Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B17/00—Systems involving the use of models or simulators of said systems
  • G05B17/02—Systems involving the use of models or simulators of said systems electric
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09B—EDUCATIONAL OR DEMONSTRATION APPLIANCES; APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE; MODELS; PLANETARIA; GLOBES; MAPS; DIAGRAMS
  • G09B23/00—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes
  • G09B23/28—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for medicine
  • G09B23/285—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for medicine for injections, endoscopy, bronchoscopy, sigmoidscopy, insertion of contraceptive devices or enemas
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
  • A61B1/005—Flexible endoscopes
  • A61B1/0051—Flexible endoscopes with controlled bending of insertion part

Definitions

• the present invention relates to modeling a workspace and, more particularly, to modeling the workspace of a device according to internal and external constraints.
• Deformable models have been implemented in computer graphics and animation, in surgery simulation (deformable tissues) , and in medical imaging (model-based segmentation) .
• surgery simulation deformable tissues
• medical imaging model-based segmentation
• a model of an endoscope has been described as a part of a virtual endoscope system and method with force sensation.
• the model includes a collection of rigid links, interconnected by joints.
• a simplified Newton- Euler equation of motion can be used.
• the simplified Neuton- Euler equation disregards velocity and acceleration.
• a small number of joints are used as part of the virtual endoscope system, with increasing length from the endoscope tip to the
• Another method proposes a deformable model for long, thin instruments like catheters.
• a snake approach has been used.
• the shape of the catheter is represented by a fourth order B- spline, the control points of the B-spline are moved in an optimation process, to find a minimum energy representation.
• a method for simulating a flexible tube in an environment.
• the method comprises representing the flexible tube in the environment according to a model, and determining a model of the flexible tube according to a plurality of internal constraints of the flexible tube and a plurality of external constraints of the flexible tube.
• the method further comprises determining a workspace of the flexible tube according to a model of the flexible tube, and determining a model of an active bending behavior of a tip of the flexible tube .
• the model of the flexible tube is a chain of rigid links, interconnected by discrete joints.
• the workspace is a spatial tree, wherein the growth of the spatial tree is controlled by one or more filter functions .
• the spatial tree is a tree data structure comprising a plurality of nodes, wherein each node represents a joint in three-dimensional space.
• the spatial tree is a tree data structure comprising a plurality of edges, wherein each edge connects a node with its child and represents a link in three- dimensional space.
• the spatial tree is a tree data structure comprising a plurality of paths, wherein each path from a root to a leaf represents a flexible tube, and wherein all paths from the root to the leafs represent the workspace of the modeled flexible tube under a plurality of constraints.
• the method further comprises determining the filter functions, wherein determining the filter functions comprises the step of determining at least one of a geometry filter, a joint filter, a bounding tube filter, a gravity filter, and a stopping criteria filter.
• the method further comprises building the spatial tree, wherein building the spatial tree comprises determining an interaction of the flexible tube with the environment, and determining a length of the flexible tube to a target. Building the spatial tree further comprises determining a length for each link of the flexible tube, determining a diameter for each link of the flexible tube, determining a maximum angle for each joint of the flexible tube, and restricting the workspace to a portion of the environment .
• the spatial tree is built one of recursively and iteratively.
• Determining a model for the active bending of the flexible tube's tip comprises finding the center of a circle that best approximates the movement of the tip.
• the flexible tube is one of an endoscope and a catheter.
• a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for simulating a flexible tube in an environment.
• the method comprises determining a model of the flexible tube according to a plurality of internal constraints of the flexible tube and a plurality of external constraints of the flexible tube, determining a workspace of the flexible tube according to a model of the flexible tube, and determining a model of an active bending behavior of a tip of the flexible tube.
• a method for modeling a workspace of a flexible tube.
• the method comprises determining a joint filter according to a flexibility of the tube, determining a geometry filter according to an interaction of the tube with its physical confines, and determining a gravity filter.
• the method further comprises determining a bounding tube filter according to a portion of the physical confines in which the tube has been inserted, and determining a stopping criteria filter according to one of a dock or a tube length.
• the method comprises representing a model of the workspace of the flexible tube.
• Determining a joint filter comprises determining a maximum joint angle according to a position of a joint within a chain of interconnected links, wherein the flexible tube is modeled as the chain of interconnected links.
• the method comprises determining a model of the physical confines .
• Determining a bounding tube filter limits the workspace to a portion of the physical confines.
• the stopping criteria is a number of links of the flexible tube needed to reach a target site.
• the stopping criteria is fulfilled upon determining a dock between a link and the target site.
• Fig. 1 is a diagram of a flexible endoscope according to an embodiment of the present invention.
• Fig. 2a is an illustration of possible endoscope tip positions according to an embodiment of the present invention.
• Fig. 2b is a circle approximated by segments according to another embodiment of the present invention.
• Fig. 3a is a graph of two different bending behaviors according to an embodiment of the present invention.
• Fig. 3b is a graph of joint range functions corresponding to Fig. 3a;
• Fig. 4a is an illustration of two joints with different rotation rates according to an embodiment of the present invention.
• Fig. 4b is a graph of joint range functions corresponding to Fig. 4a;
• Fig. 5 is an illustration of a model according to an embodiment of the present invention.
• Fig. 6 is a flowchart of a method according to an embodiment of the present invention.
• the term "workspace” denotes that volume of space which the end-effector of a robot can reach.
• the workspace of a flexible endoscope is the volume of space that can be occupied by the entire endoscope. From the endoscope' s perspective, the workspace can be determined by its internal mechanical constraints, as well be its external constraints, for example, organ geometry and gravity. According to an embodiment of the present invention, the workspace of an endoscope can be determined under insertion into a patient specific organ model.
• a method according to the present invention provides a model of an endoscope that takes the internal constraints into account .
• a method which simulates the insertion of an endoscope into an organ is also provided.
• the method determines the workspace by recursively building a spatial tree whose growth can be constrained by a series of filter functions.
• Knowledge of an endoscope' s workspace can be used to assess the accuracy of a model by comparing it to a real endoscope in a test environment .
• a model E can be configured to represent any given endoscope.
• the model E represents an endoscope as a chain of rigid links, interconnected by discrete ball and socket joints.
• a link can be represented by a cylinder of a given length and diameter.
• a method AE can be provided that determines the endoscope' s workspace. The method simulates possible insertions of the endoscope by creating a spatial tree. The growth of the spatial tree can be restricted by a series of filter functions. The filters enforce the internal and external constraints, given by the endoscope and organ properties.
• a model B is provided for describing the bending process of the endoscope' s tip. With model B, the parameters needed to align the tip with the biopsy target can be determined.
• the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof.
• the present invention is implemented as a combination of hardware and software.
• the software is preferably implemented as an application program tangibly embodied on a program storage device.
• the application program may be uploaded to, and executed by, a machine comprising any suitable architecture.
• the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU) , a random access memory (RAM) , and input/output (I/O) interface (s) .
• the computer platform also includes an operating system and microinstruction code.
• various processes and functions described herein may either be part of the microinstruction code or part of the application program (or a combination thereof) that is t executed via the operating system.
• various other peripheral devices may be connected to the computer platform such as an additional data storage device and a printing device .
• a flexible endoscope is a surgical instrument that uses, for example, fiberoptics or a CCD camera to allow the surgeon to look inside the human body.
• an endoscope comprises four basic components: a control head, shaft (insertion tube) , working (biopsy) channel and bending section.
• a control head for example, a control head, shaft (insertion tube) , working (biopsy) channel and bending section.
• the transition of the shaft into the bending section is realized by a rigid sleeve (1) . It follows a chain of links that allows the active bending of the tip (2) .
• the chain connects to another rigid sleeve that can include an optical system (3) .
• the bending section has a larger diameter than the endoscope shaft.
• a TBNA can be based on a preoperative calculation of a "TBNA- protocol".
• the protocol can comprise four patient specific parameters.
• the estimation of these parameters ( 1 ;p 2 ,-P 3 ;p4) can be based on the calculation of the endoscope ' s workspace:
• a model E should take the following internal constraints of an endoscope into account, for example, (1) shaft geometry like length and diameter, (2) shaft behavior like flexibility (3) torsional stiffness, (4) bending section geometry like length of the sleeves and length of the part, (5) bending section behavior under "active" bending.
• Method A E modeling the external constraints can include the determination of: (1) the interaction of the entire endoscope with the organ, (2) the length 1 to the biopsy site S, (3) the endoscope' s workspace W and (4) the restriction of W to the branch of interest (branch that includes S) .
• An endoscope comprises several mechanical parts, like flexible tubes and rigid sleeves.
• a model according to the present invention has been developed using a mechanical approach.
• An endoscope model E models an endoscope as a chain of rigid links, interconnected by discrete ball and socket joints.
• a link can be represented by a cylinder of a given length and a given diameter.
• the length of the links and the joint range determines the flexibility.
• the endoscope shaft and the part of the bending section are modeled in substantially the
• the bending section sleeves are links at a specific position, with a given length and diameter.
• the external constraints of the model are considered.
• the insertion of an endoscope into an organ can be simulated by method A E , which is based model E.
• the method recursively (depth-first search) creates a spatial tree under a set of given geometrical constraints.
• a spatial tree is a tree data structure, where each node represents a joint in 3D space. Each edge that connects a node with its child represents a link in 3D space.
• Each path from the root to a leaf represents a chain of links and therewith an endoscope. All paths from the root to the leafs represent the workspace of the modeled endoscope under the given constraints.
• Constraints can be implemented by a series of filters. Each filter restricts the growth of the spatial tree and therewith the possible shapes an endoscope can take. For example a joint filter controls the flexibility of the endoscope, a gravity filter enforces gravity and a geometry filter controls the interaction of the endoscope with the organ. A bounding tube filter restricts the spatial tree to the branch of interest and the choice between two stopping criteria filters determines the calculation of either IV or I .
• Model B describes the bending behavior of bending section.
• a model according to an embodiment of the present invention can be described by defining a link, and based on the link introducing the set ⁇ of all possible sets of links. Starting with the unstructured set ⁇ , constraints can be introduced stepwise that impose structure and narrow the number of possible configurations, which leads to a definition of a tube. One structure imposed on ⁇ leads to the set of all chains C, which can be constrained to the set of all tubes T, so T _ C _ ⁇ . Based on T, a bending section can be defined, and thus an endoscope can be defined as a length of bending sections .
• Link 1 can be defined for a model according to the present invention.
• a matrix F 0 M can be a representation (homogenous transform) of a reference frame in 3D space.
• A can be written as :
• a set C_--- that includes only those link sets that describe a chain like structure can be determined.
• a collection of n links CO--- is called a chain of length n, if the links in C satisfy certain conditions:
• the set J of all joints that satisfy the joint specifications can be written as:
• a method according to an embodiment of the present invention comprises a flexibility function, f ⁇ .
• the flexibility function imposes structure on a chain by introducing the notion of flexibility.
• the flexibility of a chain can be determined by the link length s and the maximal joint range ti x -
• a flexibility function can be implemented that derives a joint range from a given link length and an intuitive flexibility value r ⁇ R.
• the idea of flexibility is related to the notion minimal radius, in the sense that the more flexible an endoscope is, the smaller the minimal radius of a circle one can form with the endoscope.
• a circle can be linear approximated by segments. Given a circle of radius r and the length s of each segment then the absolute value of the angle between two segments is the same as the angle at the center. This angle defines the maximal joint range ⁇ riA dependent of r and s and is given by the flexibility function:
• a chain is a collection of links, with no other constraint regarding the relation between two adjacent links than that they are connected.
• a flexible tube like structure can be defined by inserting joints between two adjacent links of a chain.
• n t T,n,s,d,r ( 10 )
• T ⁇ li, 1 2 , ..., l n ⁇
• . 2 fe ( s, r)
• the conditions . (l f ,l ⁇ )0J 2 & .(l n ,l ⁇ )0J 2 says that the first (last) link of the bending section is connected to the first (last) link of the flexible tube via a discrete joint.
• e is an endoscope ⁇ (14)
• a real endoscope has a high torsional stiffness, since twisting the endoscope head by V degrees leads to a rotation of the tip camera by V degrees.
• a piecewise linear tube is maximal torsional stiff if there is no rotation about the z- axis in between any two adjacent links.
• An endoscope e r 0 E r has a maximal torsional stiffness.
• a model can determine external constraints. Including, for example geometry O and Gravity Fn. G.
• the geometry of an organ can be described as a subset of the 3D-space and the gravity unit vector as given with respect to the world coordinate system:
• the first describes the maximum joint range fimax [ ⁇ MAX of an individual joint in dependency of the distance of this joint to the collision.
• the second function describes the steps (rate) in which an individual joint turns until its maximum joint range ( [ # MAX ) is reached.
• Fig. 3 shows two different bending behaviors induced by the corresponding joint range functions on the right.
• Fig. 4 shows two joints with different angle rates and the corresponding joint rate functions .
• E For a real endoscope e r , let E be the set of all endoscopes : c2
• a set of endoscopes E r ⁇ E is called the set of all real endoscopes, if an endoscope e r satisfies certain constraints: e r GE r , (21) e r e E
• an endoscope model can take the passive bending of the bending section into account that is caused by interaction with the organ walls.
• a model B describes the active bending behavior of the bending section, caused by the surgeon, rotating the bending wheel.
• Fig. 5 shows the distal end of an endoscope, including the first link l fb of the bending section, target t and semicircle center c. The figure shows that the sought bending angle of a straight bending section can be approximated by the angle between t and unit vector z of link C that includes c.
• attachLink In order to find "real endoscopes" that satisfy the internal and external constraints, possible configurations can be enumerated, beginning with a given start link 1*. This approach can be implemented as a recursive backtracking method: attachLink:
• the method attachllink can be written as follows:
• links that passed filter f 5 which implements the stopping criteria, these links can be added to the endoscope and leave the recursion (line 14 - 16) . If not, the links that passed filter f 5 represent the links that satisfy all constraints, but have not reached the target yet. With each of those links, the recursion can be called to continue attaching links (line 19) .
• the joint filter can be expressed as:
• the gravity filter can be written as:
• the workspace of an endoscope inserted into a tree-like structure like the bronchus can generally reach into many branches.
• a method, and in particular, the bounding filter considers that part of the workspace that reaches into the branch of interest (target branch) .
• An embodiment of the present invention has been implemented on a SGI PC540, 550Mhz (single), 0.5 GB RAM, running Windows 2000 and OpenGL.
• a lung phantom using transparent PVC tubes was used for testing. Thirty-seven marker sticks were randomly placed as artificial targets in ? the model. The phantom was then scanned (512x512x382, 1 mm slice distance, 1.2 thickness) and a model of the tracheobronchial tree was reconstructed.
• Endoscope OLYMPUS GIF 100 Videoscope.
• the accuracy of the endoscope model reflects the behavior of an OLYMPUS GIF 100 videoscope.
• the model was compared to the real endoscope parameters needed to hit a marker in the lung phantom to the estimated parameters derived from a model AE . Out of all 37 markers, 5 were chosen as biopsy targets. For each target, the TBNA was executed 20 times and the four parameters needed to touch the marker stick with the biopsy needle were recorded. Furthermore, the parameters for the same 5 targets were estimated by using the implementation of AE and B.
• Computation time was 2.6 minutes for building the entire spatial tree with a recursion depth of 13 links.
• the average error between the respective estimated and experimentally obtained alignment parameter is 12°, 3° and lmm.
• a model was used to simulate the insertion of a catheter into a brain artery.
• a catheter is a very thin, highly flexible tube used, among others to place stints for the treatment of aneurysms.
• input parameters were specified as :
• a flexible tube is described as a chain of links and joints 600.
• the method determines at least one internal constraint, for example, a shaft geometry 602, a shaft behavior 603, a torsional stiffness 604, a bending section geometry 605, and a bending section behavior 606.
• the method determines at least one external constraint 611, for example, interactions between the tube and a physical confine 612 (e.g., as between the models of the tube and the organ) , a length to a target 613, a
• a spatial tree is grown 621.
• An active bending model of the tip of the flexible tube can be implemented 622, which can, for example, model the alignment of the flexible tube relative to a target.

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• 2002
  • 2002-03-20 US US10/102,580 patent/US7277833B2/en not_active Expired - Fee Related
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