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Research Papers

Measurement and Optimization of Minimally Invasive Intervention Device Design Fitness Using a Multiobjective Weighted Isotropy Index

[+] Author and Article Information
Frank L. Hammond1

Department of Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213fhammond@cmu.edu

Kenji Shimada

Department of Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213shimada@cmu.edu

Marco A. Zenati

Division of Cardiothoracic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213zenatim@upmc.edu

1

Corresponding author.

J. Med. Devices 4(1), 011002 (Mar 10, 2010) (9 pages) doi:10.1115/1.4001107 History: Received October 04, 2009; Revised January 24, 2010; Published March 10, 2010; Online March 10, 2010

The recent transition from multiple-port to single-port systems in minimally invasive intervention (MII) procedures has created a need for more flexible, dexterous robotic manipulation devices capable of spanning an entire surgical workspace without the risk of collateral damage. The design of such devices requires a careful balance of the mechanical complexity needed to facilitate clinical functionality and the cost of manufacturing and operating the device. This paper presents a novel metric for measuring the design fitness of kinematically redundant robotic MII devices and for optimizing them to achieve that balance. The proposed fitness metric rewards designs that are conducive to collision avoidance and energy conservation while penalizing those with exorbitant design complexities that adversely affect the economic feasibility of an MII system. The authors’ metric is used here to design a kinematically redundant, single-port MII device capable of accessing the cardiothoracic cavity through a single subxiphoid port and reaching several regions of interest, consistent with procedures such as epicardial ablation and therapeutic substance injection, with minimal physiologic disturbance. The design of this device is determined by a morphological optimization process, which searches a discrete mechanical design parameter space, consisting of linkage parts, part dimensions, and actuator types, using genetic algorithms. The execution of specific surgical maneuvers is simulated for each candidate MII device design, and the design is improved until the fitness metric is maximized. The results of this optimization study demonstrate that redesigning a 20 degree-of-freedom (DOF) MII device using the proposed metric decreased the DOF in the design by 45% while ensuring near-optimal levels of kinematic flexibility. The results also demonstrate the ability of the fitness metric to elucidate the relationship between functionality and complexity and to produce suitable device designs over a broad range of performance and cost goals. The authors conclude that this new design fitness metric, while heuristic in nature, holds the potential to improve both the clinical value and the economy of a wide variety of single-port MII devices, including those used in cardiothoracic surgery.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

Motion path selected for subxiphoid MII approach to the pericardium

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Figure 4

Anatomical location of the aortic arch on the 3D model used in simulations

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Figure 6

Torque-weighted isotropy when an external force FEXT is applied

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Figure 7

The shape of penalty function Γ(x), with α=5 and basex=120 units

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Figure 8

The basic architecture of the MII device and the location of the DOFs being designed

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Figure 9

The link type design space used in these experiments

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Figure 10

The actuator design space and associated properties

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Figure 11

A flow diagram of the MII device optimization process and the organization of its algorithms

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Figure 12

The initial, 20DOF MII device design and its design fitness properties

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Figure 13

The 20DOF MII device reaching an area of interest

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Figure 14

The optimal 13DOF MII device design and its design fitness properties

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Figure 15

The 13DOF MII device reaching an area of interest on the pericardium

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Figure 5

Collision-avoidance-weighted isotropy in the presence of a motion impediment

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Figure 17

The 11DOF MII device reaching an area of interest on the pericardium

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Figure 18

The optimal 7DOF MII device design and its design fitness properties

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Figure 19

The 7DOF MII device failing to reach an area of interest on the pericardium and assuming configurations capable of causing collateral damage

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Figure 20

Changes in MWGII, Γ(x), and QMII with design complexity at 13DOF

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Figure 2

A minimally invasive subxiphoid approach to the cardiothoracic cavity

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Figure 16

The 11DOF MII device design and its design fitness properties

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Figure 1

Example of a multiple-port MII cardiac procedure

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