Tomographic apparatus and method for reconstructing planar slices from non-absorbed and non-scattered radiation

• US 4,365,339 A
• Filed: 09/11/1978
• Issued: 12/21/1982
• Est. Priority Date: 12/23/1975
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Pavkovich, John M., Nunan, Craig S.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Grigsby, T. N.
• Application Number:
  US05/941,506
• Time in Patent Office: 1,562 Days
• Field of Search: 250/445 T, 364/414, 378/15, 378/16, 378/901
• US Class Current: 378/15
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4258 for detecting non x-ray radiation, e.g. gamma radiation A61B6/037 takes precedence
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: G06T 2211/416 Exact reconstruction
• CPC Class Codes: G06T 2211/421 Filtered back projection [FBP]
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

In a tomographic apparatus and method for reconstructing two dimensional planar slices from linear projections of non-absorbed radiation useful in the fields of medical radiology, microscopy, and non-destructive testing, a beam of radiation in the shape of a fan is passed through an object lying in the same quasi plane as the object slice and non-absorption thereof is recorded on oppositely situated detectors aligned with said source of radiation. There is relative rotation between the source-detector configuration and the object within the quasi-plane. Periodic values of the detected radiation are taken, convolved with certain functions, and back-projected to produce a two-dimensional output picture on a visual display illustrating a facsimile of the object slice. A series of two-dimensional pictures obtained simultaneously or serially can be combined to produce a three-dimensional portrayal of the entire object. The invention is the first device which uses a fan beam source of radiation coupled with the application of a convolution method of data reduction with no intervening reordering of fan beam rays, thereby eliminating errors and delays in computation time which would be involved in such reordering. The invention is the first method for providing an exact reconstruction of a two-dimensional picture of an object slice from a series of one-dimensional projections of radiation not absorbed by the slice when the superior fan beam source is employed.

Claims

1. Apparatus for examining an object with radiation, said apparatus comprising:

support means mounted for rotation about a fixed axis;

source means forming a fan shaped planar beam of radiation, said source means being mounted on said support means with said beam directed toward said axis;

detector means for detecting said fan beam, said detector means being mounted on said support means and positioned on the side of said axis of rotation opposite from said source means; and

said source means and detector means being rigidly attached to said support means during operation;

whereby

in operation of said apparatus said support means, source means and detector means are all constrained against motion in any direction except rotation about said fixed axis;

means for continuously rotating said support means;

means for turning said beam on and off periodically during said continuous rotation;

means for performing a non-reordering convolution operation on signals derived from the fan beam received by said detector means at positions of the fan beam, thus arranging said signal in convolved form representative of radiation absorbed by said object at each of said positions; and

display means responsive to said means for performing a non-reordering convolution operation for providing a visual portrayal of radiation absorbed by said object.