X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2000-05-08
2002-04-02
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S015000, C378S004000
Reexamination Certificate
active
06366637
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to tomographic imaging, and more particularly to methods and apparatus for generating computed tomographic imaging data using a multi-slice imaging system.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two-dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
In known CT systems the x-ray beam is projected from the x-ray source through a pre-patient collimator that defines the x-ray beam profile in the patient axis, or z-axis. The collimator typically includes x-ray-absorbing material with an aperture therein for restricting the x-ray beam.
CT imaging systems typically provide image resolution within limitations imposed by such factors as collimator aperture size and slice thickness. A minimum slice thickness for at least one CT system is 1.25 millimeters, as determined primarily by detector element pitch size. In order to improve image resolution, it is desirable to reduce slice thickness to less than 1 millimeter, and to achieve such reduction with minimal impact on imaging system hardware.
It is known to reduce slice thickness of a single-slice imaging system by irradiating a portion of a detector element and deconvolving imaging data, for example, projection data or image data, to reduce the full-width-at-half-maximum (FWHM) interval of a reconstructed slice profile. It is desirable to achieve similar slice-width reductions on multi-slice systems without impacting system hardware. Difficulties can arise, however, in implementing this approach for a multi-slice imaging system, because multi-slice sampling is limited, for example, by joints between adjacent detector rows.
It would be desirable to use double-slice imaging data collection and deconvolution techniques to reduce slice thickness on a multi-slice imaging system without having to change system hardware.
BRIEF SUMMARY OF THE INVENTION
There is therefore provided, in one embodiment, a method for reducing slice thickness of a computed tomography imaging system including a source configured to direct an x-ray beam through an object toward a plurality of rows of detector elements configured to collect projection data in slices, the method including the steps of obtaining imaging data from a pair of adjacent rows, each of the adjacent rows having an outer edge; deconvolving at least a portion of the imaging data obtained from an area bounded by the adjacent row outer edges; and combining the deconvolved imaging data to obtain a slice sensitivity profile for the adjacent row pair.
The above-described method allows a multi-slice imaging system user to implement imaging data deconvolution to reduce slice thickness to less than one millimeter. Thus image resolution is improved without having to modify hardware in existing multi-slice imaging systems.
REFERENCES:
patent: 5262946 (1993-11-01), Heuscher
patent: 5864598 (1999-01-01), Hsieh et al.
patent: 6061419 (2000-05-01), Hsieh et al.
patent: 6243438 (2001-06-01), Nahaliel et al.
Hsieh Jiang
Li Jianying
Armstrong Teasdale LLP
Bruce David V.
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
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