Abstract:
A method of using a frame of pixels of a specified characteristic such as a maximal intensity projected frame and a depth location “virtual” frame to locate and image ROI&#39;s in patients.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to single proton emission computerized tomography (SPECT) and more particularly to apparatus and methods for locating and displaying various regions of interest (ROI) within the patient being subjected to computerized tomographic imaging. 
   BACKGROUND OF THE INVENTION 
   SPECT imaging produces two-dimensional tomograms; that is, planar images of the body that are generally oriented either in an axial direction, coronal direction or a sagittal direction. In applying imaging methods, it is well-known to acquire images of multiple slices in the body. This is done either by helical scanning or by individual circular scans while moving the patient step-by-step relative to the scanner. 
   At the present time, in order to locate a particular ROI in three dimensions in the body, such as one containing a lesion, it is necessary for the radiologist or physician to inspect the many parallel images that have been acquired. For example in a whole body scan it is not unusual to acquire as many as 200 parallel images having one or more of axial, coronal or sagittal orientations. The physician or radiologist in charge of the examination then studies each of the 200 images to determine the location of the lesion in the body. When the location of the lesion is determined, then more detailed scans are undertaken to provide maximum information about the lesion. For example, if the lesion is discovered in an image in the axial plane, then the operator of the equipment will acquire sagittal and coronal, as well as more axial images in the region of interest, to further examine the lesion, for surgical planning, for example. To discover specific lesions, the physician or radiologist in charge of examination must look for “hot” spots that are on the order of one square centimeter, a very time-consuming job. 
   At the present time, some of the ways used to lessen the burden of reviewing the large group or set of images of slices include cinematic displays of the slice set, and/or a cinematic display of a volume rendered as a 3-D presentation. When using the first of these prior art solutions, the user has to concentrate on the moving presentation in which only one slice is activated at a time. When a lesion is detected, the viewer has to immediately stop the cinematic display and use a cursor to point to the lesion. Then, additional images are taken at the point that the cursor is positioned. 
   When cinematic volumetric images are displayed, according to the second prior art solution, the display gathers into one view the 3-D information of the slices. Here again, when the lesion is found the viewer has to immediately pause the movie and point to the lesion with the cursor. Then, additional views are taken at the cursor location. These prior art solutions often require additional viewing to locate a lesion. 
   Maximum intensity projection (MIP) are known in the prior art. It is a commonly used technique in imaging for such things as for displaying 3-D vascular image data. For example, see U.S. Pat. No. 5,570,404 the disclosure of which is hereby included herein by reference. In that patent, the MIP is used for removing undesirable structures from a series of parallel images. As noted in the patent, the MIP frame is developed from a stack of acquired parallel images. The MIP frame contains pixels, wherein each pixel holds the maximum intensity along a ray perpendicular to the MIP frame. The patent does not use the MIP for locational purposes. A preferred aspect of the present invention is to use MIP&#39;s for locating regions of interest in a patient being imaged, for example, for locating lesions in the patient. A preferred aspect of the invention also includes displaying the located lesions in three orthogonal planes, or in a 3-D image. 
   SUMMARY OF THE INVENTION 
   Thus, a preferred aspect of some preferred embodiments of the invention relates to a method for expeditiously locating and displaying particular regions of interest in a patient or object being imaged. The method includes:
         acquiring a plurality of parallel frames of two-dimensional intensity data for use in detecting and imaging said regions of interest assembling at least one group of said plurality of parallel frames;   acquiring a two-dimensional specified projection characteristic frame such as a maximal intensity projection (MIP) frame comprised of a plurality of pixels arranged in a two-dimensional array wherein each pixel contains the maximum intensity, any fraction thereof or any derived function of the plurality of pixels along a ray through all similarly placed pixels in the plurality of parallel frames of the group;   determining the third dimension of each pixel that contains the maximum intensity along the ray;   storing the determined third dimensions;   placing the cursor on a region of interest, as indicated by a hot spot in the MIP;   fetching the three-dimensional location and intensity data responsive to the position of the cursor; and   generating axial, coronal and sagittal images, using the fetched data.       

   In yet another aspect of the present invention the plurality of parallel frames are coronal frames. 
   In accordance with yet another aspect of the present invention, the plurality of parallel frames are sagittal frames. 
   In another aspect of the present invention the plurality of parallel frames are axial frames. 
   In accordance with yet another aspect of the present invention, the parallel frames can be in non-orthogonal directions i.e., oblique directions. 
   In yet another preferred aspect of the present invention, the third dimension is stored in a virtual frame that is never displayed, thus the two dimensions of the maximum intensity frame reveals the third dimension to precisely locate the maximum intensity pixels. Thus, when the cursor is clicked on a given location, for example the X,Y location, a “fetch” order is directed to the virtual frame which provides a Z dimension. Thus, the virtual frame primarily provides dimensional data. 
   According to yet another preferred aspect of the present invention, a method is provided for expeditiously locating and displaying regions of interest in a patient. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, regarding organization apparatus and operation together with further objects and advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings, which: 
       FIG. 1  is a schematic block diagram showing a preferred ECT system for carrying out the invention; 
       FIG. 2  shows a schematic illustration of a helical whole-body scan; 
       FIG. 3  is a flow chart showing a method according to a preferred embodiment of the invention; 
       FIG. 4A  is a collection of images of slices in the axial direction; 
       FIG. 4B  is a collection of images of slices in the coronal direction; 
       FIG. 4C  is a collection of images of slices in the sagittal direction; 
       FIG. 5  is a two-dimensional coronal MIP frame produced in accordance with a preferred embodiment of the invention; 
       FIG. 6  is a virtual frame that defines a third dimension for each of the pixels of the MIP frames in accordance with a preferred embodiment of the invention; and 
       FIGS. 7A–C  show axial, coronal, and sagittal planes acquired by clicking on the coronal MIP frame of  FIG. 5 , in accordance with a preferred embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A SPECT system, also sometimes referred to as an emission computerized tomographic (ECT) system  21  of  FIG. 1  includes a gantry  22  on which are mounted detectors, such as first detector head  23  and an oppositely-disposed second detector head  24 . Within the scope of the invention a single detector head or more than two detector heads can be used. Equipment such as this is well-known in gamma camera nuclear medicine imaging field. It is described in detail in U.S. Pat. No. 5,554,848, the disclosure of which is hereby included herein by reference. Detector heads  23  and  24  are mounted, spaced apart from each other, with room therebetween for the insertion for a patient table  26 , which may be mounted on its own mobile base  27 . Gantry  22  is shown as including a non-rotating stationary gantry base  25 . In the ECT system of  FIG. 1 , the gantry rotates the detector heads about a central axis  32 . The rotation may be accomplished by any well-known means, such as a motor  33 A operated in conjunction with gears  34  and  35 . The rotating gantry causes detector heads  23  and  24  to rotate about a patient shown at  36 . Detector heads  23  and  24  are capable of moving towards and away from the patient through the use of such apparatus as a motor  38  cooperating with gear arrangements  39  and  40 . Motor  38 , along with gears arrangements  39  and  40  are used to maintain the detector heads proximate to the patient at all times. Thus, the detector heads are maintained juxtaposed to the patient in a non-circular orbit. 
   To provide a helical scan about patient  36  as demonstrated in  FIG. 2 , means are provided for moving table  26  and scanners  32  relative to each other. Thus, one arrangement providing relative motion is shown in  FIG. 1  as a motor  31 , operating in conjunction with a gear box  30  to move table  26  relative to gantry  22 . The motor and gear arrangement rotates wheels such as a wheel  33 , moving table  26  along a rail  29 . 
   Within the scope of the invention, the scan does not have to be helical. It can be a plurality of separate orbital scans made while there is no relative longitudinal motion between the patient and the scanner; in which case the bed is moved relative to the scanner in steps prior to each rotation of the scanner about the patient. Furthermore, while the scanner shown in  FIG. 1  is of the SPECT type, the invention is equally applicable to other 3-D imaging systems such as STET, PET, etc. 
   Detector heads  23  and  24  detect emitted gamma rays, for example. The gamma rays strike the detectors, which include scintillators which scintillate in response to the impact of the gamma rays. Photo-multiplier tubes are included in the detectors, and convert the light flashes of the scintillators into electrical signals, in the well-known manner of gamma radiation nuclear medicine imaging. The electrical signals are sometimes referred to as beta signals. The beta signals are transmitted by conductors such as conductors  41 ,  42  to a control processor  37 . The control processor converts the beta signals into images in a well-known manner. The image thus provided is displayed on the image or display monitor  43 . 
   The flow diagram of  FIG. 3  outlines a method for determining the 3-D position of a lesion (hot spot) in accordance with a preferred embodiment of the invention. The method, in block  46 , calls for positioning the patient or object in a scanner such as scanner  21 . The scanner is then operated to acquire a set or group of images of slices, as indicated in block  47 . 
   From a stacking of the group of slices, the maximum intensity pixel is determined in straight line rays or projections perpendicular to the stack of slices and going through all of the pixels similarly placed in each slice. The maximum intensity pixel two-dimensional location and intensity for each ray is determined and posted in an MIP frame. The determination of the MIP frame is shown in block  48 . 
   While finding the maximum intensity pixel along each ray, a determination is also made of the third dimension location of each of the maximum intensity pixels for each pixel in the MIP frame. The determination of the third dimension of each of those pixels is shown in block  49 . 
   From the determination of the maximum intensity pixels, a two-dimensional maximum intensity projection (MIP) frame  51  is assembled, based on the first and second dimensions, and locations of each of the maximum intensity pixels in the MIP frame. This frame can be considered as a projection image of the stack, with the highest value in the projection shown. At the same time, the third dimension of each of the pixels that have the maximum intensity along each ray is stored in a virtual frame  52 . Thus, for example, if frame  51  is defined by X and Y coordinates, then for each of the X and Y coordinates frame  52  would provide a Z value, or a depth measurement of the position in the Z direction of the highest value pixel. 
   The MIP frame assures that it is relatively easy to determine a lesion, since a lesion is hot, and therefore brighter than surrounding pixels; i.e., the pixels of the lesion are brighter than surrounding pixels. The MIP frame is displayed on the monitor as indicated in block  53 . The position of the lesion on the MIP frame is determined either automatically or by the operator. For example, in accordance with a preferred embodiment of the invention a cursor is placed somewhere on the lesion, as indicated by block  54 . The cursor on the lesion is clicked, as shown in block  56 . This, according to a preferred embodiment of the invention, initiates a fetch command. The fetch command indicated by block  57  assembles both the two-dimensional locational values, as shown in block  58  and the third dimension of the virtual frame shown in block  59 , plus optionally the intensity of the pixel that the cursor is on. 
   With this information, three orthogonal planes can be displayed, as shown at blocks  61  for example for the sagittal frame,  62  for the coronal frame and  63  for the axial frame. Preferably each of these images contain the lesion. This enables an automatic display of the lesion in the three orthogonal planes, or a three-dimensional image shown in dashed lines at  64  can be easily developed with the information at hand. Alternatively, any one or two orthogonal slices containing the lesion are shown. Alternatively or additionally, several slices around the lesion are shown (for example in a cine mode or side-by-side) to provide a view of the entire lesion and its surroundings. 
     FIG. 4A  shows a group of axial slices, while  FIG. 4B  shows a group of coronal slices, and  FIG. 4C  shows a group of sagittal slices. In each figure the slices are arranged side by side as they would be on a standard display or hard copy. Bright spots indicated in the slices are caused by the lesions. 
   The lesion is more clearly depicted in  FIG. 5 , a coronal MIP. It would also be shown in the sagittal MIP, or an axial MIP. 
   If a cursor is placed on the lesion, as indicated by the origin of arrow  66  in  FIG. 5 , the coronal MIP, and the cursor is clicked, then the computer provides fetch commands to fetch the data necessary for providing orthogonal images. 
     FIG. 6  shows a frame used for storage of depth information for each of the maximum-intensity pixels depicted in the MIP. Thus, for example, if the virtual frame of  FIG. 6  is an X-Z frame, then Y values will be stored at the X-Z locations, so that when an X-Z location from an MIP is known, the depth value Y is immediately called out in the virtual frame of  FIG. 6 . 
   The virtual frame does not need to be displayed. While a frame type memory is shown, other type memories can be used within the scope of the invention. Finally,  FIG. 7A  shows the three orthogonal images  7 A,  7 B and  7 C, automatically provided for example by clicking on the lesion. Three orthogonal views at the origin of arrow  66  provides a 3-D location, as emphasized with the hot circle in each of the axial ( FIG. 7A ), coronal ( FIG. 7B ) and sagittal ( FIG. 7C ) images. More particularly, the circles are shown at  67 ,  68  and  69 , in  FIGS. 7A ,  7 B and  7 C. Thus, by determining the third dimension at the same time as determining the first and second dimension of the pixel having the maximum intensity, it becomes possible to simultaneously create MIP and third dimension frames. The addition of a user interface, as shown in  FIG. 1 , which senses a mouse click and responds to the mouse click with a “fetch” command enables the display of the region of interest; i.e., the lesion indicated by a selected pixel of the MIP frame Thus, the necessity of reviewing up to 200 images of the group of images is eliminated. 
   It should be apparent that the embodiment described herein is merely exemplary, and that a person skilled in the art may make many variations and modifications to the embodiments as described herein. Any and all such variations or modifications, as well as others, which may become apparent to those skilled in the art, are intended to be included within the scope of the invention as defined by the appended claims. 
   The terms “include”, “comprise” and “have” and their conjugates, as used herein mean “including but not necessarily limited to.”