X-ray or gamma ray systems or devices – Beam control – Filter
Reexamination Certificate
2002-06-18
2004-12-28
Glick, Edward J. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Filter
C378S156000, C378S004000
Reexamination Certificate
active
06836535
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates generally to diagnostic imaging and, more particularly, to a method and apparatus of dynamically filtering radiation emitted toward a subject during radiographic imaging.
Typically, in radiographic imaging systems, an x-ray source emits x-rays toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” may be interchangeably used to describe anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-rays. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
In computed tomography (CT) imaging systems, the x-ray source and the detector array are rotated about a gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-rays as a beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and a photodiode for receiving the light energy from an adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
There is increasingly a need to reduce radiation dosage projected toward a patient during an imaging session. It is generally well known that significant dose reduction may be achieved by using a “bowtie” filter to shape the intensity profile of an x-ray beam. Surface dose reductions may be as much as 50% using a bowtie filter. It is also generally known that different anatomical regions of a patient may advantageously mandate different shaped bowtie filters to reduce radiation dosage. For example, scanning of the head or small region of a patient may require a bowtie filter shaped differently than a filter used during a large body scanning session. It is therefore desirable to have an imaging system with a large number of bowtie filter shapes available to best fit each patient. However, fashioning an imaging system with a sufficient number of bowtie filters to accommodate the idiosyncrasies encountered during scanning of numerous patients can be problematic in that each individual patient cannot be contemplated. Additionally, manufacturing an imaging system with a multitude of bowtie filters increases the overall manufacturing cost of the imaging system.
Therefore, it would be desirable to design an apparatus and method of dynamically filtering the radiation emitted toward the subject during imaging data acquisition with a single filter.
BRIEF DESCRIPTION OF INVENTION
The present invention is a directed method and apparatus of dynamically filtering radiation projected toward a subject for data acquisition overcoming the aforementioned drawbacks.
The present invention includes a filtering apparatus for a CT imaging system or equivalently for an x-ray imaging system. The filtering apparatus is designed such that its shape may be changed prior to or during an imaging session. The shape of the filtering apparatus can be modulated to mirror an attenuation pattern of a subject thereby optimizing radiation dose exposure to the subject. Furthermore, by implementing two opposing filters that are orthogonally oriented with respect to one another, the x-ray attenuation may be controlled along the x as well as z axes to shape the x-ray intensity. A number of filtering apparatuses are contemplated.
In accordance with one aspect of the present invention, a method of diagnostic imaging comprises the steps of positioning a subject to be scanned into a scanning bay and projecting a radiation beam along a beam path toward the subject. The method further includes positioning a filter having an attenuation profile in the beam path. The attenuation profile of the filter is then modulated to define a desired attenuation profile. The method further includes acquiring diagnostic data of the subject and reconstructing an image of the subject from the diagnostic data.
In accordance with another aspect of the present invention, a method of acquiring diagnostic data of a subject comprises the steps of determining an attenuation pattern for acquiring diagnostic data of a subject to be scanned and presetting a first filter to a desired attenuation profile. The method further includes the step of projecting high frequency electromagnetic energy toward the subject to acquire diagnostic data of the subject. During the projection of high frequency electromagnetic energy, a second filter having an attenuation profile is translated such that the attenuation profiles of the first filter and the second filter is a function of the attenuation pattern of the subject.
In accordance with a further aspect of the present invention, a method of diagnostic imaging includes the steps of positioning a subject to be scanned on a table in a scanning bay and projecting high frequency electromagnetic energy toward the subject. The method further includes dynamically filtering the high frequency electromagnetic energy with at least one filter and acquiring imaging data of the subject. A set of images of the subject from the imaging data are then reconstructed. With the subject removed from the scanning bay, high frequency electromagnetic energy is again projected toward the detector absent the subject and table and dynamically filtered with the at least one filter. The method further includes acquiring scan data attributable to the at least one filter and generating a set of calibration data attributable to the at least one filter to be used in reconstructing artifact free images of the subject.
In accordance with yet another aspect of the present invention, a radiation emitting system comprises a scanning bay configured to position the subject to be scanned in a path of radiation as well as a radiation projection source configured to project radiation toward the subject. The system further includes a radiation filter having a variable attenuation profile. A computer is also provided and programmed to determine an attenuation pattern of the subject and modulate the variable attenuation profile of the radiation filter as a function of the attenuation pattern of the subject.
In accordance with a further aspect of the present invention, a radiation emitting imaging system is provided. The imaging system includes a scanning bay and a moveable table configured to move a subject to be scanned fore and aft along a first direction within the scanning bay. The system further includes an x-ray projection source configured to project x-rays toward the subject. A first attenuator is provided and configured to attenuate x-rays along a first axis. A second attenuator is also provided and configured to attenuate x-rays along a second axis. Both the first attenuator and second attenuator are translatable in the first direction. The imaging system further includes a computer programmed to calibrate the first attenuator to have a desired attenuation profile and calibrate the second attenuator to have a desired attenuation profile. The computer is further programmed to move the subject along the first direction and simultaneously therewith, translate at least one of the first attenuator and the second attenuator in the first direction.
In accordance with yet another aspect of the present invention, a computer readable storage medium is provided and has stored thereon a computer program representing a set of instructions that when executed by a computer c
Bernstein Tsur
Toth Thomas L.
Della Penna Michael A.
General Electric Company
Glick Edward J.
Horton Carl B.
Song Hoon
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