Process and apparatus for scatter reduction in radiography

A process and apparatus for reducing detected radiation scatter in radiography. The process comprises interposing synchronized rotating radiation shields between the object being radiographed and the detector and desirably between the radiation source and the object. Openings in the shields are aligned in such a way as to permit primary radiation to pass to the detector while stopping most radiation scatter. The apparatus comprises the shields with openings, means for mounting the shields and means for rotating the shields at appropriate speeds.

The invention described herein was made in the course of work under a grant 
or award from the Department of Health, Education and Welfare. 
BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
This invention relates to diagnostic radiology and in particular relates to 
the use of high energy radiation to form images of internal structures 
upon a sensing means such as x-ray film. The invention more particularly 
relates to a method and apparatus for reducing detection of radiation 
scatter in forming such images. 
(b) History of the Prior Art 
Originally, x-ray photographs were taken simply by directing x-rays from a 
source, e.g., an original rontgen ray tube, through an object such as an 
anatomical structure to a detector such as an x-ray film. This historical 
arrangement did not include additional devices to reduce hazards to a 
patient or to enhance the quality of the detected x-ray image. 
Later x-ray devices not only provided improved x-ray tubes such as tubes 
which could independently control intensity and wave length of x-rays but 
also incorporated filters for eliminating radiation outside of the useful 
x-ray range and included means for enhancing the contrast of the image by 
eliminating at least a portion of radiation scatter from the object such 
as a patient to the detector. Such scatter often results when high energy 
radiation interacts with molecular fields or particles. Scattered 
radiation is usually emitted in a direction different than the direction 
of the incoming primary radiation. The scattered radiation thus causes 
exposure of the detector to radiation at all locations thus reducing 
contrast of the detected image with the background. 
The most usual method for reducing scatter historically has been and 
remains radiographic grids which consist of a series of lead foil strips 
separated by x-ray partially transparent spacers. The lead foil acts to 
intercept secondary or scattered radiation which approaches the detector 
at an inappropriate angle. Such grids have, however, certain undesirable 
characteristics. For example, contrast is still not as high as desired 
since all scatter is still not eliminated, primaries are absorbed by 
interspaces and grid lines become apparent on the x-ray image since the 
lead strips absorb primary radiation from the radiation source. 
Attempts have been made to eliminate the appearance of the grid pattern in 
the x-ray image by moving the grid in a direction essentially 
perpendicular to radiation passing from the source to the detector; 
however, such a moving grid did nothing to increase contrast. There has 
also been an attempt to utilize linearly moving aligned slit devices to 
increase contrast. The devices have to be moved at a uniform speed and 
have to reach that speed before the x-ray is taken. This requires that the 
x-ray be taken in a precisely timed relationship to slit motion. 
Furthermore, vibration within the system cannot be tolerated and 
absolutely uniform x-ray output must be maintained during exposure to 
prevent unwanted patterns on the detector. Currently and perhaps 
subsequent to the present invention, an attempt is being made to increase 
contrast by mounting two slitted discs on a single axis and rotating the 
discs about the single axis while directing x-rays from the axis through 
the first slitted disc to the object or patient through the second slitted 
disc and a grid to the detector. This device has not proven desirable 
since a patient or object and detector, in order to be placed in a 
perpendicular relationship to incoming radiation, must of necessity be at 
an angle to the rotating discs. Such arrangement permits very little 
flexibility with respect to the location of the patient in relationship to 
the x-ray source and the rotating discs and contrast is not as good as is 
desirable. Furthermore, due to the use of the grid, grid lines are still 
present.

BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the present invention, there is provided a process and 
apparatus which eliminates all grid lines and simultaneously dramatically 
enhances image contrast yet permits adjustments of the object or patient 
with respect to the source and the detector which therefore permits 
acceptable images to be formed with lower radiation doses thus permitting 
reduction in patient exposure. 
The apparatus, in accordance with the invention, for reducing detection of 
radiation scatter from an object through which high energy radiation 
passes within a flux pyramid from a source to a radiation detection means 
comprises a series of at least two radiation shields, each of which has 
front and rear surfaces which are large relative to the thickness of the 
shield. The apparatus further comprises means for rotatably mounting the 
shields in a spatially separated relationship with each other between the 
object and the detection means so that each of the shields covers an 
entire section of the flux pyramid and so that each of the shields is 
rotatable about its own central axis through its center of gravity. 
For conventional radiography, the shields are mounted so that the front 
surface of each shield faces toward the source and the rear surface of 
each shield faces away from the source. The surfaces are approximately 
parallel to the plane of the detector. The apparatus further comprises a 
means for rotating each of the shields at its own angular velocity at a 
constant angular velocity ratio. The rate of rotation of each shield is 
preferably constant and most preferably the same as the angular velocities 
of the remaining shields. 
Each of the shields is further provided with a series of openings smaller 
than the object. The openings pass through the shield from the front to 
the rear surfaces and allow radiation to pass through the shield from the 
source to the detection means. Each of the shields is provided with the 
openings in shapes and positions such that at least a portion of the 
radiation in a straight line from a uniform source toward the detection 
means passes through openings in all of the shields to strike the 
detection means in essentially uniform coverage of the detection means 
when the object is absent and when each of the shields is in rotation 
about its central axis at its own angular velocity at a constant angular 
velocity ratio. "Essentially uniform coverage" means uniform coverage +10% 
between square millimeter areas on the detector not considering the 
effects of different distances of each of such areas from the uniform 
source. 
Desirably, the apparatus further comprises an additional shield similar to 
the other shields which is rotatably mounted between the source and the 
object in a spatially separated related relationship with the other 
shields so that the additional shield also covers an entire section of the 
flux pyramid and is also rotatable about its own central axis through its 
center of gravity. The additional shield is also mounted so that its front 
surface faces toward the source and the rear surface faces away from the 
source and so that the surfaces, when planar and parallel, are 
approximately parallel to the plane of the detector. Means is provided for 
rotating each of the shields including the additional shield at its own 
angular velocity at a constant angular velocity ratio. The angular 
velocity of the additional shield is desirably constant and preferably the 
same as the velocities of the remaining shields when the opening shapes 
and patterns on the shields are proportionally the same. The additional 
shield is also provided with a series of openings passing through the 
shield from the front to the rear surface which allow radiation to pass 
through the shield from the source to the detection means. The additional 
shield is provided with the openings in shapes and positions such that at 
least a portion of radiation in a straight line from a uniform source 
toward the detection means passes through openings in all of the shields 
to strike the detection means in essentially uniform coverage of the 
detection means when the object is absent and when each of the shields is 
in rotation about its central axis at its own angular velocity at a 
constant angular velocity ratio. 
The process for reducing detection of radiation scatter from an object by a 
radiation detector which receives high energy radiation within a flux 
pyramid through the object from a radiation source comprises interposing a 
series of at least two spatially separated radiation shields between the 
object and a utilized surface of the detector such that each of the 
shields covers an entire section of the flux pyramid. Each of the shields 
have front and rear surfaces, which are large relative to the thickness of 
the shield. The surfaces are approximately parallel to the plane of the 
detector. The front surface of each shield faces the radiation source, 
i.e., within a 50 degree deviation from being normal to a line from the 
center of the source to the center of detector. Each shield has a central 
axis passing through its center of gravity in a direction substantially 
perpendicular to the front surface and each shield is provided with 
openings smaller than the object passing through the shield from the front 
to the rear surface. The ratio of the sum of the widths of the openings to 
the sum of the widths of solid shield areas on each shield is usually 
constant as such widths are measured along the arc of any circle having 
its center at the central axis of the shield and passing through the flux 
pyramid. 
The process further comprises aligning the shields so that at least a 
portion of radiation in a straight line from the source toward the 
detector within the flux pyramid passes through openings in each of the 
shields to strike the detector. The process also comprises rotating each 
of said shields about its central axis at its own angular velocity to 
permit at least a portion of radiation in a straight line from a uniform 
source toward the detector within the flux pyramid to pass through 
openings in all of the shields to strike the detector in essentially 
uniform coverage of the utilized detector surface when the object is 
absent. Essentially uniform coverage is as previously defined. 
Desirably, the process further comprises interposing an additional 
radiation shield between the source and the object such that the 
additional shield covers an entire section of the flux pyramid. The 
additional shield also has front and rear surfaces approximately parallel 
to the plane of the detector when the surfaces are planar and parallel and 
a central axis and openings as previously described. In all cases, the 
central axis of all shields are approximately perpendicular to the 
detector plane, i.e., the plane containing the detector surface. 
Approximately perpendicular may be perpendicular or within 10 and 
preferably within 5 degrees of perpendicular. Most desirably, the central 
axes are within 1 degree of perpendicular to the detector plane. When the 
additional radiation shield is utilized, the process also includes 
aligning all of the shields so that at least a portion of radiation in a 
straight line from the source toward the detector within the flux pyramid 
passes through openings in each of the shields to strike the detector. The 
process utilizing the additional shield further comprises rotating each of 
the shields about its central axis at its own angular velocity at a 
constant angular velocity ratio to permit at least a portion of radiation 
in a straight line from a uniform source toward the detector within the 
flux pyramid to pass through openings in all of the shields to strike the 
detector in essentially uniform coverage of the utilized detector surface 
when the object is absent. In both the apparatus and the process of the 
invention, the center of gravity of the shields preferably lie along the 
same straight line from the source. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention is an apparatus and process for reducing detection of 
radiation scatter from an object through which high energy radiation 
passes within a flux pyramid from a source to a radiation detector or 
detection means. 
"High energy radiation", as used herein, means radiations having energies 
of from about 2 kiloelectron volts to about 2 megaelectron volts at wave 
lengths of from about 6.2 to about 0.0062 angstrom units. The radiation 
for medical diagnosis preferably has an energy of from about 10 to about 
100 kiloelectron volts at wave lengths of from about 1.24 to about 0.124 
angstrom units. In general, such radiation is x-ray radiation produced by 
an x-ray tube; however, the radiation may also be emitted from specially 
selected radioactive substances. 
"Detector" or "detection means", may be considered equivalent and refer to 
any means for receiving radiation containing image information from an 
object in such a way that the received radiation is or can be converted 
into a visual display in photographic or video form. Video form means an 
image produced upon the phosphorescent or luminescent surface of a 
cathoderay tube, an image produced in liquid crystal or an image produced 
by light emitting diodes or the equivalent. 
"Radiation scatter", as used herein, means deflected or secondary radiation 
resulting from the interaction of primary radiation with molecular or 
atomic forces or atomic particles within an object. 
"Flux pyramid", as used herein, means the pyramid formed by radiation 
passing in a straight line from a radiation source such as an x-ray tube 
or a radioactive isotope to the utilized surface of the detector or 
detection means. The utilized surface of the detector or detection means 
is the actual surface intended to receive radiation containing image 
information. The utilized surface may be smaller than the entire surface 
of the detector since at any given time, there may not be a desire to 
utilize the entire detector surface to receive an image. The flux pyramid 
may be a pyramid comprising planar sides, may be a cone or may have 
curvilinear sides. 
"Uniform source", as used herein, means a uniform point source of radiation 
which is constant over the time period of exposure, which time period is 
the time it takes for all of the shields to make an integral number of 
revolutions. 
"Constant angular velocity ratio" means that the ratio of the angular 
velocities of any two shields is constant but is not necessarily the same 
as the ratio of the angular velocities of any other two shields. 
The process in accordance with the invention comprises interposing a series 
of at least two spacially separated radiation shields between the object 
and the utilized surface of the detector. Each of the shields covers an 
entire section of the flux pyramid. For conventional radiography and 
usually for tomography, the section which is covered is a section of the 
pyramid formed by the intersection of a plane with the pyramid which plane 
is essentially parallel to the utilized surface of the detector. In 
general, the radiation shields are in parallel planes although a deviation 
of up to about 10.degree. but preferably less than 5.degree. from the 
parallel position, (i.e., approximately parallel) with the utilized 
surface (plane) of the detector can be tolerated. 
Each of the shields have a front surface and a rear surface which are large 
relative to the thickness of the shield. The front surface of each shield 
faces the radiation source and the rear surface of each shield faces the 
utilized surface of the detector. The shields are manufactured of a 
material, such as lead, which will not permit the passage of radiation 
from the object to the detector surface. 
Each shield is provided with a central axis which passes through its center 
of gravity in a direction substantially perpendicular to the front surface 
and to the intersected section of the flux pyramid. Each shield is 
provided with openings smaller than the object passing through the shield 
from the front to the rear surface. The ratio of the sum of the widths of 
the openings to the sum of the widths of solid shield areas is constant as 
such widths are measured along the arc of any circle having its center at 
the central axis of the shield and which circle passes through the flux 
pyramid. The openings in the shields are desirably in proportionally the 
same shapes and are disposed in proportionally the same patterns as in the 
remaining shields. The shapes of the openings are preferably circular 
sectors or trapezoids bounded by radii eminating from the central axis on 
two sides and by either straight parallel lines or arcs of circles having 
their centers at the central axis of the shields on the remaining two 
sides. The openings may also be of any other shape provided that the ratio 
of the sum of the widths of the openings to the sum of the width of the 
solid shield areas is constant along any arc of a circle having its center 
at the center of the shield as previously discussed. 
The process further comprises aligning the shields so that at least a 
portion of radiation in a straight line from the source toward the 
detector within the flux pyramid passes through openings in each of the 
shields to strike the detector, and rotating each of the shields about its 
central axis at a constant angular velocity ratio to permit at least a 
portion of radiation in a straight line from the source toward the 
detector within the flux pyramid to pass through openings in all of the 
shields to strike the detector in essentially uniform coverage of the 
utilized detector surface when the object is absent. While each shield is 
rotated at its own angular velocity at a constant angular velocity ratio, 
it is obvious that the velocity ratio must be chosen to maintain alignment 
of the openings in the shields so that radiation can pass through the 
shield series to strike the detector. Furthermore, the angular velocities 
and ratios should be chosen so that radiation from the source actually 
uniformly scans the utilized detector surface through one or more sets of 
aligned openings in the shields. 
In the process, it is desirable that an additional radiation shield be 
interposed between the source and the object such that the additional 
shield covers an entire section of the flux pyramid. The additional shield 
is of essentially the same construction as the previously described shield 
series, ie., the shield has front and rear surfaces, a central axis and 
openings. 
The additional shield is aligned with the previously described shields so 
that at least a portion of radiation in a straight line from the source 
toward the detector within the flux pyramid passes through the openings in 
each of the shields to strike the detector. The additional shield is also 
rotated about its central axis at its own angular velocity at a constant 
angular velocity ratio again to permit at least a portion of radiation in 
a straight line from a uniform source toward the detector within the flux 
pyramid to pass through openings in all of the shields to strike the 
detector in essentially uniform coverage of the utilized detector surface 
when the object is absent. Interposing the additional shield between the 
source and the object reduces exposure of a patient to radiation which 
would not reach the detector surface because it is trapped by the series 
of shields between the patient and the detector surface. The additional 
shield only permits radiation which would pass through the series of 
shields between the patient and the detector to initially enter the 
patient. In addition, the additional shield reduces scatter by eliminating 
a substantial quantity of radiation which would strike the patient to 
cause increased scattering. 
The apparatus in accordance with the invention, as previously discussed, 
comprises a series of at least two radiation shields, means for rotatably 
mounting each of the shields at its center of gravity and means for 
rotating each of the shields at its own angular velocity at a constant 
angular velocity ratio as previously discussed. The means for rotatably 
mounting the shields can be any suitable means but generally comprises a 
shaft to which the shield is perpendicularly mounted which shaft is 
supported by a suitable bearing such as a sleeve, roller or ball bearing. 
The bearings are in turn supported in a spatially separated relationship 
with each other by means of a suitable frame. Each of the shields are most 
desirably mounted on a single straight line passing from the source 
through the centers of gravity of the shields. The straight line is 
preferably not perpendicular to the shield surfaces for conventional 
radiography thus permitting radiation to pass almost perpendicularly 
through the shields and the straight line is usually, but not essentially, 
outside of the flux pyramid. 
The means for rotating each of the shields at its own angular velocity at a 
constant angular velocity ratio and preferably at constant angular 
velocities is again any suitable means for accomplishing such rotation. 
Examples of such means include a synchronous motor for each of the shields 
to which each shield is directly or indirectly connected which rotates 
each shield at a speed to provide a constant angular velocity ratio or 
positive belt or chain drives, each connected to a constant speed shaft 
driven by a single motor or a series of gears connecting each of the 
shields to a single constant speed shaft. 
The apparatus of the invention and its use in the process of the invention 
can be more particularly and clearly described by reference to the 
drawings. 
FIG. 1 is a perspective view of an apparatus in accordance with the 
preferred embodiment of the invention. FIG. 1 also illustrates the 
application of the process. 
As can be seen in FIG. 1, radiation from a source 10 which is generally an 
x-ray tube, passes in a pyramid shape 12 to the utilized surface 14 of 
detector 16. Detector 16 is usually a luminescent screen. Pyramid 12 is 
defined by radiation passing from source 10 to the perimeter 18 of 
utilized surface 14. Radiation from source 10 passes through an object 20, 
usually in the form of a medical patient, having structures varying in 
density. The more dense portions of object 20 absorbs a relatively larger 
amount of radiation 22. Radiation 22 which has passed through object 20 
therefore contains image information which is received by detector 16. A 
portion of radiation 22 may interact with molecular forces or particles 
within object 20 thus causing radiation scatter 26. When detector 16 is a 
luminescent screen, the image formed on the screen is either viewed 
directly, enhanced by amplification or photographed by means of 
photographic film 28 as shown in FIG. 1. 
The apparatus, in accordance with the invention comprises a series 30 of 
radiation shields 31 and 32 interposed between object 20 and detector 16. 
The apparatus also desirably includes an additional shield 34 interposed 
between source 10 and object 20. Each of the shields is mounted by means 
of its own shield shaft 35, 36 and 37 so that each of the shields can be 
rotated about its center of gravity 38. Shields 31 and 32 are mounted in a 
spatially separated relationship by any suitable means and may be mounted 
separately in such a relationship. As shown in FIG. 1, shields 31 and 32 
are mounted on shafts 36 and 35 respectively. Shafts 35 and 36 are 
rotatably mounted through bearings 40 and 42 so that shields 31 and 32 are 
free to rotate about their centers of gravity 38 and about central axes 49 
which pass through the center of gravity 38 and in accordance with any 
embodiment of the present invention are approximately perpendicular to 
detector plane 51 containing the surface of detector 16. The shields are 
desirably mounted in a direction such that the upper surface 44 desirably 
faces radiation source 10 and is perpendicular to a line 46 from the 
center of radiation source 10 to the center 48 of utilized detector 
surface 14. Additional shield 34 is similarly mounted on an additional 
shield shaft 37 through bearing 50. Shafts 35 and 36 are provided with 
shaft sprockets 52 and 53 which are connected by means of chains 54 and 55 
to drive shaft sprockets 56 and 57 which are mounted on drive shaft 58. 
Similarly, additional shield shaft 37 is provided with a sprocket 60 
connected by means of chain 62 to drive shaft sprocket 64. Bearings 40, 42 
and 50 are supported by means of arms 66, 68 and 70 respectively. Arms 66, 
68 and 70 are connected to frame upright 72. Drive shaft 58 is provided 
with drive sprocket 74 which is connected to motor sprocket 76 by means of 
drive chain 78. Motor sprocket 76 is connected to a shaft 80 of motor 82. 
Each of the shields 31 and 32 and additional shield 34 is provided with 
openings 84 which are preferably in the shape of truncated circular 
sectors. Openings 84 in each of shields 31, 32 and 34 are aligned in such 
a way that at least some of the radiation passing from source 10 to 
detector 16 can pass through openings 84 while most of radiation from 
source 10 which is scattered radiation, such as radiation 26, is absorbed 
by shields 31 and 32 and does not reach detector 16. 
Desirably, each of shields 31 and 32 and 34 have openings 84 in 
proportionally the same locations and each of the shields 31, 32 and 34 
completely intersect a section 86 of radiation pyramid 12. When it is said 
that openings 84 are in proportionally the same locations in shields 31, 
32 and 34, it is meant that at any given time openings 84 constitute 
proportionally the same area in the pyramid sections 86 intersected by the 
respective shields and are in proportionally the same shapes and in 
proportionally the same locations within such sections. When this is the 
case, shields 31, 32 and 34 rotate at the same angular velocity about 
their respective centers of gravity 38. 
In general, the shields, e.g., 31, 32 and 34, each individually have a 
constant ratio R for any circle passing through the flux pyramid. 
EQU R=.SIGMA.WO/SA 
where .SIGMA.WO is the sum of the widths of the openings around the circle 
and .SIGMA.SA is the sum of the widths of the solid shield areas around 
the circle as all of such widths are measured on the arc of the circle. 
The R for any shield is desirably equal to or greater than the R for any 
shield which is between the source and the object, e.g., shield 34 and is 
desirably equal to or greater than the R for any shield closer to the 
source. 
It is possible for openings 84 through respective shields 31, 32 and 34 to 
occupy proportionally different areas within pyramid sections 86; however, 
when this is the case, as shown in FIGS. 3 and 4, the shields having fewer 
openings with the largest widths are rotated at a higher speed than the 
shields having more openings with proportionally smaller widths as 
measured along the arcs. The relative speed of the wheels is the same as 
the relative proportions of opening widths to total arc circumference. For 
example, the relative speeds of shields 90 and 92 at approximately the 
same pyramid section within the radiation pyramid would be the same as the 
ratio of WO.sub.3, the width of the opening of the shield shown in FIG. 3 
to the circumference of arc 3 divided by the ratio of the opening width of 
the openings, WO.sub.4, in FIG. 4, to the circumference of the measuring 
arc A.sub.4 or given in formula form: 
EQU RV=(WO.sub.3 /CA.sub.3)/(WO.sub.4 /CA.sub.4) 
where RV is the ratio of angular velocities of shields 92 and 90, WO.sub.4 
is the width of an opening as measured along measuring arc A.sub.4 in 
shield 90, CA.sub.4 is the circumference of measuring arc A.sub.4, 
WO.sub.3 is the width of the opening in shield 92 as measured along arc 
A.sub.3 and CA.sub.3 is the circumference of measuring arc A.sub.3. As 
previously discussed, the measuring arcs A.sub.3 and A.sub.4 are 
proportionally the same distance from the centers of gravity 38 of the 
shields but are not necessarily and in fact, usually are not precisely the 
same distance from centersoof gravity 38. The distances of A.sub.3 and 
A.sub.4 from centers of gravity 38 are proportionally the same when they 
cross the intersected radiation pyramid sections at proportionally the 
same locations. The most desired shield shape is circular due to the fact 
that it is rotated; however, other shield shapes can be used. 
When varying shield angular velocities are used, in order to optimize the 
amount of radiation passing from the shield closest to the source through 
the remaining shields, it is desirable that the angular velocity and the 
number of openings in shields be related by the following formula: 
EQU NP=X 
where N is the number of intersected flux pyramid sections which will fit 
around the shield (360.degree./.theta..sub.F =N) where .theta..sub.F is 
the angle of the widest arc of the flux pyramid; X is the width of the 
openings+adjacent solid shield areas divided by opening width; and P 
equals the fractional increase in angular velocity. 
In operation, motor 82 drives motor sprocket 76 and by means of chain 78, 
in turn drives sprocket 74 which turns drive shaft 58. Sprocket 64 
attached to drive shaft 58 in turn moves chain 62 and additional shield 
sprocket 60. Shield sprocket 60 then turns shaft 37 which is attached to 
and rotates additional shield 34. Sprockets 56 and 57 are similarly 
rotated by drive shaft 58 and move chains 54 and 55 which rotate sprockets 
52 and 53. Sprockets 52 and 53 are attached to and turn shafts 35 and 36 
respectively which rotate shields 32 and 31. As shown in FIG. 1, shields 
31, 32 and 34 rotate at the same angular velocity and openings 84 are 
aligned in proportionally the same locations within their respective 
intersected pyramid sections 86. Radiation passes from source 10 toward 
detector 16; however, shield 34 intersects and stops all radiation except 
radiation which passes through openings 84 in shield 34. Radiation passing 
through openings 84 in shield 34 passes through object, ie., patient 20 
and through aligned holes 84 in shields 31 and 32 to detector 16. 
As the shields rotate, openings 84 in all of the shields move in such a way 
that radiation actually scans through patient 20. Radiation passing from a 
uniform source though openings 84 when shields 31, 32 and 34 are rotated, 
would scan utilized detector surface 14 in a uniform manner, not 
considering unequal distances from various positions in the detector to 
the source. 
Radiation which passes through openings 84 in shield 34 and is scattered 
within patient 20 is usually absorbed by shields 31 and 32 since after 
scattering it is generally no longer properly aligned with holes 84 in 
shields 30. Shield 34, as previously mentioned, absorbs all radiation 
except radiation which passes through openings 84 in alignment with 
appropriate openings in shields 31 and 32. Patient 20 is therefore not 
being unnecessarily exposed to radiation which would normally be 
intercepted by the solid shield areas 88 of shields 84. Shields 31 and 32 
as previously mentioned, absorb scattered radiation, therefore, radiation 
which is actually detected by utilized surface 14 of detector 16 has much 
sharper contrast since the background of any image detected by detector 16 
has very low contamination from scattered radiation. 
Due to the much higher contrast obtainable through the utilization of the 
apparatus and process of the invention, it is possible to use lower 
radiation dosages to obtain acceptable images or else when radiation 
dosages are used, which are comparable to those utilized in the prior art, 
substantially superior images are obtained with the process and apparatus 
of the invention. 
It is to be understood that any suitable means for rotatably mounting the 
shields in a spatially separated relationship with each other can be used 
without departing from the spirit of the invention and any suitable means 
for rotating each of the shields at its own appropriate angular velocity 
to obtain a constant angular velocity ratio can be used, such as stepping 
motors, chains and sprockets, positive drive belts or gears. 
The openings through the shields can be any desirable shape provided that 
they are selected to appropriately align with openings in the remaining 
shields and provided that as previously discussed, the ratio (R) of the 
sum of the widths of the openings to the sum of the widths of solid shield 
areas is the same around any circle passing through the flux pyramid 
having its center at the center of gravity. Although it is not necessary, 
in general, both the front shield surface 44 facing the radiation source 
and the rear shield surface 45 facing the detector are planar and are 
relatively large compared with the thickness 47 of the radiation shields. 
The shafts 35, 36 and 37 which rotate the shields, generally each lie 
along its own axis 49 which passes through the center of gravity 38 of its 
shield and is most desirably perpendicular to the plane of the section of 
the flux pyramid intersected by the shield. The centers of the shields lie 
on a single straight line 101 which passes through the centers of the 
shields to the source. Line 101 is generally outside of the flux pyramid. 
Axes 49 all intersect with but are not the same as line 101. The shields 
are most desirably in planes parallel to the plane of the detector. 
In an alternative embodiment of the process of the invention, the source, 
object, rotatable shields and detector are all moved in relationship to 
each other while the radiation source is active and while the object, 
detector and shields all continue to intersect the flux pyramid, continue 
to remain in planes parallel to the plane of their initial position and 
while constant proportional distances are maintained. "Constant 
proportional distances" means that the relationship of the distances 
between the source, object, shields and detector (collectively called 
components) to constant points on the components remains constant even 
though such distances may be increased or decreased by movement of the 
components. That is, if any one distance between two components increase 
the distances between the remaining components increase proportionally the 
same amount and if any one distance between components decreases, the 
distances between remaining components decreases by proportionally the 
same amount. In accordance with an apparatus of an alternative embodiment, 
means is provided for changing the relationship of the source, object, 
detector and shields to each other from initial positions even while the 
radiation source is active and while the object, detector and shields all 
continue to intersect the flux pyramid, continue to remain in planes 
parallel to the plane of their initial position and while constant 
proportional distances are maintained. In other respects, the process and 
apparatus is as previously described. FIG. 2 shows an alternative 
embodiment of the invention as previously described. 
Referring to FIG. 2, the shields 32A, 33A and optionally additional shield 
34A are each provided with their own synchronous drives, which may be 
stepping motors 42A, 43A and 44A respectively. Source 10A, is secured to 
rotatable arm 110 which is pivotally mounted on bearing 112 to automatic 
cam drive 114. Arm 110 is provided with a U shaped portion 111 which 
permits bearing 112 to be located on a line 113 which passes through the 
centers 115 of shields 32A, 33A and 34A. Motors 42A, 43A and 44A and 
detector 16A are pivotally secured to arm 110 by means of hinged pivot 
rods 61A, 63A, 65A and 67A respectively, which rods are behind the shields 
as viewed in the drawing. Cam drive 114 in turn is secured to rotatable 
cylinder 116 which is secured by means of cylinder pivot 118 to cylinder 
cam drive 120. Cylinder 116 is provided with L shaped portion 117 which 
permits cylinder 116 to rotate about a line passing through bearing 112. 
Cylinder cam drive 120 is in turn secured to support arm 122 which in turn 
is mounted to frame 128. An object 20A is placed on table 130 which is 
secured to frame support 132. Arm 110 can rotate on pivot 112 in the 
direction shown by arrows 134 and cylinder 116 can rotate on pivot 118 in 
the directions shown by arrows 136. Motors 42A, 43A and 44A are provided 
with slide arms 52A, 53A and 54A respectively and detector 16A is provided 
with slide arm 55A. Slide arms 52A, 53A, 54A and 55A pass through guide 
openings (not shown) in leveling arms 71A, 73A 75A and 77A respectively. 
Leveling arms 71A, 73A, 75A and 77A pass through guide openings (not 
shown) in rotatable guides 81A, 83A, 85A and 87A respectively. Rotatable 
guides 81A, 83A, 85A and 87A are rotatably mounted to frame upright 128 so 
that they rotate about the longitudinal axis of upright 128. Source 10A is 
similarly secured by slide arm 57A and leveling arm 77A. 
In operation, the apparatus as shown in the alternative embodiment can be 
used for conventional tomography or fluoroscopy. For tomography, it is 
apparent that the source, detector and shields can move relative to object 
20A in multiple degrees of motion and is thereby able to blur out all but 
a selected plane within object 20A which one desires to examine, while 
shields 32A, 33A and 34A are held in horizontal parallel positions by 
their respective slide arms and leveling arms. The multiple degrees of 
motion can be exercised independently or simultaneously to form any 
desired pattern by selecting appropriate cam motions in drives 114 and 
120. Shields 32A, 33A and 34A are secured to shafts of synchronous drives 
42A, 43A and 44A and drives 42A, 43A and 44A are secured to arm 110 by 
means of hinged pivot rods 61A, 63A and 65A respectively and detector 16A 
is secured to arm 110 by hinged pivot rod 67A. 
For changing shield distance, eg., if desired for fluoroscopy, the rods can 
be loosened so that shields 32A, 33A and 34A and detector 16A can be moved 
along arm 110 as shown by arrows 138 and 140 and again securely fastened. 
Motion along arm 110 by shields 32A, 33A and 34A can be accomplished 
without changing alignment of openings in the shields especially when 
openings are in the form of circular sectors in the same number at 
proportionally the same spacing. The object itself can be moved by 
changing the position of table 130 on frame support 132 as shown by arrows 
142.