Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-09-28
2001-05-15
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S425000, C600S436000, C600S437000, 36, 36, 36, C378S008000
Reexamination Certificate
active
06233478
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for radiographic imaging of a selected object and, in particular, to an apparatus and method for radiographic imaging of an object undergoing a cyclic motion.
BACKGROUND OF THE INVENTION
Imaging systems, such as computed tomography (CT) scanners, are widely used for diagnostic purposes in medical and industrial applications. However, radiographic imaging of an object is complicated when the object is not stationary. The time resolution of conventional imaging systems is typically insufficient to effectively “freeze” the motion of the object. As a result, the images produced suffer from blurring effects caused by the movement of the object. Accordingly, various techniques have been developed to enable radiographic imaging of moving objects.
One such technique has focused on the pre-alignment of a gantry associated with a computed tomography (CT) scanner. The gantry is provided to synchronously rotate a radiation source and detector. Accordingly, image data can be recorded for various source and detector positions within the rotational plane of the gantry. For the pre-alignment technique to be effective, the main motion of the object must be in one direction and the gantry must rotate in a plane perpendicular to the object's motion. Therefore, the pre-alignment technique is capable of correcting for only simple motion. Accordingly, the technique is not suitable for imaging objects, such as a beating heart, which undergo complicated motions.
Another technique, which is useful for imaging an object undergoing a cyclic motion, involves the use of retrospective gating. In that technique, a continuous stream of image data is recorded but only the data collected at the desired phase of the object is utilized. Although the retrospective gating technique may collect enough projections at the same phase of the motion for reconstruction, the data acquisition time is unpredictable and the object will be subjected to a higher radiation dose than is necessary.
A third technique for imaging a moving object requires prospective gating. In the prospective gating technique, the scanner is operated in such a way that the radiation exposure and data collection occur only when the object is at the desired phase. The prospective gating technique suffers from the same uncertainty of data acquisition time as for the retrospective gating technique.
Additionally, electron beam computed tomography systems have been developed. The time resolution of these systems is generally sufficient to record images of even rapidly moving objects, such as a beating heart. However, a high capital investment, the lack of insurance reimbursement and low image quality have prevented the acceptance of electron beam CT as a routine clinical procedure.
In light of the foregoing, it would be highly beneficial to provide an apparatus and method for producing image slices of an object undergoing cyclic motion wherein the images are essentially free from blurring effects caused by the movement of the object. Additionally, the apparatus and method should enable the image slices to be constructed on-line in a quick and robust manner. Further, the apparatus and method should minimize the object's exposure to radiation.
SUMMARY OF THE INVENTION
The problems associated with the known techniques for producing radiographic image slices of an object undergoing cyclic motion are solved to a large degree by an apparatus in accordance with the present invention. The apparatus comprises a scanner for collecting image data associated with the object, a probe for detecting a signal associated with the cyclic motion of the object, end a controller for generating a command signal which enables the scanner to collect appropriate image data such as at preselected times or at preselected phases of the cyclically-moving object.
The scanner comprises a radiation source for irradiating the object and a detector for detecting radiation from the radiation source. A gantry, having a continuously controllable speed, is provided for rotating the radiation source with respect to the selected object. The detector may be mounted on the gantry for synchronously rotating with the source or the detector may be provided as a stationary detector ring. The scanner may further comprise a bed or other support platform having a continuously controllable linear speed for supporting the object and translating the object in a selected direction relative to the scanner.
A probe is provided to detect the relative movement and/or phase of the cyclically-moving object. The controller is operatively connected to the probe for receiving a signal from the probe. The controller utilizes the probe signal to generate the command signal for enabling the scanner to collect image data for producing one or more image slices through the object at one or more selected phases of the cyclic motion. The command signal is used to control and optimize the speed of the gantry and/or the bed thereby enabling the apparatus to construct image slices through the object which are not marred by blurring effects, while subjecting the object to a minimum dose of radiation. In one embodiment, the command signal enables the scanner to operate in a single-slice mode which provides for the collection of image data at only a single predetermined phase of the cyclic motion of the selected object. In an alternate embodiment, the command signal enables the scanner to operate in a continuous mode for collecting image data of multiple image slice positions at a single phase of the motion or of a single image slice at multiple phases.
The apparatus may further comprise an image reconstructing unit for manipulating the image data to construct image slices through the selected object. The image reconstructing unit comprises a reordering unit for generating reordered image data. Since the image data is not necessarily collected in the proper order for image reconstruction, the reordering unit organizes the data to create a complete data section. The reconstructing unit further comprises a rebinning unit for generating parallel beam data from the reordered image data. The rebinning unit converts the reordered fan beam data to parallel beam data using formulas that relate fan beam parameters to corresponding parallel beam parameters. An image slice reconstructing unit is provided for constructing an image slice of a specific phase of the object from the parallel beam data.
In another of its aspects, the present invention relates to a method for constructing image slices through an object undergoing a cyclic motion. The method comprises the steps of generating an average period of the cyclic motion from a signal derived from the object. A window width is then selected to be less than a predetermined portion of the average period of the cyclic motion. When a single slice of a selected phase is desired, the window width represents the time that the radiation source is turned on for each cyclic motion period. When multiple slices are to be reconstructed, the radiation source is turned on for a consecutive time period and the window width is instead used for selecting proper sections of the data to reconstruct image slices with a desired phase.
A gantry rotation period is generated from the average period of the cyclic motion and the window width. The average period of the cyclic motion, the window width, and the gantry rotation period are then used to determine a minimum number of cyclic motion periods required to obtain a complete set of data. Then, a sampling period is generated from the gantry rotation period and the number of source beams in a complete gantry rotation. Additionally, when a single image slice at a selected phase is to be constructed, a time delay for a selected phase condition is generated from the average period. The time delay insures that the object will be in the desired place when image data is collected. Therefore, a series of images may be acquired of the object while in the same phase of motion.
When
Advanced Research & Technology Institute
Dann Dorfman Herrell & Skillman P.C.
Lateef Marvin M.
Lin Jeoyuh
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