Biomedical Engineering Reference
In-Depth Information
Fig. 20.3
Image of a liver lobule; the center shows the central vein surrounded by the sinusoids
Hall (
2006
). The hepatic microcirculation was observed with an optical device using the technique
of Orthogonal Polarization Spectral (OPS) Imaging (Cytoscan, Cytometrics, Inc., Philadelphia,
PA, USA). This device allows real-time microscopic observation of the microcirculation of organ
surfaces in vivo. The probe is gently placed on a serous organ surface and emits polarized light
with a wavelength of 550 nanometers. Light penetrates into the tissue where most of it depolarizes
and creates a virtual light source in the tissue
20.2 Methods
The general structure of the liver can be divided into a macroscopic, mesoscopic,
and microscopic part as given in Fig.
20.2
. At the macroscopic level, the human
liver is divided in segments, whereas rodent livers consist of clearly separated liver
lobes. Each lobule is connected with inflow vessels and one outflow vessel as shown
in Fig.
20.2
. Inside the liver lobule, the blood flows from the ingoing vessels (hepatic
artery and portal vein) to the outgoing vessel (hepatic vein) through sinusoids; see
the micro level in Fig.
20.2
and the OPS (orthogonal polarization spectroscopy, see,
e.g., Nadeau and Groner,
2001
) figure of the center of a lobule, see Fig.
20.3
.
20.2.1 Biphasic Material Model for Liver
The two phases, namely the solid and the fluid phase, are presented as a bipha-
sic continuum
ϕ
ϕ
F
which consists of the porous solid phase
ϕ
S
filled
with the fluid phase (blood)
ϕ
F
. Both phases are assumed to be material incom-
pressible see also Sect.
20.2.1.2
. The solid phase represents the porous tissue struc-
ture with an anisotropic pore distribution since the blood flow is assumed so, but
transversely isotropic in the direction of the vein. The fluid flow is influenced by
both the outer pressure gradient and the anisotropic permeability. Here, we use the
theory of porous media, a coupled, superimposed, continuum mechanical frame-
work.
ϕ
S
=
+
