WO2006126150A2

WO2006126150A2 - Automatic extraction and display of the tracheobronchial plane

Info

Publication number: WO2006126150A2
Application number: PCT/IB2006/051596
Authority: WO
Inventors: Rafael Wiemker; Thomas Buelow; Thomas Blaffert
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2005-05-25
Filing date: 2006-05-19
Publication date: 2006-11-30
Also published as: WO2006126150A3

Abstract

Usually orthogonal slices of a three-dimensional image set of a tracheobronchial tree (40) of a body do not show the tracheobronchial plane. Thus, the plane has to be adjusted manually by the user by trial and error, which is a tedious and time consuming process. The concept of the invention suggests a method of automated extraction and display of at least one oblique slice (49) of the tracheobronchial plane from a three- dimensional image set of a body. The method is fully automated without any user interaction. According to the invention the method comprises the step of: automatically identifying set of image points being part of a tracheobronchial tree (40); automatically identifying at least one oblique slice (49) as a fit to the image points; automatically performing a reformation step on the three-dimensional image set to extract the oblique slice (49); and automatically displaying (Fig. 6, 7) the oblique slice (49) of the tracheobronchial plane. The concept also provides a respective system (1), image acquisition device, workstation and computer program product and information carrier.

Description

Automatic Extraction and Display of the Tracheobronchial Plane

The invention relates to a method of extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set of a body.

The invention further relates to a system for extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set of a body. The invention further relates to a respective image acquisition device, image workstation, computer program product and information carrier.

Contemporary medical image view methods provide pictures in digital form, which can be directly processed on systems for medical information, image and data handling. Here, computer aided detection and quantification of body aspects is based on a three-dimensional image set of the body. Meanwhile, as well two-dimensional as also three- dimensional depiction of image data can be used for diagnostics on computer monitors.

Data may be provided by any suitable data acquistion device, in particular by a CT apparatus, however, also as well for instance by means of 3D-RA, MR, PET, SPECT etc. Control and display elements being part of a workstation are used for user interaction to display relevant data in a perspective which is most appropriate for specific diagnostics.

In contemporary systems, in particular CT systems, cross sectional views are originally acquired in two-dimensions, i.e. in a coplanar or a transversal plane, the latter is essentially perpendicular to the body axis. A preferred way of diagnostics necessitates an interactive revision of these so called orthogonal slices which are provided in an orthoview. However, this kind of orthoviews may not provide the best view to a certain physiology in any case. Thus, in contemporary concepts the view plane has to be adjusted manually by the user by trial and error which is a tedious and time consuming process.

Two-dimensional cross sectional views of a plane may differ from an orthoview, which is usually the transversal plane or a perpendicular plane thereto. Amended views having angle shifts and/or views, which are based on an amended slice thickness as compared to the thickness of a single slice, are in general referred to as multiplanar reformations. Contemporary reformation steps demand for a user interaction to provide a proper view different from an orthoview for specific diagnostic situations. This involves manual three-dimensional shifts and rotations about two axes in three dimensions to shift the perspective from an orthoview of orthogonal slices to an appropriate view of an oblique slice, which may be adequate for a specific diagnostic situation.

This kind of interactive diagnostics is meanwhile assisted by automated elements of computer implemented displaying a three-dimensional rendering of a structure. Such concepts assist the user to identify and segment the structure to be observed.

An embodiment of such a method and system is disclosed in US 6,272,366 or similarly in US 6,694,163. A method and system are provided for effecting interactive three- dimensional renderings of selected body organs for purposes of medical observation and diagnosis. A series of Computer Tomography (CT) images of the selected body organs are acquired. The series of CT images is stacked to form a three-dimensional volume file. To facilitate interactive three-dimensional rendering, the three-dimensional volume file may be subjected to an optional dataset reduction procedure to reduce pixel resolution and/or to divide the three-dimensional volume file into selected sub-volumes. From a selected volume or sub- volume, the image of a selected body organ is segmented or isolated.

Image segmentation may be effected by various techniques. For example, an image slice through the three-dimensional volume file may be subjected to a thresholding process in which a physical property of the two-dimensional image slice, such as x-ray attenuation, may be used to establish a particular threshold range, such as a range of x-ray attenuation values, that correspond to the organ of interest. After an appropriate threshold range is determined, the entire three-dimensional volume file is then thresholded to segment the organ of interest. For example, in order to segment the tracheobronchial tree or the lung, a threshold range corresponding to the air column within the tracheobronchial tree or the lung could be selected to isolate the inner wall of the tracheobronchial tree or the lung.

An alternative segmentation technique may be employed in which a region growing technique is used to isolate the air column within the tracheobronchial tree or the lung. Using the region growing technique, a "seed" is planted by selecting a data point or voxel within the air column. Neighboring voxels are progressively tested for compliance with a selected acceptance criteria, such as x-ray attenuation values falling within a selected threshold range representing air. As such, the seed region continues to expand or grow until the entire air column within the lumen of the tracheobronchial tree or the lung is filled. A surface, or isosurface, of the air column representing the tracheobronchial tree or the lung can then be produced. A wire frame model of the isosurface can then be generated using a selected image processing technique such as a marching cubes algorithm. From the wireframe model, a three-dimensional interactive rendering is produced that enables the user to rapidly view a series of three-dimensional images of the lumen of the tracheobronchial tree or the lung for purpose of detection of pathological conditions.

US 5,920,319 and US 2002/0193687 Al disclose a computer system and a computer-implemented method provided for interactively displaying a three-dimensional rendering of a structure having a lumen and for indicating regions of abnormal wall structure. A three-dimensional volume of data is formed from a series of two-dimensional images representing at least one physical property associated with the three-dimensional structure. An isosurface of a selected region of interest is created by a computer from the volume of data based on a selected value or values of a physical property representing the selected region of interest. A wireframe model of the isosurface is generated by the computer wherein the wireframe model includes a plurality of vertices. The wireframe model is then rendered by the computer in an interactive three-dimensional display.

Hence, in all cases the user must manually identify the best view for the relevant clinical parameters that are for example relevant in determining a diagnosis.

This is a particular tedious and time consuming process in case the respiratory physiology is to be evaluated. Desirable is an easy and less time consuming extraction and display of an effective view of the tracheobronchial system.

This is where the invention comes in, the object of which is to provide a method of and system for extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set of a body, which offers easy access to the tracheobronchial system and also a better view to the system as compared to an orthoview.

As regards the method the object is achieved by the method of extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set of a body comprising the steps of: - automatically identifying a set of image points being part of a tracheobronchial tree; automatically identifying at least one oblique slice as a fit to the image points; automatically performing a reformation step on the three-dimensional image set to extract the oblique slice; automatically displaying the oblique slice of the tracheobronchial plane.

As regards the system the object is achieved by a system for extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set of a body comprising: means for automatically identifying a set of image points being part of a tracheobronchial tree; means for automatically identifying at least one oblique slice as a fit to the image points; - means for automatically performing a reformation step on the three- dimensional image set to extract the oblique slice; means for automatically displaying the oblique slice of the tracheobronchial plane.

In its basic idea the present invention is directed to provide an automated extraction and display of at least one oblique slice of the tracheobronchial plane, i.e. the trachea and the main left and right bronchus, from a three-dimensional image set of a tracheobronchial tree of a body without any user interaction.

It has been realized by the invention that the tracheobronchial plane is usually lying obliquely in the three-dimensional image volume and therefore, the usual orthogonal slices offered by an ortho viewer do not show the tracheobronchial plane. As compared to commonplace concepts, where the tracheobronchial plane has to be adjusted manually by the user, the inventive concept achieves the advantage, that the oblique plane is provided automatically.

In other words, the suggested concept of the invention estimates the position of the tracheobronchial plane by providing an appropriate number of image points being part of the tracheobronchial tree and subsequently identifying at least one oblique slice as a fit to the image points. The plane may have the flatness of a single slice and also may have a certain thickness and can be represented for instance by a slab of slices. Thereafter, a planar image reformation to a single or a slab of slices is performed and displayed automatically. In essence the automated concept provides the user with a better view to the tracheobronchial system than an orthoview. The tracheobronchial plane is displayed by the system automatically or after a one click demand of the user without any further user interaction.

Developed configurations of the invention are further outlined in the dependent claims of the method and system respectively. In particular automatically segmenting of at least a part of the trachoebronchial tree from the three-dimensional image set of the body is provided. Thereby, a sufficient area of the tracheobronchial tree can be identified without the necessity of a full segmenting process. Advantageously, it is sufficient to segment only the main branches of the tracheobronchial tree for the purpose to provide a sufficient number of image points as a basis for a reliable fit of one or more oblique slices. A variety of segmentation processes may be used. In particular the segmenting step may comprise a tresholding and/or a seeding process. A preferred example of a segmenting step and seeding process is described in the detailed description with regard to the figures. Advantageously the step of identifying at least one oblique slice as a fit comprises: determining a best fit slice by solving an extremal problem based on the image points. In particular such solving of an extremal problem may comprise one or more of the measures selected from the group consisting of: - computing a covariance and/or variance matrix and a set of eigenvectors for the matrix, applying a least squares method.

Of course, any other kind of solving to an extremal problem may be applied if convenient. A preferred embodiment of the oblique plane mean position and orientation is provided in the detailed description with regard to the figures. A reformation step follows after having identified the points of the oblique slice. Reformation in particular achieves to assign respective image voxels to the points of the oblique slice. As the latter usually will not coincide with vertices of a mesh or available image voxels the reformation step in general may also comprise an interpolating step for interpolating image values between available image voxels and assigning the interpolated image values to the points of the oblique slice.

Preferably the step of performing a reformation comprises extracting a single oblique slice. This developed configuration may be used to allow the reading physician to appreciate in a very quick and efficient way in one glance possible anomalies in the tracheobronchial system. Advantageously, in a more elaborated developed configuration performing a reformation comprises extraction a slab of oblique slices. For instance, the number of slices may be determined by providing a thickness value of the tracheobroncial plane and adapting a number of slices to the thickness value. In a displaying step the physician may run over each single oblique slice of the slab. In an advanced development a projection of a number of one or all slices of the slab of oblique slices is provided to the physisian in one single view. This has the advantage, that the depth of field is largely increased and the physician is able to inspect also slices which lie before or beyond a mean position of the tracheobronchial plane.

In an elaborated development a time series of the breathing motion of the tracheobronchial tree can be recorded and for each moment of the time series of breathing motion an oblique slice of the tracheobronchial plane can be extracted and displayed automatically according to one or more developments of the inventive concept as outlinded above. This has the advantage, that the oblique slices can be collated in an animated movie. Thereby, the reformated image allows the reading physician to appreciate in one glance possible anomalies in the trachea and main bronchia such as tumors and constrictions during one or more periods of a breathing motion.

The method and system and developed configurations thereof as outlined above may be implemented by digital circuits of any preferred kind, whereby the advantages associated with digital circuits may be obtained. A single processor or other unit may fullfil the functions of several means recited in the claims. A digital circuit processor of the mentioned kind may be implemented in one or more multi-processor system.

In particular, the inventive concept also leads to an image acquisition device and image workstation each comprising the system as described above.

Also the invention leads to a computer program product storable on a medium readable by a computing, imaging and/or printer system, comprising a software code section which induces the computing, imaging and/or printer system to execute the method as described above when the product is executed on the computing, imaging and/or system. The invention also leads to an information carrier comprising the computer program product as described above.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

It is, of course, not possible to describe every conceivable configuration of the components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible.

In particular, as regards the method, the described embodiments are not mandatory. A person skilled in the art may change the order of steps or perform steps concurrently using threading models, multi-processor systems or multiple processes without departing from the concept as intended by the current invention. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In particular in claims enumerating several means, several of these means can be embodied by one and the same item of computer readable software or hardware.

Whereas the invention has particular utility for and will be described as associated with a CT acquisition device, it should be understood that the invention is also operable with other forms of imaging devices capable for reproducing volumetric image data. Such imaging device in particular comprise systems for medical acquisition of data like 3D- RA, MR, PET, SPECT etc. .

For a more complete understanding of the invention, reference should be made to the accompanying drawing, wherein:

Fig. 1 depicts a diagrammatic scheme of a system for automated extraction and display of at least one oblique slice of the tracheobronchial plane from a three- dimensional image set of a body according to a preferred embodiment of the invention;

Fig. 2 is an image of a prior art orthoview of an axial slice (xy-plane) of the tracheobronchial system;

Fig. 3 is an image of a prior art orthoview of a saggital slice (yz-plane) of the tracheobronchial system;

Fig. 4 is an image of a prior art orthoview of a coronal slice(xz-plane) of the tracheobronchial system; Fig. 5 indicates a thickness of a set of oblique slices of the tracheobronchial plane which slab or a single oblique slice thereof is fully automatically extracted and displayed according to a preferred embodiment of the invention;

Fig. 6 is an image of a single oblique slice on a mean position and orientation of the tracheobronchial plane according to a preferred embodiment of the invention;

Fig. 7 is an image of maximum intensity projections of slices of a slab of a tracheobronchial plane as indicated in Fig. 5 according to a preferred embodiment of the invention. The human lung consists of two major parts, the left lung and the right lung. There are three lobes in the right lung, which are separated by the so-called major fissure and minor fissure. The left lung shows a slightly different structure. Because there is no defined minor fissure, it consists of only two lobes, whereby the part that anatomically corresponds to the right middle lobe is merged with the upper lobe. Each lobe is again divided into two or more lung segments of which ten exist for each side of the lung. These segments are supplied by a complex system of branching trees that conduct blood and air into the distal regions where the gas exchange takes place. The bronchial tree has a pipe structure that is filled with air. It starts at the trachea and extends into the distal regions repeatedly splitting into smaller and smaller branches. In the human lung, the splitting occurs usually in bifurcations, for instance the parent branch splits up into two child branches, but trifurcations also exist. The general tendency for child branches is that they decrease in diameter and length although this might be different in individual cases. Siblings don't necessarily have the same diameter.

The bronchi are classified into lobar bronchi that supply the lobes, segmental bronchi, that supply the individual segments, and sub-segmental bronchi. The bronchial wall surrounds the air- filled lumen of the bronchi. The thickness of this wall is correlated to the diameter of the segment in the sense that it gets thinner for smaller diameters. High- resolution multi-slice CT reveals bronchi segments in the 6^th branching generation and higher which have diameters in the mm range. For diagnosis and treatment of asthmatic and emphysematic patients, the bronchial lumen, bronchial wall thickness, and the ratio of inner bronchial to accompanying arterial diameter are parameters which are used in clinical practice in order to detect and quantify airway narrowing, bronchial dilation, bronchial wall thickening, bronchiectasis, hyperresponsiveness, etc..

The concept of the instant invention suggests an automated extraction and display of the tracheobronchial plane consisting of the trachea and main left and right bronchus without user interaction. Generally, the concept quickly, i.e. in a second or so, estimates the position of the tracheobronchial plane, then a planar image reformation to a single oblique slice or a slab of a set of slices is performed and displayed. The concept has recognized that a most advantageous single view to evaluate the respiratory physiology is the plane in which the trachea and the main left and right bronchi lie. As indicated this view can be used to check at one glance whether the airways are dilated or constricted, for instance by tumors. The invention recognizes also that the plane formed by the trachea and the main left and right bronchi is usually lying obliquely in the three-dimensional image volume, which will be illustrated with reference to Fig. 5 to 7. Therefore, the usually orthogonal slices of the axial, saggital and coronal slice offered by an ortho viewer do not show the tracheobronchial plane which will be illustrated with reference to Fig. 2 to 4. Usually the plane has to be adjusted manually by the user by trial and error which is a tedious and time consuming process as it involves three-dimensional shifts and rotation about two axes in three dimensions.

As shown in Fig. 1 a system 1 for automated extraction and display of at least one oblique slice of the tracheobronchial plane from a three-dimensional image set 3 of a body essentially comprises:

A means 5 for automatically identifying a set of image points being part of the tracheobronchial tree. In the embodiment shown in Fig. 1 the identifying means 5 comprises means 21 for automatically segmenting at least a part of the tracheobronchial tree from the three-dimensional image set of the body. The segmenting means 21 of this embodiment comprises a seeding means 23 which is essentially capable to perform the following steps.

At first the seeding means 23 may start an automated finding of a seed point in the trachea. This can be performed by finding small round air filled patches in the two- dimensional axial slice images and an iterative weighted k-means clustering. Thereafter, the diameter of the trachea can be estimated by the seeding means

23. This can be performed by starting a region growing from the seed point. The growing extents into the trachea voxels until the area of the already encountered trachea wall is greater than the area of the growth front. The current area of the growth front is then taken as estimation for the trachea cross section area. Thirdly, the region growing proceeds into trachea and bronchi.

Fourthly the seeding means 23 comprises a criterium to automatically terminate the region growing. In particular the growth terminates when the growth front area becomes larger than for instance twice the trachea cross section area. Then the growth has either begun to split into the segmental airways or started to leak into the lung parenchyma, but in either case has probably left the main bronchia.

By this or similar kind of segmenting process a set of image points being part of the tracheobronchial tree can be identified automatically.

Futhermore, the identifying means 5 may also comprise means 25 for extracting centerlines of trachea, bronchi and/or smaller airways based upon the tracheobronchial tree. This measure can help to find a mean position of the tracheobronchial tree. As indicated above, the segmenting means 23 can also comprise a means 27 for determining branching points of the tracheobronchial tree based upon the extracted centerlines. Although not illustrated in detail here a centerline point can be determined from at least one of the item selected from the group consisting of: a bronchial lumen, a lumen diameter, an inner radius from the centerline point to an inner bronchial wall, - an inner diameter based upon the inner radius, an outer radius from the centerline point to an outer bronchial wall, an outer diameter based upon the outer radius, an artery radius of an accompanying artery, an artery diameter based upon the artery radius; wherein the centerline point comprises a point on a centerline of the extracted centerlines.

As an alternative to the segmentation process described above it is also possible to automatically segment the lungs and extract the whole bronchial tree, to label the tree segments, and then to derive an inertia ellipsoid from the centerlines of the segments labeled as trachea and left and right bronchus.

Furthermore, the system 1 comprises a means 7 for automatically identifying at least one oblique slice as a fit to the image points. In particular, the means 7 comprises a means 29 for determining a best fit slice by solving an extremal problem based on the image points. In general, any means adapted for computing the oblique plane mean position and orientation is suitable in this position. The extremal problem can be solved in various ways known to a person skilled in the art. One possibility is to compute a covariance and/or variance matrix on basis of the set of points and to compute a set of eigenvectors for the matrix. In particular a computation of the covariance matrix of the second order spatial moments (inertia tensor or ellipsoid) and its eigenvectors (principal component analysis) is performed. The eigenvector corresponding to the smallest eigenvalue of the inertia matrix is supposed to be the normal vector of the tracheobronchial plane. The normal vector and a local vector identify a plane in three-dimensional space according to the Hesse-Normal form. As a local vector the vector to the center of mass point of the set of points identified as described above may be chosen. The described method of fitting works particularly well as the tracheobronchial system is of longish extent (trachea), having lateral flanks (bronchi and lungs) and remains rather flat. So intertia tensor and center of mass point can be easily identified upon regarding the identified set of points as a set of mass points. An alternative possibility for identifying the oblique slice is for instance applying a least squares method. With regard to the computational efforts the former method is more advantageous.

Furthermore, the system 1 comprises means 9 for automatically performing a reformation step on the three-dimensional image set to extract the oblique slice. In other words, the identified tracheobronchial plane is planary reformated and possibly interpolated. This can be formed for instance by a means 31 for extracting a single oblique slice. The view of a single oblique slice is shown in Fig. 6.

Alternatively or additionally furthmore a means 33 can be provided for extracting a slab of the oblique slices. Advantageously the slab extracting means 33 comprises a means 34 for providing a thickness value of the tracheobronchial plane and means 38 for adapting a number of slices to the thickness value. This allows to provide a projection of all the slices in the slab for instance as a minimum or maximum intensity projection or a mean projection as will be shown in Fig. 7.

Respectively, a means 37 for displaying a single oblique slice like in Fig. 6 or a means 39 for projection of a number of slices of a slab of oblique slices like in Fig. 7 is comprised in the displaying means 11.

As a particularly preferred embodiment a dynamic CT series can automatically be converted into an animated movie to allow appraisal of the respiratory motion. If the plane is selected from image volumes from different time points in the respiratory cycle, then an animated movie can be generated showing the breathing motion. This animation can be used to diagnose abnormalities, such as collapsing of the trachea, uneven breathing motion etc. For this purpose in the reformation means 9 a means 35 for automatically extracting oblique slices of the tracheobronchial plane out of the time series is provided. Respectively, a displaying means 11 provides a means 36 for collating the oblique slices in an animated movie.

The system 1 as described above can be part of an image acquisition device 13 like a CT apparatus and/or an image workstation 15 further comprising input devices 17 like a mousepad or keypad, a monitor 19 and a computer station 18. As indicated above Fig. 2 shows the tracheobronchial system 40 in a cross sectional orthoview in the xy-axial plane. The trachea 41, the bronchia 43 and the right lung 45 and left lung 47 are only fragmentarily visible. The tracheobronchial system 40 is shown in another orthoview in the yz-saggital plane in Fig. 3. Again, the respective parts 41, 43 and 45, 47 of the tracheobronchial system 40 are visible only fragmentarily.

The same holds for another better but still fragmentary orthoview in the xz- coronal plane of Fig. 4. The same reference marks as in Fig. 2 and Fig. 3 are used.

Fig. 5 shows in principal the ortho views as shown in Fig. 2 and Fig. 3, however, here the planparallel lines 49 indicate a mean position and orientation of an automatically extracted oblique slab of slices of the tracheobronchial plane which extraction has been effected without any user interaction by the method and system as described with regard to the embodiment of Fig. 1. This also proves that an orthoview of Fig. 2, Fig. 3 or Fig. 4 is insufficient to give a satisfactory view for diagnostics of the tracheobronchial system. According to the inventive concept as shown in Fig. 6 full details of the whole trancheobronchial system 40 can be derived already from a single oblique slice lying somewhere between the lines 49 of Fig. 5. As a most remarkable feature the full trachea 41 and bronchi 43 are visible and all lobes of the right lung 45 and left lung 47 are visible as well. Such automated display of a single oblique slice can be provided quite instantly on a one click demand of the user or by the system without request of the user.

A more elaborated however still quick response of the system is possible even in case of a projected slab view as shown in Fig. 7.

As an example in this embodiment twenty planparallel slices of a slab of slices between the lines 49 indicated in Fig. 5 are displayed simultaneously by averaging the respective intensities. Alternatively a maximum intensity may be chosen for each point in the plane of the slab of slices, the maximum is chosen from a beam perpendicular to the slab (maximum intensity projection). Here, not only the details of Fig. 6 are visible but also the full information of the whole bronchi system 43 is visible by increased depth of field. Such depth of field can be for instance in the range of 20 mm as shown in this embodiment. In summary, usually orthogonal slices of a three-dimensional image set of a tracheobronchial tree 40 of a body do not show the tracheobronchial plane. Thus, the plane has to be adjusted manually by the user by trial and error, which is a tedious and time consuming process. The concept of the invention suggests a method of automated extraction and display of at least one oblique slice 49 of the tracheobronchial plane from a three- dimensional image set of a body. The method is fully automated without any user interaction. According to the invention the method comprises the step of: automatically identifying set of image points being part of a tracheobronchial tree 40; automatically identifying at least one oblique slice 49 as a fit to the image points; automatically performing a reformation step on the three-dimensional image set to extract the oblique slice 49; and automatically displaying (Fig. 6, 7) the oblique slice 49 of the tracheobronchial plane.

The concept also provides a respective system 1, image acquisition device, workstation and computer program product and information carrier.

While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.

The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing further developed configurations of the invention in diverse forms thereof. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that combinations of these measures cannot be used to advantage.

Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. In particular any reference signs placed between parentheses in the claims shall not be construed as limiting the scope of the invention. The wording "comprising" does not exclude other elements or steps than those listed in the claim. The wording "a" or "an" does not exclude the presence of a plurality of a respective feature.

REFERENCE NUMERALS:

I system

3 three-dimensional image set

5 means for automatically identifying a set of image points

7 means for identifying at least one oblique slice 9 means for automatically performing a reformation step

I 1 means for automatically displaying an oblique slice 13 image acquisition device

15 image workstation

17 input devices 18 computer station

19 monitor

21 segmenting means

23 seeding means

25 means for extracting centerlines 27 means for determining a centerline

29 means for determining a best fit

31 means for extracting a single oblique slice

33 means for extracting a slab of oblique slices

34 means for providing a thickness value 35 means for automatically extracting oblique slices

36 means for collating the oblique slices

37 means for displaying

38 means for adapting a number

39 means for projection 40 tracheobronchial tree, tracheobronchial system

41 trachea

43 bronchi system

45 right lung

47 left lung oblique slice, planparallel lines

Claims

CLAIMS:

1. Method of extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set of a body comprising the steps of: automatically identifying a set of image points being part of a tracheobronchial tree (40); - automatically identifying at least one oblique slice (49) as a fit to the image points; automatically performing a reformation step on the three-dimensional image set to extract the oblique slice (49); automatically displaying (Fig. 6, 7) the oblique slice (49) of the tracheobronchial plane.

2. Method as claimed in claim 1 characterized in that the step of identifying a set of image points comprises: automatically segmenting at least a part of the tracheobronchial tree from the three-dimensional image set of the body.

3. Method as claimed in claim 2 characterized in that the segmenting step comprises a thresholding and/or a seeding process.

4. Method as claimed in claim 2 or 3 characterized in that the segmenting step comprises one or more of the steps selected from the group consisting of: extracting centerlines of trachea, bronchi and/or smaller airways based upon the tracheobronchial tree; determining branching points of the tracheobronchial tree based upon the extracted centerlines.

5. Method as claimed in claim 4 characterized in that the segmenting step comprises determining for at least one centerline point from at least one of the items selected from the group consisting of: a bronchial lumen, a lumen diameter, an inner radius from the centerline point to an inner bronchial wall, an inner diameter based upon the inner radius, - an outer radius from the centerline point to an outer bronchial wall, an outer diameter based upon the outer radius, an artery radius of an accompanying artery, an artery diameter based upon the artery radius; wherein the centerline point comprises a point on a centerline of the extracted centerlines.

6. Method as claimed in one of the claims 1 to 5 characterized in that the step of identifying at least one oblique slice as a fit comprises: determining a best fit slice by solving an extremal problem based on the image points, in particular by one or more measures selected from the group consisting of: computing a covariance and/or variance matrix and a set of eigenvectors for the matrix, applying a least squares method.

7. Method as claimed in one of the claims 1 to 6 characterized in that the step of performing a reformation comprises extracting a single oblique slice (Fig. 6).

8. Method as claimed in one of the claims 1 to 6 characterized in that the step of performing a reformation comprises extracting a slab of oblique slices (Fig. 7).

9. Method as claimed in one of the claims 1 to 8 characterized in that the step of displaying comprises displaying a single oblique slice (Fig. 6) alone or a projection of a number of slices of a slab of oblique slices (Fig. 7).

10. Method as claimed in one of the claims 1 to 9 characterized by further providing a thickness value of the tracheobronchial plane and adapting a number of slices (49) to the thickness value.

11. Method as claimed in one of the claims 1 to 9 characterized by further comprising: providing a time series of a breathing motion of the tracheobronchial tree; automatically extracting oblique slices of tracheobronchial planes out of the time series.

12. Method as claimed in claim 11 characterized by further comprising: collating the oblique slices in an animated movie.

13. System ( 1 ) for extraction and display of at least one slice of the tracheobronchial plane from a three-dimensional image set (3) of a body comprising: means (5) for automatically identifying a set of image points being part of a tracheobronchial tree; means (7) for automatically identifying at least one oblique slice as a fit to the image points; means (9) for automatically performing a reformation step on the three- dimensional image set to extract the oblique slice; means (11) for automatically displaying the oblique slice of the tracheobronchial plane.

14. System as claimed in claim 13 characterized in that the means (5) for identifying a set of image points comprises: means (21) for automatically segmenting at least a part of the tracheobronchial tree from the three-dimensional image set of the body.

15. System as claimed in claim 14 characterized in that the segmenting means (21) comprises a thresholding and/or a seeding means (23).

16. System as claimed in claim 14 or 15 characterized in that the segmenting means (21) comprises one or more of the means selected from the group consisting of: means (25) for extracting centerlines of trachea, bronchi and/or smaller airways based upon the tracheobronchial tree; means (27) for determining branching points of the tracheobronchial tree based upon the extracted centerlines.

17. System as claimed in claim 16 characterized in that the segmenting means (21) comprises means (27) for determining for at least one centerline point from at least one of the items selected from the group consisting of: - a bronchial lumen, lumen diameter, an inner radius from the centerline point to an inner bronchial wall, an inner diameter based upon the inner radius, an outer radius from the centerline point to an outer bronchial wall, - an outer diameter based upon the outer radius, an artery radius of an accompanying artery, an artery diameter based upon the artery radius; wherein the centerline point comprises a point on a centerline of the extracted centerlines.

18. System as claimed in one of the claims 13 to 17 characterized in that the means (7) for identifying at least one oblique slice as a fit comprises: means (29) for determining a best fit slice by solving an extremal problem based on the image points, in particular by one or more measures selected from the group consisting of: means for computing a covariance and/or variance matrix and a set of eigenvectors for the matrix, means for applying a least squares method.

19. System as claimed in one of the claims 13 to 18 characterized in that the means (9) for performing a reformation step comprises means (31) for extracting a single oblique slice.

20. System as claimed in one of the claims 13 to 18 characterized in that the means for performing a reformation step comprises means (33) for extracting a slab of oblique slices.

21. System as claimed in one of the claims 13 to 20 characterized in that the means (11) for displaying comprises means (37) for displaying a single oblique slice alone or means (39) for a projection of a number of slices of a slab of oblique slices.

22. System as claimed in one claims 13 to 21 characterized by means (34) for providing a thickness value of the tracheobronchial plane and means (38) for adapting a number of slices to the thickness value.

23. System as claimed in one claims 13 to 22 characterized by further comprising: - means for providing a time series of a breathing motion of the tracheobronchial tree; means (35) for automatically extracting oblique slices of tracheobronchial planes out of the time series.

24. System as claimed in claim 23 characterized by further comprising: means (36) for collating the oblique slices in an animated movie.

25. Image acquisition device (13) comprising the system as claimed in one of the claims 13 to 24.

26. Image workstation (15) comprising the system as claimed in one of the claims 13 to 24.

27. Computer program product storable on a medium readable by a computing, imaging and/or printer system, comprising a software code section which induces the computing, imaging and/or printer system to execute the method as claimed in any of the claims 1 to 12 when the product is executed on the computing, imaging and/or printer system.

28. Information carrier comprising the computer program product as claimed in claim 27.