Abstract:
A method for defining a volume of interest (VOI) in a medical image is presented. A user interface is used to select a point on an initial linear border segment of a volume of interest. The user drops the point at a new position and a processor forms a new, non-linear border segment which includes the point. A 3D presentation of the volume of interest is created.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to medical imaging systems. In particular, the present invention relates to method and apparatus for defining a region of interest in a medical image. 
   Various methods are available for drawing the contour of an object, within a medical image. For example, the object may be a fetus, organ, cyst, or tumor which the user is interested in further analyzing. The area enclosed by the contour represents the “region of interest” (ROI) of the image. Typically the user is uninterested in the other features shown on the image and selecting a ROI allows the user to concentrate the processor power of the system on the part of the image which is of most interest to the user. 
   Problems exist with the current methods for selecting the border segments of a ROI. For example, one method is to employ known shapes, such as rectangles, circles and ovals, then require the user to drag the contour of the shape to the desired location around the object. Still another method has the user draw the contour of the object using a mouse or various keyboard keys, which can be quite time consuming, with accuracy being affected by the display size and resolution, and the minimum distance the user may move the cursor on the display. Also, working with 3D images adds an additional element of complexity. 
   Thus, a method is desired to obtain the border segments of a ROI within an image that addresses the problems noted above and others previously experienced. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one embodiment, a method for displaying a ROI within an image comprises a user interface for defining an initial ROI within said image by surrounding said ROI with linear border segments wherein said user interface is adapted to allow a user to redefine said initial ROI by replacing at least one of said linear border segments with a non-linear border segment to form a new ROI which differs art least partially from the initial ROI. 
   In one embodiment, a method for displaying a ROI within an image comprises a user interface for defining an initial ROI within said image by surrounding said ROI with linear border segments arranged to form a rectangle wherein said user interface is adapted to allow a user to redefine said initial ROI by replacing at least one of said linear border segments with a non-linear border segment to form a new ROI which differs art least partially from the initial ROI. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a block diagram of an ultrasound system formed in accordance with an embodiment of the present invention. 
       FIG. 2  illustrates an ultrasound system formed in accordance with an embodiment of the present invention. 
       FIG. 3  illustrates the interface devices and display of  FIG. 2  in accordance with an embodiment of the present invention. 
       FIG. 4  illustrates orthogonal and 3D images produced by a prior art ultrasound system. 
       FIG. 5  shows a schematic image of an ultrasound scan. 
       FIG. 6  shows stages in the formation of a new region of interest in accordance with an embodiment of the present invention. 
       FIG. 7  shows stages in the formation of a new region of interest in accordance with another embodiment of the present invention. 
       FIG. 8  shows stages in the formation of a new region of interest in accordance with a further embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a block diagram of an ultrasound system  100  formed in accordance with an embodiment of the present invention. The ultrasound system  100  includes a transmitter  102  which drives elements  104  within a transducer  106  to emit pulsed ultrasonic signals into a body. A variety of geometries may be used. The ultrasonic signals are back-scattered from structures in the body, like blood cells or muscular tissue, to produce echoes which return to the elements  104 . The echoes are received by a receiver  108 . The received echoes are passed through a beamformer  110 , which performs beamforming and outputs an RF signal. The RF signal then passes through an RF processor  112 . Alternatively, the RF processor  112  may include a complex demodulator (not shown) that demodulates the RF signal to form IQ data pairs representative of the echo signals. The RF or IQ signal data may then be routed directly to RF/IQ buffer  114  for temporary storage. A user input  120  may be used to input patient data, scan parameters, a change of scan mode, and the like. 
   The ultrasound system  100  also includes a signal processor  116  to process the acquired ultrasound information (i.e., RF signal data or IQ data pairs) and prepare frames of ultrasound information for display on display system  118 . The signal processor  116  is adapted to perform one or more processing operations according to a plurality of selectable ultrasound modalities on the acquired ultrasound information. Acquired ultrasound information may be processed in real-time during a scanning session as the echo signals are received. Additionally or alternatively, the ultrasound information may be stored temporarily in RF/IQ buffer  114  during a scanning session and processed in less than real-time in a live or off-line operation. 
   The ultrasound system  100  may continuously acquire ultrasound information at a frame rate that exceeds 50 frames per second—the approximate perception rate of the human eye. The acquired ultrasound information is displayed on the display system  118  at a slower frame-rate. An image buffer  122  is included for storing processed frames of acquired ultrasound information that are not scheduled to be displayed immediately. Preferably, the image buffer  122  is of sufficient capacity to store at least several seconds&#39; worth of frames of ultrasound information. The frames of ultrasound information are stored in a manner to facilitate retrieval thereof according to its order or time of acquisition. The image buffer  122  may comprise any known data storage medium. 
     FIG. 2  illustrates an ultrasound system formed in accordance with one embodiment of the present invention. The system includes a transducer  10  connected to a transmitter  12  and a receiver  14 . The transducer  10  transmits ultrasonic pulses and receives echoes from structures inside of a scanned ultrasound image or volume  16 . Memory  20  stores ultrasound data from the receiver  14  derived from the scanned ultrasound image or volume  16 . The image or volume  16  may be obtained by various techniques (e.g., conventional B-mode scanning, 3D scanning, real-time 3D or 4D imaging, volume scanning, 2D scanning with an array of elements having positioning sensors, freehand scanning using a Voxel correlation technique, 2D or matrix array transducers and the like). 
   The transducer  10  is moved, such as along a linear or arcuate path, while scanning a volume of interest (VOI). At each linear or arcuate position, the transducer  10  obtains 3D volume data or 2D scan planes  18 . The volume data or scan planes  18  are stored in the memory  20 , and then passed to a 2D/3D scan converter  42 . In some embodiments, the transducer  10  may obtain lines instead of the scan planes  18 , and the memory  20  may store lines obtained by the transducer  10  rather than the scan planes  18 . The 2D/3D scan converter  42  creates a data slice from the volume data or from single or multiple 2D scan planes  18 . The data slice is stored in slice memory  44  and is passed to the video processor  50  and display  67 . 
   The position of each echo signal sample (pixel for scanned image or Voxel for scanned volume) is defined in terms of geometrical accuracy (i.e., the distance from one pixel/Voxel to the next) and ultrasonic response (and derived values from the ultrasonic response). Suitable ultrasonic responses may include gray scale values, color flow values, and angio or power Doppler information, and the like. 
     FIG. 3  illustrates the interface device  52  and display  67  of  FIG. 2 . The interface device  52  may comprise one or more of a keyboard  170 , mouse  172 , track ball  174 , and touch pad  176 . The display  67  may also comprise a touch screen  178 . The keyboard  170 , mouse  172 , track ball  174 , touch pad  176  and touch screen  178  will be referred to collectively as interface devices  180 . The user may use one or more of the interface devices  180  to interactively select points, areas and/or lines on the display  67 . 
     FIG. 4  shows schematically images  150 A- 150 D comprising diagnostic ultrasound data which can be displayed simultaneously or individually on display  67 . It should be understood that although the below methods and apparatus are discussed with respect to ultrasound, other diagnostic data may be used, such as, but not limited to, X-ray, MR and CT. The images  150 A- 150 D includes an object  152 . By way of example only, the object  152  may be an organ, such as a liver or kidney, a tumor, cyst, blood vessel, and the like. Image  150 A represents the ultrasound data from a first plane Aplane, image  150 B shows the same data from a second plane Bplane which is orthogonal to the first viewing angle, image  150 C shows the same data from a third plane Cplane which is orthogonal to both the first and second viewing angles, and  FIG. 150D  shows a 3D representation of the same data taken from a viewing angle. Each image  150 A-C contains a rectangular region of interest box  151 A- 151 C respectively and image  150 D shows a cuboid region of interest volume  151 D. Typically each region of interest box  151 A- 151 D is individually user selectable by means of interface device  180  and once a user has selected a box the user is able to change the dimensions of the box as shown by the double headed arrows in  FIG. 4 . Changes made to the dimensions of a box in one image  150 A- 150 C may be automatically followed by corresponding changes in the other images  150 A- 150 D. 
     FIG. 5  shows a view corresponding to image  150 A of  FIG. 4  in which the object  152  is a fetus inside its mother&#39;s womb  153  viewed using a transvaginal probe with a semi-spherical transponder head. It is clear from  FIG. 5  that the curvature C of the transponder head is reflected in the images  150 A- 150 D and make it impossible to form a ROI box which completely encloses the object  152  while at the same time excludes the mother&#39;s tissue—for example part of the wall of the womb  154 . 
     FIG. 6  illustrates an embodiment of a method for redefining the border segments of an initial region of interest box  150 A- 150 C so that the shape of the region of interest box more closely corresponds to that of the contour of the object within the image  150 A- 150 C. The user selects one of the images  150 A- 150 C to work on. In this case, purely as an example, the user starts with image  150 A as shown in  FIG. 6A  in which an initial region of interest box  151 A is shown—in this interests of clarity the object of interest is not shown in  FIGS. 6A-6C . The linear border segment B 1  of the initial region of interest box  151 A which the user wishes to modify in this case is the top border segment B 1  and this is selected by use of an interface device  180 . A point P 1  is displayed in the center of the selected border segment B 1  by the processor. The user can select the point P 1  with the interface device, move it to a new position P 1 ′ and drop it there. The processor draws a spline S 1  comprised of two smooth curve line segments C 1 , C 2  from point P 1 ′—curve line segment C 1  extends to the top end of the vertical left hand border segment B 2  of the region of interest box  151 A and curve line segment C 2  extends to the top end of the vertical right hand border segment B 3  of the region of interest box  151 A. Curve line segments C 1  and C 2  form the new border segment B 1 ′ of region of interest box  151 A. At the same time the processor calculates a virtual point Pv which is where the new border segment B 1 ′ passes though the plane Bplane of the image  151 B and displays this point on image  151 B along with a spline S 2  comprised of two curve line segments C 3  and C 4 . Spline S 2  replaces the originally linear top border B 21  of image  151 B. Curve line segment C 3  extends from Pv to the top end of the vertical left hand border segment B 22  of the region of interest box  151 A and curve line segment C 24  extends to the top end of the vertical right hand border segment B 23  of the region of interest box  151 A as shown in  FIG. 6B . The processor also redraws the 3D presentation of the region of interest volume as shown in  FIG. 6C  by producing further splines S 1   1 -S 1   n  parallel to S 1  and S 2   1 -S 2   n  parallel to S 2 . These splines S 1   1 -S 1   n , S 2   1 -S 2   n  are attached to curve line segments C 1 -C 2  and C 3 -C 4  respectively. 
     FIGS. 7A-7C  illustrates a second embodiment of a method for redefining the border segments of a region of interest, in which, after the user has moved point P 1  to position P 1 ′ in image  151 A, the user is provided with the possibility of moving a point P 2  in the image  151 B to a new position P 2 ′ and dropping it there. The processor draws a new spline S 2 ′ which is made of two smooth curve line segments C 3 ′, C 4 ′ and which replaces spline S 2 . At the same time the processor calculates a virtual point Pv′ which is where the new spline S 2 ′ passes though the plane Aplane of the image  151 A and displays this point on image  151 A along with a spline S 1 ′ comprised of two curve line segments C 1 ′ and C 2 ′. Curve line segments C 1 ′ and C 2 ′ may be formed by the calculating the distance between Pv′ and the point Pn vertically above it on spline S 1 , calculating what a proportion this distance is of the distance between Pn and the point e.g. P 1  vertically above on the original border segment B 1  and moving all the points on lines C 1  and C 2  by the same proportion of their respective vertical distances from original border segment B 1 . For example if the distance between Pv′ and Pn is 100% of the distance between Pn and P 1  then all the points on C 1  and C 2  are moved a further 100% of their distances from border segment B 1  to form curved lines C 1 ′ and C 2 ′. Spline S 1 ′ replaces spline S 1 . The processor also redraws the 3D presentation of the region of interest volume as shown in  FIG. 7C  by producing further splines S 1   1 ′-S 1   n ′ parallel to S 1 ′ and S 2   1 ′-S 2   n ′ parallel to S 2 ′. These splines S 1 ′-S 1   n ′, S 2 ′-S 2   n ′ are attached to curve line segments C 1 ′-C 2 ′ and C 3 ′-C 4 ′ respectively. 
   In a further embodiment of a method for redefining the border segments of a region of interest, illustrated in  FIG. 8  the user is permitted to move a plurality of points P 1   a -P 1   m  in an image to new positions P 1   a ′-P 1   m ′ in order to produce a border segment B 1 ′ comprised of an n-order curve comprising curve line segments C 1 -Cm. 
   In another embodiment of a method for redefining the border segments of a region of interest, the user is permitted to modify the linear boundary segments of more than one side of an initial region of interest box. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.