JPS6347393B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an X-ray imaging apparatus suitable for, for example, medical diagnosis. [Technical Background and Problems of the Invention] In X-ray photography using X-ray photography devices that are in practical use today, the resolution and contrast of reproduced images are often impaired by scattered X-rays generated from within the subject. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 53-7190, the X-ray generator is of an electron beam scanning type and the X-ray focal point is moved, and the X-ray beam is placed between the X-ray generator and the subject.
An X-ray photographing apparatus has been proposed in which a slit plate having a slit for transmitting radiation is arranged, an X-ray image detector is placed behind the slit plate, and an X-ray image is reproduced. However, since the device disclosed in the same publication uses an X-ray generator that uses a fixed target, it is difficult to obtain a sufficient amount of X-rays, and the X-ray detector is discontinuous. There are several problems that need to be improved, such as the difficulty in obtaining high resolution. Furthermore, US Pat. No. 4,179,100 states:
An apparatus has been disclosed in which an X-ray beam that has passed through a slit in a slit plate is passed through an object, and then detected by a scintillator such as a fluorescent plate or an X-ray image intensifier (hereinafter referred to as X-ray II) to reproduce an image. ing. However, since this method involves mechanically moving the subject, the slit plate, or the X-ray generator itself, high-speed, short-term imaging is still difficult. Furthermore, there is blurring and noise due to Bering glare, that is, the wraparound of scattered light, and undesired floating electron emission within the X-ray II, making it difficult to obtain sufficiently satisfactory resolution and contrast characteristics. [Purpose of the invention] This invention solves the above-mentioned problems, enables high-speed and short-time photography, and reduces scattering X within the subject.
An object of the present invention is to provide an X-ray imaging apparatus that can obtain excellent resolution and contrast characteristics by suppressing rays and the like. [Summary of the Invention] The present invention relates to an X-ray system which has a rotating cylindrical target and is configured such that an electron beam is electrically deflected and scanned parallel to the axis of the target so that the X-ray focal point is moved at a predetermined speed. a slit plate having a slit for transmitting X-rays arranged at a predetermined distance from the X-ray generator and elongated in a direction perpendicular to the moving direction of the X-ray focal point; an X-ray image detector that converts an X-ray image by X-rays modulated by
A signal processing device extracts a signal corresponding to the position on the X-ray image detector where the slit plate is projected from the focal position of the X-ray generator from among the electrical signals obtained by the ray image detector; X that reproduces the image signal into an image corresponding to an X-ray image and displays or records it.
This is an X-ray imaging apparatus including a ray image reproduction device. As a result, X-ray images with excellent resolution and contrast characteristics can be obtained at high speed. [Embodiments of the Invention] Examples of the invention will be described below. Note that the same parts are represented by the same symbols. An X-ray imaging apparatus according to a preferred embodiment of the present invention includes:
As shown in FIGS. 1 and 2, the X-ray generator 21
A collimator or slit plate 23 having elongated X-ray transmitting slits 22 arranged at predetermined intervals, an X-ray II 25 arranged behind the subject 24, and an output screen 26 for the X-ray II 25. an image pickup tube 28 that images an optical image of the camera through an optical lens 27, and a signal processing device 30 that processes the electrical signals obtained by the image pickup tube 28 and sends a reproduced image signal to a display device 29 or a recording device (not shown). ing. The X-ray II 25 and the imaging tube 28 constitute an X-ray image detector that converts an X-ray image into an electrical signal. The X-ray generator 21 includes a cylindrical target 32 provided in an enlarged part of a vacuum container 31 and a drive motor 33.
The electron gun 34 can be rotated on the other side.
is built in, and the electron beam generated therefrom can be scanned over a cylindrical target 32 parallel to its axis by means of an electromagnetic deflection coil 35.
An elongated X-ray emission window 36 is provided at a position corresponding to the cylindrical target 32 of the vacuum container 31, and the X-ray beam from the moving X-ray focal point F is directed to the slit plate 2.
It is designed to emit in the direction of 3. This X-ray generator 21 is energized by a power source 37 via a high-voltage cable 38, and also provides deflection power to a deflection coil 35, and constantly receives information on the position of the X-ray focal point F determined by the deflected and scanned electron beam. The signal processing device 30 is provided with an electrical signal. The slit plate 23 is made of a thin plate of heavy metal such as lead, and has an elongated slit 22 formed therein, the longitudinal direction of which is arranged in a direction perpendicular to the moving direction of the X-ray focal point F. The X-ray II 25 has an input screen large enough to cover the area to be imaged of the subject, and has a slit 22 as shown by P in the figure.
The input screen receives an X-ray image resulting from the scanning of the X-ray beam that has passed through the input screen, and a corresponding intensified optical image is displayed on the output screen 26. The image pickup tube 28 is suitably one having a photoconductive target, and a video signal is sent from the signal electrode to the signal processing device 30. The image pickup tube 28 is energized by its power source 39, and its video signal reading position is specified by the signal processing device 30. The signal processing device 30 receives a signal indicating the X-ray focal position from the X-ray generator 21 , a video signal from the image pickup tube 28, and a signal indicating its reading position, and operates a spatial filter to be described later to detect the scattering generated from the object. Electrically removes blurring components caused by X-rays, etc.
A signal corresponding to the line image is generated and displayed on the cathode ray tube display device 29. Incidentally, if necessary, image information is given to a recording device (not shown) and recorded. In particular, as in the embodiment described later, this signal processing device has a built-in function for instructing the imaging tube 28 to scan the scanning area of the reading electron beam in accordance with the position of the X-ray focal point F. By means of this device, the cylindrical target 32 of the X-ray generator 21 is rotated and the X-ray focal point F is moved parallel to the axis above it. To give a specific example where the subject is a human chest with a width of approximately 40 cm, the moving distance S of the X-ray focal point F on the rotating cylindrical target 32 of the X-ray generator 21 is 30 cm, and the electron beam focal point on the target is is an elliptical shape with a minor axis of 0.5 mm and a major axis of 2.5 mm, and the effective X-ray focal point F seen from the slit direction is applied obliquely to the target surface so that it is a circle of 0.5 mm. The width G of the slit 22 is 0.34 mm, the slit length is 17 cm,
The effective diameter of the input screen of the X-ray II 25 is approximately 57
cm, the distance L1 between the focal trajectory of the X-ray generator 21 and the slit plate is approximately 65 cm, the distance L2 between the slit plate and the X-ray II is approximately 87 cm, and the number of horizontal scanning lines of the image pickup tube 28 and display device is approximately 1024. It is. Thus the X-ray focus F
One image signal of the subject is obtained by one electrical movement scan. Note that the X-ray focal point F of the X-ray generator 21 is not limited to the above-mentioned example of dimensions; the dimensions of the electron beam on the target are 0.5 mm (minor axis) x 12.5 mm (long axis), and the dimensions are elliptical, and It is also possible to set the effective X-ray focal point as an ellipse of 0.5 mm (minor axis) x 2.5 mm (long axis), and to make the direction of the short axis coincide with the longitudinal direction of the slit. Thereby, even higher output X-rays can be obtained. By the way, such an image signal is a signal mixed with blur and noise components caused by scattered X-rays generated within the object, Bering glare (scattered light wraparound in X-ray II), and undesired stray electron emission. However, good resolution and contrast cannot be obtained. Therefore, as shown in FIG. 3a, b, c, and d, an electrical spatial filter is applied to remove the blurred components. That is, FIG. 3a shows the projection X when the X-ray beam is projected onto an arbitrary position V0 in the imaging area P.
A line image Q is shown. At this time, the video signal in the vertical scanning direction of the signal reading electron beam of the image pickup tube 28 has a distribution as shown in FIG. 3b. This means that blurred components exist as bases on both sides of the desired image signal due to scattered X-rays and the like. A spatial filter having characteristics as shown in FIG. 3c is applied to such a signal at a position corresponding to the position of the X-ray focal point F. This is possible through digital arithmetic processing within the signal processing device. As a result, as shown in FIG. 3d, an image signal is obtained in which the blur component in the moving direction of the X-ray focal point F is almost completely removed. This process is sequentially performed over the entire imaging area, and an X-ray image corresponding to one movement scan of the X-ray focal point F is reconstructed and displayed on the display device. The filter characteristics shown in FIG. 3c can be easily set by storing in advance in the signal processing device the appearance of scattered X-rays and the blurring of the system, which are predicted depending on the nature of the subject and the imaging conditions. Note that the scanning time for one movement of the X-ray focal point F can be, for example, 0.5 seconds or less, and the screen of one frame can be scanned at a fast speed (for example, 0.1 seconds or less).
The image may be reproduced by scanning the image twice or more at a speed of 30cm/sec/30cm) and calculating the scan rate. In this way, high-speed, short-time X-ray imaging is possible, and images with excellent resolution and contrast can be reproduced. In addition, since the X-ray generator 21 is configured to rotate the cylindrical target 32 and electrically deflect and scan the electron beam e, a large amount of X-rays can be obtained and high-speed, short-time imaging with a good S/N ratio can be performed. is possible. In the above embodiment, the image signal is obtained by repeatedly scanning the signal reading electron beam of the image pickup tube 28 over the entire surface of the screen in the vertical direction V, but this is not limited to the position of the X-ray focal point at a certain time. It is also possible to read and scan only the position corresponding to and its vicinity, and move this partial scanning area in accordance with the movement of the X-ray focal point. This is illustrated by FIGS. 4a-d. Considering the moment when the X-ray focal point is at a position corresponding to position V1 on the screen as shown in Figure 4a, this X-ray beam scans the projected area Q and its vicinity horizontally and vertically, and An image signal as shown in FIG. Next, when the X-ray focus moves to position V2, Fig. 4b
The vertical scanning area of the reading electron beam is also moved correspondingly as shown in FIG. Similarly, as shown in FIGS. 4c and 4d, the signals are read by moving one after another, and the signals are processed while being applied with a spatial filter to display an image. Note that the symbol H in the figure represents the scanning line of the reading electron beam. That is, an elongated X-ray beam region Q of a predetermined width that reaches the X-ray image detector from the position of the X-ray focal point through the slit and the subject at a certain moment during the movement of the X-ray focal point;
Then, X-ray image signals are read in a plurality of rows adjacent to each other in the width direction of the X-ray beam region along the longitudinal direction corresponding to the longitudinal direction of the slit and close to each other in the width direction. Then, from the X-ray image signals of the X-ray beam region Q and its widthwise outer adjacent region, arithmetic processing including a spatial filter function that subtracts a component corresponding to the signal component of this widthwise outer adjacent region is performed to generate a noise component. An image signal with the imaged part of the subject reduced is obtained, and the image of the photographed part of the subject is reproduced, displayed, or recorded. Note that in signal processing to apply this spatial filter, the X-ray image signals of the X-ray beam region Q read by the X-ray image detector and the adjacent region outside in the width direction are temporarily stored in the signal processing device, and later this signal is stored in the signal processing device. Filter processing may be performed based on the signal. In this way, the elongated X-ray beam region Q of a predetermined width that reaches the X-ray image detector from the X-ray focal position through the slit and the object at a certain moment, and the outer adjacent region in the width direction of this X-ray beam region, X-ray image signals are read over multiple rows along the longitudinal direction corresponding to the longitudinal direction of the slit and close to each other in the width direction, and arithmetic processing including a spatial filter function is performed to obtain an image signal with noise components reduced. Since the image of the photographed part of the subject is reproduced, displayed, or recorded, the information contained in the X-ray beam that has passed through the subject can be utilized for image reproduction processing with high efficiency. Therefore, it is possible to analyze the intensity and distribution of noise components caused by X-rays scattered by the subject, and include the suspicious signals in the removal calculation, thereby improving the fidelity of the reproduction of the X-ray image of the subject. In addition, since the reading beam scan only needs to be moved in accordance with the movement of the X-ray focal point while scanning a small portion of the vertical scanning area, the reading scanning must be performed at a sufficiently high speed compared to the moving speed of the X-ray focal point. This makes it possible to further shorten the shooting time. Furthermore, since the amount of information in the X-ray image signal to be read is increased, an X-ray image with excellent S/N ratio, contrast, and resolution can be reproduced. Furthermore, the X-ray image detector is not limited to a system that combines an X-ray II and an image pickup tube as in the above embodiment, but also an X-ray II that has a built-in output structure that directly converts an output image into an electrical signal. Alternatively, a configuration may be used in which a phosphor screen that stores energy corresponding to an X-ray image is used, and the image information on this screen is excited by a laser or the like, read, and converted into an electrical signal. . Next, an embodiment of the X-ray generator 21 will be described. The embodiment shown in FIGS. 5 and 6 has the following structure. The vacuum container 31 is made of metal and has a shape similar to a flattened television cathode ray tube, and includes an enlarged part 41 in which a cylindrical target 32 is housed;
It has a glass container part 43 in which an electron emitting cathode 42 constituting an electron gun is housed, and a cone part 44, an airtight joint part 45, and a ceramic cylindrical part 4 are arranged between them.
6, a bellows part 47 and a cylindrical accelerating electrode part 48, which constitutes a part of the electron gun 34 (shown in FIG. 1, hereinafter the same), are successively hermetically joined. The airtight joint 45 can be assembled or disassembled if necessary.
To facilitate reassembly, they are removably connected by bolts 50 through electrically conductive gas-tight packings 49. An electromagnetic deflection coil 35 for deflecting the electron beam is arranged outside the ceramic cylindrical portion 46. A conductive thin film such as carbon is deposited on the inner surface of the ceramic cylinder to minimize eddy current losses due to the deflection magnetic field. Bellows part 47
is provided to enable fine adjustment of the center axis of the electron gun 34 section and the axis of the enlarged section 41. An electromagnetic focusing coil 51 for electron beam focusing is fitted around the outer periphery of the accelerating electrode section 48 . Both coil parts are covered by a cylindrical cover 52 and mechanically connected. Further, these metal container parts are used at ground potential. Around the glass container part 43, an insulating oil container 53 is fixed to a flange 54 of the vacuum container with bolts 55, and an insulating cylinder is provided at the end thereof to connect a high voltage cable (corresponding to the reference numeral 38 shown in FIG. 1). A receptacle 56 made of aluminum is inserted, and a lead wire of the cathode 42 is connected to its connection terminal 57. Note that the cathode 42 is operated by being given a negative high potential with respect to the vacuum vessel section which is at ground potential. The container 53 is filled with insulating oil and connected to an external cooler (not shown) through a pipe 58 so that the oil can be circulated. An ion pump 59 is connected to a part of the cone portion of the vacuum container, and an exhaust pipe 61 connected to an exhaust device 60 shown by a dotted line is sealed. The cylindrical target 32 is made of a cylinder made of a heavy metal with a high melting point such as tungsten W, and is rotatably supported at both ends within the enlarged portion 41 of the vacuum vessel 31 by support shafts 62, 63 and bearings 64. One upper bearing 64 is placed inside a vacuum-tight lid 65 and a bolted flange 66, and is supported by two ball bearings 67. The other lower bearing 68 has a magnetic seal 69 as shown in FIG.
and is supported by a ball bearing 70 on the outside thereof. The magnetic seal 69 has a permanent magnet 71, magnetic poles 72 and 73 made of ferromagnetic material, and a ferromagnetic cylinder 74 fixed to the outer periphery of the support shaft.
A magnetic fluid is interposed in a minute gap between 73 and cylinder 74, thereby maintaining vacuum tightness. A ball bearing 70 is integrally provided outside the magnetic seal 69, that is, on the atmosphere side. As the ball bearing 70, an angular contact type bearing is used to mechanically support the heavy cylindrical target 32. In this way, the inner magnetic seal 69 maintains vacuum tightness, and the atmosphere-side ball bearing 70 supports the weight of the cylindrical target 32. These bearings are forcibly cooled from the outside by a cooling pipe 75, and are mechanically fixed to the vacuum container 31 by a flange 76. The bearing part of the support shaft 63 is hollow, and a pipe 77 for refrigerant circulation is inserted inside the bearing part, and the refrigerant is introduced into the pipe so as to circulate from the outside to the inside as shown by the arrow.
It is discharged. This prevents the magnetic seal 69 from overheating. A drive motor 33 is connected to the support shaft via a gear 78 and is driven to rotate. The motor 33 has a support frame 79 and a fixed flange 8.
0 mechanically fixed to the vacuum container 31. Note that the reference numeral 82 in the figure represents a refrigerant jacket. An elongated X-ray emission window 36 is provided in the vacuum vessel 31 at a position close to the cylindrical target 32, and is formed of a beryllium plate and held airtight by a window frame 81. During operation, the cylindrical target 32 is rotated by a drive motor at a predetermined speed and receives the impact of the deflected and scanned electron beam e.
emit a line. The electron beam e is directed towards a cylindrical target 3.
It is applied at a position slightly away from the central axis O of 2,
Create an X-ray focal point F. This is because, as shown in Figure 8, when an electron beam e with an elliptical cross section hits the target, it hits a slope such that the effective X-ray focal point F as seen from the X-ray emission window is almost a perfect circle. is set to As a result, a small X-ray focus F can be obtained with a sufficiently large amount of electron beam. Since such an X-ray generator 21 emits X-rays by scanning a cylindrical target 32 with an electron beam e parallel to the axis while rotating the target, it is possible to obtain a sufficiently large amount of X-rays. , and the X-ray focal point F can be moved at a desired high speed. Furthermore, by using a bearing that is an integrated combination of an internal magnetic seal 69 and an external ball bearing 70 as a bearing that supports this cylindrical target 32, it is possible to maintain sufficient vacuum tightness and to support a large weight target. It can be supported stably and rotated at high speed. magnetic seal 69
It is possible to maintain the pressure inside the vacuum vessel to a pressure of 1×10 ^-7 torr or less, and the ball bearing 70
Since it can be used in the atmosphere, it can be used while replenishing lubricant and can withstand long-term high-speed rotation of heavy targets. In this embodiment, the heat generated in the target is mainly radiated to the outside through heat radiation to the wall of the vacuum chamber. In order to improve heat dissipation, the inner wall of the vacuum container is blackened.
Alternatively, it may be configured to forcibly cool by attaching heat dissipation fins or cooling pipes to the outside. As shown in FIG. 5, such an X-ray generator 21 has an integrated bearing 68 consisting of a magnetic seal and a ball bearing on the lower side, and a ball bearing 64 placed in a vacuum inside an airtight lid 65 on the upper side. Suitable for installation and use. In other words, the lower bearing maintains vacuum tightness with a magnetic seal, supports the weight of the target with a ball bearing placed in the atmosphere, and the upper bearing only needs to prevent the swing of the support shaft, so it is not a conventional rotating anode type. A bearing similar to that used in an X-ray tube is sufficient. As a result, a relatively heavy cylindrical target can be rotated at high speed, and the X-ray focal point can be moved and scanned at a desired speed, making it possible to perform high-speed X-ray imaging as in the embodiments described above. The X-ray generator 21 of the embodiment shown in FIG. 9 has spacers 91 stacked vertically around a support shaft 63 as a cylindrical target 32, the outer periphery of which is coated with a heavy metal target layer 32a. As a result, a target with a large diameter can be obtained without substantially increasing the weight of the cylindrical target 32. Part of the heat from the target layer is transmitted to the support shaft 63 by the spacer 91, and other heat is transmitted to the wall of the vacuum vessel by radiation, thereby achieving a balance between them. Both sides of the support shaft 63 use bearings 68, which are a combination of a magnetic seal 69 and a ball bearing 70 similar to that shown in FIG. The support shaft 63 is formed of a hollow body and is separated into two sides at the center by a partition plate 92, through which pipes 77, 77 for refrigerant circulation are inserted, and the refrigerant is circulated as shown by the arrows. The drive motor 33 is connected to one end of the support shaft 63 via a gear 78. The refrigerant introduced from the outside first cools down the magnetic seal 69, then directly enters the target, absorbs heat, and passes through the pipe 77 to the jacket 82.
is discharged to the outside. The magnetic seal 69 is always kept at a low temperature by this coolant, and vacuum tightness is reliably maintained. Moreover, since this cooling mechanism also serves to cool the cylindrical target 32, the structure can be simplified. The flanges of both bearings 68, 68 are fitted into the opening of the vacuum vessel 31, and are hermetically sealed and fixed by arc welding parts 85, 85. The electron gun 34 of this embodiment includes a plurality of cylindrical electrodes 9 forming an electrostatic focusing lens in front of the cathode 42.
3, 94, and an accelerating electrode 95 are arranged inside a ceramic insulating container 96. Note that the symbols 97, 97... in the figure
... represents a corona discharge prevention ring. The X-ray generator 21 of this embodiment has the same functions as those of the previous embodiment, in particular can reduce the weight of the target, and also has a magnetic seal 69 and a ball bearing 70 on the outside thereof. Since it is used in both directions, it can be installed either vertically or horizontally, and vacuum-tightness and mechanical retention are stable regardless of the installation position or direction. [Effects of the Invention] As described above, according to the present invention, it is possible to realize an X-ray imaging apparatus that has good resolution and contrast characteristics, is capable of high-speed imaging, and is highly reliable.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a configuration diagram thereof, and Fig. 3 a, b, c, d.
are characteristic diagrams representing the symbol processing, Figure 4a,
b, c, and d are conceptual diagrams and characteristic diagrams showing other examples of signal reading processing, FIG. 5 is a vertical cross-sectional view showing an example of the X-ray generator of the present invention, and FIG. 6 is a top view of the essential parts cut away. , FIG. 7 is an enlarged sectional view of the main part, FIG. 8 is a conceptual diagram of the main part, and FIG. 9 is a longitudinal sectional view showing another example of the X-ray generator of the present invention. 21 ...X-ray generator, 22...slit, 23
...Slit plate, 32...Cylindrical target, 3
4... Electron gun, F... X-ray focus, e... Electron beam, 24... Subject, 25... X-ray II, 28...
Image pickup tube, 30...signal processing device, 31...vacuum container, 63...support shaft, 68...bearing, 69...magnetic seal, 70...ball bearing.

Claims (1)

[Scope of Claims] 1. An X-ray generator configured such that an X-ray focal point is moved; A fixed slit plate having an elongated slit for X-ray transmission with a predetermined width, and an X-ray image generated by an X-ray beam that is modulated by passing through the slit of this slit plate and a subject placed behind the slit plate. An X-ray image detector that converts into a signal, and from among the electrical signals obtained by this X-ray image detector, a position corresponding to the position on the X-ray image detector where the slit is projected from the focal position of the X-ray generator. A signal processing device that extracts the signal and performs arithmetic processing to obtain an image signal of the imaged part of the subject;
an X-ray image reproducing device that reproduces and displays or records an image corresponding to the X-ray image; An elongated X-ray beam region having a predetermined width that has reached the detector through the slit and the subject, and an outer adjacent region in the width direction of the X-ray beam region are both arranged along the longitudinal direction and close to each other in the width direction. The signal processing device is configured to read X-ray image signals over a plurality of columns, and the signal processing device extracts a component corresponding to a signal component of the outer adjacent region from the X-ray image signals of the X-ray beam region and its outer adjacent region. An X-ray imaging apparatus characterized by having a configuration in which an image signal with reduced noise components is obtained by performing arithmetic processing including a spatial filter function for subtraction. 2. The X-ray imaging apparatus according to claim 1, wherein the X-ray image detector includes an X-ray image intensifier and an imaging device that converts an output image thereof into an electrical signal. 3. The X-ray image detector is equipped with a photoconductive image pickup tube, and scans its reading electron beam at a speed sufficiently faster than the X-ray focus movement speed of the X-ray generator, and scans only the position corresponding to the X-ray beam and its vicinity. 2. The X-ray imaging apparatus according to claim 1, wherein the X-ray photographing apparatus is configured to move the scanning area in accordance with the movement of the X-ray focal point while partially scanning. 4. In the X-ray generator, a cylindrical target is rotatably held in a vacuum container by a support shaft, and at least one of the support shafts is kept airtight by a magnetic seal and is supported by a ball bearing on the outside. An X-ray imaging apparatus according to claim 1. 5. The X-ray imaging apparatus according to claim 4, wherein the magnetic seal has a structure in which it is forcibly cooled by a refrigerant circulated within the support shaft. 6. The X-ray imaging apparatus according to claim 1, wherein the X-ray generator is configured to circulate a coolant within the support shaft of the cylindrical target to dissipate heat from the cylindrical target to the outside. 7. The X-ray generator according to claim 5 or 6, wherein the X-ray generator has a path in which the refrigerant that cools the magnetic seal is guided into the support shaft of the cylindrical target portion and then discharged to the outside. Photography equipment.