GB2133611A - Radiographic magnifying device - Google Patents

Abstract

A radiographic magnifying device (4) suitable for use in radiation diagnostic apparatus comprises a cylindrical vacuum envelope (21), having at one end a photoelectric layer (7) and at the other a phosphor layer (8). A scintillator (5) is optically coupled by an optical device (6) such as a fiber plate, to photoelectric layer (7) and first and second focussing coils (11, 12) are arranged around the envelope (21) and means (9, 10) for generating an electric field to accelerate electrons emitted from the photoelectric layer (7) towards phosphor layer (8) are provided. A deflection device (14), preferably comprising two pairs of magnetic deflection coils, capable of deflecting electrons passing through the envelope is disposed about the envelope. The radiographic magnifying device produces a visible image as a result of the radiation impinging on scintillator (5) causing a light image to impinge on photoelectric layer (7) which emits electrons which impinging on phosphor layer (8) produce a visible image the magnification of which is determined by the currents in focussing coils (11, 12). A diagnostic apparatus can be formed using a combination of the radiographic magnifying device, a radiation source, a television camera and a display means, such as a picture monitor. <IMAGE>

Description

SPECIFICATION Radiographic Magnifying Device The present invention relates to a radiographic magnifying device, in particular a radiographic magnifier usuable for obtaining magnified visible images by means of radiography, and to a diagnostic apparatus containing such a device.

There are a number of X-ray radiographic devices which satisfy the physician's demands to observe siteswithin an organ, such asa human organ,without destruction of the organ during diagnosis, and these devices have wide use at present. Furthermore, radiation CT (computed tomography) techniques are also widely used to obtain three dimensional radiographic images of sites within organs.

It is also possible using optical microscopes to observe samples taken from the body. Samples of a human organ taken from the body are fixed by 10% formalin, sliced into sheets, dyed by hematoxylineosin, and, using an optical microscope, the magnified organ sample can be observed at the cell level.

An optical microscope can be used only for a specimen through which visible radiation may pene trate, andthusthe specimen should be sliced intothin sheets.

Micro-angiography can be carried out on the extracted specimen.

There is however a need for means by which a magnified image ofan organ in situ may be observed without destruction of the organ by magnifying the primary image obtained by irradiating the organ containing contrast medium in its blood vessels.

An objective ofthe present invention isto provide a radiographic magnifying device which can provide variable magnification of an obtained primary radiographic image.

According to one aspect of the present invention there is provided a radiographic magnifying device comprising: a cylindrical vacuum envelope having a photoelectric layer formed on a surface at one end of said envelope, a phospher layer formed on a surface at the other end of said envelope, a scintillator to convert radiation impinging thereon into a corres ponding optical image, and an optical device to direct the optical image from said scintillator on to said photoelectric layer; first and second focusing coils arranged around said cylindrical vacuum envelope and coaxial therewith; means for generating an electric field to accelerate electrons emitted from said photoelectric layer toward said phosphor layer; a deflection device to deflect electrons emitted from said photoelectric layer; and a focussing current generating means to feed currents to said first and second focussing coils in accordance with a pre determined ratio thereby to determine the magnifica tion factor of the images formed on said phosphor layer.

An arbitrary portion of the primary radiographic image can be formed in visible form on the phosphor layer of the radiographic magnifier at a magnification factor which can be modified in accordance with the predetermined ratio of the currents in the focussing coils.

It will be realised that, although it is preferred, the cylindrical vacuum envelope need not be of perfect circular cross section and accordingly the term "cylindrical vacuum envelope" is used herein to mean a vacuum envelope of uniform cross section, e.g. circular, having end faces parallel to each other and perpendicular to the envelope axis.

In the radiographic magnifying device ofthe invention, the optical device which serves to direct the optical image emitted by the scintillator onto the photoelectric layer is conveniently a fibre plate, preferably a fibre optics plate having fibres arranged at a spacing between centres of about 4.5 ,um with the open ends of each fibre directed towards the surfaces of the scintillator and the photoelectric layer.

The deflection device in the rddiographic magnifying device of the present invention preferably comprises a set of two paired electromagnetic deflection coils disposed about the cylindrical vacuum envelope, preferably to create two mutually perpendicular independantly variable magnetic fields perpendicular to the cylindrical axis of the envelope, to deflect electrons passing through the envelope and so select the portion of the (magnified) image which is displayed on the phosphor layer.

According to a further aspect of the present invention there is provided a diagnostic apparatus comprising: a radiation beam source; a radiographic magnifying device in accordance with the present invention, the scintillator thereof being arranged to receive a radiation beam emerging from an object interposed between said radiation beam source and said radiographic magnifying device; a television camera arranged to scan a part or all of the optical image formed on the phosphor layer of said radiographic magnifying device; and display means to display the output of said camera.

In the apparatus of the invention, the scintillator is arranged to receive the radiation beam penetrating through the object upon which the radiation beam issued from the radiation beam source is incident.

The television camera is suitably arranged such that an optical image formed on the phosphor layer ofthe radiographic magnifying device is projected into the photoelectric layer of the television camera and such thatthe entire area or an arbitrary portion of an image formed on the photoelectric layer of the television camera tube can be scanned. The display means conveniently comprises a picture monitor capable of reproducing the video signals from the television camera.

Thus a selected portion of an optical image formed on the phosphor layer of the radiographic magnifier can be projected onto the photoelectric layer of the television camera at a magnification factor which can be modified.

The apparatus of the present invention utilizing penetrating X-rays allows for image formation where different organs have different X-ray penetration coefficients even if the optical contrast is not so high between those organs. Magnified X-ray images can thus be observed by using the radiographic magnify ing device according to the present invention when barium is injected into the internal organs, e.g. digestive organs, or when iodine contrast medium is injected into the blood vessels.

When the X-ray penetration coefficients forthe various digestive organs and blood vessels are different (e.g. in the bone marrow), or when the X-ray penetration coefficients can be changed by injection of contrast medium, magnified images ofthese organs can be monitored using the apparatus of the invention.

A preferred embodiment ofthe radiographic magnifying device and of the diagnostic apparatus of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram showing an embodiment of the radiographic magnifying device in accordance with the present invention; Figure 2 is a graph showing the dependence of the magnification factor on the currents through the first and second focussing coils ofthe radiographic magnifying device of Figure 1; and Figure 3 is a block diagram showing a diagnostic apparatus in accordance with the present invention.

Referring to Figure 1, a glass vacuum envelope 21 constituting the main body of a radiographic magnifier 4 is a cylindrical envelope with a diameter of 50 mm and a length of 300 mm. One end of said glass vacuum envelope is formed by optical fiber plate 6, with scintillator 5 formed on its outer face and photoelectric layer7 formed on its inner face. On the other end of said glass vacuum envelope is formed phospher layer 8.

In use, the radiographic magnifying device of the invention will generally be operated in conjunction with a shielded X-ray source. The "optical" axis of radiation from the X-ray source through the opening in the shielding plate is herein termed the "axial line".

Scintillator Sin the diagnostic apparatus ofthe inven- tion will be disposed such that the axial line is perpendicularto and passes through the centre of scintillator 5. Scintillator 5 comprises an active layer made of Ag-doped lead sulfide containing 7.5 mg of PbS:Ag/100 mm2 of active area.

The optical fiber plate 6 which forms an end of the vacuum envelope is an optical device which directs light from scintillator 5 onto photoelectric layer7. The optical fibers making up the optical fiber plate 6 are arranged at a pitch of 4.5 ,um.

The photoelectric layer 7 is a highly sensitive thin layer made of antimony, potassium, sodium and caesium sensitive to radiation of a wide wavelength range between 4000 and 8000 A (400 and 800 nm).

Thus an X-ray image projected onto scintillator 5 is converted by scintillator 5 into an optical image which in turn is directed onto photoelectric layer 7 by the optical device 6 and there is converted into the corresponding electrical image.

A mesh electrode 9 is located within the envelope and adjacent photoelectric layer 7 and cylindrical electrode 10 is disposed against the inner wall ofthe envelope.

Mesh electrode 9 is parallel to photoelectric layer7, the space between being 5 mm. Cylindrical electrode 10, located along the cylindrical inner wall of the vacuum envelope, is in the form of an aluminium thin film lying between mesh electrode 9 and the phosphor layer 8. Phosphor layer 8 is made of a ZnS:Ag phosphor which on stimulation emits a blue coloured light with a peak wavelength of 460 nm and is formed on the inner wall of the end of the vacuum envelope remote from the scintillator, the optical device and the photoelectric layer.

Electric-field generating means or accelerator power supply 16 is used to provide the electric potentials to the electrodes in the magnifying device that are used to accelerate electrons emitted from the photoelectric layer 7 towards phosphor layer 8. The photoelectric layer 7 is set at -7 kV; phosphor layer 8, mesh electrode 9, and cylindrical electrode 10 are grounded.

First and second focussing coils 11 and 12 are arranged around and coaxial with the cylindrical vacuum envelope. First focussing coil 11 extends along the vacuum envelope close to the photoelectric layer 7 with its centre offset from that of photoelectric layer 7 by 20 mm along the line connecting the centres of photoelectric layer 7 and phosphor layer 8. Second focussing coil 12 extends along the vacuum envelope close to phosphor layer 8 with its centre offset from that of photoelectric layer 7 by 150 mm along the line connecting the centres of photoelectric layer 7 and phosphor layer 8. The respective currents flowing through the first and second focussing coils 11 and 12 from the focussing current generation circuit 13, determine the magnification factor of the image formed on phosphor layer8. The magnification factor can thus be modified without shifting the focussing plane.

When 400 mA flows through first focussing coil 11 and 220 mA through second focussing coil 12, the magnification factor of the image is unity. When 1300 mA flows through first focussing coil 11 and 0 mA through second focussing coil 12, the magnification factor of the image becomes 6.

When currents flowing through these coils are changed in accordance with the theoretical relation shown in Figure 2, the magnification factor can be modified continuously within the range of unity to 6.

Two pairs of deflection coils 14 are arranged about the cylindrical vacuum envelope so asto deflect electrons passing through. When a current in the range of O to 500 mA flows through each oftwo pairs of deflection electrodes 14, photoelectrons emitted from an arbitrary point on photoelectric layer 7 can be incidentonthe corresponding point on phosphor layer 8.

Thus by varying the currents in the two sets of deflection coils the portion of the electrical image emitted by photoelectric layer 7 which is incident on phosphor layer 8 can be selected.

The same current source 15 can be used to supply current to the two focussing coils 11 1 and 12, and the two pairs of deflection coils 14.

A diagnostic apparatus incorporating a radiographic magnifying device in accordance with the present invention will be described hereafter referring to Figure 3.

X-ray point source 1 is used as a radiation beam source. It would be most preferable if the X-ray emitterwere a perfect point source butthis of course is not realizable and thus an X-ray beam source 1 with a beam diameter of 50 to 60 ym is used as X-ray point source 1. Commercially available X-ray tubes, e.g.

spot radiation beam generation tubes, of the type in which X-rays are generated by an electron beam which is passed through a small cross-sectional area aperture on to a revolvable anode, can conveniently be used.

Alternatively, a conventional X-ray tube can be used if only the parallel X-ray beam component from the center ofthe divergent X-ray beam is used. A high power X-ray tube provides an X-ray beam of high energy density and so the X-ray component selected by passing the beam through a fine collimator can be used. It can be said that a fine collimator lens is advan- tageous for minimizing harmfui exposure of the human body to X-rays.

The conventional organism observation device providing the capability to observe the object at higher magnification factor can be used to observe only a small portion, i.e., 2 mm2, of the object being used as the specimen. The objective of the present invention can be accomplished by using a fine beam to project a two-dimensional image signal containing much information onto scintillator 5.

The point-source X-ray tube 1 emits X-rays when the electron beam with an acceleration energy of 60 kV at a current of 50 mA with a cross-section diameter of 50 lim strikes the tungsten target.

A circular opening about 10 mm in diameter and located 150 mm from the target of the X-ray tube is provided at the center of lead shielding plate 2. Object 3 is irradiated by the X-ray beam emerging through the opening. The angle of divergence of the X-ray beam is approximately four degrees.

A penetrating image of object 3 is thus formed on scintillator 5 by disposing the radiographic magnifier 4 with the outer face of scintillator 5 perpendicular to and centred about the axial line which passes from the X-ray source through the centre of the opening in shielding plate 2, through object 3 to scintillator 5.

Relay lens 20 is used to form an image on the second photoelectric layeroftelevision camera 17 by projecting onto the second photoelectric layer an image obtained from phosphor layer 8 of the radiographic magnifier 4.

A vidicon imaging tube with a silicon image intensifying target (SIT) is used for television camera 17.

The vidicon imaging tube with a silicon image inten sifying target (SIT) can pick up an image with a diminished light intensity from the phosphor layer 8 while the object is being exposed to a low intensity of X-ray energy.

It has been found that a micro-channel-plate can be disposed within the radiographic magnifier 4 of the invention between the photoelectric layer and the phosphor layer to enhance the image formed on the phosphor layer.

Deflection current source 18 of television camera 17 can feed a scanning current with a standard sawtooth waveform and another scanning current with a small amplitude to the imaging tube of television camera 17. The entire area of the second photoelectric layer or a partial area of that layer can thus be scanned.

Picture monitor 19 is used to reproduce a video signal sent from television camera 17.

An example of the operation of the above mentioned diagnostic apparatus will be explained below.

The operator should first turn on the power supply for all the apparatus components and then set object 3 in the required location between X-ray source 1 and radiographic magnifying device 4.

It is preferable that a set of currents of 400 mA and 220 mA (corresponding to point P in Figure 2) are respectively fed to first and second focussing coils 11 and 12 from focussing current generation circuit 13 so as to set the magnification factor at unity. The electron beam from the center of photoelectric layer 7 should than strike the center of phosphor layer 8 when no current is fed from deflection current source 15 to deflection coils 14.

The vertical sawtooth-wave deflection signal current with an amplitude of 500 mAp-p and the horizontal sawtooth-wave deflection signal current with an amplitude of 800 mAp-p are fed from deflection current source 18 to the deflection coils of television camera 17 so asto scan the entire area on the second photoelectric layer of the imaging tube.

With the X-rays from point-source X-ray tube 1 projected onto object 3 the entire image of object 3 appearing on phosphor layer 8 can be displayed on picture monitor 19. Watching the entire image of the object displayed on picture monitor 19! the operator can find the area to be checked. Suitable deflection currents can then be fed from deflection current source 15 to the deflection coils 14 of the radiographic magnifying device 4 so that the point to be checked may be placed at the center of the frame of picture monitor 19.

When currents flowing through first and second focussing coils 11 and 12 are changed so that the curve goes to point S in Figure 2, the magnification factor of the image on phosphor layer 8 is increased.

An arbitrary image on picture monitor 19 can thus be magnified. For larger size images, when deflection current source 18 for television camera 17 supplies a set of standard sawtooth-wave scanning currents to the deflection coils of television camera 17 while reducing their effective amplitudes by limiting the scanningtimewidth, each by a factorofupto 1/5, the image on picture monitor 19 can be magnified 6 x 5 (=30) times compared to the X-ray image incident scintillator 5.

Examples of the use of the diagnostic apparatus of the inventon will now be described: Example 1 Barium was injected into the veins of the liver of a mouse. The liverwas extracted and the extracted liver was fixed by formalin and sliced into a sheet with a thickness of 1 mm. The sliced sheet was placed in the diagnostic apparatus 1000 mm apart from the X-ray emitting point on the axial line. Thereafter,the following experiments were carried out: (a) When the entire area of the photoelectric layer on the television camera was scanned with the magnification factor set at unity in the radiographic magnifying device, blood vessels, each with a diameter of 100 gm, as well as blood vessels with relatively larger diameter were observed on the picture monitor.

(b) When the entire area ofthe photoelectric layer on the television camera was scanned with the magnification factor set at 1.2 in the radiographic magnifying device, some blood vessels, each with a diameter of less than 100 ,am, as well as blood vessels with relatively larger diameters were observed on the picture monitor.

(c) When the entire area ofthe photoelectric layer on the television camera was scanned with the magnification factor set at 2.5 in the radiographic magnifying device, blood vessels, each with a diameter of 30 ,m, branching into the organism were visually confirmed.

(d) When one half of the normal length on the photoelectric layer of the television camera was scanned with the magnification factor set at 2.5 in the radiographic magnifying device, the total magnification factor being 5, renal glomerula and hepatic sinusoid were confirmed to exist.

Example 2 The spleen extracted from a human body was fixed by formalin an sliced into a sheet with a thickness of 1 mm. The sliced sheet was placed in the diagnostic apparatus 1000 mm apart from the X-ray emitting point on the axial line.

(a) When the entire area of the photoelectric layer on the television camera was scanned with the magnification factor set at 1.2 in the radiographic magnifying device, the entire image of the thorotrast granule deposited on the spleen extracted from the human body was observed on the picture monitor.

(b) When the entire area ofthe photoelectric layer on the television camera was scanned with the magnification factor set at 2.5 in the radiographic magnifying device, the disordered granules were easily observed on the picture monitor.

(c) When the entire area of the photoelectric layer on the television camera was scanned with the magnification factor set at 6 in the radiographic magnifying device, the tadpole-like granules, each with a width of 150,um, were observed on the picture monitor.

The radiation-beam diagnostic apparatus is such that the penetrating X-ray image obtained when an object is irradiated by a radiation beam source can be observed on the picture monitor. The radiation-beam diagnostic apparatus may be operated in conjunction with a variety of contrast generation techniques, e.g.

penetrating X-ray image observation techniques as are used in the prior art.

The radiographic magnifying device in accordance with the present invention can thus be used to display, on a picture monitor through a television camera, a visible image generated by the electrons transmitted from a photoelectric layer onto a phosphor layer with a magnification factor which is dependent on the currents flowing through the first and second focussing coils and which can be varied bythevariation of these currents in accordance with a certain theoretical function.

The resolution of the image formed at the photoelectric layer is excellent and an image on the scintillator can actually be magnified without degradation of resolution.

The radiographic magnifying device provides deflection means so that a selected portion of the image formed at the photoelectric layer can be caused to impinge on the phosphor layer and thereafter be displayed as an image on the picture monitor.

However, it should be noted that resolution on the phosphor layer is much inferior to that on the photoelectric layer of the television camera tube if images on the phosphor layer are optically magnified, and that resolution on the scintillator cannot be kept unchanged. The radiation-beam diagnostic apparatus can nevertheless be used to magnify images on the scintillator several tens of times of magnification factor without degradation of resolution.

The present invention, however, is particularly advantageous insofar as it permits observation of magnified penetrating X-ray images of organs without destruction of the organ.

Claims (10)

1. A radiographic magnifying device comprising: a cylindrical vacuum envelope having a photoelectric layer formed on a surface at one end of said envelope.

a phosphor layer formed on a surface at the other end of said envelope.

a scintillator to convert radiation impinging thereon into a corresponding optical image, and an optical device to direct the optical image from said scintillator on to said photoelectric layer; first and second focussing coils arranged around said cylindrical vacuum envelope and coaxial therewith; means for generating an electric field to accelerate electrons emitted from said photoelectric layer toward said phosphor layer; a deflection device to deflect electrons emitted from said photoelectric layer; and a focussing current generating means to feed currents to said first and second focussing coils in accordance with a predetermined ratio thereby to determine the magnification factor of the images formed on said phosphor layer.

2. A radiographic magnifying device as claimed in claim 1, wherein said optical device comprises a fiber plate.

3. A radiographic magnifying device as claimed in either of claims 1 and 2, wherein said deflection device comprises a setoftwo paired electromagnetic deflection coils disposed about said cylindrical vacuum envelope and capable of deflecting electrons passing through said cylindrical vacuum envelope.

4. A radiographic magnifying device substantially as hereinbefore described with reference to the accompanying drawings.

5. A diagnostic apparatus comprising: a radiation beam source; a radiographic magnifying device as claimed in any one of the preceding claims, the scintillator thereof being arranged to receive a radiation beam emerging from an object interposed between said radiation beam source and said radiographic magnifying device; atelevision camera arrangedtoscan a partorall of the optical image formed on the phosphor layer of said radiographic magnifying device; and display means to display the output of said camera.

6. A diagnostic apparatus as claimed in claim 5 wherein said display means comprise a picture monitor capable of reproducing video signals from said camera.

7. A diagnostic apparatus as claimed in either of claims 5 and 6, wherein said radiation beam source is provided with a shielding plate with an aperture therein through which a radiation beam may pass to impinge on an object before impinging on said scintillator.

8. A diagnostic apparatus as claimed in claim 7 wherein said radiation beam source comprises a spot radiation beam generating tube.

9. A diagnostic device as claimed in any one of claims 5 to 8 wherein a deflection current source used to scan the electron beam over the photoelectric layer of television camera issues an output which provides a variable scanning width.

10. A diagnostic apparatus substantially as hereinbefore described with reference to the accompanying drawings.