JP2007202916A - Medical image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a medical image display device and a X-ray imaging device capable of reducing moire while the effect to other areas caused by partly correcting the image is decreased. <P>SOLUTION: An image obtaining part obtains an image including moire, and a measuring part is a local area including every target pixel of the obtained image, and it measures the total amount of pixel value in the area of parallel direction to the running direction of moire (S1). A decision part decides the size of a filter for reducing moire based on the measured total amount (S3). A filter part performs filtering treatment to the target pixel with the decided size in the orthogonal direction of the moire running direction (S4). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a medical image display apparatus, and more particularly to a medical image display apparatus that attenuates a stripe pattern (moire) in an X-ray image.

  Conventionally, when X-ray imaging is performed using a grid, image data in which a striped pattern (moire) due to the presence of the grid is superimposed on the subject image may be obtained.

  FIG. 9 is a schematic diagram for explaining conventional X-ray imaging using the grid 93. Of the X-rays irradiated from the X-ray source 91 and transmitted through the subject 92, scattered X-rays are removed by the grid 93. Then, the X-ray detector 94 outputs X-ray projection data.

  FIG. 10 is a schematic diagram for explaining an image 95 on which a moire 97 caused by the grid 93 is superimposed. In the image 95, a subject image 96 indicating the anatomy of the subject 92 and a vertical stripe moire 97 are superimposed.

As a conventional method and apparatus for attenuating moire superimposed on an image, there is a method for attenuating moire by applying a steep attenuation aiming at a repetition frequency of moire by fast Fourier transform (FFT) (see Non-Patent Document 1). ).
Motoaki Kato, 8 others, “Usefulness of clinical operation of grid line detection / suppression processing GDS in computed radiography”, Journal of Japanese Society of Radiological Technology, 2005, Vol. 61, No. 8, p. 1158-1169

  However, since moire does not exist uniformly in the entire image, in the conventional method and apparatus for attenuating the repetition frequency of moire, a fringe pattern corresponding to frequency attenuation appears in an image area where moire is low, and the reverse. There is a problem of adversely affecting.

  The present invention has been made in view of such circumstances, and a medical image display apparatus and an X-ray capable of reducing moiré while reducing the influence on other regions caused by correcting a part of an image. An object is to provide a photographing apparatus.

  In order to achieve the above object, a medical image display apparatus according to the present invention includes an image acquisition unit that acquires a medical image, and a local region that includes the target pixel for each target pixel of the acquired medical image. , Measuring means for measuring a statistic of pixel values in at least one direction parallel to or perpendicular to one of the traveling directions of the matrix of the medical image, and striped noise based on the measured statistic Determining means for determining the size of a filter for attenuating components; filtering means for performing a filtering process on the pixel of interest in a direction perpendicular to the traveling direction at the determined size; and after the filtering process And a display means for displaying the medical image.

  According to the present invention, it is possible to reduce the moire while reducing the influence on other regions caused by correcting a part of the image.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.

  In the image data in which the moiré is superimposed on the subject image, the moiré is generally not parallel to the Y axis of the image as shown in FIG. 10, but in the following, for the sake of easy explanation, the moiré is assumed to be parallel to the Y axis. To do.

  FIG. 1 is a conceptual diagram showing a schematic configuration of an X-ray imaging apparatus 10 according to the present embodiment.

  An X-ray imaging apparatus 10 in FIG. 1 includes an X-ray apparatus 1 that performs X-ray imaging and generates a medical image of a subject, and a medical image display apparatus 2 that displays a medical image. The image display device 2 is connected to each other by a communication cable 3.

  The X-ray apparatus 1 includes an X-ray source that irradiates X-rays, an X-ray detector that is disposed opposite to the X-ray source across the subject, detects X-rays, and outputs X-ray projection data, and a subject And a grid for removing scattered X-rays, and an image generating means for generating a medical image based on the X-ray projection data output after removing scattered X-rays.

  The medical image display apparatus 2 includes a central processing unit (CPU) 11 that mainly controls the operation of each component, a main memory 12 that stores a control program for the apparatus and that serves as a work area during program execution, and an operating system. (OS), a device drive of a peripheral device, a magnetic disk 13 storing various application software including a program for performing moire attenuation processing described later, a display memory 14 for temporarily storing display data, and this display The monitor 15 such as a CRT monitor or a liquid crystal monitor that displays an image 31 based on data from the memory 14, the mouse 16 as an input device, and the state of the mouse 16 are detected, and the position of the mouse pointer on the monitor 15 and the mouse 16 are detected. A controller 16a for outputting signals such as the state of the signal to the CPU 11, and a keyboard 17 , And a bus 18 which connects the above components.

  Next, a program executed by the medical image display apparatus 2 will be described.

  The program includes an image acquisition unit that acquires a medical image including moire, and a local region that includes the target pixel in a direction parallel to or perpendicular to the traveling direction of the moire for each target pixel of the acquired medical image. In at least one direction, a measurement unit that measures a statistic of a pixel value, a determination unit that determines a size of a filter that attenuates moire based on the measured statistic, and a moiré with a size determined for the pixel of interest. In the direction perpendicular to the traveling direction, a filter unit for performing a filter process and a display unit for displaying a medical image after the filter process are configured.

  In the present embodiment, the measurement unit measures, for each target pixel of the acquired medical image, a statistic of pixel values in a local region including the target pixel and in a direction parallel to the moire running direction.

  The CPU 11 of the medical image display apparatus 2 reads the program from the magnetic disk 13, loads it into the main memory 12, and executes it.

  Next, processing executed by the medical image display apparatus 2 will be described based on FIGS. FIG. 2 is a flowchart showing the flow of processing of the first embodiment. FIG. 3 is a schematic diagram for explaining the processing.

(Step S1)
In S <b> 1, the image acquisition unit acquires a medical image 31 including the moire 32 (hereinafter simply referred to as “image 31”) from the X-ray apparatus 1.

  In the image 31, the X axis (the horizontal direction of the image 31) and the Y axis (the vertical direction of the image 31) are set, and the moire 32 is superimposed on the subject image 33. The traveling direction (Y-axis direction) of the moiré 32 may be automatically detected by the medical image display device 2 or may be manually input to the medical image display device 2 by an operator.

  The measurement unit specifies the first pixel of interest in the image 31. For example, the measurement unit designates the origin. The origin is usually at the upper left of the image 31 and is represented by (X, Y) = (0, 0).

  Then, the measurement unit designates a region that is a local region including the target pixel and is parallel to the direction of the moire 32. The measurement unit designates, for example, region (X, Y) = (0, a value corresponding to half the length of the region for which the statistic is calculated). The width of this area is smaller than the width of the moire 32. In FIG. 3, the area of the arrow 34 is designated (S1).

(Step S2)
In S <b> 2, the measurement unit measures the statistic of the pixel value for each target pixel of the image 31 in a local region including the target pixel and parallel to the traveling direction of the moire 32. In FIG. 3, the measurement unit obtains a standard deviation (or variance) value (sd1) within a region (arrow 34) designated by S1 and parallel to the moire 32 (S2).

(Step S3)
In S3, the determination unit determines the size of the filter that attenuates the moire 32 based on the statistic measured in S2. Specifically, the determination unit performs processing for relatively reducing the size of the filter as the statistical amount is relatively large.

  The determination unit refers to a predetermined relationship table showing the relationship between the standard deviation (or variance) value (sd1) and the filter size, and determines the filter size corresponding to sd1 (S3).

  In the relationship table, the filter size (number of pixels) is described for each standard deviation (or variance) value (sd1). For example, 10 pixels (2 pixels in the X-axis direction, 5 pixels in the Y-axis direction, 2 pixels × 5 pixels = 10 pixels) are described.

  In general, when the standard deviation (or variance) value (sd1) is large, the filter size is decreased because there is a sudden change in density. Conversely, when the standard deviation (or variance) value (sd1) is small, the filter size is decreased. Enlarge.

  That is, the filter size is made smaller in the area where the subject is shown, and the filter size is made larger only at the moire 32.

(Step S4)
In S4, the filter unit performs a filtering process on the pixel of interest in a direction perpendicular to the moire 32 with the filter size determined in S3. For the filter processing, a pixel in a rectangular area having a length of arrow 35 is used.

  Then, the filter unit outputs a filter processing result for the pixel of interest. The processing result is recorded in an area different from the memory area (not shown) in which the original image 31 (the image 31 acquired in S1) is recorded in the medical image display apparatus 2 (S4).

  The known filters for reducing the moire 32 are typically low-pass filters, high-pass filters, median filters, band-pass filters, notch filters, etc., but other filters may be used.

(Step S5)
In S5, it is determined whether all pixels have been processed (S5). When all the pixels have been processed, the display unit displays the image 31 after the filter processing and ends. If all the pixels have not been processed, the process proceeds to S6.

(Step S6)
In S6, if there is an unprocessed pixel, the next pixel to be processed is sequentially designated, and the process returns to S2 (S6).

FIG. 4 is a schematic diagram for explaining processing in which the target pixel is sequentially designated and the statistic is measured. In FIG. 4, first, pixels indicated by X = 0... X _j ... X _k ..., Y = Y _i are sequentially designated, and statistics are calculated for each region 41. Next, pixels indicated by X = 0... X _j ... X _k ..., Y = Y _{i + 1} are sequentially specified, and statistics are calculated for each of the regions 42.

  FIG. 5 is a schematic diagram for explaining the filter size determined for each pixel of interest.

  In the area 51, only the moire 32 exists and the subject image 33 does not exist. For this reason, the standard deviation (or variance) value (sd1) of the area 34 (specified in S1) for calculating the statistic is small in the pixels in the area 51.

  Therefore, the filter size 52 is set larger than the regions 53, 54, and 55 in the pixels in the region 51.

  On the other hand, in the regions 53, 54, and 55, the moire 32 is superimposed on the subject image 33. For this reason, in the pixels of the regions 53, 54, and 55, the standard deviation (or variance) value (sd1) of the regions 35, 36, and 37 designated for calculating the statistic is large.

  Accordingly, the filter sizes 56, 57, and 58 are set smaller than the region 51 in the pixels in the regions 53, 54, and 55.

  According to the first embodiment, the size of the filter is determined based on a statistic such as a dispersion value or a standard deviation value in a direction parallel to the moire 32 in the real space without using the Fourier transform, and the filter is moved in the running direction of the moire 32. Therefore, the moire 32 can be attenuated while reducing the influence on other regions caused by correcting a part of the image 31.

<Second embodiment>
In the present embodiment, the measurement unit measures a statistic for a local region including the target pixel for each target pixel of the image 31 and in a direction perpendicular to the traveling direction of the moire 32.

  Hereinafter, based on FIG. 6, the process of this embodiment is demonstrated. FIG. 6 is a flowchart showing a flow of processing according to the second embodiment.

(Step S21)
In S21, the image acquisition unit acquires the image 31 as in S1. The measurement unit designates the first pixel of interest, and designates a region (including the pixel of interest) perpendicular to the traveling direction of the moire 32 (S21).

(Step S22)
In S22, the measurement unit obtains a standard deviation (or variance) value (sd2) of the pixel value in the region designated in S21 in order to consider patterns other than the moire 32 (S22).

(Step S23)
In S23, the determination unit refers to a relation table indicating the relationship between the standard deviation (or variance) value (sd2) and the filter size, and determines the filter size corresponding to sd2 (S23).

(Steps S24 to S26)
In S24 to S26, as in S4 to S6, the filter unit performs a filtering process on the target pixel in the direction perpendicular to the traveling direction of the moire 32 with the determined filter size (S24).

  Then, it is determined whether or not all the pixels have been processed (S25). If all the pixels have been processed, the process ends. If all the pixels have not been processed, the next pixel is designated ( S26), returning to S22. The display unit displays the image 31 after the filter processing.

  According to the second embodiment, since the filter processing is performed in the real space, the moire 32 can be attenuated while reducing the influence on other regions caused by correcting a part of the image 31. Further, the filter processing can be performed in consideration of the pattern of the image other than the moire 32.

<Third embodiment>
In the present embodiment, the measurement unit is a local region including the target pixel of the image 31 and designates a region parallel to the traveling direction of the detected moire 32 and a region perpendicular thereto.

  Based on FIG. 7, processing according to the present embodiment will be described. FIG. 7 is a flowchart for explaining the processing flow of the third embodiment.

(Step S31)
In S31, the image acquisition unit acquires the image 31 as in S1. The measurement unit designates the first pixel of interest (usually, the upper left origin of the image 31) (S31).

(Step S32)
As in S1, the measurement unit designates a region that is a local region including the target pixel designated in S31 and is parallel to the traveling direction of the moire 32. Then, similarly to S2, the measurement unit obtains the standard deviation (or variance) value (sd1) of the pixel value in the designated region (in the direction parallel to the moire 32) (S32).

(Step S33)
In S <b> 33, the measurement unit designates a region that is a local region including the target pixel designated in S <b> 31 and is perpendicular to the traveling direction of the moire 32, as in S <b> 22. Then, the measurement unit obtains the standard deviation (or variance) value (sd2) of the pixel value in the designated region (perpendicular to the moire 32) in order to consider patterns other than the moire 32, as in S22. (S33).

(Step S34)
In S34, the determination unit refers to the relationship table indicating the relationship between sd1, sd2, and the filter size, and determines the filter size corresponding to the combination of sd1 and sd2 (S34).

  FIG. 8 is a schematic diagram showing an example of a relationship table showing the relationship between sd1, sd2, and filter size.

  In the relationship table 81, the value of sd1 is assigned to the row and the value of sd2 is assigned to the column. In each cell, a filter size set for each combination of sd1 and sd2 is described. Moreover, the shape (for example, parallelogram) of the area | region used for a filter process may be described in each cell.

  For example, when both sd1 and sd2 are small values, it is considered that the variation in pixel values in the Y-axis direction and the X-axis direction of the image 31 is small, so the filter size is increased and the shape of the region used for the filter processing Set to square.

  When both sd1 and sd2 are large values, it is considered that both the pixel value variations in the Y-axis direction and the X-axis direction of the image 31 are large. Therefore, the filter size is reduced, and the shape of the region used for the filter processing is square. Set to.

  When sd1 is small and sd2 is large, the pixel value variation in the Y-axis direction of the image 31 is small, and the pixel value variation in the X-axis direction of the image 31 is considered large. Therefore, the shape of the region used for the filter processing is Set to a vertically long rectangle.

  When sd1 is large and sd2 is small, the pixel value variation in the Y-axis direction of the image 31 is large, and the pixel value variation in the X-axis direction of the image 31 is considered to be small. Therefore, the shape of the region used for the filter processing is , Set to a horizontally long rectangle.

(Steps S35 to S37)
In S35 to S37, as in S4 to S6, the filter unit performs the filtering process on the target pixel in the direction perpendicular to the traveling direction of the moire 32 with the determined filter size (S35).

  Then, it is determined whether or not all the pixels have been processed (S36). If all the pixels have been processed, the process ends. If all the pixels have not been processed, the next pixel is designated ( S37), the process returns to S32. The display unit displays the image 31 after the filter processing.

  According to the present embodiment, since the filter process is performed in the real space, the moiré 32 can be attenuated while reducing the influence on other regions caused by correcting a part of the image 31.

  In the above-described embodiment, when the filter size is determined for each pixel of interest, the filter process is performed immediately. However, the filter size is determined for all the pixels, and then the filter size is collectively applied to all the pixels. Processing may be performed.

  Moreover, in the said embodiment, although the medical image display apparatus 2 acquired the image 31 from the X-ray apparatus 1, it should just acquire the image 31 from what can collect the image 31, not only this. For example, the medical image display apparatus 2 may acquire the image 31 from a medical image management system (Pictures Archive and Communication System, PACS) that stores and manages medical images or other computers.

1 is a conceptual diagram showing a schematic configuration of an X-ray imaging apparatus according to the present embodiment. The flowchart which shows the flow of the process of 1st embodiment. Schematic diagram explaining the processing of the first embodiment Schematic diagram explaining the process in which the target pixel is sequentially specified and the statistic is measured Schematic diagram explaining the filter size determined for each pixel of interest The flowchart which shows the flow of a process of 2nd embodiment. The flowchart explaining the flow of processing of the third embodiment Schematic diagram showing an example of a relationship table showing the relationship between sd1, sd2, and filter size Schematic diagram explaining conventional X-ray imaging using a grid Schematic diagram explaining an image on which moire caused by the grid is superimposed

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray apparatus, 2 ... Medical image display apparatus, 3 ... Communication cable, 10 ... X-ray imaging apparatus, 11 ... CPU, 12 ... Main memory, 13 ... Magnetic disk, 14 ... Display memory, 15 ... CRT, 16 ... Mouse, 16a ... Controller, 17 ... Keyboard, 18 ... Bus

Claims (3)

Image acquisition means for acquiring medical images;
For each target pixel of the acquired medical image, a pixel value of a local region including the target pixel is obtained in at least one direction parallel to or perpendicular to one of the traveling directions of the matrix of the medical image. A measuring means for measuring statistics,
Determining means for determining the size of the filter for attenuating the striped noise component based on the measured statistics;
Filter means for performing a filtering process on the pixel of interest in a direction perpendicular to the traveling direction with the determined size;
Display means for displaying the medical image after the filter processing;
A medical image display device comprising: The image acquisition means includes
An X-ray source that emits X-rays;
An X-ray detector disposed opposite to the X-ray source across the subject, detecting X-rays and outputting X-ray projection data;
A grid disposed between the subject and the X-ray detector to remove scattered X-rays;
An X-ray imaging apparatus configured by image generation means for generating a medical image based on the X-ray projection data output after the scattered X-rays are removed,
The medical image display apparatus according to claim 1. The determining means relatively reduces the size of the filter as the statistic is relatively large.
The medical image display device according to claim 1, wherein the medical image display device is a medical image display device.

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