U.S. patent number 3,838,287 [Application Number 05/413,442] was granted by the patent office on 1974-09-24 for fluoroscopic localization system for angular radiography.
This patent grant is currently assigned to General Electric Company. Invention is credited to David M. Barrett, Ralph K. Chrapkowski.
United States Patent |
3,838,287 |
Barrett , et al. |
September 24, 1974 |
FLUOROSCOPIC LOCALIZATION SYSTEM FOR ANGULAR RADIOGRAPHY
Abstract
A diagnostic x-ray table has a film cassette supported on a
Bucky carriage beneath the table top. A fluoroscopic image tube is
fixedly located below the Bucky carriage. An x-ray tube is mounted
above the table top for being translated and angulated
correspondingly for providing oblique view radiographs. For
tomographic procedures and for oblique radiographs a fulcrum bar
couples the x-ray tube to the Bucky carriage, so the central ray of
the x-ray beam always coincides with the center of the film. The
pivot axis of the fulcrum bar is vertically adjustable so it may
extend laterally through any selected layer of a patient reposed on
the table top, through the plane of a film in the cassette and
through the plane of the sensitive surface of the image intensifier
tube. During angular radiography, the fulcrum axis can be located
in the plane of the image tube wherein automatic means are provided
for shifting the Bucky in the same direction as the x-ray tube so
that the area being radiographed corresponds with the image viewed
by means of the image tube.
Inventors: |
Barrett; David M. (Brookfield,
WI), Chrapkowski; Ralph K. (St. Francis, WI) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
23637242 |
Appl.
No.: |
05/413,442 |
Filed: |
November 7, 1973 |
Current U.S.
Class: |
378/26; 378/22;
378/196; 378/155 |
Current CPC
Class: |
A61B
6/587 (20130101); A61B 6/02 (20130101); A61B
6/4283 (20130101) |
Current International
Class: |
A61B
6/02 (20060101); G01n 023/00 () |
Field of
Search: |
;250/442,444,446,445,451,490,491 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Archie R.
Assistant Examiner: Anderson; B. C.
Attorney, Agent or Firm: Hohenfeldt; Ralph G. Wiviott;
Fred
Claims
We claim:
1. In diagnostic x-ray apparatus having x-ray tube means movable
over an x-ray table which comprises a table body means and an x-ray
permeable top mounted thereon for supporting an examination
subject, means for supporting a radiographic film for movement
relative to said top in a plane on one side thereof opposite from
the x-ray tube, a fixed fluoroscopic means having an x-ray
sensitive surface more remote from said top than said film plane,
the improvement for automatically obtaining substantially the image
of an area of an examination subject on the film as is viewed with
the fluoroscopic device, comprising:
a. means movable along a line substantially normal to said film
plane,
b. fulcrum arm means having a first pivot connection to said
movable means, said fulcrum arm means being coupled on one side of
said first pivot connection to said x-ray tube means and being
engaged by a second pivotal connection with said film supporting
means, the axes of said first and second pivotal connections being
directed laterally of said table top and the second pivotal axis
lying substantially in said film plane, the x-ray beam from said
tube being directed in the direction of said fulcrum arm means
through said pivotal axes, and
c. means for adjusting said movable means through a range of
positions for said first pivotal axis to be at selected levels on
the x-ray tube side of said film plane, coincident with said film
plane and coincident with said x-ray sensitive surface of said
fluoroscopic device whereby said film supporting means will move in
the opposite direction of fulcrum arm rotation when said first
pivot axis is on the x-ray tube side of said film plane and will
move in the same direction when said first axis is on said
sensitive surface of said fluoroscopic device so that the central
ray of said x-ray beam will pass through said first axis on said
film and said second axis on said surface whereby the central ray
of the x-ray tube will be simultaneously coincident with the center
of the film and the center of said sensitive surface and
substantially the same x-ray image area may be recorded on said
film as occurs on said sensitive surface.
2. The invention defined in claim 1 wherein:
a. said fulcrum arm means between said first and second pivot axes
comprises at least a pair of elements which are joined for relative
sliding motion whereby to compensate for radius changes between
said axes when said fulcrum arm means is rotated.
3. The invention defined in claim 1 including:
a. lead screw means having a rotation axis coincident with the line
of movement of said movable means,
b. said movable means having a thread engaging it with said lead
screw means, rotation of said lead screw means changing the
position of said movable means on the axis of said screw means,
and
c. a reversible motor and means coupling said motor means in
driving relation to said lead screw means.
4. In diagnostic x-ray apparatus adapted for perpendicular
radiographic, tomographic and angular radiographic examination of a
subject and for fluoroscopic examination thereof, said apparatus
cooperating with a movable x-ray tube means, said apparatus
including an x-ray table comprising a table body and an x-ray
permeable top panel mounted thereon for supporting an examination
subject, a carriage for supporting a radiographic film cassette for
movement of a film therein in a plane on one side of the table top
opposite from the x-ray tube, a fluoroscope device fixedly mounted
in said table body and having an x-ray image insert surface more
remote from said top than said film plane, the improvement for
assuring that the central ray from said x-ray tube and the center
of the image on said fluoroscope device will be coincident with the
center of the image on the film, said improvement comprising:
a. movable means and means for guiding said movable means in a line
of travel substantially perpendicular to said film plane and said
x-ray image insert surface,
b. fulcrum arm means connected for angular movement on said movable
means about an axis projecting in the lateral direction of said
table top,
c. said fulcrum arm means having a portion on one side of said axis
coupled to said x-ray tube means and another portion on the other
side of said axis connected to said film support means,
d. said movable means being selectively adjustable along its line
of travel to locate said fulcrum arm axis in selected planes a
predetermined distance from said table top, whereupon movement of
said x-ray tube means in one direction will move film support in an
opposite direction,
e. said movable means being further adjustable along its line of
travel to locate said fulcrum arm axis on said image insert surface
whereby to dispose said axis on an opposite side of said film plane
whereby rotation of said fulcrum arm due to movement of said x-ray
tube will cause said film support to move in the same direction as
said x-ray tube whereby to maintain the central ray from said x-ray
tube on the center of a film on said support and coincidentally on
the center of said insert plane, the image area recordable on said
film thereby being the same as that viewed with said fluoroscopic
device, and
f. means supporting said x-ray tube for rotation by said fulcrum
arm means coordinately with said x-ray tube movement to maintain
alignment of said x-ray tube beam with said fulcrum arm.
Description
BACKGROUND OF THE INVENTION
This invention relates to diagnostic x-ray tables.
X-ray tables that are designed for performing radiography with the
central x-ray normal to the patient supporting surface as well as
tomography and angular radiography, usually support a film cassette
on a Bucky carriage underneath the x-ray table top. The x-ray tube
is mounted over the table top on an independent tube support or on
an arm extending from a tube stand which is integral with the
table. The independent support or integral stand as the case may be
are movable relative to the table top. For radiography with the
central x-ray perpendicular to the table top or patient support the
focal spot of the x-ray tube is directly over the center of the
film in the cassette beneath the table top. The tube support and
the Bucky can be interlocked to maintain this alignment.
For tomography, a fulcrum bar is used to connect the x-ray tube to
the Bucky carriage. The elevation of the axis of the fulcrum bar is
adjustable so it can be made to coincide with any plane of interest
in a patient supported on the table top. As is well known, during
tomography, the x-ray tube is moved lengthwise of the table top in
one direction in which case the fulcrum bar turns and causes the
Bucky carriage to move in the opposite direction since the tube and
Bucky carriage are on opposite sides of the fulcrum axis. Hence,
all planes above and below the plane which contains the fulcrum
axis are blurred on the radiographic film and the plane which
contains the fulcrum axis is sharply imaged since it experiences no
relative motion. In many tomographic tables, the lowest elevation
to which the fulcrum axis may be adjusted is the top surface of the
table top since there is nothing of interest to radiograph beneath
the surface.
In some x-ray tables that are adapted for angular radiography, that
is, taking a view through the patient at an angle instead of
perpendicularly, as is done when it is desired to localize an
embedded object or to view under an otherwise intervening part of
the anatomy, the fulcrum axis of the bar can be adjusted to the
level of the film plane but no lower than this level. With this
adjustment, the x-ray tube may be shifted longitudinally through an
arc and angulated so that the central x-ray beam always points at
the center of the film which is held stationary for this technic.
The x-ray tube is adjusted to its final longitudinal and angulated
position before a radiograph is initiated.
In radiographic x-ray tables that are adapted for fluoroscopic
localization using an x-ray image intensifier tube the latter is
typically fixedly mounted with its sensitive input surface at a
certain distance beneath the plane of the film in the cassette and
with the center of this input surface in the same vertically
lateral plane as the fulcrum axis of the fulcrum bar. When using
this system with the fulcrum bar attached and with the central
x-ray normal to the patient support surface, the center of the
fluoroscopic input surface and the film center both coincide with
the central x-ray beam regardless of the height of the fulcrum
axis. In certain prior art x-ray apparatus it is possible and
necessary to lower the fulcrum axis to the film plane to permit
very slight angulation of the central ray with the least possible
relative shift of the fluoroscopic image relative to the
radiographic image assuming there is no film cassette in the Bucky
tray and the Bucky carriage has a suitable opening in its bottom so
as to not attenuate the x-ray image beam. However, due to the
physical separation of the sensitive surface of the image
intensifier tube from the film plane, in this prior art apparatus
angular positioning of the central x-ray beam at larger angles
results in the central ray intersecting the image intensifier input
plane at a point which is at a considerable distance from the
center. In other words, during angular fluoroscopy and radiography
with prior art x-ray apparatus, the area recorded on the
radiographic film does not correspond exactly with that which had
been viewed fluoroscopically by means of the image intensifier
tube.
SUMMARY OF THE INVENTION
A primary object of the present invention is to overcome the
above-noted problem and to provide means for obtaining accurate
correspondence between an image recorded on a radiographic film and
an image viewed by way of an image intensifier tube system at any
position or angle which the system is capable of attaining.
How this general object and other more specific objects are
achieved will appear in the course of the more detailed description
of an illustrative embodiment of the invention which will be set
forth hereinafter.
In general terms, the invention is characterized by coupling an
x-ray tube and a Bucky carriage together by means of a fulcrum bar
whose rotational axis is adjustable to coincide with the input
plane of the image intensifier device. The fulcrum bar is coupled
to the Bucky carriage above the fulcrum axis so that when the x-ray
tube is shifted either to the right or left of the center of the
table and angulated for angular radiography, the Bucky and film
cassette supported thereon will shift in the same longitudinal
direction as the x-ray tube to thereby maintain coincidence between
the image on the image tube and the image recorded on the film.
A more detailed description of a preferred embodiment of the
invention will now be set forth in reference to the drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a diagnostic x-ray table adapted
for performing a variety of x-ray technics including angular
fluoroscopy and radiography in accordance with the invention;
FIG. 2 is a front elevation view of the x-ray table showing the
x-ray tube stand in solid line in its position for perpendicular
radiography and also showing it in phantom in one of its angular
radiography positions, the fulcrum axis being adjusted to the level
of the film plane;
FIG. 3 is a side elevation of the x-ray table depicted in the
previous figure but with the fulcrum axis adjusted to its lowest
position;
FIG. 4 is an elevation view, partly in section, of a mechanism in
the table for adjusting the elevation of the fulcrum bar pivot
axis;
FIG. 5 is a side elevation view of the assembly shown in the
preceding figure, partially in section, and with some parts
removed;
FIG. 6 is a transverse section taken on a line corresponding with
6--6 in FIG. 5;
FIG. 7 is a side view of the x-ray tube support arm isolated from
the apparatus and with the x-ray tube omitted;
FIGS. 8 and 9 are diagrams which are useful for explaining the
invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
The general features of a diagnostic x-ray table adapted for
improved angular radiography and fluoroscopy, in accordance with
the invention will now be discussed in reference to FIGS. 1-3
primarily. These figures show a diagnostic x-ray table comprising a
floor mounted table body or base assembly 10. There is a table top
assembly 11 mounted on base 10. The top assembly comprises
rectangularly arranged frame members such as the one marked 12. An
x-ray permeable top panel 13 for supporting a patient is fastened
to the frame. The mounting means for the frame or top assembly are
not shown but it will be understood that the top assembly 11 may be
mounted for being shifted lengthwise or longitudinally in opposite
directions from the center position in which it is shown and being
shifted laterally, that is, toward and away from the observer in
FIGS. 1 and 2.
A substantially conventional x-ray tube casing 14 is supported over
the table top. Associated with the tube casing is an x-ray beam
collimator 15 which defines the boundaries of the x-ray beam that
is projectd from tube casing 14 toward the table top 13 such as to
penetrate a portion of the anatomy of a patient who is reposed on
the table top. There is an x-ray tube, not visible, inside of
casing 14. The focal spot of the x-ray tube is marked 16 in FIG. 2
and its position in profile is similarly marked in FIG. 3. X-ray
tube casing 14 is mounted on the end of an arm 17 which extends
from a column 18. Arm 17 is adjustable vertically on column 18.
Normally, for perpendicular radiography, arm 17 and, hence, focal
spot 16 will be adjusted to a fixed distance from table top 13. For
angular radiography, the tube casing 16 is rotatable on arm 17
about an axis that passes through focal spot 16 and is
perpendicular to the plane of the drawing in FIG. 2. Tube casing 14
and collimator 15 are shown in one of their angulated positions in
phantom lines in FIG. 2.
FIG. 3 shows that column 18 is mounted on the back of the table
body or base 10 for being moved longitudinally in parallelism with
table top 13. Thus, column 18 is supported on a carriage 19 in
which there are rollers, not shown, for running on tracks 20, 21
and another track, not shown. The mechanism for driving column 18
longitudinally is not shown since such mechanisms are known. It is
sufficient for the purposes of the present invention to realize
that the tube supporting column 18 can be driven or moved
longitudinally of the table in opposite directions.
Another general feature of the table exhibited in FIGS. 1-3 is the
Bucky carriage which is designated generally by the reference
number 25 in FIGS. 2 and 3. The Bucky carriage 25 has rollers for
running on tracks in the table body so the Bucky may be shifted
under table top 13 longitudinally to a limited extent. The details
of the Bucky carriage such as the rollers and cooperating tracks
are not shown. The Bucky carriage has a tray for supporting a film
cassette 26 which is merely symbolized by a dashed line rectangle
in FIG. 2. The center of a film in the cassette is designated with
a point marked 27 in FIG. 2. When the x-ray tube casing 14 is
positioned as it is in FIG. 2 for perpendicular radiography, the
focal spot 16 is positioned on a true vertical line which passes
through the center point 27 of the film in cassette 26
perpendicularly to the film plane. Point 27 is centered in both
directions with respect to the edges of the film and may be
considered as coinciding with the top surface of the film.
Immediately below Bucky carriage 25 there is an image intensifier
tube 28 for fluoroscopy procedures. The tube has an internal x-ray
sensitive photocathode which is symbolized by the curved dashed
line 29. Image tube 28 may be a known type characterized by its
ability to convert an x-ray image to an optical image. The optical
image is directed by an objective lens, not shown, to an angularly
disposed mirror 30 which reflects the image to a television camera
31. It will be understood that the television camera 31 is coupled
to a television monitor, not shown, which enables the radiologist
to view the x-ray image. This procedure is usually referred to as
fluoroscopy. A horizontal plane tangent to the center of
photocathode 29 may be considered the x-ray image input plane of
image tube 28. The photocathode receives the x-ray image and
converts it to a light image which is, in turn, converted to an
electron image and then to a highly intensified light image again
which is received by mirror 30. During fluoroscopy, the x-ray film
cassette 26 is removed to avoid exposing it and the x-ray image
beam passes through an opening 32 in the bottom of the Bucky
carriage. It is evident that when focal spot 16 of the x-ray tube
is directly centered perpendicularly over sensitive surface 29 of
image intensifier 28 the central ray of the x-ray beam emanating
from the focal spot will also pass through the center point 27 of a
film when the cassette 26 is inserted. Thus, during vertical
fluoroscopy followed by radiography, the image formed on the film
will coincide substantially with that formed on the image
intensifier sensitive surface 29.
In some x-ray technics, however, the cone of x-rays emanating from
focal spot 16 and, particularly, the central ray thereof does not
intersect the table top nor the film plane in the cassette
perpendicularly. This is the case when angular radiography is being
performed at angles up to 45.degree. at which time the x-ray tube
is shifted in one direction or the other from the center of the
table top and turned at an angle. One angular position of the x-ray
tube is illustrated in FIG. 2 where the x-ray tube casing 14 is
shifted to the left and rotated about the laterally projected axis
of focal spot 16 as indicated by phantom lines in FIG. 2. One may
see that with the x-ray tube in phantom line position and
angulated, the central x-ray beam marked 33 will intersect table
top 13 and a patient reposed thereon at an angle. This technic is
used when it is desired to localize an embedded object in the
patient and it is also used to obtain a better view of an organ
which underlies an interfering organ.
In FIG. 2 it is evident that the central x-ray 33 still passes
through center point 27 of a film lying in a horizontal plane
within cassette 26. However, it is evident that if central ray 33
is extrapolated it will not coincide with the center of sensitive
surface 29 of image intensifier tube 28. In some prior art tables
and the present invention as well, the x-ray tube can be, in
effect, rotated about a lateral axis extending through point 27 in
the film plane so that the central ray always coincides with the
center of the film. To accomplish this purpose, the x-ray tube
casing 14 is connected to the Bucky carriage 25, which supports the
film cassette 26, by a fulcrum bar 34 which pivots about a
horizontal axis extending through point 27 and normal to the plane
of the drawing in FIG. 2. However, it will be evident that if the
height of the fulcrum axis 61 is at point 27 or above, the central
ray will pass through the center of the film but not through the
center of the x-ray sensitive surface 29 of the image intensifier
and the image viewed during fluoroscopy will not agree with that
recorded on the subsequently inserted film. It is evident that such
would not be the case if image intensifier 28 were shifted far
enough to the right in FIG. 2 for central ray 33 to intersect both
center point 27 of the film and the center of sensitive surface 29
in the image intensifier 28 within the x-ray table body so,
heretofore, during angular radiographic procedures the radiologist
had to tolerate an image from the intensifier which was not
coincident with the image to be recorded on film in cassette 26. As
indicated earlier, the present invention solves this problem by
shifting the Bucky carriage and, hence, the film cassette in the
same direction in which the x-ray tube is shifted during angular
radiography so that the central ray 33 will intersect the center of
sensitive surface 29 and the center point 27 of the film cassette
at the same time. For this arrangement, the center of the area of
the anatomy which is recorded on the film when the cassette is
inserted will agree with that which had been previously observed
during fluoroscopy with the image tube.
In accordance with the invention, recording on the film the same
view that is observed with the image intensifier is assured by
pivoting fulcrum arm 34 and the x-ray tube about a lateral axis
that lies on the input plane or sensitive surface 29 of the image
intensifier tube. Means are also provided for automatically
shifting the Bucky carriage 25 and the film cassette supported
thereon in the same direction in which the x-ray tube is translated
longitudinally to thus maintain alignment of the center points of
the film and sensitive surface at all times. How this is
accomplished will now be discussed.
In FIG. 3 one may see that a fulcrum bar 34, otherwise known as a
tomographic bar, couples the x-ray tube cross-arm 17 to a mechanism
which is generally designated by the reference numeral 40. A
property of this mechanism is that it can be adjusted to cause
Bucky carriage 25 to translate beneath the table top in the
opposite direction to which the x-ray tube is moved over the table
top or it may be adjusted so that the Bucky carriage does not move
at all when the x-ray tube is moved and, in accordance with the
invention, it may be adjusted so that the Bucky carriage is moved
in the same direction as the x-ray tube is moved.
Rotation of fulcrum bar assembly 34 is obtained by driving the
x-ray tube casing away from the center of the table for angular
radiography. As indicated earlier, in the illustrative embodiment,
this is accomplished by driving column 18 in a longitudinal
direction on its supporting tracks 20 and 21 which are symbolized
in FIG. 3. As can be seen in FIG. 7, the x-ray tube supporting arm
assembly 17 has a carriage 41 with sets of rollers such as 42 and
43 which enable the arm to be positioned at the desired height on
column 18. Sometimes during angular radiography, the carriage 41
and arm 17 extending therefrom are locked at a fixed height with
respect to table top 13. If the x-ray tube 14 height is fixed by
locking the vertical carriage 41, the distance from the focal spot
16 of the x-ray tube to the film plane center point 27 will
increase when the x-ray tube is shifted longitudinally along a
horizontal line provided there is a slidable connection between the
x-ray tube casing 14 and fulcrum bar 34. This situation may be
considered to exist in FIG. 2 where it is evident that the length
of central ray 33 between focal spot 16 and film center point 27 is
greater when the casing is translated and rotated as shown in
phantom than it is when the focal spot 16 is perpendicularly
aligned with the film center 27 as shown in solid lines when the
tube casing is centered with the table. It is customary to lock the
tube arm against vertical movement and let the fulcrum bar turning
radius and, hence, the focal spot to film distance increase when
doing tomography but there is a preference for swinging the x-ray
tube through an arc of constant radius for angular radiography to
maintain a constant focal spot to film distance.
To maintain the constant distance during angular radiography the
tube carriage 41 may be unlocked so it is free to move with a
vertical component and thereby follow an arc. The fulcrum bar 34 is
clamped to a rotatable shaft 45 on which the x-ray tube is
supported to thereby fix the fulcrum bar radius. When the vertical
column 18 is shifted from table center, the x-ray tube is angulated
on the shaft 45 axis and moved through an arc since the carriage 41
can go up and down as the column 18 moves and the fulcrum bar 34
swings.
In FIG. 7 the x-ray tube is omitted but it will be understood to be
mounted on a bracket 44 which is, in turn, fastened to shaft 45.
This shaft may be selectively locked against rotation or it may be
released for rotation by a mechanism which is enclosed in the
housing of arm 17 and need not be discussed in detail since it is
not pertinent to the present invention. For present purposes,
rotatability of shaft 45 is assumed. In a broken-away portion of
arm housing 17 one may see that shaft 45 is effectively coupled to
a yoke 46. Yoke 46 is provided with recesses 47 and 48 in which
fulcrum bar 34 nests. The arrangement is such that fulcrum bar 34
may be permitted to slide vertically within the recesses to
compensate for distance changes between focal spot 16 and center
point 27 of the film when the x-ray tube casing is translated
generally longitudinally. The rear ends of recesses 48 and 49 are
open so that fulcrum bar 34 can be backed out and disengaged from
yoke 46 for some radiographic technics. For this reason bar 34
extends through a collar 49 which attaches to an axially movable
shaft 50. The collar has a clamping element 51 which enables bar 34
to slide selectively in collar 49.
By means of a mechanism not shown, which is operable by a manual
lever 52 on the side of tube arm 17, shaft 50 may be shifted
axially to the right as viewed in FIG. 7 so as to effectively
disengage fulcrum bar 34 from yoke 46. The fulcrum bar can then
slide in the yoke 46 while still turning the yoke and x-ray tube.
When engaged as depicted in FIG. 7, the longitudinal shifting of
tube arm 17 will rotate fulcrum bar 34 and shaft 50 which will
cause x-ray tube supporting shaft 45 to be rotated. Longitudinal
movement and rotation of the x-ray tube will assure that central
ray is always in parallelism with fulcrum bar 34 but laterally
spaced thereof so that the longitudinal axis of the fulcrum bar and
of the central ray from the x-ray tube lie in the same laterally
extending plane. Thus, the x-ray beam is always directed to the
center of the film plane and the angular direction of the fulcrum
bar may be considered the angular direction of the central x-ray
beam. During angular radiography, fulcrum bar 34 may be engaged
with yoke 46 so the yoke cannot slide relative to the bar while the
tube angulates and swings through a longitudinal arc and vertical
carriage 41 is unlocked so the fulcrum radius and, hence, the focal
spot-to-film distance stays constant. During tomography, vertical
carriage 41 is locked and bar 34 is unclamped from yoke 46 so the
yoke can slide on the bar to allow the bar radius to change when
the x-ray tube is moved longitudinally on a horizontal line and not
in an arc.
Mechanism 40 for engaging the fulcrum bar 34 with Bucky carriage 25
for driving the latter in selected directions relative to the x-ray
tube will now be described. Referring to FIG. 2, one may see that
there is a stand or frame 55 fixedly mounted to the table body
behind the top 13 thereof. Stand 55 and the mechanism associated
therewith is shown in greater detail in FIGS. 4-6. In FIG. 4 there
is a motor 56 and a gear train 57 coupling the motor to a lead
screw 58. There is an internally threaded cross-head 59 engaged
with lead screw 58. Rotation of motor 56 in one direction will
elevate head 59 and rotation in the other direction will lower it.
The head is also guided on an unthreaded rod 54 and there is a
suitable hole in the head through which rod 54 passes. There is a
horizontal shaft 60 journaled for rotation in head 59. The axis of
shaft 60 is marked 61. At its rear, shaft 60 has a crank arm 62
fastened to it. The back of stand 50 has a vertical slot 63 in it
so that head 59, shaft 60 and crank arm 62 may move vertically
bidirectionally without interference. Crank arm 62 is provided with
an upwardly extending pin 63 which facilitates coupling it to the
end of fulcrum bar 34. The details of the socket in the end of
fulcrum bar 34 for engaging pin 63 are not shown. In any event,
crank arm 62 always remains in alignment with fulcrum bar 34 and
the x-ray beam is in the direction of the fulcrum bar. Shaft 60 and
its axis 61 can be adjusted in height by moving head 59 so the axis
61 extends laterally at various elevations such as through
selective planes about table top 13, through the film plane or, in
accordance with the invention, through planes below the film plane
including the image intensifier input surface plane 29 which is
shown in dotted lines in FIG. 4.
FIG. 5 shows another arm 64 which is pinned to shaft 60 for joint
rotation with crank arm 62. Arm 64 is fastened to a distance
compensating linkage including a link 65 and another link 66 which
is slidable relative to link 65. These links may be considered
extensions of the fulcrum bar beyond its rotational axis 61. Link
66 has a pad or base element 67 fastened to it and an arm 68 which
extends downwardly is fastened to a shaft 69 by means of a pin 70.
Shaft 69 is journaled in bearings 71 which are recessed in base
element 67 as can be seen clearly in FIG. 6. In FIG. 6 it is
evident that link 65 is provided with a pair of channels 72 and 73.
The other link 66 has a complementary pair of channels 74 and 75
which are so shaped that they retain a plurality of bearing balls
such as 76 and 77 between them. This sliding link assembly is known
in the art and need not be discussed in greater detail except to
create awareness that link 66 is slidable on link 65 and the links
are inseparable and maintain their alignment at all times.
In FIG. 3, it is evident that downwardly extending arm 68 and,
particularly, the T-shaped head 78 thereof is fastened to a
cross-bracket 79 which has an upwardly extending portion 80
connected rigidly to Bucky carriage 25. The axis of arm 68
supporting shaft 69 extends laterally across the table top and
projects through the film plane or the plane in which film center
point 27 is lying during the radiographic procedure. In FIG. 4, the
film plane is indicated with a broken line marked 27'. The plane of
the top surface of the table top is indicated with a broken line
marked 13'. Since Bucky carriage 25 is constrained to move in one
plane only, axis 69 of arm 68 will always extend through the
corresponding film plane even though the arm extends below it and
then upwardly again where its end portion 80 fastens to Bucky
carriage 25.
Since arm 68 remains fixed in elevation even though fulcrum bar 64
turns links 65 and 66 jointly about the axis 61 of shaft 60 in the
cross-head 59, the radius between cross-head axis 61 and axis 69 of
arm 68 varies for distance compensation because of link 65 being
slidable on link 66.
In FIG. 4, the x-ray tube casing would be to the left of the center
of the table viewing it from the front and the central ray would be
at the same angle as link 65 and 66. With cross-head 59 adjusted to
the high level in which it is shown in FIG. 4, the cross-head shaft
axis 61 would extend through a plane above x-ray table top 13 such
as might be the case if the apparatus were being used for
conducting tomography. In such case, if the x-ray tube were shifted
to the right or clockwise as viewed in FIG. 4, the links 65 and 66
would swing in the opposite direction to drive the Bucky carriage
oppositely from the direction in which the tube is moved. This
procedure results in all planes of the table top supported subject
being radiographed which planes are above and below cross-head
shaft axis 61 to be blurred on the film while the plane in which
shaft axis 61 lies remains in focus and is sharply imaged on the
film.
If cross-head 59 is shifted downwardly until fulcrum bar rotational
axis 61 lies on film plane 27', the x-ray tube, in effect, is
rotatable about the film plane and the Bucky carriage is not
shifted longitudinally when the x-ray tube is shifted
longitudinally. Some prior art tables permit the fulcrum axis 61 to
be lowered to the level of film plane 27'. This facilitated
directing the central ray at the center of the film at all times
during angular radiography for any position of the x-ray tube.
In accordance with the invention, cross-head 59 may be lowered on
lead screw 58 until the fulcrum bar pivot shaft axis 61 lies on the
input surface of the image intensifier tube which surface is
defined by a curved dotted line marked 29. It is evident that
cross-head shaft or fulcrum bar axis 61, with this adjustment, is
well below the film plane 27'. Now, if the long radius defined by
fulcrum bar 34 with respect to rotational axis 61 is rotated in one
direction as viewed in FIG. 4, pivot axis 69 and Bucky carriage 25
engaged thereto will shift in the same direction along the film
plane 27'. This is so because the fulcrum axis 61 is now below the
film plane 27' and coincident axis 69. Since the central x-ray
passes through axis 69 which is on the film plane and fulcrum axis
61 is on the plane 29 of the sensitive surface of the image
intensifier, the central x-ray beam will pass through the center of
the film and the center of the sensitive surface simultaneously. As
long as fulcrum axis 61 is on the plane of sensitive surface 29 of
the image intensifier, this alignment will be maintained and
whatever image is viewed centrally on the image intensifier tube
will be recorded centrally on the film in the cassette.
The situtation which exists when cross-head 59 is adjusted
vertically so that fulcrum bar axis 61 coincides with sensitive
surface 29 is shown schematically in FIG. 8 where it will be seen
that the film center point 26 lying on the film plane is slightly
to the left of the center image tube input surface center point 61
so that central ray 33 passes through both center points. The plane
of an object such as 81 in FIG. 8 will thus be imaged
correspondingly on the film and the input surface 29 of image
intensifier tube 28. When the x-ray tube focal spot 16 is moved
longitudinally through an arc for taking a fluoroscopic view and a
radiograph at a different angle such as at the angle of central
beam 33' in FIG. 8, the central ray 33' will still pass through the
center point 26" of the film because the Bucky 25 has been shifted
to its phantom line position. Thus, central ray 33 and the cone of
rays surrounding it effectively rotate about laterally projected
fulcrum bar axis 61 so the image viewed on surface 29 is the same
as that on the film for all angular fluoroscopic and radiographic
views. FIG. 9 shows diagramatically how link 65 has shifted along
link 66 when the axis of the cross-head is adjusted to coincidence
with sensitive surface 29. It is also evident in FIG. 9 that when
the x-ray tube 14 and its focal spot 16 are shifted to the right,
rotation will occur about axis 61 and Bucky carriage 25 will move
to the right slightly to maintain the points 26 and 61 on the line
of sight of the central x-ray 33. Of course, if tube 14 is shifted
further to the left in FIG. 9, Bucky carriage 25 will shift further
to the left a short distance and the alignment of the x-ray beam 33
and the centers of the film and intensifier will still be
maintained.
The fulcrum bar 34 may be selectively removed or installed for
various procedures. When the bar 34 is installed it couples tube
rotation yoke 46 to the fulcrum mechanism crank arm 62. For
performing perpendicular radiography the fulcrum bar may be
installed and the x-ray tube locked against angulation so as to
maintain perpendicularity from the x-ray tube focal spot and the
film plane for all positions of the tube stand. The bar may be
removed for perpendicular radiography if, as in some tables, other
means are provided for maintaining perpendicularity.
In some prior table designs it is possible to remove the fulcrum
bar and manually angulate the x-ray tube for angular radiography
and to shift the Bucky carriage and cassette thereon in the same
direction in which the x-ray tube is shifted to provide coincident
alignment of the film center and the center of a image intensifier
input plane. However, in accordance with the present invention this
is done accurately, rapidly and essentially automatically by having
the installed fulcrum bar provide this coincidence.
The fulcrum bar in the illustrated x-ray table may also be removed
for the vertical radiography procedure where the cassette is
supported in a vertical plane on a floor mounted stand, not shown.
In this procedure, tube arm 17 is swung with column 18 so the arm
extends lengthwise of the table and the tube is rotated so its
central x-ray beam projects laterally across the table top toward
the vertical cassette stand.
To summarize operation of the equipment for angular radiography and
body localization, column 18 is moved until the x-ray tube is
pointed at the angle which the radiologist deems necessary for
radiographing an underlying organ or embedded object in the
patient. The x-ray tube is automatically turned at an angle which
will maintain the central x-ray beam on the center of the film
cassette. At this time, the cross-head or fulcrum axis will be
lowered coincident with the input surface of the image intensifier
tube and the Bucky carriage and film cassette thereon will be
shifted in the same direction in which the x-ray tube is moved
longitudinally from the center line of the x-ray table. The
radiologist then energizes the x-ray tube for the fluoroscopic mode
and views the image produced by the image intensifier on a
television monitor. When the desired angular view and area of the
anatomy is obtained, the x-ray tube is turned off and a film
cassette is inserted in the Bucky carriage. The x-ray tube,
current, voltage and exposure time factors are then set for the
radiographic mode and a radiograph is quickly taken. Then, if the
radiologist desires a view at another angle, tube column 18 is
driven longitudinally of the table top and the x-ray tube is moved
through an arc and is angled correspondingly and automatically. The
rotational axis 61 for fulcrum bar 34 will again be coincident with
the input surface of the image intensifier if sequential
fluoroscopy and radiography are desired. If the tube is moved from
the angle which is shown in phantom in FIG. 2 beyond center to the
opposite angle from perpendicular, the Bucky carriage and film
cassette thereon will move in the same direction to maintain the
alignment of the focal spot, the center of the film plane and the
center of the image intensifier tube. In apparatus in which there
is no image intensifier tube, the cross-head axis 61 may merely be
adjusted downwardly to the level of the film plane so that the
x-ray tube rotates about an axis lying in the film plane for in
such case it would not make any difference if the image lying in a
plane below the film plane were displaced or cut off.
To operate in the perpendicular radiographic mode, the x-ray tube
is oriented with the focal spot directly over the center of the
film in the cassette and the patient is aligned with the beam to
get the desired view by shifting the table top 13 laterally and
longitudinally.
The tomographic mode of operation is somewhat similar to the
angular radiography mode except that the axis of the fulcrum bar,
as is known, will extend through the plane of interest of a patient
lying on table top 13. The central ray from the x-ray tube will
penetrate the center of the film. However, as the x-ray tube is
shifted longitudinally of the table top in one direction, the film
cassette on the Bucky carriage will be moved in the opposite
direction from the x-ray tube since the tube is on the opposite
side of the pivot from the Bucky carriage. For tomography, the
x-ray tube may be moved horizontally and angulated in which case
the distance between the focal spot and the film plane will vary.
This requires that the tube arm be locked against vertical motion
on its supporting column and that the tube casing slide axially
relative to the fulcrum bar 34.
In the illustrative embodiment, the x-ray tube casing is mounted on
a column which translates longitudinally of the table body. It will
be understood that the x-ray tube might also be mounted on an
overhead tube hanger similar to a traveling crane independently of
the x-ray table. Moreover, the illustrative table is one which is
not adapted for tilting but those skilled in the art will
appreciate that the invention may be used in conjunction with
tiltable tables as well in which case the tube supporting column 18
would not only translate longitudinally of the table top but would
tilt with the body as well. All of the angular relationships
between the parts of the apparatus discussed above in connection
with the table top being maintained horizontal would exist if the
table top and patient thereon were tilted at an angle with respect
to horizontal.
Although a preferred embodiment of the invention has been described
in considerable detail, such description is intended to be
illustrative rather than limiting for the invention may be
variously embodied and is to be limited only by interpretation of
the claims which follow.
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