCT signal of the measurement light and the reference light. In the case of Fourier domain OCT, the spectral intensity of the interference light (spectral OCT signal) is detected by the detector 120, and the OCT signal is acquired by the Fourier transform on the spectral intensity data. For example, by calculating the absolute value of the amplitude in the complex OCT signal, the profile (A scan signal) in the depth direction (A scan direction) in a predetermined range is acquired. OCT image data (tomographic image data) is acquired by arranging the brightness profiles in the depth direction at each scanning position of the measurement light scanned by the optical scanner 108. Here, the luminance profile in the OCT image data is a sequence in which the luminance values of each pixel are arranged in the depth direction on the A-Scan line, and is a graph of the luminance values in the depth direction.

The OCT three-dimensional data may be acquired by scanning the measurement light two-dimensionally. In addition, an OCT front image (for example, an integrated image integrated in the depth direction) may be acquired from the OCT three-dimensional data.

Further, the functional OCT signal may be acquired by signal processing of the OCT signal. The functional OCT image data (motion contrast image data) is acquired by arranging the functional OCT signals (motion contrast data) at each scanning position of the measurement light scanned by the optical scanner 108. Further, the three-dimensional function OCT image data (three-dimensional motion contrast data) may be acquired by scanning the measurement light two-dimensionally. Further, an OCT function front (En-face) image (for example, a Doppler front (En-face) image, a speckle variance front image) may be acquired from the three-dimensional function OCT image data.

Examples of the OCT optical system 100 include Spectral-domain OCT (SD-OCT) and Swept-source OCT (SS-OCT). Further, it may be Time-domain OCT (TD-OCT).

In the case of SD-OCT, a low coherent light source (broadband light source) is used as the light source 102, and the detector 120 is provided with a spectroscopic optical system (spectrum meter) that disperses the interference light into each frequency component (each wavelength component). .. The spectrometer consists of, for example, a diffraction grating and a line sensor.

In the case of SS-OCT, a wavelength scanning light source (wavelength variable light source) that changes the emission wavelength at high speed in time is used as the light source 102, and for example, a single light receiving element is provided as the detector 120. The light source 102 is composed of, for example, a light source, a fiber ring resonator, and a wavelength selection filter. Then, as the wavelength selection filter, for example, a combination of a diffraction grating and a polygon mirror, and a filter using Fabry-Perot Etalon can be mentioned.

The light emitted from the light source 102 is divided into a measured luminous flux and a reference luminous flux by the coupler 104. Then, the measured luminous flux is emitted into the air after passing through the optical fiber. The luminous flux is focused on the fundus Ef via the optical scanner 108 and other optical members of the measurement optical system 106. Then, the light reflected by the fundus Ef is returned to the optical fiber through the same optical path.

The optical scanner 108 scans the measurement light two-dimensionally (in the XY direction (transverse direction)) on the fundus. The optical scanner 108 is arranged at a position substantially conjugate with the pupil. The optical scanner 108 is, for example, two galvano mirrors, and the reflection angle thereof is arbitrarily adjusted by the drive mechanism 50.

As a result, the luminous flux emitted from the light source 102 changes its reflection (traveling) direction and is scanned in an arbitrary direction on the fundus Ef. As a result, the imaging position on the fundus Ef is changed. The optical scanner 108 may have a configuration that deflects light. For example, in addition to a reflection mirror (galvano mirror, polygon mirror, resonant scanner), an acoustic optical element (AOM) that changes the traveling (deflection) direction of light is used.

The reference optical system 110 generates a reference light that is combined with the reflected light acquired by the reflection of the measurement light at the fundus Ef. The reference optical system 110 may be of the Michaelson type or the Machzenda type. The reference optical system 110 is formed by, for example, a reflective optical system (for example, a reference mirror), and the light from the coupler 104 is reflected by the reflective optical system to be returned to the coupler 104 again and guided to the detector 120. As another example, the reference optical system 110 is formed by a transmission optical system (for example, an optical fiber) and guides the light from the coupler 104 to the detector 120 by transmitting it without returning it.

The reference optical system 110 has a configuration in which the optical path length difference between the measurement light and the reference light is changed by moving the optical member in the reference optical path. For example, the reference mirror is moved in the optical axis direction. The configuration for changing the optical path length difference may be arranged in the measurement optical path of the measurement optical system 106.

<Front observation optical system>
The front observation optical system 200 is provided to obtain a front observation image of the fundus Ef. The observation optical system 200 is, for example, via an optical scanner that scans measurement light (for example, infrared light) emitted from a light source two-dimensionally on the fundus, and a symfocal aperture arranged at a position substantially conjugate with the fundus. It is provided with a second light receiving element that receives the reflected light from the fundus, and has a device configuration of a so-called ophthalmic scanning laser ophthalmoscope (SLO). The front observation optical system 200 may acquire a front observation image at any time in parallel with the acquisition of the OCT signal by the OCT optical system 100, for example.

The observation optical system 200 may have a so-called fundus camera type configuration. Further, the OCT optical system 100 may also be used as the observation optical system 200. That is, the front observation image may be acquired by using the data forming the tomographic image obtained two-dimensionally (for example, the integrated image in the depth direction of the three-dimensional tomographic image, each position of XY). Integrated value of spectrum data in, brightness data at each position of XY in a certain depth direction, surface layer image of retinal, etc.).

<Focus target projection unit>
The fixation target projection unit 300 has an optical system for guiding the line-of-sight direction of the eye E. The fixation target projection unit 300 has an fixation target presented to the eye E, and can guide the eye E in a plurality of directions.

For example, the fixation target projection unit 300 has a visible light source that emits visible light, and changes the presentation position of the target in two dimensions. As a result, the line-of-sight direction is changed, and as a result, the imaging region is changed. For example, when the fixation target is presented from the same direction as the imaging optical axis, the central portion of the fundus is set as the imaging region. Further, when the fixation target is presented upward with respect to the imaging optical axis, the upper part of the fundus is set as the imaging region. That is, the imaging portion is changed according to the position of the optotype with respect to the imaging optical axis.

The fixation target projection unit 300 has, for example, a configuration in which the fixation position is adjusted according to the lighting positions of LEDs arranged in a matrix, the light from the light source is scanned by using an optical scanner, and fixation is performed by controlling the lighting of the light source. Various configurations such as a configuration for adjusting the position can be considered. Further, the projection unit 300 may be an internal fixation light type or an external fixation light type.

<Control unit>
The control unit 70 includes a CPU (processor), RAM, ROM, and the like. The CPU of the control unit 70 controls the entire device (OCT control system 1, OCT optical system 100) such as each member of each configuration. The RAM temporarily stores various types of information. The ROM of the control unit 70 stores various programs, initial values, and the like for controlling the operation of the entire device. The control unit 70 may be composed of a plurality of control units (that is, a plurality of processors).

As shown in FIG. 1, the control unit 70 is electrically connected to a non-volatile memory (storage means) 72, an operation unit (control unit) 76, a display unit (monitor) 75, and the like. The non-volatile memory (memory) 72 is a non-transient storage medium capable of retaining the stored contents even when the power supply is cut off. For example, a hard disk drive, a flash ROM, a detachable USB memory, or the like can be used as the non-volatile memory 72. The memory 72 stores a photographing control program for controlling the photographing of the front image and the tomographic image by the OCT optical system 100. Further, the memory 72 stores a signal processing program that enables signal processing of the OCT signal obtained by the OCT control system 1. Further, the memory 72 stores various information related to imaging such as a tomographic image (OCT data) in the scanning line, a three-dimensional tomographic image (three-dimensional OCT data), a fundus front image, and information on the imaging position of the tomographic image. Various operation instructions by the inspector are input to the operation unit 76.

The operation unit 76 outputs a signal corresponding to the input operation instruction to the control unit 70. For the operation unit 76, for example, at least one of a mouse, a joystick, a keyboard, a touch panel, and the like may be used.

The display unit 75 may be a display mounted on the main body of the device or a display connected to the main body. A display of a personal computer (hereinafter referred to as "PC") may be used. A plurality of displays may be used together. Further, the display unit 75 may be a touch panel. When the display unit 75 is a touch panel, the display unit 75 functions as an operation unit. Various images including a tomographic image and a frontal image taken by the OCT optical system 100 are displayed on the display unit 75.

<Shooting motion contrast images>
Hereinafter, the operation method and control operation of the present device 10 when capturing a motion contrast image will be described with reference to FIG. The control unit 70 includes, for example, a processor (for example, a CPU) that controls various control processes and a storage medium for storing a program. The processor executes the process described below according to the program. In the following description, numbers for identifying each step of control are assigned, but the order of the assigned numbers and the actual order of control do not always match.

First, the examiner instructs the subject to gaze at the fixation target of the fixation target projection unit 300, and then the display unit 75 displays an anterior segment observation image taken by an anterior segment observation camera (not shown). While observing, the alignment operation is performed using the operation unit 76 (for example, a joystick not shown) so that the measurement optical axis comes to the center of the pupil of the eye to be inspected.

(Step 1: OCT shooting)
The control unit 70 acquires at least two frames of OCT signals at different times at the same position. For example, the control unit 70 controls the drive of the optical scanner 108 to scan the measurement light on the fundus. For example, the measurement light is scanned in the x direction along the first scanning line S1 shown in FIG. Scanning the measurement light in the transverse direction (for example, the x direction) is called "B scan". Hereinafter, the OCT signal of one frame will be described as an OCT signal obtained by one B scan. The control unit 70 acquires the OCT signal detected by the detector 120 during scanning. In FIG. 4, the direction of the z-axis is the direction of the optical axis of the measurement light. The direction of the x-axis is perpendicular to the z-axis and to the left and right. The direction of the y-axis is perpendicular to the z-axis and up and down.

When the first scan is completed, the control unit 70 performs the second scan at the same position as the first scan. For example, the control unit 70 scans the measurement light along the scanning line S1 shown in FIG. 4, and then scans the measurement light again along the scanning line S1. The control unit 70 acquires the OCT signal detected by the detector 120 during the second scan. As a result, the control unit 70 can acquire two frames of OCT signals at the same position and at different times. In this embodiment, scanning at the same position is repeated four times to acquire continuous four-frame OCT signals at different times. The control unit 70 repeats scanning on the scanning line S1 four times, for example, and acquires an OCT signal of four frames. However, the OCT signal is not limited to 4 frames, and at least 2 frames or more with different times may be acquired.

If it is possible to acquire signals at the same position at different times in one scan, it is not necessary to perform the second scan. For example, when two measurement lights whose optical axes are deviated by a predetermined interval are scanned at one time, it is not necessary to scan two times. It suffices if OCT signals at the same position in the subject and at different times can be acquired.

In addition, the control unit 70 similarly acquires signals of at least two frames having different times at different positions. As shown in FIG. 4, it is assumed that the first scanning line S1 is, for example, y = y1. Further, it is assumed that the second scanning line S2 is, for example, y = y2. When the acquisition of the signals having different times is completed in the first scanning line S1, the control unit 70 subsequently acquires the signals of at least two frames having different times in the second scanning line S2.

As shown in FIG. 4, the control unit 70 raster scans the measurement light (raster scan), and obtains at least two frames or more of OCT signals having different times at each scanning line. This makes it possible to acquire three-dimensional information inside the fundus.

The raster scan is a pattern in which the measurement light scans the fundus in a rectangular shape. The raster scan is used, for example, as an En-face image scan.

(Step 2: Acquisition of complex OCT signal group)
Subsequently, the control unit 70 processes the OCT signal acquired by the OCT optical system 100 to acquire the complex OCT signal. For example, the control unit 70 Fourier transforms the OCT signal (interference signal) acquired in step 1. Here, the signal at the nth (x, z) position in the N frame is represented by An (x, z). The control unit 70 obtains a complex OCT signal An (x, z) by Fourier transform. The complex OCT signal An (x, z) includes a real number component and an imaginary number component.

(Step 3: Acquisition of vascular tomographic image group)
Next, the control unit 70 processes the complex OCT signal acquired in step 2 to acquire a vascular tomographic group (motion contrast image group). As a method of processing the complex OCT signal, for example, a method of calculating the phase difference of the complex OCT signal, a method of calculating the vector difference of the complex OCT signal, a method of multiplying the phase difference and the vector difference of the complex OCT signal, and the like can be considered. Be done. In this embodiment, a method of calculating the phase difference will be described as an example.

First, the control unit 70 calculates the phase difference for the complex OCT signals A (x, z) acquired at at least two or more different times at the same position. The control unit 70 calculates the change in phase by using, for example, the equation (1). In this embodiment, for example, in order to perform measurements at four different times, a total of three calculations of T1 and T2, T2 and T3, and T3 and T4 are performed, and three data are calculated. In the formula, An indicates the signal acquired at time Tn, and * indicates the complex conjugate.

The control unit 70 may, for example, add and average the signals of three frames to remove noise. Since the noise component exists randomly in each frame, it becomes smaller than the signal component by averaging.

As described above, the control unit 70 acquires a profile in the depth direction regarding the phase difference of the complex OCT signal, and acquires a functional OCT image of the subject by adding shading according to the size of the profile. The control unit 70 repeats the above process for each scanning line, and generates a tomographic blood vessel image for each scanning line as shown in FIG. As a result, the control unit 70 acquires a three-dimensional motion contrast image.

<Measurement of blood flow>
A method of obtaining the blood flow velocity by using the motion contrast image taken as described above will be described with reference to FIG. In this embodiment, the absolute velocity of blood flow is determined using the three-dimensional structure of blood vessels obtained from a three-dimensional motion contrast image. In determining the absolute velocity of blood flow, the control unit 70 first associates the motion contrast image with the observation image (for example, SLO image, infrared fundus image, etc.) taken by the observation optical system 200 (step). 2-1). The observation image associated with the motion contrast image may be an observation image taken while the OCT signal is being acquired by the OCT optical system 100, or an observation image taken after the motion trust image is generated. ..

For example, as shown in FIG. 7, the control unit 70 associates the coordinates in the XY direction in the two-dimensional observation image D2 with the coordinates in the XY direction in the three-dimensional motion contrast image D1. Examples of the method of associating include a method of utilizing the lighting position of the fixation lamp, a method of utilizing the position of a blood vessel, and the like. When using the lighting position of the fixation lamp, for example, from the relationship between the lighting position of the fixation lamp when the motion contrast image D1 is acquired and the lighting position of the fixation lamp when the observation image D2 is acquired, the motion The contrast image D1 and the observation image D2 may be associated with each other. When using the position of a blood vessel, for example, the position of the blood vessel shown in the observation image D2 and the position of the blood vessel shown in the motion contrast image D1 are detected by image processing, and both are matched so that the positions of the blood vessels match. You may attach it.

The control unit 70 may associate, for example, the pixel positions of the motion contrast image D1 and the observation image D2. For example, assuming that the coordinates of a certain pixel of the motion contrast image D1 are (x1, y1), the coordinates (x2, y2) of the corresponding pixel of the observation image D2 may be associated.

In this way, the control unit 70 may associate the observation image D2 with the motion contrast image D1 and use the corresponding information acquired thereby when obtaining the absolute velocity of the blood flow. The control unit 70 may store the corresponding information in the memory 72.

Subsequently, as shown in FIG. 8, the control unit 70 displays the motion contrast image D1 acquired by the above method on the screen of the display unit 75 (step 2-2). The motion contrast image D1 displayed on the display unit 75 may be, for example, a three-dimensional image or a two-dimensional image. In the example of FIG. 8, a two-dimensional image obtained by adding three-dimensional data in a certain depth region is displayed. In this case, the depth region for addition processing may be arbitrarily set.

The examiner confirms the motion contrast image D1 and specifies a blood vessel for measuring blood flow. For example, the examiner may specify a blood vessel by inputting the position of the motion contrast image D1 by clicking or touching a pointing device (for example, a mouse, a touch panel, etc.) of the operation unit 76. In the example of FIG. 8, the control unit 70 displays a pointer 76a that can be moved according to the operation of the operation unit 76. The examiner designates a blood vessel by, for example, moving the pointer 76a displayed on the screen onto a desired blood vessel and performing an operation such as clicking. In this case, the pointer 76a is used to specify an arbitrary position on the display unit 75. In the following description, the blood vessel designated by the examiner will be referred to as a designated blood vessel.

The control unit 70 receives an instruction from the examiner (steps 2-3). For example, the control unit 70 receives an examiner's instruction based on the signal output from the operation unit 76. For example, the control unit 70 may acquire a position (designated position) designated by the examiner by the pointing device of the operation unit 76.

The control unit 70 acquires which position of the observation image D2 the designated position designated on the motion contrast image corresponds to (step 2-4). For example, the control unit 70 acquires the corresponding position on the observation image corresponding to the xy coordinate of the designated position on the motion contrast image based on the correspondence information between the observation image D2 and the motion contrast image D1 stored in the memory 72. To do. For example, the control unit 70 acquires the xy coordinates on the observation image corresponding to the xy coordinates of the designated blood vessel from the corresponding information stored in the memory 72.

When the corresponding position of the designated blood vessel on the observation image is obtained, the control unit 70 sets the corresponding position as the tracking position (step 2-5) and starts scanning (step 2-6). The control unit 70 scans a plurality of times at time intervals while always tracking the corresponding position so that it can be scanned. For example, the control unit 70 may take an observation image at any time in parallel with scanning the measurement light, and may correct the scan position according to the positional deviation of the fundus reflected in the updated observation image.

More specifically, the control unit 70 compares the still image of the observation image D2 used for associating with the motion contrast image D1 with the current observation image D2, and obtains an image of the misalignment direction and the amount of misalignment. Detect (calculate) by processing. For example, the control unit 70 uses the still image data of the observation image D2 at the time of associating with the motion contrast image D1 as a reference image, and determines the position shift direction and the position shift amount between the reference image and the observation image acquired in real time. calculate. As a result, the position shift information with respect to the still image can be obtained.

When the misalignment direction and the misalignment amount are detected as described above, the control unit 70 appropriately drives and controls the two galvanometer mirrors of the optical scanner 108 so that the misalignment of the scanning position is corrected. As a result, the scanning position is corrected. As described above, even when the eye to be inspected is displaced, the scanning position is corrected, and the control unit 70 can always acquire a plurality of OCT signals having different times at the same scanning position.

The control unit 70 calculates the absolute velocity of blood flow using the multiple OCT signals acquired in step 2-6 and the three-dimensional structure of the blood vessel obtained from the three-dimensional motion contrast image (step 2). -7). For example, the control unit 70 obtains the Doppler phase shift from a plurality of OCT signals. Then, the control unit 70 may calculate the absolute velocity of the blood flow from the obtained phase difference and the blood flow direction obtained from the three-dimensional structure of the blood vessel.

As a method of obtaining the direction of blood flow from the three-dimensional structure of the blood vessel obtained from the motion contrast image D1, for example, a method of thinning the three-dimensional structure of the blood vessel can be mentioned. For example, as shown in FIG. 9, the three-dimensional vascular structure K can be represented by one line L0 by the thinning process. For example, the control unit 70 may consider the slope of the line L0 with respect to the measurement light scanned on the scan line SL as the direction of blood flow, and calculate the absolute velocity of blood flow from the above-mentioned phase difference.

<Calculation of blood flow velocity>
The absolute velocity of blood flow will be described. The component v _{z in} the optical axis direction of the absolute velocity v of blood flow can be expressed by the following equation (2) using the measurement light and the angle α formed by the blood vessel.

Here, the component v _z can be expressed by the following equation (3) using the phase difference ΔΦ _Doppler (−π to π), the refractive index n of the vascular tissue, the central wave number k, and the time interval T.

Using the above two equations, the absolute velocity v of blood flow can be obtained from the phase difference as in the following equation (4).

As described above, in the present embodiment, the control unit 70 measures the blood flow of the eye to be inspected by using the three-dimensional motion contrast image D1 and a plurality of temporally different OCT signals related to the same scanning position. Since the control unit 70 can acquire the blood flow direction from the three-dimensional structure of the blood vessel obtained by the three-dimensional motion contrast image D1, the absolute blood flow velocity of the eye to be inspected can be measured from the Doppler shift. As a result, the control unit 70 can acquire information useful for diagnosing the eye to be inspected, for example, by comparing the blood flow velocities with respect to a plurality of subjects.

Further, in this embodiment, the control unit 70 uses the blood flow direction obtained from the three-dimensional motion contrast image D1 acquired in advance for calculating the absolute velocity of the blood flow. Therefore, if a plurality of OCT signals that differ in time at the same position of the eye to be inspected are continuously acquired by the OCT optical system, the control unit 70 will perform dynamic blood flow in consideration of the influence of the pulsation of the subject. The absolute velocity of can be obtained (see FIG. 10). In this way, the control unit 70 can provide information that can be used to detect a disease such as arteriosclerosis by acquiring a change in blood flow velocity over time.

Further, in this embodiment, the control unit 70 associates the position of the blood vessel confirmed in the motion contrast image D1 with the observation image D2, and performs tracking based on the corresponding information. For example, in the motion contrast image D1, it takes time to generate an image, so it is difficult to acquire deviation information for following the fine movement of the eye to be inspected. On the other hand, since the observation image D2 takes a shorter time to acquire the image than the motion contrast image, it is suitable for acquiring the deviation information for following the fine movement of the eye to be inspected. By associating the positions of small blood vessels that are difficult to confirm in the observation image D2 from the motion contrast image as in the control unit 70 of the present embodiment, tracking can be performed even for small blood vessels that are difficult to confirm in the observation image D2. .. As a result, the control unit 70 can easily continuously acquire a plurality of OCT signals at the same position at different times, and can appropriately obtain the absolute velocity of the dynamic blood flow of the subject.

The control unit 70 may automatically set the scan width when scanning the blood vessel designated by the examiner according to the diameter of the blood vessel obtained from the motion contrast image. Of course, the examiner may set it manually.

The control unit 70 may set the time interval T when scanning the blood vessel designated by the examiner according to the diameter of the blood vessel obtained from the motion contrast image. Of course, the examiner may set it manually.

The scanning direction when scanning the blood vessel designated by the examiner may be perpendicular to the blood flow direction. For example, the control unit 70 may calculate a direction perpendicular to the blood flow direction of the designated blood vessel in En-face (direction perpendicular to the measurement light) and perform scanning in this direction. The blood flow direction of the blood vessel may be obtained by thinning the three-dimensional structure of the blood vessel as described above. For thinning, for example, morphology processing, distance conversion processing, or existing algorithms such as Hilditch and Deutsch may be used.

In this way, the control unit 70 scans perpendicularly to the blood flow direction, so that it is not necessary to consider the scan angle with respect to the blood flow direction when calculating the blood flow, and the calculation process is simplified. Can be done. The control unit 70 may automatically set the radial direction of the designated blood vessel to the scan direction, for example. Of course, the control unit 70 may set the scan line based on the operation signal output from the operation unit 76 according to the operation of the examiner.

In the motion contrast image as shown in FIG. 8, each time the examiner designates a new blood vessel, the control unit 70 scans while tracking the designated blood vessel as described above to obtain the blood flow velocity. You may.

<Position detection method>
As a method for detecting the positional deviation between the two observed images during tracking, various image processing methods (methods using various correlation functions, methods using Fourier transform, methods based on matching of feature points) are used. It can be used.

For example, a predetermined reference image (for example, a past front image) or a target image (current front image) is displaced by one pixel, the reference image and the target image are compared, and when both data match most (correlation is high). A method of detecting the positional deviation between both data (when it becomes the highest) can be considered. Further, a method of extracting common feature points from a predetermined reference image and a target image and detecting the positional deviation of the extracted feature points can be considered.

Further, a phase-limited correlation function may be used as a function for obtaining the positional deviation between the two images. In this case, first, each image is Fourier transformed to obtain the phase and amplitude of each frequency component. The obtained amplitude component is normalized to a magnitude 1 for each frequency component. Next, after calculating the phase difference for each frequency between the two images, the inverse Fourier transform is applied to these.

Here, if there is no positional deviation between the two images, only the cosine wave is added, and a peak appears at the origin position (0,0). If there is a misalignment, a peak appears at the position corresponding to the misalignment. Therefore, the positional deviation between the two images can be obtained by obtaining the detection position of the peak. According to this method, the misalignment of the front image can be detected with high accuracy and in a short time.

As described in the above equation (2), the phase difference ΔΦ _Doppler is in the range of −π to π by the inverse tangent operation. Therefore, when the time interval (time interval T) between scans is long, the phase difference ΔΦ _Doppler exceeds the range of −π to π when the blood flow is fast, and scans are performed, for example, as shown in FIG. 11 (a). Directional phase difference ΔΦ _Doppler profile becomes discontinuous. In such a case, it is difficult to diagnose the eye to be inspected including speed measurement from the detected profile. Therefore, as in this embodiment, for example, the control unit 70 searches for an appropriate time interval T and performs scanning.

Hereinafter, in the process of acquiring the scan signal in step 2-6, a method of scanning at an appropriate time interval T so that the phase difference ΔΦ _Doppler does not exceed the range of _−π to π will be described. In the following description, the occurrence of a discontinuity point where the phase difference ΔΦ _Doppler exceeds the range of _−π to π is expressed as “wrapped”.

As a method of scanning at an appropriate interval, for example, the control unit 70 may perform scanning while sequentially changing the time interval T for each scan. In the following description, the control unit 70 performs scanning while sequentially changing the time interval T from a long interval to a short interval. In this case, the control unit 70 sequentially calculates the phase difference ΔΦ _Doppler having different time intervals T using the acquired plurality of OCT signals, and determines whether or not the calculation result of the phase difference ΔΦ _Doppler is wrapped. .. Then, for example, the control unit 70 fixes the time interval T when it is determined that the phase difference ΔΦ _Doppler is no longer wrapped, or a time interval T shorter than that, and continues the scan.

Examples of the method for determining whether or not the phase difference ΔΦ _Doppler is wrapped include a method for determining based on the magnitude of the change in the phase difference ΔΦ _Doppler between adjacent pixels. In this case, the control unit 70 may apply an edge detection filter (for example, a differential process such as a Laplacian filter) to the phase difference ΔΦ _Doppler acquired from a plurality of OCT signals. For example, when an edge detection filter is applied to the profile of the wrapped phase difference ΔΦ _Doppler as shown in FIG. 11 (a), the intensity of the wrapped position is applied as shown in FIG. 11 (b). Becomes locally larger. On the other hand, as shown in FIG. 11 (c), when the edge detection filter is applied to the profile of the unwrapped phase difference ΔΦ _Doppler , the intensity is locally increased as shown in FIG. 11 (d). There is no such thing. Therefore, for example, the control unit 70 may determine that the wrapping is stopped when the average value of the profile after applying the edge detection filter becomes equal to or less than a predetermined value. Of course, when the maximum value after applying the edge detection filter becomes less than a predetermined value, it may be determined that the wrapping is stopped.

As described above, the control unit 70 can acquire the unwrapped phase difference ΔΦ _Doppler regardless of the difference in the speed of blood flow by appropriately setting the time interval T. By acquiring the unwrapped phase difference ΔΦ _Doppler , the laminar flow state of blood flow can be obtained satisfactorily, which can be used for diagnosis of the eye to be inspected. In addition, the examiner can save the trouble of setting the time interval T by himself / herself.

The control unit 70 may search for a time interval T such that the signal strength of the phase difference ΔΦ _Doppler becomes as large as possible. For example, when the control unit 70 determines that the phase difference ΔΦ _Doppler is no longer wrapped, the time interval T is gradually set so that the maximum value of the profile of the phase difference ΔΦ _Doppler becomes as large as possible within the range of −π to _π. It may be changed for a long time to search for an appropriate time interval T.

In the above description, the control unit 70 sequentially changes the time interval T from a long interval to a short interval. When the time interval T is large, the phase difference ΔΦ _Doppler of the Doppler signal due to blood flow becomes large, and there is a high possibility of being wrapped. In this way, when the time interval T is intentionally shortened from the lap state to the unwrapped state, there is a high possibility that a high-intensity signal can be obtained in the range of −π to π.

Of course, the control unit 70 may change the time interval T from a short interval to a long interval. When the time interval T is short, the phase difference ΔΦ _Doppler of the Doppler signal due to blood flow is small, and the unwrapped phase difference ΔΦ _Doppler can be quickly acquired. However, if the time interval T is short, as shown in FIGS. 11 (e) and 11 (f), the signal strength becomes small and the signal may be buried in the noise floor. Therefore, the control unit 70 is not wrapped. You may search for the longest possible time interval T.

In the above example, the time interval T is gradually changed to be longer or shorter, but the present invention is not limited to this. For example, the control unit 70 may alternately change the time interval T between a long interval and a short interval, or may randomly change the interval of the time interval T. Whether the time interval T is shortened or lengthened may be set by the operation signal output from the operation unit by the operation of the examiner.

The control unit 70 uses a plurality of OCT signals acquired to generate the three-dimensional motion contrast image D1 to obtain the absolute velocity of blood flow at a certain time point, and based on the magnitude, the first time. The interval T may be set. After that, as described above, an appropriate time interval T may be obtained by sequentially changing the time interval T. In this way, by setting the time interval T from the absolute velocity of the blood flow at the time when the three-dimensional motion contrast image D1 is acquired, the time required to set an appropriate time interval T can be shortened.

The magnitude of blood flow velocity can be estimated to some extent by the thickness and type of blood vessels (for example, arteries or veins). Therefore, the control unit 70 may set the time interval T based on the blood flow velocity estimated from the thickness, type, and the like of the designated blood vessel. In this case, for example, the control unit 70 acquires the correspondence relationship between the thickness and type of the blood vessel and the magnitude of the blood flow velocity from the past measurement data and the like, and stores it in the memory 72 as a correspondence table. Then, the control unit 70 collates at least one of the types of blood vessels estimated from the size of the designated blood vessel, the depth of the retina in which the blood vessel exists, and the like with the correspondence table stored in the memory 72, and the designated blood vessel. Blood flow velocity may be estimated.

The control unit 70 acquires, for example, a plurality of OCT signals at a plurality of different time intervals T, and among the ΔΦ _Doppler calculated from the obtained plurality of OCT signals, the unwrapped blood flow velocity. It may be used for the calculation of.

In the above description, for example, the control unit 70 changes the time interval T, but the present invention is not limited to this. For example, the control unit 70 scans at a constant time interval T, selects a combination of OCT signals in which the calculated phase difference ΔΦ _Doppler is not wrapped from the obtained plurality of OCT signals, and the absolute blood flow is absolute. The speed may be calculated. For example, the control unit 70 may perform scanning at a short time interval T and thin out data from a plurality of acquired OCT signals to calculate ΔΦ _Doppler . For example, when scanning is performed with a time interval T of 0.5 msec, data is thinned out from a plurality of acquired OCT signals to obtain a time interval T (for example, 1.0 msec, 1.) which is a multiple of 0.5. ΔΦ _Doppler may be calculated from the OCT signal acquired in 5 msec, 2.0 msec, etc.). In this case, the control unit 70 may use, for example, the OCT signal acquired at each time interval T in which ΔΦ _Doppler is not wrapped for calculating the blood flow velocity, or the one having a large maximum value is blood. It may be used to calculate the flow velocity. Further, among the OCT signals acquired at each time interval T, the one having the smallest minimum value of the slope (for example, the differential value) of ΔΦ _Doppler may be used for calculating the blood flow velocity.

In this way, an appropriate time interval T may be searched for by changing the calculated time interval T without changing the time interval T that actually irradiates the measurement light.

1 Optical coherence tomography device 70 Control unit 72 Memory 75 Monitor 76 Operation unit 100 Interference optical system (OCT optical system)
108 Optical scanner 120 Detector 200 Front observation optical system 300 Fixed target projection unit

Claims (4)

An optical coherence tomography apparatus including an OCT optical system for acquiring an OCT signal by a measurement light scanned on a subject by a scanning means and a reference light corresponding to the measurement light.
An acquisition means for acquiring the motion contrast of a plurality of OCT signals acquired at time intervals between the B scans by performing the B scan that scans the measurement light in the transverse direction a plurality of times with respect to the same position on the subject. When,
A determination means for determining whether or not the profile of the phase difference between the plurality of OCT signals, which is the basis of the motion contrast, is continuous.
When the determination means determines that the profile is discontinuous, the drive control means that controls the drive of the scanning means and changes the time interval between each B scan.
A control means for calculating the blood flow velocity of the subject based on the motion contrast of the plurality of OCT signals acquired at the time interval changed by the drive control means.
An optical coherence tomography apparatus characterized by being equipped with. The control means uses a plurality of OCT signals acquired to generate a three-dimensional motion contrast image to obtain the blood flow velocity at a certain time point, and determines the time interval based on the magnitude of the blood flow velocity. The optical coherence tomography apparatus according to claim 1, wherein the optical coherence tomography apparatus is set. An optical coherence tomography apparatus including an OCT optical system for acquiring an OCT signal by a measurement light scanned on a subject by a scanning means and a reference light corresponding to the measurement light.
By performing the B scan that scans the measurement light in the transverse direction a plurality of times with respect to the same position on the subject, the motion contrasts of the plurality of OCT signals acquired at the first time interval between the B scans are acquired. Acquisition method and
A blood vessel information acquisition means for acquiring at least one of the diameter and type of the blood vessel based on the three-dimensional structure of the blood vessel of the subject is provided.
The acquisition means is different from the first time interval preset according to the diameter or type of the acquired blood vessel based on the diameter or type of the blood vessel acquired by the blood vessel information acquisition means. An optical coherence tomography apparatus characterized by acquiring motion contrasts of a plurality of OCT signals acquired with a second time interval between each B scan . A control program used in an optical coherence tomography apparatus including an OCT optical system for acquiring an OCT signal by a measurement light scanned on a subject by a scanning means and a reference light corresponding to the measurement light. By being executed by the processor of the optical coherence tomography apparatus,
An acquisition step of acquiring the motion contrast of a plurality of OCT signals acquired at time intervals between the B scans by performing the B scan that scans the measurement light in the transverse direction a plurality of times with respect to the same position on the subject. When,
A determination step for determining whether or not the profile of the phase difference between the plurality of OCT signals, which is the basis of the motion contrast, is continuous, and
When it is determined in the determination step that the profile is discontinuous, a drive control step that controls the drive of the scanning means and changes the time interval between each B scan.
A calculation step of calculating the blood flow velocity of the subject based on the motion contrast of the plurality of OCT signals acquired at the time interval changed in the drive control step, and a calculation step.
Is executed by the optical coherence tomography apparatus.