X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-07-29
2004-12-07
Bruce, David V (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S901000
Reexamination Certificate
active
06829323
ABSTRACT:
BACKGROUND OF INVENTION
The present disclosure relates generally imaging systems and, more particularly, to improving the dose efficiency for an imaging system through a method and system for image simulation at lower doses.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system, wherein the X-Y plane is generally referred to as an “imaging plane”. An array of radiation detectors, wherein each radiation detector includes a detector element, are within the CT system so as to receive this fan-shaped beam. An object, such as a patient, is disposed within the imaging plane so as to be subjected to the x-ray beam wherein the x-ray beam passes through the object. As the x-ray beam passes through the object being imaged, 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 attenuation at the detector element location. These electrical signals are referred to as x-ray attenuation measurements.
In addition, 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.
One method for reconstructing an image from a set of projection data is referred to as the “filtered back-projection technique”. This process converts the attenuation measurements from a scan into discrete integers, ranging from −1024 to +3071, called “CT numbers” or “Hounsfield Units” (HU). These HU's are used to control the brightness of a corresponding pixel on a cathode ray tube or a computer screen display in a manner responsive to the attenuation measurements. For example, an attenuation measurement for air may convert into an integer value of −1000 HU's (corresponding to a dark pixel) and an attenuation measurement for very dense bone matter may convert into an integer value of +2000 (corresponding to a bright pixel), whereas an attenuation measurement for water may convert into an integer value of 0 HU's (corresponding to a gray pixel). This integer conversion, or “scoring” allows a physician or a technician to determine the density of matter based on the intensity of the computer display.
Although imaging systems, such as the CT imaging system, are excellent diagnostic and evaluation tools, each time a scan is performed the patient being scanned is exposed to radiation. In fact, CT scans account for only about 2% to 3% of medical examinations using imaging systems. However, they account for 30% to 50% of the population radiation dose from these procedures. Given that exposure to greater than average amounts of radiation is known to cause health problems, there is concern within the medical community that a patient may be over exposed. As such, there is a continuing but increasingly limited effort to reduce the amount of patient exposure by improving the imaging dose efficiency. This effort includes researchers investigating and determining the minimum dose required to obtain the image quality necessary to make an accurate and confident diagnosis for a given clinical application. As patient dose is decreased, the image noise is increased, making lesions more difficult to detect.
In order obtain the data needed to find the minimum dose necessary to make a confident diagnosis a reference object, such as a patient, must undergo multiple scans at different dose levels. Unfortunately, this may be considered unethical, inappropriate and potentially detrimental to the patient(s) being scanned for these purposes. Accordingly, it is desirable to be able to determine minimum dose information without the need for exposing a patient to excessive radiation doses.
SUMMARY OF INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for generating a simulated patient image. In an exemplary embodiment, the method includes obtaining image data from an actual patient image and generating simulated noise data. The image data is then combined with the simulated noise data to create the simulated patient image. In one embodiment, scan data from the actual patient image is combined with the generated simulated noise data to create pre-image data, and the pre-image data is then reconstructed to create simulated image data. In another embodiment, a set of individual noise pattern images for each a plurality of phantom objects is created. At least one of the individual noise pattern images is selected for combination with the actual patient image. The at least one selected individual noise pattern image is then combined with the actual patient image, thereby creating the simulated patient image.
In another aspect, a method for generating a simulated computer tomography (CT) patient image includes obtaining image data from an actual CT patient image taken at a first radiation dose, and generating simulated noise data. The image data is then combined with the simulated noise data to create the simulated patient image, wherein the simulated image simulates the actual CT patient image taken at a second, reduced radiation dose with respect to the first radiation dose.
In another aspect, an imaging system includes a gantry having an x-ray source and a radiation detector array, wherein the gantry defines a patient 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 patient cavity. A patient support structure is movingly associated with the gantry so as to allow communication with the patient cavity. In addition, a processing device is used for obtaining image data from an actual patient image. The imaging system further includes means for generating simulated noise data, and means for combining the image data with the simulated noise data to create a simulated patient image.
In still another aspect, a storage medium includes a machine readable computer program code for generating a simulated patient image, and instructions for causing a computer to implement a method. The method includes obtaining image data from an actual patient image, generating simulated noise data and combining the image data with the simulated noise data to create the simulated patient image.
In still another aspect, a computer data signal includes code configured to cause a processor to implement a method for generating a simulated patient image. The method includes obtaining image data from an actual patient image, generating simulated noise data and combining the image data with the simulated noise data to create the simulated patient image.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
REFERENCES:
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H. Greess, A. Homayr, H. Wolf, U. Baum, M. Lell, B. Bowing, W. Kalender, W. Bautz; “Dose reduction in CT examination of children by an attenuation-based on-line modulation of tube current (CARE Dose);” Eur. Radiol; (2002); pp. 1571-1576.
P. Lahorte, S Vandenberghe, K. Van Laere, K. Audenaert, I Lemahieu, and R. A. Dierckx; “Rapid Communication—Assessing the Performance of SPM A
Hsieh Jiang
Li Jianying
McOlash Scott Matt
Toth Thomas Louis
Bruce David V
Cantor & Colburn LLP
GE Medical Systems Global Technology Company LLC
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