JP2002272724A - Filter for decreasing noise and x-ray diagnostic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter for decreasing noises and an X-ray diagnostic system by which the noises can be appropriately eliminated without imposing a burden on an operator and an image with no afterimage can be obtained even when an imaging object and an imaging system are moved and stopped. SOLUTION: The X-ray diagnostic system in which when at least one of a movable bed 12 for arranging a body to be inspected or a movable imaging system 11 for irradiating the body to be inspected with X-rays and obtaining a digital image data based on the X-rays passing through the body to be inspected is moved, the relative velocity V of the movable imaging system 11 to the movable bed 12 is calculated by a relative velocity calculating part 15 and weight factor of the traveling filter is controlled in accordance with the value of the relative velocity V, is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a noise reduction filter and an X-ray diagnostic system.

[0002]

2. Description of the Related Art A digital filter realizes a filter function by performing a predetermined process on a digital signal. This digital filter is also used, for example, in an image display device for displaying collected image data in real time. , As a noise reduction filter. Generally, a digital filter includes a recursive filter (hereinafter, referred to as a "recursive filter") and a nonrecursive filter.
r). The former recursive filter is a filter that removes noise so that information that is older in time is weighted less and is less affected by motion.
For example, it is frequently used in X-ray diagnostic systems for medical imaging equipment.

FIG. 3 is a diagram for explaining a recursive filter usually used in an X-ray diagnostic system. In FIG. 3, X represents a filter input pixel value, and Y represents a filter output pixel value. The subscript indicates the newness of the pixel value, and the value with i is the pixel value collected this time,
The value assigned i-1 represents the pixel value collected last time (that is, the currently displayed pixel value). As shown in FIG. 3, in the recursive filter, the expression (1) Y _i = aY
Images were averaged according to _{i-1 + (1-a} ) X i, is performed noise reduction. That is, in the equation (1), when an organ or the like moves, increasing the weight a can increase new image information and follow the movement.
When there is little movement, new image information can be reduced and noise can be further reduced by reducing the weight a. The photographer sets the recursive coefficient according to the shooting target by setting before shooting or manually switching during shooting,
Reduce noise.

[0004] As another means for removing noise,
A method that cancels noise components by adding and averaging multiple images without relying on recursive coefficients.Automatically detects moving and immovable parts in the image, and removes noise using a recursive filter only for those that do not move There is a known technique.

[0005] For example, in continuous imaging by digital fluorography using an X-ray diagnostic system, the recursive filter functions even when the moving imaging system or the moving bed is moving. In such cases,
As described above, temporally old image information may remain in the perspective image displayed as an afterimage, making the image difficult to see. On the other hand, when the recursive coefficient is changed to a low value in order to eliminate the afterimage, strong noise is generated in the perspective image, and the function as a noise removal filter is not performed.

Further, it is possible to manually switch ON / OFF of the recursive filter depending on whether the movable portion of the normal photographing system is operating or not operating, but a great burden is imposed on the operator. Will be applied.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is applicable to a case where a subject or a photographing system moves or stands still without burdening an operator. It is an object of the present invention to provide a noise reduction filter and an X-ray diagnostic system that can remove noise from an image and obtain an image without an afterimage.

[0008]

The present invention takes the following measures in order to achieve the above object.

According to a first aspect of the present invention, there is provided a movable bed on which a subject is placed, and a movable bed for irradiating the subject with X-rays and obtaining digital image data based on the X-rays transmitted through the subject. A photographing system, a filter means for performing noise removal processing on each of the digital image data, and when at least one of the movable photographing system or the movable bed is moved, the movable photographing system of the movable photographing system moves. Speed detecting means for detecting a first relative speed with respect to the bed or a second relative speed of the movable bed with respect to the movable imaging system; and a first or second relative speed detected by the speed detecting means. And a filter control means for controlling the filter means.

According to a third aspect of the present invention, there is provided a mobile couch on which a subject is placed, and imaging for irradiating the subject with X-rays and obtaining digital image data based on the X-rays transmitted through the subject. System, filter means for performing noise removal processing on each of the digital image data, detection means provided in the movable bed, and detects the movement of the movable bed,
An X-ray diagnostic system comprising: a filter control unit that controls the filter unit when the detection unit detects movement.

According to a fourth aspect of the present invention, there is provided a bed for arranging a subject, and mobile imaging for irradiating the subject with X-rays and obtaining digital image data based on the X-rays transmitted through the subject. System, filter means for performing a noise removal process on each of the digital image data, detection means provided in the mobile imaging system for detecting movement of the mobile imaging system, and detection means for detecting the movement In this case, the X-ray diagnostic system comprises a filter control means for controlling the filter means.

According to a sixth aspect of the present invention, there is provided a recursive noise reduction filter for performing noise removal processing on digital image data, wherein a movement detecting means for detecting a moving speed of the subject, and wherein the movement detecting means comprises A weight control means for controlling weighting of the latest information in time according to the moving speed of the noise reduction filter.

According to a seventh aspect of the present invention, there is provided a recursive noise reduction filter for performing a noise removal process on digital image data, wherein a movement detecting means for detecting a movement of a subject, and wherein the movement detecting means detects the movement of the subject. A noise reduction filter comprising: weighting control means for performing control to increase weighting of the latest information in time when movement is detected.

According to such a configuration, even when the subject or the photographing system moves or stands still, noise is appropriately removed without imposing a burden on the operator, and an image having no residual image is obtained. A noise reduction filter and an X-ray diagnostic system that can be obtained can be provided.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and repeated description will be made only when necessary. Note that the present invention is applicable to any medical image equipment (such as an ultrasonic diagnostic apparatus) having real-time properties. Hereinafter, an X-ray diagnostic system will be described as an example for simplicity.

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

In FIG. 1, an X-ray diagnostic system 10 comprises:
Mobile imaging system 11, mobile couch 12, imaging system / couch movement control unit 13, A / D converter 14, relative speed calculation unit 15, image processing unit 16, storage unit 18, external storage medium 19, window processing unit 20, It has a gradation processing unit 21, a display processing unit 22, a monitor 24, and an input device 30.

The mobile imaging system 11 includes an X-ray tube 110, a C-arm 111, and an X-ray detector 112. X-ray tube 110
Is a vacuum tube that generates X-rays, accelerates electrons by a high voltage generated by a high-voltage generator (not shown),
X-rays are generated by colliding with a target. The X-ray detection unit 112 generally has an I.D. I. (Image intensifier) and an optical system. The X-ray detection unit 112 outputs the I.D. I. X transmitted through the subject
The line information is converted into optical information, and the optical information is condensed by an optical lens by an optical system. Further, as the X-ray detection unit 112, an X-ray flat panel detector having a relatively small thickness and a flat detection surface can be used. The X-ray flat panel detector generates electron holes by applying X-rays transmitted through a subject to a photoelectric film, accumulates the holes in a semiconductor switch,
The X-ray signal is detected by reading the signal as an electric signal. In general, the X-ray flat panel detector performs A / D conversion.
There is no need to provide the A / D converter 14.

The C-arm 111 is a support arm that fixes and holds the X-ray tube 110 and the X-ray detector 112 so as to face each other. The C-arm 111 is movable by a slide mechanism including a rail, a holder, and a roller (each not shown), and can secure any angle with respect to the subject.

The moving bed 12 is an imaging table for appropriately positioning the subject with respect to the moving imaging system 11, and is movable. In other words, at the time of X-ray imaging, the mobile couch 12 or the mobile imaging system 11 is moved to position the mobile imaging system 11 and the subject.

The photographing system / bed moving control unit 13 includes the photographing system 1
1 or the movement of the bed 12 is controlled. When the imaging system 11 or the couch 12 is moved, the imaging system / couch movement control unit 13 outputs the respective moving speed information to the relative speed calculation unit 15. Here, the moving speed information is information including at least the moving direction and the moving speed of the imaging system 11 or the bed 12.

The A / D converter 14 converts an analog signal from the X-ray detector 112 into a digital signal.

The relative speed calculating unit 15 calculates relative speed information of the photographing system 11 with respect to the bed 12 based on the moving speed information of the photographing system 11 or the bed 12 input from the photographing system / bed moving control unit 13, Output to the processing unit 16.

The image processing section 16 applies a recursive filter to the input digital image data to perform a noise removal process. At this time, the recursive coefficient of the recursive filter is automatically controlled according to the relative speed information input from the relative speed calculator 15 based on a recursive coefficient control pattern stored in a storage unit (not shown) in advance. . As described above, the function of automatically controlling the recursive coefficient according to the speed information of the subject (in this case, the relative speed information of the imaging system 11 and the bed 12) to reduce noise or reduce the afterimage is referred to as “auto switch recursive”. This is referred to as “filter function”. The details will be described later. In addition,
The recursive filter according to the present embodiment has a configuration similar to the equation (1) shown in FIG. In the present embodiment, the recursive coefficient indicates a in equation (1) of FIG.

The image processing section 16 performs various image processing such as edge enhancement processing on the collected image data. Further, the image processing unit 16 calculates the brightness of the collected X-ray image data, determines an X-ray condition based on the calculated brightness, and feeds back the X-ray condition to a high-voltage generating unit (not shown). Execute control.

The storage unit 18 is a storage unit that receives digital fluoroscopic image data from the A / D converter 14 and stores it for each frame. The external storage medium 19 is a removable recording medium (for example, DVD, M
O etc.).

The window processing unit 20 performs a conversion process for converting the pixel values to a density (gray level) for displaying as a grayscale image. The gradation processing unit 21 converts the image data input from the image processing unit 16 based on the conversion rule determined by the window processing unit 20. In addition, depending on the image,
Further, a non-linear conversion (a conversion using a so-called γ curve) may be performed.

The display processor 22 converts the input signal sequence of the X-ray fluoroscopic image data into a format corresponding to the output destination. The monitor 24 displays the image data output by the display processor 22. The input device 30 is input means including a keyboard, various switches, a mouse, and the like.

Next, the auto switch recursive filter function of the X-ray diagnostic system will be described. The function is to reduce newly acquired image information when the imaging system 11 or the bed 12 is stopped or when the relative speed between the imaging system 11 and the bed 12 is equal to or less than a predetermined threshold. The noise is reduced by changing the recursive coefficient. On the other hand, when the imaging system 11 or the bed 12 is moving at a relative speed equal to or higher than a predetermined threshold value, newly acquired image information is increased and an old image is acquired. This is a function for automatically executing control to reduce afterimages due to information. This function is particularly useful for continuous fluoroscopy in digital fluorography, for example.

FIG. 2A shows the relative speed V in the X-ray diagnosis.
3 shows an example of a temporal change of the time. 2 (b) to 2
(D) is a diagram for explaining a recursive coefficient a numerical control pattern corresponding to each relative speed V.

Hereinafter, automatic control of the recursive coefficient a will be described with reference to FIGS. 2 (b) to 2 (d). In this embodiment, the relative speed V is defined as the relative speed of the imaging system 11 with respect to the bed 12;
2 may be defined as a relative speed with respect to the imaging system 11.

(Embodiment 1) FIG. 2B shows that the relative speed V
Threshold V₀, The recursive coefficient is set to a ₀From
A at a stretch₁FIG. 8 is a diagram for explaining a control example of increasing
You.

In FIG. 2A, for example, after performing a diagnostic operation without moving the imaging system or the bed for a predetermined period of time, the imaging system / bed movement control unit 13 At time t0, the movement of the imaging system or the bed is started. When the movement of the imaging system or the couch is started in this way, the imaging system / couch movement control unit 13 sends the moving speed of the moving imaging system 11 and the moving couch 12 to the relative speed calculation unit 15 at any time until the movement is completed. Output information. The relative speed calculation unit 15 calculates the relative speed V based on the movement speed information input from the imaging system / bed movement control unit 13 as needed, and outputs the result to the image processing unit 16.

The image processing unit 16 evaluates the relative velocity V that is input based on the threshold V ₀ which speed which is set in advance. That is, if the velocity V input is not reached V _0, the initial value without changing the recursive coefficients (Fig. 2
In (b), a ₀ ) is held. On the other hand, the input speed V
Has reached V ₀ , the image processing unit 16 performs control to increase the recursive coefficient to a value a ₁ higher than a ₀ .
Thereafter, if the movement of the imaging system and the bed at time t2 is stopped, that is, when the relative speed V becomes 0, the image processing unit 16 resets the recursive coefficient to the initial value a _0. In shooting further continued, the relative velocity V is when the threshold is reached V _0, the same control is executed.

[0035] The threshold value V _0, taking into account the influence of the afterimage current image by noise reduction and recursive filtering by recursive filter can obtain the optimal image value is set in advance. Further, the threshold value of the relative speed V can be arbitrarily changed.

According to such a configuration, when the subject is not moving with respect to the imaging system or when moving at a low speed, new image information is reduced by a low recursive coefficient to reduce noise. can do. on the other hand,
When the subject is moving at a predetermined speed or higher with respect to the imaging system, new image information can be increased by a high recursive coefficient and can follow the movement. Therefore, appropriate filter settings can be automatically performed according to the imaging system or the moving state of the subject. As a result, when the subject is not moving with respect to the imaging system, for example, an X-ray image with little afterimage and noise is obtained, and when the subject is moving at a predetermined speed or more with respect to the imaging system, Thus, an image with little afterimage can be automatically obtained, and the burden on the operator can be reduced.

[0037] (Embodiment 2) FIG. 2 (c), at the same time the relative speed starts to increase, for explaining a control example for increasing gradually a ₁ combined recursive coefficients in the relative velocity increases from a ₀ FIG.

In FIG. 2A, for example, after performing a diagnostic operation without moving the imaging system or the bed for a predetermined time, based on a predetermined input from the operator, the imaging system / bed movement control unit 13 At time t0, the movement of the imaging system or the bed is started. When the movement of the imaging system or the couch is started in this way, the imaging system / couch movement control unit 13 sends the moving speed of the moving imaging system 11 and the moving couch 12 to the relative speed calculation unit 15 as needed until the movement is completed. Output information. The relative speed calculation unit 15 calculates the relative speed V based on the movement speed information input from the imaging system / bed movement control unit 13 as needed, and outputs the result to the image processing unit 16.

The image processing unit 16, if it is positive relative velocity V input increases the recursive coefficient from the initial value a ₀ at a predetermined ratio. The rate of increase is determined based on a table in which the rate of increase of the recursive coefficient and the rate of increase of the relative speed V are stored in advance in a storage unit (not shown).

It is to be noted that the present invention is not limited to the example of the movement control in which the relative speed is monotonously increased as shown in FIG. The same control can be realized by storing a table in which the rate of decrease of the recursive coefficient and the rate of decrease of the recursive coefficient are stored. In addition, when performing a movement control in which the relative speed is randomly increased / decreased by combining a plurality of linear functions, a table is provided for each of the relative speed increase / decrease ratios, and the above-described controls are performed. Good.

[0041] Thereafter, if the movement of the imaging system and the bed at time t2 is stopped or the like, that is, when the relative speed V becomes 0, the image processing unit 16 resets the recursive coefficient to the initial value a ₀ . In the continued shooting,
When the relative speed V increases, the same control is performed.

With such a configuration, the same effect as in the first embodiment can be obtained. Further, in the present embodiment, the recursive coefficient is controlled as a linear function (specifically, the ratio of new image information is increased in response to the movement of the imaging system or the couch becoming faster). It is possible to perform the afterimage removal with a more appropriate balance.

(Embodiment 3) FIG. 2D is a diagram for explaining a control example in which the recursive coefficient is always set to 0 while the relative speed V is a positive value.

The operations of the imaging system / bed movement control unit 13 and the relative speed calculation unit 15 are the same as in the above embodiments.

The image processing section 16 keeps the input relative speed V being a positive value (that is, except that the imaging system and the bed are moving at the same speed in the same direction or both are stationary).
Increases the recursive coefficient from the initial value a ₀ (a ₀ = 0 in FIG. 2D) to a ₁ .

Thereafter, when the movement of the imaging system and the bed is stopped at time t2, that is, when the relative speed V becomes 0, the image processing section 16 sets the recursive coefficient to the initial value a0 again. In a case where the relative speed V becomes a positive value in the continuous shooting, the same control is performed.

With such a configuration, the same effect as in the first embodiment can be obtained.

While the present invention has been described based on the embodiments, various changes and modifications may be made by those skilled in the art within the scope of the present invention. It is understood that examples also fall within the scope of the present invention. For example, as shown in the following (1) to (3), various modifications can be made without changing the gist.

(1) In the above embodiment, the recursive coefficient is controlled based on the relative speed. On the other hand, the recursive coefficient may be controlled depending on whether the imaging system or the bed is in a moving state.
This configuration includes a means for generating a signal indicating that the imaging system or the couch is in a moving state when the imaging system or the couch is moving, and controlling the recursive coefficient when the image processing unit detects the signal. This can be realized. Alternatively, the configuration may be such that the threshold value V ₀ = 0.

(2) The technical concept of the present invention can be applied to medical imaging equipment having real-time properties. For example, in the case of an ultrasonic diagnostic apparatus, a configuration may be considered in which a means for generating a signal when the probe moves is provided in the probe, and a recursive coefficient is controlled when the image processing unit detects the signal.

(3) The control form of the recursive coefficient described in each of the above embodiments may be such that the operator can arbitrarily select a desired form at the time of diagnosis.

Further, the embodiments may be combined as appropriate as much as possible, in which case the combined effects can be obtained. Furthermore, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some components are deleted from all the components shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effects described in the column of the effect of the invention can be solved. When at least one of the above is obtained, a configuration from which this configuration requirement is deleted can be extracted as an invention.

[0053]

As described above, according to the present invention, even when a subject or a photographing system moves or stands still, noise is appropriately removed without imposing a burden on an operator, and an image without an afterimage remains. , A noise reduction filter and an X-ray diagnostic system that can obtain the above.

[Brief description of the drawings]

FIG. 1 is an X-ray diagnostic system 1 according to the present embodiment.
FIG. 3 is a diagram showing a schematic configuration of a zero.

FIG. 2A shows an example of a temporal change of a relative speed V in X-ray diagnosis. 2 (b) to 2
(D) is a diagram for explaining a recursive coefficient a numerical control pattern corresponding to each relative speed V.

FIG. 3 is a diagram for explaining a recursive filter normally used in an X-ray diagnostic system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... X-ray diagnostic system 11 ... Moving imaging system 12 ... Moving bed 13 ... Imaging system / bed movement control unit 14 ... A / D converter 15 ... Relative speed calculation unit 16 ... Image processing unit 18 ... Storage unit 19 ... External storage Medium 20 Window processing unit 21 Tone processing unit 22 Display processing unit 24 Monitor 30 Input device 110 X-ray tube 110 X-ray tube 111 C-arm 112 X-ray detection unit

Claims (7)

[Claims] A mobile couch for arranging a subject; a mobile imaging system for irradiating the subject with X-rays and obtaining digital image data based on the X-rays transmitted through the subject; Filter means for performing noise removal processing on each digital image data; and when at least one of the movable imaging system or the movable couch moves, a first relative position of the movable imaging system with respect to the movable couch. Speed detecting means for detecting a speed or a second relative speed of the movable bed with respect to the movable photographing system; and controlling the filter means based on the first or second relative speed detected by the speed detecting means. An X-ray diagnostic system, comprising: 2. A filter according to claim 1, wherein said filter means is a recursive filter, and said filter control means increases a weight for temporally latest information when said relative speed exceeds a predetermined threshold value. The X-ray diagnostic system according to claim 1. 3. A movable bed for placing a subject, an imaging system for irradiating the subject with X-rays and obtaining digital image data based on the X-rays transmitted through the subject, and each of the digital cameras Filter means for performing noise removal processing on the image data; detection means provided on the movable bed, for detecting movement of the movable bed; and filter means for detecting movement of the bed. An X-ray diagnostic system, comprising: a filter control unit configured to control the X-ray diagnostic system. 4. A bed for placing a subject, a mobile imaging system for irradiating the subject with X-rays, and obtaining digital image data based on the X-rays transmitted through the subject; Filter means for performing noise removal processing on the image data; detecting means provided in the mobile imaging system for detecting movement of the mobile imaging system; and An X-ray diagnostic system, comprising: filter control means for controlling a filter means. 5. The filter unit is a recursive filter, and the filter control unit increases the weight for temporally latest information when the movement determining unit determines that the imaging system is moving. The X-ray diagnostic system according to claim 3, wherein: 6. A recursive noise reduction filter for performing noise removal processing on digital image data, wherein the movement detection means detects a movement speed of a subject, and wherein the movement detection means detects the movement speed of the subject in accordance with the movement speed of the subject. And a weight control means for controlling weighting of the latest information in terms of time. 7. A recursive noise reduction filter for performing noise removal processing on digital image data, comprising: movement detection means for detecting movement of a subject; Is
A weight control unit for performing control to increase weighting of the latest information in time, and a noise reduction filter.