RF/Microwave Delivery Systems for Therapeutic Applications - RF/Microwave Interaction with Biological Tissues - page 284

1 2 3 4

0

Time (min)

FIGURE 6.16 Blood perfusion of muscle as function of temperature and time.

microwave signal having a predetermined repetition rate, amplitude, and fre-
quency to elevate the temperature of a volume of the tissue to a predeter-
mined temperature and measuring the rate of decay of the temperature of
tissue (Figs. 6.16 and 6.17). This decay is indicative of the thermal conductiv-
ity of the volume of tissue and thus the fluid perfusion of that volume. Figure
6.17 depicts the system used, where the temperature change was measured
with the help of a thermocouple.
The temperature elevation in the volume of tissue should not be so great
as to damage or injure the tissue. Moreover, the tissue should not be heated
so much as to dilate the blood vessels within it, since such dilation may artifi-
cially affect the blood perfusion and thereby preclude an accurate deter-
mination of the state of the tissue. Since the purpose of the process is
diagnostic, it is critically important that the blood perfusion be determined
accurately with a minimum of disturbance to the tissue. Thus, the increase in
temperature within tissues should be no more than 1°C, and preferably less
than 0.5°C.

6.8.3 Lumen Measurement of Arteries Utilizing Microwave Apparatus

This section describes a microwave-aided balloon angioplasty catheter in
which the balloon bears a metallization pattern that allows measurements to
be made of the expanded lumen [126, 127]. Figure 6.18 illustrates the general
steps involved in the procedure. The procedure begins with the insertion of
the catheter (cable/antenna) and placement of the distal end adjacent to an
obstruction to be treated, then measured. As illustrated in Figure 6.18 a , the