JP2005006918A - Radiation imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation imaging apparatus with which an image where influence of X-ray absorption by a specific substance like a bone is suppressed at high speed without degrading an SN ratio. <P>SOLUTION: This apparatus comprises an image processing part 5 which obtains two kinds of X-ray images of different energy characters from a same subject and images the X-ray absorption by the specific substance in the subject by using the difference of the two kinds of X-ray images. The image processing part 5 is provided with a gradation conversion processing part 521 for controlling the parameter of image processing with respect to the two kinds of X-ray images of different energy characters or a synthetic image obtained by synthesizing them by using an X-ray absorption image made by the specific substance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a radiographic imaging apparatus, and more particularly to a technique that can contribute to improving the image quality of two types of X-ray images obtained from the same subject and having different energy characteristics, and their combined images.
[0002]
[Prior art]
Conventionally, an imaging method called the energy subtraction method that images the same subject with two line qualities, images the difference in absorption coefficient due to the line qualities by weighting the captured images and taking the difference. There is. This imaging method is used for diagnosing the presence of a nodule in the lung field by removing a bone image that is a shadow of an obstacle from a chest image (see [Non-Patent Document 1]).
[0003]
There is also an energy subtraction method that uses two imaging plates and sandwiches a quality filter between them to obtain two types of images with different energy characteristics in one image (see [Non-Patent Document 2]).
[0004]
[Non-Patent Document 1]
“X-ray imaging”, Iinuma et al., Corona (Tokyo), 2001, p. 36,160)
[Non-Patent Document 2]
“Medical Imaging / Radiological Equipment Handbook” (2001), Japan Imaging Medical System Association, p. 80-81
[0005]
[Problems to be solved by the invention]
However, since the energy subtraction method of the above prior art images the difference between the two images, the SN ratio is basically lower than that of the original image. In order to prevent degradation of image quality due to a decrease in the S / N ratio, it may be necessary to increase radiation exposure such as X-rays harmful to the human body, and it is difficult to meet the demand for examination of less radiation exposure to the subject. .
[0006]
In addition, although there is an iterative process that uses the soft part extracted image and the bone part extracted image alternately, the process includes a process for determining whether each pixel belongs to the edge part, which is called edge preservation smoothing, and requires a lot of processing time. . For this reason, it has been difficult to meet the need to quickly perform the energy subtraction method.
[0007]
An object of the present invention is to provide a radiographic imaging apparatus capable of obtaining an image in which the influence of X-ray absorption by a specific substance such as bone is suppressed at high speed without reducing the SN ratio.
[0008]
[Means for Solving the Problems]
The object is to use X-ray image acquisition means for obtaining two types of X-ray images having different energy characteristics from the same subject and X-ray absorption by a specific substance in the subject by using the difference between the two types of X-ray images. In the radiographic imaging apparatus provided with the image processing means for imaging the image, the image processing means uses the X-ray absorption image of the specific substance to synthesize two types of X-ray images having different energy characteristics or a combination thereof. This is achieved by a radiographic imaging apparatus comprising means for controlling image processing parameters for the synthesized image.
[0009]
Further, the control means controls an image processing parameter for two types of X-ray images having different energy characteristics or a composite image thereof using an image obtained by smoothing an X-ray absorption image of the specific substance. Also good.
[0010]
In addition, the control means may control parameters of the synthesis process of two types of X-ray images having different energy characteristics, using an X-ray absorption image of the specific substance.
[0011]
In addition, the control means may control the parameters of gradation conversion processing for two types of X-ray images having different energy characteristics or a composite image thereof using an X-ray absorption image of the specific substance.
[0012]
Further, the control means may control parameters of spatial filter processing for two types of X-ray images having different energy characteristics or a composite image thereof using an X-ray absorption image of the specific substance.
[0013]
Specifically, instead of using the extracted soft part or bone part image with a reduced SN ratio as it is, image processing on the original image or its composite image is performed according to the degree to which each part of the image is included in the soft part or bone part. The image processing parameters are controlled using the extracted image so as to optimize.
[0014]
In order to prevent local changes in image processing parameters from becoming a new noise source, it may be possible to apply a smoothing process to the extracted image used for image processing parameter control. It does not extend to processed images.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A radiographic imaging device of the present invention will be described with reference to the drawings.
1 is a block diagram of the overall configuration of the radiographic image capturing apparatus of the present invention, FIG. 2 is a block diagram of the image processing unit 5 in FIG. 1, and FIGS. 3 to 6 are the contents of a weighting coefficient LUT storage unit 519 in the image processing unit 5 It is a graph which shows.
[0016]
As shown in FIG. 1, the radiographic image capturing apparatus is disposed so as to face each other with an X-ray tube 1, an X-ray high voltage generator 2 electrically connected to the X-ray tube 1, and the X-ray tube 1 sandwiching a subject. X-ray flat panel detector 3, imaging controller 4 electrically connected to X-ray high voltage generator 2, image processor 5 electrically connected to X-ray flat panel detector 3, and image The image observation apparatus 6 is electrically connected to the processing unit 5, and the photographing switch 7 is electrically connected to the photographing controller 4.
[0017]
The X-ray tube 1 irradiates the subject with X-rays. The X-ray high voltage generator 1 supplies power for generating X-rays in the X-ray tube 1. The X-ray plane detector 3 detects X-rays that have passed through the subject, converts them into X-ray images, and outputs them. The imaging controller 4 receives a signal from the imaging switch 7 and supplies a control signal to the X-ray high voltage generator 2. The image processing unit 5 processes the X-ray image output from the X-ray flat panel detector 3 so as to be used for diagnosis and outputs it. The image observation device 6 displays the image-processed X-ray image from the image processing unit 5. The imaging switch 7 is used to input an operation so that the operator can generate X-rays from the X-ray tube 1 at a desired timing.
[0018]
Next, as shown in FIG. 2, the image processing unit 5 is electrically connected to a logarithmic conversion lookup table (LUT) 510 electrically connected to the X-ray flat panel detector 3 and a logarithmic conversion LUT 510. The switch 511, the low energy image storage unit 513 and the high energy image storage unit 512 electrically connected to the switch 511, and the low energy image storage unit 513 and the high energy image storage unit 512 are electrically connected. A weighted difference processing unit 514, a bone extracted image storage unit 515 electrically connected to the weighted difference processing unit 514, a smoothing processing unit 516 electrically connected to the bone extracted image storage unit 515, and a smoothing The smoothed bone portion extracted image storage unit 517 electrically connected to the smoothing processing unit 516 and the weight coefficient LUT storage unit 5 electrically connected to the smoothed bone portion extracted image storage unit 517 9, an addition average processing unit 518 electrically connected to the weighting factor LUT storage unit 519, a composite image storage unit 520 electrically connected to the addition average processing unit 518, a weighting factor LUT storage unit 519, A gradation conversion processing unit 521 that is electrically connected to the image storage unit 520, the bone gradation characteristic storage unit 522, and the soft gradation characteristic storage unit 523, and a floor that is electrically connected to the gradation conversion processing unit 521. A tone conversion composite image storage unit 524 and a high-frequency emphasis spatial filter processing unit 525 electrically connected to the tone conversion composite image storage unit 524 are included.
[0019]
The logarithmic conversion LUT 510 performs logarithmic conversion on the image signal 31 and outputs it. A switcher 511 switches between a high energy image and a low energy image. The high energy image storage unit 512 stores a high energy image. The low energy image storage unit 513 stores a low energy image. The weighting difference processing unit 514 performs a weighting difference between the high energy image stored in the high energy image storage unit 512 and the low energy image stored in the low energy image storage unit 513 to obtain a bone part extracted image. The bone part extracted image storage unit 515 stores the bone part extracted image. The smoothing processing unit 516 performs a smoothing process on the bone part extracted image. The smoothed bone part extracted image storage unit 517 stores the smoothed bone part extracted image. The weighting coefficient LUT storage unit 519 supplies various weighting coefficients to the addition average processing unit 518, the gradation conversion processing unit 521, and the high frequency emphasis spatial filter 525. The addition average processing unit 518 includes a high energy image stored in the high energy image storage unit 512 based on the low energy image weight WL 5190 and the high energy image weight WH 5191 supplied by the weight coefficient LUT storage unit 519, and the low energy image storage unit 513. Are weighted and averaged with the low energy images stored in the image to obtain a composite image. The composite image storage unit 520 stores the composite image obtained by the addition average processing unit 518. The gradation conversion processing unit 521 includes a gradation LUT selection weight WG5192 from the weighting coefficient LUT storage unit 519, a bone portion gradation characteristic from the bone portion gradation characteristic storage unit 522, and a soft portion gradation characteristic from the soft portion gradation characteristic storage unit 523. Tone characteristics are supplied, and the composite image read from the composite image storage unit 520 is subjected to gradation conversion processing. The tone conversion composite image storage unit 524 stores the composite image processed by the tone conversion processing unit 521. The high frequency emphasis spatial filter processing unit 525 performs high frequency emphasis spatial filter processing on the output image read from the gradation conversion synthesized image storage unit 524 based on the high frequency emphasis coefficient KF5193 supplied from the weighting factor LUT storage unit 519. The processed image signal 50 is output to the image observation device 6.
[0020]
Next, the operation of the radiographic image capturing apparatus will be described.
When the operator presses the shooting switch 7, a shooting trigger signal 70 is input to the shooting controller 4. After the imaging trigger signal 70 rises, the imaging controller 4 outputs an irradiation start signal 40 to the X-ray high voltage generator 2, and the X-ray high voltage generator 2 receives the high signal that is normally in a “high” state. / A high voltage tube voltage is applied to the X-ray tube 1 in accordance with the low energy switching signal 41 to perform the first X-ray irradiation. When the first irradiation is completed, the X-ray flat panel detector 3 stores the original image signal 30 as a high energy image in the high energy image storage unit 512 via the switch 511 according to the high / low energy switching signal 41.
[0021]
When the first output of the original image signal 31 is finished, the imaging controller 4 switches the high / low energy switching signal 41 to the “low” state, and then outputs the second irradiation start signal 40, and the X-ray high voltage generator In response to this, 2 applies a low voltage tube voltage to the X-ray tube 1 in accordance with the high / low energy switching signal 41 to perform the second X-ray irradiation. When the second irradiation is finished, the X-ray flat panel detector 3 outputs the original image signal 30 to the image processing device 5, and the image processing device 5 performs switching according to the high / low energy switching signal 41 after logarithmic conversion by the logarithmic conversion LUT 510. The low energy image is stored in the low energy image storage unit 513 via the device 511. The photographing controller 4 switches the high / low energy switching signal 41 to the “high” state when the output of the second original image signal 30 is completed.
[0022]
The image processing device 5 performs a weighted difference between the high energy image stored in the high energy image storage unit 512 and the low energy image stored in the low energy image storage unit 513 by the weighted difference processing unit 514, thereby extracting the bone part extracted image. And stored in the bone extracted image storage unit 515. The smoothing processing unit 516 performs smoothing processing on the image to obtain a smoothed bone extracted image 517, which is input to the weighting coefficient LUT storage unit 519, thereby controlling image processing parameters.
[0023]
That is, when a high-energy image and a low-energy image are added and averaged by the weighted average processing unit 518 to obtain a composite image 520, the smoothed bone portion extracted image is simultaneously read from the smoothed bone portion extracted image storage unit 517, and the weight coefficient Referring to the LUT storage unit 519, a low energy image weight WL5190 and a high energy image weight WH5191 are obtained for each pixel, and using these, the addition average WL · (low energy image) + WH · (high energy image)
I do. Here, as shown in FIG. 3, the weights WL and WH are set so that the contribution of the high-energy image with less obstacle shadows due to the bone becomes large in the portion where the X-ray absorption of the bone portion is large.
[0024]
In addition, when the composite image stored in the composite image storage unit 520 is subjected to gradation conversion processing by the gradation conversion processing unit 521 and a gradation conversion composite image is obtained, the smoothed bone extracted image 517 is also read at the same time, and the weight coefficient With reference to the LUT storage unit 519, the gradation LUT selection weight WG5192 is obtained for each pixel, and using this, the tone characteristics for the bone part and the soft part floor stored in the tone characteristic storage unit 522 for the bone part are used. The soft part gradation characteristics stored in the tone characteristic storage unit 523 are combined with the combined WG · (bone part gradation characteristic) + (1−WG) · (soft part gradation characteristic).
Conversion is performed with the specified characteristics.
[0025]
Here, the weight WG is set so as to rise in a region corresponding to the rib in the lung field in accordance with the X-ray absorption of the bone as shown in FIG. Since the tonal characteristics are set to give almost the same output value as shown in FIG. 5 in the rib area and lung field, respectively, the change of the output value is suppressed by the transition from the lung field to the rib area, Reduced shadows due to bone.
[0026]
Further, when the tone conversion synthesized image stored in the tone conversion synthesized image storage unit 524 is subjected to the high frequency enhancement spatial filter processing by the high frequency enhancement spatial filter processing unit 525 to obtain the processed image signal 50, the smoothed bone The smoothed bone extracted image is also read from the partial extracted image storage unit 517 at the same time, and the high-frequency enhancement coefficient KF5192 is obtained for each pixel by referring to the weighting coefficient LUT storage unit 519, and the degree of enhancement is controlled using this. . Here, as shown in FIG. 6, the coefficient KF increases the degree of emphasis at a place where the X-ray absorption of the bone part is small and the SN ratio is high.
[0027]
According to the present embodiment, since the lung field area of the soft part tone characteristic and the rib area of the bone part tone characteristic are set to output substantially the same output value, the transition from the lung field area to the rib area is performed. Thus, the change of the output value can be suppressed, and the shading caused by the bone can be reduced.
[0028]
【The invention's effect】
The present invention has an effect of providing a radiographic imaging apparatus capable of obtaining an image in which the influence of X-ray absorption by a specific substance such as bone is suppressed at high speed without reducing the SN ratio.
[Brief description of the drawings]
FIG. 1 is a block diagram of the overall configuration of a radiographic image capturing apparatus according to the present invention.
FIG. 2 is a block diagram of the image processing unit 5 in FIG.
FIG. 3 is a graph showing the contents of various coefficients LUT 516 in the image processing unit 5;
FIG. 4 is a graph showing contents different from FIG. 3;
FIG. 5 is a graph showing contents different from those shown in FIGS. 3 to 4;
6 is a graph showing contents different from those in FIGS. 3 to 5. FIG.
[Explanation of symbols]
5 Image processing unit,
521 gradation conversion processing unit

Claims (5)

X-ray absorption by a specific substance in a subject is imaged using an X-ray image acquisition unit that obtains two types of X-ray images having different energy characteristics from the same subject and the difference between the two types of X-ray images. In the radiographic imaging apparatus provided with the image processing means, the image processing means uses the X-ray absorption image of the specific substance to the two types of X-ray images having different energy characteristics or a synthesized image obtained by synthesizing them. A radiographic imaging apparatus comprising means for controlling image processing parameters. The control means controls an image processing parameter for two types of X-ray images having different energy characteristics or a composite image thereof using an image obtained by smoothing an X-ray absorption image of the specific substance. The radiographic image capturing apparatus according to claim 1. 2. The radiographic image according to claim 1, wherein the control unit controls an X-ray absorption image of the specific substance to control a parameter for synthesizing two types of X-ray images having different energy characteristics. Imaging device. The control means controls a parameter of gradation conversion processing for two types of X-ray images having different energy characteristics or a composite image thereof using an X-ray absorption image of the specific substance. Item 2. The radiographic imaging device according to Item 1. The said control means controls the parameter of the spatial filter process with respect to two types of X-ray images from which the said energy characteristic differs, or those composite images using the X-ray absorption image by the said specific substance. The radiographic imaging apparatus according to 1.

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