JP2002065613A - Method and system for displaying image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for improving the capability of displaying an image of two comparable subjects when the images of these comparable subjects are to be displayed by an image display system. SOLUTION: This system is equipped with an image display device 10 that displays the mammographs, P1 and P2, of two comparable mammae, Pa and Pb, on a display screen thereof, a means 11 for positioning both images P1 and P2 so that the corresponding positions of right and left mammae, Pa and Pb (nipples, Na and Nb) can be lined up on the display screen with respect to the vertical direction, and the positioning means 11 is supported by a manual moving means 13 that manually moves at least one of these two images, P1 and P2 toward the vertical direction on the display screen of the device 10 using a mouse 12, and a means 14 that uses lower luminance for uniformly covering a partially lost portion PO of an image caused by the means 13 that manually moves the one image on the display screen of the display device 10 is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display method and an image display system, and more particularly to an image display method and an improvement of a display system of two subject images to be compared.

[0002]

2. Description of the Related Art Conventionally, in a medical field, a radiation image of a patient is photographed, and a film on which the obtained radiation image is recorded is read on a shakasten for interpretation.
They are used to diagnose injuries and other conditions. In recent years, instead of directly exposing a radiation image to a film,
The radiation image is stored in a stimulable phosphor sheet (radiation image conversion panel) for storing and storing the radiation image, and the excitation light is applied to the stimulable phosphor sheet to emit the stimulated emission light in a light amount corresponding to the stored and stored radiation image. To obtain a digital image signal, and thereafter, the digital image signal is reproduced as a visible image by printing it on a recording medium such as a film or displaying it on an image display device such as a CRT. (Radiation image recording and reading system (computed radiography);
No. 29, No. 56-11395, No. 56-11397).

According to such a radiation image recording and reading system, by performing various signal processing on the digital image signal, the gradation characteristics and frequency characteristics of the output visible image are more suitable for image reading than before. The diagnostic performance based on images can be improved.

[0004] The obtained digital image signal is analyzed using a computer, and abnormal shadows such as tumor shadows and microcalcification shadows appearing in the image are automatically detected. A system that secures a certain detection level even when the degree is low and is useful for diagnosis has been developed (abnormal shadow candidate detection system; Japanese Patent Application Laid-Open No. 8-294479, etc.).

This system evaluates the degree of concentration of a density (signal value) gradient vector of a digital image signal representing a radiographic image (mammography) of a breast obtained mainly by a breast cancer screening, thereby identifying a candidate for a tumor shadow in the image. The tumor is automatically detected, or a morphological operation (dilation processing, erosion processing, opening processing, closing processing, etc.) is performed on the digital image signal to automatically detect candidates for microcalcification shadows. This system detects abnormal shadow candidates such as shadows and microcalcifications. The abnormal shadow candidates detected by this system are marked on a mammography, for example, by using a rectangular ROI (region of interest) frame, and the like. It can be used for diagnosis by displaying it on a liquid crystal display device or printing it on a diagnostic film. Rukoto can.

[0006]

By the way, when a mammography including an abnormal shadow candidate detected by the above-mentioned abnormal shadow candidate detection system is displayed on an image display surface of an image display device, and a doctor or the like observes and interprets the image, the left and right images are displayed. It is often practiced to simultaneously display a set of breast images back to back. This is because, for example, when an abnormal shadow candidate is detected in one of the left and right breast images, it is to confirm whether or not an abnormal shadow candidate exists at a similar position in the other image. Also, mammography,
A so-called front image (MLvi) of the breast taken from above and below
ew (or MLOview); Medio-lateral view (or
Medio-lateral oblique view)) and so-called side view images (CCview; Cranio-caudal vie
Since w) is photographed, two images on the right side of one of the left and right breasts may be displayed side by side, and these may be compared and contrasted for observation and interpretation.

[0007] Further, not only when the subject is a breast,
In some cases, images of two objects to be compared (left and right hands, arms, legs, and the like) are displayed side by side on an image display device, and are compared and interpreted.

[0008] However, as described above,
When images of two subjects are displayed at the same time, the corresponding positions of the two subjects may be displayed irregularly on a horizontal line or a vertical line. In this case, there is a problem that it is difficult to perform comparative image interpretation. This is a problem specific to displaying an image on a display device. That is, for example, when one of the subjects is recorded on a separate film and the two films are compared and interpreted, even if the recording position of the subject on the film is different between the two films. However, when the film is fixed to the shakasten, the problem is solved by adjusting the fixing position of the film so that the corresponding positions are aligned.

On the other hand, when an image is displayed on an image display device, it is difficult to adjust the display position so that the corresponding positions of the two subjects are aligned.

[0010] This means that the image displayed on the display surface of the image display device displays two images in which two subjects are separately recorded one by one (two subjects and two images). ), Two images are combined into a single image, and a single image obtained by combining the two images is displayed (when there are two subjects and one image). It is the same as above.

The present invention has been made in view of the above circumstances, and when displaying images of two subjects to be compared and contrasted, an image display method and an image display system in which the comparative reading performance of these two subjects is improved. The purpose is to provide.

[0012]

According to an image display method and an image display system of the present invention, when displaying medical images of two subjects to be compared and contrasted on a display surface of an image display device, corresponding positions of the subjects are aligned. In this way, the direction of movement of the line of sight of the person performing observation and interpretation is limited to the horizontal direction or the vertical direction to facilitate comparative interpretation and improve the interpretation performance.

That is, in the image display method of the present invention, when displaying the medical images of the two objects to be compared and displayed on the display surface of the image display device, the corresponding positions of the objects are aligned on the display surface. The method is characterized in that the medical images are aligned and displayed.

Here, "so that the corresponding positions of the subjects are aligned" means that when the images of the two subjects are displayed one by one on the left and right sides of the display surface, the corresponding positions of the two subjects are displayed on the display surface. This means that the positions in the vertical direction are aligned. In the case where images of two subjects are displayed one by one on the upper and lower sides of the display surface, the corresponding positions of the two subjects are the horizontal positions on the display surface. It means that they are aligned.

Further, the medical image displayed on the display surface is
When two images each include two subjects, that is, one subject is recorded in one image, and two subjects are displayed by displaying two images, two images are displayed. By moving at least one of them on the display surface, the corresponding position of the subject may be aligned on the display surface. On the other hand, when the medical image displayed on the display surface is a single image including two subjects, that is, when two subjects are originally recorded in a single image, or when originally a single image is used. Has recorded only one subject, but before the image was displayed on the display surface, the two images were combined into one image, and finally a single image including the two subjects was obtained. If so, the single image is divided into two images each including two objects, and at least one of the two images obtained by the division is moved on the display surface, so that the The corresponding positions may be aligned on the display surface.

The movement of the image and the division of the image described above may be performed automatically, or may be performed manually by an interpreter such as a doctor.

The medical images of the two subjects to be compared and contrasted include radiation images of the left and right breasts (front images, side images, or front and side images of one breast) described above, and orthopedic fields and the like. Images of the right and left hands, arms, lower limbs, and the like can be applied.

As the corresponding position of the subject, for example, it is preferable to apply a characteristic portion of the subject (external characteristic portion, characteristic portion of density or luminance, etc.). Because these characteristic portions can be detected by various automatic detection processes, it is particularly effective when the above-described positioning is automated. When the images of the two subjects to be compared and contrasted are, for example, radiation images of the left and right breasts, it is preferable to use the nipples of the breasts as the characteristic portions.

When the image is aligned on the display surface by the image display method of the present invention, when a missing portion of the image occurs on the display surface, it is preferable to fill the missing portion of the display surface with low luminance. . Generally, in an image display device, an area where no image data is present is displayed at the highest brightness. However, when observing and interpreting a medical image, an interpreter sees light from the portion displayed at the highest brightness. There is a danger that the image reading power may be reduced due to entering, but it is effective to prevent the image reading power from lowering by filling the image missing portion on the display surface with low luminance.

Here, the low luminance may be any luminance as low as negligible influence of glare. Specifically, it is sufficient if the luminance is equal to or lower than the intermediate luminance, and preferably the luminance is the minimum.

Note that it is preferable that the image missing portion on the display surface be painted with a uniform low luminance, because it does not hinder image reading.

An image display system according to the present invention is a system for implementing the image display method according to the present invention, wherein the medical image of two subjects to be compared and displayed is displayed on a display surface of an image display device. And a positioning unit for positioning the medical image so that the corresponding positions of the subject are aligned on the display surface.

Here, the medical image displayed on the display surface is
In the case of two images each including two subjects, the positioning means includes a manual moving means for manually moving at least one of the two images on the display surface so as to be positionable, or A corresponding position detecting means for automatically detecting a corresponding position of one subject; and an automatic moving means for automatically moving at least one image to the corresponding position detected by the corresponding position detecting means. Is preferred. When the medical image displayed on the display surface is a single image including two subjects, the alignment unit divides the single image into two images each including two subjects. And manual moving means for manually moving at least one of the two images obtained by the division on the display surface so as to be aligned, or to convert a single image into two images. A dividing unit that divides the subject into two images each including a separate subject, a corresponding position detecting unit that automatically detects a corresponding position of the two subjects, and a corresponding position detected by the corresponding position detecting unit. It is preferable to include an automatic moving means for automatically moving at least one of the two images.

Further, it is preferable that the positioning means performs the positioning by using the characteristic portion of the subject as a corresponding position. In a case where the images of the two subjects to be compared are radiographic images of the left and right breasts. Preferably, the alignment is performed with the nipple of the breast as a characteristic portion.

It is preferable that the image forming apparatus further includes a low-luminance processing unit that fills in a low-luminance portion of an image missing on the display surface by the alignment by the alignment unit. This is because it is effective in preventing the reading ability of a reading person such as a doctor reading the image displayed on the display surface from being deteriorated. In addition, when painting with low luminance, it is more preferable to paint with uniform low luminance.

[0026]

According to the image display method and the image display system of the present invention, when displaying the medical images of the two subjects to be compared and displayed on the display surface of the image display device, the corresponding positions of the subjects are aligned and displayed. By doing so, it is possible to limit the direction of movement of the line of sight for comparison of those who observe and interpret, to the horizontal direction or the vertical direction, thereby facilitating comparative image interpretation and improving image interpretation performance.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of an image display method and an image display system according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an image display system for implementing the image display method of the present invention, and FIG. 2 is a comparative image displayed on the image display surface by the image display system shown in FIG. FIG. 4 is a diagram illustrating an example of two subject images, in which left and right breasts Pa and Pb are applied as subjects. Further, the image display system 2 of the present embodiment
0 displayed on the image display device 10 are two mammograms P1 and P2. The mammography P1 is a lateral image of the right breast Pa, and the mammography P2 is a left breast Pa.
5 is a side view image of FIG.

The illustrated image display system 20 is an image display device 10 that displays the mammography P1, P2 of the two breasts Pa, Pb to be compared and contrasted on the display surface.
And a positioning means 11 for positioning the two images P1 and P2 such that the corresponding positions of the left and right breasts Pa and Pb are aligned in the vertical direction on the display surface of the display device 10. 11 is two images P
1 and P2, a manual moving means 13 for manually moving at least one of them on the display surface of the display device 10 in the vertical direction using the mouse 12, and as a result of being moved by the manual moving means 13, the display on the display device 10 is displayed. And a low-luminance processing unit 14 for uniformly filling the missing portion P0 of the image generated on the surface with low luminance.

Next, the operation of the image display system 20 of the present embodiment will be described.

First, two mammograms P1 and P2 shown in FIG. 2A are input to the positioning means 11 of the image display system 20 of the present embodiment. The positioning means 11 outputs this as it is to the image display device 10, and the image display device 10 displays the image P1 of the right breast Pa in the right half area on the display surface as shown in FIG. Then, the image P2 of the left breast Pb is displayed in the left half area.

Here, the two images P1 and P2 displayed on the display surface of the display device 10 are as shown in FIG.
Corresponding positions of left and right breasts Pa, Pb (eg, nipple Na,
P1 and P2 in which the positions of Nb in the vertical direction are substantially aligned
, The left and right breasts Pa and Pb are displayed as they are.
Images P1 and P2 displayed on the display device 10 are not aligned, but the corresponding positions of the left and right breasts Pa and Pb are not aligned.
In the case of P2, the left and right breast P
It is difficult to perform comparative interpretation of a and Pb.

Here, the interpreter moves the right image P1 vertically upward by the manual moving means 13 so that the position of the nipple Na of the right breast Pa coincides with the position of the nipple Nb of the left breast Pb. Figure (3)). As a specific operation, the cursor C linked to the operation of the mouse 12 on the display surface of the image display device 10 is moved to the right image P1 portion by the operation of the mouse 12, and the right image P1 is dragged and dropped. Thus, the right image P1 may be moved. In this case, for each of the right image P1 and the left image P2, the position of each nipple Na, Nb is designated by the mouse 12 or the like, and a mark (horizontal line or the like) corresponding to the designated position is defined as a boundary between the two images. If the right image P1 is moved (FIG. 3 (2)) after being displayed in the vicinity (FIG. 3 (1)), alignment of the corresponding position becomes easy.

By the above-described operation, the right image P1 and the left image P2 are converted into nipples Na and Nb of the left and right breasts Pa and Pb on the display surface of the display device 10 as shown in FIG.
Are displayed as being substantially aligned in the vertical direction, so that comparative interpretation of the left and right breasts Pa and Pb is facilitated.

Here, since the right image P1 is moved vertically upward by the manual moving means 13, an area P0 in which no image exists in the lower right portion of the display surface of the display device 10 is displayed.
This causes the image missing area P0 to be clipped to the highest brightness in a general image display device, and the radiologist feels more dazzling due to the brightness of the area P0, and the image P1,
Although the interpretation of P2 is hindered, in the image display system 20 of the present embodiment, the image missing area P0 is clipped to the lowest luminance by the low luminance processing means 14 as shown in FIG. . As a result, the radiologist reads the image missing area P0.
It is possible to prevent a decrease in image reading power without being dazzled.

As described above, according to the image display system 20 of the present embodiment, the left and right breasts P to be compared and contrasted.
When displaying the images P1 and P2 of a and Pb on the display surface of the image display device 10, the corresponding positions of the left and right breasts Pa and Pb are aligned and displayed, so that the line of sight of the person performing observation and interpretation is moved in the horizontal direction. It is possible to limit the image interpretation, facilitate comparative image reading, and improve the image reading performance.

The image display system 20 of the present embodiment
Is a configuration that employs a positioning means 11 that requires a manual positioning operation by a radiogram interpreter, but employs a positioning means 15 that performs automatic positioning without requiring this positioning operation by a radiogram interpreter. FIG. 4 shows an image display system 20 having the configuration described above.

The positioning means 15 is used for the left and right breasts P
The corresponding position detecting means 16 for automatically detecting the corresponding positions of a and Pb (for example, the positions of the nipples Na and Nb), and at least one of the images are automatically adjusted so that the corresponding positions detected by the corresponding position detecting means 16 are aligned. It is provided with an automatic moving means 17 for moving the image in a horizontal direction and a brightness reduction processing means 14.

Here, the corresponding position detecting means 16 may provide, for example, information that the input mammography P1, P2 is a mammography (the information may be header information of the mammography P1, P2, or may be input by an image reader. ), A corresponding structure (for example, a nipple) is determined by referring to a look-up table or the like stored in advance based on a template corresponding to this structure.
The position (corresponding position) of the structure in each of the images P1 and P2 may be detected by performing template matching using a template on the image 2 or the cursor may be linked to the mouse 12 by the reader. C, for example, in the right image P1, a corresponding structure is defined by a rectangular frame (ROI).
), And an image portion substantially the same as or symmetrical to the image in the selected ROI frame is searched in the left image P2 to detect the corresponding position. Further, as shown in FIG. 5, a boundary between the breast and the direct X-ray part (uncut part) is detected by edge detection or the like, and the distance l from the image end on the chest wall side of this boundary is the smallest. A distant point (the vertex of the semicircular boundary line: lmax) may be set as the nipple position (corresponding position).

The automatic moving means 17 operates such that the corresponding positions detected by the corresponding position detecting means 16 are aligned.
The moving operation of the right image P1 manually performed by the radiogram interpreter by the manual moving means 13 is automatically performed. Finally, after the movement, the luminance reduction processing means 14 lowers the brightness of the image missing area P0. Accordingly, the same effect as that of the image display system 20 according to the above-described embodiment can be obtained.

FIG. 6 shows an image displayed on the display surface of the image display device 10 as shown in FIG.
1 is a diagram illustrating an embodiment of an image display system according to the present invention corresponding to a case where images P1 and P2 including left and right breasts Pa and Pb, which are two subjects, are a single image P synthesized.

That is, the image P shown in FIG.
Similarly to the images shown in (1) and (2), two images including a mammography P1 which is a lateral image of the right breast Pa and a mammography P2 which is a lateral image of the left breast Pa are image data. For convenience of handling, the image is synthesized into a single image P by a synthesis process (not shown). Therefore, as it is, the right image P1 and the left image P2 cannot be moved alone on the image display surface as in the image display systems of the embodiments shown in FIGS. 1 and 4.

The image display system 20 of the embodiment shown in FIG. 6 is different from the image display system of the embodiment shown in FIG. 1 in that this single image P is divided into images P3 and P4 for the respective subjects Pa and Pb. The dividing means 18 employs a configuration in which a single image P is divided into an image P3 of the right breast Pa and an image P4 of the left breast Pb by the dividing means 18. Divide (Fig. 8
(1)) Then, similarly to the image display system of the embodiment shown in FIG.
May be moved (FIG. 2B), and the brightness reduction processing means 14 may lower the brightness of the image missing area P0 (FIG. 3C).

It should be noted that a single image P
Is divided into two images P3 and P4. Specifically, the interpreter moves the cursor C interlocking with the operation of the mouse 12 on the display surface of the image display device 10 by operating the mouse 12 to the right breast Pa. In order to set a boundary line Ps to be divided into the image P3 and the image P4 of the left breast Pb, the user moves to the broken line position (broken arrow position) in FIG. Position) and one click. By this operation, a boundary Ps connecting the position clicked above the image P and the position clicked below is set, and the dividing means 18 divides the single image P along the right breast Pa along the boundary Ps. Image P3 and left breast Pb image P
Divide into four.

A single image P is composed of two images P3 and P4
Since the operation after the division is the same as that of the image display system of the embodiment shown in FIG. 1, the description is omitted.

Then, the image display system 20 of the present embodiment
According to this, when displaying a single image P including the left and right breasts Pa and Pb to be compared and contrasted on the display surface of the image display device 10, first, the image P including the left and right breasts Pa and Pb, respectively.
3 and P4, and by displaying the corresponding positions of the left and right breasts Pa and Pb in a coordinated manner, it is possible to limit the direction of the line of sight of the person performing observation and interpretation to the horizontal direction, thereby facilitating comparative image interpretation and image interpretation. Performance can be improved.

In the image display system 20 of the embodiment shown in FIG. 6, as in the embodiment shown in FIG.
A configuration for automating the alignment may be employed.
That is, as shown in FIG. 9, for example, the dividing means 18 of the positioning means 11 'shown in FIG. 6 may be added to the positioning means 15 of the image display system shown in FIG.
In this case, the dividing means 18 may be further automated, for example, over the entire surface of the single image P from above to below.
The image P is scanned in the horizontal direction, edges where the luminance sharply changes are detected in the vicinity of the center of the image P in the horizontal direction, and a straight line in which a plurality of edges obtained for each scan are connected in the vertical direction is defined as an image. By automatically setting P as a boundary line Ps to be divided into two images P3 and P4, the division can be automated.

The image display system of each of the embodiments described above uses the left and right breasts as subjects to be compared and compared. However, the image display method and image display system of the present invention are not limited to this mode. Instead, images of the left and right hands, arms, lower limbs, and the like can be applied as the images of the subject to be compared and compared.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an image display system of the present invention.

FIG. 2 is a view for explaining the operation of the image display system according to the embodiment shown in FIG. 1;

FIG. 3 is a diagram showing a state in which a horizontal line for facilitating alignment of corresponding positions is displayed.

FIG. 4 is a diagram showing another embodiment of the image display system of the present invention (part 1).

FIG. 5 is a diagram illustrating an example of a method for detecting a nipple position as a corresponding position.

FIG. 6 is a diagram showing another embodiment of the image display system of the present invention (part 2).

FIG. 7 is a diagram showing a single image including two subjects displayed on an image display device included in the image display system of the present invention.

FIG. 8 is a view for explaining the operation of the image display system according to the embodiment shown in FIG. 5;

FIG. 9 is a diagram showing another embodiment of the image display system of the present invention (part 3).

[Explanation of symbols]

10 Image display device 11,11 ', 15,15' Alignment means 12 Mouse 13 Manual moving means 14 Low brightness processing means 16 Corresponding position detecting means 17 Automatic moving means 18 Dividing means P1 Image including right breast P2 Image including left breast P Single image including left and right breasts P0 Image missing area Pa, Pb breast (subject) Na, Nb nipple (corresponding position) C cursor

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takeshi Okubo Takeshi 798- Address Miyagidai, Kaisei-cho, Ashigara-gun, Kanagawa F-Term (in reference) 4C093 AA01 CA21 DA06 FG20 5C054 AA01 EA05 FC12 FE12 FE18 FE19 HA12

Claims (14)

[Claims] When displaying medical images of two subjects to be compared and contrasted on a display surface of an image display device, the medical images are aligned so that corresponding positions of the subjects are aligned on the display surface. An image display method characterized by displaying the image. 2. The medical image displayed on the display surface,
Two images each including the two subjects separately, and by moving at least one of the two images on the display surface, a corresponding position of the subject is aligned on the display surface. The image display method according to claim 1. 3. The medical image displayed on the display surface,
A single image including the two subjects, dividing the single image into two images each including the two subjects, and displaying at least one of the two images obtained by the division. The image display method according to claim 1, wherein the corresponding position of the subject is aligned on the display surface by moving the object on the surface. 4. The image processing apparatus according to claim 1, wherein when the alignment causes a missing portion of the image on the display surface, the missing portion of the display surface is filled with low luminance. The image display method according to claim 1. 5. The image display method according to claim 1, wherein the alignment is performed by using a characteristic portion of the subject as the corresponding position. 6. The image display method according to claim 5, wherein the images of the two subjects to be compared and contrasted are radiation images of left and right breasts, and a nipple of the breast is used as the characteristic portion. 7. An image display system for displaying medical images of two subjects to be compared and contrasted on a display surface of an image display device, wherein the medical images are arranged so that corresponding positions of the subjects are aligned on the display surface. An image display system, further comprising positioning means for positioning. 8. The medical image displayed on the display surface,
Two images each including the two subjects, wherein the positioning means manually adjusts at least one of the two images so that the corresponding position of the subject is aligned on the display surface. 8. The image display system according to claim 7, further comprising a manual moving means for moving the image display on the screen. 9. The medical image displayed on the display surface,
Two images respectively including the two subjects, wherein the positioning means automatically detects a corresponding position of the two subjects, and a corresponding position detected by the corresponding position detecting means. 8. An image display system according to claim 7, further comprising: automatic moving means for automatically moving said at least one image so that the images are aligned on said display surface. 10. The medical image displayed on the display surface is a single image including the two subjects, and the positioning unit includes the single image separately for the two subjects. Dividing means for dividing the image into two images; and manually moving at least one of the two images obtained by the division on the display surface so that the corresponding position of the subject is aligned on the display surface. The image display system according to claim 7, further comprising a moving unit. 11. The medical image displayed on the display surface is a single image including the two subjects, and the alignment unit includes the single image separately for the two subjects. A dividing unit that divides the image into two images, a corresponding position detecting unit that automatically detects a corresponding position of the two subjects, and a corresponding position detected by the corresponding position detecting unit is aligned on the display surface. 8. The image display system according to claim 7, further comprising: an automatic moving unit that automatically moves at least one of the two images obtained by the division. 12. The image processing apparatus according to claim 7, further comprising a low-luminance processing unit that fills in a low-luminance portion of the image generated on the display surface by the alignment. The image display system according to the paragraph. 13. The image according to claim 7, wherein the positioning means performs the positioning by using a characteristic portion of the subject as the corresponding position. Display system. 14. The image of the two subjects to be compared and contrasted is radiation images of left and right breasts, and the positioning means uses the nipple of the breast as the characteristic portion. The image display system according to claim 13.