Method of and means for scanning a body to enable a cross-section thereof to be reconstructed
First Claim
1. In apparatus for calibrating a scanner of the type having a source for producing at least one pencil beam of penetrating radiation originating at essentially a point and passing through a cross-section to be reconstructed, a detector mounted in predetermined relationship to the source for measuring the intensity of the beam emerging from the cross-section, and means for rotating the source in a circular path coplanar with the cross-section, the improvement comprising means for periodically interrupting the beam during rotation of the source through a portion of the revolution, and means responsive to radiation from a reference source incident on the detector for calibrating the detector during the interval that the beam is interrupted.
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Accused Products
Abstract
A fan beam of the type described herein is oriented so as to be coplanar with the cross-section of a body to be reconstructed. Pure rotational movement is imparted to the fan beam by rotating the same about a fixed center of rotation such that the fan beam sweeps out an area in the plane of the cross-section; and the absorption coefficients over such area can be computed in a known manner from measurements of the intensities of the beams emerging from the area swept out thereby.
When one extremity of the fan beam passes through the fixed center of rotation, the area swept-out by the fan beam during one revolution thereof is circular, the center of which is coincident with the fixed center and the periphery of which is tangent to the other extremity of the fan beam. When the fixed center lies outside the fan beam, the area swept-out is annular and is defined by concentric circles whose centers are coincident with the fixed center and whose peripheries are respectively tangent to the extremities of the fan beam.
By sequentially rotating the fan beam about the fixed center, and shifting the fan beam relative thereto after each revolution (e.g., by rotating the fan beam about its apex), a circular area of arbitrary size can be swept-out by the fan beam after a number of revolutions. The size of such area is thus independent of the apical angle of the fan beam.
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Citations
34 Claims
- 1. In apparatus for calibrating a scanner of the type having a source for producing at least one pencil beam of penetrating radiation originating at essentially a point and passing through a cross-section to be reconstructed, a detector mounted in predetermined relationship to the source for measuring the intensity of the beam emerging from the cross-section, and means for rotating the source in a circular path coplanar with the cross-section, the improvement comprising means for periodically interrupting the beam during rotation of the source through a portion of the revolution, and means responsive to radiation from a reference source incident on the detector for calibrating the detector during the interval that the beam is interrupted.
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6. A method for scanning a body as part of a process for reconstructing a cross-section thereof using a source of penetrating radiation that produces a plurality of coplanar beams defining a fan beam passing through the body coplanar with the cross-section, the method comprising:
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(a) positioning the fan beam relative to a spatially fixed center at a first position; (b) rotating the fan beam about the fixed center and measuring the intensity of each beam after it passes through the cross-section; (c) repositioning the fan beam relative to the fixed center to a second position; and (d) repeating step (b). - View Dependent Claims (7, 8, 9, 10, 11)
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- 12. In apparatus for calibrating a scanner of the type having a source for producing a fan beam of penetrating radiation co-planar with a cross section to be reconstructed, a plurality of detectors mounted in predetermined relationship to the source for measuring the x-ray transmissivity of the cross-section, and means for rotating the fan beam about a center perpendicular to the cross-section the improvement comprising alternately applying to the detectors during rotation of the fan beam through one revolution, reference radiation that is independent of the angular position of the fan beam and dependent on the angular position of the fan beam.
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14. In a method for scanning a body to enable a cross-section thereof to be reconstructed by:
- (a) producing from a point source of penetrating radiation, a fan beam of the type described having an apical angle α and
being coplanar with and passing through the cross-section;
(b) rotating the fan beam through one revolution about a spatially fixed center for causing the fan beam to sweep out an area in the plane of the cross-section, the area being contained within a reference circle tangent to the extremities of the fam beam most remote from the fixed center, and the tangents to the reference circle passing through the source intersecting at an apical angle β
; and
(c) computing the absorption coefficients over such area from measurements of the intensities of the beams of the fan beam;the improvement comprising the steps of selecting the apical angle α
such that it is less than the apical angle β
, and shifting the fan beam, upon completion of one revolution, relative to the fixed center, and again carrying out steps (b) and (c). - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
- (a) producing from a point source of penetrating radiation, a fan beam of the type described having an apical angle α and
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29. Apparatus for scanning a body to enable a cross-section thereof to be reconstructed comprising:
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(a) a movable head assembly having a point source of penetrating radiation for producing a fan beam of the type described having an apical angle α
, and which is coplanar with, and passes through, the cross-section;(b) driver means for rotating the head assembly about a spatially fixed center for causing the fan beam to sweep out of area in the plane of the cross-section, the area being contained within a reference circle tangent to the extremities of the fan beam most remote from the fixed center, the tangents to the reference circle passing through the source intersecting at an apical angle β
;(c) the apical angle α
being less than the apical angle β
; and(d) means for shifting the head assembly relative to the fixed center and in the plane of the fan beam. - View Dependent Claims (30, 31, 32, 33, 34)
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Specification