Introduction - Microsurgery: Advances, Simulations, and Applications - page 8

with an acoustic lens. The stone fragments then move outside the
body through the urinary tract. Since the supersonic wave does not
attenuate easily in water and it penetrates human body and acts only
on the stone, it is possible carry out this treatment with no invasion.
Larger stone evacuation through the urinary tract may be assisted
using a stent.

1.1.6 Stereotactic Gamma Radiosurgery

This is an operation that uses high-precision irradiation of gamma
rays to treat cerebral artery deformity and a metastatic brain tumor
among others. Gamma rays are emitted from multiple sources located
in a hemisphere coniguration, and focused to the same point; the
cells in the focus are brought to morbid state. The energy of gamma
rays emitted by the individual sources is generally low avoiding
surrounding tissue damage. In case of brain cancer, the treatment is
achieved by blockading the blood low to the tumor. Arteriovenous
malformations are treated by destroying the vasculature with
abnormal morphology.

1.2 Medical Robotics

1.2.1 Control Systems

Control theory is used in robotics and automated systems to adapt
a dynamic system to obtain a desired output. The principal signals
in a control system are the reference and the output : The irst one
represents the expected behavior of the dynamic system and the
output is the resulting behavior. Conventional reference signals used
for control analysis in linear systems are the step function, ramp,
and parabolic. During the analysis, the response of the dynamic
system to these functions is analyzed. The dynamic system to
be controlled is often called the process and in linear system has
transfer function with ixed order and coeficients. The controller is
another component of the control system and has a transfer function
that is adaptable depending on the process transfer function and the
reference signal to obtain the desired output. The error signal is
deined as the difference between the output and reference signals
[22] (Fig. 1.6).