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Title: Apparatus for examining objects by means of penetrating radiation
Claims: What I claim is: 1. A medical diagnostic X-ray machine for examining a patient and for building up and displaying a two-dimensional picture of the X-ray response coefficients of the elements into which a slice of the patient extending along a planar section to the patient is divided by a finite Cartesian matrix notionally superimposed on the slice, comprising: means for passing X-radiation along each beam path of fan-shaped distributions of beam paths of finite lengths, each fan-shaped distribution being made up of beam paths which substantially coincide with said section and have one of their ends at a common apex on one side of the patient and their other ends spaced from each other along the section at the opposite side of the patient, said apices being circumferentially spaced from each other along an orbit which extends at least half way around the patient and substantially coincides with said section, at least the central beam paths of each of said fan-shaped distributions of beam paths passing through the patient along said section, and means for deriving first output signals each of which is a measure of a response encountered by the X-radiation in passing from one end to the other of a corresponding one of said beam paths, means for deriving second output signals each of which is a measure of a response encountered by the X-radiation in passing along at least a portion of selected ones of said beam paths, which portion does not pass through the patient, each one of said fan-shaped distributions of beam paths including at least two of said selected beam paths angularly spaced from each other within the fan-shaped distribution by intermediate beam paths of the same distribution which pass through the patient, and means for deriving correcting factors for each fan-shaped distribution from said second output signals derived for selected beam paths of the distributions, which correcting factors are related to differences in the X-radiation passing along said intermediate beam paths of the distribution; and means for building up said picture based on said output signals and on said correcting factors and for displaying said picture of the slice of the patient examined with the X-ray machine. 2. A medical diagnostic X-ray machine as in claim 1 in which the means for building up said picture comprise means for weighting the first output signals derived for a fan-shaped distribution of beam paths in accordance with respective correcting signals for the same distribution and means for building up said picture based on the so weighted first output signals. 3. A medical diagnostic X-ray machine as in claim 1 in which the means for building up said picture comprise means for producing the X-ray response coefficient of each element of the patient slice based on each first output signal corresponding to a beam path passing through the element weighted by: (i) the respective correcting factors derived for the fan-shaped distribution to which the beam path for the first output signal belongs; (ii) on the respective positions of the last recited beam path and slice element, and (iii) on contributions based at least in part on other output signals. 4. A medical diagnostic X-ray machine as in claim 1 including means for causing the first output signals for a fan-shaped distribution to correspond to X-radiation of substantially constant hardness impinging on the patient along each of the beam paths of the distribution. 5. A medical diagnostic X-ray machine as in claim 4 in which said causing means comprise a wedge of a material interposed in the path of the X-radiation along the beam paths of each fan-shaped distribution prior to impingement of said radiation on the patient, said material having a selected X-ray characteristic which increases from one beam path to an adjacent one within a distribution in moving from one side of the distribution to the other. 6. A medical diagnostic X-ray machine for examining a patient and for building up and displaying a two-dimensional picture of the X-ray response coefficients of the elements into which a slice of the patient extending along a planar section through the patient is divided by a finite Cartesian matrix notionally superimposed on the slice, comprising: X-ray source means producing a beam of X-radiation starting from each of a number of orbital locations distributed along at least a half an orbit around the patient and fanning out in said section into a fan of radiation at least a central portion of which passes through the patient, each fan being made up of a number of beam paths which start out from a common apex at the X-ray source means and are angularly distributed within the fan, all of the beam paths being along said section, and means for detecting the radiation travelling along the beam paths of each set at the other side of the patient from the apex of the fan and for deriving an output signal corresponding to the amount of the radiation received by the detecting means along each of said beam paths; means for disposing a selected material between the apex of each of said fans and the patient to cause the beams of each fan to pass through said material, said material having an X-ray characteristic causing the X-radiation travelling along the beam paths after leaving the material to have about the same hardness along each beam path of a fan; and means for processing the output signals derived for beam paths after passage thereof through said material to build up and display said picture of the patient slice examined by the X-ray machine. 7. A medical diagnostic X-ray machine as in claim 6 in which said material comprises a wedge of material disposed between the source of the X-radiation and the patient and having X-ray absorption which increases in moving from one side of the fan of radiation from the source to the other. Other info: Inventors: Hounsfield, Godfrey Newbold (Newark, EN) Application Number: 819543 Filing Date: 1977-07-27 Publication_date: 1978-06-20 Assignee: EMI Limited (Hayes, EN) Primary Class(es): 378/5 378/159 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Borchelt, Archie R. Assistant Examiner: Attorney: Cooper, Dunham, Clark, Griffin & Moran |
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