JP2001145603A - Oxygen concentration detector of fundus oculi blood vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen concentration detector for the fundus oculi blood vessels which is capable of simultaneously photographing the fundus oculi by light of different wavelengths and measuring the oxygen content condition of the arbitrary blood vessels of the fundus oculi without being affected by the change in the fundus oculi state with lapse of time from these fundus oculi images. SOLUTION: Relating to the images of the same blood vessels of the fundus oculi simultaneously photographed by the 560 nm light having a small difference between the absorption spectra of oxidized hemoglobin and the absorption spectra of reduced hemoglobin with the 600 nm light having the large difference described above, the blood vessels on the one image are extracted and the optical mispositioning of both images is corrected. The distribution of the brightness in a direction perpendicular to their longitudinal direction relating to the multiple points along the blood vessels is detected and the average value along the longitudinal direction of the lower value of the brightness of the blood vessel portions and the average value along the longitudinal direction of the highest value of the brightness near the blood vessel are computed. The concentration in the blood vessels is calculated from the ratio between both average values, by which the oxygen concentration in the fundus oculi blood vessel is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting oxygen concentration in a fundus blood vessel. More specifically, the present invention relates to a device for illuminating and photographing the fundus of a subject's eye with illumination light of different wavelengths, and detecting the oxygen concentration in the fundus blood vessels from the photographed image.

[0002]

2. Description of the Related Art In addition to ophthalmological purposes, imaging of the fundus is widely performed in order to obtain many useful medical findings regarding arteriosclerosis, hypertension and the like.

A fundus photographing apparatus used for such a purpose is disclosed in Japanese Patent Application Laid-Open No. 8-154924. This fundus photographing apparatus is intended to select an arbitrary part of an artery from a fundus image obtained by a television camera and measure the oxygen content of arterial blood at the position.

The configuration includes a first filter and a second filter for the purpose of measuring the contents of reduced hemoglobin and oxyhemoglobin, respectively. Then, the fundus image by the illumination light transmitted through the first filter and the fundus image by the illumination light transmitted through the second filter are respectively stored in the frame memory, and the memory values of the pixels at the same position in both fundus images are compared and calculated. The oxygen content at the position is determined.

However, in this fundus photographing apparatus, a fundus image formed by light transmitted through the first filter and a fundus image formed by light transmitted through the second filter are photographed with a slight time difference. Then, since blood in the blood vessels of the fundus originally pulsates, the blood flow in the arterial blood vessels is different at different imaging points, so whether the difference is due to the filter or the blood volume in the optical analysis. Inconveniences such as unclearness occur.

Further, the above publication does not disclose a technique for detecting the oxygen concentration of a blood vessel from a fundus image.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. The fundus is simultaneously photographed with light of different wavelengths, and the fundus image is not affected by the temporal change of the fundus state from these fundus images. An object of the present invention is to provide an oxygen concentration detecting device for a fundus blood vessel that can measure the oxygen content of a blood vessel.

[0008]

According to the oxygen concentration detecting device of the present invention, the same portion of the fundus is irradiated with the first light having a wavelength at which the difference between the absorption spectrum of oxyhemoglobin and the absorption spectrum of reduced hemoglobin is small. A photographing means for simultaneously photographing with the second light having a large wavelength, a position correcting means for correcting an optical positional shift between the photographed image by the first light and the photographed image by the second light, and specifying a blood vessel on the photographed image And a blood vessel density calculating means for detecting the brightness of the blood vessel and the brightness near the blood vessel from each of the captured images and calculating the density of the blood vessel.

According to such a configuration, data at different wavelengths can be obtained depending on the photographing means for photographing at the same time.
There is no need to consider and correct the temporal variation of this data, and the content of oxyhemoglobin and reduced oxyhemoglobin can be easily identified. Further, the position correcting means enables such identification at the same position on the fundus of both images only by extracting blood vessels in one image, and accurate data can be obtained.

Next, the blood vessel density calculating means detects a brightness distribution in a direction perpendicular to the trajectory along an arbitrary trajectory on the photographed image of the fundus, and calculates the average value of the brightness of the blood vessel and the blood vessel. First brightness detection means for obtaining an average value of brightness in the vicinity of, and first blood vessel density calculation means for obtaining the density of the blood vessel from the average value of the brightness of the blood vessel and the average value of the brightness in the vicinity of the blood vessel,
In the oxygen concentration detection device comprising: the blood vessel extraction means, the brightness distribution in the direction perpendicular to the longitudinal direction of the blood vessel is obtained along the blood vessel specified by the blood vessel extraction means, the brightness of the blood vessel and its Brightness in the vicinity can be easily obtained. The result is a relative blood vessel concentration. When the blood vessel concentration is obtained, the oxygen concentration can be determined from the artery and vein concentrations.

Further, the first lightness detecting means may detect a plurality of points along the blood vessel specified by the blood vessel extracting means.
Detecting the distribution of brightness in the direction perpendicular to the longitudinal direction, configured to detect the lowest value of the brightness of the blood vessel portion and the highest value of the brightness near the blood vessel, the first blood vessel density The calculating means calculates the average value along the longitudinal direction of the blood vessel of the lowest value and the average value along the longitudinal direction of the blood vessel of the highest value, and obtains the concentration of the blood vessel from the ratio of the two average values. In the oxygen concentration detecting device thus constituted, a highly accurate blood vessel concentration can be obtained.

Alternatively, the blood vessel density calculating means specifies two points on an arbitrary trajectory on the photographed image of the fundus, and moves while moving the trajectory in a direction perpendicular to a straight line connecting the two points. Second lightness detecting means for continuously detecting the brightness on the trajectory and calculating the average value of the brightness on the trajectory; and a second blood vessel density for obtaining a blood vessel density from the highest value and the lowest value of the average value In the oxygen concentration detecting device having the calculating means, the blood vessel concentration with higher accuracy can be obtained.

Further, the blood vessel extracting means has a photographed image display device, and is configured to be input as a series of coordinate positions by tracing an image displayed on the photographed image display device. In such an oxygen concentration detecting device, extraction of blood vessels is facilitated.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an apparatus for detecting oxygen concentration in a fundus blood vessel according to an embodiment of the present invention.

The oxygen concentration detecting apparatus 1 is obtained by adding various mechanisms to a conventional fundus photographing apparatus. The oxygen concentration detecting device 1 includes an observation illumination light source 2 and a photographing illumination light source 3.
An illumination optical system 4 is provided for illuminating the observation region and the imaging region of the fundus of the eye E with illumination light from the eye.

The illumination optical system 4 includes an observation illumination optical system 4a having the observation illumination light source 2 and a photographing illumination optical system 4b having the photography illumination light source 3. From the observation illumination optical system 4a, infrared light (may include near-infrared light)
However, visible light from the imaging illumination optical system 4b is guided to the fundus of the eye E through the objective lens 5. The examiner selects an examination site on the fundus while observing the fundus with illumination by the observation illumination optical system 4a. Then, the inspection site is photographed by illumination by the photographing illumination optical system 4b.

The optical paths of the two optical systems 4a and 4b are integrated by inserting a so-called hot mirror 6 in the illustrated form. The hot mirror reflects infrared light and transmits visible light.

On the other hand, a photographing optical system 7 for observing and photographing the fundus by illumination by the illumination optical systems 4a and 4b.
Are arranged. The photographing optical system 7 is a photographing illumination optical system 4.
An area sensor 8 is provided as light receiving means for photographing a part of the fundus based on the illumination light from b.

The photographing optical system 7 is provided with a pair of dichroic mirrors 9a and 9b. Eye to be examined (upstream side)
The dichroic mirror 9a separates the optical path of the illumination light from the illumination optical system for photographing 4b into two systems of light in a short wavelength range and light in a long wavelength range. And it is configured to reach the area sensor 8 via the other dichroic mirror 9b in a slightly shifted state. The dichroic mirror transmits light at a short wavelength (long wavelength) side of a specific wavelength and reflects light at a long wavelength (short wavelength) side.

Each of the separated two optical paths has a wavelength selection filter (bandpass filter) 10a, 10b that transmits only light in a wavelength range (narrow band) having a specific wavelength as a peak.
Are arranged. In the present embodiment, the one band-pass filter 10a transmits light in a wavelength range having a peak at a wavelength of 600 nm (hereinafter, referred to as 600-nm light), and the other band-pass filter 10b transmits 569 light.
light in a wavelength range having a peak at the nm wavelength (hereinafter referred to as 569 nm).
Light). Here, when the absorption spectrum curves of oxyhemoglobin and reduced hemoglobin are superimposed and drawn, there is a difference in the absorption spectrum values of oxidized hemoglobin and reduced hemoglobin for light of 600 nm wavelength, and almost the same value for light of 569 nm wavelength. It becomes. Of course, the present invention is not limited to the combination of the wavelength ranges of 600 nm and 569 nm. From a similar selection criterion, for example, a combination of 640 nm and 505 nm or a combination of 600 nm and 805 nm may be used.

In the present embodiment, short-wavelength light and long-wavelength light are separated by the dichroic mirror 9a on the upstream side, for example, at a wavelength of 580 nm. Then, in one of the optical paths, 60
0 nm light and a bandpass filter 1 in the other optical path.
The 569 nm light selected by Ob forms an optical path slightly separated from each other by the dichroic mirror 9b on the downstream side, and reaches the area sensor 8. As a result, in the area sensor 8, the fundus image by the 600 nm light and 569
The fundus image due to the nm light is received. A control device 11 and a monitor device 12 are connected to the area sensor 8. Each image is stored in a frame memory in the control device 11.
Further, both images (images within the field of view) P1 and P2 are displayed separately on a screen D of the monitor device 12 shown in FIG. With this configuration, two types of fundus images captured simultaneously by light in different wavelength ranges are separated and displayed on one screen at the same time. An artery A and a vein V are shown in each of the images P1 and P2.

Then, as described later, by selecting an arbitrary portion on the image and performing optical analysis, the content of reduced hemoglobin and oxyhemoglobin is detected.

The monitor device 12 displays the two images P1,
A function to match the optical position of P2 is provided. That is, any two of the image P1 (P2) on the screen D
By inputting a point and two corresponding points of the other image P2 (P1), the shift amount of the coordinate position (X, Y, θ) between the corresponding points is mathematically calculated. Then, it is corrected and matched when detecting a brightness distribution described later. This is because the two images P1 and P2 are separated by an inclination of a dichroic mirror or the like, and therefore rotate mutually on the screen D or are displaced in the XY directions. It is a thing. As a mechanism for this, for example, a grid-like image with fixed coordinates may be displayed, or the image may be automatically processed by known pattern matching in image processing.

The control device 11 has a mechanism for specifying a target blood vessel whose concentration is to be detected. In the case of manual operation, the target blood vessel B on the screen is operated by operating a mouse or the like.
Is traced by the cursor. By tracing, the locus is recorded as a continuous coordinate position. In the case of automatic processing, there is a method of recognizing a density difference between a blood vessel and its vicinity by image processing to obtain a center line of the blood vessel. More specifically, a binarization is performed at a certain threshold to extract a blood vessel portion, and then thinning is performed to obtain a center line of the blood vessel.

Further, there is provided a mechanism for detecting the brightness of the blood vessel specified as described below and the brightness near the blood vessel. Then, the blood vessel density is calculated using the detected brightness values. As a mechanism for detecting the brightness of the blood vessel and the brightness near the blood vessel, the following two types are exemplified.

First, the first mechanism is a mechanism for calculating a brightness distribution in a direction perpendicular to the longitudinal direction of the traced trajectory (or thinned blood vessel) in the image stored in the frame memory. is there. This is illustrated in FIG.

FIG. 3A shows the brightness distribution in the direction perpendicular to the longitudinal direction of the blood vessel, where the vertical axis is the brightness and the horizontal axis is the coordinate position in the vertical direction. In the figure, the symbol L indicates the position of the traced trajectory. The trace line L does not always coincide with the center line of the blood vessel. Symbols F and G indicate points having the highest brightness near the blood vessel. The point between the points j and k roughly represents the thickness of the blood vessel. Symbols M and N indicate the brightness of the blood vessel. The position between the code M and the code N is the position where the illumination light is specularly reflected by the blood vessel, and does not indicate the true brightness of the blood vessel.

FIG. 3B shows the result of detecting the brightness distribution of FIG. 3A at a predetermined pitch along the longitudinal direction of the blood vessel. Then, the brightness of each of the points F, G, M, and N is detected along the longitudinal direction of the blood vessel. Next, the average of the values of many F points and G points is calculated, and many M points and N points are calculated.
Calculate the average of the points and the values. To exclude abnormal data, only data within standard deviation, mean (mean value) ± 2SD are adopted. Next, the density of the blood vessel is calculated by dividing the average value of the brightness near the blood vessel by the average value of the brightness of the blood vessel. That is defined as the concentration of blood vessels = log ₁₀ (average brightness value of the brightness average value / vessel of the vessel near).

Next, the second mechanism is to make a traced trajectory (or a line specifying a thinned blood vessel and set as a center line) L parallel to the trajectory (the center line) on both sides. The brightness is measured while moving.

More specifically, as shown in FIG. 4, a starting point Q and an ending point R are input on a traced trajectory L, for example, including a range of a blood vessel whose concentration is to be detected. The trace locus or the center line of the blood vessel is moved in a direction perpendicular to the straight line (reference S in FIG. 4) that connects The moved trace trajectory (or center line) LL is a set of points for measuring the brightness. Then, the average value of the brightness of the trace locus or the center line is continuously calculated while moving.

The moving distance is not particularly limited, but is suitably about three times the blood vessel width. The blood vessel width serving as this reference is extracted by binarizing the brightness with a certain threshold value. The blood vessel width obtained in this way is indicated by hatching in FIG. The lowest value of the average brightness value measured and calculated while moving is defined as the blood vessel brightness, and the highest value is recorded as the brightness near the blood vessel. Standard deviation, mean to eliminate abnormal data in obtaining the average value of the brightness of each trace locus (or center line) LL
(Average value) Only data within ± 2SD is adopted.

Then, as in the case of the first mechanism,
The blood vessel density is calculated by dividing the brightness near the blood vessel by the brightness of the blood vessel. That is, blood vessel concentration = log
Defined as ₁₀ (brightness of blood vessel / brightness of blood vessel).

With this mechanism, first, one image P1
The blood vessel density of the artery A and the vein V (described as A569 and V569, respectively) for (the image with the light of 569 nm) is calculated.

Next, the blood vessel density is similarly obtained for the image P2 (image with 600 nm light), but it is not necessary to trace the blood vessels for the image P2. That is, the trajectory (or thinned blood vessel) of the artery A traced in the image P1 is calculated for the image P2 by the coordinate positions (X, Y) related to the orthogonal coordinates and the polar coordinates between the two images already mathematically calculated. , Θ) are corrected.

Then, in the case of the first mechanism,
The brightness distribution in the direction perpendicular to the longitudinal direction of the corrected trace line of the artery A in the image P2 is detected. Similarly, the brightness distribution in the direction perpendicular to the longitudinal direction of the corrected trace line of the vein V in the image P2 is detected. From these detection results, the brightness average value of the blood vessel and the brightness average value near the blood vessel are calculated, and the blood vessel density of the artery A and the vein V (described as A600 and V600, respectively) is obtained.

In the case of the second mechanism, the starting point and the ending point determined in the image P1 are recorded in the corrected trace line of the artery A in the image P2, and the moving direction and the moving distance are also recorded. ing. Therefore, the same operation as in the image P1 is automatically performed. That is, the average value of the brightness of the trace line is calculated while moving the trace line in the same direction and the same distance as in the image P1. Then, the lowest value of the average brightness calculated in the image P2 is set as the brightness of the blood vessel, and the highest value is recorded as the brightness near the blood vessel. From these detection results, the blood vessel concentrations of the artery A and the vein V in the image P2 (described as A600 and V600, respectively) are obtained.

The average value of the brightness of the trace line can be calculated while moving the trace line in the image P2 in the same direction as the image P1 by a different distance. Further, in the image P2, the average value of the brightness on the line corresponding to the trace line having the lowest value of the average value of the brightness determined in the image P1 is defined as the brightness of the blood vessel, and the image P2 is determined in the image P1. The average value of the brightness on the line corresponding to the trace line having the highest average brightness value may be adopted as the brightness near the blood vessel.

When the brightness near the blood vessel is obtained by the first mechanism and the second mechanism described above, the maximum value of the brightness on a point (first mechanism) or a line (second mechanism) is selected. . However, in the case of the first mechanism, the point can be obtained as a line, and in the case of the second mechanism, the line can be obtained as a plane. Specifically, according to the first mechanism, instead of the brightness distribution of points in the direction perpendicular to the trace line, the maximum position of the average value in a predetermined range (e.g., equivalent to the blood vessel width) on the line in the vertical direction is determined. Can be the brightness near the blood vessel. Further, according to the second mechanism, while moving a trace line (actually a plane) of a predetermined width (for example, a blood vessel width) in a direction perpendicular to the straight line S, the maximum value of the average value of the trace surface of the predetermined width is obtained. The position can be the brightness near the blood vessel.

In any of the above-described mechanisms, when brightness is obtained, a so-called "blur operation" such as an average filter is executed in the vicinity of the blood vessel in order to reduce as much as possible an error due to the influence of the choroid where many capillaries are distributed. It is also possible to obtain the brightness in the vicinity of the blood vessel after the calculation. The average filter is a known technique in image processing technology.

If there is no mechanism for correcting the displacement between the two images, it is necessary to trace the target blood vessel in both images. However, in that case, the trace lines hardly match. As a result, the accuracy of the obtained data decreases.

The blood vessel density (A) determined as described above
569, V569, A600, V600), the oxygen content of arterial blood and venous blood is calculated. The oxygen content is defined as a value obtained by dividing the blood vessel density obtained from an image with light having a wavelength having a difference in absorption spectrum value between oxyhemoglobin and reduced hemoglobin by the blood vessel density obtained from an image with light having no difference in wavelength. . That is, in the present embodiment, the oxygen content of arterial blood is calculated from the formula A600 / A569, and the oxygen content of venous blood is calculated from the formula V600 / V569.

In the above-described example, two systems of photographing optical systems having different bandpass filters are provided. However, the present invention is not limited to two systems, and three or more systems of photographing optical systems are provided. An image may be obtained. In this case, generally, one optical path in a wavelength range where the absorption spectrum values of oxyhemoglobin and reduced hemoglobin have a difference, and two optical paths in a wavelength range where there is no difference may be set.

The present oxygen concentration detecting apparatus can be applied to a known fundus photographing apparatus, and has been proposed by the present applicant in Japanese Patent Application Nos. 11-101438 and 11-101443. The present invention can be suitably applied to a fundus photographing apparatus.

[0045]

According to the present invention, data can be obtained from the same portion of the fundus which is simultaneously photographed with light of different wavelengths. This makes it possible to measure the oxygen content of an arbitrary portion of the fundus without being affected by temporal changes in the condition of the fundus. Further, only by extracting blood vessels from one of the obtained images, data on the same position in the fundus of both images can be obtained, and accurate data can be obtained easily.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an oxygen concentration detection device of the present invention.

FIG. 2 is a plan view schematically showing an example of a fundus photographed image by the oxygen concentration detecting device of FIG.

FIG. 3A is a two-dimensional graph showing a brightness distribution in a direction perpendicular to the longitudinal direction of the blood vessel, and FIG. 3B is a graph showing a number of the brightness obtained along the longitudinal direction of the blood vessel. 3 is a three-dimensional graph showing the distribution of the height.

FIG. 4 is a schematic view showing a point of brightness measurement on a center line of a blood vessel while moving the center line in parallel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oxygen concentration detecting device 2 ... Illumination light source for observation 3 ... Illumination light source for photography 4 ... Illumination optical system 4a ... Illumination optical system for observation 4b ... Illumination optical system 5 Object lens 6 Hot mirror 7 Imaging optical system 8 Area sensor 9a, 9b Dichroic mirror 10a, 10b Bandpass filter 11 Control device 12 Monitor device D Monitor screen E Eye P1, P2 Fundus image

Claims (5)

[Claims] 1. An imaging means for simultaneously photographing the same portion of the fundus with a first light having a wavelength having a small difference between an absorption spectrum of oxyhemoglobin and an absorption spectrum of reduced hemoglobin, and a second light having a wavelength having a large difference. Position correction means for correcting an optical positional shift between the image captured by the first light and the image captured by the second light; blood vessel extraction means for specifying a blood vessel on the captured image; and brightness of the blood vessel from the captured image. And a blood vessel density calculating means for calculating the density of the blood vessel by detecting the brightness of the blood vessel in the vicinity of the blood vessel. 2. The blood vessel density calculating means detects a distribution of brightness in a direction perpendicular to the locus along an arbitrary locus on the photographed image of the fundus, and calculates an average value of the brightness of the blood vessel and the blood vessel. First brightness detection means for obtaining an average value of brightness in the vicinity of; and first blood vessel density calculation means for obtaining the density of the blood vessel from the average value of the brightness of the blood vessel and the average value of the brightness in the vicinity of the blood vessel. The apparatus for detecting oxygen concentration in a fundus blood vessel according to claim 1, further comprising: 3. The first lightness detecting means detects a distribution of brightness in a direction perpendicular to a longitudinal direction of a plurality of points along a blood vessel specified by the blood vessel extracting means, and detects a brightness of a blood vessel portion. Detecting the lowest value and the highest value of the brightness near the blood vessel, wherein the first blood vessel density calculating means calculates the average value along the longitudinal direction of the blood vessel of the lowest value and the highest value. 3. The apparatus according to claim 2, wherein an average value along the longitudinal direction of the blood vessel is calculated, and the density of the blood vessel is obtained from a ratio of the two average values. 4. The blood vessel density calculating means specifies two points on an arbitrary trajectory of the fundus on the photographed image,
While moving the trajectory in a direction perpendicular to a straight line connecting the two points, a second brightness detection means for continuously detecting the brightness on the moving trajectory and calculating an average value of the brightness on the trajectory, 2. The apparatus according to claim 1, further comprising a second blood vessel density calculating means for calculating a blood vessel density from a maximum value and a minimum value of the average value. 5. The blood vessel extracting means has a photographed image display device, and is configured to be input as a series of coordinate positions by tracing on an image displayed on the photographed image display device. The apparatus for detecting oxygen concentration in a fundus blood vessel according to claim 2 or 4.