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Figure 1. Local impedance in action
A) Electric fish use sensors on their sides to feel the expansion and
compression of the field lines created between their head and tail. In
open ocean the field lines spread uniformly, but when an object enters
the field the field compresses. If that object’s resistivity decreases
due to heat, the field expands proportional to volume heating. B) A
local electrical field (~) is created by driving
non-stimulatory current from the tip of the catheter to the proximal
ring electrode, while voltage (V) is measured from the tip to distal
ring electrode. This allows the catheter to sense changes in volumetric
dielectric properties surrounding the tip electrode. C) In this bench
study, temperature profiles at varying depths were correlated with the
local impedance measured during RF lesion creation. Thermocouples were
placed into the tissue at the surface, at 2 mm depth, and at 4 mm depth.
The local impedance drop was seen to dynamically follow the rate of
intramural temperature rise at both low and high powers.