CA1112280A - Remote focus x-ray tube - Google Patents
Remote focus x-ray tubeInfo
- Publication number
- CA1112280A CA1112280A CA301,063A CA301063A CA1112280A CA 1112280 A CA1112280 A CA 1112280A CA 301063 A CA301063 A CA 301063A CA 1112280 A CA1112280 A CA 1112280A
- Authority
- CA
- Canada
- Prior art keywords
- tube
- focus
- target
- remote
- ray
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/16—Vessels; Containers; Shields associated therewith
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
- H01J35/153—Spot position control
Landscapes
- X-Ray Techniques (AREA)
- Apparatus For Radiation Diagnosis (AREA)
Abstract
ABSTRACT:
Remote-focus X-ray tubes, in particular dental X-ray tubes, have the problem that the focus is shifted as a result of which the emission distribution changes. It has now been found that a cause of said shifting is the earth magnetic field and, sometimes, magnetic fields pro-duced by electromagnetic elements of the apparatus. In order to eliminate these magnetic fields the anode tube is surrounded by a soft-magnetic layer which is dimensioned so that it serves at the same time as prefilter for the useful radiation emitted by the target.
Remote-focus X-ray tubes, in particular dental X-ray tubes, have the problem that the focus is shifted as a result of which the emission distribution changes. It has now been found that a cause of said shifting is the earth magnetic field and, sometimes, magnetic fields pro-duced by electromagnetic elements of the apparatus. In order to eliminate these magnetic fields the anode tube is surrounded by a soft-magnetic layer which is dimensioned so that it serves at the same time as prefilter for the useful radiation emitted by the target.
Description
The invention relates to a remote-focus X~ray tube, electrons emitted by the cathode following a compara-tively long path to a preferably conical target. Such x-ray tubes are employed in particular for intracavitary diagnos-tic and therapeutic purposes. The anode and the X-ray emit-ting target respectively are then generally located at an end of a comparatively long tube, which can be inserted into the body cavity.
Such X-ray tubes are ~or example employed in dentistry for recording the overall teeth condition, the anode tube containing the target being inserted into the patient's mouth. The target which is disposed at the end of said anode tube has the shape of a cone, on whose ape~ the electron beam is centred by means of suitable focussing coils. These dental X-ray tubes are known (German Offen-legungsschrift 15 64 738 which issued to Siemens AG with an Of~enlegungstag date of January 2, 1970).
If in such X-ray tubes the point of the -target is disposed only a fraction off the centre of the (round 100 mm long) electron path, a non uniform radiation distri-bu~ion results, which may for example lead to the radiation intensity at the location of the right half of the jaw being substantially greater than at the location of the left half of the jaw, which may give rise to an incorrect exposure of at least one half of a film which records the teekh condit-ion, which film is placed on the skin o~ the patient's face.
In order -to prevent the focus from being sh.ifted out of a position which is syrnmetrical relative to the cone .j - 2 ~
8~ PHD 77~028 apex, use has been made of flexible retaining members bet-ween the housing of the X-radiator and the X-ray tube which can take up a shock to which the anode kube is subjected, without said tube being bent, but even in such X-ray tubes the focus may still be shifted.
It is therefore the object of the present inven-tion to construct a remote-focus X-ray tube of the type men-tioned in the preamble in such a way that said shifting of the focus can be prevented or at least mitigated.
In accordance with the invention this object is achieved by a layer of a soft-magnetic material which sur rounds the electron path, which at the same time serves as prefilter for the useful radiation emitted by the target.
The invention is based on the recognition that external magnetic fields, in particular the earth magnetic field, may give rise to shifting of the focus or a substant-ial departure from the desired symmetrical intensity distri-bution. The influence of these magnetic fields on the elec- , tron path is substantially eliminated by the soft-magnetic layer which surrounds the electron path. Owing to the pre-liminary filtration of the useful radiation by said layer, which is achieved by a suitable dimensioning of the thick-ness of said layer, for which allowance is to be made for the filtration of the effective radiation by further compon-ents, as for example the anode tube of the X-ray tube, an additional prefilter may be dispensed w.ith. This i8 a special advantage ~or dental X-ray tubes, because the part of the X-ray tuhe to be inserted into the patient's mouth should have a minimal diameter.
.Y - 3 -PHD 77~028 In accordance with a further embodiment of the inven~ion which may be used in remote focus X-ray tubes with an anode tube, the soft-magnetic layer has the shape of a tube, whose inner diameter is greater than the outer dia-meter of the tube portion constitu-ting the anode tube. If desired, this tube may be slid over the anode tube. It may be arranged in an applicator, which during an X-ray exposure is slid over the actual anode tube and which serves to shield the areas not to be exposed against X-radiation.
The invention will be described in more detail with reference to the drawing.
The drawing shows a dental X-ray tube, which i5 located in the interior of a protective housing 3 and of which only the target 1 and the anode tube 2, through which the electron beam passes, are shown, because further this X-ray tube may fully correspond to the known X-ray tubes in accordance with German Offenlegungsschrift 15 64 738.
The useful radiation beam emitted by the conical target substantially has an aperture designated ~ and is rotation-symmetrical relative to the longitudinal axis of the anode tube 2. In the area through which the useful rad-iation passes it may consist in known manner of beryllium tGerman Offenlegungsschrift 15 64 738), but it may also be a thin ceramic tube.
In accordance with the invention a tube 4 is slid over the anode tube 2, which tube ~ extends from the end face of the tube shield in the direction of the target at least so far that the useful radiation always passes through this tube. The tube consists of an extremely '. .~ ~ ~
J 7 ~
.
~;Z28~
so~t-magnet:ic rnateri.lL o:f hi.gh perrlleabi:L.ity and wlthout remanence. A part:icllla:rly sui-tab:le tnc~ter:ia:l ls :t`ound -to l~e the shielding materia:L which is available in sheet f-orm ~rom the Magne-tic Shield Division, Per~ection Mica Co.; USA, under the trade name ~CO-N~TIC". However, it is alternat:ively possible -to employ a mu-metal tube. T:he thickness o:f this -tube should be between 0.05 mm and 0.1 mm, so t:ha-t in additi~
to magnetic shield:ing a satis~actory prelimincLry f`iL-tra-tion is obtained.
Although the inven-tion has been described in connection w:i-th a den-tal X-ray -tube, it may also be employed in other remote-focus X-ray tubes with a long electron path, pre~erably in such tubes in which the target is situated at the end of a hollow anode -tube; the target may also have a shape other than that of a cone~
Such X-ray tubes are ~or example employed in dentistry for recording the overall teeth condition, the anode tube containing the target being inserted into the patient's mouth. The target which is disposed at the end of said anode tube has the shape of a cone, on whose ape~ the electron beam is centred by means of suitable focussing coils. These dental X-ray tubes are known (German Offen-legungsschrift 15 64 738 which issued to Siemens AG with an Of~enlegungstag date of January 2, 1970).
If in such X-ray tubes the point of the -target is disposed only a fraction off the centre of the (round 100 mm long) electron path, a non uniform radiation distri-bu~ion results, which may for example lead to the radiation intensity at the location of the right half of the jaw being substantially greater than at the location of the left half of the jaw, which may give rise to an incorrect exposure of at least one half of a film which records the teekh condit-ion, which film is placed on the skin o~ the patient's face.
In order -to prevent the focus from being sh.ifted out of a position which is syrnmetrical relative to the cone .j - 2 ~
8~ PHD 77~028 apex, use has been made of flexible retaining members bet-ween the housing of the X-radiator and the X-ray tube which can take up a shock to which the anode kube is subjected, without said tube being bent, but even in such X-ray tubes the focus may still be shifted.
It is therefore the object of the present inven-tion to construct a remote-focus X-ray tube of the type men-tioned in the preamble in such a way that said shifting of the focus can be prevented or at least mitigated.
In accordance with the invention this object is achieved by a layer of a soft-magnetic material which sur rounds the electron path, which at the same time serves as prefilter for the useful radiation emitted by the target.
The invention is based on the recognition that external magnetic fields, in particular the earth magnetic field, may give rise to shifting of the focus or a substant-ial departure from the desired symmetrical intensity distri-bution. The influence of these magnetic fields on the elec- , tron path is substantially eliminated by the soft-magnetic layer which surrounds the electron path. Owing to the pre-liminary filtration of the useful radiation by said layer, which is achieved by a suitable dimensioning of the thick-ness of said layer, for which allowance is to be made for the filtration of the effective radiation by further compon-ents, as for example the anode tube of the X-ray tube, an additional prefilter may be dispensed w.ith. This i8 a special advantage ~or dental X-ray tubes, because the part of the X-ray tuhe to be inserted into the patient's mouth should have a minimal diameter.
.Y - 3 -PHD 77~028 In accordance with a further embodiment of the inven~ion which may be used in remote focus X-ray tubes with an anode tube, the soft-magnetic layer has the shape of a tube, whose inner diameter is greater than the outer dia-meter of the tube portion constitu-ting the anode tube. If desired, this tube may be slid over the anode tube. It may be arranged in an applicator, which during an X-ray exposure is slid over the actual anode tube and which serves to shield the areas not to be exposed against X-radiation.
The invention will be described in more detail with reference to the drawing.
The drawing shows a dental X-ray tube, which i5 located in the interior of a protective housing 3 and of which only the target 1 and the anode tube 2, through which the electron beam passes, are shown, because further this X-ray tube may fully correspond to the known X-ray tubes in accordance with German Offenlegungsschrift 15 64 738.
The useful radiation beam emitted by the conical target substantially has an aperture designated ~ and is rotation-symmetrical relative to the longitudinal axis of the anode tube 2. In the area through which the useful rad-iation passes it may consist in known manner of beryllium tGerman Offenlegungsschrift 15 64 738), but it may also be a thin ceramic tube.
In accordance with the invention a tube 4 is slid over the anode tube 2, which tube ~ extends from the end face of the tube shield in the direction of the target at least so far that the useful radiation always passes through this tube. The tube consists of an extremely '. .~ ~ ~
J 7 ~
.
~;Z28~
so~t-magnet:ic rnateri.lL o:f hi.gh perrlleabi:L.ity and wlthout remanence. A part:icllla:rly sui-tab:le tnc~ter:ia:l ls :t`ound -to l~e the shielding materia:L which is available in sheet f-orm ~rom the Magne-tic Shield Division, Per~ection Mica Co.; USA, under the trade name ~CO-N~TIC". However, it is alternat:ively possible -to employ a mu-metal tube. T:he thickness o:f this -tube should be between 0.05 mm and 0.1 mm, so t:ha-t in additi~
to magnetic shield:ing a satis~actory prelimincLry f`iL-tra-tion is obtained.
Although the inven-tion has been described in connection w:i-th a den-tal X-ray -tube, it may also be employed in other remote-focus X-ray tubes with a long electron path, pre~erably in such tubes in which the target is situated at the end of a hollow anode -tube; the target may also have a shape other than that of a cone~
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A remote-focus X ray tube, electrons emitted by the cathode following a comparatively long path to a conical target, characterized in a tube of a soft-magnetic material surrounding the electron path serves as prefilter for useful radiation emitted by the target.
2. A remote-focus x-ray tube as claimed in claim 1 characterized in that an anode tube in which interior the target is positioned has an outer diameter which is smaller than the inner diameter of the tube of soft magnetic mater-ial surrounding the anode tube.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2717054.3 | 1977-04-18 | ||
| DE19772717054 DE2717054A1 (en) | 1977-04-18 | 1977-04-18 | FAR FOCUS ROUND TUBE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1112280A true CA1112280A (en) | 1981-11-10 |
Family
ID=6006535
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA301,063A Expired CA1112280A (en) | 1977-04-18 | 1978-04-13 | Remote focus x-ray tube |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5923064B2 (en) |
| BE (1) | BE866052A (en) |
| CA (1) | CA1112280A (en) |
| DE (1) | DE2717054A1 (en) |
| FR (1) | FR2388404A1 (en) |
| GB (1) | GB1604051A (en) |
| IT (1) | IT1094150B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3342688A1 (en) * | 1983-11-25 | 1985-06-05 | Siemens AG, 1000 Berlin und 8000 München | X-RAY TUBES |
-
1977
- 1977-04-18 DE DE19772717054 patent/DE2717054A1/en not_active Ceased
-
1978
- 1978-04-13 CA CA301,063A patent/CA1112280A/en not_active Expired
- 1978-04-14 GB GB14739/78A patent/GB1604051A/en not_active Expired
- 1978-04-14 IT IT22334/78A patent/IT1094150B/en active
- 1978-04-15 JP JP53044721A patent/JPS5923064B2/en not_active Expired
- 1978-04-17 BE BE186848A patent/BE866052A/en unknown
- 1978-04-18 FR FR7811321A patent/FR2388404A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IT7822334A0 (en) | 1978-04-14 |
| JPS53129991A (en) | 1978-11-13 |
| IT1094150B (en) | 1985-07-26 |
| GB1604051A (en) | 1981-12-02 |
| JPS5923064B2 (en) | 1984-05-30 |
| DE2717054A1 (en) | 1978-10-26 |
| FR2388404B3 (en) | 1980-12-12 |
| FR2388404A1 (en) | 1978-11-17 |
| BE866052A (en) | 1978-10-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |