JP2012019958A - Image processor, program, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To specify a retina layer boundary without a mistake even in an area existing in the back of an abnormal site based on a fundus surface, when the abnormal site causes which shows the change of a laminar structure due to a disease and a structure different from a normal structure in a tomographic image.SOLUTION: An image processor includes: a forward detection part for detecting a layer boundary candidate of a retina layer of a subject's eye by analyzing the tomographic image along a forward direction toward the depth side of the fundus from the fundus surface of the tomographic image of the subject's eye; an abnormal site detection part for analyzing the tomographic image to detect the position of the abnormal site in the retina layer; a backward detection part for detecting a layer boundary candidate of the retina layer of the subject's eye by analyzing the tomographic image along a backward direction toward the fundus surface from the depth side of the fundus of the tomographic image when the abnormal site is detected; and a layer boundary specifying part for specifying the layer boundary from the fundus surface to the abnormal site using the layer boundary candidate detected by the forward detection part, and specifying the layer boundary from the depth side of the fundus to the abnormal site using the layer boundary candidate detected by the backward detection part.

Description

  The present invention relates to an image processing apparatus, a program, and a storage medium.

  Eye examinations are widely performed for the purpose of early diagnosis of lifestyle-related diseases and diseases that occupy the top causes of blindness. An ophthalmic tomographic imaging apparatus such as an optical coherence tomography (OCT) can observe the state inside the retinal layer three-dimensionally, so that disease diagnosis can be performed more accurately. Expected to be useful.

  A macular tomographic image of the retina taken by OCT will be described with reference to FIG. As shown in FIG. 11A, an image (volume image) composed of a plurality of tomographic images can be obtained by OCT imaging. In FIG. 11A, T1 to Tn are two-dimensional tomographic images (B-scan images, hereinafter referred to as tomographic images) of the macular portion in the volume image. In the tomographic image Tn, L1 represents the inner boundary membrane, L2 represents the boundary between the nerve fiber layer and its lower layer (hereinafter referred to as the nerve fiber layer boundary), and L2 'represents the nerve fiber layer. L3 represents a boundary between the inner reticulated layer and its lower layer (hereinafter referred to as inner reticulated layer boundary), and L4 represents a boundary between the outer reticulated layer and its lower layer (hereinafter referred to as outer reticulated layer boundary). L5 represents the inner and outer segment junction of photoreceptor cells, and L6 represents the retinal pigment epithelium boundary.

  In addition, although the expression “normal structure” is used in the specification, it represents a structure when the layers L1 to L6 are present in the image as luminance values as described above. When there is no luminance value in any layer due to artifacts, it is assumed that the structure is not normal.

  In order to perform image diagnosis using OCT, development of a technique for identifying each retinal layer boundary by image analysis is required. For example, if the inner limiting membrane L1 and the nerve fiber layer boundary L2 can be identified in each line in the depth direction (hereinafter referred to as A-scan line), the thickness of the nerve fiber layer L2 ′ that is important information for glaucoma diagnosis is quantified. Can be Further, if the inner boundary membrane L1 and the retinal pigment epithelium boundary L6 can be specified, the thickness of the retinal layer sandwiched between these boundaries, which is important information for diagnosis such as macular edema, can be quantified.

  Actually, in the conventional technique of retinal layer analysis, the retinal layer boundary is determined by various methods. Patent Document 1 discloses a technique for obtaining a layer boundary position by sequentially referring to pixel values of a tomographic image along the depth direction of the fundus. In Patent Document 2, focusing on the fact that the inner boundary membrane and the retinal pigment epithelium have a large luminance change from the background, two strong edges are detected along the depth direction of the tomographic image, and the shallower edge is detected as the inner boundary. The membrane, the deeper edge, is the retinal pigment epithelium.

JP 2008-073099 A U.S. Pat. No. 7,347,548

  However, the conventional techniques have the following problems. The method for specifying the retinal layer boundary in Patent Documents 1 and 2 described above can be used in a normal structure in which each layer normally exists as shown in FIG. However, at a site showing a layer structure change due to a disease or a structure different from the normal structure, the retinal layer boundary cannot be specified only by the edge strength or the order information of the layers appearing in the normal structure. For example, in cases such as diabetic macular disease, a low-luminance cavity region due to a cyst often occurs in the retina.

  FIG. 11B shows a schematic diagram of a macular tomographic image of a case including a cyst in the retina. In FIG. 11 (b), L1 to L6 are the inner boundary membrane, nerve fiber layer boundary, inner reticular layer boundary, outer reticular layer boundary, photoreceptor inner / outer joint junction, Represents the retinal pigment epithelium layer boundary. CY represents a cyst. In such a case, the cyst CY and the layer boundary are joined (L4 is joined to the cyst CY in FIG. 11B), and the layer boundary around the cyst may not appear on the image. In such a case, in Patent Document 1, since the layer boundary that normally exists is sequentially specified, an error occurs in the identification of the layer boundary existing in the back of the cyst due to the effect of the disappearance of the layer boundary around the cyst on the image. End up.

  In addition, a large luminance difference occurs at the boundary between the low luminance cyst edge and the high luminance peripheral region. Therefore, in the method of detecting two strong edges along the depth direction as in Patent Document 2 and specifying the inner boundary membrane and the retinal pigment epithelium boundary in order from the shallower side, the second detected cyst end is detected. It is possible to mistakenly identify an edge as a retinal pigment epithelium boundary.

  In a tomographic image of the retina, when an abnormal site that shows a layer structure change due to a disease or a structure different from the normal structure occurs, the retina can be accurately detected even in an area existing behind the abnormal site with reference to the fundus surface. An object is to provide an image processing technique capable of specifying a layer boundary.

An image processing apparatus according to one aspect of the present invention that achieves the above object is characterized by analyzing the tomographic image along a forward direction from the fundus surface of the tomographic image of the eye to be examined toward the back side of the fundus. Forward direction detecting means for detecting a layer boundary candidate of the retinal layer of the optometry,
An abnormal part detecting means for analyzing the tomographic image and detecting the position of the abnormal part of the retinal layer;
When the position of the abnormal part is detected by the abnormal part detection means, the retina of the eye to be examined is analyzed by analyzing the tomographic image along the reverse direction from the back side of the fundus to the fundus surface of the tomographic image. A reverse direction detecting means for detecting a layer boundary candidate of the layer;
A layer boundary from the fundus surface to the abnormal part is identified using a layer boundary candidate detected by the forward direction detection means, and a layer boundary from the back side of the fundus to the abnormal part is detected in the reverse direction. A layer boundary specifying means for specifying using a layer boundary candidate detected by the means;
It is characterized by providing.

  According to the present invention, in a tomographic image of the retina, when an abnormal part that shows a structure change due to a disease or a structure different from a normal structure occurs, an area existing behind the abnormal part with respect to the fundus surface is used. However, the retinal layer boundary can be specified accurately.

The figure which shows the function structure of the tomographic image imaging apparatus which concerns on 1st Embodiment. The figure which shows the process sequence of the tomographic imaging apparatus which concerns on 1st Embodiment. The figure which shows a mode that a layer boundary is specified in the case where an abnormal site | part is included in a retina. The figure which shows the function structure of the tomographic imaging apparatus which concerns on 2nd Embodiment. The figure which shows the process sequence of the tomographic imaging apparatus which concerns on 2nd Embodiment. The figure which shows the function structure of the tomographic imaging apparatus which concerns on 3rd Embodiment. The figure which shows the process sequence of the tomographic imaging apparatus which concerns on 3rd Embodiment. (A) The figure which shows a mode that a layer boundary is specified in the case where the retinal layer was interrupted at the upper end of an image, (b) The figure which shows a mode that a layer boundary is specified in the case where the retinal layer was interrupted at the lower end of an image. The figure which shows the function structure of the tomographic imaging apparatus which concerns on 4th Embodiment. The figure which shows the process sequence of the tomographic imaging apparatus which concerns on 4th Embodiment. (A) The schematic diagram of the macular part tomographic image of the retina image | photographed by OCT, (b) The schematic diagram of the macular part tomographic image of the case which contains a cyst in a retina.

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

(First embodiment)
In this embodiment, layer boundary candidates are detected by performing image analysis in a direction (forward direction) from the fundus surface to the back side of the retina along each A-scan line on the tomographic image. Next, when an abnormal part is detected on the A-scan line, image analysis is further performed in the direction (reverse direction) from the back side of the retina to the fundus surface to detect a layer boundary candidate. Then, the detection result in the forward direction is specified for the region on the nearer side of the retina than the detected abnormal part (the region on the front of the abnormal part), and the region on the back side of the retina (the abnormal region on the back) is specified as the layer boundary. This provides a mechanism that can identify a layer boundary without being affected by an abnormality in the layer structure of the retina that occurs around the abnormal site.

  In the following embodiment, a case where analysis processing is performed on three-dimensional image data including a plurality of tomographic image groups to be acquired will be described. However, the configuration may be such that a notable two-dimensional tomographic image is selected from a plurality of three-dimensional image data, and processing is performed on the selected two-dimensional tomographic image. For example, the processing may be performed on a tomographic image including a predetermined specific part of the fundus (for example, the fovea). In this case, the detected layer boundaries are all two-dimensional data on the cross section.

(Configuration of the image processing apparatus 10)
The configuration of the image processing apparatus 10 according to the present embodiment will be described with reference to FIG. The image processing apparatus 10 includes an image acquisition unit 101, a storage unit 102, an image conversion unit 103, a forward direction detection unit 104, an abnormal site detection unit 105, a reverse direction detection unit 106, a layer boundary specification unit 107, and a display unit 108. The image processing apparatus 10 is connected to the tomographic image acquisition apparatus 20. The tomographic image acquisition apparatus 20 shoots an eye to be examined (not shown) in response to an operation by an operator (not shown), and transmits the obtained image to the image processing apparatus 10.

(Processing of the image processing apparatus 10)
A specific processing procedure executed by the image processing apparatus 10 will be described with reference to FIG. In step S <b> 201, the image acquisition unit 101 acquires the OCT tomographic image captured by the tomographic image acquisition device 20 and stores it in the storage unit 102. Hereinafter, this OCT tomographic image is referred to as an “original image”.

  In step S <b> 202, the image conversion unit 103 performs image conversion on the original image stored in the storage unit 102. In the present embodiment, a Sobel filter that emphasizes a luminance change in the depth direction is applied to a tomographic image (original image) for the purpose of enhancing a layer boundary in the image. This Sobel filter has a property of emphasizing both an edge from a pixel having a low luminance value to a high pixel and an edge from a pixel having a high luminance value to a low pixel along the depth direction. In this step, a Sobel image is created by image conversion and transmitted to the forward direction detection unit 104 and the backward direction detection unit 106.

  The image conversion method is not limited to this, and a smoothing filter such as a median filter or an average value filter for the purpose of image noise removal may be used as preprocessing. In addition, image conversion may be performed using a gradation conversion filter such as gamma correction or a morphological filter. Further, the image conversion may not be performed and the luminance value of the original image may be used as the input for the next step. Furthermore, the number of images to be input in the next step is not limited, and one or more images may be input in the next step.

  In step S203, the forward direction detection unit 104 detects a retinal layer boundary candidate (layer boundary candidate) by analyzing the Sobel image acquired from the image conversion unit 103 in the forward direction along the A-scan line.

  In this embodiment, for the Sobel image, the luminance value is referred to in units of one pixel in the forward direction along each A-scan line, and when the luminance value exceeds a predetermined threshold, the position is set as a layer boundary candidate. Detect sequentially. The predetermined threshold can be determined empirically. Further, by applying a threshold value that divides the Sobel image into a high-brightness edge region and other low-brightness regions using a discriminant analysis method or a P-tile method, the threshold value may be variable depending on the case.

  The layer boundary candidate detection method is not limited to this. For example, each A-scan line may be analyzed in the forward direction with reference to the luminance value of a block area composed of a plurality of pixels, not in units of one pixel. Good. Further, as a feature for detecting the layer boundary candidate, in addition to the edge strength of the original image using the Sobel image, a block area is set in the original image. For example, the difference between the luminance values of the upper half and the lower half of the block area is set. Etc. may be used.

  Next, the forward direction detection unit 104 transmits the detected position information of the layer boundary candidate (forward direction detection information) to the layer boundary identification unit 107.

  In step S204, the abnormal part detection unit 105 analyzes the original image stored in the storage unit 102 and detects the position of the abnormal part. In the present embodiment, as an example, a detection method when the abnormal site is a cyst will be described. Since the cyst is a hollow area generated in the retina, for example, as shown by CY in FIG. 11B, the image shows a very low luminance value compared to the surrounding retinal area. Therefore, by applying threshold processing with a predetermined threshold to the luminance value of the original image and extracting an area below the threshold, a cyst area candidate (cyst area candidate) can be extracted. At this time, the predetermined threshold value can be determined empirically.

  In addition, since the luminance value of the cyst region is close to the background region such as the vitreous region on the tomographic image, the tomographic image is divided into a high luminance retinal layer region and a low luminance background region using the discriminant analysis method or the P-tile method. By applying a threshold that roughly divides into two, it may be a threshold that becomes variable depending on the case.

  Next, it is determined whether or not the extracted cyst region candidate is a cyst region by analyzing luminance information and morphological information of the region. In the present embodiment, the luminance information and the morphological information are input as feature quantities to a discriminator that has previously learned in a large number of cases to determine whether or not the region is a cyst region. Specifically, the average luminance value in the area, the variance, the skewness, the kurtosis, and the contrast difference inside and outside the boundary of the area can be used as the feature amount based on the luminance information. As the feature amount based on the shape information, the size of the region or the circularity of the region can be used. As the discriminator, a neural network or a support vector machine can be used.

  However, the method of determining the cyst region is not limited to this, and for example, a method of determining the cyst region only when the feature amount based on the luminance information and the shape information is within a predetermined range may be used. At this time, the predetermined range may be determined empirically or based on clinical knowledge.

  Moreover, the abnormal part which the abnormal part detection part 105 detects is not limited to a cyst. For example, when the abnormal part is a vitiligo, the vitiligo region is drawn with higher brightness than the normal layered tissue, so the threshold value processing is performed on the luminance value of the original image with a predetermined threshold value, and the region above the threshold value is extracted. Thus, candidates for the vitiligo region are extracted. Then, as in the case of the cyst region, it is possible to classify the candidate for the vitiligo region into whether or not it is a vitiligo region using a discriminator. In addition, regarding the peeled area where the layers are peeled, the peeled area is depicted with a much lower luminance than the surrounding layered tissue, and thus can be detected by the same method as the detection of the cyst area.

  Further, the abnormal part detection by the abnormal part detection unit 105 is not limited to fully automatic processing. For example, the same type of luminance value region is extracted based on the position of the abnormal part specified by the operator. It may be a semi-automatic detection process. Next, the abnormal part detection unit 105 transmits position information (abnormal position information) of the detected abnormal part to the layer boundary specifying unit 107.

  In step S205, the abnormal part detection unit 105 checks the abnormal position information detected in step S204 and determines whether or not there is an abnormal part in each A-scan line. If it is determined that an abnormal part exists (S205—Yes), the position information of the A-scan line determined to have an abnormal part is transmitted to the backward direction detection unit 106, and the process proceeds to step S206. If it is determined that there is no abnormal part (S205—No), the process proceeds to step S207.

  In step S <b> 206, the reverse direction detection unit 106 acquires the position information of the A-scan line acquired from the abnormal part detection unit 105 and the Sobel image from the image conversion unit 103. Then, the layer boundary candidate is detected by analyzing only the A-scan line from which the position information is acquired, in the reverse direction along the A-scan line.

  In this embodiment, for the Sobel image, the luminance value is referred to in units of one pixel in the reverse direction along each A-scan line, and when the luminance value exceeds a predetermined threshold, the position is set as a layer boundary candidate. Detect sequentially. The predetermined threshold value may be determined empirically as in step S203, or may be a variable threshold value according to the case using a discriminant analysis method or a P-tile method. In addition, the layer boundary candidate detection method is not limited to this, and for example, a method similar to that exemplified in step S203 may be used.

  Next, the reverse direction detection unit 106 transmits the detected position information of the layer boundary candidate (reverse direction detection information) to the layer boundary specifying unit 107.

  In step S207, the layer boundary specifying unit 107 acquires the forward direction detection information from the forward direction detection unit 104, the abnormal position information from the abnormal part detection unit 105, and the reverse direction detection information from the reverse direction detection unit 106, respectively. Identify retinal layer boundaries.

  FIG. 3 is a diagram illustrating a state in which a layer boundary is specified in a case including an abnormal part in the retina. A specific method for identifying the retinal layer boundary will be described with reference to FIG. In FIG. 3, L1 to L6 are the inner boundary membrane, nerve fiber layer boundary, inner reticular layer boundary, outer reticular layer boundary, photoreceptor inner / outer node junction, retinal pigment, in the same manner as in FIG. Represents the cortical boundary. At this time, in the A-scan line in which no abnormal site exists, the layer structure of the retina is normal and the layer boundaries exist in order, so the layer boundary specifying unit 107 specifies the forward direction detection information as it is as the retinal layer boundary. . In FIG. 3, A1 represents an A-scan line in which no abnormal site exists on the tomographic image, and DP1 represents the positions of a plurality of layer boundary candidates detected when A1 is analyzed in the forward direction (6 points in FIG. 3). ). In this example, the layer boundary specifying unit 107 determines each point of the layer boundary candidate DP1 as a layer boundary of L1, L2,..., L6 in order along the forward direction of the A-scan line.

  On the other hand, in the A-scan line where the abnormal site exists, the layer structure of the retina is different from normal, and the layer boundary disappears on the image near the abnormal site, or the brightness of the surrounding layer tissue at the end of the abnormal site There may be a strong edge due to the difference. For this reason, in the present embodiment, the region on the near side of the retina from the abnormal part (the region near the abnormal part) specifies the forward direction detection information as the retinal layer boundary. In addition, the region on the back side of the retina (abnormal region back region) specifies the reverse direction detection information as the retinal layer boundary.

  Here, based on the abnormal position information acquired from the abnormal part detection unit 105, the abnormal front side area and the abnormal part back area are divided into a front side and a back side across the abnormal part region. Can be sought. In FIG. 3, A2 represents an A-scan line in which an abnormal site on a tomographic image exists, and CY represents a cyst region that is an example of an abnormal site, as in FIG. DP2 represents the position of the layer boundary candidate detected in the region before the abnormal part when A2 is analyzed in the forward direction (three points in FIG. 3), and UP2 is the abnormal part when A2 is analyzed in the reverse direction. The position of the layer boundary candidate detected in the back area (2 points in FIG. 3) is represented. In this example, each point of DP2 is determined as L1, L2, and L3 in order along the forward direction of the A-scan line, and each point of UP2 is determined as L6 and L5 in order along the reverse direction of the A-scan line. To do.

  Thus, by identifying the layer boundary along the forward direction and the reverse direction on the front side and the back side of the cyst CY, respectively, the disappearance of the layer boundary of L4 on the line A2 and the end of the cyst CY The layer boundaries of L5 and L6 in the abnormal region deep region can be accurately identified without being affected by the generated edge.

  At this time, the layer boundary L4 disappearing on the image is not specified by the above method, but L4 may be left unspecified, or the position of L4 specified around A2 by the following method is used. May be specified by interpolation. For example, the point L2 closest to A2 among the positions of L4 specified in the area on the left side of the image with respect to the line A2 is set as the point PL, and the position of L4 specified in the area on the right side of the image with respect to the line of A2 is set. The point closest to A2 is set as the point PR. Then, by performing linear interpolation between the points PL and PR, the layer boundary corresponding to L4 can be specified even in the region where the layer boundary disappears due to the influence of the cyst such as A2.

  As another method, it is assumed that L4 disappearing on the image is joined to the end of the cyst, and the positions of the upper and lower ends of the cyst on the line A2 are point PU and PD, respectively. The shorter one of the two points from the points PL and PR may be specified as a point on L4. Thereby, even in the region where the layer boundary disappears, it is possible to trace the end of the abnormal part closer to the line of the layer boundary that can be specified in the surrounding area as the layer boundary.

  In the above-described method, the example of specifying the layer boundary when the cyst is included in the A-scan line as the abnormal part has been described. However, the white spot or the peeled area described in step S204 is included in the A-scan line as the abnormal part. In this case, the layer boundary can be specified by the same method. In FIG. 3, A3 represents an A-scan line in which vitiligo on a tomographic image exists, EX represents a vitiligo region, and SH represents a shadow region caused by a signal being blocked in the depth direction by vitiligo. This shadow region SH often occurs on the back side of the vitiligo region, and no layer boundary appears on the image at the location where SH occurs. DP3 represents the position of the layer boundary candidate detected in the front region of the abnormal part when A3 is analyzed in the forward direction, and UP3 is detected in the rear part of the abnormal part when A3 is analyzed in the reverse direction. Indicates the position of the layer boundary candidate.

  In this example, the points of DP3 are determined as L1, L2, and L3 in order along the forward direction of the A-scan line. On the other hand, for UP3, no layer boundary is determined because there is no detection point in the abnormal part back region (the back of the retina from the vitiligo). In this way, by identifying the layer boundary along the forward direction and the reverse direction on the front side and the back side of the vitiligo EX, respectively, the disappearance of the L4 layer boundary due to the vitiligo EX or the edge generated at the end of the vitiligo EX The layer boundary can be identified without being affected by Further, even when the layer boundary disappears due to the shadow region SH, by scanning the region from the back of the retina to the white spot EX in the reverse direction to identify the layer boundary, an erroneous location can be identified as L5 or L6. And can leave those layer boundaries unspecified. The layer boundaries of L4, L5, and L6 that have disappeared due to the presence of vitiligo may be interpolated in the same manner as in the case of the cyst.

  Further, in FIG. 3, A4 represents an A-scan line where a layer peeling region on the tomographic image exists, and DT represents a peeling region. DP4 represents the position of the layer boundary candidate detected in the front region of the abnormal part when A4 is analyzed in the forward direction, and UP4 is detected in the rear part of the abnormal part when A4 is analyzed in the reverse direction. Represents the position of the layer boundary candidate. In this example, each point of DP4 is determined as L1, L2, L3, L4, and L5 in order along the forward direction of the A-scan line, and each point of UP4 is determined as L6 in order along the reverse direction of the A-scan line. And decide. Thus, by specifying the layer boundary along the forward direction and the reverse direction on the near side and the far side of the separation region DT, respectively, without being affected by the edge generated at the boundary between the separated layer and the separation region DT. The layer boundary of L6 can be specified.

  In the present embodiment, the six layers L1 to L6 are specified, but the specified layers are not necessarily limited to these. The actual retinal layer is the inner boundary membrane, nerve fiber layer, ganglion cell layer, inner reticular layer, inner granular layer, outer reticular layer, outer granular layer, outer boundary membrane, in order from the fundus surface to the back of the retina. It has a photoreceptor cell layer and a retinal pigment epithelium layer. The layer boundary specifying unit 107 can specify at least one position among layer boundaries existing between these layers.

  Then, the layer boundary specifying unit 107 stores the position information (layer boundary position information) of the retinal layer boundary specified for each A-scan line in the storage unit 102.

  In step S208, the display unit 108 acquires the original image and the layer boundary position information from the storage unit 102, and displays the layer boundary position information on the monitor (not shown) by superimposing the layer boundary position information on the original image.

  With the above configuration, even in a tomographic image in which an abnormal part exists, it is possible to accurately identify the layer boundary existing in the back of the retina rather than the abnormal part without being affected by the abnormality of the layer structure around the abnormal part. .

(Second Embodiment)
In this embodiment, a layer boundary candidate is detected by scanning in the forward or reverse direction along the A-scan line on the tomographic image, and at the same time, the presence of an abnormal part is detected, and the layer boundary is specified based on the detection result in both directions. To do.

  More specifically, in the first embodiment, since an abnormal part is detected as a process separate from the detection of the layer boundary candidate, extra time is required for the process. In the first embodiment, the detection result of the abnormal part back region in the forward direction and the detection result of the abnormal part front region in the reverse direction are temporarily A in both directions, although they are not adopted for specifying the layer boundary. The -scan line was scanned from the top to the bottom of the image (or from the bottom to the top). Therefore, it led to extra processing time.

  Therefore, this embodiment scans in the forward direction along the A-scan line on the tomographic image to detect the layer boundary candidate and simultaneously detects the presence of the abnormal part. When the abnormal part is detected, the forward direction is detected. Is stopped and switched to scanning in the reverse direction. Similarly to the forward direction, while scanning in the reverse direction to detect the layer boundary candidates, the presence of the abnormal part is also detected at the same time, and the reverse scanning is stopped at the point where the abnormal part is detected. Then, the layer boundary candidates detected until the scanning is stopped by detecting the abnormal part in each of the forward direction and the reverse direction are specified as final layer boundaries. As a result, as in the first embodiment, a mechanism is provided in which the layer boundary can be specified without being affected by the abnormality in the layer structure of the retina that occurs around the abnormal part. In addition, since the presence of the abnormal part is detected simultaneously with the layer boundary candidate, it is possible to save the trouble of detecting the abnormal part as a separate process. Furthermore, since scanning is stopped when the presence of an abnormal part is detected in both the forward and reverse directions, the analysis processing time can be shortened.

(Configuration of Image Processing Device 40)
FIG. 4 shows the configuration of the image processing apparatus 40 according to this embodiment. The image processing apparatus 40 includes an image acquisition unit 401, a storage unit 402, an image conversion unit 403, a forward direction detection unit 404, an abnormal site detection unit 405, a reverse direction detection unit 406, a layer boundary specification unit 407, and a display unit 408. The image processing device 40 is connected to a tomographic image acquisition device 50. Since the tomographic image acquisition apparatus 50 has the same function as the tomographic image acquisition apparatus 20 of the first embodiment, description thereof is omitted.

(Processing of the image processing apparatus 40)
FIG. 5 is a flowchart of the present embodiment, and a specific processing procedure executed by the image processing apparatus 40 will be described along this flowchart. However, steps S501, S502, and S511 are the same as steps S201, S202, and S208 in FIG.

  In step S <b> 503, the forward direction detection unit 404 detects a retinal layer boundary candidate by analyzing the Sobel image acquired from the image conversion unit 403 in the forward direction along the A-scan line. Details of the analysis process in this step are the same as in step S203 in FIG.

  Further, the forward direction detection unit 404 holds a value of a forward direction abnormality detection flag D_FLG (forward direction abnormality detection information) indicating the presence or absence of an abnormal part in the A-scan line being analyzed in the forward direction. If the reference pixel indicated by the forward abnormality detection information indicates that it is not an abnormal part (D_FLG = FALSE), the analysis is continued. Processing in a case where the reference pixel indicated by the forward abnormality detection information indicates an abnormal part (D_FLG = TRUE) will be described in step S506. Next, the forward direction detection unit 404 transmits the position information (forward direction position information) of the pixel being referred to in the analysis to the storage unit 402.

  In step S <b> 504, the forward direction detection unit 404 checks the forward direction position information stored in the storage unit 402. If the forward direction position information has not yet reached the lower end of the image, the forward direction position information is always sent to the abnormal part detection unit 405. Then, the process proceeds to step S505. On the other hand, if it has reached the lower end of the image, the forward direction detection information stored in the storage unit 402 is transmitted to the layer boundary specifying unit 407, and the process proceeds to step S510.

  In step S505, the abnormal part detection unit 405 is based on the original image stored in the storage unit 402 and the position information (forward position information indicating the analysis position in the forward direction) that is always acquired from the forward direction detection unit 404. The presence or absence of an abnormal part is determined. The abnormal part detection unit 405 functions as a first abnormality detection unit that detects the position of the abnormal part by analyzing a tomographic image in association with a forward analysis position (forward position information). If it is determined that the reference pixel indicated by the forward direction position information is an abnormal part, the forward abnormality detection flag D_FLG = TRUE is set and transmitted to the forward direction detection unit 404, and the process proceeds to step S506. On the other hand, if it is determined that the reference pixel is not an abnormal part, D_FLG = FALSE is set and transmitted to the forward direction detection unit 404, and the process proceeds to step S503.

  In the present embodiment, a method for detecting an abnormal site when a cyst region as shown in FIG. 3 or FIG. 11B exists on a tomographic image will be described. As described in step S <b> 204 in FIG. 2, since the cyst is a hollow area generated in the retina, the image shows a very low luminance value compared to the surrounding retinal area. Therefore, the pixel on the original image corresponding to the acquired forward direction position information is referred to, and when the pixel falls below a predetermined threshold, it is determined that it is an abnormal part. At this time, the predetermined threshold is determined by the same method as in step S204 in FIG.

  Here, the abnormal site detected by the abnormal site detector 405 is not limited to a cyst. For example, for the vitiligo region rendered with higher brightness than the normal layer structure, the threshold value processing is performed on the brightness value of the original image with a predetermined threshold value as in step S204 in FIG. By extracting, a candidate for a vitiligo region is extracted. In addition, the separation region where the layers are separated can be detected by the same method as in step S204. By such processing, the abnormal part can be detected simultaneously with the detection of the forward layer boundary candidate in step S503, so that it is possible to save the processing time compared to detecting the abnormal part by completely different processing.

  In step S506, the forward direction detection unit 404 checks the value of the forward direction abnormality detection flag D_FLG set by the abnormal part detection unit. Then, after confirming that D_FLG = TRUE (indicating that the reference pixel is an abnormal part), the forward direction detection unit 404 stops the analysis along the forward direction of the A-scan line. Then, the detected forward direction detection information is transmitted to the layer boundary specifying unit 407, and the position information (A-scan position information) of the A-scan line being scanned is transmitted to the storage unit 402, and the process proceeds to step S507. As described above, the scanning is stopped when an abnormal part is detected during the forward scanning, and the analysis of the back region of the retina is not performed, so that the analysis processing time can be shortened.

  In step S507, the reverse direction detection unit 406 analyzes the Sobel image acquired from the image conversion unit 403 in the reverse direction along the A-scan line indicated by the A-scan position information stored in the storage unit 402. Detect retinal layer boundary candidates. Details of the analysis process in this step are the same as in step S206 in FIG.

  The reverse direction detection unit 406 holds a value of a reverse direction abnormality detection flag U_FLG (reverse direction abnormality detection information) indicating the presence or absence of an abnormal part in the A-scan line being analyzed in the reverse direction. If the reference pixel indicated by the reverse direction abnormality detection information indicates that it is not an abnormal part (U_FLG = FALSE), the analysis is continued. Processing in a case where the reference pixel indicated by the reverse direction abnormality detection information indicates that it is an abnormal part (U_FLG = TRUE) will be described in step S509.

  Next, the reverse direction detection unit 406 transmits the position information (reverse direction position information) of the pixel being referred to in the analysis to the storage unit 402.

  In step S <b> 508, the abnormal part detection unit 405 is based on the original image stored in the storage unit 402 and position information (reverse direction position information indicating a reverse analysis position) that is always acquired from the reverse direction detection unit 406. The presence or absence of an abnormal part is determined. The abnormal part detection unit 405 functions as a second abnormality detection unit that detects the position of the abnormal part by analyzing the tomographic image in association with the analysis position in the reverse direction (reverse direction position information). If it is determined that the reference pixel pointed to by the reverse direction position information is an abnormal part, the reverse direction abnormality detection flag U_FLG = TRUE is set and transmitted to the reverse direction detection unit 406, and the process proceeds to step S509. On the other hand, if it is determined that the reference pixel is not an abnormal part, U_FLG = FALSE is set and transmitted to the backward direction detection unit 406, and the process proceeds to step S507. The method for detecting the abnormal part is the same as the method for detecting the abnormal part being analyzed in the forward direction described in step S505, and thus the description thereof is omitted.

  By such processing, the detection of the abnormal part can be performed at the same time as the detection of the layer boundary candidate in the reverse direction in step S507, so that it is possible to save processing time compared to detecting the abnormal part by completely different processing.

  In step S509, the reverse direction detection unit 406 checks the value of the reverse direction abnormality detection flag U_FLG set by the abnormal part detection unit, confirms that U_FLG = TRUE, and then follows the reverse direction of the A-scan line. Stop the analysis. Then, the detected reverse direction detection information is transmitted to the layer boundary specifying unit 407, and the process proceeds to step S507. In this way, by stopping scanning when an abnormal site is detected during scanning in the reverse direction and not analyzing the near side region of the retina, the analysis processing time can be shortened.

  In step S510, the layer boundary specifying unit 407 acquires the forward direction detection information from the forward direction detection unit 404 and the reverse direction detection information from the reverse direction detection unit 406, and specifies the retinal layer boundary.

  A specific method for identifying the retinal layer boundary will be described with reference to FIG. When an abnormal part is not included on A-scan as in A1, as a result of analysis while scanning in the forward direction in step S503, it is determined in step S504 that the lower end of the image has been reached, and only forward direction detection information is included in the layer. It is transmitted to the boundary specifying unit 407. In this case, since there is no abnormal part that causes the forward analysis to fail, the layer boundaries L1 to L6 are assigned in the forward direction to the points of the layer boundary candidate DP1 in the forward direction detection information as they are. As a typical layer boundary.

  On the other hand, when an abnormal part is included on the A-scan as in A2, forward direction detection information until the abnormal part is detected by forward scanning and reverse direction detection information until the abnormal part is detected by reverse scanning. Is transmitted to the layer boundary specifying unit 407. In this case, a layer boundary is assigned in the forward direction to each point of the layer boundary candidate DP2 in the forward direction detection information, and a layer boundary is assigned in the reverse direction to each point of the layer boundary candidate UP2 in the reverse direction detection information. Identifies as final layer boundary. More specifically, L1, L2, and L3 layer boundaries are assigned to each point of DP2 in order from the forward direction of A-scan, and L6 is assigned to each point of UP2 in order from the reverse direction of A-scan. , L5 layer boundaries are allocated.

  As a result, the L5 and L6 layer boundaries can be accurately identified even in the abnormal region back region without being affected by the disappearance of the L4 layer boundary on the A2 line or the edge generated at the end of the cyst CY. Can do. At this time, the layer boundary L4 disappearing on the image is not specified by the above-described method, but L4 may be left unspecified, or may be specified around A2 by the method described in step S207 of FIG. Alternatively, the position may be specified by interpolation using the position of L4.

  Further, in the case of the A-scan line A3 including the white spot EX in FIG. 3 and the A-scan line A4 including the peeling region DT, the layer boundary can be specified by the same method. In the present embodiment, the six layers L1 to L6 are specified. However, the layers to be specified are not necessarily limited to these, and the layers described in step S207 in FIG. 2 may be specified. Then, the layer boundary specifying unit 407 stores the layer boundary position information specified for each A-scan line in the storage unit 402.

  With the above configuration, even in a tomographic image in which an abnormal part exists, it is possible to accurately identify the layer boundary existing in the back of the retina rather than the abnormal part without being affected by the abnormality of the layer structure around the abnormal part. . In addition, since the presence of the abnormal part is detected simultaneously with the layer boundary candidate, it is possible to save the trouble of detecting the abnormal part as a separate process. Furthermore, since scanning is stopped when the presence of an abnormal part is detected in both the forward and reverse directions, the analysis processing time can be shortened.

(Third embodiment)
In this embodiment, the analysis is performed in both the forward and reverse directions along the A-scan line on the tomographic image, and the characteristics indicated by each analysis result (detection result) are compared with the characteristics of the correct layer boundary. The layer boundary is specified by selecting a detection result close to the correct layer boundary feature.

  More specifically, when a volume image of a subject eye is acquired when the subject eye is intense myopia, the retinal layer is often interrupted at the upper and lower ends of the image in the tomographic image at the end of the volume image. For example, when a retinal layer boundary is specified from a tomographic image in which the retinal layer is interrupted at the upper end of the image, a layer boundary appears from the inner boundary film as usual when analyzed in the forward direction along the A-scan line. Because it appears from the middle layer boundary instead of, the layer boundary is specified by mistake.

  Therefore, in the present embodiment, each layer boundary candidate is detected by analyzing in both the forward and reverse directions along each A-scan line on the tomographic image. Next, a layer boundary is temporarily assigned to the detection results in these two directions in order in each direction. Then, compare the assigned layer boundary characteristics with the correct layer boundary characteristics stored in advance, select the layer boundary in the similar direction according to the correct layer boundary characteristics, and identify it as the final layer boundary To do. As a result, when the retinal layer is interrupted at the edge of the image, if the analysis is performed from the edge of the image on the interrupted side, the layer boundary is erroneously assigned and the similarity to the correct layer boundary is low, but from the opposite direction In the case of analysis, the layer boundary is correctly assigned, so the similarity becomes high. As a result, it is possible to provide an image processing technique capable of specifying the layer boundary without making a mistake.

(Configuration of Image Processing Device 60)
FIG. 6 shows the configuration of the image processing apparatus 60 according to the present embodiment. The image processing apparatus 60 includes an image acquisition unit 601, a storage unit 602, an image conversion unit 603, a forward direction detection unit 604, a backward direction detection unit 605, a detection result evaluation unit 606, a layer boundary specification unit 607, and a display unit 608. The image processing device 60 is connected to the tomographic image acquisition device 70. The tomographic image acquisition apparatus 70 has the same function as the tomographic image acquisition apparatus 20 of FIG.

(Processing of the image processing device 60)
FIG. 7 is a flowchart of the present embodiment, and a specific processing procedure executed by the image processing apparatus 60 will be described along this flowchart. However, steps S701, S702, and S707 are the same as steps S201, S202, and S208 in FIG.

  In step S <b> 703, the forward direction detection unit 604 acquires a Sobel image from the image conversion unit 603 and analyzes the image in the forward direction along the A-scan line to detect a retinal layer boundary candidate. Details of the analysis process in this step are the same as in step S203 in FIG. Next, the forward direction detection unit 604 transmits the detected forward direction detection information to the detection result evaluation unit 606.

  In step S704, the reverse direction detection unit 605 acquires a Sobel image from the image conversion unit 603, and analyzes the image in the reverse direction along the A-scan line to detect a retinal layer boundary candidate. Details of the analysis process in this step are the same as in step S206 in FIG. Next, the reverse direction detection unit 605 transmits the detected reverse direction detection information to the detection result evaluation unit 606.

  In step S <b> 705, the detection result evaluation unit 606 stores the forward direction detection information acquired from the forward direction detection unit 604 and the backward direction detection information acquired from the backward direction detection unit 605 in advance in the storage unit 602. Compare with the characteristics of Here, the storage unit 602 stores in advance the correct feature amount of the layer boundary to be specified from the image.

  The correct feature amount refers to a feature amount extracted from an image based on the position specified by a specialist such as a doctor in advance on the tomographic image. Hereinafter, this is referred to as “correct feature amount”. As feature values of each layer boundary, for example, the luminance average, variance, kurtosis, skewness of the upper and lower layers, the difference in luminance average between the upper and lower layers, the edge strength of the layer boundary It is possible to apply. The features listed are exemplary, and it is necessary to use all of the luminance average, variance, kurtosis, skewness, the difference in luminance average between the upper and lower layers, and the edge strength at the layer boundary. There is no. It is possible to determine the feature amount using at least one of the listed items.

  In the present embodiment, for each A-scan line, a layer boundary is provisionally assigned in order in each direction to each detection result (layer boundary candidate position) of the forward direction detection information and the backward direction detection information. These are called the forward layer boundary and the reverse layer boundary, respectively. Next, for the assigned layer boundary in each direction, the feature amount corresponding to the layer boundary in each direction is extracted from the original image based on the position. Then, the similarity between the extracted feature quantity in each direction and the correct feature quantity is calculated, and the calculation results are compared. Thereafter, the similarity between the forward feature quantity and the correct feature quantity (first similarity) and the similarity degree between the backward feature quantity and the correct feature quantity (second similarity) are respectively “forward similarity”. , Called “reverse direction similarity”.

FIG. 8A is a diagram illustrating a state in which the layer boundary is specified in a case where the retinal layer is interrupted at the upper end of the image. The comparison method between the forward direction detection information and the correct feature amount and the comparison method between the reverse direction detection information and the correct feature amount in the present embodiment will be specifically described with reference to FIG. L1 to L6 in FIG. 8A are the inner boundary membrane, the nerve fiber layer boundary, the inner reticular layer boundary, the outer reticular layer boundary, the photoreceptor inner and outer node junction, and the retinal pigment in the same manner as in FIG. 11B. It represents the epithelial layer boundary. In the present embodiment, these are the layer boundaries to be specified. At this time, the storage unit 602 is saved correct feature amount of up to L1 to L6, respectively a vector of correct feature amounts f _1, f ₂ corresponding to each layer boundary, ..., and f _6. Here, the feature quantity vector f _i corresponding to the i-th layer boundary (i satisfies 1 <= i <= 6) is a vector composed of a plurality of feature quantities as described above. To express.

  In the equation (1), N represents the number of elements of the feature vector.

Here, R _N represents the normal of the imaging region (normal region) retinal layers is not interrupted from the image of FIG. 8 (a), A1 represents A-scan lines included in the normal region. DP1 represents forward direction detection information (positions of six layer boundary candidates) detected when A1 is analyzed in the forward direction. UP1 represents reverse direction detection information (positions of six layer boundary candidates) detected when A1 is analyzed in the reverse direction. For each point of DP1, layer boundaries L1 to L6 are assigned in order along the forward direction of the A-scan line, and these are defined as forward layer boundaries. Then, each point on the forward layer boundary is set to P _d1 , P _d2 ,..., P _d6 in order. Similarly, P _u6 , P _u5 ,..., P _u1 are the points on the reverse layer boundary obtained by assigning layer boundaries along the reverse direction to the points of UP1. Next, as in the case of the correct feature quantity, feature quantities corresponding to these layer boundaries are extracted from the image. Then, the point _P d1 _{to P d6} and the point _P u6 _{to P u1} each d ₁ feature quantity vectors corresponding to, d _2, · · ·, d _6, and u _6, u _5, · · ·, and u ₁ To do. Here, forward and backward feature vectors d _i and u _i corresponding to the i-th layer boundary are expressed by the following equations (2) and (3), respectively.

At this time, the similarity s _{d, i} (forward similarity) between d _i and f _i can be obtained by the expression (4) based on the Euclidean distance between the two in this embodiment.

Similarly, the similarity s _{u, i} (reverse direction similarity) between u _i and f _i can be obtained by equation (5).

As described above, for all i satisfying 1 <= i <= 6, the forward similarity s _{d, i} corresponding to the forward layer boundary point P _di and the backward layer boundary point P _ui The corresponding reverse similarity _{su, i} is obtained.

On the other hand, R _U in FIG. 8 (a) represents the area of a portion retinal layer is broken by an image upper end, A2 represents A-scan lines included in the site. DP2 represents forward direction detection information (positions of four layer boundary candidates) detected when A2 is analyzed in the forward direction. UP2 represents reverse direction detection information (positions of four layer boundary candidates) detected when A2 is analyzed in the reverse direction. At this time, each point of DP2 and UP2 is assigned as a forward layer boundary and a reverse layer boundary as in the case of A1. In this case, since the layer boundary by interruption of retinal layers from the image is missing, the forward layer boundary point P _{d1 to P d4,} reverse layer boundary point P _u6 to P _u3, and the layer originally present respectively Less than the number of boundaries (6 points).

Therefore, in the present embodiment, the assigned layer boundary is compared with only the common feature amount (feature amount corresponding to the assigned layer boundary) among the correct feature amounts (f _{1 to} f ₆ ). Calculate the degree. Specifically, in the case of the forward layer boundary, only the layer boundaries corresponding to L1 to L4 are common, so the feature quantity vectors d _{1 to} d ₄ and f _{1 to} f ₄ are compared. For reverse layer boundary, to compare the feature vector _u 3 ~u ₆ and _f 3 ~f ₆ since only the layer boundary corresponding to L3~L6 are common. Then, the similarity is calculated based on the equations (4) and (5), respectively. Thus, in the forward direction, the forward similarity s _{d, i} corresponding to the point P _di is obtained for all i satisfying 1 <= i <= 4, while in the reverse direction, 3 The reverse similarity s _{u, i} corresponding to the point P _ui is obtained for all i satisfying ≦ i <= 6.

  Then, the detection result evaluation unit 606 performs forward layer boundary and reverse layer boundary data obtained by assigning layer boundaries for each A-scan line in this step, and forward similarity corresponding to each point. And the value of the reverse direction similarity is transmitted to the layer boundary specifying unit 607.

  In step S706, the layer boundary specifying unit 607 obtains the forward layer boundary and reverse layer boundary data from the detection result evaluation unit 606, and the forward similarity and the reverse similarity values corresponding to the respective points. To do. Then, by comparing the similarities in the forward direction and the reverse direction, the direction having a higher similarity value, that is, the layer boundary data in the direction close to the normal layer boundary is selected and specified as the final layer boundary.

In this embodiment _, the average value s _{d, ave} of the forward similarity s _{d, i} at each point on the forward layer boundary and the average value s of the reverse similarity s _{u, i} at each point on the reverse layer boundary. _{u and ave} are calculated and specified as the final layer boundary using data in the direction corresponding to the larger value. For example, when the retinal layer is interrupted at the upper end of the image as shown by A2 in FIG. 8A, the forward layer boundary is assigned to the layer boundary candidates in order from the inner boundary film that is actually missing on the image. An error occurs. On the other hand, since the reverse layer boundary is assigned to the layer boundary candidates in order from the retinal pigment epithelium layer boundary in the image, no error occurs. Accordingly, the average value s _{d, ave} in the forward direction is a very low value, while the average value _{su, ave in} the reverse direction is a high value, the reverse layer boundary having a high similarity is the final layer. Selected as a boundary. Thereby, even when the retinal layer is interrupted at the upper end of the image, the layer boundary can be specified without making a mistake.

On the other hand, the same effect can be expected even when the retinal layer is interrupted at the lower end of the image. FIG. 8B is a diagram illustrating a state in which the layer boundary is specified in a case where the retinal layer is partially interrupted at the lower end of the image. L1 to L6 in FIG. 8B are the inner boundary membrane, the nerve fiber layer boundary, the inner reticular layer boundary, the outer reticular layer boundary, the photoreceptor inner and outer node junction, and the retinal pigment in the same manner as in FIG. 11B. It represents the epithelial layer boundary. _{R N} in FIG. 8 (b), represents a region of the normal imaging site, A3 represents the A-scan line at that site. DP3 represents forward direction detection information, and UP3 represents backward direction detection information. R _D of FIG. 8 (b), the region R _U shown in FIG. 8 (a) represents the site where retinal layer is broken by the image bottom Conversely, A4 represents an A-scan lines included in the site. DP4 represents forward direction detection information, and UP4 represents backward direction detection information. In this case, an error occurs because the layer boundary is assigned to the layer boundary candidates in order from the retinal pigment epithelium layer boundary that is actually missing on the reverse layer boundary. On the other hand, since the layer boundary is assigned to the layer boundary candidates in order from the inner boundary film appearing on the image, no error occurs in the forward layer boundary. Accordingly, the average value _{su, ave} in the reverse direction is a very low value. On the other hand, since the forward average value s _{d, ave} is higher than the reverse average value _{su, ave} , the forward layer boundary having a high degree of similarity is selected as the final layer boundary. Thereby, even when the retinal layer is interrupted at the lower end of the image, the layer boundary can be specified without making a mistake.

In addition, in the A-scan line of a normal imaging region such as A1 in FIG. 8A or A3 in FIG. 8B, if there is no error in detection of layer boundary candidates in steps S703 and S704, It is possible to assign the layer boundaries without making a mistake in either the forward direction or the reverse direction. Therefore, both the forward average value s _{d, ave} and the forward average value s _{d, ave} are high, and the correct layer boundary can be specified regardless of which is selected. In addition, if an error occurs in either forward or reverse layer boundary candidate detection, the result closer to the correct feature value is selected, so the error can be prevented by final identification of the layer boundary. Can do.

In this embodiment, the average value of the similarity between the forward layer boundary and the correct feature value is compared with the average value of the similarity between the reverse layer boundary and the correct feature value, and the layer boundary data having a higher value is compared. The final layer boundary is identified as it is. However, the method for identifying the layer boundary is not limited to this. For example, for each point (P _di and P _ui ) on the forward layer boundary and the reverse layer boundary, the corresponding similarities (s _{d, i} and _{su, i} ) are individually compared, and the similarities are large in each. A method of selecting a point corresponding to a direction may be used. At this time, for example, the points of the forward layer boundary and the backward layer boundary may be paired in the order in which they are arranged along the A-scan forward direction, and the degree of similarity may be compared. A method may be used in which similarities are compared with each other having a close relationship.

  With this method, when the forward layer boundary assignment is correct in one part and the reverse layer boundary assignment is correct in the other part on the A-scan line, the correct assignment result is finally determined as the layer boundary. It can be reflected. The case where an abnormal site is included in the retinal layer described in the first embodiment corresponds to this case. In this case, the region on the front side of the retina across the abnormal part has a higher degree of similarity, and the region on the back side of the retina has a higher degree of similarity in the reverse direction, and can be adopted as a layer boundary. If the presence of an abnormal site is not known in advance, the presence of an abnormal site in the retina can be detected by detecting the A-scan line in which the results of the forward and reverse directions are partially adopted. You can also Furthermore, it is possible to specify a region sandwiched between points adopted in the forward direction as layers boundaries and points adopted in the reverse direction as regions of abnormal parts.

  Then, the layer boundary specifying unit 607 stores the layer boundary position information specified for each A-scan line in the storage unit 602. With the above configuration, even in a case where the retinal layer is interrupted at the upper end or the lower end of the image, the layer boundary can be accurately identified without being affected by the loss of the layer boundary due to the interruption of the retinal layer.

(Fourth embodiment)
In the present embodiment, layer boundary candidates are detected in both the forward and reverse directions along the A-scan line on the tomographic image. Next, when the missing region at the layer boundary is determined based on the detection result, the layer boundary is specified by comparing the detection result in each direction with the feature extracted from the layer boundary of the normal region in the target image.

  More specifically, in the third embodiment, the correct feature amount to be compared with the forward layer boundary and the reverse layer boundary is stored and determined in advance, and thus the layer boundary feature existing for each case is determined. The comparison corresponding to the variation is not possible.

  Therefore, in the present embodiment, each layer boundary candidate is detected by analyzing in both the forward and reverse directions along each A-scan line on the tomographic image. Next, with respect to the detection results in these two directions, layer boundaries are temporarily assigned in each direction, and the correspondence between the layers is compared to determine whether or not there is a layer boundary defect. At this time, a region determined to have a missing layer boundary is referred to as a “layer boundary missing region”. If it is determined that there is a layer boundary defect, the layer boundary features assigned in each direction are detected in the region that is not the layer boundary defect region determined above (normal region). Compare with As a result, a layer boundary in a direction more similar to the feature of the layer boundary in the normal region is selected and specified as the final layer boundary. As a result, when the retinal layer is interrupted at the edge of the image, the result of analysis from the image edge in turn decreases the similarity with the correct layer boundary because the layer boundary is incorrectly assigned, but the analysis was performed from the opposite direction. The result is highly similar because the layer boundaries are assigned correctly. As a result, it is possible to provide an image processing technique capable of specifying the layer boundary without making a mistake. In addition, since the detection result in each direction is compared with the feature of the layer boundary of the normal region in the target image, a comparison corresponding to the variation in the feature of the layer boundary existing for each case becomes possible.

(Configuration of image processing apparatus 90)
FIG. 9 shows a configuration of an image processing apparatus 90 according to the present embodiment. The image processing apparatus 90 includes an image acquisition unit 901, a storage unit 902, an image conversion unit 903, a forward direction detection unit 904, a backward direction detection unit 905, a detection result evaluation unit 906, a layer boundary identification unit 907, a display unit 908, and a defect detection. Part 909. The image processing device 90 is connected to the tomographic image acquisition device 110. Since the tomographic image acquisition apparatus 110 has the same function as the tomographic image acquisition apparatus 70 of the third embodiment, a description thereof will be omitted.

(Processing of image processing apparatus 90)
FIG. 10 is a flowchart of this embodiment, and a specific processing procedure executed by the image processing apparatus 90 will be described along this flowchart. However, Steps S1001, S1002, and S1009 are the same as Steps S701, S702, and S707 of the third embodiment, and thus the description thereof is omitted.

  In step S1003, the forward direction detection unit 904 detects a retinal layer boundary candidate by analyzing the Sobel image acquired from the image conversion unit 903 in the forward direction along the A-scan line. The details of the analysis process in this step are the same as in step S703 in the third embodiment, and a description thereof will be omitted. Next, the forward direction detection unit 904 transmits the detected forward direction detection information to the defect detection unit 909.

  In step S1004, the backward direction detection unit 905 detects a retinal layer boundary candidate by analyzing the Sobel image acquired from the image conversion unit 903 in the backward direction along the A-scan line. The details of the analysis process in this step are the same as in step S704 in the third embodiment, and a description thereof will be omitted. Next, the reverse direction detection unit 905 transmits the detected reverse direction detection information to the defect detection unit 909.

  In step S1005, the defect detection unit 909 detects the layer boundary defect for each A-scan line based on the forward direction detection information acquired from the forward direction detection unit 904 and the reverse direction detection information acquired from the reverse direction detection unit 905. The presence or absence of is determined. If it is determined that the layer boundary is missing, the forward direction detection information and the backward direction detection information are transmitted to the detection result evaluation unit 906, and the process proceeds to step S1007. If it is determined that the layer boundary is not missing (is a normal region), forward direction detection information (or reverse direction detection information) may be transmitted to the layer boundary specifying unit 907, and the process proceeds to step S1006. Proceed with

  In the present embodiment, the defect detection unit 909 determines whether or not the region in which the forward layer boundary candidate is detected is a normal region, the correspondence between the forward layer boundary candidate and the backward layer boundary candidate, and The determination is made based on the positional relationship between the forward layer boundary candidate and the backward layer boundary candidate. For each detection result in the forward direction and in the reverse direction, a layer boundary is provisionally assigned in each direction in order, and is set as a forward layer boundary and a reverse layer boundary, respectively. Then, the positions of the corresponding layer boundaries are compared between the forward direction and the reverse direction, and if all the layer boundaries correspond to each other and the positions coincide with each other, it is determined that the region is a normal region. Conversely, if there is a shift in the correspondence relationship between the assigned layer boundaries or the positions of the corresponding layer boundaries do not match, it is determined that the layer boundary is missing.

This process will be specifically described with reference to FIG. In FIG. 8A, six layer boundaries L1 to L6 are objects to be specified. When determining the loss of the layer boundary with respect to the A1 line, since six points of the forward layer boundary candidates DP1 are detected in the A1 line, for each point, L1 to L1 in order along the forward direction. L6 layer boundaries can be assigned. This is assumed to be a forward layer boundary (each point is in order P _d1 , P _d2 ,..., P _d6 ) as in step S705 of the third embodiment. In addition, since six layer boundary candidates DP2 in the reverse direction are detected, the layer boundaries L6 to L1 can be assigned to each point in order from the reverse direction. Similarly, this is defined as a reverse layer boundary (where each point is P _u6 , P _u5 ,..., P _u1 ). At this time, when the correspondence relationship between the layer boundaries is seen on both sides, P _d1 and P _u1 , P _d2 and P _u2 ,..., P _u6 and P _u6 correspond to each other, and all the layer boundaries of L1 to L6 are It corresponds. Further, when these positions are compared with each other, the positions of the points DP1 and DP2 are all coincident with each other, so that the A1 line is determined to be a normal region.

On the other hand, when determining the loss of the layer boundary for the A2 line, only four points each of the layer boundary candidates DP2 and UP2 are detected. Accordingly, when a layer boundary is assigned to each point of the forward layer boundary candidate DP2, only P _{d1 to} P _d4 corresponding to L1 to L4 are assigned. Also, for each point of the reverse layer boundary candidates UP2, it is assigned only _P u6 _{to P u3} corresponding to L6～L3. At this time, when looking at the correspondence between the layer boundaries, only L3 and L4 correspond (P _d3 and P _u3 and P _d4 and P _u4 only), and the correspondence relationship between the assigned layer boundaries is shifted. . Therefore, it is determined that the A2 line is a layer boundary defect region.

  Further, even if all the assigned layer boundaries correspond to each other, if the positions are different when the positions of the points are compared, in the present embodiment, it is determined as a layer boundary missing region. This is considered to be the case where there is an error in either the forward direction or the backward direction detection result even in the normal region. At this stage, since it cannot be determined whether the detection result in the forward direction or the reverse direction is correct, it is treated as a layer boundary defect region here. This is because if it is determined that the region is a normal region, the detection result used for the processing is treated as highly reliable in step S1006 described later.

  In step S <b> 1006, the layer boundary specifying unit 907 specifies the layer boundary based on the forward direction detection information (or reverse direction detection information) acquired from the defect detection unit 909. The forward direction detection information acquired in this step is determined as a normal region as a result of the correspondence between the layer boundary candidates in the forward direction and the reverse direction in step S1005, and the positions of the respective detection results match. Therefore, the reliability of the detection result is considered high. Therefore, in the present embodiment, the result of assigning the layer boundary (forward layer boundary) to the forward direction detection information is directly specified as the final layer boundary. Next, the layer boundary specifying unit 907 transmits the layer boundary position information (normal layer boundary information) of the specified normal region to the detection result evaluating unit 906.

  In step S <b> 1007, the detection result evaluation unit 906 extracts the forward direction detection information and the backward direction detection information of the layer boundary defect region acquired from the defect detection unit 909 from the normal layer boundary information acquired from the layer boundary specification unit 907. Compare with the characteristics of the layer boundary.

  In the present embodiment, on the original image stored in the storage unit 902, the feature amount of each layer boundary is extracted for each A-scan line from the position information of the layer boundary in the normal region indicated by the normal layer boundary information. Then, an average value in the entire normal region is obtained with respect to the extracted feature values of each layer boundary, and this is set as a correct feature value of each layer boundary. This is because, as described in step S1006, the layer boundary is specified from the detection result with high reliability in the normal region. Further, as the feature amount, the same feature amount as that described in step S705 of the third embodiment is extracted.

In FIG. 8A, since the A-scan line of A1 is determined to be a normal region in step S1005, the layer boundary is assigned to the layer boundary candidate DP1 on the A-scan line of A1. A feature amount is extracted from each point (P _d1 , P _d2 ,..., P _d6 ). Similarly to the A1, in any A-scan lines included in the normal region R _N, extracts a feature vector corresponding to each point of the forward layer boundaries on A-scan lines. Then, an average value of all of the feature vectors of these contained in R _N for each layer boundary, correct feature value f _1, f _2, · · ·, and f _6. Thus, by calculating the correct features from the normal region R _N of the target image, it is possible to use the correct feature amount corresponding to variation in the characteristics of the layer boundary present in each case (individual differences) .

Next, with respect to the detection results in the forward direction and the reverse direction in the layer boundary defect region (region R _U in FIG. 8A), the above feature amount is extracted from the original image for each A-scan line based on those positions. To do. Then, the extracted feature quantities in each direction are compared by calculating the degree of similarity with the correct feature quantity obtained above. Here, since the similarity calculation method is the same as that in step S705 of the third embodiment, the description thereof is omitted. Also, the similarity between the forward feature quantity and the correct feature quantity is defined as the forward similarity, and the similarity between the reverse feature quantity and the correct feature quantity is defined as the backward similarity. Then, the detection result evaluation unit 906 receives the data of the forward layer boundary and the backward layer boundary in the layer boundary defect region, and the forward similarity and the backward similarity value corresponding to each of those points, the layer boundary specifying unit To 907.

  In step S1008, the layer boundary specifying unit 907, from the detection result evaluation unit 906, forward layer boundary and reverse layer boundary data in the layer boundary defect region, and forward similarity and backward similarity corresponding to each point. Get the degree value. Then, by comparing the similarities in the forward direction and the reverse direction, the direction having a higher similarity value, that is, the layer boundary data in the direction close to the normal layer boundary is selected and specified as the final layer boundary. Since the layer boundary specifying method in this step is the same as that in step S706 in the third embodiment except that the target region is only the layer boundary defect region, description thereof will be omitted.

  With the above configuration, even in a case where the retinal layer is interrupted at the upper end or the lower end of the image, the layer boundary can be accurately identified without being affected by the loss of the layer boundary due to the interruption of the retinal layer. Furthermore, since the similarity is calculated by comparing the detection results in the forward and reverse directions with the characteristics of the layer boundary of the normal region in the target image, it is possible to make a comparison corresponding to the variation in the characteristics of the layer boundary existing for each case. become.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (10)

Forward direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a forward direction from the fundus surface of the tomographic image of the eye to be examined to the back side of the fundus;
An abnormal part detecting means for analyzing the tomographic image and detecting the position of the abnormal part of the retinal layer;
When the position of the abnormal part is detected by the abnormal part detection means, the retina of the eye to be examined is analyzed by analyzing the tomographic image along the reverse direction from the back side of the fundus to the fundus surface of the tomographic image. A reverse direction detecting means for detecting a layer boundary candidate of the layer;
A layer boundary from the fundus surface to the abnormal part is identified using a layer boundary candidate detected by the forward direction detection means, and a layer boundary from the back side of the fundus to the abnormal part is detected in the reverse direction. A layer boundary specifying means for specifying using a layer boundary candidate detected by the means;
An image processing apparatus comprising: When the position of the abnormal part of the retinal layer is not detected by the abnormal part detection means,
The reverse direction detection means does not detect the layer boundary candidate,
The image processing apparatus according to claim 1, wherein the layer boundary specifying unit specifies a boundary of the retinal layer of the eye to be examined using the layer boundary candidate detected by the forward direction detection unit. Forward direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a forward direction from the fundus surface of the tomographic image of the eye to be examined to the back side of the fundus;
First abnormality detection means for detecting the position of the abnormal part of the retinal layer by analyzing the tomographic image in association with the analysis position in the forward direction of the forward direction detection means;
A reverse direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a reverse direction from the back side of the fundus of the tomographic image to the fundus surface;
Second abnormality detection means for detecting the position of the abnormal part of the retinal layer by analyzing the tomographic image in association with the analysis position in the reverse direction of the reverse direction detection means;
A layer boundary from the fundus surface to the abnormal site detected by the first abnormality detection unit is specified using a layer boundary candidate detected by the forward direction detection unit, and the second abnormality is detected from the back side of the fundus. A layer boundary specifying means for specifying the layer boundary to the abnormal site detected by the detecting means using the layer boundary candidate detected by the reverse direction detecting means;
An image processing apparatus comprising: The forward direction detection means stops detecting the forward layer boundary candidate by the forward direction detection means when the position of the abnormal part of the retinal layer is detected by the first abnormality detection means,
The reverse direction detection means stops detecting the layer boundary candidate in the reverse direction by the reverse direction detection means when the position of the abnormal part of the retinal layer is detected by the second abnormality detection means. The image processing apparatus according to claim 3. Forward direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a forward direction from the fundus surface of the tomographic image of the eye to be examined to the back side of the fundus;
A reverse direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a reverse direction from the back side of the fundus of the tomographic image to the fundus surface;
An acquisition means for acquiring each feature amount from a forward layer boundary candidate detected by the forward direction detection means and a backward layer boundary candidate detected by the backward direction detection means;
Comparison means for comparing the feature quantity acquired by the acquisition means with the feature quantity of the layer boundary stored in advance in the storage means;
Based on the comparison by the comparison means, the one indicating the feature quantity close to the feature quantity of the layer boundary stored in the storage means is selected from the forward layer boundary candidate and the reverse layer boundary candidate, and the selected one is selected. Layer boundary specifying means for specifying the layer boundary candidate of the other eye as the layer boundary of the retinal layer of the eye to be examined;
An image processing apparatus comprising: The comparison means includes
A first similarity between the feature amount of the forward layer boundary candidate and the feature amount of the layer boundary stored in advance in the storage unit;
Calculating a second similarity between the feature quantity of the layer boundary candidate in the reverse direction and the feature quantity of the layer boundary stored in advance in the storage unit;
Layer boundary identification means
6. The image processing apparatus according to claim 5, wherein a layer boundary candidate showing a higher similarity among the first similarity and the second similarity is specified as a layer boundary of the retinal layer of the eye to be examined. . Forward direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a forward direction from the fundus surface of the tomographic image of the eye to be examined to the back side of the fundus;
A reverse direction detecting means for detecting a layer boundary candidate of the retinal layer of the eye to be examined by analyzing the tomographic image along a reverse direction from the back side of the fundus of the tomographic image to the fundus surface;
Whether the region where the forward and reverse layer boundary candidates are detected is a normal region, the correspondence between the forward layer boundary candidate and the reverse layer boundary candidate, and the forward direction Determination means for determining by a positional relationship between the layer boundary candidate and the layer boundary candidate in the reverse direction;
With respect to the one area where the forward and reverse layer boundary candidates are detected, it is determined that the one area is a normal area by the determination means, and thus the tomogram corresponding to the normal area Extraction means for extracting the feature amount of the region of the image from the tomographic image;
With respect to the other areas in which the forward and reverse layer boundary candidates are detected, the determination means determines that the other areas are not normal areas, and the forward layer boundary candidates and Acquisition means for acquiring each feature quantity from the layer boundary candidates in the reverse direction;
Comparison means for comparing the feature quantity acquired by the acquisition means with the feature quantity extracted by the extraction means;
Based on the comparison by the comparison unit, the one indicating the feature amount close to the feature amount extracted by the extraction unit is selected from the forward layer boundary candidate and the reverse layer boundary candidate, and the selected one A layer boundary specifying means for specifying a layer boundary candidate as a layer boundary of the retinal layer of the eye to be examined;
An image processing apparatus comprising:   The determination means corresponds to the forward layer boundary candidate and the backward layer boundary candidate, and the position of the forward layer boundary candidate matches the position of the backward layer boundary candidate. The image processing apparatus according to claim 7, wherein the image processing apparatus determines that the area where the forward layer boundary candidate is detected is a normal area.   The program for functioning a computer as each means of the image processing apparatus of any one of Claims 1 thru | or 8.   A computer-readable storage medium storing the program according to claim 9.

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