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MRI
Compatible Manipulator
Principal
Investigator
Prof. Steven
Dubowsky
Prof.
Richard Wiesman
Group
Members
Lauren DeVita,
MS student
Sam Kesner, MS student
Cristina Paul, visiting student
Dr. Jean Sebastien Plante,
Postdoctorate
Collaborators
Daniel
Kacher,
Harvard
Medical
School
Simon DiMaio,
Harvard
Medical
School
Joseph Roebuck, Partners HealthCare
Overview
Early detection and treatment of prostate cancer is crucial in patient
survival rates. Both processes require precise needle placement.
MRI compatible robotic systems will play an important role in future
needle manipulation.
Courtesy of
Daniel Kacher
Objectives
The
goal of this research is to design a manipulator that is able to position
a biopsy or treatment needle in a prostate tumor under the real-time
control of a surgeon while the patient is in the bore of a closed MRI.
Design
Concept
An
antagonistic position control manipulator will be developed based on bistable
Dielectric Elastomer (DE) actuators.
These actuators have been shown to be MRI compatible. DE
actuators operate normally within an MR scanner and do not affect the
image produced. They are lightweight, inexpensive and simple.
Their bistable structure, using build
in compliant members, allows for a simple solution.
Bistable
Dielectric Elastomer Actuators
Current
Methods
Current methods for imaged guided placement include the ultrasound-guided
needles and open MRI needle placement.
Closed-bore MRI is more effective than either of these systems as
it yields an image with substantially greater detail.
However, the high MRI magnetic fields limit the types of tools,
particularly the actuators, which can be used with the real-time imaging. Also, current open MRI methods use a guidance template.
BWH uses a template that has evenly spaced holes, 5mm apart.
This limits the needle accuracy in the of X-Y directions.
Further, the real-time adjustment of the angle of penetration is
not possible.
Ultrasound
Guided Needles
www.prostatecancercentre.co.uk
Proposed
Design Performance
The proposed manipulator
will meet the following specifications, referring to the figure below:
- The needle
workspace will cover a 2cm diameter circular plate in the x’y’
plane at the perineum extending 0.5cm in the z’ direction.
-
The
manipulator’s horizontal and vertical ranges of motion will produce
an effective 10cm diameter workspace in the x”y”
plane, which is approximately a circular plate of 2cm thickness in the
z” direction, assuming the prostate is 10 to 12cm from the perineum.
This workspace will be comparable to the workspace provided by the
template at BWH.
System
Coordinates
Theory
of Operation
-
There
will be two end effectors: the needle tip and the needle guide tip.
-
The
needle guide will be positioned approximately 1cm in the z-direction
from the perineum before the patient is moved into the magnet, as
shown above.
-
The
manipulator will be mounted to the table of the MRI between the
patient’s legs on an adjustable mount.
-
The
patient and manipulator will be slid into the magnet together.
-
The
manipulator will orient the needle guide and press it against the
perineum using a specified target location and needle orientation
based on real-time MR images with a resolution of ±5mm in the x’y’
plane.
-
The
angle of the needle guide will be adjusted if necessary based on a
real-time MR image.
-
Once
needle penetration begins, the manipulator will only move the needle
in the axial direction of the needle guide a distance of 10 to 12cm
with respect to the z-axis with a resolution of less than 5mm.
Sponsor
NASA Institute for Advanced Concepts (NIAC)
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1995-2006 by MIT.
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