Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-12-30
2002-10-22
Smith, Ruth S. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C378S008000, C378S095000
Reexamination Certificate
active
06470208
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) imaging and, more particularly, to methods and apparatus for controlling x-ray exposure during gated cardiac scanning.
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.
Methods are known for controlling patient exposure to x-rays during gated cardiac scanning. For example, it is known to control patient exposure based upon a prediction of when a heartbeat will occur. Heartbeat timing predictions often are inaccurate, and resulting image quality can be degraded by unpredicted cardiac motion. It would be desirable to provide a method for controlling x-ray exposure during cardiac scanning without sacrificing image quality. It also would be desirable to control patient exposure while scanning patients having irregular heart rates.
BRIEF SUMMARY OF THE INVENTION
There is therefore provided, in one embodiment, a method for controlling x-ray exposure during gated cardiac scanning, including the steps of detecting a first cardiac signal; starting scanning after a pre-selected wait time after detecting the first cardiac signal; and stopping the scanning after a first to occur of passage of a pre-selected data collection time and detection of a second cardiac signal. The above-described method allows scanning exposure to be controlled for patients having heart rates as high as 92 beats per minute without sacrificing image quality for patients having slower heart rates.
REFERENCES:
patent: 4382184 (1983-05-01), Wernikoff
patent: 4547892 (1985-10-01), Richey et al.
patent: 5803914 (1998-09-01), Ryals et al.
patent: 6068595 (2000-05-01), Miyazaki et al.
patent: 6195408 (2001-02-01), Acharya et al.
Acharya Kishore C.
Woloschek Steven J.
Woodford Mark E.
Armstrong Teasdale LLP
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
Smith Ruth S.
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