Whole-body dual-energy bone densitometry using a narrow angle fan beam to cover the entire body in successive scans

- Lunar Corporation

A scanning radiographic densitometer constructs a broad area, two dimensional projection image from a combination of a set of smaller fan beam scans by tilting the axis of each such smaller scan to construct an effective larger fan beam to reduce artifacts caused by height dependant overlap of the multiple fan beams. The data is projected to a non-planar image surface to eliminate local area distortion such as may cause error in density measurements and to permit some overlap without height sensitive effects.

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Claims

1. An imaging system for obtaining diagnostic images of a patient comprising:

a radiation source for directing a fan beam of radiation toward the patient, the fan beam diverging about a radiation axis but substantially within a beam plane from a focal spot;
a radiation detector opposing the radiation source along the radiation axis for receiving the diverging beam of radiation after passage through the patient to produce a projection signal indicating the attenuation of the beam of radiation for multiple rays within the beam;
a translating means for translating the radiation axis along a first and second path across the patient, the first and second paths being spaced apart and substantially perpendicular to the beam plane;
a repositioning means for rotating the radiation axis about the focal spot by a displacement angle, within the beam plane so as to move the radiation axis from the first path to the second path; and
means for combining the projection signal obtained along the first and second path to produce a two dimensional projection image.

5. The imaging system of claim 4 wherein the non-planar image surface is a section of a cylinder having a constant radius equal to the distance between the surface and the radiation source to substantially bisect the patient.

6. An imaging system for obtaining diagnostic images of a patient comprising:

a radiation source for directing a fan beam of radiation toward the patient, the fan beam diverging about a radiation axis but substantially within a beam plane from a focal spot;
a linear array of detector elements opposing the radiation source along the radiation axis, each detector element subtending a first width of the fan beam along the linear array, the linear array for receiving the diverging beam of radiation after passage through the patient to produce a projection signal which includes a plurality of element signals corresponding to the detector elements and indicating the attenuation of the beam of radiation for given rays within the beam; and
a projector for mapping the element signals to pixels of a non-planar image surface generally normal to the radiation axis, each pixel subtending second widths of the fan beam varying from the first widths.

7. The imaging system of claim 6 wherein the non-planar image surface is a section of a cylinder having a constant radius equal to the distance between the surface and the radiation source the radius selected to substantially bisect the patient..Iadd.

8. The imaging system of claim 1 wherein the means for combining provides a weighting of the projection signal of areas of overlap between areas of the fan beam when the radiation axis scanning of the first and second paths..Iaddend..Iadd.9. The imaging system of claim 1 wherein the imaging system is a bone densitometer..Iaddend..Iadd.10. The imaging system of claim 9 wherein the bone densitometer is a dual energy bone densitometer..Iaddend..Iadd.11. The imaging system of claim 9 wherein the radiation source is a polychromatic x-ray source..Iaddend..Iadd.12. The imaging system of claim 9 wherein the fan beam is scanned in a raster pattern over the patient, the raster scan formed of the first and additional paths wherein the number of paths and the separation of the paths is chosen to ensure complete illumination of the total body of the patient.

.Iaddend..Iadd.13. The imaging system of claim 1 wherein the repositioning means rotates the radiation axis about the focal spot by a displacement distance within the beam plane while translating the focal spot by displacement distance within the beam plane so as to move the radiation axis from the first path to the second path..Iaddend.

Referenced Cited
U.S. Patent Documents
4709382 November 24, 1987 Sones
4811373 March 7, 1989 Stein
5123056 June 16, 1992 Wilson
5132995 July 21, 1992 Stein
5132996 July 21, 1992 Moore et al.
5177776 January 5, 1993 Ohmari et al.
5432834 July 11, 1995 Gershman
Other references
  • Variable Resolution Fan-Beam CT Scanner For Peripheral Bone Evaluation, T. N. Hangartner et al., J. Comput Assist Tomogr, vol. 9, No. 3, 1985 no month.
Patent History
Patent number: RE36162
Type: Grant
Filed: Aug 26, 1996
Date of Patent: Mar 23, 1999
Assignee: Lunar Corporation (Madison, WI)
Inventors: Joseph P. Bisek (Oregon, WI), Richard B. Mazess (Madison, WI), Jixing Chen (Lakewood, CO)
Primary Examiner: David P. Porta
Law Firm: Quarles & Brady
Application Number: 8/703,250
Classifications
Current U.S. Class: Scanner (378/146); Imaging (378/62); With Movable Source (378/196)
International Classification: G21K 510;