X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1998-11-25
2001-05-08
Church, Craig E. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S004000
Reexamination Certificate
active
06229870
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the diagnostic imaging arts. The invention finds particular application in conjunction with volume CT imaging for medical purposes and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in conjunction with industrial, security, and other types of volume imaging apparatus and techniques.
In diagnostic imaging with CT scanners, a thin, fan shaped beam of radiation is projected from an x-ray source through a region of interest. The radiation source is rotated about the region of interest such that the same thin slice of the region of interest is irradiated from a multiplicity of directions spanning 360°. In a third generation scanner, an arc of radiation detectors is mounted to the same gantry as the radiation source such that the two rotate together. In a fourth generation scanner, the x-ray detectors are mounted stationarily in a ring 360° around the subject.
To image a volume of interest, a single slice image is typically generated. After a first slice image is generated, a subject support is indexed by a slice width generally on the order of a few millimeters, and another slice is generated. This slice image and index technique is repeated until slices spanning the volume of interest are generated. One drawback to this type of imaging is the relatively long time necessary to generate a large plurality of slices. Because the first and last slice are taken at a significantly different time, the volume image is distorted by a time evolution of the region of interest.
In spiral scanning techniques, the patient is generally moved continuously through the x-ray beam as the x-ray source rotates around the region of interest. In this manner, the fan shaped beam of radiation and the region of interest move in a spiral pattern relative to each other. The continuous motion is faster than indexing between slices, but still relatively slow.
In order to reduce the imaging time, some scanners collimate the beam of radiation into two slices. When the beam of radiation is collimated into two slices, two sets of radiation detectors disposed end to end are commonly provided. Typically, the thickness of the irradiated slice and the spacing between slices are adjustable. Such adjustments are relatively straight forward for two beams of radiation. However, the requirement that each beam of radiation strike only a single set of radiation detectors renders collimation into more than two beams mechanically awkward. Moreover, because the two beams originate from a common focal point, they are divergent, not parallel to each other. The divergent rays complicate and introduce errors into reconstruction techniques in which data is reconstructed into parallel slices. Moreover, as radiation from a single source is collimated into more beams, such beams become more widely divergent.
Systems have been proposed for examining the region of interest with a cone beam of radiation. However, cone beam image reconstruction is computationally intensive and slow. Moreover, cone beam imaging has a fixed resolution, based on detector size. Further, cone beam reconstructions tend to suffer from insufficiency of data problems, image artifacts, and other reconstruction errors.
The present invention contemplates a new, improved CT system which overcomes the above difficulties and others.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, a CT scanner includes a stationary gantry portion defining an examination region. A rotating gantry portion selectively rotates about the examination region. A plurality of anode elements, associated with the rotating gantry portion for selective bombardment by an electron stream, generate a plurality of parallel x-ray beams. Also included are a plurality of x-ray detectors receiving the x-ray beams which have passed through the examination region. The detectors generate signals indicative of the x-ray beams received and a reconstruction processor processes these generated signals into an image representation.
In accordance with another aspect of the present invention, the CT scanner further includes an x-ray tube body defining a vacuum envelope. The plurality of anode elements, each defining at least one target face, are disposed within the vacuum element.
In accordance with another aspect of the present invention, the CT scanner further includes a collimator externally adjacent to the body defining a series of alternating openings and septa. The openings have fan-shaped sides forming fan-shaped x-ray beams parallel to others of the x-ray beams and perpendicular to an axis through the examination region.
In accordance with another aspect of the present invention, the CT scanner further includes a plurality of x-ray tubes each including at least one of the anode elements. The x-ray tubes are spaced along an axis at a common angle relative to the examination region.
In accordance with another aspect of the present invention, the CT scanner includes a plurality of x-ray tubes, each comprising one of the anode elements where the x-ray tubes are spaced along an axis at a plurality of predefined angles relative to the examination region.
In accordance with the present invention, a method of diagnostic imaging includes simultaneously bombarding a plurality of axially spaced, parallel anode elements with electrons generating a plurality of x-ray beams. The x-ray beams are passed through an examination region where they are received and used to generate signals proportional to an amount of radiation received.
In accordance with another aspect of the present invention, the method of diagnostic imaging further includes receiving a desired imaging profile. A first set of anode elements to bombard for a first amount of time is determined based on the desired imaging profile received. A cathode assembly associated with each of the first set of anode elements is selectively powered for the first amount of time.
In accordance with the present invention, a method of diagnostic imaging includes concurrently generating a plurality of thin fan beams of penetrating radiation. The plurality of thin fan beams are passed through an examination region while the fan beams are concurrently rotating around the examination region. Each of the fan beams is detected after passing through the examination region and are used to generate electronic signals indicative of an amount of radiation which has passed through the examination region.
In accordance with another aspect of the present invention, the fan beams are rotated about an axis of rotation and the method further includes causing a relative axial movement along the axis of rotation between the examination region and the parallel fan beams.
In accordance with another aspect of the present invention, the method includes each of the parallel thin fan beams spaced equidistantly from each other wherein relative motion between the examination region and the parallel beams extend over a preselected distance such that each beam of radiation moves in a spiral pattern through a contiguous subvolume of the region of interest.
One advantage of the present invention resides in significantly improved imaging time as compared with conventional single fan beam CT systems.
Another advantage is that volumes can be imaged substantially in real time.
Another advantage of the present invention resides in the ability to use existing reconstruction algorithms to generate images.
Other benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.
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Church Craig E.
Fay Sharpe Fagan Minnich & McKee LLP
Picker International Inc.
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