Raster scan anode X-ray tube

An apparatus and method are provided for X-ray imagery of an object comprising an X-ray source adapted to variably dispose of a point source of X-rays about a first surface of the X-ray source and a detector adapted to receive the X-rays and translate the X-rays into electrical signals. The detector is adapted to selectively respond to incident X-rays, e.g., in accordance with the angle of incidence of the X-rays upon the surface of the detector. The detector may be formed of an array of individual detector elements, or may comprise a light transducer disposed adjacent the input to a television camera. The interrogation of the detector elements, or scan of the television camera image, may be synchronized with the movement of the X-ray source such that the spacial relationship between the movement of the point source and the sampled detector element, or scan point of the television camera, remain substantially constant as the point source moves.

BACKGROUND OF THE INVENTION 
The present invention relates to X-ray imaging devices. More particularly, 
the invention relates to devices for selectively imaging objects by 
limiting detector responses to variably selected portions of the X-ray 
beam. 
X-rays are shortwave electromagnetic vibrations which can penetrate solid 
matter. They are produced when, in a vacuum, electrons are released, 
accelerated and then abruptly retarded. To release electrons, the tungsten 
filament in an X-ray tube is heated to incandescence (white heat) by 
passing an electric current through it. The electrons are accelerated by a 
high voltage (ranging from about ten thousand to some hundreds of 
thousands of volts) between the anode (positive) and the cathode 
(negative) and impinge on the anode. When the stream of very fast 
high-energy electrons strikes a metallic anode, the electrons are rapidly 
slowed down, and some of them penetrate into the metal. High energy 
electrons that penerate into the metal atom may dislodge one or more inner 
electrons of that atom. The vacant place is then taken by one of the outer 
electrons which thus leap from the outer to an inner "shell" and, in so 
doing, emit energy in the form of radiation, i.e., X-rays. 
In some contemporary X-rays tubes, the anode, usually referred to as the 
"target", is of the rotating disk type, so that the electron beam is 
constantly striking a different point of the anode perimeter. The X-ray 
tube itself is made of glass, but enclosed in a protected casing that may 
be filled with oil to absorb the heat produced. The high voltage for 
operating the tube is supplied by a transformer with the alternating 
current rectified by means of rectifier tubes, or by means of 
barrier-layer rectifiers. 
Because of their short wavelength (10.sup.-8 to 10.sup.-10 cm) X-rays can 
pass through objects that are opaque to ordinary light, and form shadow 
images of those objects on a film or fluorescent screen. Aside from the 
well recognized medical application of X-ray devices, they are also used 
to determine the mechanical integrity of structures that cannot readily be 
examined, such as structural members within an aircraft, or the like. In 
those applications X-ray devices permit the user to make an onsight 
inspection of, for example, a hidden structural joint, without having to 
remove the aircraft to a maintenance facility and disassemble outer 
surface members. 
In order to take fullest advantage of the use of X-ray devices to perform 
structural examinations in field use, it is necessary that the device be 
readily portable and require a minimum of precise alignment before useful 
results can be obtained. Many contemporary X-ray devices require a fixed 
relation between the X-ray source and the X-ray detector, and are 
therefore unsuitable for many field uses. The present invention is 
directed to a device wherein the X-ray source and X-ray detector may be 
independently moved, and the device satisfactorily operated to produce 
X-ray imagery of an object through selective synchronization of the X-ray 
generating and X-ray detecting functions. 
In most instances, X-rays are imaged on a film consisting of an acetate 
cellulose base coated with an emulsion of silver halide and gelatin. 
Alternatively, "live" X-ray images may be created on a fluorescent screen 
coated with barium platinocyanide. In yet another construction, X-ray 
images may be focused on a detector or array matrix formed of individual 
detector elements that generate an electrical voltage or current 
proportional to the intensity of the incident X-rays. Such a detector 
matrix may be scanned, or "interrogated" at a very high rate in order to 
produce a pattern or electrical signals representative of the X-ray 
pattern incident upon the matrix. That pattern may then be communicated to 
a monitor such as a television screen where it is illustrated for viewing. 
X-ray sources typically generate X-rays in a fan-like pattern from a point 
source. When the point source is moved about in a pattern, each point in 
the pattern generates a separate fan-like pattern of X-rays. As a 
consequence of the movement of the X-ray point source, the X-ray beams 
pass through the object being X-rayed at differing angles and form shadows 
as ther paths overlap on route to the photographic or detection surface. 
The resulting images may, therefore, exhibit a lack of sharpness and 
uniformity. Various devices have been utilized to collimate the X-rays 
emitted from the point source, or otherwise enhance the sharpness of the 
image. Those devices include diaphragms that have narrow slits or 
appertures, as well as other selectively transmissive members that are 
disposed in front of the point source so as to restrict passage of oblique 
X-ray beams. Such devices typically require precise placement with respect 
to the point source of X-rays and the detection surface. Consequently, 
those devices are inadequate for many field uses in that they lack the 
flexibility to vary the angle at which the incident X-rays may be directed 
and observed in order to get a clearer picture of an irregular shaped 
object. 
The present invention is directed to addressing those and other 
deficiencies in providing an X-ray imaging system that is portable and is 
adapted to readily permit selective imaging of X-rays impinging the 
detector surface from different angles so as to enhance the image quality, 
and reduce shadows generated by the interaction of overlapping X-ray 
beams. 
SUMMARY OF THE INVENTION 
An apparatus and method are disclosed for X-ray imagery of an object. The 
invention permits selective X-ray imagery of the object from different 
angles to reduce shadows generated by the interaction of overlapping X-ray 
beam paths. The present invention comprises an X-ray source adapted to 
variably dispose of a point source of X-rays about a first surface of the 
X-ray source and a detector adapted to receive the X-rays and translate 
the X-rays into electrical signals. The detector is adapted to selectively 
respond to incident X-rays, e.g., in accordance with the angle of 
incidence of the X-rays upon the surface of the detector. The detector may 
be formed of an array of individual detector elements, or may comprise a 
light trnsducer operatively coupled to the input to a television camera. 
The interrogation of the detector elements, or scan of the television 
camera image is synchronized with the movement of the X-ray source such 
that the spatial relationship between the movement of the point source and 
the sampled detector element, or scan point of the television camera, 
remain substantially constant as the point source moves. 
The synchronization may be varied to permit normal or oblique angle views 
of the object to be imaged. Each view may be stored and subsequently 
processed to provide three dimensional imagery of the object.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, X-ray imaging apparatus at 10 is illustrated therein. 
The apparatus includes an X-ray tube 11 and detector 13, preferably formed 
as an array matrix of detector elements 27. X-ray tube 11 may be any of a 
number of commercially available X-ray tubes adapted to generate X-ray 
beams from variable locations along a surface 15 of tube 11. 
In the presently preferred embodiment, tube 11 is operative to generate an 
electron beam 17 that is deflectable within the tube 11 to impact at 
various points along the target 19, which is within tube 11 opposite outer 
surface 15. Electron beam 17 may be deflected to traverse various 
patterns, such as beam raster pattern 21. It is to be understood, however, 
that beam 17 may alternatively be deflected to traverse other patterns 
such as a circular or rectangular pattern, instead of the raster pattern 
21. 
As a consequence of electron beam 17 striking target 19, X-rays are emitted 
from outer surface 15 of X-ray tube 11 in accordance with conventional 
radiographic principles well understood by those in the art. At each point 
that the electron beam 17 traverses along raster pattern 21, a fan like 
pattern of X-rays 23 is emitted from the corresponding point on opposing 
surface 15. As illustrated at FIG. 1, at Time T.sub.0 electron beam 17 is 
directed to point 25, resulting in a fan-like pattern of beams 23 
eminating from the corresponding point on the opposite surface of tube 11. 
Detector array matrix 13 is preferably formed of a plurality of detector 
array elements 27 innerconnected to form a planner surface disposed 
generally opposite surface 15 of tube 11. Though the detector array matrix 
13 is preferably disposed substantially parallel to surface 15 of tube 11, 
the present invention does not require array 13 to be situated in any 
particular angular relation to the tube 11. It is also anticipated that 
the relationship between the point source and the selected detector 
element may be dynamically varied in accordance with a predetermined 
function. As described more fully below in connection with FIGS. 4 and 5, 
various methods and apparatus for sampling the outputs of a predetermined 
pattern of detector array elements may be effected utilizing components 
and processing techniques well known to those of ordinary skill in the 
art. 
As shown at FIG. 1, the rays 23 eminating from point 25 on tube 11 impact 
the surface of detector array matrix 13 at various angles. Rays 23 include 
rays 29 that impact the surface of detector array matrix 13 at an oblique 
angle, and ray 31 that impacts normal to the surface of detector array 
matrix 13. Though each of the array elements 27 are individually excitable 
by the incident X-rays, the present invention is operative to selectively 
sample outputs from the detector elements, e.g., only those elements 
excited by incident X-ray beams striking the detector elements 27 at a 
desired angle of incidence i.e., with the respect to the plane of the 
dector surface. The invention thus selects outputs only from those 
detector array elements in a predetermined position with respect to the 
contemporaneous location of the point source 25 of the X-ray beams. Though 
the distance between tube 11 and array matrix 13 is variable and need not 
be limited to any particular range, it is anticipated that in many 
practical applications the tube 11 may be disposed close to the surface of 
array matrix 13, e.g., approximately three to eight inches (3"-8" ). 
FIG. 2 illustrates the same structure disclosed at FIG. 1, except that the 
point source is disposed at a different position 26 along the surface of 
tube 11. As was the case with FIG. 1, a fan of X-ray beams eminates from 
point 26 and strikes the surface of the detector array matrix 13 at 
various angles. Though each detector element 27 upon which an X-ray beam 
is incident may be excitable by that beam, the outputs of only a selected 
one or more of the detector elements is contemporaneously output for 
processing and/or display. The relationship between the point source and 
the selected element remains the same, e.g., only the element directly 
opposite the point source 26 is sampled as the point source traverses the 
surface of tube 11. 
The selected relationship between the detector element whose output is 
sampled and the location of the point source along the opposing surface of 
tube 11, may be selected in accordance with the particular application or 
the physical characteristics of the object being imaged. That spatial 
relationship may be varied to permit viewing of the object to be X-rayed 
from various angles of incidence. Views from different angles of incidence 
may provide greater detail of the three dimensional object being examined. 
Moreover, the selective time varient interrogation of detector array 
elements in conjunction with the instantaneous position of the source of 
the x-ray beam avoids contemporary problems associated with the appearance 
of shadows on the image. Such shaddows result from the combined effects of 
overlapping x-ray beams having differing angles of incidence, yet 
impacting the detector surface at the same location, i.e., X-ray beams 
that were transmitted from different positions and pass through the object 
at different angles. 
FIG. 3 illustrates an alternative embodiment of the present invention 
utilizing a different X-ray generator. Though the alternative X-ray 
generator 37 functions to transmit a pattern of X-ray beams in a different 
manner than tube 11, illustrated at FIGS. 1 and 2, the location and 
direction of the X-rays emitted from the X-ray generator 37 may also be 
varied, and the sampled detector element output may be selected in 
accordance with such location and direction variations, in substantially 
the same manner as described in connection with FIGS. 1 and 2. 
FIG. 4 illustrates an exemplary circuit diagram that may be used to effect 
selective sampling of the detector array matrix 13 in conjunction with the 
movement of the X-ray point source. As previously indicated, detector 
array 13 is preferably formed of a planner array of detector elements 27. 
Each of the elements 27 is separately exciteable so as to produce an 
output signal when an X-ray beam is incident upon that element. The output 
of each element 27 may be separately coupled to a multiplexer 43 within 
output control circuit 50. Multiplexer 43 may be any of various 
commercially available devices such as the model 7100 Multiplexer produced 
by ITI Switching Inc. Multiplexer 40 operative to selectively communicate 
the output of one or more detector elements 27 to a display 52 in 
accordance with control signals received from interrogator sequencer 45. 
Microprocessor 47 is operative to regulate the sequencing function of 
interrogator sequencer 45 such that sequencer 45 enables the appropriate 
output signals from multiplexer 43 at the correct time. 
Synchronization circuit 51 is in electrical communication with X-ray tube 
driver 49 and interrogator sequencer 45, which controls the particular 
detector element 27 being interrogated at a particular time. 
Synchronization circuit 51 provides clock signals to driver 49 and 
sequencer 45 so as to synchronize the instantaneous movement of the X-ray 
source along the surface of tube 11, and the interrogation of the detector 
elements 45. Synchronization circuit 51 is preferably responsive to 
control signals from microprocessor 47, in output control circuit 50, 
which also communicates control signals to interrogator sequencer 45. 
Those control signals from microprocessor 47 effectively permit variations 
of the relationship between the location of the X-ray source and the 
contemporaneous location of the sampled detector elements. 
In one application, synchronization circuit 51 and output control circuit 
50 cooperate such that only the detector element directly opposite the 
point source is sampled as the X-ray source traverses a pattern along the 
surface of tube 11. In such a scenario the detector array may effectively 
respond only to X-rays having an angle of incidence substantially normal 
to the upper surface of the detector elements. Alternatively, 
synchronization circuit 51 and output control circuit 50 can cooperate to 
adjust the sampling of the detector array such that only detector elements 
laterally offset from the contemporaneous location of the point source are 
interrogated. In that scenario the circuitry is effective to limit the 
response of the detector matrix only to X-rays having an angle of 
incidence oblique to the upper surface portion of the detector. 
Consequently, the precise angle of X-ray imagery of the object under 
investigation may be varied under the control of microprocessor 47, i.e., 
the relative positions between the instantaneous location of the point 
source and the location of the sampled detector element(s) may be 
selectively varied. 
Microprocessor 54 is connected to display 52 and is adapted to map images 
of the object under examination from various angles. Microprocessor 54 
will then communicate signals back to display 52 in order to illustrate a 
composite representation of the object being examined, showing features of 
the object in three dimensions. 
By the foregoing technique, it should be apparent to those of ordinary 
skill in the art that the present invention is effective to selectively 
focus an X-ray image at any of a wide range of angles of incidence. Thus, 
objects having irregular shapes and surfaces may be imaged from various 
angles without degradation of image quality due to overlapping X-ray 
beams. 
In field use, it may be difficult to determine whether the array 13 is 
disposed substantially parallel to and opposite the lower surface of tube 
11. Accordingly, it may be difficult to determine the desired 
synchronization based solely upon the supposed relative positions of the 
tube 11 and array 13. However, visual inspection of display 52, in 
conjunction with variation of synchronization circuit 51 permits dynamic 
modification of the synchronization relationship between the movement of 
the X-ray point source and the sampling of the detector elements 27 in 
order to arrive at the clearest synchronization setting for the surface 
area that the operator desires to view. 
Though one exemplary synchronization and sampling circuit is illustrated at 
FIG. 4, it will be recognized by those of ordinary skill in the art that 
various other equivalent sampling and synchronization circuits may be 
utilized without departing from the spirit and scope of the present 
invention. Moreover, it will also be recognized that although the above 
description is principally directed to variable selective interrogation of 
the detector array element in relation to a fixed pattern of movement of 
the X-ray source, it is recognized that, in an alternative embodiment, the 
detector sampling pattern may remain constant and the contemporaneous 
location and/or activation of the X-ray source may be varied. In either 
case, i.e., selective variation of the detector sampling pattern or 
selective variation of the X-ray point source, the significant consequence 
is that the contemporaneous spacial relationship between the point source 
and the sampled detector element is made selectively variable so as to 
limit X-ray imagery to a desired angle of incidence. 
FIG. 5 illustrates an alternative embodiment of the present invention 
wherein the detector array matrix 13 is replaced by screen 57 and a 
television camera 62 comprising detection tube 53, and sweep control 55. 
In the embodiment illustrated at FIG. 5 transducer screen 57 is operative 
to translate incident X-ray beams into light signals at points 
corresponding with the location at which the incident X-ray beam strikes 
the surface of screen 57. Camera tube 53 and sweep control 55 are 
operative to perform a raster scan the surface of camera tube 53 opposite 
screen 57 to generate electrical output signals representative of the 
instantaneous location of light signals incident on the surface of camera 
tube 53. 
Synchronization circuit 51 provides clock signals to sweep control 55 and 
x-ray tube driver 49, which collectively control the instantaneous 
movement of the scan point along the surface of camera tube 53 and the 
contemporaneous location of the X-ray point source along the lower surface 
of X-ray tube 11, respectively. As discussed in connection with FIG. 4, 
synchronization circuit 51 is preferably responsive to control signals 
from microprocessor 47 in output control circuit 60. Microprocessor 47 is 
adapted to generate a control signal to synchronization circuit 51 in 
order to vary the timing of the scan of the surface of camera tube 53 in 
relation to the movement of the point source of the surface of X-ray tube 
11. Thus, the spacial relationship between the scan point(s) and the 
location of the x-ray point source may be varied through a wide range of 
relative positions such that, as with the circuit described at FIG. 4, the 
object to be imaged may be viewed from any of a variety of angles of 
incidence. 
As was also described in connection with Figure 4, the circuitry 
illustrated in FIG. 5 may be varied such that the scan of the camera tube 
53 remains constant and the activation and/or contemporary location of the 
X-ray point source within tube 11 may be varied to effect the desired 
spacial relationship between the location of the point source and the scan 
point. 
In the presently preferred embodiment, X-ray tube 11 may be based on any of 
a variety of commercially available cathode ray tubes such as those 
manufactured by EMI/THORENS of New Jersey, with an operating voltage 
increased to a minimum of approximately 50 kv. The higher voltage level 
provides sufficient energy so as to measure the emission of photons as the 
electron beam strikes the target. It is also preferred that a normal 
phosphorous interior coating be replaced with a coating of alternative 
material, such as tungsten, which is more effective in translating the 
impacted electron beam into X-rays. A 0.002.varies. to 0.003" layer of 
tungsten is presently believed to be sufficient to facilitate operation of 
the invention. Alternative types of cathode Ray tubes that irradiate a 
point on the face of the tube from the front of the tube, rather than from 
the rear, e.g. Sinclair tubes may also be used in conjunction with the 
present invention. 
Detector array matrix 13 may be any of a number of rays of detector 
elements, such as the CCD222 detector, manufactured by Fairchild 
Corporation. 
Transducer screen 57 may be any of a number of commercially available 
screens adapted to translate incident X-rays into light signals, such as 
the image intensifying screen manufactured by Hamamatsu Corporation. 
Another exemplary device suitable for use in connection with the present 
invention is an intensifier tube adapted to form a visable image of an 
object irradiated by X-rays. Such advice, described in connection with 
associated circuitry, is disclosed in U.S. Pat. No. 4,543,605 for "X-ray 
Examination Apparatus." The television camera, including camera tube 53 
and sweep control 55 may be any of a number of commercially available 
television cameras such as the Vidicon camera manufactured by RCA. 
Microprocessors 47 and 54 may be commercially available devices such as 
the model PCXT microprocessor produced by IBM. 
Though the present invention has been described in connection with the 
presently preferred embodiment, it is anticipated that various 
modifications and additions may be made to that embodiment without 
departing from the spirit and scope of the present invention, which is 
defined by the appended claims.