U.S. patent number 3,857,039 [Application Number 05/320,757] was granted by the patent office on 1974-12-24 for x-ray device.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Johann Finkenzeller, Kurt Franke.
United States Patent |
3,857,039 |
Franke , et al. |
December 24, 1974 |
X-RAY DEVICE
Abstract
An X-ray device includes an X-ray tube with at least two
different focal point paths which can be selectively switched on
and which are differently inclined to the central X-ray. A switch
is provided for the selection of one of the focal point paths. An
adjustable primary X-ray screen is located in the bundle of X-rays.
The device is particularly characterized by an automatic switching
device which permits operation only with the focal point path which
is more strongly inclined to the central X-ray when a predetermined
opening is exceeded during setting of the pair of screen plates of
the primary X-ray screen, while removing the earlier selection of a
more weakly inclined focal point path.
Inventors: |
Franke; Kurt (Erlangen,
DT), Finkenzeller; Johann (Tennenlohe,
DT) |
Assignee: |
Siemens Aktiengesellschaft
(Munich, DT)
|
Family
ID: |
5832421 |
Appl.
No.: |
05/320,757 |
Filed: |
January 3, 1973 |
Foreign Application Priority Data
Current U.S.
Class: |
378/115; 378/125;
378/134; 378/150 |
Current CPC
Class: |
H01J
35/26 (20130101); H05G 1/58 (20130101) |
Current International
Class: |
H01J
35/00 (20060101); H01J 35/26 (20060101); H05G
1/58 (20060101); H05G 1/00 (20060101); G03b
041/16 () |
Field of
Search: |
;250/402,406,505,511,512
;313/60 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Archie R.
Assistant Examiner: Church; C. E.
Attorney, Agent or Firm: Richards & Geier
Claims
What is claimed is:
1. An X-ray device, comprising in combination, an X-ray tube of the
rotating anode type having a rotatable stem and an anode plate
mounted upon said rotatable stem, at least two electron-emitting
cathodes spaced from said anode plate, and at least two concentric
annular target tracks of different obtuse face angles formed on
said anode plate, each of said target tracks being associated to
one of said cathodes, a manually operated switch for selecting one
of said cathodes to be activated, an X-ray screen for fluoroscopy
mounted at a radial distance from the anode in a plane parallel to
the axis of revolution of said rotating anode and being adjusted to
X-rays emitted from the target tracks in a radial direction
rectangular to said axis of revolution, two pairs of adjustable
collimator plates mounted between the target tracks and said X-ray
screen parallel to said X-ray screen and an automatic switching
device comprising at least one changeover switch for said cathodes,
actuated by said pair of collimator plates adjustable in a
direction parallel to the axis of revolution, said automatic
switching device switching on said cathode being associated to the
target track having the bigger face angle when the selected
adjustment of said pair of collimator plates exceeds a
predetermined opening of the radiation beam larger than twice the
angle of the surface of said target track having the smaller face
angle with a plane normal to the axis of revolution, said switching
device switching out said cathode being associated to the target
track having the smaller face angle even when it has been manually
selected, and wherein said predetermined opening of the radiation
beam is effected when the planes of the X-ray emitting areas of the
respective target tracks touch the edges of the collimator plates
and the opposed edges of the usual film sizes being fixed in the
plane of said X-ray screen.
Description
This invention relates to an X-ray device having at least two
different focal point paths which can be selectively switched on
and which are differently inclined to the central X-ray, a switch
for the selection of one of the focal point paths and an adjustable
primary X-ray screen located in the X-ray bundle.
It is generally known that the geometrical lack of clearness during
photographing with X-rays due to central projection is proportional
to the size of projection of the focal point path ( = focus) of the
X-ray tube in the direction of the central ray of the X-ray cone.
Since the X-ray radiation from the anode surface of an X-ray tube
is uniform in all directions it has been the practice for a long
time to use the part of the emitted X-ray radiation which is
radiated stripwise from the surface of the anode. This makes it
possible to diminish the size of the projection of the focal point
path serving as the image although the size of the focal point path
remains uncharged. Thus a smaller geometrical lack of clearness is
provided. It is also known that due to the final load capacity of
the anode material when the focal point path gets smaller the
maximum admissible X-ray tube output must be reduced. For very many
years the anodes have been constructed as so-called rotary plates
to provide a better and more uniform heat radiation from the anode.
A corresponding construction of the cathode provides that the
electrons strike only a comparatively narrow rectangular surface of
the inclined edge of the rotary anode plate, the focal point path.
The edge lengths of the focal point path are then so selected that
the focal point path projects as a square in the direction of the
central X-ray.
Depending on the nature of examination a doctor will either place a
greater value upon a smaller geometrical lack of clearness or upon
a small lack of clarity of movement. In the first case he will wish
to operate with the smallest possible focal point path and in the
second case with a larger focal point path to provide shorter
illumination time periods with larger tube output. For a better
adaptation to these different requirements the rotary anode plate
of X-ray tube is often provided with an inner only slightly
inclined edge and an outer edge which is more strongly inclined. A
separate cathode is located opposite the two anode plate edge
surfaces, which can send out an electron ray bundle corresponding
in length and width. In case of such X-ray tubes it is left to the
examining doctor to select the focal point path which he believes
to be most suitable. However, there is the drawback that in X-ray
tubes which due to a small inclination of the focal point path to
the central X-ray permit exposures with a comparatively small
geometrical lack of clarity, there is the danger that the
photographs will be spoiled since during the screening of a film of
a large size a part of the primary X-ray bundle is covered by an
edge of the rotary anode.
An object of the present invention is to avoid these bad exposures
without giving up at the same time the advantages of a particularly
small lack of precision.
Other objects of the present invention will become apparent in the
course of the following specification.
In the accomplishment of the objectives of the present invention an
X-ray device of the described type is provided with an automatic
switching device which when a predetermined opening during setting
of the pair of screen plates of the primary X-ray screen is
exceeded, permits operation only with the central X-ray of the
focal point path which is greater inclined and removes the eventual
preliminary selection of the lesser inclined focal point path.
This makes it certain that the examining doctor when selecting a
large film size and thus a large opening of the primary ray screen
located at will between the focal point path and the object being
examined in the primary X-bundle, will be able to operate only with
that focal point path wherein the X-ray bundle emerging from the
focal point path fully illuminates the film area without shading
from the edge of the anode plate. If the switch is set for a
selection of the focal point path to the smallest focal point path,
that the exposure for all film sizes will take place automatically
with the smallest possible focal point path for the specific film
size and the smallest possible geometrical lack of sharpness.
According to a particularly advantageous embodiment of the present
invention the different angles of inclination of the individual
focal point paths can be adapted relatively to the central X-ray to
the location of the pairs of screen plates of the primary ray
screen for generally used film sizes. Due to this construction in
the case of these usual film sizes it is possible to make exposures
with the theoretically smallest possible inclination of the focal
point path relatively to the central X-ray, whereby the end rays of
the X-ray fundle leave the anode surface with barely a strip. In
this manner in case of these usual film sizes at a given focal
point size, i.e. at a specific X-ray tube output, there is the best
possible result as far as the smallest possible geometrical lack of
clarity is concerned.
The invention will appear more clearly from the following detailed
description when taken in connection with the accompanying drawing
showing by way of example only, a preferred embodiment of the
inventive idea.
In the drawing:
FIG. 1 is a diagrammatic sectional view of an X-ray device during
exposure with the smallest possible geometrical lack of sharpness
with a film of small size.
FIG. 2 is a partial top view of the rotary anode plate of FIG. 1
with an indicated focal point path.
FIG. 3 is similar to FIG. 1 but shows exposure with the smallest
possible geometrical lack of sharpness when using a film of large
size.
FIG. 4 is a partial top view of the rotary anode plate of FIG. 3
with an indicated focal point path.
FIG. 1 shows a rotary anode plate 1 of an X-ray tube 2, the outer
and inner edge portions 3 and 4 of the plate having different
inclinations to the plate axis 5. Separate cathodes 6 and 7 are
located above these edge portions, so that a sharply limited
electron ray bundle can be sent to the corresponding edge portion
of the rotary anode plate. Two adjustable screen plate pairs 12, 13
of a primary ray screen are located in the direction of the central
X-ray 8 extending in a direction perpendicular to the plate axis 5,
the plates being used for limiting the X-ray bundle 3 relatively to
the selected film 10 and the object 11 which is being examined and
which is placed directly in front of the film. The doctor can
select by the use of a switch 14 the desired cathode 6, 7 and thus
the edge range of the rotary anode plate 1 from which the X-rays
are to be emitted. Two change-over switches 15, 16 connected in
series with the screen plate pairs of the primary ray screen are
located in the circuit of the cathode 7 used for the edge section 4
of the rotary anode plate which is less inclined to the central ray
8. These change-over switches are used to switch on the cathode 6
related to an edge section 3 of the rotary anode plate which is
stronger inclined to the central ray, for a specific opening of the
screen plate pairs independently from the location of the switch
14.
FIG. 2 shows in top view the rotary anode plate 1 of FIG. 1 and
indicates the location of the focal point path 17, i.e. the range
which is struck by the electron ray bundle emitted from the cathode
7. The relationships of the edges of this focal point path are so
adapted to the relatively small inclination 23 of this edge range
to the central ray, that the projection 18 of this focal point path
appears in the direction of the central ray 8 as a small square.
The inclination 23 of this edge range 4 is the illustration of
FIGS. 1 and 2 relatively to the central ray 8 is equal to one half
of the angle at which appears the selected film size 10 looking
from the focal point path 17. This is set at the same time the
inclination at which the selected film size at the provided focal
point path distance from the film can be illuminated with the
smallest possible lack of geometrical sharpness.
FIG. 3 shows the same arrangement as in FIG. 1 with the difference
that the screen plate pairs 12, 13 are arranged for the use of a
larger film size 19 and a wider opened X-ray stray bundle 20. Due
to the wider opened screen plate pairs 12, 13 the switched 15, 16
(FIG. 3) are moved into a position in which the cathode 6 is always
switched on irrespective of the position of the switch 14, the
cathode 6 being related to the rotary anode plate edge 3 which is
stronger inclined to the central ray 8.
FIG. 4 shows in its top view of the rotary anode plate of FIG. 3
that the surface of the focal point path 21 upon which strike
electrons emitted by the cathode 6 toward the outer edge section 3
of the rotary anode plate is wider than the focal point path 17 of
FIG. 2 due to the different bundle arrangement of the electrons by
this cathode. The projection 22 of this focal point path 21 is the
direction of the central ray 8 is again a square one due to the
greater inclination 24 of the edge of the rotary anode plate.
In modern X-ray examining devices the adjustment of the primary ray
screen takes place automatically depending upon the size of the
inserted cassette or the selected film size. This fixes the opening
angle of the X-ray bundle 9, 20 due to the provided distance
between the focal point path and the film. The examining doctor has
the selection by correspondingly actuating the switch 14 of
carrying out the exposure with a greater focal point path or with a
smaller focal point path and smaller geometrical lack of clarity.
Since the output of the larger focal point path is generally
greater in the first case it is possible to operate usually with a
shorter illumination time period and thus with lesser lack of
movement clarity.
Even if the doctor decides to use the smaller focal point path, the
changeover switches 15, 16 operated by the screen plate pairs 12,
13 of the primary ray screen will switch the cathode 6 without his
action to the focal point path 17 of the following greater size as
soon as the screen plate pairs have reached a position due to the
selected film size wherein one half of the opening angle of the
X-ray bundle is greater than the angle of the selected inner edge
section of the rotary anode plate. This eliminates illumination
errors caused by a selection of a focal point path which is too
small in comparison with the selected film size. In addition the
adaptation of the different anode angles to the distance between
the focal point path and the film and the usual film sizes,
provides that the operation always takes place with the
theoretically smallest possible focal point path.
The operation of the change-over switch 15 by the pair of screen
plates 13 can be eliminated in all cases wherein the pair of screen
plates 13 can be moved only perpendicularly to the plate axis. For
primary ray screens which are rotatable about the central X-ray the
setting of the change-over switches is to be considered only for
those vectors of the path which lie in the direction of the plate
axis. In cases wherein the individual screen plates are adjustable
independently from each other, a change-over switch is provided
only for those screen plates which are shiftable under the horizon
provided by the plane of the rotary anode plate. When X-ray tubes
with more than two focal point paths are used it is advantageous to
use multi-stage rotary switches instead of the ordinary change-over
switches.
* * * * *