Data processing: structural design – modeling – simulation – and em – Simulating nonelectrical device or system – Mechanical
Reexamination Certificate
1999-07-16
2004-03-30
Teska, Kevin J. (Department: 2123)
Data processing: structural design, modeling, simulation, and em
Simulating nonelectrical device or system
Mechanical
C703S006000, C703S011000, C434S262000
Reexamination Certificate
active
06714901
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of the processing of digital image data from a set representative of a three-dimensional (3D) image, for simulating the deformable behavior of an object.
The invention applies more particularly, but nonexclusively, to the processing of a set of image data from a so-called medical image.
In numerous fields, it is very beneficial to be able to simulate interventions by an operator, with the aid of one or more known tools, on one or more deformable objects. Here, the term intervention is understood to mean either a manipulation, with a view for example to a displacement, or a local transformation, such as for example, in the case of a surgical intervention, incision or extraction of a part of an organ.
Simulation consists in displaying the image of an object and possibly of the region in which it customarily lies, and the representation of one tool at least whose <<virtual>> (in this document, words which appear within double-arrowhead brackets reflect the fact that a concept, in the context of this document, is designated with such words) displacement, relative to the object, is defined by a user interface of which a harness is maneuvered by an operator, with a view to simulating the handling of the said tool. In order to be able to simulate the reaction of the object on the tool, the user interface is capable of generating a force feedback, in accordance with the reactions of the tool. The term reaction force of an object is understood to mean force feedback.
In known devices, a reaction module makes it possible to determine this reaction force of the object on the basis of an estimated deformation of this object. This deformation is obtained with the aid of an internal forces module and of an image refresh module. The internal forces module is capable, on designation of a 3D. object appearing in a set of image data, of establishing a field of internal forces, which is representative of the deformation of the object, between nodes of a volume meshing dependent on a surface meshing of this object, on the basis of a deformation law and of an action defined by the user interface and representative of a maneuver of the tool.
The refresh module then makes it possible to calculate new image data of the object, in the presence of the estimated deformations supplemented with the representation of the tool. These new image data which form the new image of the object and possibly that of the region which surrounds it, are then displayed on a display device so that the operator can see in real time the result of the manipulation of the harness which simulates the action on the tool.
Such a device must allow the training of an operator or else the tailoring of new techniques of intervention on the object. In a field such as surgery, and more particularly still in the field of laparoscopic surgery, this type of device may make it possible to save human lives. To do this, it is imperative that the simulation makes it possible to reproduce the operator's gesture (or in other words his action on a tool, here virtual) as faithfully as possible. This requires real-time processing of the image data, coupled with reconstruction of the forces induced by the object in response to the deformation generated by the <<tool>>.
Now, on account of the calculation techniques used by known devices, estimation of the internal forces requires considerable calculation times which are incompatible with continuous dynamic simulation. In other words, contemporary devices do not make it possible to display, in a manner which is continuous in respect of a human eye, the entire action of a tool on a deformable object.
Moreover, no contemporary device makes it possible to simulate in real time an action such as incision, or tearing, or the removal of material from a deformable object.
SUMMARY OF THE INVENTION
The aim of the present invention is therefore to solve all or some of the aforesaid drawbacks in the field of the processing of digital image data of a 3D object.
It therefore proposes an electronic device for processing image data of the type described in the introduction, in which, on the one hand, there is provision for a <<collision>> module capable of estimating a point of intersection between a straight line embodying a displacement derived from the defined action and the surface meshing, and on the other hand, the internal forces module is devised so as to estimate the internal force exerted on each node of a first part at least of the volume meshing of the object on the basis of the displacement derived from the action, and applied to the nodes belonging to the surface mesh cell containing the point of intersection, of boundary conditions, and of node tensors and link tensors emanating respectively for each node and each link of at least the first part at least, from stiffness matrices specific to each volume mesh cell of at least the first part and dependent on the deformation law.
Of course, the first part of the volume mesh cell to which the above technique is applied, which will subsequently be referred to as <<masses/tensors>>, can be equal to the complete volume mesh cell. In the contrary case (when dealing in fact with a part of this volume mesh cell), the internal forces applied to the nodes of the part complementary to this first part (referred to for example as the second part) are determined on the basis of another technique, such as for example that of finite elements relying on precalculations which are stored so as to allow real-time calculations. Such a technique is taught in particular in the article by S. Cotin, H. Delingette, M. Bro-Nielsen and N. Ayache, <<Geometric and physical representations for a simulator of hepatic surgery>>, published in the proceedings of the conference Medicine meets with virtual reality, January 1996. In what follows, the dual technique of calculating internal forces and the deformation of the object will be referred to as a hybrid model.
This so-called masses/tensors technique used for calculating the internal forces and the deformation of the volume mesh cell of the object permits continuous simulation of an action exerted on a virtual tool at least. It is clear that the smaller the dimension of the first part of the volume mesh cell, the less will be the calculation time.
According to another characteristic of the invention, the device can comprise a meshing module allowing it to designate the 3D object(s) on which the simulation is to be performed by determination of an external envelope, then to decompose this or these envelopes into surface mesh cells, preferably of triangular form, and lastly to decompose the internal volume of each envelope into volume mesh cells on the basis of the corresponding surface meshing so as to provide the volume meshing of the associated object. It is clear that in the preferred case of a triangular surface meshing the volume mesh cells will be tetrahedral in shape. These shapes are currently preferred since they allow accurate modeling of an object of complex shape. However, of course, other types of meshing may be used.
Such external envelopes and volume mesh cells may be obtained by methods of segmentation (for example by extracting iso-surfaces) and of the Delaunay-Voronoï type respectively. All these methods are well known to the person skilled in the art.
In one embodiment of the device, its internal forces module is capable itself of calculating the stiffness matrices of each volume mesh cell, as well as the node tensors and link tensors.
These calculations are, as was stated earlier, performed on the basis of a deformation law which is preferably of volume linear elastic type. In other words, the force exerted on a node depends on the displacements respectively of this node and of the nodes to which it is connected, relative to their respective positions of equilibrium. Of course, other more complex deformation laws could be used, in particular non-linear laws.
The internal forces module co
Ayache Nicholas
Cotin Stéphace
Delingette Hervé
Garcia-Otero Eduardo
Inria Institut National de Recherche en Informatique et en Autom
Rabin & Berdo P.C.
Teska Kevin J.
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