SURGICAL SIMULATION
USING Haptics in Virtual Environments
B.OBULIRAJ
B.E CSE
ABSTRACT
Engineering
as it finds its wide range of application in each and every field does not have
an exception in the medical field.
Adv in instrumentation, visualization
and monitoring have enabled continual growth in the medical field. The
information revolution has enabled fundamental changes in this field. Of the
many disciplines arising from this new information era, virtual reality holds
the greatest promise. The term virtual reality was coined by Jaron Lanier,
founded of VPL research, in the late 1980’s. Virtual reality is defined as
human computer interface that simulate realistic environments while enabling
participant interaction, as a 3D digital world that accurately models actual
environment, or simply as cyberspace.
Even though virtual reality is employed
to carry out operations the surgeon’s attention is one of the most important
parameters.
In surgery, the life of the patient is of utmost importance and surgeon
cannot experiment on the patient body. So, one may think of a
technology that reduces the burdens of a surgeon by providing an efficient
interaction to the surgeon than VR. Now our dream came to reality by means of a
technology called “HAPTIC
TECHNOLOGY”.
Haptic is the “science
of applying tactile sensation to human interaction with computers”. In our
paper we have discussed the basic concepts behind haptic along with the haptic
devices and how these devices are interacted to produce sense of touch and
force feedback mechanisms. Also the implementation of this mechanism by means
of haptic rendering and contact detection were discussed.
We mainly focus on ‘Application of
Haptic Technology in Surgical Simulation and Medical Training’. Further we
explained the storage and retrieval of haptic data while working with haptic
devices. Also the necessity of haptic data compression is illustrated.
Haptic Technology
Introduction:
Haptic,
is the term derived from the Greek word, haptesthai, which means ‘to
touch’. Haptic is defined as the “science of applying tactile sensation
to human interaction with computers”.
It enables a manual interaction with real, virtual and remote
environment. Haptic permits users to sense (“feel”) and manipulate
three-dimensional virtual objects with respect to such features as shape,
weight, surface textures, and temperature.
A Haptic Device is one that
involves physical contact between the computer and the user. By using Haptic devices, the
user can not only feed information to the computer but can receive information
from the computer in the form of a felt sensation on some part of the body.
This is referred to as a Haptic interface.
In
our paper we explain the basic concepts of ‘Haptic Technology and its
Application in Surgical Simulation and Medical Training’.
Haptic Devices:
Force feedback is the area of haptics that deals with devices
that interact with the muscles and tendons that give the human a sensation of a
force being applied—hardware and software that stimulates humans’ sense of
touch and feel through tactile vibrations or force feedback.
These devices mainly consist of robotic
manipulators that push back against a user with the forces that correspond to
the environment that the virtual effector’s is in. Tactile feedback makes use of devices that
interact with the nerve endings in the skin to indicate heat, pressure, and
texture. These devices typically have
been used to indicate whether or not the user is in contact with a virtual
object. Other tactile feedback devices
have been used to stimulate the texture of a virtual object.
PHANToM and CyberGrasp are some
of the examples of Haptic Devices.
PHANTOM:
A small robot arm with three revolute joints each
connected to a computer-controlled electric DC motor. The tip of the device is
attached to a stylus that is held by the user. By sending appropriate voltages
to the motors, it is possible to exert up to 1.5 pounds of force at the tip of
the stylus, in any direction.
CYBER GRASP:
The CyberGlove is a lightweight glove with flexible
sensors that accurately measure the position and movement of the fingers and
wrist. The CyberGrasp, from Immersion Corporation, is an exoskeleton device
that fits over a 22 DOF CyberGlove, providing force feedback. The CyberGrasp is
used in conjunction with a position tracker to measure the position and
orientation of the fore arm in three-dimensional space.
Haptic
Rendering:
It is a process of applying
forces to the user through a force-feedback device. Using haptic rendering, we
can enable a user to touch, feel and manipulate virtual objects. Enhance a
user’s experience in virtual environment. Haptic rendering is process of
displaying synthetically generated 2D/3D haptic stimuli to the user. The
haptic interface acts as a two-port system terminated on one side by the human
operator and on the other side by the virtual environment.
Contact Detection
A fundamental problem in
haptics is to detect contact between the virtual objects and the haptic device
(a PHANToM, a glove, etc.). Once this contact is reliably detected, a force
corresponding to the interaction physics is generated and rendered using the
probe. This process usually runs in a tight servo loop within a haptic
rendering system.
Another
technique for contact detection is to generate the surface contact point
(SCP), which is the closest point on the surface to the actual tip of the
probe. The force generation can then happen as though the probe were physically
at this location rather than within the object. Existing methods in the
literature generate the SCP by using the notion of a god-object, which forces
the SCP to lie on the surface of the virtual object.
APPLICATIONS
OF HAPTIC TECHNOLOGY:
Haptic
Technology as it finds it wide range of Applications some among them were
mentioned below:
1.
Surgical simulation & Medical training.
2.
Physical rehabilitation.
3.
Training and education.
4.
Museum display.
5.
Painting, sculpting and CAD
6.
Scientific Visualization.
7.
Military application.
8.
Entertainment.
The role of Haptic Technology
in “Surgical Simulation and Medical
Training” is
discussed in detail below.
SURGICAL SIMULATION AND MEDICAL TRAINING:
Haptic is usually classified as:-
Human haptics: human touch perception and
manipulation.
Machine haptics: concerned with robot arms and hands.
Computer haptics: concerned with computer mediated.
A primary application area for
haptics has been in surgical simulation and medical training. Haptic rendering
algorithms detect collisions between surgical instruments and virtual organs
and render organ-force responses to users through haptic interface devices. For
the purpose of haptic rendering, we’ve conceptually divided minimally invasive
surgical tools into two generic groups based on their functions.
1. Long, thin, straight
probes for palpating or puncturing the tissue and for injection (puncture
and injection needles and palpation probes)
2. Articulated tools for pulling, clamping,
gripping, and cutting soft tissues (such as biopsy and punch forceps, hook
scissors, and grasping forceps).
A 3D computer model of an
instrument from each group (a probe from the first group and a forceps from the
second) and their behavior in a virtual environment is shown. During real-time
simulations, the 3D surface models of the probe and forceps is used to provide
the user with realistic visual cues. For the purposes of haptic rendering of
tool–tissue interactions, a ray-based rendering, in which the probe and forceps
are modeled as connected line segments. ‘Modeling haptic interactions between a
probe and objects using this line-object collision detection and response has
several advantages over existing point based techniques, in which only the tip
point of a haptic device is considered for touch interactions’.
·
Users feel torques if a proper haptic device is
used. For example, the user can feel the coupling moments generated by the
contact forces at the instrument tip and forces at the trocar pivot point.
·
Users can detect side collisions between the
simulated tool and 3D models of organs.
·
Users can feel multiple layers of tissue if the
ray representing the simulated surgical probe is virtually extended to detect
collisions with an organ’s internal layers. This is especially useful because
soft tissues aretypically layered, each layer has different material
properties, and the forces/torques reflected to the user depends on the
laparoscopic tool’s orientation.
·
Users can touch and feel multiple objects
simultaneously. Because laparoscopic instruments are typically long slender
structures and interact with multiple objects (organs, blood vessels,
surrounding tissue, and so on) during a MIS (Minimally Invasive Surgery),
ray-based rendering provides a more natural way than a purely point-based
rendering of tool-tissue interactions. To simulate haptic interactions between
surgical material held by a laparoscopic tool (for example, a catheter, needle,
or suture) and a deformable body (such as an organ or vessel), a combination of
point- and ray-based haptic rendering methods are used.
In case of a catheter insertion
task shown above, the surgical tools using line segments and the catheter using
a set of points uniformly distributed along the catheter’s center line and
connected with springs and dampers. Using our point based haptic rendering
method; the collisions between the flexible catheter and the inner surface of a
flexible vessel are detected to compute interaction forces.
The concept of distributed
particles can be used in haptic rendering of organ–organ interactions (whereas a single point is insufficient for
simulating organ–organ interactions, a group of points, distributed around the contact region, can be used) and
other minimally invasive procedures, such as bronchoscope and colonoscopy,
involving the insertion of a flexible material into a tubular body .
Deformable objects:
One of the most important
components of computer based surgical simulation and training systems is the
development of realistic organ-force models. A good organ-force model must
reflect stable forces to a user, display smooth deformations, handle various
boundary conditions and constraints, and show physics-based realistic behavior
in real time. Although the computer graphics community has developed
sophisticated models for real-time simulation of deformable objects,
integrating tissue properties into these models has been difficult. Developing
real-time and realistic organ-force models is challenging because of viscoelasticity,
anisotropy, nonlinearity, rate, and time dependence in material properties of
organs. In addition, soft organ tissues are layered and nonhomogeneous.
Tool–tissue interactions
generate dynamical effects and cause nonlinear contact interactions of one
organ with the others, which are quite difficult to simulate in real time. Furthermore, simulating surgical
operations such as cutting and coagulation requires frequently updating the
organ geometric database and can cause force singularities in the physics-based
model at the boundaries. There are currently two main approaches for developing
force-reflecting organ models:
1. Particle-based
methods.
2. Finite-element methods (FEM).
In particle-based models, an
organ’s nodes are connected to each other with springs and dampers. Each node
(or particle) is represented by its own position, velocity, and
acceleration and moves under the influence of forces applied by the surgical
instrument.
In finite-element modeling, the
geometric model of an organ is divided into surface or volumetric elements,
properties of each element are formulated, and the elements are assembled
together to compute the deformation states of the organ for the forces applied
by the surgical instruments.
Capture,
Storage, and Retrieval of Haptic Data:
The newest area in haptic is
the search for optimal methods for the description, storage, and retrieval of
moving-sensor data of the type generated by haptic devices. This
techniques captures the
hand or finger movement of an expert performing a skilled movement and “play it
back,” so that a novice can retrace the expert’s path, with realistic touch
sensation; The INSITE system is capable of providing instantaneous comparison
of two users with respect to duration, speed,
acceleration, and thumb and finger forces.
Techniques
for recording and playing back raw haptic data have been developed for the
PHANToM and CyberGrasp. Captured data include movement in three dimensions,
orientation, and force (contact between the probe and objects in the virtual
environment).
Haptic
Data Compression:
Haptic data compression and
evaluation of the perceptual impact of lossy compression of haptic data are
further examples of uncharted waters in haptics research.
Data about the user's interaction with objects in the
virtual environment must be continually refreshed if they are manipulated or
deformed by user input. If data are too bulky relative to available bandwidth
and computational resources, there will be improper registration between what
the user sees on screen and what he “feels.”
On analyzing data obtained
experimentally from the PHANToM and the CyberGrasp, exploring compression
techniques, starting with simple approaches (similar to those used in speech
coding) and continuing with methods that are more specific to the haptic data.
One of two lossy methods to compress the data may be employed: One approach is
to use a lower sampling rate; the other is to note small changes during
movement. For example, for certain grasp motions not all of the fingers are
involved.
Further, during the approaching
and departing phase tracker data may be more useful than the CyberGrasp data.
Vector coding may prove to be more appropriate to encode the time evolution of
a multi-featured set of data such as that provided by the CyberGrasp. For cases
where the user employs the haptic device to manipulate a static object,
compression techniques that rely on knowledge of the object may be more useful
than the coding of an arbitrary trajectory in three-dimensional space.
CONCLUSION:
We
finally conclude that Haptic Technology is the only solution, which provides
high range of interaction that cannot be provided by BMI or virtual reality.
Whatever the technology we can employ, touch access is important till now. But,
haptic technology along with virtual reality has totally changed this trend. We are sure
that this technology will make the future world as a sensible one.
REFERENCES:
- http://haptic.mech.nwu.edu
- http://www.webopedia.com/TERM/H/haptic.html
- http://www.stanford.edu/dept/news/report/news/2003/april2/haptics-42.html
- http://www.utoronto.ca/atrc/rd/vrml/haptics.html
- http://www.haptics-e.org/vol_02/he-v2n2.pdf
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