X-ray or gamma ray systems or devices – Beam control – Scanner
Reexamination Certificate
1999-11-03
2001-08-07
Dunn, Drew (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Scanner
C378S149000, C378S150000
Reexamination Certificate
active
06272206
ABSTRACT:
FIELD OF INVENTION
This invention relates to a dual beam modulator capable of providing both a series of discrete pencil beams and a fan beam particularly useful in X-ray imaging devices.
BACKGROUND OF INVENTION
X-ray beam collimators form an unshaped X-ray beam into a specific, desired shape. Fan beam collimators simply use a lead sheet or other blocking material with a slit in it to form a fan beam. See U.S. Pat. No. 3,808,444. Chopper wheel collimators use a plurality of generally radial slots to chop a fan beam into pencil beams. See the above patent and U.S. Pat. No. 5,181,234. These are often called flying spot scanners because the pencil beam moves cross-wise back and forth or up and down as the chopper wheel rotates. See also U.S. Pat. No. 4,745,631. A rotating wheel collimator has an X-ray source at its center and a plurality of radial channels extending outward to create pencil beams. See U.S. Pat. No. 5,493,546. Two other designs use helical slits to create a continuous or flying spot pencil beam from a fan beam. In one approach, U.S. Pat. No. 4,745,631, there are helical slits on the surface of a cylinder which create a fly spot pencil beam as the cylinder rotates. In another approach there is a helical slit on the surface of the cylinder. See U.S. Pat. Nos. 5,493,596 and 5,528,656.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved dual beam modulator.
It is a further object of this invention to provide such an improved dual beam modulator which produces both pencil and fan beams.
It is a further object of this invention to provide such an improved dual beam modulator which leaves the center of the modulator free for simple drive mechanisms and reinforcing structure.
It is a further object of this invention to provide such an improved dual beam modulator which provides a series of discrete pencil beams.
It is a further object of this invention to provide such an improved dual beam modulator which is simple in design and can be made smaller and more compact.
It is a further object of this invention to provide such an improved dual beam modulator which is easier and less expensive to manufacture.
The invention results from the realization that a simpler, smaller, more compact beam modulator which forms both pencil and fan beams and which can be easily rotated with a central drive can be achieved by locating a plurality of discrete chordal passages through the annular wall of a rotatable cylinder with each passage being spaced radially and longitudinally in a series about the wall and providing reduced radius sections on opposite sides of the cylinder so that rotation of the cylinder alternately passes an incident fan beam or modulates it into a series of discrete pencil beams.
This invention features a dual beam modulator includes a rotatable cylinder having an annular wall. There is a plurality of discrete chordal passages extending through the wall between opposing holes on its outer surface. Each of the passages is spaced radially about the wall and longitudinally in the direction of the longitudinal axis of the cylinder for producing in response to an incident fan beam of radiation a series of discrete pencil beams as the cylinder rotates. The cylinder has a reduced radius section on the outer surface of the wall for periodically passing the incident fan beam alternately with the series of pencil beams as the cylinder rotates.
In a preferred embodiment the cylinder may be a circular cylinder or it may be a polygonal cylinder. The reduced radius section may be flat and it may be a chordal planar surface. The passages may be approximately 1-10 mm diameter and may be spaced radially approximately 1°-5° and longitudinally approximately {fraction (1/10+L )}-{fraction (1/500+L )} of the angular range. The reduced radius section may subtend an angle of approximately 10°-180°. The cylinder may be made of lead loaded epoxy. The annular wall may form an internal chamber for receiving a drive shaft. The chamber may be centrally disposed coincident with the longitudinal axis of the cylinder. There may be a drive mechanism for rotating the cylinder. The drive mechanism may rotate the cylinder at approximately 100-2000 rpm. The cylinder may have an outer diameter of 5-30 inches. There may be a number of reduced radius sections and a number of sets of a plurality of discrete chordal passages.
REFERENCES:
patent: 3808444 (1974-04-01), Schneeberger et al.
patent: 4745631 (1988-05-01), Paolini
patent: 4769829 (1988-09-01), Webb et al.
patent: 4995066 (1991-02-01), Harding et al.
patent: 5181234 (1993-01-01), Smith
patent: 5282656 (1994-02-01), Fizer
patent: 5493546 (1996-02-01), Kasahara
patent: 5493596 (1996-02-01), Annis
Dunn Drew
Iandiorio & Teska
PerkinElmer Detection Systems, Inc.
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