SYSTEM AND METHOD FOR NAVIGATING A TOMOSYNTHESIS STACK INCLUDING AUTOMATIC FOCUSING

Abstract

A system and method for reviewing a tomosynthesis image data set comprising volumetric image data of a breast, the method comprising, in one embodiment, causing an image or a series of images from the data set to be displayed on a display monitor and selecting or indicating through a user interface an object or region of interest in a presently displayed image of the data set, thereby causing an image from the data set having a best focus measure of the user selected or indicated object or region of interest to be automatically displayed on the display monitor.

Claims

1. (canceled)

2. A method for navigating and displaying breast tissue images, the method comprising: obtaining a tomosynthesis image data set, the data set comprising volumetric image data of at least a portion of a breast; displaying a series of images from the data set on a display of a computer-controlled workstation; detecting, through a user interface associated with the computer-controlled workstation, an input by a user selecting or indicating a region of interest in an image that is one of the series of images and currently displayed on the display; highlighting on the display, in response to the input by the user, the region of interest with a visual indicia comprising a geometric shape; and displaying on the display other images of the series while continuing to highlight the region of interest with the visual indicia in each of other images of the series as the each of the images is displayed, wherein the highlighting the region of interest comprises modifying at least one visual characteristic of the geometric shape of the visual indicia based on respective focus measures of the region of interest in the respective ones of the series of images being displayed.

3. The method of claim 2, wherein the respective focus measures comprising respective single focus measure values calculated for the region of interest in the respective images.

4. The method of claim 3, wherein each of the respective focus measures is computed based upon one or more of: a sharpness of detected edges of the region of interest, a contrast of the region of interest, and a ratio between a measured magnitude of one or more high frequency components and a measured magnitude of one or more low frequency components.

5. The method of claim 2, wherein each of the displayed images of the image data set is a tomosynthesis reconstructed image, detecting user input comprises detecting user input selecting or indicating the region of interest in a currently displayed tomosynthesis reconstructed image, and each additional image that is displayed while continuing to highlight the region of interest in respective images is a tomosynthesis reconstructed image of the image data set.

6. The method of claim 2, wherein at least one visual characteristic of the geometric shape is a size of the geometric shape.

7. The method of claim 3, wherein at least one visual characteristic of the geometric shape is a size of the geometric shape, wherein the size of the geometric shape decreases with increasing focus measure value.

8. The method of claim 2, wherein the geometric shape comprises a rectangular shape.

9. The method of claim 2, wherein the user selected or indicated region of interest is highlighted in a manner indicating that the region includes a specified type of tissue structure.

10. The method of claim 2, wherein the display the images of the series of images comprises displaying the images in succession.

11. A system for navigating and displaying breast tissue images, the workstation comprising: an operatively associated user interface; a display; at least one processor; and a memory coupled to the at least one processor, the memory comprising computer executable instructions that, when executed by the at least one processor, perform a method comprising: obtaining a tomosynthesis image data set, the data set comprising volumetric image data of at least a portion of a breast; displaying a series of images from the data set on the display; detecting, through the user interface, an input by a user selecting or indicating a region of interest in an image that is one of the series of images and currently displayed on the display; highlighting on the display, in response to the input by the user, the region of interest with a visual indicia comprising a geometric shape; and displaying on the display other images of the series while continuing to highlight the region of interest with the visual indicia in each of other images of the series as the each of the images is displayed, wherein the highlighting the region of interest comprises modifying at least one visual characteristic of the geometric shape of the visual indicia based on respective focus measures of the region of interest in the respective ones of the series of images being displayed.

12. The system of claim 11, wherein the respective focus measures comprising respective single focus measure values calculated for the region of interest in the respective images.

13. The system of claim 12, wherein each of the focus measures are computed based upon one or more of: a sharpness of detected edges of the region of interest, a contrast of the region of interest, and a ratio between a measured magnitude of one or more high frequency components and a measured magnitude of one or more low frequency components.

14. The system of claim 13, wherein the user selected region of interest is highlighted in a manner indicating that the region includes a specified type of tissue structure.

15. The system of claim 13, wherein the images of the series of images are displayed in succession.

16. The system of claim 11, wherein geometric shape comprises a rectangular shape.

17. The method of claim 11, wherein the at least one visual characteristic of the geometric shape is a size of the geometric shape.

18. An automated method employing a computer-controlled workstation for navigating and displaying breast tissue images, the workstation comprising an operatively associated user interface and display, the method comprising: obtaining a tomosynthesis image data set, the data set comprising volumetric image data of at least a portion of a breast; displaying a series of images from the data set on the display; detecting, through the user interface, an input by a user selecting or indicating a region of interest in an image that is one of the series of images and currently displayed on the display; highlighting on the display, in response to the input by the user, the region of interest with a visual indicia comprising a geometric shape; and displaying on the display other images of the series while continuing to highlight the region of interest with the visual indicia in each of other images of the series as the each of the images is displayed, wherein the highlighting the region of interest comprises modifying at least one visual characteristic of the geometric shape of the visual indicia based on respective focus measures of the region of interest in the respective ones of the series of images being displayed.

19. The method of claim 18, wherein the respective focus measures are computed based upon one or more of: a sharpness of detected edges of the region of interest, a contrast of the region of interest, and a ratio between a measured magnitude of one or more high frequency components and a measured magnitude of one or more low frequency components.

20. The method of claim 19, wherein: the respective focus measures comprising respective single focus measure values calculated for the region of interest in the respective images; and the modifying at least one visual characteristic of the geometric shape of the visual indicia comprises the least one visual characteristic of the geometric shape for the image having the highest focus measure value different from the at least one visual characteristic of the geometric shape for all other images.

Description

BRIEF DESCRIPTION OF FIGURES

[0016] FIG. 1 illustrates a conceptual diagram of a breast x-ray tomosynthesis imaging environment, including a tomosynthesis CAD processor.

[0017] FIG. 2 illustrates exemplary breast x-ray tomosynthesis projection and reconstruction geometries.

[0018] FIG. 3 depicts adjacent display monitors of an exemplary tomosynthesis image review workstation, including a left-hand monitor displaying respective R.sub.MLO and L.sub.MLO image slices; and a right-hand monitor displaying respective R.sub.CC and L.sub.CC image slices.

[0019] FIG. 4 depicts a single monitor displaying an L.sub.CC image slice from the same image set as the L.sub.CC image displayed in FIG. 3.

[0020] FIG. 4A is a close up view of a slice indicator that is displayed alongside the respective image slices that indicates the slice number of a presently-displayed image slice.

[0021] FIG. 5 depicts displayed L.sub.CC image slices obtained from the same tomosynthesis image set as the L.sub.CC images of FIGS. 3 and 4, illustrating a difference in visibility and clarity of a round tissue mass, depending on a relative z-axis location of the image slice.

[0022] FIG. 6 depicts a displayed best focus L.sub.CC slice out of still the same tomosynthesis image set as FIGS. 3-5.

[0023] FIG. 7 depicts a series of displayed near-focus L.sub.CC slices from the (same) tomosynthesis image set, including the best focus image slice plus subsequent slices along the z-axis.

[0024] FIG. 8 depicts the series of displayed near-focus L.sub.CC image slices shown in FIG. 7, but in reverse order, wherein the round mass is highlighted with a visual indicia in the form of rectangular brackets.

[0025] FIG. 9 depicts the displayed best focus L.sub.CC slice in a center area of the monitor, with the series of near-focus L.sub.CC slices displayed in a stacked formation alongside the best focus slice.

[0026] FIG. 10 is a flow diagram illustrating an exemplary process for displaying a best focus image slice or a series of near-focus slices of an object or region of interest in a tomosynthesis image set.

[0027] FIG. 11 is a flow diagram illustrating exemplary processes for computing a focus measure of an object or region of interest in a tomosynthesis image set.

[0028] FIG. 12 illustrates a process for identifying an image having a highest relative focus measure of all images in a tomosynthesis image set with respective to a selected object or region of interest.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0029] In describing the depicted embodiments of the disclosed inventions illustrated in the accompanying figures, specific terminology is employed for the sake of clarity and ease of description. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. It is to be further understood that the various elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other wherever possible within the scope of this disclosure and the appended claims.

Tomosynthesis Imaging Acquisition and Computation

[0030] In order to provide additional background information, reference is made to FIG. 1 and FIG. 2 taken from U.S. Pat. No. 8,223,916, entitled “Computer-aided detection of anatomical abnormalities in x-ray tomosynthesis images,” which is incorporated herein by reference in its entirety.

[0031] FIG. 1 illustrates a conceptual diagram of a breast x-ray tomosynthesis imaging environment, including Computer Aided Detection (CAD) capability. Shown in FIG. 1 is a network 112, which may be a HIS/RIS (Hospital Information System/Radiology Information System) network, to which is coupled a breast x-ray tomosynthesis acquisition device 104. The acquisition device 104 includes an x-ray source 106 projecting x-rays toward a woman's breast that is supported on a breast platform 108, along with an x-ray imager 110 underlying the breast platform 108. The x-ray source 106 is moved in an arcuate path relative to the breast platform 108 and emits x-ray radiation at specified angles therealong which are captured by the x-ray imager 110 to form a set of tomosynthesis projection images. The tomosynthesis projection images are processed by a tomosynthesis processor 114 according to one or more tomosynthesis reconstruction algorithms to form tomosynthesis reconstructed images, these images being formed and filtered with a view toward optimal visual display to a radiologist (“for presentation”). In a separate process, the tomosynthesis projection images are processed by a tomosynthesis CAD processor 115 to detect anatomical abnormalities in the breast volume. The tomosynthesis image information is then viewed in conjunction with the associated CAD results at a radiology review workstation 118.

[0032] FIG. 2 illustrates a conceptual diagram of breast x-ray tomosynthesis projection imaging at different angles. Incident radiation impinges upon a compressed breast volume at a plurality “N” of breast x-ray tomosynthesis projection angles φ.sub.n, n=1 . . . N, to result in a corresponding plurality “N” of tomosynthesis projection images Tp.sub.φn(x,y), n=1 . . . N. In typical scenarios, there can be N=11 or N=15 projection images, each projection image Tp.sub.φn(x,y) containing roughly 1710×2140 pixels, which would correspond to an x-ray detector that is roughly 24 cm×30 cm in size having a pixel resolution of 140 μm.

[0033] Also illustrated in FIG. 2 is a three-dimensional geometry 202 for the imaged breast volume, along with a conceptual icon of a tomosynthesis reconstruction algorithm in which, for a particular plane “m” having a predetermined height h.sub.m above the detection plane, the “N” projection images Tp.sub.φn(x,y), n=1 . . . N, are processed into a two-dimensional tomosynthesis reconstructed image Tr.sub.m(x,y). More specifically, the N projection images Tp.sub.φn(x,y), n=1 . . . N are combined by backprojection (or other tomosynthesis reconstruction algorithm) to form the tomosynthesis reconstructed image Tr.sub.m(x,y) based on that specific value of h.sub.m in a manner that highlights (e.g., does not blur) the effects of x-ray attenuating tissues located near that predetermined height h.sub.m and that de-emphasizes (e.g., blurs) x-ray attenuating tissues located away from that predetermined height h.sub.m.

[0034] In theory, the number of different predetermined heights h.sub.m for which distinct two-dimensional tomosynthesis reconstructed images Tr.sub.m(x,y) can be generated is arbitrarily large, because h.sub.m is simply a selectable parameter fed to the reconstruction (backprojection) algorithm. In practice, because the ultimate amount of useful information is limited by the finite count of “N” projection images, the tomosynthesis reconstruction geometry is usually limited to a predetermined number “M” of reconstructed image arrays Tr.sub.m(x,y). Preferably, the number “M” is selected such that the reconstructed image arrays Tr.sub.m(x,y) uniformly fill out the vertical extent of the imaged breast volume between the lower and upper compression plates, at a vertical spacing (such as 1 mm) that is small enough to capture smaller-sized micro-calcifications.

[0035] The lateral extent of each tomosynthesis reconstruction image Tr.sub.m(x,y), can be similar to that of each projection image Tp.sub.φn(x,y), i.e., the number of pixels and the spatial resolution of the tomosynthesis reconstructed images Tr.sub.m(x,y) can be similar as for the projection images Tp.sub.φn(x,y). However, such correspondence is not required, with supersampling, subsampling, or other resampling being available for various reasons. For example, the particular geometries of different tomosynthesis reconstruction algorithms could be different from each other, in which case such resampling is incorporated therein as needed to cause the resultant arrays that will be being compared, added, multiplied, mapped, or otherwise jointly processed to be in registration with each other. Depending on the particular tomosynthesis reconstruction algorithm being used, the lateral resolution of the different tomosynthesis reconstructed images Tr.sub.m(x,y) can be different for different levels, for example, the uppermost level could be 95 μm per pixel while the lowermost level be 108 μm per pixel.

[0036] As used herein, three-dimensional geometry of the imaged breast volume refers to a space-limited three-dimensional grid having a defined number of levels that extends at least throughout a clinically relevant portion of the breast (for example, including the breast parenchyma but excluding the skin and the empty space around the breast between the compression plates). In the event only a single predefined tomosynthesis reconstruction algorithm is involved, the three-dimensional geometry of the imaged breast volume can be based upon the number of levels in that predefined tomosynthesis reconstruction algorithm. In the event multiple predefined tomosynthesis reconstruction algorithms are involved having different geometries, the three-dimensional geometry of the imaged breast volume can be based on one of them, with resampling being incorporated into the others to result in appropriate registration. Alternatively, the three-dimensional geometry of the imaged breast volume could be based on the tomosynthesis reconstruction algorithms that were, or will be, used to generate the “for presentation” tomosynthesis reconstructed images.

Navigation and Review of Displayed Tomosynthesis Image Set

[0037] Preferred embodiments of a tomosynthesis workstation employing an automated focus capability according to the presently disclosed inventions will now be described. It is to be appreciated by those skilled in the art that the particular components of the review workstation are described in a very basic (generic) fashion, and that the inventions disclosed herein may be practiced on any of a wide number, type and variety of computer (processor) controlled workstations, which are common place as of this time. As used herein, the terms “user” and “reviewer” are intended to be used interchangeably.

[0038] In particular, an exemplary system for navigating and reviewing a tomosynthesis image data set includes an image processor (e.g., a computer), an image display monitor operatively associated with the image processor; and a user interface operatively coupled to the image processor and display monitor, wherein the user interface may in fact comprise in whole or part the display monitor (i.e., in a touch screen device such as a “tablet”, “pod” or other “smart” device). The image processor is configured to display user-selected image slices from a tomosynthesis data set on the display monitor in response to one or more user commands received through the user interface. The image processor is further configured to detect through the user interface a user selection or indication of an object or region of interest in a then-displayed image from the data set (e.g., when the user positions a graphic arrow controlled by a “mouse device” over the respective object or region for a certain amount of time and/or affirmative actuates (e.g., by clicking) same while in that position.

[0039] For purposes of more specific illustration, FIG. 3 depicts adjacent display monitors 32 and 34 of an exemplary tomosynthesis image review workstation 30, including a left-hand monitor 32 displaying respective right and left mediolateral oblique (“R.sub.MLO” and “L.sub.MLO”) image slices 32L and 32R; and a right-hand monitor 34 displaying respective right and left craniocaudal (“R.sub.CC” and “L.sub.CC”) image slices 34L and 34R. The R.sub.MLO, L.sub.MLO, R.sub.CC, and L.sub.CC images are obtained from respective tomosynthesis image sets (“tomo stacks”) containing right and left breast image data for each of the mediolateral oblique and craniocaudal orientations, for a total of four different tomo stacks. In particular, the displayed R.sub.MLO view is image 18 out of a 48 slice R.sub.MLO tomo stack; the displayed L.sub.MLO view is image 28 out of a 48 slice L.sub.MLO tomo stack; the displayed R.sub.CC view is image 18 out of a 48 slice R.sub.CC tomo stack; and the displayed L.sub.CC view is image 24 out of a 48 slice L.sub.MLO tomo stack. It will be appreciated by those skilled in the art that different tomo stacks may comprise differing numbers of image slices, and that the example tomo stacks having 48 image slices each are merely for example.

[0040] Notably, a round tissue mass 38 is visible in each of the L.sub.MLO and L.sub.CC image slices. It will be appreciated that the particular views of the tissue mass in the respective L.sub.MLO and L.sub.CC image slices differ in both clarity and orientation, since the image slices are taken along different (orthogonal) image planes, i.e., with the L.sub.MLO slice 28 comprising a cross-section taken along the z-axis of a “side view”, and the L.sub.CC slice 24 comprising a cross-section taken along the z-axis of a top-down view that is orthogonal to the z-axis of the L.sub.MLO image set.

[0041] For purposes of simplifying the discussion, the remainder of the present specification refers just to the L.sub.CC (left breast craniocaudal) tomo stack, although the inventive concepts and features described apply equally to the navigation and review of any tomo image stack, as well as for other, non-breast, body tissue image volumes.

[0042] FIG. 4 depicts monitor 34L displaying L.sub.CC slice 16 of the same tomo stack as L.sub.CC slice 24 displayed in FIG. 3. The round mass 38 is visible in L.sub.CC slice 16, but is not as focused as in L.sub.CC slice 24 of FIG. 3, indicating that the actual location of the mass along the z-axis of the L.sub.CC tomo stack is closer to slice 24 than slice 16. As best seen in FIG. 4A, a slice indicator 40 including an animated “sliding knob” is provided at a lower right-hand corner of each display to provide the reviewer with the slice number (i.e., relative z-axis location) of a presently-displayed slice of a tomo stack. Thus, as the reviewer scrolls through the image slices of a tomo stack using a suitable user interface (i.e., computer mouse), the knob 42 on the slice indicator moves to reflect the currently displayed slice. An audible tone (e.g., a “clicking”) may also be provided to indicate to the reviewer that the displayed slice has changes to a next one in the tomo stack.

[0043] In order to provide the perspective of the reviewer, FIG. 5 depicts the respective image slices 1, 16, 32 and 48 of the (same) L.sub.CC tomo stack as the images depicted in FIGS. 3 and 4, which clearly illustrate the differences in visibility and clarity of the round mass 38, depending on a relative z-axis location of the respective image slice. In particular, the mass is hard to make out in slice 1, but becomes more visible in slice 16, and is still more visible and clear (in terms of the edges, brightness, etc.) in slice 32, only to become blurred and difficult to make out in slice 48.

[0044] In one embodiment, the system detects through the user interface a user selection or indication of an object or region of interest in a then-displayed image from the tomo stack, and in response, displays an image from the data set having a best focus measure of the user selected or indicated object or region of interest. For example, FIG. 6 depicts a displayed “best focus” L.sub.CC image slice (slice 25) out of the (same) tomosynthesis image set with respect to the visibility and clarity of the round tissue mass 38. As explained in greater detail herein, the best focus slice 25 with respect to the tissue mass 38 was determined by the system processer based on a comparison of a computed focus measure of the tissue mass 38 for each image slice 1-48 of the L.sub.CC tomo stack. It is, of course, possible that the image slice displayed at the time the reviewer selects or otherwise indicates a particular object or region of interest make in fact turn out to be the image having the best focus of the user selected or indicated object or region of interest. In this case, the image processor may provide a visual or audible signal to the reviewer to indicate same (e.g., a beeping tone and/or highlighting of the object), since the image slice being displayed will not otherwise change.

[0045] In another embodiment, the system detects through the user interface a user selection or indication of an object or region of interest in a then-displayed image from the tomo stack, and in response, displays a series of near-focus images from the data set on the display monitor, the series of near focus images comprising images of the data set having computed focus measure values within a predetermined range of, and including, a best focus measure value computed for any image of the data set depicting the user selected or indicated object or region of interest. For example, FIG. 7 depicts a series of displayed near-focus L.sub.CC image slices from the (same) tomosynthesis image set, including the best focus L.sub.CC slice 25, plus subsequent L.sub.CC slices 27, 29 and 31, demonstrating slight changes in visibility and clarity of the round tissue mass 38 as the respective image slices progress along the z-axis from the best-focused slice 25 (far left displayed image) to the relatively least-focused slice 31 (far right displayed image).

[0046] In one embodiment, such as depicted in FIG. 9, the series of near-focus images are displayed simultaneously, so as to allow for a static review and comparison of the user selected or indicated object or region of interest in each image of the near-focus series. In particular, FIG. 9 depicts the best focus L.sub.CC image slice 25 displayed in a center area of the monitor, with the subset near-focus L.sub.CC image slices 21, 23, 25, 27 and 29 displayed in a stacked formation alongside the best focus image slice 25 to allow the reviewer to see the changes in the tissue mass in each direction along the z-axis from slice 25.

[0047] In another embodiment, the series of near-focus of images are displayed in succession, so as to allow for a dynamic review and comparison of the user selected or indicated object or region of interest in each image of the near-focus series. For example, the images slices 25, 27, 29 and 31 of FIG. 7 may be automatically displayed in consecutive order, one at a time, and each for a predetermined amount of time (e.g., 1 second) in order to convey to the reviewer the changes in the object or region of interest along the z-axis of the tomo stack. This “video loop” functionality may be optionally configured to be repeated multiple times, and further optionally with the respective images slices displayed in a different order (e.g., lowest slice to highest, then reverse order) during different loop sequences. Preferably, specific parameters for displaying the images of a series of near-focus images is configurable through the user interface.

[0048] In some embodiments, in order to assist the reviewer, the system employs known image processing techniques to identify different breast tissue objects and structures in the various source images, and the reviewer may (optionally) cause the system to highlight such objects and structures in the respective best focus image and/or near-focus images, in particular, tissue structures comprising or related to abnormal objects, such as micro-calcification clusters, round-or-lobulated masses, spiculated masses, architectural distortions, etc.; as well as benign tissue structures comprising or related to normal breast tissues, such as linear tissues, cysts, lymph nodes, blood vessels, etc. For example, a user selected or indicated object or region of interest is highlighted by a contour line representing a boundary of the highlighted object or region. Furthermore, objects or regions of interest consisting of or including differing types of tissue structures may be highlighted in different manners when they are a respective subject of a focusing process.

[0049] By way of non-limiting illustration, FIG. 8 depicts the series of displayed near-focus L.sub.CC image slices shown in FIG. 7, but in reverse order, i.e., slices 31, 29, 27 and 25. wherein the round mass is highlighted with a visual indicia in the form of rectangular brackets 58a-d, which move progressively closer around the tissue mass 38, as the image slices progress along the z-axis from the relatively least-focused slice 31 (far left image) to best-focused slice 25 (far right image). Again, the presentation of the respective images slices of the series of near-focus images may be presented at the same time (for a static comparison), or in a video-loop style format, for a dynamic comparison.

[0050] FIG. 10 is a flow diagram illustrating an exemplary process for displaying an image slice from a tomosynthesis data set having a best focus measure of a user selected or indicated object or region of interest in a previously displayed image slice from the set. Initially, at step 1002, the reviewer causes the system to initiate review of a tomosynthesis image set, e.g., of the prior illustrated and described L.sub.CC tomo stack having 48 slices. Thereafter, the reviewer scrolls through the image slices, typically but necessarily in an ascending order beginning at slice 1.

[0051] At step 1004, the reviewer selects or otherwise indicates an interest (i.e., for clinical evaluation) in an object or region of tissue in a then-displayed image slice of the tomo stack. Upon detecting the user selection or indication of an object or region of interest (hereinafter collectively referred to as “ROI” for purposes of describing the processes in FIGS. 10 and 11), at step 1006, the system thereafter computes a focus measure for the selected/indicated ROI in each image slice of the tomo stack.

[0052] As explained in greater detail below in conjunction with FIGS. 11 and 12, depending on the desired display protocol indicated by the reviewer, at step 1008, the system displays the image slice from the tomo stack having a best, (e.g., “highest” depending on the measuring protocol) focus measure out of all image slices of the tomo stack for the ROI. Alternatively or additionally, at step 1010, the system may display a series of near-focus image slices of the ROI, as described above. The range of slices that fall into a near-focus series may be pre-configured by the system, or user configurable. For example, a user may indicate through the user interface that the displayed series is include a selected number of images (e.g., five) out of the tomo stack having focus measures within a range of the five percent of one another and including the image having the best focus measure.

[0053] FIG. 11 is a flow diagram 1100 illustrating exemplary processes for computing a focus measure of a user selected or indicated object or region of interest in a displayed image slice of a tomosynthesis image set. As discussed above, the process begins, at step 1102, upon the reviewer selecting or otherwise indicating an ROI in a presently displayed (or “then-displayed”) image slice. The image slice having a best focus measure of the ROI out of the entire tomo stack is then determined by the system based on a comparison of a focus measure of the ROI for each image slice of the tomo stack.

[0054] In accordance with the presently disclosed inventions, a determination of focus score and, thus, a best focus score, may be accomplished in a number of ways including, at step 1104A, wherein the focus measure is computed according to known image processing techniques based on a sharpness of detected edges of the object or region of interest. For example, the total gradient magnitude of detected edges inside region of interest is a known measure for sharpness of detected edges. Alternatively and/or additionally, at step 1104B, the focus measure may be computed according to known image processing techniques based on a computed contrast of the object or region of interest, wherein the contrast can be defined as the absolute difference of a pixel with its eight neighbors, summed over all the pixels in region of interest. Alternatively and/or additionally, at step 1104C, the focus measure may be computed according to known image processing techniques based on a ratio between a measured magnitude of one or more high frequency components and a measured magnitude of one or more low frequency components, wherein high frequency components correspond to sharp edges of the object in the foreground, while low frequency components correspond to a blur area in the background. A high value of the ratio between a measured magnitude of high frequency components and a measured magnitude of low frequency components indicates that the object or region of interest is in focus.

[0055] Once the focus measure for each slice has been determined, at step 1106, the system may cause to be displayed the image slice having the best focus measure score and/or a series of images having focus measures within a predetermined range, e.g., within 5% of the best focus measure. This process is illustrated for the above-described and illustrated L.sub.CC tomo stack in FIG. 12, which depicts for purposes of illustration respective computed focus measure values of the round tissue mass 38 for images slices 15, 20, 25, 30 and 35, progressing along the z-axis of the L.sub.CC tomo image stack. In particular, the focus measure scores plotted in the graph of FIG. 12 were computed using a ratio between the measured magnitude of high frequency components and the measured magnitude of low frequency components within the selected image ROI. As can be seen, image slice 25 has the highest focus measure value, which in this case also means the “best” focus measure.

[0056] Having described exemplary embodiments, it can be appreciated that the examples described above and depicted in the accompanying figures are only illustrative, and that other embodiments and examples also are encompassed within the scope of the appended claims. For example, while the flow diagrams provided in the accompanying figures are illustrative of exemplary steps; the overall image merge process may be achieved in a variety of manners using other data merge methods known in the art. The system block diagrams are similarly representative only, illustrating functional delineations that are not to be viewed as limiting requirements of the disclosed inventions. Thus the above specific embodiments are illustrative, and many variations can be introduced on these embodiments without departing from the scope of the appended claims.