X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-09-16
2001-07-24
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S116000, C378S901000
Reexamination Certificate
active
06266387
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to computed tomography (CT) imaging apparatus; and more particularly, to the control of the x-ray source and data acquisition system during a scan.
In a current computed tomography system, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system, termed the “imaging plane”. The x-ray beam passes through the object being imaged, such as a medical patient, and impinges upon an array of radiation detectors. The intensity of the transmitted radiation is dependent upon the attenuation of the x-ray beam by the object and each detector produces a separate electrical signal that is a measurement of the beam attenuation. The attenuation measurements from all the detectors are acquired separately and digitized by a data acquisition system to produce the transmission profile.
The x-ray source and detector array in a conventional CT system are rotated on a gantry within the imaging plane and around the object so that the angle at which the x-ray beam intersects the object constantly changes during a scan. A group of x-ray attenuation measurements from the detector array at a given angle is referred to as a “view” and a “scan” of the object comprises a set of views made at different angular orientations during one revolution of the x-ray source and detector. In a 2D scan, data is processed to construct an image that corresponds to a two dimensional slice taken through the object. The prevailing method for reconstructing an image from 2D data is referred to in the art as the filtered backprojection 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.
The operation of the x-ray generator and the acquisition system during a scan is controlled by a programmed computer. The operator prescribes a scan and in response to the prescribed scan parameters, the computer executes a program which controls the various elements of the CT imaging system to carry out the scan. The computer produces an output signal that repeatedly turns the x-ray source on and off as the gantry is rotated. It also produces an output signal that directs the data acquisition system to repeatedly sample the signals produced by the radiation detectors during the scan.
Modern CT imaging systems are called upon to conduct many different types of scans. For each of these different scans specific software is developed to operate system elements such as the x-ray source and the data acquisition system. Such software has become very complex and difficult to develop. This results from the increasingly complex and sophisticated scans that have been developed and from the increased demand for high speed scans.
SUMMARY OF THE INVENTION
The present invention is a command sequence for a CT imaging system which receives a series of commands from a programmed processor and which controls the operation of an x-ray source and the operation of a data acquisition system to carry out a prescribed scan. More particularly, the command sequence includes: a command FIFO memory which stores a series of commands required to carry out a prescribed scan; a counter responsive to a count field in each command to establish the duration of each command read from the FIFO memory; an x-ray command line responsive to an x-ray enable bit in each command to energize or de-energize an x-ray source during the duration of the command; a data acquisition clock gate responsive to a data acquisition enable bit in each command to produce a data acquisition signal during the duration of the command; and control logic for reading out the next command in the command FIFO memory at the completion of each command. Once the series of commands are stored in the FIFO memory, the programmed processor is free to carry out other functions during the scan. The command sequencer operates autonomously to produce the signals necessary to operate the x-ray source and data acquisition system during the scan.
REFERENCES:
patent: 4300096 (1981-11-01), Harrison et al.
patent: 4694404 (1987-09-01), Meagher
patent: 5056006 (1991-10-01), Acharya et al.
patent: 5417218 (1995-05-01), Spivey et al.
Dunahee Kenneth G.
Gscheidmeier Jason M.
Bruce David V.
Cabou Christian G.
GE Medical Systems Global Technology Company LLC
Quarles & Brady LLP
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