X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1998-12-22
2001-08-14
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S095000
Reexamination Certificate
active
06275560
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) imaging and more particularly, to a cardiac gated CT 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.
To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a one fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed.
With known CT system, projection data is collected from a helical or axial scan to generate sequential frames of images of an area, or organ, within a patient. A frame corresponds to a two dimensional slice taken through the imaged object, e.g., the patient. Typically, an operator attempts to minimize the amount of time required to generate each frame to minimize motion related image degradation.
At least one known CT system, images of a patient's heart are generated and reviewed to identify certain types of conditions. However, as a result of the movement of the heart and the blood, the heart images are blurred. The blurring causes difficulty in identifying conditions within the heart.
To improve the quality of the images, it is desirable to provide an imaging system which gathers data during a selected period of a heart cycle. It would also be desirable to provide such a system which controls the emission of x-rays to reduce the x-ray dosage to the patient.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained by an imaging system which, in one embodiment, synchronizes the emission of x-rays and the collection of data to a selected portion of a heart cycle to provide improved image quality. In an exemplary embodiment, the imaging system utilizes an synchronization unit to determine the selected period of the heart and to generate a short burst of x-ray beams during the selected period. As the x-ray beams are emitted toward a detector array, data is collected for a view angle. As the heart continues to cycle, data is collected for a series of view angles so that a complete image of the heart during the selected period is generated.
The above described imaging system gathers data during a selected period of the heart cycle so that image quality is improved. In addition, the imaging system controls the emission of x-ray beams so that x-ray dosage to the patient is reduced.
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Blake James A.
Senzig Robert F.
Armstrong Teasdale LLP
Cabou Christian G.
General Electric Company
Porta David P.
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