WO2006064439A1

WO2006064439A1 - A method, an apparatus and a computer program for processing an object in a multi-dimensional dataset

Info

Publication number: WO2006064439A1
Application number: PCT/IB2005/054162
Authority: WO
Inventors: Marcel J. Quist
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-12-16
Filing date: 2005-12-09
Publication date: 2006-06-22

Abstract

The invention concerns a method of processing an object in a multi dimensional dataset, the method comprising the steps of accessing the results of a segmentation of the multi-dimensional dataset providing the object, determining values of a pre-defined feature of the object, coding the values of the pre-defined feature using graphic means in accordance with a pre-selected criterion and mapping the coded values of the pre¬ defined feature to the object. The invention also relates to an apparatus for enabling a processing of an object in a multi-dimensional dataset, the apparatus comprising an input arranged to access results of segmentation of the multi-dimensional dataset providing the object and a processor arranged to determine values of a pre-defined feature of the object. The invention further relates to a computer program.

Description

A method, an apparatus and a computer program for processing an object in a multidimensional dataset

The invention relates to a method of processing an object in a multidimensional dataset, said method comprising the steps of: accessing results of segmentation of the multi-dimensional dataset obtaining the object; - determining values of a pre-defined feature of the object.

The invention further relates to an apparatus for enabling a processing of an object in a multi-dimensional dataset, said apparatus comprising: an input arranged to access results of segmentation of the multi-dimensional dataset providing the object; - a processor arranged to determine values of a pre-defined feature of the object.

The invention still further relates to a computer program.

An embodiment of a method as is set forth in the opening paragraph is known from US 2003/0053697 Al . The known method is arranged to generate suitable representations of objects, notably blood vessels, ducts or bony structures of an organism. In order to establish a cross-sectional extent of the object the known method accesses results of a segmentation of the multi-dimensional dataset providing the object and finds local extrema in a suitable medialness function, constructed, for example, using a convolutional kernel formed by a ring of boundary operators. In order to suitably represent the segmented object, the known method enables a user to manually color code the selected vessels within the vessel tree, for example to differentiate one sub-branch of the vessel tree from the other. It must be noted that in this embodiment of the known method, each sub-branch will be given a unique color within a pre-selected color palette. In a further embodiment of the known method, the user may load a set of vascular trees to selectively color or hide any vessel or sub-tree with a suitable command. Additionally, a volume-rendered region can be animated in so that the colored feeding vessels are fading in and out in accordance with their spatial position with respect to the volume of interest. Summarizing, the known method is suitable for reconstructing objects, notably vessels, calculating running values of suitable geometric properties of tubes, whereby the user is allowed to manually color code the visualized vessels to differentiate between sub-branches.

It is a disadvantage of the known method that the user still has to inspect the great plurality of sectional images for identifying abnormalities within the vascular tree, in particular within an isolated sub-branch. In particular, a detection of partial occlusions is complicated, as vessels in slices will in general have different orientations. Therefore, it is not possible to assess vessel size on a single slice alone. The size of a visualized vessel on a single slice can easily be misinterpreted because of the oblique cut-planes. In addition, when the same sub-branch is ascribed the same color along its entire length for all slices, it may obstruct the underlying anatomy of the vessel and make it more difficult for the user to examine the vessel for abnormalities, like occlusions.

It is an object of the invention to provide a method of processing an object in a multi-dimensional dataset, whereby a change in a running value of a pre-defined feature of the object is accurately detected and is automatically made available for visualization in true value, spatially matched to the object.

To this end the method according to the invention further comprises the steps of: - coding the values of the pre-defined feature using graphic means in accordance with a pre-selected criterion; mapping the coded values of the pre-defined feature to the object. The technical measure of the invention is based on the insight that the results of a suitable segmentation step yielding the object can be automatically used for determination of a suitable feature of the object. As preferred embodiment for the object a vessel or a vessel-tree is selected, whereby the suitable feature may comprise a radius, a diameter or another dimension of the vessel, or a circularity of the vessel. By accessing the results of the segmentation, preferably a three-dimensional image segmentation, the local dimensions of the vessel reflect the true three-dimensional size, which equals, for example, a diameter of a rolling ball that fits in the vessel. Therefore, the true value of the pre-defined feature is used, irrespective of a future visualization view, thereby avoiding misinterpretation due to a partial projection. Thus, even if a truly large vessel appears tiny on a selected cross- sectional image, for example, because this slice only touches the border of the vessel, its true dimension at this location will be coded and will be shown because its true dimension was initially coded and referenced to the vessel. It must be understood that the term 'mapping' is defined as a procedure of correlating the respective coordinates of the segmented object and the map of coded values. Due to the mapping, any arbitrary projection will be accompanied with the correct map of coded values, which will always be presented in true size. The method according to the invention preserves the original pixel values, whereby the color- coding is a preferred embodiment of the coding operation. However, other graphic coding may be used, like shadowing, hatching, underlying, etc. The coding may be in absolute values, or may be expressed as a percentage of the largest detected value. The size-encoded color overlay reflects the three-dimensional vessel size, rather than the arbitrary size corresponding to a two-dimensional cut-plane.

In an embodiment of the method according to the invention, the method further comprises the steps of: overlaying an image of the object with the coded values of the pre-defined feature in accordance with said mapping; - displaying the image of the object overlaid with the coded values of the predefined feature on a display.

It is found that the method according to the invention is surprisingly suitable for the application for detection of emboli, whereby the specificity of the detection is substantially improved with respect to a human inspection based on a plurality of two- dimensional slices. The anatomical coarse-to-fine vessel structures in a distal direction are preferably reflected in the color distribution, which human observers can quickly perceive. Also variations between different human observers are minimized.

An apparatus according to the invention comprises: a coder arranged to code the determined values of the pre-determined feature using graphic means in accordance with a pre-selected criterion; mapping means arranged to reference the object with the coded values of the pre-determined feature.

In a preferred embodiment the coder is implemented as a computer program, arranged to calculate a range in the determined values of the pre-defined feature of the object and to assign a certain graphic feature to each running value of the pre-defined parameter, for example, in accordance with its percentage of the maximum value. This way of coding is particularly suitable for variations within a small range. Alternatively a higher than a linear power function or a lower than a liner power function may be used to assign a color code or any other suitable graphic coding to a particular running value. For the mapping means a look-up table with stored coordinates of the object and the coded values may be used. Alternatively, the mapping means may be adapted to use a suitable function, like a spline to define the object, whereby the coordinates of the coded values are defined within the terms of the function. A suitable combination of the above methods is also possible.

The output of the apparatus according to the invention comprises the object, segmented within the multi-dimensional dataset, said object being mapped with coded information about the true value of the pre-defined feature of the object. This output may be remotely accessed, for example using internet or wireless access by a remote user, for visualization and inspection purposed. This embodiment of the apparatus according to the invention is advantageous, as the remote user does not have to acquire all necessary and frequently expensive software means to process the multi-dimensional dataset on his computer.

In an embodiment of the apparatus according to the invention, the apparatus further comprises a graphic unit arranged to overlay an image of the object with the coded values of the pre-determined feature.

For inspections and visualizations it is advantageous that the apparatus according to the invention comprises the graphic unit suitable to overlay the image of the object with the coded values of the pre-determined feature. The output of such a device is an image of the object appended with a suitable graphic representation of the coded values of the feature of interest. Such images may be advantageously used for archiving purposes, for video-conferencing, reporting, etc. Preferably, the apparatus still further comprises a display for displaying the image of the object overlaid with the coded values of the pre-determined feature for inspection of a suitable medical specialist. In a further embodiment of the apparatus according to the invention, the apparatus further comprises a data acquisition unit arranged to obtain the multi-dimensional dataset.

For usage in a professional diagnostic environment, like diagnostic procedures in a hospital, it is advantageous that the apparatus according to the invention is further provided with a suitable data acquisition unit. Various embodiments of data acquisition units are contemplated, including, but not limited to, a computer tomography unit, a magnetic resonance imaging unit, an ultra-sound imaging unit, etc. A computer program according to the invention is arranged to comprise the instructions for causing a processor to carry out the steps of the method as is set forth in the foregoing.

These and other aspects of the invention will be discussed in further details with reference to figures.

Fig. 1 presents a schematic view of an embodiment of an apparatus according to the invention. Fig. 2 presents a schematic view of a further embodiment of the apparatus according to the invention.

Fig. 3a presents a schematic view of an embodiment of an overlay of coded data on a two-dimensional image.

Fig. 3b presents a schematic view of an embodiment of an overlay of coded data on a three-dimensional image.

Fig. 1 presents a schematic view of an embodiment of an apparatus according to the invention. The apparatus 10 comprises an input 2 for accessing results of a segmentation of the multi-dimensional dataset comprising the object under consideration. The segmentation step may be carried out on a different hard-ware, or, alternatively may be implemented as a preparatory step for practicing the invention using the same hard-ware. In the latter case, the input 2 may be arranged to receive the multi-dimensional dataset in any suitable form. For example, the apparatus 10 may be involved in the acquisition of the image data. In this case the multi-dimensional dataset may be acquired in an analogue form and converted using a suitable A/D converter to a digital form for further processing. The multidimensional dataset may also be received in a digital form, e.g. through direct acquisition in a digital form or via a computer network after having been acquired by another computer/medical instrument. The multi-dimensional dataset is then made available by the input 2 to a suitable computing engine (not shown) arranged to carry out the image segmentation step yielding the object.

The core of the image processing apparatus is formed by a processor 4 which is arranged to determine values of a pre-defined feature of the object. An example of a suitable processor 4 is a conventional microprocessor or signal processor, a background storage 8 (typically based on a hard disk) and working memory 6 (typically based on RAM). The background storage 8 can be used for storing suitable data (or parts of it) when not being processed, and for storing results of the image segmentation step. The main memory 6 typically holds the (parts of) data being processed and the results of the coding and mapping operations.

The apparatus 10 according to the invention further comprises a coder 5 arranged to code the determined values of the pre-determined feature using graphic means in accordance with a pre-selected criterion. The criterion may be selectable from a list of valid criteria, stored in a file 5a. The coder is arranged to assign a suitable coding value to a running value of the pre-determined criterion automatically, for example based on a percentage of the running value in the total range of determined values of the selected feature. The apparatus further comprises mapping means 7 arranged to map the coded values of the selected feature to the object. Preferably, the mapping means is arranged to create a file with correlated coordinates of the object and the coordinates of the coded values representing the selected feature. Preferably, the coder 5, the mapping means 7 and the processor 4 are operable by a computer program 3, preferably stored in memory 8. An output 9 is used for outputting the results of the processing, like results of the mapping step, preferably stored in one file.

Figure 2 presents a schematic view of a further embodiment of the apparatus 20 according to the invention. The apparatus 20 is arranged for processing an object based on a multi-dimensional dataset 29, acquired using a suitable data acquisition unit 31. The output of the processor 28 comprises the object, mapped with graphically coded values of selected feature of the object. Preferably, the coding comprises a color coding. Preferably, the output comprises an image of the object overlaid with the coded values of the feature, said image being stored in a suitable file. The output of the processor 28 is made available to the further input 25 of a suitable viewer 21. Preferably, the further input 25 comprises a suitable further processor arranged to operate a suitable interface using a program 26 adapted to control a user interface 24 so that an image 23 is visualized, comprising a graphic representation of overlaid coded values 23a of the object (not shown). Preferably, for user's convenience, the viewer 21 is provided with a high-resolution display means 22, the user interface being operable by means of a suitable interactive means 27, for example a mouse, a keyboard or any other suitable user's input device. Preferably, the apparatus 20 further comprises a data acquisition unit 31. However in this example an X-ray device is shown, other data acquisition modalities, like a CT, magnetic resonance apparatus or an ultra-sound device are contemplated as well. The apparatus 31 is arranged to acquire image data from an object, for example a patient, positioned in an acquisition volume V of the apparatus 31. For this purpose a beam of X-rays (not shown) is emitted from the X-ray source 33. The transmitted radiation (not shown) is registered by a suitable detector 35. In order to enable an oblique imaging, the X-ray source 33 and the X-ray detector 35 are mounted on a gantry 34 which is rotatably connected to a stand 37. A signal S at the output of the X-ray detector 35 is representative of the multi-dimensional dataset 29.

Figure 3a presents a schematic view of an embodiment of an overlay of coded data on a two-dimensional image. Preferably, the overlay of coded data is presented using a suitable user interface 42a of a viewer. The user interface 42a comprises a graphics window 44a wherein a visualized image of a tubular structure, for example a vessel, 47a overlaid with a color coded data of local diameter values is presented. The image may also comprise other supplementary information 46a, like a surrounding anatomy for localization purposes. The user interface 42a further comprises suitable controls 49a, arranged to control the visualization mode. In this example a two-dimensional image is presented, however a presentation of a three-dimensional image is contemplated as well. Using the controls 49a, the user may adjust an orientation of a projection plane, scroll over different slices of the same projection orientation, etc. The informative window 48a preferably presents absolute values of the selected feature (in this example a diameter of the vessels) corresponding to respective color codes. Alternatively, presentation of a percentage difference with respect to a certain value, for example a maximum value within a sub-branch or a full tree is possible.

Figure 3b presents a schematic view of an embodiment of an overlay of coded data on a three-dimensional image. Preferably, the overlay of coded data is presented using a suitable user interface 42b of a viewer. The user interface 42b comprises a graphics window 44b wherein a visualized image of a tubular structure, for example a vessel, 47b overlaid with a color coded data of local diameter values is presented. In this example results of volume rendering are presented. The user interface 42a further comprises suitable controls 49b, arranged to control the visualization mode. Using the controls 49b, the user may adjust an orientation of a viewing angle, control the coding mode, for example change between scales, or select different color palette, etc. The informative window 48b preferably presents absolute values of the selected feature (in this example a diameter of the vessels) corresponding to respective color codes. Alternatively, presentation of a percentage difference with respect to a certain value, for example a maximum value within a vascular sub-branch or a full vascular tree is possible. Still alternatively, it is possible to deselect the current feature and to select another feature for visualization purposes.

Claims

1. A method of processing an object in a multi-dimensional dataset, said method comprising the steps of: accessing results of a segmentation of the multi-dimensional dataset providing the object; - determining values of a pre-defined feature of the object; coding the values of the pre-defined feature using graphic means in accordance with a pre-selected criterion; mapping the coded values of the pre-defined feature to the object.

2. A method according to claim 1, wherein for the object a tubular structure is selected, the pre-defined feature being a dimension of the tubular structure in a direction substantially perpendicular to a longitudinal direction of said tubular structure.

3. A method according to claim 1, wherein for the object a tubular structure is selected, the pre-defined feature being a circularity of the tubular structure.

4. A method according to anyone of the preceding claims, wherein for the coding a color coding is selected.

5. A method according to any one of the preceding claims, further comprising the steps of: overlaying an image of the object with the coded values of the pre-defined feature in accordance with said mapping; displaying the image of the object overlaid with the coded values of the pre- defined feature on a display.

6. An apparatus (10) for enabling a processing of an object in a multidimensional dataset (29), said apparatus comprising: an input (2) arranged to access results of segmentation of the multidimensional dataset (29) providing the object; a processor (4) arranged to determine values of a pre-defined feature of the object; - a coder (5) arranged to code the determined values (48a, 48b) of the predetermined feature using graphic means in accordance with a pre-selected criterion; mapping means (7) arranged to map the coded values of the pre-determined feature to the object.

7. An apparatus according to claim 6, wherein the apparatus further comprises a graphic unit (42a, 42b) arranged to overlay an image of the object with the coded values of the pre-determined feature.

8. An apparatus according to claim 7, wherein the apparatus further comprises a display (22) for displaying the image (23) of the object overlaid with the coded values (23a) of the pre-determined feature.

9. An apparatus according to any one of the preceding claims 6-8, further comprising a data acquisition unit (31) arranged to obtain the multi-dimensional dataset (29).

10. A computer program (3, 26) for processing an object in a multi-dimensional dataset, said computer program comprising instructions for causing a processor to carry out the steps of the method according to any one of the preceding claims 1 to 5.