Biomedical Engineering Reference
In-Depth Information
Figure 6.2
A half-model of soft tissue which contains a lump (See Plate 12)
restrictive assumptions and relationships are required in order to formulate the response
of the system with respect to the variation of inputs. This is particularly important when
constructing an inverse model in which information about a lump could be extracted
from the tactile image or stress distribution on the contact surface. Therefore, introducing
substitutive parameters obtained by combining several parameters is preferred.
As an example of parameter reduction: in general at least three parameters are required
to determine the size of a lump, namely height, width, and depth. Since tumors can largely
be approximated as spherical features, the number of parameters to characterize the size
of the tumors or lumps can be reduced to one value, the lump radius. The cross section of
the finite element model of a hidden mass embedded in soft tissue is shown in Figure 6.2.
In the following sections, the impact of variation of each involved parameter is pre-
sented. To demonstrate the variations of the tactile image in each case study, and to
produce clearer results than 3D graphs, the stress distribution recorded on a path defined
by a straight line passing from the middle of the bottom surface was recorded and plotted.
The variation of pressure is represented by the pressure ratio
P/P
in
,inwhich
P
is the
pressure distribution across the contact surface caused by the lump and
P
in
is the applied
pressure. This ratio, therefore, defines how much the pressure distribution is influenced
by the lump and other associated parameters.
6.4.1 The Effect of Lump Size
It is evident that early detection of any medical condition affords greater opportunities
for healthcare workers to provide effective intervention. Therefore, in this regard, early
detection of tumors (lumps) ranks as being among the most important since, particularly
in such cases, early diagnosis is often crucial to eventual efficacious treatment and cure.
In our simulation, spherical lumps of varying sizes were implanted in bulk soft tissue to
show their effect on the pressure distribution and consequently on the system output.
In this set of simulations, the diameter of the lump was changed from 2 to 8 mm
corresponding to
D/ T
≈
0.2 to
D/ T
≈
0.8inwhich
D
and
T
are the diameter of the lump
