JP2002354341A - Digital subtraction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital subtraction device, by which a subtracted image of an imaging part of a subject can be obtained appropriately and speedily. SOLUTION: The digital subtraction device is provided with a supply control circuit 33 for performing subtraction of the image with high-frequency components eliminated (mask image) and a basic image (live image) which is an X-ray transmission image which has been shot separate from the X-ray transmission image for generating the mask image. Accordingly, a basic image (live image) which does not include the delay corresponding to the time necessary for frequency characteristic conversion can be an object of subtraction. Since the high-frequency components of primary concern is included in the basic image (live image) which is shot separately, even though the time following the properties of the low-frequency components to be eliminated become worse, a subtracted image and the like can be displayed with a minimum delay and a subtracted image which can follow the movement of the subject can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital subtraction apparatus used in the medical field, the industrial field, and the like, which obtains a subtraction image of an imaged part by performing X-ray fluoroscopic imaging of an imaged part of a subject. The present invention relates to a technique for suitably obtaining a subtraction image of an imaging part of a sample at high speed.

[0002]

2. Description of the Related Art As a conventional digital subtraction apparatus, for example, there is a digital angiography apparatus used in the medical field for obtaining a subtraction image of a predetermined imaging region of a subject. As this digital angiography apparatus, for example, an apparatus capable of obtaining a subtraction image of an imaging part by performing only one X-ray fluoroscopic imaging of an imaging part of a subject, as described in Japanese Patent Application Laid-Open No. 8-308823. There is. Hereinafter, an operation of obtaining a subtraction image of a predetermined imaging region of a subject by the digital angiography apparatus will be described.

[0003] First, a predetermined imaging site of a subject to which a contrast agent has been administered is converted into an X-ray fluoroscopic imaging apparatus (an X-ray tube, an imaging system including an image intensifier, a television camera, and the like). ) And take it as an X-ray transmission image,
The captured X-ray fluoroscopic image is converted into digital data to obtain an X-ray transmissive image. This X-ray transmission image is an image in which high frequency components such as a blood vessel image to which a contrast agent has been administered remain, and is used as a live image. On the other hand, a frequency characteristic conversion circuit extracts a frequency component constituting an X-ray transmission image (live image) by a space / frequency conversion process, removes a frequency component above a predetermined threshold frequency, and performs frequency / space conversion on the frequency component. Processing is performed to obtain a high-frequency component-removed image in which frequency components equal to or higher than the threshold frequency have been removed from the X-ray transmission image (live image). The high-frequency component-removed image is an image from which high-frequency components such as a blood vessel image to which a contrast agent is administered have been removed, and is used as a mask image. The space / frequency conversion processing includes FFT
(Fast Fourier Transform), Karhunen-Loeve Transform, DC
There are various conversion methods such as T (discrete cosine transform) and Hadamard transform. As the frequency / space conversion processing, there is an inverse conversion of the space / frequency conversion processing (inverse FFT, inverse Karhunen-Loeve transform, inverse DCT, inverse Hadamard transform, etc.).

Next, the supply of an X-ray transmission image (live image) to a subsequent processing unit is delayed by a delay circuit by the processing time of the frequency characteristic conversion circuit, thereby providing an X-ray transmission image (live image). And a high-frequency component-removed image (mask image) are supplied in synchronization with a subsequent computing unit. Then, the arithmetic unit subtracts the high frequency component removed image (mask image) from the X-ray transmission image (live image) to obtain a subtraction image (subtraction image). Note that the above-mentioned predetermined threshold frequency is a frequency value at which an object of interest (such as a blood vessel image) to be left in the subtraction image can be suitably removed. By obtaining and setting, a subtraction image is obtained.

[0005] As described above, a subtraction image of a predetermined imaging region of a subject to which the contrast agent has been administered can be obtained by performing only one X-ray fluoroscopic imaging. Compared to the case of performing X-ray fluoroscopic imaging twice, the X-ray exposure dose to the subject can be reduced, and a high frequency component removal image (mask image) is generated from the X-ray transmission image (live image). Therefore, it is possible to completely eliminate the image shift between the mask image and the live image due to the body motion of the subject in the two imagings before and after the administration of the contrast agent.

[0006]

However, the prior art having such a configuration has the following problems. That is, in the above-described conventional example, a high-frequency component-removed image (mask image) is generated by removing a frequency component higher than a predetermined threshold frequency from an X-ray transmission image (live image) obtained by imaging. Since the frequency characteristic conversion process takes a certain amount of time, an X-ray transmission image (live image) is captured, and then a high-frequency component-removed image (mask image) is subtracted from the X-ray transmission image (live image). There is a problem that a certain time delay occurs until the subtraction image to be generated is generated, and the followability of the subtraction image display to the movement of the subject is poor.

[0007] Frequency characteristic conversion in which a high frequency component-removed image (mask image) is generated by removing a frequency component higher than a predetermined threshold frequency from an X-ray transmission image (live image) obtained by photographing. Since the processing must be performed for each X-ray transmission image (live image) obtained by imaging, there is a problem that the imaging rate cannot be further improved.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a digital subtraction apparatus capable of obtaining a subtraction image of an imaging part of a subject in a suitable and high-speed manner.

[0009]

The present invention has the following configuration to achieve the above object. That is, the digital subtraction apparatus according to claim 1 is a digital subtraction apparatus for obtaining a subtraction image of a predetermined imaging region of a subject,
(A) X-ray fluoroscopy means for irradiating the imaging site with X-rays and capturing an X-ray transmission image of the site, and (b) data conversion means for converting the X-ray transmission image into digital data.
(C) frequency characteristic conversion means for obtaining an image in which frequency components equal to or higher than a predetermined threshold frequency have been removed from the X-ray transmission image converted into the digital data (hereinafter referred to as a high frequency component removed image); Calculating means for performing subtraction between the image and the high-frequency component-removed image to obtain a subtraction image of the imaged site; and (e) combining the high-frequency component-removed image with a basic image which is a separately captured X-ray transmission image. Supply control means for supplying the data in synchronization with the calculation means.

According to a second aspect of the present invention, there is provided the digital subtraction apparatus according to the first aspect, wherein the supply control means includes the high frequency component removal image and an X-ray transmission image separately shot. A basic image, which is an X-ray transmission image captured after the time when the high frequency component-removed image is generated, is supplied in synchronization with the arithmetic means.

According to a third aspect of the present invention, there is provided the digital subtraction apparatus according to the first or second aspect, wherein the supply control means controls the supply of the high-frequency component-removed image and an X-photographed separately. A basic image, which is an X-ray transmission image taken before the generation of the high-frequency component-removed image as a line transmission image, is supplied in synchronization with the arithmetic means.

[0012]

The operation of the present invention is as follows. That is,
According to the first aspect of the present invention, an X-ray transmission image is captured by an X-ray fluoroscopic unit at a predetermined imaging site of a subject, and the captured X-ray transmission image is converted into digital data by a data conversion unit. Obtain a converted X-ray transmission image. This X-ray transmission image is an image in which the high frequency component of the object of interest remains, and is used as a live image. On the other hand, the frequency characteristic conversion means obtains a high-frequency component-removed image obtained by removing a frequency component higher than a predetermined threshold frequency from the X-ray transmission image. The high frequency component removed image is an image from which the high frequency component of the object of interest has been removed, and is used as a mask image. The supply control means includes a high-frequency component-removed image (mask image),
Basic image (live image) which is an X-ray transmission image taken separately
Are supplied in synchronization with the arithmetic means. The calculating means is a high-frequency component removed image (mask image) from the basic image (live image).
Is subtracted to obtain a subtraction image.

Therefore, the X-ray transmission image from which the high-frequency component-removed image (mask image) is generated is not the X-ray transmission image (live image) from which the high-frequency component-removed image (mask image) is generated. Since the high-frequency component-removed image (mask image) is subtracted from the basic image (live image), which is a separately transmitted X-ray transmission image, the basic image does not include a delay corresponding to the time required for the frequency characteristic conversion processing. (Live image) can be the target of subtraction, and although the low-frequency component to be removed has poor time tracking, the high-frequency component of interest is added to the separately captured basic image (live image). Since it is included, a subtraction image or the like is displayed with a minimum delay.

According to the second aspect of the present invention, an X-ray transmission image (live image) and a high-frequency component-removed image (mask image) can be obtained by the same operation as the first aspect. . Then, the supply control means includes a high-frequency component removal image (mask image) and an X-ray transmission image taken separately.
A basic image (live image), which is an X-ray transmission image captured after the time at which the high-frequency component-removed image (mask image) is generated, is supplied to the arithmetic unit in synchronization. The calculation means subtracts the high-frequency component-removed image (mask image) from the basic image (live image) to obtain a subtraction image. Therefore, it is not an X-ray transmission image (live image) from which the high frequency component removed image (mask image) is generated, but an X-ray transmission image after the time when the high frequency component removed image (mask image) is generated. Since the high-frequency component-removed image (mask image) is subtracted from the basic image (live image), the basic image (live image) that does not include the delay for the time required for the frequency characteristic conversion processing should be subtracted. Although the low-frequency component to be removed has poor time-tracking capability, the high-frequency component of interest remains in the basic image (live image) after the time when the high-frequency component-removed image (mask image) is generated. Since it is included, a subtraction image or the like is displayed with a minimum delay.

According to the third aspect of the present invention, an X-ray transmission image (live image) and a high-frequency component-removed image (mask image) are obtained by the same operation as the first aspect of the invention. . Then, the supply control means includes a high-frequency component removal image (mask image) and an X-ray transmission image taken separately.
An X-ray transmission image (live image) taken until the high frequency component-removed image (mask image) is generated is supplied in synchronization with the arithmetic means. Therefore, a plurality of X-ray transmission images (live images) are individually subtracted with the same high-frequency component-removed image (mask image), and each X-ray transmission image (live image) obtained by photographing is subtracted. Since it is not necessary to generate a high-frequency component-removed image (mask image), the frequency conversion processing time can be reduced by that time, and the shooting rate can be improved, that is, the display interval can be shortened.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an X-ray digital angiography apparatus as an embodiment of a digital subtraction apparatus according to the present invention will be described with reference to the drawings.

<First Embodiment> FIG. 1 is a front view showing the entire configuration of an X-ray digital angiography apparatus according to a first embodiment of the present invention. FIG. 2 is a side view of the X-ray fluoroscope. FIG. 3 is a block diagram illustrating a configuration of the image processing unit.

The X-ray digital angiography apparatus according to the first embodiment includes a bed 1, an X-ray fluoroscope 2 as X-ray fluoroscopic means, an image processing unit 3, a monitor 4, a control unit 5, an operation panel 6, and the like. It is configured.

The bed 1 includes a bed base 11 and a top plate 12 installed on the floor. The subject M is placed on the top 12. The table 12 can be moved horizontally by driving a motor 13, and the subject M on the table 12 and the X-ray fluoroscopic device 2
Can be displaced in the body axis direction of the subject M. The drive control of the motor 13 is performed by the control unit 5.

The X-ray fluoroscope 2 includes an X-ray tube 21 and an imaging system 2.
2 is configured to be supported on an upper portion of a device base 24 fixed near the bed 1.
The C-arm 23 is supported by the apparatus base 24 so as to be displaceable in the direction of the arrow in FIG.
1. The imaging system 22 is configured to be displaceable around the body axis of the subject M, so that the direction of imaging the X-ray transmission image can be adjusted.
The drive control of the motor 25 is performed by the control unit 5.

The X-ray tube 21 and the imaging system 22 are connected to the C-arm 2
3, and are opposed to each other with the subject M on the top 12 sandwiched therebetween. X-ray tube 21
The X-rays emitted from the device to an arbitrary imaging site of the subject M and transmitted through the subject M are received by the imaging system 22, and an X-ray transmission image of the site is captured. Irradiation of X-rays from the X-ray tube 21 is performed by supplying predetermined power (X-ray tube voltage and X-ray tube current) to the X-ray tube 21 from the X-ray high voltage generator 26. The supply of predetermined power from the X-ray high voltage generator 26 to the X-ray tube 21 is performed under the control of the control unit 5. The imaging system 22 includes an image intensifier, a television camera, and an FPD (Flat Panel Detecto).
r) and the like. The captured X-ray transmission image is provided to the image processing unit 3.

As shown in FIG. 3, the image processing unit 3 has an A / D (analog to digital data) converter 31 as data conversion means and a frequency control circuit 32 as a high frequency removal means. Supply control circuit 33 as means, arithmetic unit 34 as arithmetic means, gradation conversion circuit 35, D / A (digital to analog) converter 36
It is composed of

When an X-ray transmission image of a predetermined imaging site of the subject M to which the contrast agent is administered is captured, an image signal (analog signal) of the image from the imaging system 22 is transmitted to the A / D converter 31.
Is converted into digital data, and an X-ray transmission image is obtained. The X-ray transmission image is an image including a low frequency component such as a skeleton and a high frequency component such as a blood vessel image to which a contrast agent is administered, and is used as a live image. This X-ray transmission image (live image) is provided to the frequency characteristic conversion circuit 32. The frequency characteristic conversion circuit 32 obtains a mask image by removing high frequency components such as a blood vessel image from an X-ray transmission image (live image) by a process described later. The supply control circuit 33 includes the high-frequency component-removed image (mask image) and the high-frequency component-removed image (mask image) as a separately captured X-ray transmission image.
And a basic image (live image), which is an X-ray transmission image captured after the time at which the is generated, is supplied to the arithmetic unit in synchronization with the basic image. The function of the supply control circuit 33 is one feature of the present invention.

The arithmetic unit 34 subtracts the directly supplied basic image (live image) from the high-frequency component-removed image (mask image) supplied via the frequency characteristic conversion circuit 32 to obtain a subtraction image. To the gradation conversion circuit 35. The gradation conversion circuit 35 adjusts the density of each pixel constituting the subtraction image (adds a predetermined density to the density of each pixel for all pixels) in order to make the subtraction image easy to see when displayed on the monitor 5. Or subtract). The gradation-converted subtraction image is supplied to a D / A converter 36, where the D / A
It is converted and displayed on the monitor 4. The image processing unit 3
The control of the operation of each component of the control is performed by the control unit 5.

The frequency characteristic conversion circuit 32 of the first embodiment
An object of the present invention is to perform high-speed processing of removing a high-frequency component such as a blood vessel image from an X-ray transmission image (live image) to obtain a high-frequency component-removed image (mask image) as it is in real space data. Things.

The frequency characteristic conversion circuit 32 includes a real space filtering section 32a for removing a high frequency component of an X-ray transmission image (live image) in a real space by a template filter represented by a linear shape in a real space. ing. The template filter shape of this real space filtering unit 32a is, for example, as shown in FIG.
In a three-dimensional orthogonal coordinate system in a real space represented by Y and Z axes, a rectangular prism shape in which the X and Y axis directions are the base size, which is the rectangular shape of the template filter, and the Z axis direction is the gain of this template. It is assumed to be represented by As shown in FIG. 8, a processing method using a rectangular column-shaped template filter (hereinafter, appropriately referred to as a “box filter”) in this real space is performed by using a pixel (i, j) in an input image (an input basic image). ) Is defined as the value of the pixel (i, j) of the output image using the average density of the neighborhood (for the square of N × N points),
By performing this averaging process for all pixels, a high-frequency component-removed image (mask image) is obtained by removing a frequency component (high-frequency component) higher than a predetermined threshold frequency from an X-ray transmission image (live image). And it is appropriately referred to as a moving average filter method.

FIG. 8 is a view looking down from the Z-axis direction when the box filter shown in FIG. 7 is positioned on a plurality of predetermined pixels of an X-ray transmission image (live image) to be filtered. FIG. In FIG. 8, the filter size of the box filter is illustrated as a 3 × 3 square for convenience of description, and the average value of 9 pixels (9 points) including the pixel (i, j) and the surrounding 8 pixels is represented by the pixel. Although the value of (i, j) is used, this filter size is set to a size that removes a frequency component (high frequency component) equal to or higher than a predetermined threshold frequency, as described below. That is, in this box filter, the threshold frequency is changed according to the filter size. That is, if the filter size is increased, the threshold frequency is lowered and the degree of blur is increased, and if the filter size is reduced, the threshold frequency is increased and the degree of blur is reduced. As shown in FIG. 7, the filter size of the box filter is, for example, 21 × 21 points (TA
(P number × TAP number). This TAP number is also the score of the kernel. Further, the threshold frequency at which the blood vessel image having the standard spatial shape can be preferably removed can be obtained experimentally or theoretically, so that the blood vessel image having the standard spatial shape can be suitably removed. Similarly, the filter size of the box filter that can be obtained may be obtained experimentally or theoretically, or the filter size may be set as an initial value.

The moving average filter method described above has been improved so that arithmetic processing can be performed at high speed, as described below. For example, in order to obtain a moving average using a box filter having a filter size of N points × N points, a total value obtained by honestly adding pixels of N × N points where the box filter is located is equal to the number of points of the box filter (N By averaging at (× N points), the value of the pixel at the center of the box filter is calculated, and if this calculation is performed individually for all pixels, the amount of calculation becomes enormous and high-speed calculation processing cannot be performed. However, the amount of calculation increases as the filter size increases.

Therefore, as described below, the above-mentioned moving average filter method is improved so as to be capable of high-speed arithmetic processing. That is, as shown in FIG. 9, in order to obtain a moving average of N × N points, the addition of the N × N points is not honestly calculated for each pixel. By performing the addition and subtraction, the calculation can be easily performed, and the calculation time can be reduced. For example, one-dimensional "A" ~
A case will be described as an example where a moving average is performed on a pixel “F” by a one-dimensional three-point box filter. "A"
If there is a box filter in the pixels of “−C”, “A”
The average value of the three points of “+ B + C” is the value of the “B” pixel. Then, when the box filter is moved to the next position (the position of the pixel of “B” to “D”), the previous value (“A + B
+ C ”) is updated from the part (“ D ”
Is removed), it is only necessary to perform the addition and subtraction (−A + D), and the waste of performing the overlapped addition between the previous time and the current time can be eliminated, and even if the filter size becomes large, the amount of calculation (total amount of calculation) Is constant while decreasing. In this example, for convenience of explanation, the box filter is set to three points. However, as the number of points of the box filter increases, only the amount of operation for sequentially and honestly adding all points and the addition and subtraction of a part to be updated are reduced. It can be seen that the difference from the amount of calculation to be performed is large and is effectively improved. As shown in FIG. 7 and FIG.
In the case of the three-dimensional moving average, the accumulated value of N rows in the vertical direction is calculated as shown in FIG.
The same method as in FIG. 9 may be obtained, and the same method as in FIG. That is, even in the case of a two-dimensional moving average of an N × N point box filter, addition and subtraction of an updated portion is only addition of one pixel and subtraction of one pixel. Since the total amount of calculation is reduced as described above, the real space filtering unit 3 uses a general-purpose chip.
2a, and a high-frequency component-removed image can be generated in a very short time (near real time) from an X-ray transmission image (live image) obtained by imaging.

Returning to FIGS. 1 and 2, the control unit 5 performs drive control and operation control of each device and each unit in accordance with various instructions from the operation panel 6. The control unit 5 is composed of, for example, a CPU (Central Processing Unit) that executes a program for implementing an operation described later.

The operation panel 6 is used by an operator to set an imaging part and conditions, and to instruct processing start.

The operation of the embodiment apparatus having the above configuration will be described below. First, an operation for obtaining a subtraction image of a certain imaging site (for example, the chest) of the subject M will be described.

In this case, first, the control unit 5 controls the driving of the motor 13 according to the imaging region and conditions (such as the imaging direction) set from the operation panel 6 by the operator, and the top plate on which the subject M is mounted. The X-ray tube 2 is moved horizontally so that the set imaging region (to be referred to as a chest) is positioned at an imaging position between the X-ray tube 21 and the imaging system 22, and the motor 25 is driven and controlled.
1. The imaging system 22 is displaced around the body axis of (the imaging site of) the subject M to adjust the imaging direction. This state is shown in FIG. In FIG. 4, the imaging direction is adjusted so that X-rays are emitted from below the imaging site SB to capture an X-ray transmission image.

Next, a contrast agent is administered to the subject M. Note that the positioning operation or the like may be performed after the contrast agent is administered. In any case, before the following imaging operation,
The contrast agent is administered to the subject M, and the operator instructs the start of processing from the operation panel 6 in a state where the contrast agent is diffused to the imaging site SB, and the following imaging operation is performed.

When the processing start is instructed, the control unit 5 controls the X-ray high voltage generator 26 to supply predetermined power to the X-ray tube 21 to irradiate X-rays, thereby diffusing the contrast agent. An X-ray transmission image of the imaged portion SB is taken. Then, the control unit 5 controls each unit of the image processing unit 3 to obtain an X-ray transmission image (live image) and the X-ray transmission image (live image).
, A high-frequency component-removed image (mask image) is obtained from the image, and the obtained mask image and a basic image (live image) which is an X-ray transmission image taken after the time when the mask image was generated
Are supplied in synchronization with the arithmetic unit 34, the arithmetic unit 34 subtracts the mask image and the basic image (live image), and the subtraction image is displayed on the monitor 4.

More specifically, the supply control circuit 33
As shown in (b), an X-ray transmission image (live image) “A” captured by the imaging system 22 and converted into digital data by the A / D converter 31 is a high-frequency component-removed image (mask image) “ A ′ ”is obtained by the frequency characteristic conversion circuit 32, and the obtained mask image“ A ′ ”and a basic image which is an X-ray transmission image taken after time t2 when this mask image“ A ′ ”was generated (Live image) For example, "B" and the arithmetic unit 34
Supply in synchronization with. The arithmetic unit 34 subtracts the mask image “A ′” from the basic image (live image) “B” to generate a subtraction image “BA ′”. In addition,
The next subtraction image is an X-ray transmission image (live image)
The high-frequency component-removed image “B ′” obtained from “B” and the basic image (live image) “C” which is an X-ray transmission image taken after time t6 when the mask image “B ′” was generated "
Are supplied in synchronization with the arithmetic unit 34, thereby generating a subtraction image “CB ′” including the mask image “B ′” and the basic image (live image) “C”. The time (for example, the time from time t2 to time t6) from when a certain X-ray transmission image (live image) to the next X-ray transmission image (live image) is set to various times. In the example,
For example, it is 1/30 second. Thereafter, a subtraction image is generated in a similar manner.

Therefore, not the X-ray transmission image (live image) from which the high-frequency component-removed image (mask image) is generated, but the X-ray transmission after the time when the high-frequency component-removed image (mask image) is generated. Since the high-frequency component-removed image (mask image) is subtracted from the basic image (live image) that is the image, the basic image (live image) that does not include the delay corresponding to the time required for the frequency characteristic conversion processing is subtracted. Although the low-frequency component to be removed has a poor time tracking property, the high-frequency component of interest is an X-ray transmission image after the time when the high-frequency component removal image is generated. Since it is included in the (live image), a subtraction image or the like can be displayed with a minimum delay, and a subtraction image that can follow the movement of the subject M can be provided.

Specifically, in the conventional apparatus, FIG.
As shown in (a), since the high-frequency component-removed image is generated for each X-ray transmission image (live image), for example, the start time of the frequency characteristic conversion processing of the X-ray transmission image (live image) “A” Since a delay time (time from t5 to t1) from t1 to time t5 from generation of the subtraction image was necessary,
A subtraction image following the movement of the subject M could not be obtained. However, according to the first embodiment, as shown in FIG. 10B, the high-frequency component-removed image (mask image) "A '" and the high-frequency component-removed image (mask image) "A'" Is a basic image (live image) which is an X-ray transmission image captured after time t2 when the image is generated.
For example, since subtraction is performed with "B", for example, X
Only a delay time (time from t5 to t3) from the imaging completion time t3 of the line transmission image (live image) "B" to the time t5 until the subtraction image is generated, and a subtraction image following the movement of the subject M is obtained. Can be.

Next, the relative positional relationship between the subject M and the X-ray fluoroscope 2 is displaced in the body axis direction of the subject M, for example, as shown in FIG. S
An operation for obtaining subtraction images of a plurality of imaging sites in R will be described. In this embodiment, the X-ray fluoroscope 2 is fixed, and the top plate 1 on which the subject M is mounted is fixed thereto.
2 is configured to move horizontally, however, in FIG.
Is fixed, and the X-ray fluoroscope 2 (X-ray tube 21,
The imaging system 22) is depicted as being displaced.

In this case, the control unit 5 positions the first imaging site (the imaging site on the left end side of the imaging region SR in the figure) at the imaging position and adjusts the imaging direction. Then, a contrast agent is administered to the subject M before the following imaging operation.

When the contrast agent diffuses into each imaging region (region SR) of the subject M and the start of the processing is instructed, a procedure similar to that for obtaining the subtraction image of the one imaging region SB is performed first. Find the subtraction image of the imaging part of
While moving the top 12 at a constant speed to the left in FIG. 5, the subtraction image of each imaging part is sequentially obtained each time the subsequent imaging part is located at the imaging position.

Therefore, the relative positional relationship between the subject M and the X-ray fluoroscope is displaced in the body axis direction of the subject M,
Even in the case of obtaining subtraction images for a plurality of continuous imaging sites, the same effect as described above is obtained.

The top plate 12 is fixed, and the X-ray fluoroscope 2
Is moved in the body axis direction of the subject M on the top plate 12 so that the relative positional relationship between the subject M and the X-ray fluoroscope is displaced in the body axis direction of the subject M. Is also good.

In a state where a part (for example, the chest) of the subject M is located at the imaging position, as shown in FIG. 6, the X-ray tube 21 and the imaging system 22 are moved around the part (around the body axis). In some cases, a subtraction image from each imaging direction may be obtained while rotationally displacing the subject M. Even in such a case, a subtraction image following the movement of the subject M may be obtained in the same manner as in each of the above operations. Can be.

The real space filtering unit 32a
The high-frequency component of the X-ray transmission image (live image) is removed in the real space by the template filter represented by a linear shape in the real space, and has the following effects.

For example, in a conventional template filter having a Gaussian function shape, as can be seen from the Gaussian curve shape shown in FIG. 17, an X-ray transmission image (live image) cannot be processed only by simple addition and subtraction. The size (N × N points) is, for example, 51 (TAP number) × 51 (TAP
The number of filtering operations becomes enormous as the number of points increases, and the amount of operation in the case of the conventional example is represented by the following equation (1). Met. Note that P in equation (1) is two times, one multiplication and one addition, and G ^{2 in} equation (1)
Is the total number of pixels of the X-ray transmission image (live image). For example, a specific numerical value is substituted into Expression (1) for reference. Operation amount = N (TAP number) × N (TAP number) × P × G ² (1) = 51 × 51 × 2 × G ²

On the other hand, in the first embodiment described above,
The real-space filtering unit 32a filters the X-ray transmission image (live image) with a rectangular column-shaped template filter that is represented by a linear shape in real space, and thus simply converts the X-ray transmission image (live image). In addition, the processing can be performed only by simple addition and subtraction, and the amount of calculation can be reduced so that the repeated calculation (addition) in the filtering processing is not repeatedly performed. The amount of computation for filtering in the case of the first embodiment is expressed by the following equation (2). Note that Q in equation (2) is two times, one addition and one subtraction, and G ^{2 in} equation (2) is
Similar to the above equation (1), it is the total number of pixels of the X-ray transmission image (live image). For example, a specific numerical value is substituted into Expression (2) for reference.

As can be seen by comparing equations (1) and (2),
The amount of computation for filtering in the case of the first embodiment is:
It is only necessary to execute a simple addition / subtraction for the part updated by the filter movement, and since the number of TAPs is not included in the equation (2), the equation (1) is a constant amount regardless of the filter size. It can be seen that the processing is greatly reduced in comparison with the processing in a short time near real time.

<Second Embodiment> Next, an X-ray digital angiography apparatus according to a second embodiment of the X-ray digital subtraction apparatus of the present invention will be described. FIG. 11 is a schematic diagram showing a template filter shape of the real space filtering unit 40 according to the second embodiment of the present invention. FIG. 12 is a block diagram of the real space filtering unit 40 according to the second embodiment. X of the second embodiment
The line digital angiography apparatus employs a real space filtering unit 40 shown in FIG. 12 instead of the real space filtering unit 32a of the first embodiment, and the template filter shape of the real space filtering unit 40 of the second embodiment is Except for the point that the quadrangular prism shape is changed to an octagonal pyramid shape as described later, the configuration is the same as that of the above-described first embodiment. Spatial filtering unit 40
Will be described in detail.

First, the template filter shape of the real space filtering unit 40 will be described. The template filter shape of the real space filtering unit 40 is shown in FIG.
In the three-dimensional orthogonal coordinate system in real space represented by X, Y, and Z axes orthogonal to each other, the X and Y axis directions are the bottom surface size that is the rectangular shape of the template filter, and the Z axis direction Is the gain of this template, and is a three-dimensional shape tapering in the Z-axis direction, and is represented by an octagonal pyramid shape from at least the center in the Z direction of the template filter to the tapered tip. Note that such a template filter shape of the real space filtering unit 40 is also referred to as a substantially octagonal pyramid shape for convenience of description.

As shown in FIG. 12, the real space filtering section 40 includes a row direction triangular filter 41 for applying a predetermined filter described later in the row direction of an input X-ray transmission image (live image), A storage unit 42 for storing data filtered by the filter 41, and a column direction for applying a predetermined filter described later in a column direction of the X-ray transmission image (live image) after row direction processing stored in the storage unit 42 A triangular filter 43, a row direction triangular filter 41, a storage unit 42, and a control unit 44 for controlling the column direction triangular filter 43 are provided.

The row direction triangular filter 41 is newly added as shown in FIG.
A first one-dimensional filter block 51 that generates a pixel value (see FIG. 15B) of a right-side descending gradient portion of a triangular shape, which will be described later, is deleted from a portion to be updated.
A second one-dimensional filter block 52 that generates a pixel value (see FIG. 15B) of a left-side ascending gradient portion of a triangle, which will be described later, and a first one-dimensional filter block 51 and a second one-dimensional filter block 51 A subtracter 53 for subtracting the image data from the dimensional filter block 52; an accumulator 54 for accumulating and outputting the output from the subtractor 53; and a first one-dimensional filter block And a delay circuit 55 for inputting the signal to the second one-dimensional filter block 52 with a predetermined delay from the signal 51.

The first one-dimensional filter block 51 converts image data (a series of image data in the row direction of the basic image) input to one input port into image data (basic image data) input from the other input port. Subtracter 6 for subtracting and outputting a series of image data in the row direction of the image)
1; a delay circuit 62 for delaying the input basic image by a predetermined amount from one input port of the subtractor 61 and inputting the delayed image to the other input port of the subtractor 61;
And an accumulating circuit 63 for accumulating the output from. The second one-dimensional filter block 52 has the same configuration as the first one-dimensional filter block 51, and includes a subtractor 61, an accumulator circuit 62, and a delay circuit 63.

The column-direction triangular filter 43 has the same configuration as the row-direction triangular filter 41 described above.
The data in the row direction of the X-ray transmission image (live image) processed by the row direction triangular filter 41 and stored in the storage unit 42 is subjected to filtering processing in the column direction.

Here, the real space filtering section 40 whose template filter shape is substantially an octagonal pyramid shape in the real space.
Will be described with respect to its filtering function.
The real space filtering unit 40 is equivalent to a one-dimensional filter shown in FIG. 14A in which the one-dimensional shape of the real space is a triangle, which is expanded to two dimensions as shown in FIG. As shown in FIG. 14C, by using a matrix (vertical and horizontal) separation type filter, it is advantageous for speeding up.
Note that examples of the filter coefficients are shown in FIGS. For example, if a one-dimensional filter having a triangular real space shape as shown in FIG.
As shown in FIG. 4 (b), “1, 2, 3, 2,
1 ". When the one-dimensional filters in the row (horizontal) direction shown in FIG. 14B are arranged in the column (vertical) direction, FIG.
A two-dimensional filter as shown on the upper right side of (c) is obtained. Further, the one-dimensional filter in the row (horizontal) direction shown in FIG. 14B is arranged in the vertical direction, that is, “1, 2, 3,
Arranging the coefficients of "2, 1" in the row (horizontal) direction results in a two-dimensional filter as shown in the upper left of FIG. 14C. Then, these two-dimensional filters are multiplied by the coefficients of the same points to form a matrix (vertical and horizontal) separation type filter as shown in the lower part of FIG. An effect equivalent to a template filter having a shape (substantially pyramid shape) can be obtained.

Note that the coefficients (“1,
2, 3, 4, 6, 9 ") as shown in FIG.
It indicates the degree of weight. That is, as shown in FIG. 15A, when the one-dimensional filter shown in FIG. 14B is located at pixels “A” to “E” in the X-ray transmission image (live image), It shows how many times the value of is multiplied. Specifically, since the pixel “A” is in the coefficient “1” of the one-dimensional filter shown in FIG. 14B, “A” is multiplied by one, that is, “A”, and the pixel “B” is the same as FIG. Since the coefficient “2” of the one-dimensional filter shown in FIG. 14B is “2”, it is twice “B”, that is, “2B”.
Since it is in the coefficient “3” of the one-dimensional filter shown in FIG. 14B, “C” is tripled, that is, “3C”, and the pixel “D” is the coefficient “2” of the one-dimensional filter shown in FIG. ”, So“ D ”is doubled, that is,“ 2 ”
D ”, and the pixel“ E ”is the coefficient“ 1 ”of the one-dimensional filter shown in FIG.
That is, "E" remains.

As shown in the lower part of FIG. 14C, a matrix (vertical and horizontal) separation type filter, that is, a template filter having a substantially octagonal pyramid shape (substantially pyramid shape) in a real space has a column (vertical) shape. Separation into the direction and the row (horizontal) direction, as shown in FIG. 15, can be calculated by extending the algorithm of the moving average in the first embodiment described above, and repeatedly performs the overlapping operation (addition) in the filtering process. The amount of calculation can be reduced so as not to occur.

That is, as shown in FIG. 15B, the first one-dimensional filter block 51 generates a pixel value of a triangle-shaped downward gradient portion which is newly added in the updated portion. . In FIG. 15B, the value of the pixel in the triangle-shaped downward gradient newly added in the updated portion is “D + E + F”.

The second one-dimensional filter block 52
Generates the value of the pixel in the triangular upward gradient portion to be deleted from the updated portion, as shown in FIG. 15B. In FIG. 15B, the value of the pixel in the triangular rising gradient portion that is deleted from the updated portion is
"A + B + C".

When the one-dimensional filter shown in FIG. 14B is located at pixels "A" to "E" in the X-ray transmission image (live image), the weighting is performed as shown in FIG. The result "A + 2B + 3C + 2D + E" is obtained. next,
When the one-dimensional filter shown in FIG. 14B moves by one pixel and is located at the pixels “B” to “F” of the X-ray transmission image (live image), it is shown in FIG. "A +
By subtracting “B + C” and adding “D + E + F”, a weighted “B + 2C + 3D + 2E + F” is obtained as shown in FIG. Therefore, when the one-dimensional filter shown in FIG. 14B is moved by one pixel and positioned at the pixels “B” to “F” of the X-ray transmission image (live image), the calculation is performed honestly from the beginning. That is,
The previous time (shown in FIG. 15A) and the current time (FIG. 15B)
15) by performing the same operation as that shown in FIG.
The weighted one shown in (b) “B + 2C + 3D + 2”
It is not necessary to obtain "E + F". Next, in the case where the one-dimensional filter shown in FIG. 14B is further moved by one pixel and positioned at pixels “C” to “G” of the X-ray transmission image (live image), similarly, As shown in FIG. 15B, “B + 2C + 3
“B + C + D” from “D + 2E + F” and “E
+ F + G ”and weighted“ C + 2D + 3 ”
E + 2F + G "is obtained.

As described above, since the addition and subtraction of the portion updated by the filter movement is only the addition of three pixels and the subtraction of three pixels, it is only necessary to perform the addition and subtraction of the updated portion.

Next, the "B + 2C + 3D + 2E + F" shown in FIG.
Is specifically described. In FIG. 15, for convenience of explanation, the filter size is set to 5 points (TAP number =
(5 points), the delay amount between the delay circuit 62 of the first one-dimensional filter block 51 and the delay circuit 62 and the delay circuit 55 of the second one-dimensional filter block 52 is calculated by the following equation (3). Are set to "3".

The parameters (delay amount) of these delay circuits
Correspond to the number of TAPs in the digital filter. By changing the TAP number, the value of the threshold frequency can be changed. In FIG. 15, for convenience of explanation, the filter size is set to 5 points. However, in the second embodiment, when the number of TAPs is set to 51 × 51 points as shown in FIG. Delay circuit 62 of filter block 51
And the delay circuit 62 of the second one-dimensional filter block 52
And the delay amount between the delay circuit 55 and the delay circuit 55 are set to “26”.
The control means 44 initializes the accumulation values of the accumulation circuit 63 of the first one-dimensional filter block 51, the accumulation circuit 63 of the second one-dimensional filter block 52, and the accumulation circuit 54,
A delay circuit 62 of the first one-dimensional filter block 51;
The delay amount between the delay circuits 62 and 55 of the second one-dimensional filter block 52 is set.

For example, “A” of an X-ray transmission image (live image)
The processing status of each configuration of the row-direction triangular filter 41 at the time when .about. "F" is input to the row-direction triangle filter 41 will be described. “F” and “C” are input to the subtractor 61 of the first one-dimensional filter block 51, and “FC” is input to the accumulation circuit 63 of the first one-dimensional filter block 51. The accumulating circuit 63 of the first one-dimensional filter block 51 calculates (“C + D + E” + “F−
C)), “D + E + F” is output. Also, since the delay amount of the delay circuit 55 is “3”, only “C” is still input to the subtracter 61 of the second one-dimensional filter block 52, and “C” is in the second one-dimensional filter block. The signal is input to the accumulation circuit 63 of the filter block 52. The accumulating circuit 63 of the second one-dimensional filter block 52 calculates (“A + B” +
“C”) outputs “A + B + C”. Subtractor 5
3, “D + E + F” output from the accumulation circuit 63 of the first one-dimensional filter block 51 and “A” output from the accumulation circuit 63 of the second one-dimensional filter block 52
+ B + C ", and (" D + E + F "-
“A + B + C”) is output. The accumulation circuit 54 accumulates the previous value “A + 2B + 3C + 2D + E” and (“D + E + F” − “A + B + C”) from the subtractor 53,
“B + 2C + 3D + 2E + F” is output to the storage unit 42.

As described above, in the above-described second embodiment, the real space filtering unit 40 is represented by a linear shape in the real space.
The high-frequency component of the X-ray transmission image (live image) is removed in the real space by the template filter having a substantially octagonal pyramid shape, and only the addition and subtraction of the updated portion need be performed. As in the case of the example, the amount of computation for filtering is expressed by Expression (2), and in Expression (2), TA
Since the number of P's is not included, the amount is constant regardless of the filter size, and is significantly reduced as compared with the conventional formula (1). Have. Further, in the second embodiment,
In the following point, the present embodiment is more excellent than the first embodiment.

That is, the template filter shape of the second embodiment (see FIG. 11) is more ideal than the template filter shape of the first embodiment (see FIG. 7) (see FIG. 17). Therefore, as shown in FIG. 16, the frequency characteristic is more excellent than that of the first embodiment. Specifically, in the template filter of the first embodiment, 0.25 lp / m
Ringing (peak having a MAX of about 0.15) occurs near m (line pair / mm), but such ringing is considerably small and slightly exists in the template filter of the second embodiment. Therefore, it can be seen that the frequency components equal to or higher than the predetermined threshold frequency can be removed more favorably than in the first embodiment.

Further, the change of the threshold frequency value can be realized by adjusting the delay amount of the delay circuit, and the amount of calculation does not increase or decrease, so that the processing can be performed in a reduced fixed time irrespective of the threshold frequency value. . Therefore, it is possible to provide a digital subtraction apparatus having a high degree of freedom in changing the value of the threshold frequency while securing a predetermined processing time.

In the second embodiment, the template filter shape of the real space filtering section 40 is
As shown in the figure, the template filter has a substantially octagonal pyramid shape that is represented by an octagonal pyramid shape at least from the center in the Z direction to the tapered tip portion, but the entire shape from the bottom surface to the tapered tip portion is an octagonal pyramid shape. It is good.

<Third Embodiment> FIG. 18 is a block diagram showing the configuration of an image processing unit of the third embodiment. This third
The embodiment is characterized in that a supply control circuit 33a, which will be described later, is provided in place of the supply control circuit 33 of the first and second embodiments. The supply control circuit 33a controls the high-frequency component-removed image (mask image) and the X-rays captured until the high-frequency component-removed image (mask image), which is a separately captured X-ray transmission image, is generated. A basic image (live image), which is a transmission image, is supplied to the arithmetic unit 34 in synchronization with the basic image (live image). In the device of the third embodiment, only the supply control circuit 33a is different from the devices of the first and second embodiments. Therefore, in the third embodiment, the supply control circuit 33a will be described in detail.

As shown in FIG. 18, the supply control circuit 33a
Is, for example, a frequency characteristic conversion circuit 32 similar to those of the first and second embodiments, and a storage circuit 71 for storing a high frequency component removed image (mask image) generated by the frequency characteristic conversion circuit 32 for a predetermined time. And a delay circuit 72 for delaying the basic image (live image) by a predetermined time and outputting the delayed image.

Here, the subtraction processing operation of the third embodiment will be described with reference to FIG.

As shown in FIG. 19, when an X-ray transmission image (live image) “A” is obtained by imaging (time t11), the frequency characteristic of this X-ray transmission image (live image) “A” is converted. Then, a frequency characteristic conversion process for generating a high frequency component removed image (mask image) “A ′” is performed. Assuming that the end time of the frequency characteristic conversion processing is t14, in the third embodiment, the X-ray transmission image (live image) "A" is different from the X-ray transmission image (live image) in the period from time t11 to t14. A basic image (live image) “A *” that is a live image is captured (time t).
13). The supply control circuit 33a outputs the high-frequency component removed image (mask image) “A” from the X-ray transmission image (live image) “A”.
′ ”And subtraction image“ A-
A ′ ”is generated, and the same high-frequency component-removed image (mask image)“ A ′ ”is obtained from the basic image (live image)“ A * ”.
And subtraction image “A * -A”
′ ”Is generated so that the storage circuit 71 and the delay circuit 72
, The synchronous supply of the live image and the mask image to the arithmetic unit 34 is controlled. The next subtraction image is an X-ray transmission image (live image) “B” and this X-ray image
A subtraction image “B-B ′” is generated by subtracting the high-frequency component-removed image “B ′” obtained from the line transmission image (live image) “B”, and an X-ray transmission image (live image)
Is subtracted from the high-frequency component-removed image "B '", which is the same as the above, to generate a subtraction image "B * -B'". The time (for example, the time from time t10 to t12) until shooting of the next X-ray transmission image (live image) from one X-ray transmission image (live image) is set to various times. In the example,
For example, it is 1/60 second. Thereafter, a subtraction image is generated in a similar manner.

Therefore, a plurality of X-ray transmission images (live images) can be individually subtracted with the same high-frequency component-removed image (mask image), and the X-ray transmission images (live images) obtained by photographing can be subtracted. Since it is not necessary to generate a high-frequency component-removed image (mask image) for each image), it is possible to reduce the frequency conversion processing time by that time and improve the shooting rate, that is, to shorten the display interval. Thus, a subtraction image that can follow the movement of the subject can be provided.

The present invention is not limited to the above embodiments, but can be modified as follows.

(1) Supply control circuit 3 of the first embodiment described above
3 and the supply control circuit 33a of the third embodiment may be combined. That is, as shown in FIG. 20, the combined supply control circuit includes a high-frequency component-removed image (mask image) and a separately photographed X-ray transmission image.
Basic image (live image) which is an X-ray transmission image taken before the generation of the high frequency component-removed image (mask image)
Is supplied to the arithmetic unit 34 in synchronization with the high-frequency component-removed image (mask image) and the time when the high-frequency component-removed image (mask image) as an X-ray transmission image captured separately is generated. A basic image (live image), which is an X-ray transmission image captured thereafter, is supplied to the arithmetic unit 34 in synchronization with the basic image (live image). In this case, as shown in FIG. 20, it is possible to configure a digital subtraction apparatus in which the delay is reduced and the shooting rate is improved.

(2) The real space filtering 32a, 32a,
It is also possible to realize 40 by software using a general-purpose chip.

(3) In the digital subtraction apparatus of each of the embodiments described above, the real space filtering units 32a and 40 are used for the frequency characteristic conversion circuit 32, but the frequency components forming the X-ray transmission image (live image) are It is extracted by a space / frequency conversion process, a frequency component higher than a predetermined threshold frequency is removed, a frequency / space conversion process is performed on the frequency component, and a frequency higher than the threshold frequency is obtained from the X-ray transmission image (live image). A frequency characteristic conversion circuit 32 for obtaining a high-frequency component-removed image (mask image) from which frequency components have been removed may be employed. The space / frequency conversion processing includes FFT
(Fast Fourier Transform), Karhunen-Loeve Transform, DC
There are various conversion methods such as T (discrete cosine transform) and Hadamard transform. As the frequency / space conversion processing, there is an inverse conversion of the space / frequency conversion processing (inverse FFT, inverse Karhunen-Loeve transform, inverse DCT, inverse Hadamard transform, etc.).

(4) The digital subtraction apparatus according to each of the above-described embodiments uses the subject M
Can be used as a human body for medical use, and the subject M can be used for various electronic components such as a BGA (Ball Grid Array) substrate and a printed wiring board for nondestructive inspection.

[0079]

As is apparent from the above description, according to the digital subtraction apparatus of the first aspect,
Since the high-frequency component-removed image is subtracted not from the X-ray transmitted image from which the high-frequency component-removed image is generated but from the base image which is a separately captured X-ray transmitted image,
A basic image that does not include a delay corresponding to the time required for the frequency characteristic conversion processing can be a target of subtraction, and although the low-frequency component to be removed has a poor time-tracking property, the high-frequency component of interest is separately provided. Since the subtraction image is included in the basic image captured at a time, a subtraction image or the like can be displayed with a minimum delay, and a subtraction image that can follow the movement of the subject can be provided.

According to the digital subtraction apparatus of the present invention, not the X-ray transmission image from which the high-frequency component-removed image is generated, but the X-ray after the time when the high-frequency component-removed image is generated. Since the high-frequency component-removed image is subtracted from the transmitted basic image, the basic image that does not include a delay corresponding to the time required for the frequency characteristic conversion processing can be subjected to the subtraction, and the low-frequency image to be removed can be removed. Although the time tracking property of the frequency component is deteriorated, the high frequency component of interest is included in the basic image after the time when the high frequency component removal image is generated, so that a subtraction image or the like is displayed with a minimum delay. Thus, a subtraction image that can follow the movement of the subject can be provided.

According to the digital subtraction apparatus of the third aspect, it is possible to individually subtract a plurality of basic images with the same high-frequency component-removed image, and obtain an X-ray transmission obtained by photographing. Since it is not necessary to generate a high-frequency component-removed image for each image, the time required for the frequency conversion processing can be reduced by that time, and the imaging rate can be improved, that is, the display interval can be shortened, and the A subtraction image that can follow the movement can be provided.

[Brief description of the drawings]

FIG. 1 is a front view showing an entire configuration of a digital angiography apparatus according to a first embodiment of the present invention.

FIG. 2 is a side view of the X-ray fluoroscope.

FIG. 3 is a block diagram illustrating a configuration of an image processing unit provided in the first embodiment device.

FIG. 4 is a diagram for explaining an operation in a case where a subtraction image of a certain imaging part is obtained.

FIG. 5 is a diagram for explaining an operation when obtaining subtraction images of a plurality of imaging sites in a body axis direction of a subject.

FIG. 6 is a diagram for describing an operation when obtaining subtraction images from a plurality of imaging directions for a certain part.

FIG. 7 is a schematic diagram showing a template filter shape according to the first embodiment.

FIG. 8 is a schematic diagram for explaining a moving average filter method according to the first embodiment.

FIG. 9 is a schematic diagram for explaining a calculation algorithm of a moving average filter according to the first embodiment.

FIG. 10A is a schematic diagram illustrating a subtraction processing operation sequence according to a conventional example, and FIG. 10B is a schematic diagram illustrating a subtraction processing operation sequence according to the first embodiment.

FIG. 11 is a schematic diagram illustrating a template filter shape according to a second embodiment.

FIG. 12 is a block diagram of a real space filtering unit according to a second embodiment of the present invention.

FIG. 13 is a block diagram showing a configuration of a row direction triangular filter according to a second embodiment of the present invention.

FIGS. 14A to 14C are schematic diagrams illustrating a pyramid-shaped filter according to a second embodiment.

FIGS. 15A and 15B are schematic diagrams for explaining a calculation algorithm of a pyramidal filter according to the second embodiment.

FIG. 16 is a characteristic diagram showing frequency characteristics of various filters.

FIG. 17 is a schematic diagram showing an ideal template filter shape represented by a conventional Gaussian function shape.

FIG. 18 is a block diagram illustrating a configuration of an image processing unit of the third embodiment.

FIG. 19 is a schematic diagram showing a subtraction processing operation sequence by the device of the third embodiment.

FIG. 20 is a schematic diagram showing a subtraction processing operation sequence when the supply control circuits of the first and third embodiments are combined.

[Explanation of symbols]

 2 X-ray fluoroscopy apparatus 3 Image processing unit 31 A / D converter 32 Frequency characteristic conversion circuit 33 Supply control circuit 33a Supply control circuit 34 Computing unit M Subject

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4C093 AA04 AA16 AA24 CA03 CA29 DA02 FD01 FF09 FF34 5B057 AA08 BA03 CA02 CA08 CA12 CA16 CB02 CB08 CB16 CC01 CE03 CE06 CH01 5C054 CA02 CC04 CE16 CF06 CF07 EA01 EB01 FC01 HA01

Claims (3)

[Claims] 1. A digital subtraction apparatus for obtaining a subtraction image of a predetermined imaging region of a subject, comprising: (a) irradiating the imaging region with X-rays and imaging an X-ray transmission image of the region; (B) the X
A data converting means for converting the X-ray transmission image into digital data; and (c) an image obtained by removing a frequency component equal to or higher than a predetermined threshold frequency from the X-ray transmission image converted into the digital data (hereinafter referred to as high frequency component removal). (D) subtracting the basic image and the high-frequency component-removed image to obtain a subtraction image of the imaged site, and (e) the high-frequency component-removed image. A digital subtraction apparatus comprising: a supply control unit that supplies a separately captured basic image as an X-ray transmission image in synchronization with the arithmetic unit. 2. The digital subtraction apparatus according to claim 1, wherein the supply control means generates the high-frequency component-removed image and the high-frequency component-removed image as a separately captured X-ray transmission image. A digital subtraction apparatus which supplies a basic image, which is an X-ray transmission image taken after a predetermined time, to the arithmetic means in synchronization with the calculation means. 3. The digital subtraction apparatus according to claim 1, wherein said supply control means removes said high frequency component removal image and said high frequency component removal image as a separately photographed X-ray transmission image. A digital subtraction apparatus which supplies a basic image which is an X-ray transmission image taken until an image is generated, in synchronization with the arithmetic means.