Radiographic imaging system

• US 4,158,770 A
• Filed: 01/03/1978
• Issued: 06/19/1979
• Est. Priority Date: 01/03/1978
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Barrett, Harrison H., Davis, Luther Jr.
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US05/866,892
• Time in Patent Office: 532 Days
• Field of Search: 250/320, 250/321, 250/322, 250/323, 250/272, 250/273, 250/274, 250/275, 250/358 R
• US Class Current: 378/2
• CPC Class Codes: G03B 42/02 using X-rays

Abstract

A system for imaging a subject, such as a human being, in which there has been injected a contrast agent which absorbs radiation of a predetermined frequency. The system utilizes a source of high energy radiation such as X or gamma radiation. The source is a composite of first and second radiating materials each of which is arranged in a predetermined pattern or code, each pattern having both luminous and dark regions. In one embodiment, the luminous regions of one pattern are in registration with the dark regions of the other pattern, these regions being spaced apart in an alternative embodiment. The characteristic frequencies of radiation emitted by the first and second materials are respectively lower and higher than the predetermined absorption frequency. A detector of radiation is positioned relative to the subject and the source such that radiation propagating through the subject is incident upon the detector. Since the absorption edge of the contrast agent lies between the two characteristic frequencies of radiation, radiation from the second material is preferentially absorbed by the contrast agent with the result that the contrast agent appears to be illuminated by a coded source while the remainder of the subject may be regarded as illuminated essentially by a uniform uncoded source. Imaging is accomplished by a decoding of a detected coded image. Substances within the subject having other absorption frequencies are not imaged since the radiations of both materials are essentially equally absorbed by the subject so that the source appears uncoded.

Claims

1. A radiographic system for imaging a subject having a substance which preferentially absorbs radiation at a predetermined frequency comprising:

a source of radiation from the class of radiation consisting of X and gamma radiation, such source having a first material for emitting such radiation having a frequency lower than said predetermined frequency and situated in a plurality of spaced apart locations about said source, said source having a second material for emitting such radiation having a frequency higher than said predetermined frequency and situated in a plurality of spaced apart locations corresponding to the spaces between the locations of the first material, the locations of said first material forming a first pattern, the locations of said second material forming a second pattern similar to said first pattern, said source being positioned to illuminate said subject;

a detector of said radiation, said subject being positioned between said source and said detector, said detector detecting radiation propagating through said subject, the pattern of a material of said source producing a coded representation of said subject on said detector; and

means operative with said detector for decoding said representation to produce an image of said subject.

2. A system according to claim 1 wherein said patterns are Fresnel patterns and said decoding means comprises a laser for illuminating a photographic film transparency of said coded representation, an optical means for viewing an off-axis image from light of said laser propagating through said transparency.

3. A system according to claim 1 wherein said patterns are in the form of a chirped checkerboard.

4. A system according to claim 1 wherein said decoding means comprises computer means for convolving said coded representation with a reference pattern.

5. A system according to claim 1 wherein said source comprises a non-luminous region positioned between a location of said first material and a location of said second material.

6. A radiographic system for imaging a subject having a substance which absorbs radiation of a predetermined frequency from the class of radiation consisting of X and gamma radiation comprising:

a source and a detector, said detector being spaced apart from said source and said subject being positioned between said source and said detector;

said source comprising a first material emitting radiation at a first frequency lower than said predetermined frequency, said source comprising a second material emitting radiation having a frequency higher than said predetermined frequency, said first material being located at positions corresponding to a first pattern, said second material being located at positions alternating with said positions of said first material to produce a second pattern similar to said first pattern;

said detector receiving an image from radiation incident thereupon, said image being coded in accordance with the pattern of said second material wherein an image of said substance is outlined by absorption of radiation from said second material by said substance, said radiation of said first material uniformly propagating through said subject with less absorption by said substance than said radiation of said second material; and

means matched to said pattern for decoding said coded image to produce a true image of said subject.

7. A system according to claim 6 wherein said decoding means comprises viewing optics oriented off the axis of a transparency of said coded image whereby the reconstruction is matched to an off-axis Fresnel pattern of said material.

8. A system according to claim 6 wherein said decoding means comprises a filter having a phase and frequency characteristic matched to a scanning along a line of said coded image.

9. A system according to claim 6 wherein said decoding means comprises means for convolving said coded image with a reference pattern.

10. In a radiographic imaging system employing a coded source and means for reconstructing an image from a coded image, a coded source comprising:

a first radiation emissive material positioned in predetermined locations in a predetermined pattern upon a face of said source for radiating a subject having a contrast agent therein, said constrat agnet having a predetermined absorption edge in its radiation absorption frequency spectrum, said first material having a characteristic frequency of its radiation lower than the frequency of said absorption edge; and

said source having a second material interleaved with said first material to produce a second pattern upon said face of said source for radiating said subject, said second material having a characteristic frequency of radiation higher than the frequency of said absorption edge.

11. A system according to claim 10 wherein said source comprises a target illuminated by an electron beam, said target illuminating said first material and said second material with X-radiation, said first material and said second material producing fluorescent radiation at said characteristic frequencies in response to said illumination by said target.

12. A method of radiographic imaging comprising the steps of:

injecting a contrast agent having a predetermined absorption edge into a subject to be imaged;

illuminating said subject by source of spatially coded radiation having first and second characteristic frequencies to provide a coded image of said subject said first frequency being lower than said absorption edge and said second frequency being greater than said absorption edge; and

decoding said coded image to provide a true image of said subject.