Abstract:
A method for x-ray scatter correction during simultaneous bi-plane imaging using digital image processing. The basic concept includes correcting the image from each plane by combining it with an image of the scatter generated from the exposures of the opposite plane in such a way that the scatter effects are removed. The correction image is formed by sampling images from the detector with only the x-ray exposure of the scatter producing plane being active. These sampled images of scatter are processed to form the scatter correction image. The scatter correction image is stored in an image memory so that it is available for combination with subsequent x-ray images to remove scatter distortion.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to x-ray systems and more particularly to bi-plane imaging systems. The invention further relates to the generation and transfer of image data generated from bi-plane imaging in conjunction with information systems.  
         [0002]     X-ray imaging is a method of taking pictures of the inside or internal portions of an object. (The inside or internal portions of an object are those which are not visible from the exterior of the object with a human eye unless the object is opened to expose the portion of interest.) Such objects may be a human (animal) body, baggage, or vehicles. As the x-ray beam passes through the object, it is absorbed by the varying structure thereof. In the case of a body, such structure would include the bones, tissues and fluid within the body, thereby varying resultant beam intensity. The intensity of the x-ray beam emerging from the object is measured by a device that converts x-ray beam data into a detailed picture.  
         [0003]     A typical diagnostic x-ray system includes a gantry, a patient support, an x-ray generation subsystem, an x-ray detection subsystem, an image display, and a user interface. The gantry supports one or more x-ray sources and associated x-ray detectors. The user, interacting through the user interface, manipulates the gantry and patient support to achieve each clinically relevant x-ray view, initiates x-ray generation when required, and observes the resultant detected image on the image display.  
         [0004]     Bi-plane imaging involves two x-ray sources and two x-ray detectors. Each source/detector pair provides a unique view of an x-ray projection through the object. The two projections may be set up orthogonal, or at any other relative angle, as required to complete the clinical procedure.  
         [0005]     Scatter radiation is caused through the deflection of radiation or particles through any angle off the focal path.  
         [0006]     Simultaneous bi-plane imaging includes coincident x-ray exposures on both planes. With this method, scatter radiation from the exposure on the opposite plane, is included with the radiation of the primary plane, distorting the detected image information.  
         [0007]     For many relative projection angles, the amount of scatter radiation is significant and renders the detected primary image unacceptable for diagnosis. To avoid the negative impact of opposite plane scatter, a system known as alternate bi-plane imaging has become the accepted standard. With the alternate bi-plane method, x-ray exposures are allowed on only one plane at a time.  
         [0008]     For series imaging, the reduction in imaging rate required to support the alternate bi-plane method is a significant impact for some diagnostic procedures. To overcome the imaging rate limitation a mechanism for the controlled interruption of x-ray detection, known as “blanking”, was developed within an image intensifier. “Blanking” the image intensifier on each plane, whenever the exposure for that plane is not active, allows the exposure on the opposite plane to take place during the image readout interval without the scatter radiation affecting the read out image. Employing the blanking capability enables the exposures on each plane to be shifted in phase resulting in an increase in the imaging rate for each plane.  
         [0009]     One disadvantage of digital x-ray detection technology is it does not support a mechanism equivalent to the “blanking” capability of the image intensifier. Because of this, as digital x-ray detectors are introduced into bi-plane applications, the aforementioned alternate bi-plane method must be utilized, but the reduction in imaging rate makes this an inefficient solution.  
         [0010]     The disadvantages associated with current, scanning systems have made it apparent that a new technique for scanning and data transfer is needed. The new technique should substantially negate the effects of scatter. Further, the new technique should provide improved image data for use in integrated health care information systems. The present invention is directed to these ends.  
       SUMMARY OF THE INVENTION  
       [0011]     In accordance with one aspect of the present invention, a method for scatter correction during simultaneous bi-plane digital imaging includes generating a first x-ray flux in a first imaging plane, generating a first image readout, digitally sampling a first scatter signal from the first x-ray flux in a second imaging plane, and generating a first compensation signal for the first scatter signal.  
         [0012]     In accordance with another aspect of the present invention, a digital imaging system includes a gantry and a first x-ray source coupled to the gantry. The first x-ray source is adapted to generate a first x-ray flux and a first plane scatter signal. A second x-ray source is also coupled to the gantry and is adapted to generate a second x-ray flux and a second plane scatter signal. A first x-ray detector system is coupled to the gantry and is adapted to generate a first detector signal in response to the first x-ray flux and further adapted to generate a first scatter signal in response to the second plane scatter signal.  
         [0013]     A second x-ray detector system is coupled to the gantry and is adapted to generate a second detector signal in response to the second x-ray flux and further adapted to generate a second scatter signal in response to the first plane scatter signal. A host computer is adapted to receive the first detector signal, the second detector signal, the first plane scatter signal, and the second plane scatter signal. The host computer is still further adapted to digitally sample the first plane scatter signal, generate a first image readout in response thereto, generate a first compensation signal for the first scatter signal, and store the first compensation signal in a first scatter correction memory.  
         [0014]     One advantage of the present invention is that it includes a method to achieve equivalent imaging rates during simultaneous bi-plane operation which are substantially similar to those achieved during single plane operation without the need of performance improvements within the x-ray source or x-ray detector to increase the imaging rates of the alternate bi-plane method. This enables the direct application of digital detector technology into bi-plane applications.  
         [0015]     Additionally, the invention promotes the use of simultaneous bi-plane, which is highly desirable. Alternate bi-plane has prevailed, as a result of superior image quality through the avoidance of the effects of scatter, but it can not provide simultaneous views of the object under study, which is the objective of bi-plane imaging. Only simultaneous bi-plane achieves this objective.  
         [0016]     Additional advantages and features of the present invention will become apparent from the description that follows and may be realized by the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     For a more complete understanding of the invention, there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which:  
         [0018]      FIG. 1  is a diagram of a bi-plane diagnostic imaging system in accordance with one embodiment of the present invention;  
         [0019]      FIG. 2  is a block diagram of  FIG. 1 ;  
         [0020]      FIG. 3  is a diagram of a computed tomography scanning system in accordance with another embodiment of the present invention;  
         [0021]      FIG. 4  is a timing diagram of a method for bi-plane scanning in accordance with another embodiment of the present invention; and  
         [0022]      FIG. 5  is a block diagram of a method for scanning an object, in accordance with another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]     The present invention is illustrated with respect to a diagnostic x-ray imaging system  10  particularly suited to the medical field. The present invention is, however, applicable to various other uses that may require scanning, as will be understood by one skilled in the art, e.g. baggage scanners, vehicle scanners, moving object scanners, liquid scanners, etc.  
         [0024]     Referring to  FIGS. 1 , and  2 , a scatter radiation compensation imaging system, including a gantry  11 , in accordance with one embodiment of the present invention, is illustrated. A first x-ray source  12 , coupled to the gantry  11 , generates a first x-ray flux  14 , which passes through an object  16  (e.g. a patient) on a table  17  and produces first scatter radiation. The system further includes a first x-ray detector  18  (first detector system), coupled to the gantry  11 , which generates a detector signal in response to x-ray flux and scatter signals.  
         [0025]     A second x-ray source  20 , also coupled to the gantry  11 , generates a second x-ray flux  21 , which passes through the object  16  and produces second scatter radiation. The system further includes a second x-ray detector  19  (second detector system), coupled to the gantry  11 , which generates a detector signal in response to x-ray flux and scatter signals.  
         [0026]     The method of compensation for the aforementioned scatter signals is discussed in detail with regard to  FIGS. 4 and 5 . The present system and method applies to bi-plane imaging, it is, however, applicable to numerous other imaging combinations including one, two, or three plane imaging (or other numbers of scanning planes), as will be understood by one skilled in the art.  
         [0027]     A system control unit  22 , including a host computer and display  24  and various other widely known x-ray control and display components, receives the detected primary and scatter signals and responds by generating image signals. The x-ray control unit  22  also includes, for example, an operator console  23 , an x-ray controller  25 , a table control  29 , a gantry motor control  30 , a mass storage  39 , and an image detection control  41 , all of which will be discussed later.  
         [0028]     Ideally, the first x-ray source  12 , first x-ray detector  18 , second x-ray source  20  and second x-ray detector  19  are coupled thereto. One skilled in the art will realize that the embodied gantry  11  is merely illustrative of the numerous possible x-ray device support structures. Additionally, for imaging different objects (e.g. baggage, vehicles, patients in various positions, etc.), the relative motion and plane directions may be reoriented (e.g. move the object relative to the sources and detectors using varying types of motion (e.g. linear with a belt, arced with various shaped arc paths, etc.))  
         [0029]     The x-ray sources  12 ,  20  are embodied as flat panel x-ray sources or extended x-ray sources, or standard x-ray tubes. The x-ray sources  12 ,  20  are activated by either the host computer  24  or the x-ray controller  25 , as will be understood by one skilled in the art. The embodied method includes the x-ray sources  12 ,  20  activated in pulses of flux, thereby generating a first flux during an “on” phase, a subsequent image readout during an “off” phase and a subsequent flux during a subsequent “on” phase, as is illustrated in the timing diagram of  FIG. 4 .  
         [0030]     The x-ray sources  12 ,  20  send the x-ray flux  14 ,  21  through an object  16  on a moveable table  27  controlled by a table control device  29  acting in response to signals from the host computer  24 , as will be understood by one skilled in the art.  
         [0031]     The first x-ray source  12  is coupled to the gantry  11  and generates a first x-ray flux  14  and a first plane scatter signal. The second x-ray source  20  is also coupled to the gantry  11  and generates a second x-ray flux  21  and a second plane scatter signal.  
         [0032]     The x-ray flux  14 ,  21  from the x-ray sources  12 ,  20  pass through the patient and impinge on the x-ray detectors  18 ,  19 . The signals pass to the host computer and display  24 , where the signals are converted to a gray level corresponding to the attenuation of the x-ray photon through the patient, for the final x-ray image.  
         [0033]     The x-ray detectors  18 ,  19  (detector systems) are typically located opposite the respective x-ray sources  12 ,  20  to receive x-ray flux  14 ,  21  and scatter radiation generated therefrom. The detectors  18 ,  19  include both standard x-ray detectors and scatter detectors, or alternately only x-ray detectors, receiving both x-ray and alternate plane scatter signals. In one embodiment, digital x-ray detectors are used. In an alternate embodiment of the detectors  18 ,  19 , a mechanism that limits the detected flux to scatter signals to simplify generation of compensation signals is included, which will be discussed later.  
         [0034]     The first x-ray detector  18  or detector system is coupled to the gantry and generates a first detector signal in response to the first x-ray flux and further generates a first scatter signal in response to second plane scatter when the second x-ray flux is off.  
         [0035]     The second x-ray detector  19  is coupled to the gantry and generates a second detector signal in response to the second x-ray flux and further adapted to generate a second scatter signal in response to first plane scatter.  
         [0036]     The present invention is illustrated with respect to x-ray; however it is alternately used for any type of x-ray system using detectors including mammography, vascular x-ray imaging, bone scanning, etc. Further embodiments include other non-medical applications such as weld inspection, metal inspection. Essentially, anything that could use a digital x-ray detector to make 1, 2 or 3 dimensional images.  
         [0037]     The host computer  24  receives the detector signals and activates the x-ray sources  12 ,  20 ; however, alternate embodiments include independent activation means for the x-ray sources  12 ,  20 . The present invention includes an operator console  23  for control of the x-ray sources  12 ,  20  by technicians, as will be understood by one skilled in the art.  
         [0038]     The host computer  24  also receives the first plane scatter signal and the second plane scatter signal. The host computer  24  samples the first plane scatter signal, generates a first image readout in response thereto, generates a first compensation signal for the first scatter signal, and stores the first compensation signal in a first scatter correction memory within the host computer  24 .  
         [0039]     One embodiment of the host computer  24  includes first and second plane scatter image formation algorithms, first and second plane scatter correction image memories, first and second plane scatter correction algorithms, and displays for both planes. All of these host computer elements will be discussed in detail in regards to the timing diagram of  FIG. 4  and the block diagram of  FIG. 5 .  
         [0040]     Data is acquired and processed, and an x-ray image, for example, is presented to a radiology technician through the image display and user interface  37  while the exam is occurring. The host computer  24  needs only read the primary and scatter signals and update the display at the appropriate locations through, for example, an image detection controller  41 . The host computer  24  alternately stores image data in a mass storage unit  39  for future reference.  
         [0041]     Referring to  FIG. 3 , a scatter radiation compensation imaging system  54  for a computed tomography (CT) system, including a gantry  55 , is illustrated in accordance with another embodiment of the present invention.  
         [0042]     The computed tomography system includes a first x-ray source  56 , coupled to the gantry  55 , generates a first x-ray flux  57 , which passes through an object  58  on the table  59  and produces first scatter radiation. The system further includes a first CT detector  60 , coupled to the gantry  55 , which generates a detector signal in response to x-ray flux and scatter signals.  
         [0043]     A second x-ray source  62 , also coupled to the gantry  55 , generates a second x-ray flux  64 , which passes through the object  58  and produces second scatter radiation.  
         [0044]     The system further includes a second CT detector  66 , coupled to the gantry  55 , which generates a detector signal in response to x-ray flux and scatter signals.  
         [0045]     The system still further includes a system control unit  68 , including a host computer and display  70 , which functions similarly to the host computer of  FIG. 1 .  
         [0046]     In other words, data is acquired and processed, and an x-ray image, for example, is presented to a CT technician through the image display and user interface while the exam is occurring. The host computer  70  needs only read the primary and scatter signals and update the display at the appropriate locations through, for example, an image detection controller. The host computer  70  alternately stores image data in a mass storage unit for future reference.  
         [0047]     The method for compensation for the aforementioned scatter signals is discussed in detail with regard to  FIGS. 4 and 5 .  
         [0048]     Regarding the block diagram  50  of  FIG. 5 , with reference to the timing diagram  49  of  FIG. 4 , an imaging sequence method is illustrated. Important to note is that the order of the following operations is merely illustrative of one example of one set of timing steps included in the present invention. Numerous alternate block diagrams including the following steps in different orders are also embodied herein, as one skilled in the art will readily understand.  
         [0049]     The block diagram  50  includes the timing diagram  49 , which is a section from the middle of a bi-plane imaging series included to illustrate a possible set of steps included in the present invention.  
         [0050]     Logic starts in operation block  90  when the first x-ray source generates the first x-ray plane exposure  93  and resultant scatter  96  in the second plane.  
         [0051]     In operation block  94 , the second detector system detects first plane scatter  96 .  
         [0052]     In operation block  98 , a scatter readout  100  is generated by the second detector system.  
         [0053]     In operation block  102 , the second plane scatter correction formation algorithm  104  activates and generates a first compensation signal to compensate for the first plane scatter  96 .  
         [0054]     In operation block  106 , the second plane scatter correction memory  108  receives the first compensation signal and stores it for retrieval during scatter correction operations.  
         [0055]     In operation block  110  subsequent second plane x-rays  112  and image readouts  114  are generated.  
         [0056]     In operation block  116 , the second plane scatter correction algorithm  118  receives the stored scatter compensation signal and the subsequent image readouts. In operation block  120 , for each image readout, the second plane scatter correction algorithm  118  generates a second plane display  121 . One skilled in the art will realize that numerous possible compensation algorithms, such as a simple subtraction method, may be used to reduce or eliminate scatter from an image signal.  
         [0057]     In operation block  122 , the second x-ray source scans the second x-ray plane  124 , generating a second x-ray flux  126  and second image readout  128 . The first x-ray source generates a third x-ray flux  130  and image readout  132 . The second x-ray source then generates a fourth x-ray flux  134  and fourth image readout  136 .  
         [0058]     In operation block  138  the first detector detects scatter  140  from the fourth x-ray flux  134  in the first image plane  92 .  
         [0059]     In operation block  142 , a scatter readout  144  is generated by the first detector system.  
         [0060]     In operation block  148 , the first plane scatter correction formation algorithm  150  activates and generates a second compensation signal to compensate for the second plane scatter  140 .  
         [0061]     In operation block  152 , the second plane scatter correction memory  154  receives the second compensation signal and stores it for retrieval during scatter correction operations.  
         [0062]     In operation block  156  subsequent first plane x-rays  158  and image readouts  160  are generated.  
         [0063]     In operation block  162 , the first plane scatter correction algorithm  164  receives the stored scatter compensation signal and the subsequent image readouts. In operation block  166 , for each image readout, the first plane scatter correction algorithm  164  generates a first plane display  166 .  
         [0064]     In operation, a method for scatter correction during simultaneous bi-plane imaging includes generating a first x-ray flux in a first imaging plane, generating a first image readout, and digitally sampling a first scatter signal from the first x-ray flux in a second imaging plane. A first compensation signal is generated for the first scatter signal.  
         [0065]     One embodiment of the present method includes activating a first scatter image formation algorithm, then generating the first compensation signal, and storing the first compensation signal in a first scatter correction memory.  
         [0066]     A second x-ray flux is generated in the second imaging plane, and a second image readout is generated, and scatter is compensated for in the second image readout with the first compensation signal.  
         [0067]     A third x-ray flux is generated in the first imaging plane; a third image readout is also generated. A fourth x-ray flux is generated in the second imaging plane, and a fourth image readout is generated therefrom. A second scatter signal is digitally sampled from the fourth x-ray flux in the first imaging plane, and a second compensation signal is generated for the second scatter signal.  
         [0068]     Alternate embodiments of the present invention include the sampling of scatter from any of the x-ray flux or image readouts from the second image plane.  
         [0069]     A fifth x-ray flux is generated in the first imaging plane, and a fifth image readout is generated therefrom. Scatter in the fifth image readout is compensated for with the second compensation signal.  
         [0070]     A first scatter correction algorithm is activated in response to the second image readout and the first compensation signal, and a first image display is generated from the first scatter correction algorithm.  
         [0071]     The first image display is periodically updated through stopping a current exposure in the second imaging plane and reading a scatter image update resulting from an exposure in the first plane.  
         [0072]     A second scatter correction algorithm is activated in response to the fifth image readout and the second compensation signal, and a second image display is generated from the second scatter correction algorithm.  
         [0073]     The host computer cycles typical image processing steps in response to the detector and scatter signals, as will be understood by one skilled in the art. In other words, data offsets are corrected and x-ray dosage is measured and normalized. Necessary calibration corrections are made, and the resulting signal is filtered, typically through a low dose filter and an adaptive filter, to reduce noise in the signal. The signal is then converted to display pixel format and subsequently displayed.  
         [0074]     From the foregoing, it can be seen that there has been brought to the art a new scanning system. It is to be understood that the preceding description of one embodiment is merely illustrative of some of the many specific embodiments that represent applications of the principles of the present invention and uses thereof.  
         [0075]     For example, present invention includes applications in a broad range of object scanners (e.g. belt and bed scanners) for use to scan baggage, packages, vehicles, liquids, mail, etc. Furthermore, the invention permits the creation of data image data files representative of improved images. These data files are configured for transmission over networks (internet, wide and local area networks, etc) to perform a broad range of functions such as medical treatment and billing, security management, image archiving, patient care and payment tracking, etc.  
         [0076]     Numerous and other arrangements would be evident to those skilled in the art without departing from the scope of the invention as defined by the following claims.