Abstract:
A method and system for reducing radiation exposure from an imaging system including determining an entry location, operating the imaging system so as to cause the imaging system to emit radiation having a radiation intensity, controlling the radiation intensity in a manner responsive to the entry location so as to create image data and processing the image data so as to create processed image data. In an alternative embodiment, a medium encoded with a machine-readable computer program code for reducing radiation exposure from an imaging system, the medium including instructions for causing a controller to implement the aforementioned method.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates generally to a radiation exposure limiting scheme and more particularly to a radiation exposure limiting scheme for reducing the radiation exposure of a physician during the operation of an imaging system.  
           [0002]    In at least one known computed tomography (CT) imaging system configuration, 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, are disposed within the CT system so as to received 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.  
           [0003]    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.  
           [0004]    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&#39;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&#39;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&#39;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.  
           [0005]    Once a suspicious mass, such as a tumor, cyst and/or lesion, is discovered an interventional procedure, such as a needle biopsy or a needle aspiration, is usually performed to obtain tissue samples needed to determine whether the mass is cancerous or benign. To do this, a needle controlled by a physician is guided to the mass using simultaneous images, such as fluoro images, produced by the imaging system. This allows a physician to manipulate the needle tip towards the suspected tumor tissue so as to obtain a tissue sample that may be used for analysis.  
           [0006]    However, although an interventional procedure using an imaging system is an excellent diagnostic and evaluation tool, each time an interventional procedure is performed by a physician, the physician&#39;s hand is exposed to radiation emitted from the imaging system. As such, if a physician performs a large number of interventional procedures over time, the cumulative radiation dose exposure to the physician&#39;s hand over time may become quite large. Given that health problems are known to be related to increasing exposure to radiation there is concern within the medical community that physicians performing these procedures may be over exposed to imaging system radiation.  
           [0007]    One method to address the problem of physician radiation dose exposure includes minimizing the emitter current of the imaging system and using special forceps to keep the physician&#39;s hands out of the radiation beam. Unfortunately, forceps have not been well received by the medical community because they restrict the tactile sensitivity and thus limits the delicate physician control required for interventional procedures. Moreover, it has been found that minimizing the emitter current of the imaging system during an interventional procedure while still providing sufficient radiation for qualitative image generation still results in a significant cumulative radiation dose to the physician repeatedly performing the interventional procedures. As such, these methods are not well suited for repeated interventional procedures.  
           [0008]    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.  
         SUMMARY OF INVENTION  
         [0009]    The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for reducing radiation exposure from an imaging system comprising: determining an entry location; operating the imaging system so as to cause the imaging system to emit radiation having a radiation intensity; controlling the radiation intensity in a manner responsive to the entry location so as to create image data; and processing the image data so as to create processed image data.  
           [0010]    In an alternative embodiment, a medium encoded with a machine-readable computer program code for reducing radiation exposure from an imaging system, the medium including instructions for causing a controller to implement the aforementioned method.  
           [0011]    In another alternative embodiment, a method for reducing radiation exposure from an imaging system comprising: obtaining an object to be scanned; operating the imaging system so as to create image data; displaying the image data on an output device; and processing the image data using a processing device, wherein the processing device, determines an entry location; operates the imaging system so as to cause the imaging system to emit radiation having a radiation intensity; controls the radiation intensity in a manner responsive to the entry location so as to create image data; and processes the image data so as to create processed image data.  
           [0012]    In another alternative embodiment, a system for reducing radiation exposure from an imaging system comprising: 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 movingly associated with the gantry so as to allow communication with the patient cavity; and a processing device, wherein the processing device, determines an entry location; operates the imaging system so as to cause the imaging system to emit radiation having a radiation intensity; controls the radiation intensity in a manner responsive to the entry location so as to create image data; and processes the image data so as to create processed image data.  
           [0013]    In another alternative embodiment, a system for reducing radiation exposure from an imaging system comprising: an imaging system; a patient support structure movingly associated with the imaging system so as to allow communication between the imaging system and a patient, wherein the imaging system generates image data responsive to the patient; and a processing device, wherein the processing device, determines an entry location; operates the imaging system so as to cause the imaging system to emit radiation having a radiation intensity; controls the radiation intensity in a manner responsive to the entry location so as to create image data; and processes the image data so as to create processed image data.  
           [0014]    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. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0016]    [0016]FIG. 1 is a perspective view of a CT imaging system and a patient disposed for imaging;  
         [0017]    [0017]FIG. 2 is a block schematic diagram of a CT imaging system;  
         [0018]    [0018]FIG. 3 is a block diagram describing a method for reducing radiation exposure from an imaging system;  
         [0019]    [0019]FIG. 4A is a distribution diagram showing the angular radiation distribution of an imaging system;  
         [0020]    [0020]FIG. 4B is a distribution diagram showing the angular radiation distribution of an imaging system in accordance with an exemplary embodiment;  
         [0021]    [0021]FIG. 5 is a graph of the radiation dose as a function of imaging system gantry angle in accordance with an exemplary embodiment; and  
         [0022]    [0022]FIG. 6 is a distribution diagram showing the angular radiation distribution of an imaging system in accordance with an exemplary embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0023]    Referring to FIG. 1 and FIG. 2 a representative CT imaging system  1  is shown and preferably includes a gantry  2  having an x-ray source  4 , a radiation detector array  6 , a patient support structure  8  and a patient cavity  10 , wherein x-ray source  4  and radiation detector array  6  are opposingly disposed so as to be separated by patient cavity  10 . A patient  12  is preferably disposed upon patient support structure  8  which is then disposed within patient cavity  10 . X-ray source  4  projects an x-ray beam  14  toward radiation detector array  6  so as to pass through patient  12 . X-ray beam  14  is preferably collimated by a collimate (not shown) so as to lie within an X-Y-Z volume a Cartesian coordinate system referred to as an “imaging volume”. After passing through and becoming attenuated by patient  12 , attenuated x-ray beam  16  is preferably received by radiation detector array  6 . Radiation detector array  6  preferably includes a plurality of detector elements  18  wherein each of the detector elements  18  receives attenuated x-ray beam  16  and produces an electrical signal responsive to the intensity of attenuated x-ray beam  16 .  
         [0024]    Although the embodiments described herein are described as applying to a computed tomography imaging system  1 , it should be stated that the embodiments described herein may be applied to any imaging system suitable to the desired end purpose, such as an imaging system having a stationary ring and/or arc of detector arrays which surround the patient cavity, wherein the radiation source moves around patient  12  irradiating the detector elements within the stationary ring and/or arc.  
         [0025]    In addition, x-ray source  4  and radiation detector array  6  are preferably rotatingly disposed relative to gantry  2  and patient support structure  8 , so as to allow x-ray source  4  and radiation detector array  6  to rotate around patient support structure  8  when patient support structure  8  is disposed within patient cavity  10 . X-ray projection data is obtained by rotating x-ray source  4  and radiation detector array  6  around patient  12  during a scan. X-ray source  4  and radiation detector array  6  are preferably communicated with a control mechanism  20  associated with CT imaging system  1 .  
         [0026]    Control mechanism  20  preferably controls the rotation and operation of x-ray source  4  and/or radiation detector array  6 .  
         [0027]    Control mechanism  20  preferably includes an x-ray controller  22  communicated with x-ray source  4 , a gantry motor controller  24 , and a data acquisition system (DAS)  26  communicated with radiation detector array  6 , wherein x-ray controller  22  provides power and timing signals to x-ray source  4 , gantry motor controller  24  controls the rotational speed and angular position of x-ray source  4  and radiation detector array  6  and DAS  26  receives the electrical signal data produced by detector elements  18  and converts this data into digital signals for subsequent processing. CT imaging system  1  also preferably includes an image reconstruction device  28 , a data storage device  30  and a processing device  32 , wherein processing device  32  is communicated with image reconstruction device  28 , gantry motor controller  24 , x-ray controller  22 , data storage device  30 , an input device  34  and an output device  36 . Moreover, CT imaging system  1  also preferably includes a table controller  38  communicated with processing device  32  and patient support structure  8 , so as to control the position of patient support structure  8  relative to patient cavity  10 .  
         [0028]    In accordance with an exemplary embodiment, patient  12  is preferably disposed on patient support structure  8 , which is then positioned by an operator via processing device  32  so as to be disposed within patient cavity  10 . Gantry motor controller  24  is operated via processing device  32  so as to cause x-ray source  4  and radiation detector array  6  to rotate relative to patient  12 . X-ray controller  22  is operated via processing device  32  so as to cause x-ray source  4  to emit and project a collimated x-ray beam  14  toward radiation detector array  6  and hence toward patient  12 . X-ray beam  14  passes through patient  12  so as to create an attenuated x-ray beam  16 , which is received by radiation detector array  6 .  
         [0029]    Detector elements  18  receive attenuated x-ray beam  16 , produces electrical signal data responsive to the intensity of attenuated x-ray beam  16  and communicates this electrical signal data to DAS  26 . DAS  26  then converts this electrical signal data to digital signals and communicates both the digital signals and the electrical signal data to image reconstruction device  28 , which performs high-speed image reconstruction. This information is then communicated to processing device  32 , which stores the image in data storage device  30  and displays the digital signal as an image via output device  36 .  
         [0030]    Referring to FIG. 3, a flow diagram describing a method for reducing radiation exposure  100  from an imaging system  1  is shown and discussed. In accordance with an exemplary embodiment, an entry location  40  is determined, as shown in step  102 . During an interventional procedure an instrument, such as a needle, is guided by a physician&#39;s hand with the help of imaging system  1  and entry location  40  represents the location of the physician&#39;s hand which is disposed within patient cavity  10  and hence within a radiation field  42 , wherein radiation field  42  includes an average radiation distribution  44  and an angular radiation distribution  46 . In addition, entry location  40  may be disposed within a predetermined entry angular range  50 . Although, entry location  40  is preferably determined via an entry cursor and/or a target location cursor, wherein the entry cursor and/or target location cursor is communicated with processing device  32  via input device  34 , entry location  40  may be determined and/or estimated using any information, method and/or device suitable to the desired end purpose, such as processing of data extracted from a Fluoro scan procedure. For example, an on-line assessment of the angular position of entry location  40  (&amp; hence physician&#39;s hand) may be performed in a manner responsive to changes of the x-ray attenuation distribution during the intervention process and/or a manner responsive to the x-ray distribution determined during the primary non-fluoro scan and/or in a manner responsive to any other suitable means of detection, such as Ultrasound and/or optical.  
         [0031]    Referring to FIG. 4 a , imaging system  1  is operated so as to cause x-ray source to emit radiation in the form of x-ray beam  14 . As x-ray source  4  and radiation detector array  6  rotate around patient cavity  10  x-ray beam  14  creates radiation field  42  within patient cavity  10  wherein radiation field  42  includes average radiation distribution  44  and angular radiation distribution  46 , as shown in step  104 . As x-ray source  4  rotates around patient cavity  10  the gantry angular position or the angle at which x-ray beam  14  intersects patient  12 , varies between 0° and 360°.  
         [0032]    Radiation intensity level  48  is then controlled in a manner responsive to entry location  40  and/or entry angular range  50  so as to create image data, as shown in step  106 . Referring to FIG. 4B and FIG. 5, for a 360° image reconstruction  52  as the gantry angular position approaches entry location  40  and/or entry angular range  50 , radiation intensity level  48  is decreased by a predetermined minimization amount so as to minimize the radiation intensity level  48  in the area of entry location  40 . Similarly, as the gantry angular position approaches 180° from entry location  40  and/or entry angular range  50 , radiation intensity level  48  is increased by a predetermined minimization amount so as to maximize the radiation intensity level  48  in the area of 180° from entry location  40 . Predetermined minimization amount may be equal to the radiation intensity level so as to reduce the radiation intensity level at entry location  40  and/or within entry angular range  50  to be zero. Moreover, predetermined minimization amount may be any value suitable to the desired end purpose.  
         [0033]    For a 180° image reconstruction  60 , as the gantry angular position approaches entry location  40  and/or entry angular range  50 , radiation intensity level  48  is decreased by a predetermined minimization amount so as to minimize the radiation intensity level  48  in the area of entry location  40 . Similarly, as the gantry angular position approaches ±90° from entry location  40  and/or entry angular range  50 , radiation intensity level  48  is increased by a predetermined minimization amount so as to maximize the radiation intensity level  48  in the area of ±90° from entry location  40  and/or entry angular range  50 . This advantageously allows for a nearly constant average radiation distribution  44  through out the scan while allowing for the angular radiation distribution  46  to be modified. This advantageously allows the noise level of the image to be compensated by amplification of the emitter tube current at the opposing angle (180° for 360° recon) or the perpendicular angles (±90° for 180° recon). Moreover, the radiation exposure to the physician&#39;s hand will be dramatically reduced by the absorption of the patient&#39;s body (and, in most cases, by the patient table).  
         [0034]    In addition, radiation intensity level  48  may be controlled by using a pre-determined radiation absorption angular profile (as measured during a previous rotation of the fluoroCT process and/or from a previously acquired static scan) as an input for additional modulation of x-ray beam  14  in order to significantly reduce patient radiation exposure dose. This pre-determined measure of radiation may be dependent upon the anatomy of patient  12  within the scan field. For example, if patient absorption at specific radiation source angles is low, as may be the case when x-ray source  4  is positioned anterior or posterior to the chest area of patient  12 , then the radiation beam intensity may be significantly reduced at these angles without affecting image quality. Alternatively, when patient absorption is high, as may be the case for lateral radiation source angles, such as through the shoulder area or hip area of patient  12 , x-ray source  4  may deliver a full un-modulated radiation exposure dose.  
         [0035]    Another related feature includes using the angular current profile as an input for a weighting function in the reconstruction of the image. As the x-ray radiation is reduced the limited photon statistics give rise to increased image noise. Special noise reduction techniques and algorithms may be applied in the reconstruction process to reduce any image performance degradation. These algorithms may be controlled either by obtaining a measure of actual photon statistics during the acquisition process and/or by the priory knowledge of the angular current profile.  
         [0036]    Furthermore, in order to eliminate streaks and other noise pattern artifacts, in the fluoro images, more than 180+fan degrees of data may be used for image reconstruction (e.g. 270 deg). The additional data beyond the last 180 degrees of scanning may be used to reduce image noise and streaks and significantly improve the image quality. The reduction in temporal resolution that this “over-scan” reconstruction entails may not be significant while using very fast rotation speed (≦0.5 sec) and a weighting function that includes only a small amount of “old” data.  
         [0037]    Furthermore, in order to eliminate streaks and other noise pattern artifacts, in the final (static) image, more than 360 degrees of data may be used for image reconstruction (e.g. 540 deg). This implementation may occur following the ‘dynamic’ image reconstruction and display phase of FluoroCT imaging and may be used as a means of improving the quality of the final static image that remains on output device  36  after the real-time imaging has stopped. The additional data beyond the last 360 degrees of scanning may be used to reduce image noise and streaks and significantly improve the static image quality of this final image. The reduction in temporal resolution that this over-scan reconstruction entails may not be significant when viewing the static image at the completion of the FluoroCT procedure.  
         [0038]    Referring to FIG. 6, the radiation intensity level  48  may also be controlled in a manner responsive to entry location  40  and/or entry angular range  50  so as to prevent radiation from being emitted from imaging system  1  while the gantry angular position approaches the entry location  40  and/or is within entry angular range  50 . Radiation may be prevented from being emitted from imaging system  1  via any means suitable to the desired end purpose, such as by an electrical means (switch), a mechanical means (shutter) and/or an electro-mechanical means. This reduces and/or eliminates radiation exposure to a physician&#39;s hand while allowing the interventional procedure to continue. Moreover, direct radiation to the physician&#39;s hand will be eliminated while indirect radiation will be dramatically reduced by the absorption of the patient&#39;s body.  
         [0039]    This image data is then processed so as to create processed image data, as shown in step  108 . This advantageously allows for a significant dose reduction to the physician during interventional procedures using a FluoroCT scan while preserving patient dose and image quality.  
         [0040]    This invention advantageously allows for interventional procedures to be performed while minimizing and/or eliminating radiation exposure to the performing physician. In addition, potential health problems may advantageously be avoided by reducing the physicians&#39; exposure to x-ray radiation to more acceptable levels.  
         [0041]    In accordance with an exemplary embodiment, a method for reducing radiation exposure from an imaging system  100  may be applied by any imaging system suitable to the desired end purpose, such as a magnetic resonance imaging (MRI), ultrasound, X-Ray, CT and/or PET.  
         [0042]    In accordance with an exemplary embodiment, processing of FIG. 3 may be implemented through processing device  32  operating in response to a computer program. In order to perform the prescribed functions and desired processing, as well as the computations therefore (e.g., the execution of Fourier analysis algorithm(s), the control processes prescribed herein, and the like), the controller may include, but not be limited to, a processor(s), computer(s), memory, storage, register(s), timing, interrupt(s), communication interfaces, and input/output signal interfaces, as well as combinations comprising at least one of the foregoing. For example, the controller may include input signal filtering to enable accurate sampling and conversion or acquisitions of such signals from communications interfaces. It is also considered within the scope of the invention that the processing of FIG. 3 may be implemented by a controller located remotely from processing device  32 .  
         [0043]    As described above, the present invention can be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. The present invention can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. Existing systems having reprogrammable storage (e.g., flash memory) can be updated to implement the invention. The present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.  
         [0044]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.