The invention relates to an image processing apparatus arranged to scale an object within an image, said image processing apparatus comprising:
a calibrator operable to scale the object based on a calibration factor derived from a relation between a true dimension of a marker and a dimension of the marker in pixel units in the image.
The invention further relates to an imaging system.
The invention still further relates to a method for enabling scaling of an object within an image.
The invention still further relates to a computer program.
An embodiment of an image processing apparatus as is set forth in the opening paragraph is known from U.S. Pat. No. 6,405,071. The known image processing apparatus is arranged to determine a length of a root canal from an X-ray image thereof, said image comprising a projection of a marker aligned with the root canal. The marker has a pre-known length and is used for calibration purposes. Thus, a relationship, notably a ratio between a length of the marker in pixel units and its true length yields an image calibration factor. The measured length of the root canal will be scaled according to its length in pixel units and the calibration factor.
It is a common practice to use a sole marker for determination of the image calibration factor. For this purpose a user manually delineates the marker, for example by indicating two points for a length measurement, using a suitably arranged graphic user interface and executes a suitable computation routine for a determination of the length of the marker in pixel units. When said length of the calibration marker is determined, the user manually enters the true dimension of the marker so that a suitable calibrator of the image processing apparatus calculates the calibration factor.
It is a disadvantage of the known image processing apparatus that a separate data acquisition is required for the calculation of the individual calibration factors for each object when those objects are oriented differently from each other in the same image.
It is an object of the invention to provide an image processing apparatus wherein scaling of differently oriented objects is enabled based on the same data set.
To this end in the image processing apparatus according to the invention the calibrator is further arranged to generate a plurality of calibration factors obtained using a plurality of differently oriented markers identified within said image.
The technical measure of the invention is based on the insight that by providing a plurality of calibration factors for differently oriented objects within the image a simultaneous calibration of these objects can be enabled, whereby these calibration factors are assigned not to the image, but are linked to the objects having the same spatial orientation as a corresponding marker. In this way it is not necessary to acquire a plurality of image data covering for a plurality of necessary calibration factors, thus improving a process of data acquisition and post-processing. It must be noted, that for the marker either an artificial object with a pre-known true dimension, or a part of the image, notably a medical image, comprising areas with known dimensions may be used.
In an embodiment of the image processing apparatus according to the invention, the image processing apparatus further comprises a linker arranged to form groups each comprising at least one object linked to a respective marker.
It is found to be particularly advantageous to interrelate a plurality of objects for calibration purposes. This measure has an advantage that in case when a calibration factor of a given group is updated, for example due to a user interaction, the true dimension of every object within the group is automatically updated. This feature further improves a user-friendliness and a reliability of the image processing apparatus according to the invention. It is considered to be advantageous to divide the differently oriented objects into a suitable number of calibration groups, whereby, for example, similarly oriented objects are linked to a similarly oriented marker thus sharing the same calibration factor. Selection of the marker to which the objects are linked can be carried out manually. In this case the user selects the objects within the group and links them to the suitable marker using suitable graphic interactive tools. Preferably, the selection of the marker is enabled automatically, whereby, for example, an a-priori information about structures in the image is used. For example, for anatomical structures a per se known pattern recognition engine may be used, or, alternatively, an information available from another image, like results of a suitable image segmentation step.
In a further embodiment of the image processing apparatus according to the invention, said apparatus further comprises a visualizer arranged to indicate each of said groups independently.
Preferably, different groups are indicated the visualizer by assigning different colors to the objects and the marker constituting different groups. Alternatively, it is possible to use different indicators for different groups, like suitable alpha-numerical information. Still alternatively, it is possible to use different attributes for objects and markers of different groups, like line formatting, shading, overlays, etc. Due to this technical measure the user is provided with a better insight into the orientation of the objects forming the image, so that there is little space for mistakably assigning a calibration factor to an object from a different calibration group.
In a still further embodiment of the image processing apparatus according to the invention the calibrator is further arranged to overlay said image with a graphic template of the marker, said graphic template being linked to a measurement tool for measuring of the dimension of the marker in pixel units.
This technical feature is based on the insight that it is advantageous to allow the user to manipulate a graphic object provided with an associated measurement, which is available in the image for calibration purposes. It must be understood that within the terms of the current invention, the term ‘marker’ is attributed to any graphic object suitable for calibration purposes. For example, the marker may comprise two landmarks, a line between two landmarks, a circle with a diameter or a radius, or any other suitable one- or multi-dimensional object comprising a plurality of pixels. Additionally, the marker may be obtained from a suitable image segmentation step, which is arranged to provide a suitable shape, for example, positioned on top of a specific part of an anatomy or an object shown in the image.
According to this feature, the calibrator is arranged to overlay the image with the graphic template of the marker linked to the associated tool enabling measurement of the dimension of the marker in pixel units. Thus, the user does not have to manually delineate the marker, which improves the accuracy and reliability of the calibration step. Suitable graphic routines operable to calculate the dimension in pixel units are known per se in the art. Preferably, if the image processing apparatus according to the invention is used for a certain type of images, for example for planning an implant, the graphic template may comprise a true length of the marker, the user having only to confirm the used marker true length, or, otherwise, to edit it accordingly. Upon a completion of the calibration step, the true dimension of the object will be determined with high precision and without a substantial user interaction. It is found to be preferable that the graphic template not only provides a suitable marker, but also automatically calculates its dimension in pixel units. A plurality of suitable measurement tools are known per se in the art, the examples comprising any suitable shape with an associated measurement function.
In a further embodiment of the image processing apparatus according to the invention the measurement tool is defined within a geometric relational application framework macro.
This technical measure is advantageous, as the graphic relational application macro can be configured to interrelate a plurality of objects in such a way, that when a single object is repositioned, the other objects related to it are repositioned accordingly. This results not only in a provision of a fully automated image processing, but also in a provision of a highly reliable delineation, measurement and calibration means.
An embodiment of the image handling using the geometric relational application framework macro is known from WO/0063844, which is assigned to the present Applicant. The geometric application framework macro is arranged to provide detailed descriptions of various geometric templates defined within the image, in particular to structurally interrelate said templates within geometry of the image, thus providing a structural handling of various geometrical templates so that a certain pre-defined geometrical consistency between the templates is maintained. The geometric application framework macro further enables analysis and/or measurement of geometrical properties of anatomical structures, when the structure is provided with a suitable landmark. A broad variety of possible geometric relations between pre-definable geometric templates, like a circle, a line, a sphere, etc., is possible and is defined within the geometric application framework macro. The geometric template is operable by the geometric application framework macro using a landmark, or a set of landmarks associated with the geometric template.
An imaging system according to the invention comprises a display and the image processing apparatus, as is set forth in the foregoing. Advantageously, the imaging system according to the invention further comprises a data acquisition unit connectable to the image processing apparatus. In this way an easy to operate data acquisition and processing system is provided, whereby the user is enabled to carry out necessary image processing steps with high reliability.
A method according to the invention comprises the steps of:
identifying a plurality of differently oriented markers within the image;
for each marker calculating a calibration factor based on a relation between a true dimension of the marker and a dimension of the marker in pixel units;
generating a plurality of the calibration factors.
According to the method of the invention, it is possible to use a single image for scaling a plurality of objects using a plurality of calibration factors assigned to different objects. For example, such an image may comprise differently oriented objects in space, each requiring a separate calibration factor for scaling purposes. Alternatively or additionally, such an image may comprise paste areas with zoom-ins or zoom-outs requiring a different calibration factor due to a different magnification factor. By providing a plurality of calibration factors, which are assigned not to the image as a whole, but to separate objects within the image, a scaling procedure for the objects requiring different calibration factors is simplified. Further advantageous embodiments of the method according to the invention are set forth in claims 9-12.
The computer program according to the invention is arranged to cause a processor to carry out the steps of the method as is set forth in the foregoing. The computer program comprises suitable subroutines arranged to load image data and to run a measurement protocol. Upon an event the suitable plurality of markers is identified in the image, either by user interaction or automatically, the computer program initiates a measurement protocol for determining a dimension of each marker in pixel units. The measurement protocol is arranged to initiate a toolkit macro that contains a marker. Preferably, the marker is positioned on the image using suitable image matching techniques. For example, when the user selects a marker to be represented by a standard geometric shape, for example a circle or a line, the matching subroutine carries out an automatic matching between a part of the image and the marker, by suitably sizing and displacing the marker. When the calibration factors are determined, they are stored with reference to the marker for which they are calculated. The calibration routine further applies the thus determined calibration factors to the objects linked to them. The user may alter the value of the true size of the markers, the calibration and scaling being updated automatically.
These and other aspects of the invention will be explained in more detail with reference to the figures.
If one element (circle 22a or line 26) is modified all other elements are automatically updated to reflect this modification. Also, in case the true length of the marker 29 is modified, the measurement of the leg length is updated instantly. According to the technical measure of this embodiment of the invention, objects 23a, 23b, 25a, 25b are associated with respective graphic objects 22a, 22b, 26. These graphic objects are arranged to position themselves automatically along edges or other features of the image data. Through specifically defined relations between graphic objects 22a, 22b, 26 inter-related by the geometric relational application macro and the graphic objects 23a, 23b, 25a, 25b, the circles 22a, 22b are positioned to fit optimally to the paths of the closed contours 23a, 23b, while the straight line 26 is positioned such that it touches both open contours 25a, 25b. The graphic template is thus coupled, so that adaptations of the circles 22a, 22b, or the straight line 26 are automatically reflected in the measured distances 28a, 28b, 28c. Preferably, the constraints and relations that exist between the geometric objects are arranged to limit the adaptation of these objects, which is in turn automatically translated into limitations for the adaptation of the multi-dimensional graphic objects. Such constraints are preferably based on knowledge of anatomical consistency.
In image 20b the inter-related objects comprise lines 32, 34 modeling the femur bone and a measurement tool 35. In this example an automatic diameter measurement of a human femur is shown. The solid lines 32, 34 represent graphic templates within the geometric relational application macro: a line 32 modeling the femoral axis, a second perpendicular line 34 modeling a direction of a diameter measurement 35. This perpendicular line 34 is arranged to contain two graphic templates, namely two point objects 33a, 33b with an associated distance measurement, all being defined within the geometric relational application macro. In this example, open contours 31 are associated with the points 33a, 33b. These contours position themselves automatically along the edges of the femoral bone using a suitable image segmentation technique. Through specifically defined relations between the line 34, the line 32 and the contours 31, the positions of the two point objects 33a, 33b are automatically adapted to the intersection of the perpendicular line 34 and each graphic object 31. The image 30 further comprises a marker 37, which is used for calibration purposes. A corresponding calibration factor or a true length of the marker is fed-back to the user in the window 37a. In case when the calibration factor of the marker is changed, for example due to editing of the true length of the marker, the reading of the true distance 36 is updated automatically. Also, the reading of the true distance 36 is automatically updated in case when a position of any of the lines 31, 32, 34 is changed, leading to a different reading of a length for a trajectory 35 between new points 33a and 33b in pixel units. Thus, in case when the user picks up the perpendicular line 34 and moves it along the femoral axis, the diameter measurement 35 will adapt dependent on the current femur diameter at a new location of the perpendicular line 34. According to this technical measure, a versatile and easy to operate image processing means is provided, whereby due to coupling between the graphic objects in a geometric relational application macro, any repositioning of the objects automatically lead to an update of the true dimension of the object of interest 35.
Although in this example it is clear for the user which regions of the image use which marker, it is preferable that the objects are combined in groups linked to a respective marker. Preferably, each group is visualized differently using suitable graphic means. Although an operation of the geometric relational application framework macro is illustrated using this particular example, whereby an image comprising two parts with different magnification factors is shown, it is possible that further groups are defined within each sub-area 20a, 20b, for objects which have different spatial orientation, as is described with reference to
Number | Date | Country | Kind |
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04102404.3 | May 2004 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB05/51705 | 5/25/2005 | WO | 11/27/2006 |