X-ray or gamma ray systems or devices – Beam control – Collimator
Reexamination Certificate
2001-01-18
2002-09-10
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Collimator
C378S152000
Reexamination Certificate
active
06449340
ABSTRACT:
FIELD OF THE DISCLOSURE
The present disclosure relates to the field of radiography and, in particular, relates to computed tomography scanners. Even more particularly, the present disclosure relates to an adjustable x-ray beam collimator for use with a computed tomography scanner.
BACKGROUND OF DISCLOSURE
In computed tomography a patient to be examined is positioned in a scan circle of a computed tomography (CT) scanner. A shaped x-ray beam is then projected from an x-ray source through the scan circle and the patient, to an array of radiation detectors. By rotating the x-ray source and the detector array about the patient (about a z-axis of the scanner), radiation is projected through an imaged slice of the patient to the detectors from a multiplicity of directions. From data provided by the detectors, an image of the scanned slice of the patient is constructed.
Within the x-ray source, an electron beam strikes a focal spot or line on an anode, and x-rays are generated at the focal spot and emitted along diverging linear paths in an x-ray beam. Collimators are normally employed for shaping a cross-section of the x-ray beam, and for directing the shaped beam toward the detector array. A pre-patient collimator is positioned between the x-ray source and the patient, while a post-patient collimator is positioned between the patient and the detector array. Conventional collimators generally comprise a plate-like structure provided with a rectangular slit of uniform width for producing a rectangular beam cross-section, as desired with systems employing a rectangular detector array.
Some CT scanners allow for flexibility in the number and thickness of slices acquired during a scan. In such scanners, the x-ray beam is collimated such that its cross-section irradiates a particular row, or rows of detectors, without irradiating adjacent rows of detectors not utilized for that scan.
What is desired, therefore, is an improved collimator for shaping a cross-section of a beam of energy, and for directing the shaped beam toward a desired target, such as a detector array. What is further desired is an adjustable collimator that produces beam cross-sections of variable widths. Preferably, the collimator will also produce beam cross-sections of variable, yet uniform widths, such that cross-sections will irradiate a specific row, or rows of detectors, without irradiating adjacent rows of detectors.
SUMMARY OF DISCLOSURE
The present disclosure, accordingly, is director to an adjustable collimator for collimating a beam of energy emitted from a focal spot of a beam source. The collimator is particularly intended for collimating an x-ray beam of a computed tomography scanner after the x-ray beam has passed through a patient being scanned.
The collimator generally includes two elongated parallel plates arranged side by side to define a collimating slit between the plates. At least one of the plates is movably relative to the other plate for varying a width of the collimating slit. The collimator also includes a movable cam operatively arranged with respect to the at least one movable plate such that movement of the cam in a first direction causes the width of the collimating slit to increase, while movement of the cam in a second direction causes the width of the collimating slit to decrease.
According to one aspect of the disclosure, the cam is rotatably movable and the collimator includes a motor having has a rotatable shaft coupled to the cam for controlling the width of the collimating slit. According to another aspect, the motor comprises a step motor for providing the collimating slit with predefined, discrete widths. Preferably, the variable slit of the collimator has a uniform width and is curved about a common axis of curvature for alignment with a focal spot of a beam source, such that the collimating slit produces beam cross-sections of variable, yet uniform widths.
The present disclosure also provides a computed tomography scanner including a collimator as described above, and further including an annular gantry rotatable about a rotation axis, a beam source mounted within the gantry and having a focal spot for emitting an x-ray beam through the rotation axis, and an array of x-ray detectors for receiving the x-ray beam from the focal spot. The collimator is mounted within the gantry between the focal spot and the detectors for collimating the x-ray beam. According to one aspect, the collimator is positioned between the axis of rotation and the detector array to act as a “post-patient” collimator.
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Duffy Michael J.
Nemirovsky Lidia
Tybinkowski Andrew P.
Tybinkowski Jack M.
Analogic Corporation
Gemmell Elizabeth
McDermott & Will & Emery
Porta David P.
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