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Rigid Needles, Steerable Needles, and Optimal Beam Algorithms Ovidiu Daescu Bio-Medical Computing Laboratory Department of Computer Science University of Texas at Dallas (Joint work with Yam Ki Cheung and Anastasia Kurdia)
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Rigid needle: cannot bend Steerable needle: can bend State of needle described by tip position, orientation, and bevel direction φ
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Composed of a highly flexible material, with a bevel tip Offers greater mobility compared to rigid needles for minimally invasive medical procedures. Needle traces out a curve path inside the tissue. Rotating the base, the needle can be steered to avoid vital organs. φ The state of the needle is described by tip position, tip orientation, bevel direction
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Rigid Needle: Optimal Directions
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Optimal Directions
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Optimal Direction in Radiation Therapy
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Weighted subdivisions
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Weighted Distance Metric a b s t p ||p||=∑|p∩R i |w i ||ab||=|ab|w i
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Cases Optimal directions in weighted regions Optimal link in weighted regions k-link minimum cost paths Steerable needle paths Most results in 2D, some extend to 3D
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L T The line L “probes” R L The line L “penetrates” R T Optimal Direction
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L T S An optimal link problem between a source S and a target T. Optimal Link
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L T The line L “probes” R L The line L “penetrates” R T Optimal Direction/Link -width
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L T Optimal Direction – Strip Cover
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T Optimal Direction – Cone Cover
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K-Link Minimum Cost Path A 9-link path. A 4-link path.
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The LinkSolver Software
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2D: Optimal link goes through a vertex Property T
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2D: Optimal link goes through a vertex Property T
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In ray space Much faster to solve than 2D optimization problems 1D Problems T v
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1D optimization The objective function is “not nice” Can approximate optimal solution do this for all subproblems at v prune-and-search: fast in practice Can model it as a 2D linear objective function problem use SOLF algorithm A subproblem at v T v
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Optimal ray Goes through vertex Goes through two edges 2D optimization problems! Extend to 3D v
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Get many 2D slices Automatically As suggested by expert
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Minimally invasive surgical techniques have been highly successful in improving patient care, reducing risk of infection, and decreasing recovery times and treatment costs. A thin flexible needle, inserted into the human body and steered them from outside. Can reach targets inaccessible to traditional stiff needles One of the ways to reduce invasiveness of radiotherapy, biopsy collection, other procedures.
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The position of the needle depends on Original insertion angle Ability of the needle to bend The number of rotations performed and angle of each rotation Bending of the needle depends on physical properties of the needle and the environment A treatment plan would consist of initial insertion point and orientation and a sequence of rotations
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Rotation at the base does not directly correspond to the rotation at the needle tip More rotations result in larger deviation of the actual position of the needle tip from the predicted position The tissue experiences deformation Implications: A desired treatment plan should minimize the number of rotation to minimize the error It should also avoid or minimize damage to vital organs
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Design algorithms to compute optimal treatment plans Create computer simulations and visualization of the interaction between the needle and the human tissue to aid the surgeons in planning the procedures.
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Can characterize the number of rotations and compute treatment plan in absence of obstacles in 2D and 3D Given a target, the minimum number of rotations required to reach the target can be found fast
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Work in progress Compute the optimal path in the presence of polygonal obstacles
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Laboratory for Computational Sensing and Robotics at Johns Hopkins University “Steering Flexible Needles in Soft Tissue“ Funding: NSF Focus on probabilistic methods of computing trajectory.
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Medical Robotics Technology Center at Carnegie Mellon University “Needle Steering for Brain Surgery” Funding: The Pittsburgh Foundation, NSF Searching for optimal physical properties of the needle Showed that constantly spinning the needle during insertion makes the needle move in straight line
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Laboratory for Biomedical Computing at UTD and UTSW research groups? Preliminary work started with Lech Papiez’s group Funding: ? Focus on deterministic methods.
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Want real time solutions Use multiple 2D slices (hundreds) Independent problems in each slice Solve in parallel on a cluster of computers Business model: outsource computation Data at UTSW Computing cluster at UTD Transfer anonimous data (random ID)
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