Beds – Invalid bed or surgical support – Adapted for imaging
Reexamination Certificate
1999-12-27
2001-08-07
Trettel, Michael F. (Department: 3628)
Beds
Invalid bed or surgical support
Adapted for imaging
C378S020000, C378S209000, C600S415000
Reexamination Certificate
active
06269501
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) imaging and, more particularly, to methods and apparatus for automatically positioning a patient for scanning using pre-scan scout data.
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 “Hounstifield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
An over-ranged signal during data acquisition can cause image artifacts. Nevertheless it is desirable to apply higher gains in data acquisition to minimize electronic noise. Because over-ranging is most likely to occur in the center of the detector, it is possible to eliminate over-range by ensuring that the patient blocks an area of the detector center. It is difficult, however, to center the patient on a table for scanning. Because of different sizes and shapes at different body locations, it is particularly difficult to center all body parts simultaneously and sufficiently to prevent over-range at the detector center. It would be desirable to provide a method for centering all of a patient's body parts during scanning to prevent over-ranging.
BRIEF SUMMARY OF THE INVENTION
There is therefore provided, in one embodiment of the present invention, a method for automatically positioning an object, such as a patient, on a movable table using pre-scan scolut data. High and low edges and a center of the object are determined as a function of the location of the object in a z-axis direction. At least one threshold is determined from which to determine whether to move the table. The table is automatically repositioned based on comparison of the thresholds to respective distances of the high edge, low edge and center of the object from isocenter.
The above described method allows automatic and dynamic adjustment of the table height to a position that prevents over-range while allowing use of higher gains to reduce image noise.
REFERENCES:
patent: 4842259 (1989-06-01), Rice
patent: 5457724 (1995-10-01), Toth
patent: 5657498 (1997-08-01), Hum
patent: 6148058 (2000-11-01), Dobbs
patent: 6173032 (2001-01-01), Besson
patent: 6185271 (2001-02-01), Kinsinger
Li Jianying
Toth Thomas L.
Armstrong Teasdale LLP
Cabou Christian G.
General Electric Company
Trettel Michael F.
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