Method of high resolution partial area scan involving concentrated high density material outside the partial area

Claim 1

In a method of high resolution computed tomography scanning of a portion of a planar region of a patient such as a section of the spine by a CT scanner of the type having a scan circle defining an examination region, a rotating source of penetrating radiation movably mounted relative to said scan circle for subjecting the scan circle to radiation, an array of stationary radiation detectors coplanar with the path of the source, spaced about the axis of rotation of the source and positioned to receive at least some of the radiation that passes from said source and through the scan circle for producing signals indicative of the intensity of radiation impinging thereon, and processing means operatively connected with said detector array for reconstructing into a visual display said signals caused by radiation attenuation in the scan circle, wherein concentrated high density material such as bone tissue is situated within the planar region but outside the portion of interest, the improvement comprising: (a) emitting a divergent beam of radiation by said rotating source at an angle sufficiently large to encompass the portion of interest of the planar region of the patient and smaller than required for subjecting the entire scan circle to radiation, the common area within the angle of the beam at different positions of the rotating source defining a small scan circle corresponding to the portion of interest; (b) selecting from said array of detectors those detectors whose signals are altered by projections of bone tissue situated outside the small scan circle; (c) acquiring from said signals of said array of detectors a plurality of projections of the portion of interest of the planar slice of the patient corresponding to a plurality of angular orientations of the source about said patient, each projection representing the irradiated portion of the object as defined by said divergent beam; (d) filtering signals produced by said selected detectors so as to minimize errors introduced into the projections by the bone tissue situated outside the small scan circle; and (e) reconstructing said portion of interest of the planar region of said scanned patient from said plurality of projections.

Claim 5

A method according to either of claims 1 or 2 wherein said filtering step comprises: providing variable filtering of said signals of said selected detectors.

Claim 6

A method of reducing errors in high resolution computed tomography scanning of a partial area of a planar region of a patient such as a section of the spine by a CT scanner of the type having a scan circle defining an examination region, a rotating source of penetrating radiation movably mounted relative to said scan circle for subjecting the scan circle to radiation, an array of stationary radiation detectors coplanar with the path of the source, spaced about the axis of rotation of the source and positioned to receive at least some of the radiation that passes from said source and through the scan circle for producing signals indicative of the intensity of radiation impinging thereon, and processing means operatively connected with said detector array for reconstructing into a visual display said signals caused by radiation attenuation in the scan circle, wherein said errors arise from concentrated high density material such as bone tissue situated within the planar region being scanned but outside the partial area, the scanning method including emitting a divergent beam of radiation by said rotating source at an angle sufficiently large to encompass the partial area of the planar region of the patient and smaller than required for subjecting the entire scan circle to radiation, the common area within the angle of the beam at different positions of the rotating source defining a small scan circle corresponding to the partial area, acquiring from said signals a plurality of projections of the partial area of the planar slice of the patient corresponding to a plurality of angular orientations of the source about said patient, each projection representing the irradiated portion of the object as defined by said divergent beam, and reconstructing said partial area of the planar slice of said scanned patient from said plurality of projections, the improvement characterized by: selectively filtering signals from those detectors which receive radiation attenuated by bone tissue situated outside the partial area but within the divergent beam emitted by the rotating source to minimize errors introduced into the projections by said bone tissue.

Claim 7

A method of reducing errors in high resolution computed tomography scanning of a partial area of a planar region of a patient such as a section of the spine by a CT scanner of the type having a scan circle defining an examination region, a rotating source of penetrating radiation movably mounted relative to said scan circle for subjecting the scan circle to radiation, an array of stationary radiation detectors coplanar with the path of the source, spaced about the axis of rotation of the source and positioned to receive at least some of the radiation that passes from said source and through the scan circle for producing signals indicative of the intensity of radiation impinging thereon, and processing means operatively connected with said detector array for reconstructing into a visual display said signals caused by radiation attenuation in the scan circle, wherein said errors arise from concentrated high density material such as bone tissue situated within the planar region being scanned but outside the partial area, the scanning method including emitting a divergent beam of radiation by said rotating source at an angle sufficiently large to encompass the partial area of the planar region of the patient and smaller than required for subjecting the entire scan circle to radiation, the common area within the angle of the beam at different positions of the rotating source defining a small scan circle corresponding to the partial area, acquiring from said signals a plurality of projections of the partial area of the planar slice of the patient corresponding to a plurality of angular orientations of the source about said patient, each projection representing the irradiated portion of the object as defined by said divergent beam, and reconstructing said partial area of the planar slice of said scanned patient from said plurality of projections, the improvement characterized by: selectively filtering signals from those detectors which receive radiation attenuated by bone tissue situated outside the partial area but within the divergent beam emitted by the rotating source to minimize errors introduced into the projections by said bone tissue.