X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-04-29
2003-03-04
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
Reexamination Certificate
active
06529575
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to a method and system for reducing noise in an X-ray image and more particularly to a method and system for using an adaptive projection filtering scheme to reduce noise in an X-ray image generated by a Computed Tomography (CT) system.
In CT imaging systems, an x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane, generally referred to as an “imaging plane”, of a Cartesian coordinate system toward an array of radiation detectors, wherein each radiation detector includes a detector element disposed within the CT system so as to receive this fan-shaped beam. An object, such as a patient, is disposed between the x-ray source and the radiation detector array so as to lie within the imaging plane and so as to be subjected to the x-ray beam, which passes through the object. As the x-ray beam passes through the object, the x-ray beam becomes attenuated before impinging upon the array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is responsive to the attenuation of the x-ray beam by the object, wherein each detector element produces a separate electrical signal responsive to the beam intensity at the detector element location. These electrical signals are referred to as x-ray attenuation measurements or x-ray images.
Moreover, the x-ray source and the detector array may be rotated, with a gantry within the imaging plane, 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 during one revolution of the x-ray source and the detector array. In an axial scan, the projection data is processed so as to construct an image that corresponds to a two-dimensional slice taken through the object. In CT systems that employ a single detector array, the slice thickness is controlled and determined by the width of the collimator, while in CT systems that employ a multiple detector array, the slice thickness is controlled and determined by summing the contributions of a plurality of detector sub-units and by physically moving the collimator to the outer edges of each slice.
With the introduction of high resolution (sub-mm) scanning and faster scan speeds, the peak and sustained CT system power requirements have increased dramatically. One reason for this is that higher resolution images require smaller slices. This effectively introduces additional signal loss due to gaps between individual cells and thus results in a significantly smaller number of detected x-ray photons. For example, the smallest slice thickness for an eight-slice scanner is 1.25 mm, wherein the smallest slice thickness for a sixteen-slice scanner is 0.625 mm. As such, assuming the same x-ray tube power, the number of detected x-ray photons for a sixteen-slice scanner will be more than a factor of two smaller than the number of detected x-ray photons for an eight-slice scanner.
One of the key obstacles in performing a smoothing operation to remove noise or statistical fluctuation is the ability to separate the real signal variation from the statistical fluctuation. If it is known prior to reconstruction that certain variations in the signal data is caused solely by statistical fluctuation, low-pass filters may be applied to the signal data without impacting the spatial resolution of the x-ray image. The key to differentiating between variations caused by the statistical fluctuations and the real signal variation or structure is the noise characteristic of the measured signal. In CT imaging, extensive pre-processing and calibration steps are performed to ensure artifact-free, or noise free, images. Unfortunately, the distribution of the statistical fluctuations following these steps is quite difficult to characterize.
SUMMARY OF INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for reducing noise in an x-ray image generated by a computed tomography imaging system using an adaptive projection filtering scheme comprising: generating system information; obtaining original projection data; determining a data characteristic of the original projection data; processing the original projection data responsive to the system information and the data characteristic so as to create filtered projection data and calculating resulting projection data responsive to the filtered projection data.
A medium encoded with a machine-readable computer program code for reducing noise in an x-ray image generated by a computed tomography imaging system using an adaptive projection filtering scheme, the medium including instructions for causing a controller to implement a method comprising: generating system information; obtaining original projection data; determining a data characteristic of the original projection data; processing the original projection data responsive to the system information and the data characteristic so as to create filtered projection data and calculating resulting projection data responsive to the filtered projection data.
A method for reducing noise in an image generated by an imaging system comprising: obtaining an imaging system and an object to be scanned; operating the imaging system so as to create original projection data responsive to the object; examining the original projection data so as to determine if the original projection data should be processed; and processing the original projection data using an adaptive projection filtering scheme wherein the filtering scheme, generates system information; determines a data characteristic of the original projection data; processes the original projection data responsive to the system information and the data characteristic so as to create filtered projection data and calculates resulting projection data responsive to the filtered projection data.
A system for reducing noise in an x-ray image comprising: a gantry having an x-ray source and a radiation detector array, wherein the gantry defines an object cavity and wherein the x-ray source and the radiation detector array are rotatingly associated with the gantry so as to be separated by the object cavity; a object support structure movingly associated with the gantry so as to allow communication with the object cavity; and a processing device having an adaptive projection filtering scheme, wherein the filtering scheme, generates system information; obtains original projection data; determines a data characteristic of the original projection data; processes the original projection data responsive to the system information and the data characteristic so as to create filtered projection data and calculates resulting projection data responsive to the filtered projection data.
A system for reducing noise in an image generated by an imaging system using an adaptive projection filtering scheme comprising: the imaging system; an object disposed so as to be communicated with the imaging system, wherein the imaging system generates original projection data responsive to the object; and a processing device, wherein the processing device, generates system information; obtains the original projection data; determines a data characteristic of the original projection data; processes the original projection data responsive to the system information and the data characteristic so as to create filtered projection data and calculates resulting projection data responsive to the filtered projection data.
REFERENCES:
patent: 5598481 (1997-01-01), Nishikawa et al.
patent: 5715334 (1998-02-01), Peters
Bruce David V.
Cantor & Colburn LLP
GE Medical Systems Global Technology Company LLC
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