Method and apparatus for computing tomographic scans

Claim 1

A computed tomography apparatus comprising: an x-ray radiation therapy simulator including a beam source for producing a width-collimated x-ray fan beam and a table supporting an object in the fan beam produced by the source so that the beam exposes substantially the entirety of the object; a detector selectively mountable to said simulator at a location in the fan beam on the opposite side of the table from the beam source and which, when removed therefrom, does not alter the original function of said simulator; said detector including a plurality of individual radiation detector elements mounted to said simulator on a line having an axis which is substantially perpendicular to the central axis of the fan beam, each of the detector elements producing an output signal having an amplitude proportional to the intensity of the radiation incident thereon; said simulator including means for rotating the beam source together with said detector mounted thereto along a substantially circular arc about a center for taking a plurality of exposures of the object at angular increments along the circular arc; and a computer operably connected to said detector programmed for receiving, storing, and processing the output signals of each of the detector elements at each angular increment, calculating the ratio of the output signals from radiation incident upon each of the detector elements traversing the object to the output signal from the same detector element for the same radiation in the absence of a target object, transforming the ratio into the frequency domain for filtering, and convolving the filtered signal to produce a value in the spatial domain representing the output signal of each detector element had the detector element detected a parallel beam of radiation from the source at each angular increment having a central axis which is contiguous and co-linear with the central axis of the fan beam.

Claim 10

An apparatus for attaching to a radiation therapy x-ray simulator for computing a CT image, the simulator comprising a radiation source for producing a fan beam, a film holder mounted substantially perpendicularly to the central axis of the fan beam produced by the radiation source, a table for supporting a target object between the radiation source and the film holder, and means for rotating the radiation source and film holder around the target object supported on the table comprising: a linear detector array adapted for mounting to the film holder of the x-ray simulator with the long axis of said array substantially perpendicular to the central axis of the fan beam produced by the radiation source of the simulator without altering the ability of the simulator to function as a simulator; said detector array comprising a plurality of detector elements, each individual detector element producing an output signal having an amplitude proportional to the energy intensity of the x-ray radiation incident thereon, the intensity of the incident x-ray radiation being proportional to the density of the target object through which the incident x-ray radiation passes before striking the individual detector element; and computer means for scaling the output signal from each detector element to account for the relative distance from the radiation source to the target object and for the distance from the radiation source to said detector array, transforming the output signal from each detector element into the frequency domain for filtering, convolving the filtered signal to produce a signal representing the signal that would have been produced by each detector element had the incident radiation been a parallel beam instead of a fan beam, and converting the transformed signal at each incremental angle into a gray scale value for a picture element having a specific set of coordinates relative to the coordinates of said detector array for output to an appropriate display means.

Claim 11

An apparatus for attaching to a radiation therapy x-ray simulator for computing a CT image, the simulator comprising a radiation source for producing a fan beam, a film holder mounted substantially perpendicularly to the central axis of the fan beam produced by the radiation source, a table for supporting a target object between the radiation source and the film holder, and means for rotating the radiation source and film holder around the target object supported on the table comprising: a linear detector array adapted for mounting to the film holder of the x-ray simulator with the long axis of said array substantially perpendicular to the central axis of the fan beam produced by the radiation source of the simulator without altering the ability of the simulator to function as a simulator; said detector array comprising a plurality of detector elements, each individual detector element producing an output signal having an amplitude proportional to the energy intensity of the x-ray radiation incident thereon, the intensity of the incident x-ray radiation being proportional to the density of the target object through which the incident x-ray radiation passes before striking the individual detector element; and computer means for scaling the output signal from each detector element to account for the relative distance from the radiation source to the target object and for the distance from the radiation source to said detector array, transforming the output signal from each detector element into the frequency domain for filtering, convolving the filtered signal to produce a signal representing the signal that would have been produced by each detector element had the incident radiation been a parallel beam instead of a fan beam, and converting the transformed signal at each incremental angle into a gray scale value for a picture element having a specific set of coordinates relative to the coordinates of said detector array for output to an appropriate display means.