CA1223091A - Method and device for operating and focusing tomographic x-ray equipment - Google Patents

Abstract

ABSTRACT OF DISCLOSURE

A method and a device for operating and focusing a tomo-graphic x-ray unit using an electron beam and embodying at least one electron gun, an anode at which the gun is aimed as well as the x-ray detectors needed to produce a tomographic images of fast-moving objects. It is par-ticularly characteristic of this invention that an electron beam emitted by an electron gun is roughly deflected at a hole in the focusing plate which, by means of focusing field lines, draws the electrons into the hole, focuses and accelerates the electron beam which strikes the surface of the anode, generating an x-ray source, and that the focusing hole is moved in regard to the anode to generate a series of x-ray sources needed to produce a "layerwise" tomographic image of the object under examination.

Description

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rhls invention relates to a method and a device for dlrec~ y all focusirlg a tomographic x-ray unit employing an electron bean. such a unit embodies at least one electron gun and an anode at which it is aimed as well as the x-ray detectors needed to produce a tomographic image.

I us a source of radiation, tomographic equipment goner-I ally enlploys an x-ray tube which, during exposure, revolves around the object to be imaged. However, it is not posy sidle to attain such a high rate of revolution for the x-ray tube as -to Intake the equipment suitable for imaging fast-moving organs of the human body, such as the heart region. In practice, exposure times shorter titan 1 second cannot be achieved, although ; exposure tummies in the order of 0.1 seconds would be regulred to produce audit images of -the hear-t region, or brain blood circ~llat:loll when using a contrast medium.

In order to achieve sufficiently short exposure port-ohs, equipment has been devised in which the x-ray tube is replace with an electron gun generating an electron beam which is focused and magnetically directed at a fixed anode encircling the object.

The problem associated with this construction is how to direct and focus a high-intensity, high-energy electron beam, and how to stabilize the high voltage involved which affects the aforementiorled factors.

Lyle present invention avoids these problems and pro-vises a method and a device which does not require focusing of-the electron gun, nor accurate collimation of -the beam. Also, no regulrements are set for high-voltage stabilization from the point of view of beam focusing or direction.

according to the present invention there is provided a method for directing and focusing a tomographic x-ray unit using pow ~Z23~39~

an electron Boyle and using at least one electron gun and an anode at wll.Lcll tile gun is aimed, including the x-ray detectors for pro-dozily a tomographic image, wherein an electron beam emitted by an electron gun is generally directed at a hole in a focusing plate which draws the electrons into -the hole, focuses and axle-crates they'll, after which they s-trike the anode generating an x-ray source, and -the focusing hole is displaced relative -to the anode so that a moving x-ray source, needed to produce a too-graphic image, is generated on the surface of the anode.

eaTIl directing is effected mechanically by means of a focusing pate, and focusing is achieved in the space between the focusirlg device and the Jo - lo -~2~36)9~ .
.
, Allah where Allah the actual acceleration of electrons takes nag (']~n]acl;erlstic of the Matilda under consideration is they'll;
; -tile ~ealll elnitted by -tile electron gun is roughly aimed at a hole ill Lowe rocuaillg pate which, by means of focusing yield lines, draws tile electrons islet the hole as Rowley Jo hocuses and J accelerates tile electron beam, direc-tillg it at the anode disc -to produce all Ray source. Moreover the focusing hole is moved in regard -to the anode in such a way no to generate a ~obl'le Ray source which produce a "lyres" image i 10 of tile object under examination, !

nettler characteristic feature of this method is that -the focusing plate fir zero potential for which reason -the acceleration of tile electron Tokyo 'plate between the focusing Ayers and the anode. I!'url;hcrll1oxe, two field line generated by the potential ¦ bel;wooll tllo focurlllG plate and two anode oxtond partly Jo the t Swahili Isle no tile foe G ply lid tllo cloctxon ~UIIJ 'tllU~
drnwill~r the electrorl~ into the focusing hole like a hopper.

¦ 20 ~notllcr characteristic feature of -this method is Tut the anode anal the f OCUSill~ plate are in the form of concentric rings, and that the Iocusin~ plate it caused -to revolve a-t a uniform speed ¦ all that the CleCtrOIl guy it timed to emit the beam in pulses whereby it hits the anode at evenly apace points In addition to a rin~-sllaped anode and focusing plate the object it sun-rewelded by a ring of x-ray detectors for Welch reason the most appropriate form of the apparatus it that of a funnel or a Swahili. irlde:~ .

~!'urtllermore, it is characteristic of the method that several electron ~UII9 are mounted along -the casing of a basically I cylinder-rllQped apparatus so that the beams emit-ted by them are j Rowley deflected in the direction of the tangent of the cawing ! towards tile holes in tile focusing plane newborn frill one to 1 35 rcveral to equal gun. In -this Ray) each deflected beam is directedj at a specific por-tiorl of the anode disc. Durincr irradiation, e focal rink -turns a distance equivalent to the distance bottle two hole }to deflection ox the electron beam can be

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ct`lccte(l a: ~ne~leve:L rough deflection which permits the use of i Lowe roc-lrilllrllo]es to coequal guy J~llr-tllexlnore~ it it characteristic of the uletllod based Oil this in-mention that when the focusing King -turns the distance it is i supposed to, the electron guns emit a beam in rapid succession in tile order determined by the direction of rotation of the okaying Renoir. In this way, several Randall ox electron be , en~issiolls are achieved during exposure. If there are several holes in tile focusitl~r ring -to each gun, deflection is effected alternatingly through different holes.

characteristic of a device utilizing one of the advantages offered by Ellis iJlVelltiOIl it that between -the electron guns and the anode lo there if; a rotating faking King with one or several holes which directs tile electron beam mostly mechanically Outtalks I :r'.lOte:r;l~t:LO Ox ugh a dcvloe is that thy allodc~ owe in Isle all tile x-r~ly detectors form ooncentrio rings and that tile focusing ring can be rotated at a uniform speed.

l~oreovcr~ it is characteristic of such a devise that several electron gun are mounted along the oaring at equal distance from one anywhere and that in the focusing ring there are one I or several holes to each gun, whereby the beams emitted by them . Call lye directed to a specific hole by Wrigley deflecting the brat in the direction of the axis of a cylinder-sll2ped unit.

Below -tile invention is described in greater detail by mean of examples all with reference -to enclosed drawings where lug 1 presents the principle of operation of -the invention;
Lowe 2 provides side view of one of the applications of the invention lug. provides front view of a device presented in Fig. 2 _ 3 .

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ovoid ire view of another applica-tioll of the invention r. 5 prevails cross-section V-V of the device presented in lily , .

Fix. 6 provides cross section VI-VI of the device presented in Lyle. 7 provide cross-section VII-VII of the device presented 1 0 i allele 1 Iota us consider a sLmplc dcvioe exetnplifying this illvell-tion.(Fig~ 1).
lo lowlier tcllsity electron pull the beam of Lowe own be turned on all owe' by Muriel Our intexn~l oontxol voltQ~o~ is used a a source Our cleol;rollo~ ~3e-twcarl tlln Ned deco (2) and tile ooze-inn rJ.rlG (3) there it a Ugh voltage Russia venerates ho field line (dashed line in Fig. 1) which focus the electrons by means ox specially designed hole I Part of the field lines generated by high voltage U extend to the vacuum between -the electron gun (l) and the focusing system I drawing the electrons (7) , islet the hole (4) after which they are accelerated.

help the focusirlg rink (3) is moved across the beau of the electron gun ( 1 ) Welch it alternatingly being turned off and on, a series ox x-ray sources it produced on the surface of the anode I in tile direction of reptilian of the ring.

example 2 Icing talc principle described above, it it possible to construct Jo -the tomograpllio devise preserlted in Fig. 2. The electron gun (1) is mourlted at tile -top of a conical vacuum -tube and the anode (2) all phonier discs (3) are formed into rings surrounding -the oh~ect (6) to be imaged. By rotating the one-holed (~) focus-ill Dow (3) ore round in owe Sunday while the electron run it .
; - 4 ~Z~3~91 elni~t:itlg, say 10~0 hi Swede electron posses and 250 of the I J.`.i.xcd dctec-liors (5) (Or tile scintillation semiconductor type) Oil tile owlet guide of the object (6) are collecting the absor~tii.on inormaliion for each pulse, i-t is possible to pro-dupe an image consist g of 500 x 500 elements.

Such a so pow placation, however, rerluire~ an extremely high-powered elecliroll Gil and quick-acting detection elements. The Social Call be remedied in -two Way (examples an example 3 Lyle beam (7) emit lied by the electron gun (1) is roughly diluted;
if, for instance, the beam (7) can be directed at a specific quarter of the cone (Fix, 2)? the nwnber of focusing holes can be .lncrear-3ed lo four. No the beam can be emulated by dixeobing I a ogle hole flier another A a rerJult~ the foousin~ rung Urania old ogle o'er ox a round derailing the lime tile image in tickle all the okay. lilt shuffles oily ogle oily of tile dip-talk railroad for a one-holed ring, which jives a siglliicarltly improved resolution.

example situaliion unaloguous to Example 3 is obtained by using a cylinder-s}la.ped structure instead of a cone (Fig. 4) and by in-creanisl~ the number of electron suns (1) as well a the correspond-trig number Or Cousin holes (4). 'this will ensure shorter outweighing distance arid facilitate the directing of the beam (7).

~xumyle 5 on optimum device can be constructed by using a combination of the equi.pmellt redescribed in Examples 3 and 4 in which both method Or retarding the focal point are employed. Tile principle of such a device is presented in Figure I I 6 and 7. the device C011S.i.S to of a cylinder-shaped casing (9) which encircle the object (6) to be imaged. The vacuum cylinder house 8 ~L2Z3~91 electron furls (1), and there are 2 holes in the focusing ring (4) -to each urn totallin¢ 1G9 and tile anode (2) forms a full rink around tl1c object under examination. The detectors (5) are also placed in a rink form around the object Tile beam i.SSUillg from tile guts are deflected tangentially along the focusing King, which roughly determines beam direction at -the desired hole I The suns are triggered in succession so that when the focusing rink (3) -turns a distance equivalent lo to tile distance between try holes, the guns are activated one after the other in the order determined by the direction of rotation o r the ring.

If, for examplc1 tile exposure time 19 owe second and an image lo oon~i~tln~ of 5()0 x 500 elements Lo requited, '1000 bursts Or C'J,eOtrt,~llS ago fixed at toe anode as derailed above while 250 detectors lotted ox tile opponlte lo ox thought obJeub oolLtJct absorption inrormabioll on each pullout deflected and ponytail beam emitted by the various Gus it the two focusing holes (~) alterllatinGly -travels about 63 -times around -the anode Renoir (2 during exposure isle the focusing ring turn 1/16 of a round.

Assuming -that the length of tile XiTlg is 5 my focal points will be venerated at a distance of 5 mm from one another, If irradiation at one point last 50 us and -the collection of data takes another 50 issue the movement of -the focus with a 16-holed rink is merely 1/2 x 1/16 x 5 my or appear owe my which is surJ:iciellt not to render the focus inaccurate.' Consequelltly~ an accurate and quick lyres tomographic image of Lowe object can be taken with the equipment described above.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for directing and focusing a tomographic x-ray unit using an electron beam and using at least one electron gun and an anode at which the gun is aimed, including the x-ray detectors for producing a tomographic image , wherein an electron beam emitted by an electron gun is generally directed at a hole in a focusing plate which draws the electrons into the hole, focusses and accelerates them, after which they strike the anode generating an x-ray source, and the focusing hole is dis-placed relative to the anode so that a moving x-ray source, needed to produce a tomographic image is generated on the surface of the anode.

2. A method as claimed in claim 1, in which the focusing plate has zero potential and the actual acceleration of electrons takes place between the focusing plate and the anode, and the hole in the focusing plate is adapted to permit the field lines generated by high voltage between focusing plate and the anode to partly extend into the space between the focusing plate and the electron gun from wherein the electron beam is drawn into the focusing hole.

3. A method as claimed in claim 1, in which the anode and the focusing plate are concentric rings, and the focusing ring is rotated at a uniform speed and the electron gun is timed to fire at the anode at appropriate times.

4. A method as claimed in claim 3, in which a plura-lity of electron guns are mounted along the casing of a basically cylinder-shaped apparatus so that the beams emitted by them are generally deflected in the direction of the axis of the casing towards the holes in the focusing plate to allow the deflected beams to be directed at a specific portion of the anode disc, and during exposure the focusing ring turns a distance equivalent to the distance between two holes.

5. A method as claimed in claim 4, in which as the focusing ring turns the predetermined distance during exposure, and the electron guns are fired in succession in the order deter-mined by the direction of rotation of the focusing ring.

6. A tomographic x-ray unit using an electron beam comprising one or more electron guns, an anode, x-ray detectors, and a rotatable focusing plate between the electron guns and the anode, said plate having therein one or more holes through which the beam passes prior to striking the anode, whereby a moving x-ray source is generated as the plate is rotated in front of the anode.

7. A method as claimed in claim 6, wherein the anode, the focusing plate and the x-ray detectors form concentric rings, and the focusing ring is rotatable at a uniform speed.

8. A method as claimed in claim 6 or 7, wherein a plu-rality of electron guns are mounted at equal distance from one another along a casing of the apparatus, and one or more holds are provided in the focusing plate for each gun, the beam of which can be directed at a specific hole by general deflection means in the direction of the tangent of a cylinder shaped apparatus.