Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05G—X-RAY TECHNIQUE
  • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
  • H05G1/08—Electrical details
  • H05G1/10—Power supply arrangements for feeding the X-ray tube
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
  • H01J35/153—Spot position control
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/24—Tubes wherein the point of impact of the cathode ray on the anode or anticathode is movable relative to the surface thereof
  • H01J35/30—Tubes wherein the point of impact of the cathode ray on the anode or anticathode is movable relative to the surface thereof by deflection of the cathode ray

Definitions

• 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 displayed on the fluoroscope located on the opposite side of the object from the x-ray source. Scanning x-ray tubes have been known in conjunction with the fluoroscopy art since at least the early 1950s. Moon, Amplifying and Intensifying the Fluoroscopic Image bv Means of a Scanning X-ra ⁇ Tube, Science, October 6, 1950, pp. 389-395.
• the entire x-ray source is packaged in a small form factor with sufficient safety features and that will allow for mounting of the source in traditional C-arms for use in medical applications without fear of danger to the patient or the treating physician.
• Fig. 14 is a diagram of a preferred x-ray tube scan ⁇ ning an electron beam in a raster scan pattern.
• Fig. 14A-F are graphical representations of the current applied to deflection coils to move an electron beam in a raster scam pattern.
• Fig. 2 is a cross-sectional diagram of the presently preferred scanning beam x-ray source 10 which comprises an electron beam source 112 and a vacuum envelope assem- bly 176.
• the electron beam 40 On reaching anode 184, the electron beam 40 has acquired an energy expressed in electron volts substantially equal numerically to the voltage applied between electron gun 198 and anode 184. In its continuing path to target 50, electron beam 40 is preferably not subjected to any additional axial forces so upon impact at focal spot 60, the energy of electron beam 40 is essentially the same as that acquired at anode 184.
• the strength of the magnetic focus lens assembly 186 is preferably varied in synchronism with the scan to maintain the optimal size of focal spot 60. This is preferably accomplished by operating the static focus coil 185 at a fixed current.
• the small changes in strength of the field generated by dynamic focus coil 187 required to maintain the optimal size of focal spot 60 are achieved by modulating the current flowing in dynamic focus coil 187 in synchronism with the currents flowing in deflection yokes 188 and 190.
• the preferred means to control and drive the currents in the dynamic focus coil 187 and static focus coil 185 are discussed more fully in copending U.S. Patent Application Serial No. 08/386861, which has been incorporated herein by reference in its entirety.
• Another embodiment is a layer of tantalum deposited directly on the target support 130.
• Yet another embodi ⁇ ment is a target layer 129 of an alloy of tungsten and rhenium.
• Still another embodiment is a target layer 139 of tungsten.
• an intermedi ⁇ ate layer of a resilient material such as niobium may be used.
• Tungsten, tantalum and tungsten-rhenium are pre ⁇ ferred materials for target layer 129 because they have high atomic numbers, making them efficient producers of x-rays, coupled with high thermal conductivity, high specific heat and high melting point.
• the thickness of target layer 129 is preferably selected to correspond with the distance traveled in the material by electrons of the highest operating energy.
• Cylindrical coil form 242 is the innermost layer of primary coil assembly 1270, as shown in Fig. 8.
• Coil form 242 is preferably formed of acrylic plastic although other electrically insulating materials with adequate thermal properties could be employed.
• Copper wire preferably low loss RF wire known as Litz wire, is wound around the central part of the outer face of coil form 242 to form the primary coil 246.
• there are 11 turns of wire in primary coil 246 although the number of turns is not germane to the essence of the invention and the actual number of turns depends on the particular usage requirements of the transformer.
• the number of turns depicted in Fig. 8 for primary coil 246 is for purposes of illustration only and should not be considered the number of turns actually employed in the present invention.
• Copper rings 248 and 250 form two short-circuited single turn coils which completely encircle the upper and lower edges of coil form 242.
• copper rings 248 and 250 are formed from 0.125" OD copper tubing and have a diameter approximately equal to that of coil form 242. Copper rings 248 and 250 are attached to the upper and lower edges of coil form 242 by means of adhesive KaptonTM tape.
• the entire assembly, consisting of ferrite bars 252, coil form 242, copper rings 248 and 250, and the primary coil 246 is then preferably wrapped toroidally with adhesive KaptonTM tape 302 to provide an electrically insulating barrier for primary coil 246.
• An electrostatic shield 304 is preferably formed of insulated copper wire wound closely and toroidally around tape 302.
• Y-step deflection coils 265 and 266 and X-step deflection coils 268 and 270 are toroidally wound with copper magnet wire in internal slots formed on the inside diameter of ferrite ring 286.
• the coils of fast deflection yoke 188 are preferably wound with fewer turns than the coils of slow deflection yoke 190 thus ensuring that the coils of fast deflection yoke 188 have substantially lower self inductances in comparison with those on slow deflection yoke 190.
• Alignment-clamp 326 contains a flat rectangular tongue which extends outward between the upper and lower C-shaped portions of the rotational support member 316.
• Locking screw 322 extends through a groove 324 in the alignment-clamp tongue into a mating hole in the rotational support member 316.
• the adjustment screws 318 and 320 tighten to form contact with the upper and lower surfaces of the alignment-clamp tongue.
• a similar assembly exists on the other side of slow yoke 190 with respect to the other alignment-clamp 328. To effect the rotational adjustment of the slow yoke 190, locking screw 322 on alignment-clamp 326 and a similar locking screw on alignment-clamp 328 are loosened to allow free rotational movement of the Alignment-clamps 326 and 328.
• Adjustment screws 318 and 320 are then adjusted to rotationally position the alignment-clamps 326 and 328, thereby effecting a corresponding rotational adjustment for the slow yoke 190 around the central ceramic cylinder 180.
• a rotational support member 330 containing two rectangular protrusions extends and attaches through upper and lower rectangular grooves in alignment-clamps 326.
• Rotational support member 330 contains a C-shaped section with an adjustment screw 332 inserted through the upper portion and adjustment screw 334 inserted through the lower portion of the C-shaped section.
• a similar rotational support member 331 and locking screws 333 and 335 extend and attach to the other alignment- clamp 328.
• Cylinder ring 338 which has the fast yoke 188 mounted along its interior surface, is formed with two rectangular adjustment plates 340 and 342 along its exterior surface. Rectangular adjustment plate 340 extends outward between the upper and lower C-shaped portions of the rotational support member 330. Locking screw 336 extends through a groove in the adjustment plate 340 into a mating hole in the rotational support member 330. The adjustment screws 332 and 334 tighten to form contact with the upper and lower surfaces of the adjustment plate 340. Adjustment plate 342 is similarly positioned between the upper and lower C-shaped portions of rotational support member 331.
• the magnetic focus lens assembly 186 can be positioned axially along the length of the vacuum envelope assembly 176 to regulate the minimum electron beam spot size on the target 50. Such positioning can prevent damage to the target 50 from minimum electron beam spot sizes which are overly concentrated, which may burn the target 50.
• Positioning rod 274 extends from front endplate 138 to an endplate 314, which is rigidly attached to the end bell assembly 266. Five such positioning rods are preferably disposed equidistantly along the outside perimeter of the endplates 314 and 138.
• the magnetic focus lens assembly 186 is mounted between a front support plate 346 and a rear support plate 344. Preferably attached to the front support plate 346 are five rectangular clamps 276, each of which encircles a corresponding positioning rod 274.
• Magnetic focus lens assembly 186 can be moved radially to align the central magnetic axis of focus lens assembly 186 with the central axis of electron beam 40 when electron beam 40 is not deflected by yokes 188 and 190. Alignment of focus lens assembly 186 is effected by means of 4 set screws (not shown) , which protrude radially from threaded holes in plate 346. The inner ends of these set screws push against the outer diameter of the U-shaped magnetic circuit member. Turning these screws causes the magnetic circuit member to move in any radial direction with respect to plate 346. For purposes of illustration only, magnetic focus lens assembly 186 is shown as a solid in Fig. 12.
• Fast deflection yokes 188 are preferably employed because conventional slow deflection yokes designed to sweep the electron beam typically require a large voltage in order to change its current fast enough to generate the necessary step pattern, particularly in the preferred embodiment of the present invention where the electron beam is preferably stepped behind an 166 by 166 array of apertures with a scanning frame rate of 30 Hz.
• the coils in the preferred fast deflection yokes 188 are wound with shorter lengths and fewer turns than the slow deflection yokes 190, allowing fast current changes.
• Fig. 14B depicts the pattern applied to the Y- deflection coils 276 and 278, to produce a conventional Y-sweep of the target 50 by the electron beam 40.
• current is not applied to the Y- step deflection coils when scanning in the horizontal flyback mode since the period of time required for the electron beam 40 to "flyback" from the end of one horizontal row to the beginning of the next horizontal row gives the Y deflection coil sufficient reaction time to modify the current in its coil such that the electron beam is correctly deflected to the proper Y position.
• the electron beam 40 is deflected in a stepped serpentine pattern across the target 50, as depicted in Fig. 15.
• the preferred method to deflect the electron beam 40 in a stepped serpentine pattern is diagrammed in Figs. 15A-F.
• Figs. 15A diagrams a sample pattern applied to the X-deflection coils 280 and 282, producing an X sweep of the target 50 by the electron beam 40.
• Fig. 15C depicts the sawtooth pattern applied to the X-step deflection coils, with a mirrored sawtooth pattern applied when the electron beam 40 begins scanning the next horizontal row, producing the resultant step pattern as shown in Fig. 15E when magnetically combined with the X deflection pattern of Fig. 15A.
• An alternate x-step pattern could comprise the use of a negative sawtooth pattern during the return horizontal step period, as shown in Fig. 15G.
• the actual current patterns applied to the X and Y deflection coils and the X-step and Y-step deflection coils are dependant upon many factors, which may include the rate of movement of the electron beam, the amount of deflection already applied, the number of collimator apertures, the dwell time for each collimator aperture location, the number of turns for each coil, and the exact placement of the deflection coils. While embodiments, applications and advantages of the invention have been shown and described with sufficient clarity to enable one skilled in the art to make and use the invention, it would be equally apparent to those skilled in the art that many more embodiments, applications and advantages are possible without deviating from the inventive concepts disclosed and described herein. The invention therefore should only be restricted in accordance with the spirit of the claims appended hereto and is not to be restricted by the preferred embodiments, specification or drawings.

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• X-Ray Techniques (AREA)
• Analysing Materials By The Use Of Radiation (AREA)

Applications Claiming Priority (3)

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• 1996
  • 1996-01-30 IL IL11696196A patent/IL116961A/xx not_active IP Right Cessation
  • 1996-01-31 DE DE69628454T patent/DE69628454T2/de not_active Expired - Fee Related
  • 1996-01-31 AU AU48651/96A patent/AU4865196A/en not_active Abandoned
  • 1996-01-31 AT AT96904583T patent/ATE241856T1/de not_active IP Right Cessation
  • 1996-01-31 EP EP96904583A patent/EP0871973B1/fr not_active Expired - Lifetime
  • 1996-01-31 WO PCT/US1996/001641 patent/WO1996025024A1/fr active IP Right Grant
  • 1996-01-31 JP JP8524399A patent/JPH11504750A/ja not_active Ceased

Patent Citations (2)

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