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[Th027] Citation: Abstract
In order to provide realistic haptic (touch) feedback, simulators
must incorporate accurate computational models of the in-vivo mechanical
behavior of soft tissues. It is important to test tissues in surgically
relevant ranges of applied force, duration, and deformation. In order
to determine these ranges, a system known as the Blue DRAGON has been
created that can track the motions of and the forces applied to
surgical tools during live procedures. Thirty-one surgeons of
varying skill were recorded performing three different surgical tasks.
The mean force applied to the tool handles during tissue grasps was
8.52 N ± 2.77 N. Ninety-five percent of the handle angle frequency
content was below 1.98 Hz ± 0.98 Hz. Average grasp time was 2.29 s
± 1.65 s, and 95% of all grasps observed were held for less than
8.86 s ± 7.06 s. The average maximum grasp time performed by surgeons
during these tasks was 13.37 s ± 11.42 s.
Using these values as design parameters, a computer-controlled,
motorized endoscopic grasper (MEG) has been designed to obtain
biomechanical properties of soft tissues in-vivo. The MEG uses a
geared DC motor to drive a Babcock grasper using a cable-and-pulley
mechanism. The motor is capable of producing the equivalent of 26.5 N
of grasping force (470 kPa) by the end effector jaws. Two strain gage
force-sensing beams are mounted in the partial pulley to accurately
measure applied force. Computer-control is provided using a proportional-derivative
position controller to command cyclic (up to 3 Hz) or step loadings. The
MEG can be hand-held, weighs about 0.7 kg, and can be inserted into the
body through standard endoscopic ports. The MEG has been calibrated and
validated on linear springs with known stiffness.
The MEG has been used to test 7 different porcine abdominal organs in-vivo
and through 24 hours postmortem. Elastic and relaxation properties have been
recorded and analyzed. Constitutive force-deformation relations have been
fit to the elastic data, and stress relaxation functions have been fit to
the stress-time data recorded during relaxation tests. An understanding of
how the tissue properties and model parameters are influenced by time
postmortem and loading condition has been obtained.
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Updated: Tue Jul 15 23:54:51 2008
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