JP2011110247A - X-ray photographing apparatus and x-ray photographing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray photographing apparatus and an X-ray photographing method for eliminating luminance non-uniformity between respective images when a plurality of images are synthesized so as to obtain a long image. <P>SOLUTION: The X-ray photographing apparatus includes: a segmenting portion 81 for segmenting the overlapping parts of the first and second images from the respective first and second images as first and second synthesizing parts; a histogram generating portion 82 for generating first and second histograms, based on pixel values in the first and second synthesizing parts; a gradation conversion table generating portion 83 for generating first and second gradation conversion tables to perform histogram equalization with respect to the first and second histograms; a gradation converting portion 84 for performing the gradation conversion of the second image with the use of the second gradation conversion table and also performing reverse gradation conversion with respect to the second image after performing the gradation conversion with the use of the first gradation conversion table; and an image synthesizing portion 85 for synthesizing the first image with the second image where the gradation conversion and the reverse gradation conversion are performed by the gradation converting portion 84. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray imaging apparatus and an X-ray imaging method for creating an X-ray image corresponding to a long imaging region of a subject, and in particular, X-ray imaging that performs image synthesis processing, also called stitching processing. The present invention relates to an apparatus and an X-ray imaging method.

  2. Description of the Related Art Conventionally, an imaging method called slot radiography is known as a method for creating an X-ray image of a long imaging region in a subject such as an entire image of a lower limb or an entire image of a spine. In this slot radiography, X-rays are continuously irradiated a plurality of times to a strip-shaped region of the subject while moving the X-ray tube and the X-ray detector along the longitudinal direction of the subject, This is a method of creating a long X-ray image by acquiring a plurality of strip-shaped images along the long direction of a subject and combining these images.

  Similarly to slot radiography, the X-ray detector is moved along the longitudinal direction of the subject, and the X-ray tube is swung to irradiate the moving X-ray detector toward the moving X-ray detector. Thus, there is also known an X-ray imaging apparatus that acquires a plurality of rectangular images along the length direction of a subject and combines these images to create a long X-ray image.

  By the way, when performing such X-ray imaging, for example, when imaging the entire lower limb, the thigh, calf, and toes are sequentially imaged from the abdomen and pelvis. Since the body thicknesses are different, the optimum values of the X-ray conditions such as tube voltage and tube current differ depending on the imaging region. For this reason, there is a difference in brightness or the like for each of a plurality of images taken continuously, and when these images are combined with a long image, a diagnosis using this long image is caused by uneven brightness between the images. It will cause troubles.

  On the other hand, in Patent Document 1, after acquiring a plurality of rectangular images, an index value is calculated from pixel values of overlapping portions in the plurality of images, and display gradations corresponding to the overlapping portion index values are calculated. However, an X-ray diagnostic apparatus that converts pixel values of a plurality of images so as to substantially match is disclosed. For the conversion of pixel values, a calculation method using an average value in overlapping areas among the areas to be combined, or a profile in which profiles in the overlapping areas among the areas to be combined are continuously connected A method of performing correction so that

JP 2004-57506 A

  In the invention described in Patent Document 1, when shooting conditions for shooting a plurality of images are different, when a plurality of images are combined to form a long image, a plurality of images shot continuously are shot. The luminance difference increases for each image, and it is difficult to suitably eliminate luminance unevenness between the images.

  The present invention has been made to solve the above problems, and when shooting a plurality of images, even if the shooting conditions differ between the images, a plurality of images are combined to create a long image. An object of the present invention is to provide an X-ray imaging apparatus and an X-ray imaging method capable of suitably eliminating luminance unevenness between images.

  The invention described in claim 1 includes an X-ray detector that moves along the subject, and an X-ray tube that irradiates the X-ray toward the X-ray detection means, and the subject is continued a plurality of times. In the X-ray imaging apparatus that obtains a plurality of images whose end portions overlap each other by imaging and creates an X-ray image corresponding to the long imaging region of the subject by combining these images, A clipping unit that cuts out overlapping portions in a plurality of images from each image as a synthesis unit, a histogram creation unit that creates a histogram from the pixel values in each synthesis unit, and a histogram equalization for each histogram A tone conversion table creating unit that creates a tone conversion table capable of executing the image, and one of images overlapping each other is created from that image. The gradation conversion is executed using the gradation conversion table, and the gradation conversion table created from the other image is used to perform the reverse gradation conversion on the image after the gradation conversion is executed. It is characterized by comprising a tone conversion unit, the other image, and an image composition unit for synthesizing one image obtained by performing gradation conversion and inverse gradation conversion in the gradation conversion unit.

  The invention according to claim 2 uses an X-ray detector that moves along the subject and an X-ray tube that emits X-rays toward the X-ray detection means, and the subject is continuously applied a plurality of times. In the X-ray imaging method of acquiring a plurality of images whose end portions overlap each other by imaging, and creating an X-ray image corresponding to the long imaging region of the subject by combining these images , For each of the histograms, a clipping step for cutting out overlapping portions in the plurality of images from each image as a synthesis unit, a histogram creation step for creating a histogram from the pixel values in each synthesis unit, and A gradation conversion table creating step for creating a gradation conversion table capable of executing histogram equalization, and a pair of adjacent images among the plurality of images On the other hand, a gradation conversion process for performing gradation conversion using a gradation conversion table created from one image for one image, and creating the image after gradation conversion from the other image A reverse gradation conversion step of performing reverse gradation conversion using the converted gradation conversion table, and combining the other image with one image that has been subjected to the gradation conversion and reverse gradation conversion. An adjacent image composition step for creating a composite image is executed, and the gradation conversion step and the reverse gradation conversion step are performed on the composite image synthesized in the adjacent image composition step and an image adjacent to the composite image. And an image synthesizing step for applying an operation for executing the synthesizing step to the plurality of images.

  According to the first and second aspects of the present invention, when a plurality of images are combined into a long image even when shooting conditions between the images are different when shooting a plurality of images. It becomes possible to eliminate the luminance unevenness between the images accurately.

1 is a schematic diagram of an X-ray imaging apparatus according to the present invention. It is a schematic diagram of the X-ray imaging apparatus which concerns on other embodiment of this invention. It is a schematic diagram which shows a mode that the whole leg of the subject 1 is image | photographed with a X-ray imaging apparatus. It is a block diagram which shows the main electrical structures of the X-ray imaging apparatus which concerns on this invention. 2 is a block diagram showing an image processing unit 8 together with an image memory 9. FIG. It is a flowchart which shows the X-ray imaging method which concerns on this invention. It is explanatory drawing which shows the concept of the X-ray imaging method which concerns on this invention. It is explanatory drawing which shows the concept of histogram equalization. It is explanatory drawing which shows the concept of histogram equalization. It is explanatory drawing which shows the concept of the reverse gradation conversion after histogram equalization.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an X-ray imaging apparatus according to the present invention.

  This X-ray imaging apparatus includes a prone position table 5 on which a subject 1 as a subject is placed, an X-ray tube 2 that irradiates the subject 1 with X-rays, and an X-ray irradiated from the X-ray tube 2. A collimator 3 that limits the irradiation region of the line to a rectangular shape and a flat panel detector 4 that measures X-rays that have passed through the subject 1 are provided. The X-ray tube 2 and the collimator 3 and the flat panel detector 4 are configured to move horizontally along the longitudinal direction of the subject 1 in synchronization with each other by a moving mechanism (not shown).

  FIG. 2 is a schematic diagram of an X-ray imaging apparatus according to another embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the member same as embodiment shown in FIG.

  The X-ray imaging apparatus according to this embodiment includes a standing stand 6 for imaging a subject 1 as a subject in a standing posture, and an X-ray tube 2 that irradiates X-rays toward the subject 1. A collimator 3 that limits the X-ray irradiation area irradiated from the X-ray tube 2 to a rectangular shape and a flat panel detector 4 that measures the X-rays that have passed through the subject 1 are provided. The flat panel detector 4 is configured to move in the vertical direction along the longitudinal direction of the subject 1 by a moving mechanism (not shown). Further, the X-ray tube 2 and the collimator 3 are swung in a direction in which the X-ray irradiation direction always faces the direction of the flat panel detector 4 in synchronization with the movement of the flat panel detector 4 by a swing mechanism (not shown).

  FIG. 3 is a schematic diagram showing a state in which the entire lower limb of the subject 1 is imaged by the X-ray imaging apparatus shown in FIG. 1 or 2.

  As shown in this figure, in order to image the entire lower limb of the subject 1, an imaging region E by X-rays irradiated from the X-ray tube 2 and limited by the collimator 3 is displayed on the subject 1. X-ray imaging is executed continuously several times while moving in the longitudinal direction. At this time, each imaging region E is imaged with its end portions overlapping each other. Then, by synthesizing the imaging region E thus imaged, an X-ray image of the entire lower limb including the bone 11 of the subject 1 and the artificial joint 12 can be obtained.

  At this time, when photographing the entire lower limb, the abdomen and pelvis have relatively large body thicknesses, and the body thicknesses gradually decrease from the thigh and calf to the toes. For this reason, it is necessary to change the X-ray conditions such as changing the tube current corresponding to these imaging regions. In order to cope with a luminance difference corresponding to the change of the X-ray condition, gradation conversion described later is executed.

  FIG. 4 is a block diagram showing the main electrical configuration of the X-ray imaging apparatus according to the present invention.

  This X-ray imaging apparatus includes an image processing unit 8 described later, and includes a control unit 7 that controls the entire apparatus. The control unit 7 is connected to the X-ray tube 2 described above via the X-ray tube control unit 21. The control unit 7 is connected to the flat panel detector 4 described above. Further, the control unit 7 is also connected to an image memory 9 that stores an image photographed by the flat panel detector 4 and a display unit 10 such as a CRT that displays an image processed by the image processing unit 8.

  FIG. 5 is a block diagram showing the above-described image processing unit 8 together with the image memory 9.

  As will be described later, the image processing unit 8 includes a cutout unit 81 that cuts out adjacent overlapping portions as a combining unit in the image of the shooting region E, and a histogram that creates a histogram from the pixel values of the combining unit. A creating unit 82; a tone conversion table creating unit 83 that creates a tone conversion table for executing histogram equalization; a tone converting unit 84 that performs tone conversion and inverse tone conversion; and an adjacent image And an image synthesis unit 85 for synthesizing.

  Next, an X-ray imaging method according to the present invention will be described. FIG. 6 is a flowchart showing the X-ray imaging method according to the present invention. FIG. 7 is an explanatory diagram showing the concept of the X-ray imaging method according to the present invention. 8 and 9 are explanatory diagrams showing the concept of histogram equalization, and FIG. 10 is an explanatory diagram showing the concept of inverse gradation conversion after histogram equalization.

  When executing the X-ray imaging method according to the present invention, X-ray imaging is first performed (step S1). At this time, as shown in FIG. 3, the X-ray imaging region E irradiated from the X-ray tube 2 and whose irradiation region is limited by the collimator 3 is continuously moved a plurality of times while moving in the longitudinal direction of the subject 1. Then, X-ray imaging is executed. At this time, each imaging region E is imaged with its end portions overlapping each other.

  Next, a cut-out process is performed to cut out overlapping portions of the images in each shooting area E as a synthesis unit (step S2). At this time, two images are first selected from the plurality of images corresponding to each imaging region E. For example, as shown in FIG. 7, when the first image A and the image B adjacent thereto are selected, the cutout unit 81 shown in FIG. The overlapping part is cut out as a combining part a, and the overlapping part in the image B is cut out as a combining part b. The combining unit a and the combining unit b are used as margins when the image A and the image B are combined in an image combining step to be described later.

  Next, a histogram creation step for creating a histogram from the pixel values of the synthesis units a and b is executed (step S3). This histogram creation step is executed by the histogram creation unit 82 shown in FIG. 8A shows the histogram Ha (x) of the synthesis unit a created by the histogram creation unit 82, and FIG. 9A shows the histogram Hb (x) of the synthesis unit b created by the histogram creation unit 82. ). In this figure, the horizontal axis indicates the pixel value, and the vertical axis indicates the frequency.

  Next, a gradation conversion table creation step for creating a gradation conversion table capable of executing histogram equalization is executed for each of the histograms Ha (x) and Hb (x) (step S4). This gradation conversion table creation step is executed by the gradation conversion table creation unit 83 shown in FIG.

  This histogram equalization is a process called histogram equalization or gradation equalization. A histogram of pixel values is taken with respect to an image, and a region having a high frequency pixel value is enlarged, and a pixel having a low frequency is enlarged. The value area is image processing that performs gradation conversion to reduce the image so that the converted histogram becomes uniform.

  A gradation conversion table capable of executing this histogram equalization can be calculated by the following equation. Here, x0 is the pixel value of the image before conversion, x is the input value of the gradation conversion table (LUT), and pmax is the maximum pixel value.

  FIG. 8B shows a tone conversion table LUTa for the synthesis unit a obtained in the tone conversion table creation step, and FIG. 9B shows a tone conversion table for the synthesis unit b obtained in the tone conversion table creation step. LUTb is shown. In this figure, the horizontal axis indicates the pixel value before conversion, and the vertical axis indicates the pixel value after conversion.

  When the X-ray imaging conditions are different between the combining unit a and the combining unit b, the histogram Ha (x) illustrated in FIG. 8A and the histogram Hb (x) illustrated in FIG. 8B are different. However, since both are images obtained by X-ray imaging of the same part from the beginning, the histogram Ha (x) shown in FIG. 8A is used by using the gradation conversion table LUTa shown in FIG. 8B. After performing histogram equalization using the gradation conversion table LUTb shown in FIG. 9B for the histogram Hae (x) after execution of equalization and the histogram Hb (x) shown in FIG. The histogram Hbe (x) is exactly the same histogram (see FIG. 8C and FIG. 9C).

  Next, gradation conversion is performed on the entire area of the image B using the gradation conversion table LUTb (step S5), and the image after gradation conversion is inverted using the gradation conversion table LUTa. Tone conversion is executed (step S6). These gradation conversion process and inverse gradation conversion process are executed by the gradation conversion unit 84 shown in FIG.

  FIG. 10B shows the histogram Hbe (x) after the histogram equalization using the gradation conversion table LUTb for the histogram Hb (x) of the synthesis unit b shown in FIG. As shown, when inverse gradation conversion is performed using the gradation conversion table LUTa, a histogram H (x) shown in FIG. 10C is obtained. This histogram H (x) is exactly the same as the histogram Ha (x) of the synthesis unit a shown in FIG. Then, by executing the above-described gradation conversion process and inverse gradation conversion process on the entire image B, it is possible to obtain the same effect on the entire image B.

  Thereafter, an image synthesizing process for synthesizing the image B and the image A thus converted is executed (step S7). This image composition step is executed by the image composition unit 85 shown in FIG. As a result, as shown in FIG. 7, even when the shooting conditions of the image A and the image B are different, the image C synthesized with the image A and the image B with the luminance unevenness between the images eliminated. Created.

  When the above steps are completed, it is further determined whether there is an image to be synthesized (step S8). If there is no image to be synthesized, the process ends. On the other hand, if there is an image to be further synthesized, the processing is continued. In this case, the gradation conversion process, the reverse gradation conversion process, and the composition process similar to those described above are performed on the image C after the composition and the image adjacent to the image C and having an overlapping portion. To do. That is, a portion where the image C and the image adjacent to the image C overlap with each other is cut out as a combining unit, and paying attention to the combining unit, the same gradation conversion process, reverse gradation conversion process, and combining process as described above Execute. By repeating such an operation, an X-ray image corresponding to the long imaging region of the subject 1 is created.

DESCRIPTION OF SYMBOLS 1 Subject 2 X-ray tube 3 Collimator 4 Flat panel detector 5 Standing table 6 Standing stand 7 Control part 8 Image processing part 9 Image memory 10 Display part 81 Cutout part 82 Histogram preparation part 83 Gradation conversion table preparation part 84 Tone conversion unit 85 Image composition unit

Claims (2)

An X-ray detector that moves along the subject, and an X-ray tube that irradiates the X-ray toward the X-ray detection means. In an X-ray imaging apparatus that acquires a plurality of images that overlap each other and creates an X-ray image corresponding to a long imaging region of a subject by combining these images,
A cutout unit that cuts out overlapping portions in the plurality of images from each image as a combining unit;
A histogram creation unit that creates a histogram from the pixel values in each synthesis unit,
A gradation conversion table creating unit that creates a gradation conversion table capable of executing histogram equalization for each histogram,
Of the overlapping images, gradation conversion is performed on one image using a gradation conversion table created from the image, and the image after gradation conversion is performed from the other image. A gradation conversion unit that performs reverse gradation conversion using the created gradation conversion table;
An image composition unit that synthesizes the other image and one image obtained by performing gradation conversion and inverse gradation conversion in the gradation conversion unit;
An X-ray imaging apparatus comprising: Using an X-ray detector that moves along the subject and an X-ray tube that irradiates the X-rays toward the X-ray detection means, and imaging the subject multiple times in succession, an end thereof In the X-ray imaging method of acquiring a plurality of images overlapping each other and creating an X-ray image corresponding to the long imaging region of the subject by combining these images,
A cutout step of cutting out overlapping portions in the plurality of images from each image as a combining unit,
A histogram creation step for creating a histogram from the pixel values in the respective synthesis units,
A gradation conversion table creating step for creating a gradation conversion table capable of executing histogram equalization for each of the histograms;
A gradation conversion step of performing gradation conversion on a pair of adjacent images among the plurality of images using a gradation conversion table created from the image, and the gradation; A reverse gradation conversion step of performing reverse gradation conversion on the image after the conversion using a gradation conversion table created from the other image, the other image and the gradation conversion An adjacent image composition step is performed for synthesizing one of the images subjected to the tone conversion to create a composite image, and for the composite image synthesized in the adjacent image composition step and an image adjacent to the composite image An image synthesizing step for applying the operations for executing the tone conversion step, the reverse tone conversion step, and the synthesis step to the plurality of images;
An X-ray imaging method comprising:

Images