X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-08-15
2004-11-16
Glick, Edward J. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S004000, C378S009000, C250S370090
Reexamination Certificate
active
06819738
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to a system and method for differentiating material characteristics using an imaging system and more particularly to a system and method for differentiating material characteristics using a hybrid scintillator/photo sensor and direct conversion (DC) imaging system.
In at least one known computed tomography (CT) imaging system configuration having single and/or multi-slice scintillator/photo diode arrays, an x-ray source projects a fan-shaped, or a cone-shaped, beam which is collimated to lie within an X-Y-Z volume of a Cartesian coordinate system, wherein the X-Y-Z volume is generally referred to as an “imaging volume” and usually includes a set of X-Y planes generally referred to as the “imaging planes”. An array of radiation detectors, wherein each radiation detector includes a detector element, is disposed within the CT system so as to receive this 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 volume, 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 two-dimensional slices 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 +3072, 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 −1000HU's (corresponding to a dark pixel) and an attenuation measurement for very dense bone matter may convert into an integer value of +3000 (corresponding to a bright pixel), whereas an attenuation measurement for water may convert into an integer value of 0HU'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 and thus locate and identify areas of concern.
Typically, radiation detector arrays used in imaging systems, such as the CT imaging system described hereinabove, include single and/or multi-slice scintillator/photo diode detectors. A scintillation detector is constructed of a scintillation material, such as cadmium tungstate (CdWO4) or rare earth ceramics and operates by receiving x-ray photons emitted by an x-ray source and converting these x-ray photons into a digital signal proportional to the attenuated x-ray energy received. These digital signals are then processed and turned into image data.
One goal of CT imaging has been to utilize multi-energy scanning techniques to differentiate between tissues and/or materials having varying atomic numbers and densities, such as calcium and/or iodine. Historically, this has been accomplished using an imaging system having a scintillation detector either by taking single slice images with a single slice CT imaging system having two different x-ray beam filters, or by taking single slice images with a single slice CT imaging system having two different x-ray tube kVp's that exactly overlap spatially, but at a slightly later time, and then processing these two images to separate materials having varying atomic numbers and densities, using suitable known methods such as image subtraction. For example, using a single slice CT imaging system a first single slice image would be obtained. The x-ray kVp or the filter at the x-ray tube would then be changed and a second single slice image would be obtained at the same patient location. As mentioned above, the two slices of image data would then be processed to separate materials of varying atomic numbers and densities within the obtained slice plane.
Unfortunately, this is an expensive, time consuming and involved process and although a CT imaging system having a DC detector could be conceivably utilized exclusively as the CT imaging system for performing the above mentioned process, the DC detector would not be able to count the x-rays fast enough to support CT flux rates and/or scan times. Thus, if used in the current mode the obtained information would suffer from very high amount of non-linearities that would be very difficult or even impossible to correct in order to achieve artifact free scanning.
The above discussed and other features and advantages of the embodiments will be appreciated and understood by those skilled in the art from the following detailed description and drawings
SUMMARY OF INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a hybrid scintillation/direct conversion computed tomography (CT) imaging system comprising: a gantry, wherein the gantry defines a patient cavity and includes an x-ray source and a radiation detection apparatus, wherein the radiation detection apparatus includes a first radiation detector and a second radiation detector and wherein the x-ray source and the radiation detection apparatus are rotatingly associated with the gantry so as to be separated by the patient cavity; a patient support structure movingly associated with the gantry so as to allow communication with the patient cavity; and a processing device, wherein the processing device is communicated with the radiation detection apparatus.
In an alternative embodiment, a method for differentiating material characteristics using a hybrid scintillation/direct conversion imaging system comprising: obtaining the hybrid scintillation/direct conversion imaging system, wherein the hybrid scintillation/direct conversion imaging system includes a radiation source and a radiation detector apparatus having a first radiation detector and a second radiation detector; operating the imaging system so as to cause the radiation source to emit a radiation beam toward the radiation detector apparatus such that the first radiation detector generates first detector data and the second radiation detector generates second detector data; and processing the first detector data and the second detector data so as to generate image data.
In another alternative embodiment, a hybrid scintillation/direct conversion imaging system, comprising: a gantry, wherein the gantry defines a patient cavity and includes a radiation source and a radiation detection apparatus, wherein the radiation detection apparatus includes a first radiation detector and a second radiation detector and wherein the radiation source and the radiation detection apparatus are rotatingly associated with the gantry so as to be separated by the patient cavity; a patient support structure movingly associated with the gantry so as to allow communication with the patient cavity; and a processing device, for obtaining data from the first radiation detector and the second radiatio
Cantor & Colburn LLP
GE Medical Systems Global Technology Company LLC
Glick Edward J.
Thomas Courtney
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