JPS5928939B2 - x-ray generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In an X-ray machine, powerful X-rays are emitted for a relatively short period of time, e.g., less than one-tenth of a second, in order to prevent blurring of the image due to the movement of human blood vessels in the case of cardiovascular images. Irradiation is often necessary.

When photographing the human skeleton, a longer time can be used if the patient is still.

The total incident energy required to create an image on a dry plate is approximately the same for short and long irradiations, so the shorter the time, the stronger the irradiation is required to create a high quality image on the plate.

A problem arises in that there is a limit to the irradiation intensity that can be provided by a typical rotating anode target in an X-ray tube due to overheating of the point on the target where the electron beam strikes.

This problem is compounded by the fact that to take high-resolution photographs, the target must emit x-rays from a relatively small spot, typically less than 10 square meters, which increases the temperature of the target.

These problems are alleviated by the present invention, which has an The radiation source or X-ray generator provides solutions and other features.

In one embodiment of the invention, the surface of the target is sloped relative to the x-ray exit window to increase the percentage of fluorescent x-rays generated by the target to the total spectrum of x-rays emitted by the target.

This promotes monochromaticity for the X-rays exiting through this window.

Cooling of the target is provided by a substrate that is thermally conductive and transparent to Xa.

-f! When using this generator for radiography as J, it is most desirable to provide a large spectral width for the spatial frequency characteristics of the radiation emitted by the target.

This is accomplished by spatially modulating the emitted X-rays using zone plates with a checkerboard pattern as shown in U.S. Pat. No. 3,748,470 or in the form of an off-axis Fresnel pattern. .

The x-ray tube includes a device for mounting thereon a zone filter or other spatial filter for modulating or streamlining the x-rays.

An x-ray tube with zone plates is positioned to direct the x-rays at the patient behind a standard plate commonly used in x-rays.

A coded picture of the internal structure of the object is obtained in terms of the coating provided by the zone plate.

The photograph on the X-ray plate is first decoded to give an image containing information that the technician can see to see its internal structure.

In the case of off-axis Fresnel pattern zone plates, photographic decoding or image reconstruction is facilitated by a relatively simple optical system using an off-axis aperture and a telescope.

Random pattern zone plates can also be used.

A halftone screen may also be placed between the zone plate and the object to spatially modulate the object hitting the incident beam to represent the object as a higher spatial frequency object that is more properly imaged within this zone plate system. is also provided.

1 and 2 show an apparatus 20 including a generator 22 of X-rays which is a detailed illustration of the present invention.

As shown in FIG. 2, generator 22 includes an x-ray tube 24 surrounded by a housing 26 and immersed in oil 28, which oil acts as an insulator from the high voltage power provided by power source 30.

The X-ray tube 24 has a base body 3 for creating an airtight area therein.
It has a metal base 34 and a glass envelope 32 which are sealed together.

A thin target 38 extends across the entire width of tube 24 and therefore has a width significantly greater than its depth.

The target 38 may be in the form of a thin foil or film of a heavy x-ray emitting element such as tungsten or gold, or such a film of a lighter x-ray emitting element such as cerium or molybdenum. It is deposited on a substrate 36 within the vacuum region of the x-ray tube 24.

Target 38 is known as a transmission target because it is thin enough to allow x-rays generated on one surface of the target to pass to the opposite surface.

Although utilized to support the substrate 36//i target 38, the present invention contemplates other support means such as a frame (not shown) mounted around the target 38 when it is a foil.

Use of this substrate 36 is preferred in that it assists in cooling the target 38.

Cathode 40 is adapted to be heated by filament 42 and has a large enough area to irradiate the entire surface of target 38.

cathode 40 (/'i) connected to cathode 40 and target 38 by power supply 30 connected thereto by wires 44 and 46;
The potential difference created between them releases electrons that move along nearly parallel paths.

A knob 47 connects to power supply 30 to adjust the voltage between wires 44 and 46 to select the energy of the x-rays.

The shield 48 protects the shield 5 from electrons from the cathode 40.
0 is positioned adjacent to the seal 50 between the envelope 32 and the metal base 34.

Substrate 36 holds target 38 and has a rigidity suitable to withstand atmospheric pressure acting against the vacuum within x-ray tube 24, while being essentially transparent to the x-rays emitted by target 38. It is preferably made of a light metal such as aluminum or beryllium.

Filament 42 is energized with current from filament power supply 52, which energizes prior to operation of generator 22 to heat cathode 40 prior to application of pulsed energy from power supply 30.

This energy pulse has a duration determined by the voltage of power supply 30 and the thickness and composition of the object 54 in FIG. 1 to be imaged by apparatus 20.

The X-rays emitted from the top surface of the target 38 are the target 3.
8 to the object 54.
It is thin, about 2 mils, and thick enough to stop incident electrons.

An X-ray transparent window 68 made of a material with a low atomic number, such as aluminum, is provided from the X-ray tube 24 to the object 54.
It is attached to one end of the housing 26 to allow the propagation of radiation to... and to retain the oil 28 within the maggot 26.

The use of target 38 and substrate 36 simplifies the mechanical design since the known rotating anode is not required.

Additionally, the thinness of the target 38, combined with the good thermal conductivity of the substrate 36, provides increased cooling effectiveness of the target 38 and higher power handling capability relative to other types of x-ray tubes.

The cooling capacity of the base body 36 can be increased by circulating a fluid, such as oil, along conduits 56 within the base body 36, as shown in FIGS.

FIG. 3 is a cross-sectional view of the base body 36 taken from 3--3 in FIG. 2 to show the conduit 56.

The base body 36 is constructed using conventional techniques by creating two disks, one of which is machined to form the conduit 56 of FIG. 3, and joining them by gluing, welding, or bolting.

The ends of the conduit 56 have a pair of passageways connected to the base 36 by a plug 60 having a pair of mating nipples 62.
A cable 5 connected to a pump 64 pumping oil from 6
Connected to 8.

As shown in FIG. 1, a zone plate 69 and a halftone screen 70, shown in detail in FIGS. 4 and 5, are located along the axis of the generator 22 and outside of it.

Screen 70 is positioned between zone plate 69 and object 54.

The position of the screen 70 is adjusted relative to the zone plate 69 in order to give the incident radiation a modified shape of the object 54, which is apparently divided into small areas similar to a mosaic with a relatively high spatial frequency spectrum. It is closer to the object 54 than the target object 54.

Such a spectrum effectively cooperates with zone plate 69 to provide a better image than the lower spatial frequency spectrum associated with object 54 would provide.

Zone plate 69, screen 70 and object 54
The modulated X-rays impinge on photographic plate 72 and provide a coded image similar to the hologram thereon.

As an example of the use of the device 20, it is convenient to consider that angiography is used for the examination of parts of a human being, in which case the object 54 (/''i) would be the part of the person to be examined.

In angiography, contrast agents such as iodine are used to better define the shadows created by tissues or blood vessels compared to the shadows of other human tissues, which have different absorbances for X-rays in the d-ray. is supplied to the patient for absorption.

In this case, cerium or its oxide, ceria, is used for the target 38 because its X-ray emission spectrum matches the absorption spectrum of iodine.

The fluorescence emission line of cerium (generated by electrons in the outer shell of the cerium atom falling into vacancies in the inner shell created by bombardment by electrons from the cathode 40) is the energy of the radiation to be absorbed (eV). occurs approximately at the peak of the iodine X-ray absorption curve with the well-known shape of iodine's X-ray absorption as a function of .

Thus, by using cerium as the target 38 and iodine, a well-resolved image of the patient is provided, the limitations of which are the monochromaticity of the radiation incident on the patient and the contrast medium placed in the patient. The choice of the energy or frequency of the incident radiation is equal to the energy or frequency at the peak of the absorption spectrum of .

FIG. 6 shows an embodiment of this invention, in which
The wire tube 24A is shown.

The X-ray tube 24A has a non-contact grid 74 in the form of a ring or cylinder whose axis coincides with the tube axis of the X-ray tube 24A.

The cathode 40 in FIG. 2 is here used as a grid 7 for uniformly irradiating the target layer 38A deposited on the substrate 36A.
4 has been modified as cathode 40A to provide a more easily directed electron emission path.

The diameter of grid 74 is approximately equal to the space between it and cathode 40A.

The use of grid 74 provides better control of beam modulation to provide sharper pulses since power supply 30 no longer needs to pulse the high voltage between cathode 40A and target 38A on and off.

A well-known circuit, shown as a grid pulser 76, is utilized to apply a potential difference between the cathode 40A and the grid 74 for modulation of the electron beam.

The X-ray tube 24A is placed within a generally lead .
An insulating layer of oil 9 between the glass envelope 98 of A
6 is placed.

This housing extends to the base of base body 36A to confine radiation emitted in the direction of zone plate 69.

Substrate 36A is sealed against envelope 98 and partially forms the base 100 of x-ray tube 24A.

The base 100 is used to seal the oil chamber 96,
The flange 102 is then provided outwardly relative to the housing 94 to form a bezel surrounding the zone plate 69.
l) Zone plate 6 with the help of nut 104 and bolt 106 pushing 108 towards base 10θ
9 can be installed.

Wires 44 and 46 (ri) connect power supply 30 to cathode 40A and base 10, similar to those used to connect power supply 30 in FIG.
0 respectively.

In FIG. 6, wire 46 is grounded so that base 100 and target 38A are in the ground position.

This allows the zone plate 69 to be installed and removed as required by the operator to examine various areas of the patient.

Since the potential difference provided by the power supply 30 is about 150KV, a specially designed transformer 110 with sufficient insulation between the primary and secondary windings to withstand 150KV converts the flyment power supply 52A to the flyment 42A. Used to connect.

The middle tap of the primary winding of transformer 110 is grounded, and the middle tap of the secondary winding connects to the high voltage on wire 44.

The surfaces of the tube 24A and the substrate 36A are inclined relative to the axis of the tube 24A.

The radiation emitted outward from the tube 24A is emitted from the surface of the targera 38A at a certain angle, and the angle is preferably about 80 to 85 degrees with respect to the normal to the surface.

The diametric end of the increasingly larger diameter of 38A is defined by the housing 94;
38A constitutes a window through which radiation emitted from the surface passes.

As shown in FIGS. 8 and 9, the spectrum of the radiation emitted from the surface of the Targera 38A changes depending on the observation angle of the radiation with respect to the surface from which the radiation is emitted.

As shown, the X-rays emitted at an angle of about 80 to 85 degrees to the normal π to the surface of the target 38A have a higher proportion of fluorescent X-ray lines in the total spectrum than the radiation seen from other angles. has.

The bremsstrahlung radiation generated within the target material 38A is also attenuated in the axial direction due to the large depth of the target material along the tube axis.

This further reduces the amount of braking radiation reaching the zone plate 69.

The observed radiation viewed in a direction generally parallel to the axis of tube 24A will therefore be of enhanced monochromatic nature, which is most advantageous for radiography as previously discussed.

Target 38A is a 20-40 micron thick layer of material consisting of a lower atomic number element such as cerium or molybdenum, which produces more pronounced emission lines than a higher atomic number element such as tungsten. It is.

As a result, X-rays that are softer and have a higher intensity than those obtained by the target 38 in FIG. 2, such as 34 KeV, which is generally used in angiography, are generated directly in response to the electron bombardment of the target 38A. Ru.

For example, if the molybdenum thickness is 20 microns, the emission line will be 17.5 KeV.

When irradiated with electrons of 35 to 40 KeV, the 95th factor or more of the total radiation is concentrated in the photon energy range of 14 to 20 KeV.

When a cerium layer of 40 microns is irradiated with 70 KeV electrons, 70 of the energy is in the range of 33 to 40 KeV when viewed at an angle of 80 degrees to the normal to the surface of the cerium layer.
generate a spectrum containing the

This emission spectrum of cerium corresponds to the region of maximum absorption of iodine, thus making iodine an ideal contrast agent for use with cerium X-ray sources.

This surface inclination is provided by the conical shape of the base body 36A and target layer 38A.

This inclined surface of target 38A is cathode 40A.
This has the advantage of increasing the area irradiated with electrons from the rays, thereby further increasing the intensity of the X-rays.

Returning to FIG. 1, apparatus 20 includes an optical system 116 that is utilized to reproduce an image from a coded photograph or hologram on film 72 onto a screen (or film) 118.

Optical system 116 includes a light source 120, which may be a laser that emits coherent light, and a condensing lens 122, which collects this light through an aperture 124 and enters a second lens 126, which collects this light through an aperture 124. Focus the light 12
Gather at 8.

Photographic plate 72 is developed and placed behind lens 126 such that the light rays exiting lens 126 pass through photographic plate 72 to focal point 128.

A telescope 130 consisting of a single-ended lens 132 and a lens 134
is disposed along an axis 136 that is at an angle to the axis of lens 126.

The telescope 130 sees the light refracted through the directional diaphragm 138 on the shaft 136 and images this light onto the screen 118 .

Optical system 116 is utilized to decode the image formed by zone plate 69 in the form of an off-axis Fresnel pattern.

A zone plate utilizing another modulation pattern is provided in the device 20.
The decoding or filtering methods of the above-mentioned US patents can be used if used in

The orientation of telescope 130 along angled axis 136 coincides with the off-axis focus of the off-axis Fresnel plate.

The light that is focused on the focal point 128 is blocked by the opaque portion of the fringes 138 and does not form any reproduced image on the screen 118.

As is apparent from FIG. 1, the use of an off-axis Fresnel pattern zone plate provides a coded image on photographic plate 72, which can be decoded with simple optical elements.

As shown in FIGS. 4 and 5, the zone plate 69 and halftone screen 70 can be formed by depositing a lead-containing material on the base.

In FIG. 4, the deposited material 140 is shown on the zone plate 69.
supported by a substrate 142 of the substrate 142, shown in FIG.
44 is supported by a base 146.

In FIG. 1, a photographic plate 72 is conveyed on a chain 148 on a rope 150 through a developing chamber 152 having well-known equipment for developing it and reducing the size of the plate 72 to increase resolution.

FIG. 7 shows another embodiment of the target 38A of FIG. 6, in which the length of the axial cone is shortened by bending its top inward along the axis; The base body and target are indicated by 36B and 38B, respectively.

In this embodiment, the surface of the target blade 38B is inclined with respect to the axis of the target blade 38B, as in FIG.

The monochromatic advantage is therefore the same.

This gradient provides improved monochromaticity regardless of whether the target 38B material is a heavy element such as gold or tungsten or a light element such as cerium or molybdenum.

Due to the strong fluorescence lines in the spectra of molybdenum and cerium, bombarding these low atomic number elements with electrons from cathode 40A in Figure 6 results in much greater monochromaticity than that obtained with gold or tungsten targets. It will be done.

It was found that the main part of the X-ray energy was generated in the emission line of the molybdenum and cerium targets.

Therefore, the x-ray tube 24A of FIG. 6 or a shortened version thereof of FIG. 7 provides the most suitable x-ray source for use with tracers such as iodine in the human body.

Good quality images are obtained with the apparatus 20 of FIG. 1 by uniformly illuminating the zone plate 69 with the X-rays of the generator 22.

One method of providing such uniform illumination is described in FIG. 6 for grid 74.

Other methods include using magnetic field focusing in conjunction with grid 74 or alone.

An example of a device for this purpose is shown in FIG. 2 and utilizes a magnet 154 that generates a magnetic field in the direction of the axis of the housing 26.

The magnet 154 is a coil power supply 15 driven by a timer 158.
6 includes a coil energized by a current from 6.

Timer 158 provides signals along line 160 that cause the coil current to vary periodically during the time that timer 158 signals power supply 30 to excite x-ray tube 24.

This periodic change in current in the coils of magnet 154 causes periodic expansion and contraction of the electron flux incident on target 38, which may result from insufficient control of the electron flux by the electrostatic field within x-ray tube 24 or from the cathode. tends to balance or neutralize the irregularities in electron flux caused by non-uniform emission of electrons.

Another example of a control device for electron irradiation of a target is magnets 162 and 164 in FIG.

Magnets 162 and 164 are arranged to orient their magnetic fields orthogonally to each other and in a plane perpendicular to the axis of x-ray tube 24A.

The currents for these magnets signal coil power supply 156A by periodically changing the magnetic field during the time that timer 158A signals grid pulser 76 to turn on the electron beam in tube 24A.

Coil power supply 156A provides varying currents to magnets 162 and 164 with a phase relationship between them suitable for magnetically deflecting the electron beam in a rask or helical scan.

This periodic deflection of the electron beam smoothes out irregularities in the electron flux and thereby provides a uniform X to zone plate 69.
Provides a uniform irradiation of 38A.

Figures 8 and 9 show the X-rays obtained from an X-ray target, such as target 38 in Figure 2 or target 38A in Figure 6, as a function of the angle of the radiation when viewed obliquely from a line normal to its surface. It is a graph showing the purity of the spectrum.

Figure 8 shows data obtained with a 20 micron thick layer target of molybdenum, and Figure 9 shows data obtained with a cerium 40 micron target.

Furthermore, shown in both figures are the yields of α-line radiation and bremsstrahlung radiation.

The purity curve is the yield measured at the alpha line divided by the total yield, which is the sum of the bremsstrahlung radiation and the alpha line radiation, and is expressed in units.

The X-ray yield shown in both figures is the result of the collision of one electron on the target (with the energy shown in the small circle in the lower left corner of figures 8 and 9), resulting in a solid angle of 1 steradian. radiated (at a given output angle) 10”-4
X-ray energy in units of KeV is shown.

The Kα yield and the bremsstrahlung radiation yield are expressed in units of 1O-4Ke/steradian/electron.

The purity curve has a peak in the range of about 80 to 85 degrees, and as mentioned in Figures 6 and 7, this peak effect is one of the reasons why the surface of the target 38 is tilted with respect to the axis of the X-ray tube. be.

This purity curve is thus a measure of the monochromaticity of the emitted radiation.

The zone plate 69 of FIG. 1 with an off-axis Fresnel pattern utilizes an average of about 50 line spaces per inch.

When halftone screen 10 of FIG. 1 is placed intermediate zone plate 69 and photographic plate 72, the screen has a density of 10 lines per inch.

In order to provide the tone screen with a line space density suitable for high quality images, the line density of this screen is determined by adding the average space density of the zone plate to the relative space between the zone plate 69, the screen 70 and the photographic plate γ2. This factor is obtained by multiplying the distance from zone plate 69 to plate 72 by a factor related to zone plate 69 and screen 70.
divided by the distance between.

[Brief explanation of the drawing]

1 is an X-ray imaging device suitable for use in the wide-mouth generator of the present invention, and FIG. 2 is a reference diagram for explaining the invention in detail.
FIG. 3 shows a fluid-cooled substrate for the target of FIG.
4 shows a Fresnel zone plate used in the generator shown in FIG. 2, FIG. 5 shows a halftone screen used in the generator shown in FIG. 2, and FIG. 6 shows an embodiment of the present invention. FIG. 7 is a diagram showing another example, and FIGS. 8 and 9 are diagrams showing the angle dependence of the radiation yield and purity of a target made of molybdenum and cerium. 22...X-ray generator, 24...X-ray tube, 26...housing, 28...oil,
30...Power supply, 32...Envelope, 38...Target, 40...Cathode, 42...Filament, 52...・
・Filament power supply, 68... Window, 69...
...Zone plate, TO...Halftone screen, 72...Photograph board.

Claims (1)

[Claims] 1. A transmission type target having a width sufficiently larger than its thickness, and an X from the target at least partially arising from a second surface opposite to the first surface of the target.
an apparatus for irradiating a first surface of the target configured to uniformly irradiate the first surface of the target with electrons having sufficient energy to excite line radiation; and a second surface of the target. an x-ray transparent substrate disposed adjacent to supporting the target in spaced relation to the irradiation device; and an x-ray opaque end of the housing. a transparent window, and the surface of the window and the second surface of the target are arranged at an angle of about 80 degrees to 85 degrees, so that the second surface of the target The housing blocks the radiated X-rays outside the range of about 80 degrees to 85 degrees with respect to the normal, and allows the radiated X-rays outside the range to pass through the window, so that the entire spectrum of the radiated X-rays is An X-ray generator characterized by increasing the proportion of optical X-rays.