Abstract:
A compact x-ray source and assembly is disclosed. The x-ray source is configured to operate without the need of a transformer within the x-ray source. Due in part to the elimination of components, and further due to the unique assembly of the x-ray source, the x-ray source is compact and can fit beneath, rather than above an x-ray transparent patient table. Accordingly, the x-ray source projects x-rays in an upwardly direction toward the object to be imaged. As a result of the unique configuration of the x-ray source, scattered x-rays are directed away from upper body areas of attending medical staff and radiation to the sensitive tissue of a patient is reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the field of x-ray imaging systems, including among other things, x-ray sources for diagnostic x-ray imaging systems. 
     2. Background 
     Real-time x-ray imaging is increasingly being utilized by medical procedures as therapeutic technologies advance. For example, many electro-physiologic cardiac procedures, peripheral vascular procedures, PTCA procedures (percutaneous transluminal catheter angioplasty), urological procedures, and orthopedic procedures benefit from the use of real-time x-ray imaging. 
     A number of real-time x-ray imaging systems are known. These include fluoroscope-based systems where x-rays are projected into an object to be x-rayed and shadows caused by relatively x-ray opaque matter within the object are detected on the fluoroscope located on the opposite side of the object from the x-ray source. 
     Reverse-geometry x-ray imaging systems are also known. In such systems, an x-ray tube is employed to generate x-ray radiation. Within the x-ray tube, high-energy charged particles are generated and focused on a small spot on the relatively large target of the tube, inducing x-ray radiation emission from that spot. The charged particles are deflected (electromagnetically or electrostatically) in a raster scan pattern or otherwise over the target. A small x-ray detector is placed at a distance from the target of the x-ray tube. The detector typically converts x-rays that strike it into an electrical signal in proportion to the detected x-ray intensity. 
     Known embodiments of x-ray imaging systems place the x-ray source above the patient, wherein each of the component parts of the x-ray scanning tube assembly are stacked on top of the other components, one component after another (e.g., from bottom to top, a vacuum envelop assembly below a charged particle generator, the charged particle generator below a high-voltage terminal assembly, etc.) In these systems, a high-voltage power supply receptacle is connected to the high-voltage terminal assembly with the longitudinal axis of the high voltage receptacle parallel with the projection axis of the charged particle generator. 
     When the x-ray imaging system is activated and radiation is projected from the x-ray scanning tube, the radiation is generally in a downward direction and some of the radiation scatters off the patient and the x-ray table supporting the patient. Since the radiation is in a generally downward direction the scattered radiation is directed predominantly in an upward direction towards the most sensitive portions of the body of the attending staff, namely the head and neck. Furthermore, since patients usually lie face up on an x-ray table, when a woman is being imaged, her breast tissue which is typically more sensitive than most other tissue types, is subjected to the direct radiation from the x-ray source. 
     Thus, there is a need for an x-ray imaging system that will minimize the risks to the patient and the attendant staff, as well as allow the x-ray imaging system to be more useful. 
     SUMMARY OF THE INVENTION 
     A compact x-ray source and assembly is disclosed. An embodiment of the present invention comprises an x-ray source wherein a high-voltage receptacle comprises a receptacle axis defined by the longitudinal axis of the high-voltage receptacle and a charged particle gun comprises a projection axis and a projection plane perpendicular to the projection axis. The high voltage receptacle and the charged particle are arranged such that an angle is formed between the receptacle axis and the projection plane, wherein the angle (which is the smallest angle formed by the intersection between the receptacle axis and projection plane) is less than 75 degrees. 
     According to another embodiment, power to the gun electronics is provided without the need for a transformer. 
     These and other objects, advantages, and aspects of the present invention will become apparent to those of ordinary skill in the art from a consideration of the drawings, description, and claims of the invention contained herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which, like reference numerals refer to similar elements and in which: 
     FIG. 1 is a block diagram showing the basic components of an x-ray imaging system; 
     FIG. 2 is a side-view of a preferred x-ray imaging system; 
     FIG. 3A is a perspective view of a preferred x-ray imaging system shown rotated to facilitate explanation; 
     FIG. 3B is a perspective view of a rotator mechanism according to one embodiment of a preferred x-ray imaging system; 
     FIG. 3C is a perspective view of an angulation mechanism according to one embodiment of a preferred x-ray imaging system; 
     FIG. 4 is a perspective view of a preferred high-voltage vessel; 
     FIG. 5 is an exploded view of a preferred high-voltage vessel with components associated therewith; 
     FIG. 6 is an exploded view of a preferred charged particle gun electronics; 
     FIG. 7 is a second exploded view of a preferred high-voltage vessel with components associated therewith; 
     FIG. 8 is an exploded view of a preferred x-ray source; 
     FIG. 9 is a perspective view of the x-ray source of FIG. 8 mounted on a gantry; 
     FIG. 10 is a block diagram of a preferred imaging system; 
     FIG. 11 is a side elevation view of FIG. 4, parallel to a projection axis. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 depicts an embodiment of a presently preferred x-ray imaging system. The x-ray source  100  preferably comprises an x-ray tube and a high-voltage charged particle source. The high-voltage charged particle source is preferably connected to an adjustable high-voltage power supply capable of generating approximately −70 kV to −120 kV. 
     According to a preferred embodiment, the high-voltage power supply provides a DC output to the x-ray imaging system. At this voltage level, x-ray source  100  produces a spectrum of x-rays ranging to 120 keV. X-ray source  100  is an example of a scanning beam x-ray source in which the charge particle beam is scanned across a target assembly. X-ray source  100  preferably includes deflection coils  104  under the control of a scan generator  108 . High-energy charged particles  112  generated within vacuum chamber  158  by gun  111  are scanned across a target assembly  120  in a predetermined pattern. For example, the predetermined pattern may be a raster scan pattern, a serpentine (or “S” shaped) pattern, a spiral pattern, a random pattern, or such other pattern as may be useful to the task at hand. The predetermined pattern may be a “stepping” pattern in which the high-energy charged particles  112  are dwelled at a particular location on the target assembly  120  for a period of time before being moved to dwell at other locations on the target assembly  120 . An apparatus that can be used in an embodiment of the invention for generating and moving charged particles across target assembly  120  is disclosed in commonly owned U.S. Pat. No. 5,644,612, which is incorporated herein by reference in its entirety. 
     Charged particles  112  pass through vacuum chamber  158  and strike target assembly  120  at focal spot  124 . X-rays  128  are emitted in all directions (although the term “x-rays” are used herein, it is for illustration purposes only—other forms of radiation can be employed according to the present invention.) For simplicity, only a portion of the x-rays  128  are shown. The x-rays  128  preferably pass through a collimator toward the object  132  to be investigated. To optimize system performance of a presently preferred embodiment, x-rays are generated that diverge in a manner that just covers the detector  136 . This is preferably accomplished by placing a collimating element between the target assembly  120  of the x-ray source  100  and the detector  136 , and more preferably between object  132  and x-ray source  100 . According to one embodiment, the x-rays  148 , after passing through collimation grid  144 , only diverge slightly from axis  150 . 
     The presently preferred configuration for the collimating element is a grid of x-ray transmissive cylinders or apertures  140 . Collimation grid  144  is designed to permit passage to only those x-rays whose axes are in a path (e.g. axis  150 ) that directly intersects the detector  136 . Collimation grid  144  preferably does not move with respect to the detector  136  while the system is in operation. Thus, as charged particles  112  are scanned across target assembly  120 , at any given moment there is only a single beam of x-rays  148  which pass through object  132  to detector  136 . According to one embodiment, detector  136  has a face having an area, wherein the area is broken into individual segments  160 . Each segment is a detector which, when combined, form a detector array, simply referred to as detector  136 . A collimation grid  144 , useful in an embodiment of the invention, is disclosed in commonly owned U.S. Pat. No. 5,859,893, which is incorporated herein by reference in its entirety. 
     The output of detector  136  is processed by an image reconstruction system  156  and displayed by a video display device  154  which is preferably attached to a workstation  152 . The video display device  154  allows attending staff to view the x-ray images. 
     FIG. 10 depicts a block diagram of an embodiment of the image reconstruction system  156 . The image reconstruction system  156  comprises a PCI interface  1010 , which connects to control workstation  152 . A detection module  1020  comprises the components of detector  136  and receives x-ray transmissiveness information. Image reconstruction chassis  1005  comprises an interface module  1030 , one or more plane reconstruction modules  1040 , an image selection module  1050  and an image preprocessor  1060 . The various components on the image reconstruction chassis  1005  are interconnected via one or more busses  1100 , which also include control lines. PCI interface  1010  and detection module  1020  are coupled to interface module  1030 , whereas image preprocessor  1060  is coupled to video post processor  1070 . Video post processor  1070  is coupled to display monitors  1080 . 
     Details of the presently preferred embodiments of the components depicted with reference to FIG. 10 are described in detail in copending U.S. patent application Ser. Nos. 09/167,318, 09/167,397, 09/167,171, 09/167,413, all of which are incorporated herein by reference in their entirety. 
     According to a preferred embodiment, information about the x-rays  148  detected at the detector  136  is fed back to scan generator  108 . Accordingly, the workstation  152  and the scan generator  108  are coupled. 
     Details of presently preferred embodiments of the elements depicted in FIG. 1, as well as elements related to the same, are described in further detail in copending U.S. patent application Serial Nos. 09/167,524, 09/167,405, 09/167,523 and 09/167,639, filed on the same day herewith, all of which are incorporated herein by reference in their entirety. 
     FIG. 2 is a side view of a presently preferred x-ray imaging system  200 . X-ray imaging system  200  comprises an x-ray source  204  connected to one end of a curved gantry  208 . At a second end of curved gantry  208  is attached a detector  212 . According to one embodiment, the curved gantry  208  is attached to a base support  216 . The gantry  208  is preferably capable of spherical movement. 
     X-ray table  220 , preferably having one or more x-ray transparent areas, supports an object for which an x-ray image is desired. According to an embodiment of the x-ray table  220 , the x-ray table  220  can be a substantially flat table, having no dips or valleys. However, according to another embodiment it may include one or more dips or valleys to more approximately match the general shape of the object being imaged. The x-ray source  204  is preferably located at the end of the gantry that is capable of movement in the lower hemisphere. 
     According to one embodiment, cabinet  218  supports a control workstation and display device (e.g., control workstation  152  and monitor  154 ). 
     FIGS. 3A-C depict, in greater detail, embodiments of mechanisms that facilitate the hemispherical movement of the gantry  208  as is known in the art. 
     In FIG. 3A, gantry  208  is depicted rotated about a rotational pivot axis  304 . Rotator mechanism  308 , depicted in further detail in FIG.  3 B and described below, supports gantry  208  and provides a force to drive gantry  208  about axis  304 . In addition, a hydraulic support arm  312  further supports the load and rotation of gantry  208  as it is rotated about axis  304  by rotator mechanism  308 . 
     According to a preferred embodiment, gantry  208  is further configured to slide along a curved path concentric with a curve following the shape of gantry  208 . Projection axis  316 , formed between x-ray source  204  and detector  212 , and pivot axis  304  intersect at point  324 . Angulation axis  320  is perpendicular to projection axis  316  and pivot axis  304 . Angulation mechanism  328  provides support and force to slide gantry  208  such that gantry  208  slides in a circular or curved path about angulation axis  320 . According to one embodiment, angulation mechanism  328  comprises bearing rails  332  and two drive belts  336 . According to one embodiment, the bearing rails  332  also provide support for gantry  208 . 
     An enlarged view of the circled area  330  of angulation mechanism  328  is depicted in FIG.  3 C. Angulation mechanism  328  further comprises an electromechanical actuator  340  and belt drives  344 . Electro-mechanical actuator  340  rotates a drive wheel  348 . Drive wheel  348  is connected via the belt drives  344  to roller  352  around which drive belts  336  are connected with tension. A control signal (not shown) is received by angulation mechanism  328  which, in turn, causes actuator  340  to begin to rotate drive wheel  348  and consequently drive belts  336  begin to move. As drive belts  336  move, they carry gantry  208  along the path formed by bearing rails  332 , or in other words, in a curved path about angulation axis  320 . 
     Turning to FIG. 3B, it depicts in further detail rotation mechanism  308 . Rotation mechanism  308  is connected to gantry  208  via a rotational support member  356  (FIG. 3A) that is connected to bearing rails  332  (FIG.  3 A). The rotational support member  356  provides not only structural support between the gantry and base support  216 , but also, in conjunction with a hydraulic support arm  312 , rotational assistance to rotation mechanism  308 . An electro-mechanical rotator actuator  360  provides force to rotate gantry  208  about rotational pivot axis  304 . As the rotator actuator  360  is actuated, internal gears (not shown) within the actuator  360  turn. While the internal gears turn, teeth  368  on rotational drive gear  364  engage the internal gears of the actuator  360  and rotate rotational drive gear  364  about axis  304 . Rotational drive gear  364  is connected to gantry  208  through rotational support member  356 , so when rotational drive gear  364  turns so does gantry  208 . 
     FIG. 4 depicts high-voltage vessel  400 . High-voltage vessel  400  houses charged particle gun electronics (not shown) that is employed to control the charged particle gun (e.g., gun  111 ). Further, high-voltage vessel  400  is also configured to receive a high-voltage power supply line (not shown), which operates at a voltage potential between −70 and −120 kV. According to a preferred embodiment, high-voltage vessel  400  is also configured to receive fiber optic control lines (not shown) that are used to control the charged particle gun electronics. 
     Because high-voltage vessel  400  receives a high-voltage power supply line and the high-voltage vessel itself has a voltage potential at ground, the interior surface of high-voltage vessel  400  is polished and free from irregularities which may cause electrostatic discharge between the high-voltage vessel  400  and any object within the high-voltage vessel  400  that is maintained at a high-voltage (e.g., gun electronics). Additionally, sharp edges on the interior surface of the high-voltage vessel  400  are preferably chamfered or rounded to minimize the possibility of electrostatic discharge. To further protect against electrostatic discharge, high-voltage vessel  400  is sealably enclosed and designed to hold a non-conducting medium to prevent such electrostatic discharge. According to a preferred embodiment, the non-conducting medium is sulfur-hexafluoride (SF 6 ) gas. The SF 6  is preferably maintained in high-voltage vessel  400  at a pressure of 4 atm. 
     According to a preferred embodiment, high-voltage vessel  400  comprises a cylindrical chamber  404 , which is larger in diameter than in height. The cylindrical chamber  404  has a chamber wall  408 , an inner surface  412 , an outer surface  416 , a top surface  420  and a bottom surface  424 . The top surface  420  of cylindrical chamber  404  preferably is connected to a washer-shaped plate  428  that creates an inner lip and an outer lip  432 , with reference to the chamber wall  408 . Circumferentially arranged about the outer lip  432  of plate  428  are a number of apertures  436  though which fasteners may pass. Additionally, along the inner most circumference of plate  428  is a mounting ring  440  comprising a number of evenly distributed apertures  444 . The apertures  444  are designed to receive fasteners that will connect the high-voltage vessel  400  to the vacuum chamber (e.g., vacuum chamber  158 ). 
     The bottom surface  424  of cylindrical chamber  404  is preferably configured to receive a chamber cover (not shown). A number of evenly distributed cover apertures  448  are circumferentially arranged about the bottom surface  424  and allow the chamber cover to be sealably attached to the cylindrical chamber  404 . When attached to bottom surface  424  of cylindrical chamber  404 , the chamber cover is preferably flush with the inner surface  412  of the cylindrical chamber  404 . Additionally, cylindrical chamber  404  preferably has smoothly chamfered interior edges  452 . 
     In the broader spirit of the invention, the high-voltage vessel  400  is not limited to having a cylindrical chamber, such as cylindrical chamber  404 , rather, high-voltage vessel comprises any suitable chamber configured to house a gun electronics. In this regard, the high-voltage vessel  400  can comprise, for example, a spherical chamber or an elliptical/oval chamber. 
     High-voltage vessel  400  preferably comprises a sleeve or tube  456 , attached to the outer surface  416  of the chamber wall  408  and which creates an opening between the interior of the tube  456  and the inner surface  412  of cylindrical chamber  404 . According to an embodiment, the tube  456  has an elliptical or oval shape about a longitudinal axis and a slight elbow near one end. 
     In an embodiment, the tube  456  and the cylindrical chamber  404  are arranged such that the longitudinal axis of tube  456  form an angle φ with a plane that is perpendicular, or substantially perpendicular to the longitudinal axis of cylindrical chamber  404 . Angle φ is the smallest angle formed by the intersection between the longitudinal axis of tube  456  and the plane perpendicular to the longitudinal axis of cylindrical chamber  404 . According to an embodiment, angle φ is less than 75 degrees, and in an alternate embodiment, angle φ is less than 30 degrees. 
     In an alternate embodiment, the longitudinal axis of the tube  456  preferably passes through the cylindrical chamber  404  to the inner surface  412  of chamber wall  408  such that the longitudinal axis of the tube  456  and the longitudinal axis of the cylindrical chamber  404  form an acute angle, as measured, generally, between the longitudinal axis of the tube  456  and a projection direction of a charged particle gun. In another embodiment the angle is substantially perpendicular, that is between approximately 60 and 120°. Finally, it should be noted that the longitudinal axis of the tube  456  and the longitudinal axis of the cylindrical chamber  404  do not have to be coaxial. 
     At one end of tube  456  a number of fastener apertures  464  are disposed about the outer edge  460 . The fastener apertures  464  are configured to engage fasteners which secure a high-voltage feed through (not shown) to the high-voltage vessel  400 . High-voltage vessel  400  preferably comprises a tube support  466  disposed between the outer lip  432  of the cylindrical chamber  404  and above the tube  456 . 
     FIG. 5 is an exploded view of a high-voltage vessel  400  and the components associated therewith. For example, high-voltage vessel  400  houses charged particle gun electronics  504 , which is connected to the charged particle gun (not shown). A vessel cover  508  sealably encloses gun electronics  504  within the cylindrical chamber  404 . 
     High-voltage mount  512  attaches to tube  456  at end  460 . According to one embodiment, high-voltage mount  512  comprises a high-voltage receptacle  524  having a feedthrough end  525 , which preferably receives one end of a −120 kV power supply line  516 , a fiber optic receptacle  520 , which preferably receives fiber optic control lines, and a high-voltage feedthrough  528 , which shields the interior of tube  456  from the end of high-voltage power supply line  516 . A receptacle vector  527  is defined by the longitudinal axis of the high voltage receptacle  524  and the direction of insertion of the high voltage cable  516  into the high voltage receptacle  524 . When enclosed, high-voltage vessel  400  preferably does not allow gas to flow from the interior of the high-voltage vessel  400  out and vise-versa. A sealant or gasket may be disposed between the cover  508  and the bottom surface  424  of the cylindrical chamber  404 , and the mount  512  and the end  460  of the tube  456 . Fiber optic receptacle  520  is preferably sealed with or comprised of an epoxy resin. 
     FIG. 6 depicts an exploded view of gun electronics  504 . According to one embodiment, the gun electronics  504  comprises an end cap  608 , a ring housing  612  and a printed circuit board  620 . The ring housing  612  mounts to the end cap  608 . Disposed between the ring housing  612  and the end cap  608  is the printed circuit board  620 . The printed circuit board  620  has on it control electronics to control charged the particle gun. According to another embodiment, the gun electronics  504  further comprises a mechanical ring housing  614  and, on top of the mechanical ring housing  614 , a second printed circuit board  618 . The mechanical ring housing  614  and the second printed circuit board  620  are disposed between the end plate  608  and the first printed circuit board  620 . Further, a fiber optic and power cable connector  628  is mounted to a side of mechanical ring housing  614 , and an electronics cover  624  is connected to the bottom surface of ring housing  612 . The electronics cover  624 , the ring housing  612  and the mechanical ring housing  614  each contain a number of openings  636  through which gas and heat may pass. Preferably, if high-voltage vessel  400  is filled with SF 6  gas, then the gas freely flows through the openings  636 . In a preferred embodiment, a charged particle gun (not shown) is mounted to end plate  608  via a gun sleeve  632 . When the x-ray source is activated, the gun is capable of projecting charged particles along the longitudinal axis of the charged particle gun and towards the target (not shown) that is above the end plate  608 . 
     FIG. 7 is a perspective exploded view that depicts the interconnections between high-voltage vessel  400  and its associated components. According to an embodiment, once the high-voltage vessel  400  is assembled, two conducting cables (not depicted in FIG. 7) run between the high-voltage receptacle  528  and gun electronics  504  (FIG.  5 ). Since the gun electronics  504  does not include a power transformer to power the electronics circuits enclosed therein, power is provided by the two conducting cables, which have a voltage differential of approximately 30 V. The gun electronics  504  is maintained at approximately −100 kV during operation of the x-ray source. In addition to the two conducting cables, fiber optic cables (not shown) are also run between connector  628  and fiber optic cable receptacle  520 . 
     FIG. 8 is an exploded view of a preferred embodiment of the x-ray source  800 . According to the preferred embodiment, the x-ray source  800  comprises a high-voltage vessel  400 , a charged particle gun, a first focus coil, a second focus coil, deflection coils, a deflection insulator, a target assembly  826  and a vacuum chamber. In one embodiment, the x-ray source is stacked, from the bottom up, such that the high-voltage vessel  400  receives an electron gun  804 . Electron gun has a projection axis  803  and a projection end  806 . A projection vector  805  is defined by the projection axis in a projection direction. the projection direction is from the electron gun towards the target assembly  826 . 
     A first focus coil  808  is positioned above the electron gun  804 . A second focus coil  812  is mounted on top of the first focus coil  808 . A deflection insulator  820  is received by openings within the first focus coil  808 , the second focus coil  812  and the deflection coils  816 . The deflection insulator  820  is attached to the electron gun  804 . A vacuum chamber  822  is attached to an end of the deflection insulator  820 , and a target assembly  826  is placed over the vacuum chamber  822 . A cradle  828 , wraps around approximately three-quarters of the x-ray source  800 , and extends between the top surface of high-voltage vessel  400  and approximately midway along the vacuum chamber  822 . Finally, the high-voltage power cable  516  is received by high-voltage vessel  400  at high-voltage receptacle  524 . 
     The currents flowing within first focus coil  808  and second focus coil  812  cause the charge particles  112  to be brought into focus at focal spot  124 . Further, deflection coils  816  cause the charged particles  112  to track a particular scan pattern across target assembly  826 . 
     FIG. 9 is a perspective view of the x-ray source  800  mounted at one end of gantry  208 . According to a preferred embodiment, x-ray source  800  is mounted on the lower end of gantry  208 . To provide further support to x-ray source  800  as it rests on one end of gantry  208 , cradle  828  is attached to gantry  208  via support arms  904 . Fiber optic communication and control cables  908  are received into fiber optic cable receptacle  520 . Both the fiber optic cables  908  and the high-voltage power supply line  516  are strung along the interior of gantry  208 . 
     Referring to FIG. 11, according to an embodiment, the high-voltage power supply line  516  is received into a high-voltage receptacle  524  on high voltage vessel  400  such that the longitudinal axis of high voltage receptacle  524 , illustrated by receptacle vector  527 , forms an angle φ with a projection plane  810  defined by the projection axis of the charged particle gun. In an embodiment, the projection plane  810  is defined as a plane perpendicular or substantially perpendicular to the projection axis of the charged particle gun and angle φ is the smallest angle formed by the intersection of the longitudinal axis (receptacle vector  527 ) of the high voltage receptacle  524  with the projection plane  810 . In one embodiment, angle φ is less than 75 degrees, and in another embodiment, angle φ is less than 30 degrees. 
     In an alternate embodiment, the high-voltage power supply line  516  (FIG. 9) is received into high-voltage receptacle  524  on high-voltage vessel  400  such that the longitudinal axis (receptacle vector  527 ) of the high-voltage receptacle  524  forms an acute angle with the projection axis  316  of the charged particle gun, as measured between the high-voltage receptacle  524  and the charged particle gun with reference to the projection direction of the charged particle gun. Alternatively, the angle is substantially perpendicular, between approximately 60° and 120°. Finally, it should be noted that the longitudinal axis (receptacle vector  527 ) of the high-voltage receptacle  524  does not need to intersect the projection axis of the charged particle gun. 
     According to an embodiment of the innovative configuration and assembly of the x-ray source described herein, the x-ray source is compact enough to fit below, rather than above, the patient and the x-ray table  220 . Consequently, when the x-ray source is activated and radiation is emitted, the x-ray scatter off the patient and x-ray table is predominantly downward, rather than upward. As a result, the risk of exposure to harmful x-rays is reduced to the attending staff, as well as depending on the procedure being performed, to the x-ray sensitive tissues of the patient. Additionally, the positioning of the x-ray source is highly adjustable, allowing movement in a spherical pattern about the x-ray table or patient. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will be evident, however, that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative, rather than a restrictive sense.