Claims
- 1. A dual-energy x-ray absorptiometry apparatus comprising:
a first source of a first conical beam of x-rays having photon energies in a first range of photon energies; a second source of a second conical beam of x-rays having photon energies in a second range of photon energies different from the first range of photon energies, the second beam co-located with the first beam; an x-ray receiver comprising an area x-ray detector for detecting x-ray intensity at a plurality of receptors distributed over an area having a length and a width; and a subject table substantially transparent to x-rays, wherein the first conical beam intersects the subject table and impinges on the area x-ray detector.
- 2. An apparatus as recited in claim 1, wherein bone mass in a subject on the subject table is determined within one percent for each receptor of the plurality of receptors.
- 3. An apparatus as recited in claim 1, the x-ray receiver further comprising a two dimensional anti-scatter grid with a plurality of holes.
- 4. An apparatus as recited in claim 1, the x-ray receiver further comprising a three dimensional anti-scatter grid with a plurality of holes.
- 5. An apparatus as recited in claim 1, wherein a distance from the first source to the area x-ray detector is about one meter.
- 6. An apparatus as recited in claim 1, wherein the area x-ray detector includes a plurality of pairs of adjacent receptors that distinguish x-ray intensity, the pairs of adjacent receptors arranged with more than two receptor pairs per millimeter.
- 7. An apparatus as recited in claim 6, wherein the pairs of adjacent receptors are arranged with at least 3.8 receptor pairs per millimeter.
- 8. An apparatus as recited in claim 1, wherein the area x-ray detector includes a plurality of receptors that measure x-ray intensity, the plurality of receptors arranged in more than two rows of receptors, each row including at least a hundred receptors.
- 9. An apparatus as recited in claim 1, wherein the area x-ray detector comprises an amorphous silicon detector.
- 10. An apparatus as recited in claim 9, wherein the width is at least 200 millimeters and the length is at least 200 millimeters.
- 11. An apparatus as recited in claim 9, wherein the amorphous silicon detector includes an array of 0.127-millimeter square receptors.
- 12. An apparatus as recited in claim 11, wherein the array includes at least 1400 rows of receptors and at least 1400 receptors per row.
- 13. An apparatus as recited in claim 1, further comprising a power supply for driving an x-ray tube at a selectable one of a first voltage and a second voltage, wherein:
the first source comprises the power supply and the x-ray tube powered with the first voltage; and the second source comprises the power supply and the x-ray tube powered with the second voltage.
- 14. An apparatus as recited in claim 13, wherein the power supply has a mass less than about 10 kilograms and provides a voltage at the x-ray tube in a range from about 50 kiloVolts (kV) to about 150 kV.
- 15. An apparatus as recited in claim 1, wherein the first source comprises:
an x-ray tube; a power supply providing a voltage of about 80 kilovolts between a cathode and an anode of the x-ray tube; and a filter comprising molybdenum and tungsten.
- 16. An apparatus as recited in claim 1, wherein the first source comprises:
an x-ray tube; and a power supply providing a voltage of about 50 kiloVolts between a cathode and an anode of the x-ray tube.
- 17. An apparatus as recited in claim 1, wherein the second source comprises:
an x-ray tube; a power supply providing a voltage of about 140 kiloVolts between a cathode and an anode of the x-ray tube; and a filter comprising gadolinium, molybdenum and copper.
- 18. A dual-energy x-ray absorptiometry apparatus comprising:
a source of a beam comprising a series of constant pulses, each pulse having x-ray photon energies in a range of photon energies; an x-ray detector for detecting x-ray intensity and providing first data indicating a number of photons received at the detector during each pulse; and an exposure control component for determining a number of pulses in the first series of constant pulses based on the first data.
- 19. An apparatus as recited in claim 18, wherein the source of the beam comprises:
an x-ray tube; and a power supply with a peak power of less than 300 Watts, the power supply providing a voltage at the x-ray tube in a range from about 50 kiloVolts (kV) to about 150 kV.
- 20. An apparatus as recited in claim 18, wherein the source of the beam comprises:
an x-ray tube; and a power supply having a mass less than about ten kilograms, the power supply providing a voltage at the x-ray tube in a range from about 50 kiloVolts (kV) to about 150 kV.
- 21. An apparatus as recited in claim 18, wherein:
the source further comprises a monitor having a first receptor for providing second data indicating x-ray intensity at the source; and the exposure control component further determines the number of pulses based on the second data.
- 22. An apparatus as recited in claim 18, wherein the exposure control component comprises a processor connected to the source and the x-ray receiver, the processor configured to perform the steps of:
determining, based on the first data, a value for average transmission of x-rays in the range of photon energies through a subject disposed between the source and the x-ray receiver; determining, based on the value for average transmission, a computed number of pulses for producing a predetermined average detector fluence indicating a total energy to be received at the detector; and sending a signal turning off the source when the number of pulses in the series of constant pulses substantially equals the computed number of pulses.
- 23. An apparatus as recited in claim 22, wherein the predetermined average detector fluence is associated with a particular signal to noise ratio.
- 24. An apparatus as recited in claim 21, wherein:
the monitor further comprises a second receptor coupled to a calibration material for providing third data indicating x-ray intensity attenuated by the calibration material at the source; and the exposure control component determines whether calibration of the apparatus has degraded below a threshold accuracy based at least in part on the third data.
- 25. A dual-energy x-ray absorptiometry apparatus comprising:
a source of a beam comprising x-ray photon energies in a range of photon energies; an x-ray detector for detecting x-ray intensity after the beam has passed through a subject; a monitor comprising a receptor coupled to a calibration material for providing first data indicating x-ray intensity attenuated by the calibration material at the source; and a calibration monitoring component for determining whether calibration of the apparatus has degraded below a threshold accuracy based on the first data.
- 26. A dual-energy x-ray absorptiometry apparatus comprising:
a first source of a first beam of x-rays having photon energies in a first range of photon energies; a second source of a second beam of x-rays having photon energies in a second range of photon energies different from the first range of photon energies, the second beam co-located with the first beam; an x-ray receiver for detecting x-ray intensity; a subject table substantially transparent to x-rays; a gantry base; and a gantry moveably connected to the gantry base, the gantry fixed to the first source, the second source and the x-ray receiver; wherein
the gantry base is configured to move the gantry to a plurality of gantry positions, the first beam intersects the subject table at a plurality of angles corresponding to the plurality of gantry positions; the first beam impinges on the x-ray receiver for each position of the plurality of positions, the first beam at one angle of the plurality of angles substantially overlaps, in a volume above the subject table, the first beam at two or more neighboring angles of the plurality of angles, and the volume would be occupied by a subject disposed on the subject table.
- 27. An apparatus as recited in claim 26, further comprising a power supply for driving an x-ray tube at a selectable one of a first voltage and a second voltage, wherein:
the first source comprises the power supply and the x-ray tube powered with the first voltage; and the second source comprises the power supply and the x-ray tube powered with the second voltage.
- 28. An apparatus as recited in claim 26, further comprising a processor connected to the gantry, the first source, the second source and the x-ray receiver, the processor configured to perform the steps of:
controlling gantry motion to each of the plurality of gantry positions; controlling firing of the first source; and controlling firing of the second source.
- 29. An apparatus as recited in claim 26, further comprising a processor connected to the x-ray receiver, the processor configured to perform the steps of
receiving first data from the x-ray receiver indicating intensity at a plurality of receptors in the x-ray receiver for each of the first beam and the second beam for each of the one angle and the neighboring angles; and determining a location for a bone of the subject in the volume based on the first data, wherein uncertainty in the location for the bone, due to variation in subject position during relative movement between the gantry and the subject table, is reduced.
- 30. An apparatus as recited in claim 26, further comprising a processor connected to the x-ray receiver, the processor configured to perform the steps of
receiving first data from the x-ray receiver indicating intensity at a plurality of receptors in the x-ray receiver for each of the first beam and the second beam for each of the one angle and the neighboring angles; and determining composition of soft tissue of the subject in the volume based on the first data.
- 31. An apparatus as recited in claim 26, further comprising a processor connected to the x-ray receiver, the processor configured to perform the steps of
receiving first data from the x-ray receiver indicating intensity at a plurality of receptors in the x-ray receiver for each of the first beam and the second beam for each of the one angle and the neighboring angles for each of one or more displacements between the gantry base and the subject table; and determining a three-dimensional model of bone structure for a bone of the subject in the volume based on the first data.
- 32. An apparatus as recited in claim 31, the processor further configured to perform the step of determining a risk of injury based on the three-dimensional model of the bone structure.
- 33. A power supply for a dual-energy x-ray absorptiometry apparatus comprising:
a direct current source providing direct current Is at voltage Vs up to a particular peak power Pmax, a pulse forming network (PFN) circuit connected to receive the direct current Is from the power source, the PFN comprising one or more capacitors to form a series of pulses, each pulse having a pulse current Ip and pulse voltage Vp for a pulse duration Tp repeated at a pulse time interval Ti, wherein Ip*Vp*Tp/Ti is less than Pmax; a pulse transformer assembly connected to receive the series of pulses and configured to step the pulse voltage Vp up to an x-ray tube voltage Vx, higher than Vp, between a first cathode and an anode of an x-ray tube.
- 34. A power supply as recited in claim 33, further comprising:
a power control input for turning the direct current supply on and off; and an exposure control system connected to the power control input, the exposure control system for determining a number of pulses in the series of pulses and causing the direct current supply to be turned off when the number of pulses have been generated by the PFN.
- 35. A power supply as recited in claim 33, wherein the pulse transformer includes a switch for selecting one of a plurality of transformer ratios for stepping up the pulse voltage Vp to a corresponding plurality of x-ray tube voltages Vx.
- 36. A power supply as recited in claim 33, wherein the particular peak power Pmax is less than about 300 Watts and the x-ray tube voltage Vx is as great as about 150 kiloVolts.
- 37. A power supply as recited in claim 33, wherein the power supply has a mass less than about ten kilograms and the x-ray tube voltage Vx is as great as about 150 kiloVolts.
- 38. A power supply as recited in claim 33, further comprising a high voltage switching circuit for bypassing the PFN and the pulse transformer to provide a direct current to a second cathode of the x-ray tube to warm up the anode.
- 39. An anti-scatter grid for an x-ray absorptiometry apparatus comprising a heavy metal sheet shaped with a plurality of openings through the heavy metal sheet, wherein:
the heavy metal sheet has a width and a length that substantially covers an area x-ray detector of the x-ray absorptiometry apparatus; each opening of the plurality of openings has side walls substantially perpendicular to a top surface of the heavy metal sheet; and each opening has a maximum opening length in the top surface selected so that an x-ray having an angle of incidence on the top surface that deviates from a direction perpendicular to the top surface by a deviation angle greater than a particular angle strikes a sidewall of the opening.
- 40. An anti-scatter grid as recited in claim 39, wherein the maximum opening length substantially equals a product of a thickness of the heavy metal sheet and a value of a tangent function of the particular angle.
- 41. An anti-scatter grid as recited in claim 39, wherein a width of a wall between two adjacent openings of the plurality of openings is less than a resolution distance of the area x-ray detector.
- 42. An anti-scatter grid as recited in claim 39, wherein a width of a wall between two adjacent openings of the plurality of openings is about 0.127 millimeters or less.
- 43. An anti-scatter grid as recited in claim 39, wherein a roughness of the top surface and a roughness of each sidewall at scales shorter than the maximum opening length is less than a particular fraction of the maximum opening length.
- 44. An anti-scatter grid as recited in claim 39, wherein the top surface of the heavy metal sheet forms a curve.
- 45. An anti-scatter grid as recited in claim 44, wherein the curve has a radius of curvature substantially equal to a particular distance from a focal spot in an x-ray tube of the x-ray absorptiometry apparatus to a location where the anti-scatter grid is disposed in the x-ray absorptiometry apparatus.
- 46. An anti-scatter grid as recited in claim 45, wherein the top surface of the heavy metal sheet substantially lies along a surface of a sphere having a radius equal to the radius of curvature.
- 47. An anti-scatter grid as recited in claim 45, wherein the heavy metal sheet is about 0.999 pure lead.
- 48. A method for fabricating an anti-scatter grid for a dual-energy x-ray absorptiometry apparatus, the method comprising:
cutting cross slots onto an electrode to produce a plurality of regularly spaced posts in a two-dimensional array; sinking the plurality of posts into a lead foil; performing electrical discharge machining (EDM) to burn a plurality of openings through the lead foil at a plurality of locations corresponding to the plurality of posts; and widening the plurality of openings by
displacing the plurality of posts a distance smaller than a spacing between posts, and performing electrical discharge machining to widen the plurality of openings.
- 49. A method as recited in claim 48, the method further comprising repeating said step of widening the plurality of holes until a wall thickness between adjacent holes of the plurality of holes is less than a particular distance.
- 50. A method as recited in claim 49 wherein the particular distance is less than a horizontal resolution of an x-ray detector in the x-ray absorptiometry apparatus.
- 51. A method as recited in claim 48, the method further comprising chemically polishing the lead foil having the plurality of openings.
- 52. A method as recited in claim 51, said step of chemically polishing the lead foil comprising:
forming a mixture of hydrogen peroxide, acetic acid, and water; and placing the foil in the mixture at room temperature for a polishing time.
- 53. A method as recited in claim 52, wherein the mixture comprises about 10:4:36 parts hydrogen peroxide to acetic acid to water, respectively.
- 54. A method as recited in claim 52, wherein the polishing time is about three minutes.
- 55. A method as recited in claim 48, the method further comprising attaching the lead foil having the plurality of openings to a curved surface of a material that is substantially transparent to x-rays.
- 56. A method as recited in claim 55, said step of attaching the lead foil comprising gluing the lead foil to the surface of a curved Plexiglas plate.
- 57. A method as recited in claim 48, the method further comprising
moving the plurality of posts to a portion of the lead foil without openings; and repeating said steps of sinking, performing EDM and widening.
- 58. A method as recited in claim 57, the method further comprising repeating said steps of moving and repeating said steps of sinking, performing EDM and widening until an area of the lead foil substantially equal to an area of a detector in the x-ray absorptiometry apparatus is covered by a second plurality of openings.
- 59. A method for fabricating an anti-scatter grid for a dual-energy x-ray absorptiometry apparatus, the method comprising:
cutting cross slots onto a copper electrode to produce a plurality of regularly spaced posts in a two-dimensional array; pouring molten lead over the electrode to a depth less than a height of the posts; allowing the lead to solidify; and chemically removing the copper to leave a lead sheet with a plurality of openings corresponding to the plurality of posts.
- 60. A method as recited in claim 59, the method further comprising attaching the lead having the plurality of openings to a curved surface of a material that is substantially transparent to x-rays.
- 61. A method for operating a dual-energy x-ray absorptiometry apparatus, the method comprising:
obtaining a pair of images at each of a plurality of projection angles for each of one or more longitudinal positions along a subject, a first image of the pair obtained using a first source of x-rays having a first range of photon energies and a second image of the pair obtained using a second source of x-rays having a second range of photon energies, each image having at least two pixels per millimeter; and constructing a three-dimensional model of a bone based on a plurality of pairs of images obtained during said obtaining step.
- 62. The method of claim 61, further comprising computing risk of injury based on the three-dimensional model of the bone.
- 63. A method for calibrating a dual-energy x-ray absorptiometry apparatus, the method comprising:
placing a phantom subject comprising a tissue calibration material on a subject table; obtaining a pair of attenuation images, a first image of the pair obtained using a first source of x-rays having a first range of photon energies and a second image of the pair obtained using a second source of x-rays having a second range of photon energies, each image having at least two pixels per millimeter; determining, based on the pair of images, coefficients for a polynomial that produces thickness of the calibration material at each pixel based on attenuation at that pixel in the pair of attenuation images.
- 64. The method of claim 63, wherein the phantom subject comprises a plurality of thicknesses of two or more materials.
- 65. The method of claim 63, wherein the phantom subject comprises a first plurality of thicknesses of acrylic and a second plurality of thicknesses of aluminum.
- 66. The method of claim 65, wherein the first plurality of thicknesses of acrylic range from about zero millimeters to about 250 millimeters of acrylic.
- 67. The method of claim 65, wherein the second plurality of thicknesses of aluminum range from about zero millimeters to about 30 millimeters of aluminum.
- 68. The method of claim 63, wherein the phantom subject comprises a plurality of thicknesses of calcium phosphate tribasic type IV as a calibration material for bone.
- 69. The method of claim 63, wherein the phantom subject comprises a plurality of thicknesses of 0.9 percent sodium chloride solution as a calibration material for lean tissue.
- 70. The method of claim 63, wherein the phantom subject comprises a plurality of thicknesses of stearic acid as a calibration material for fat tissue.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional application No. 60/242,740, filed on Oct. 24, 2000, which is hereby incorporated by reference in its entirety. This application also claims the benefit of U.S. provisional application No. 60/246,679, filed on Nov. 8, 2000, which is hereby incorporated by reference in its entirety.
STATEMENT OF GOVERNMENTAL INTEREST
[0002] This invention was made with Government support under Cooperative Agreement NCC 9-58 between the National Aeronautics and Space Administration (NASA) Johnson Space Center, Houston, Tex. and the National Space Biomedical Research Institute (NSBRI). The Government has certain rights in the invention.
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
PCT/US01/49439 |
10/24/2001 |
WO |
|