Biomedical Engineering Reference
In-Depth Information
6
Lump Detection
6.1 Introduction
Palpation is the act of feeling with the hand. Primarily, it is the application of the fingers
with light pressure to the surface of the body in order to determine the condition of the
parts beneath for the purposes of physical diagnosis. It is this crucial and fundamental
feature, however, that is missing in the current field of haptics as well as MIS (minimally
invasive surgery) and robot-assisted surgery. Palpation is routinely used by surgeons in
open surgery to differentiate between abnormal and normal tissues, or to detect the type
of tumor based on biological tissue composition and consistency, which often varies from
one tissue to another due to various diseases [1]. The localization of hidden anatomical
features has been the subject of some research [2 - 6] though these studies have largely
been focused on breast cancers, hence these findings cannot be directly used in either
haptics or robotic surgical applications. Kattavenos
et al
. [7] reported the development
of a tactile sensor for recording data when the sensor is swept over a phantom sample
containing simulated tumors although no information regarding the size and depth of any
lump was extracted from this data.
This chapter presents a hyperelastic finite element model of a slab of soft tissue embed-
ded with a lump, from which the effects of various parameters, such as tissue thickness,
size of the lump, relative Young's modulus of tissue and lump, and the distance of the
lump from the surface of the tissue is investigated. These results will help us to better
interpret any tactile information that is collected from a smart endoscopic grasper holding
tissue in which a lump is embedded.
6.2 Constitutive Equations for Hyperelasticity
The conventional theory of elasticity is primarily based on infinitesimal strains, in which
linear elastic assumptions are applied. For finite deformations, however, these assumptions
are not valid and, in general, the response of the material is different from that of the linear
theories. Any material that can experience a recoverable large elastic strain is referred to
as being hyperelastic and for which the following Helmholtz free-energy function:
ψ
=
ψ (C)
=
ψ
I
[
I
1
(C) ,I
2
(C) ,I
3
(C)
]
=
ψ
λ
(λ
1
,λ
2
,λ
3
)
