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Title: Apparatus for examining a body by means of penetrating radiation
Claims: What I claim is: 1. Apparatus for examining a body by means of radiation, such as X- or gamma radiation comprising a. a main structural frame, b. a rotary member defining a central aperture positioned on said main structural frame and being arranged to rotate relative thereto, c. a body supporting structure for positioning a body to be examined in said central aperture, said body supporting structure being located and arranged to remain stationary relative to said rotary member, d. a known medium located in proximity with the body supporting structure, e. a source of penetrating radiation and a detector for receiving a beam of penetrating radiation from said source and producing output signals responsive thereto mounted on said rotary member and located on opposite sides of said body supporting structure, f. said source, said detector, and said body supporting structure being spatially arranged such that when a body to be examined is supported by said body supporting structure, it is interposed between the source and said detector, g. an interconnection for said source and said detector to interrelate their positions on opposite sides of said body supporting structure, and to enable them to execute common lateral scanning movements relative to said rotary member, h. motor means for driving said rotary member relative to said main structural frame to produce orbital scanning about the axis of said rotary member, and for driving said source and said detector to execute repetitive common lateral scanning movement such that for each lateral scan the beam of radiation is carried into a region beyond that region to be occupied by a body when supported by said supporting structure, i. said lateral and orbital scanning being correlated for providing alternate predetermined increments of orbital and lateral scanning, j. said known medium being positioned to intercept said beam in said first mentioned region to cause said detector to produce an output signal related to the attenuation of said known medium and independent of the attenuation of the body undergoing examination, and k. a circuit for combining the last mentioned detector output signals with detector output signals related to the attenuation of the body undergoing examination to reference the latter signals. 2. Apparatus according to claim 1 in which said known medium is characterized by an absorption approximately equal to the absorption experienced by a similar beam which senses through a body of the type undergoing examination. 3. Apparatus according to claim 1 in which said known medium has a lateral extent substantially equal to that of the lateral scan, but is shaped to be of reduced attenuation in the region where the beam is liable to be intercepted by the body undergoing examination so as to substantially reduce variations in the absorption of the beam during the scanning. 4. Apparatus according to claim 1 in which said known medium comprises a water reservoir surrounding the region in which the body undergoing examination is located by said body supporting structure. 5. Apparatus according to claim 1 in which said known medium is positioned to intercept said beam at both ends of a lateral scanning movement. 6. Apparatus according to claim 1 in which said circuit operates to produce signals representative of the ratio of the absorption of the body undergoing examination to the absorption of the known medium. 7. Apparatus according to claim 1 wherein said known medium is lead. 8. Apparatus according to claim 1 wherein two such known mediums are used, one providing substantial absorption. 9. Apparatus according to claim 1 in which said known medium is located to intercept the beam near one extremity of its lateral scan. Other info: Inventors: Hounsfield, Godfrey Newbold (Newark, EN) Application Number: 447381 Filing Date: 1974-03-01 Publication_date: 1976-06-22 Assignee: EMI Patents Limited (Hayes, EN) Primary Class(es): 378/11 378/18 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Dixon, Harold A. Assistant Examiner: Attorney: Fleit & Jacobson |
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