X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1998-11-25
2001-06-05
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S095000
Reexamination Certificate
active
06243437
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to imaging and more particularly, to coronary calcification detection using an imaging system.
In at least one known imaging system generally referred to as a computed tomography (CT) 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.
To detect coronary calcification in a patient, images of the patient's heart are generated and reviewed to identify calcium deposits. However, as a result of the movement of the heart and the blood, the heart images may be blurred. The blurring causes difficulty in identifying the areas of calcium deposits.
To reduce the blurring of the images, it is desirable to provide an imaging system which gathers data as the heart motion is minimized. It would also be desirable to provide such a system which weights redundant data having different amounts motion with different weights to improve image temporal resolution.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained by an imaging system which, in one embodiment, gathers image data during the relatively motion free period and includes a modified halfscan image reconstruction algorithm which weights redundant data to provide acceptable image quality along with the benefits of an enhanced temporal response. In an exemplary embodiment, the imaging system utilizes an EKG signal to determine a diastolic period of the heart. The diastolic period is then utilized to determine an ending point of the projection data to be used to reconstruct an image. The minimum data duration is then subtracted from the ending point to determine a beginning point of the collected projection data.
In one embodiment, the modified halfscan image reconstruction algorithm unequally weights redundant projection data. More specifically, a higher weight is applied to data collected during a period of less motion of the heart.
The above described imaging system uses projection data during the period of time when heart motion is minimized. In addition, the system unequally weights redundant data having different amounts motion to improve temporal resolution of the images.
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Hu Hui
Kinsinger Richard E.
Armstrong Teasdale LLP
Cabou Christian G.
Church Craig E.
General Electric Company
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