Mathematical Models of Mass Transfer in Tissue for Molecular Medicine Reversible Electroporation - Porous Media: Applications in Biological Systems and Biotechnology - page 53

a horizontal electric field that is applied to this small sample. The value of
the transmembrane potential strongly depends on the geometrical shape of
the cells. While the peaks tend to be aligned with the external field, like as
in the case of spherical cells, the breadth and amplitude of the high trans-
membrane potential region varies significantly from cell to cell. Realistic bio-
physical models of electroporation should take into account the variation of
the transmembrane potential in solid tissue, but since even theoretical mod-
els regarding a single spherical cell are currently less than satisfying, a more
comprehensive treatment of this point would probably have to be postponed.

2.4 Electrical Impedance Tomography of in vivo

Electroporation
Medical treatment procedures that are performed deep inside the body gen-
erally require some sort of a feedback mechanism to monitor and control the
procedure. Relying on the change in tissue conductivity may be an effective
method of monitoring in vivo electroporation. One modality of imaging tissue
conductivity is known as electrical impedance tomography, or EIT (Cheney
et al. 1999; Brown 2003; Bayford 2006). Electric currents are injected into
the tissue using external electrodes. These currents flow through the tissue
using the path of least resistance, which depends, amongst other things, on
the geometrical configuration of the tissue, its internal structure, the loca-
tion of the electrodes, and also on the specific conductivity distribution. By
measuring the electric potential on the boundary of the tissue using other
electrodes it is possible to estimate the path of the current and deduce the
internal conductivity distribution.
Some of the advantages of using EIT for medical imaging include the low
cost and simplicity of the hardware components of the imaging device. The
basic system only requires a low-power current source, several electrodes, a
voltage measurement device, and a signal processing unit. All of these compo-
nents are standard, low-cost devices, with the possible exception of the signal
processing unit, which can actually be separated from the other components
to simplify the system and lower its cost (Granot et al. 2008). Other medical
imaging systems such as magnetic resonance imaging, computerized tomog-
raphy, or positron emission tomography rely on special equipment with strict
requirements for several features, which make them expensive. However, the
image quality of EIT is inferior to the quality of the images produced by these
modalities particularly in terms of image resolution and contrast. These dis-
advantages can sometimes be partially compensated for by the high frame
rate of EIT, which can image the target at 30 images or more per second.
To assess the ability of EIT to image electroporated tissue we can use a
mathematical model to simulate the changes in tissue conductivity due to elec-
troporation and then simulate the measured voltages in the EIT measurement