Design of an Optically Controlled MR-compatible Active Needle
Speaker: Seok Chang Ryu, Stanford University
Date: Friday, September 7 2012
Time: 10:00AM to 11:00AM
Location: 32-D507
Host: Daniela Rus, MIT
Contact: Mieke Moran, 617-253-5817, mieke@csail.mit.edu
Abstract:
An active needle is proposed for the development of magnetic resonance imaging (MRI) guided percutaneous procedures. The needle uses internal laser heating, conducted via optical fibers, of a shape memory alloy (SMA) actuator to produce bending in the distal section of the needle. Active bending of the needle as it is inserted allows it to reach small targets while overcoming the effects of interactions with surrounding tissue, which can otherwise deflect the needle away from its ideal path. The active section is designed to bend preferentially in one direction under actuation, and is also made from SMA for its combination of MR and bio-compatibility and its superelastic bending properties. A prototype, with a size equivalent to a standard16G biopsy needle, exhibits significant bending in the air with a tip rotation of more than 10°.
For this slender MR-compatible active needle, a distributed side optical actuation method is presented. A prototype, with multiple side heating regions made by chemical etching, demonstrates significantly fast initial response compared to fiber tip heating when given optical power is applied. Gold coated structure captures the lights, then redirects them into the wire for higher efficiency and for better safety. A single-ended optical sensor with a gold reflector at the tip is also developed to measure the curvature independently of temperature as a function of optical transmission loss. Preliminary tests with the sensor prototype demonstrate approximately linear response and a repeatable signal, independent of the bending history. An opto-thermo-mechanical model of this needle is established for the optical control.
The needle performance was studied in human prostate-equivalent tissue phantoms. The experimental results show that this needle can compensate for the usual targeting error during prostate biopsy. More flexible needle design is also suggested to improve its steerability. In addition, human tissue works as a big heat sink, resulting in fast heat dissipation from the heated SMA wire. Though this reduces the risk of tissue damage, low transition temperature SMA wire is necessary for achieving enough SMA force. It also can allow immediate needle bending even with low level of optical power, when the austenite start temperature of an SMA wire can be placed near the body temperature. A feasibility study of the fabrication of this wire is presented, combining common annealing technique for coarse tuning and pre-stressing for fine tuning.
Biography:
Seok Chang Ryu received the B.S. degree in mechanical engineering from POSTECH, Pohang, Korea, in 2002, and the M.S. degree in mechanical engineering from Stanford University, Stanford, CA, in 2007, where he is currently pursuing the Ph.D. degree in mechanical engineering. His current research interest is design and manufacturing of medical robotics devices subjected to physical interaction with humans.
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