Biomedical Engineering Reference
In-Depth Information
blood flow. Each catheter design was analyzed by placing the catheter in the
perfusion chamber, on the surface of the phantom material. The goal of the
study was to characterize the temperature profile and size of the lesions pro-
duced by various RF and microwave catheters. These data were then corre-
lated with data obtained from animals to test the validity of the results
obtained from the phantom model.
6.5
PERFUSION CHAMBER [90]
6.5.1
General Description
A perfusion chamber was constructed from 3/8-in. clear acrylic slabs. It con-
sisted of two halves which are each 10 cm in length, 4 cm in width, and 1.5 cm
in depth. The lower half was filled with phantom material through which fine
glass capillary tubes were placed every 5 mm along the length and every
2.5 mm along the depth. The phantom was separated from the top chamber by
a thin layer of cellophane to prevent it from being dissolved by the chamber
flow. The catheter of interest was placed at the center of the chamber and ade-
quate contact of the entire catheter tip with the phantom was verified by visual
inspection. The complete perfusion chamber was immersed in a saline bath
maintained at a contact temperature of 37°C. The top portion of the chamber
was perfused with 37°C saline at 4 L min
-1
via the two side ports (Fig. 6.15
a
).
Muscle-equivalent phantoms for RF or microwave were made from mix-
tures of TX150, polyethylene powder, NaCl, and water and poured into the
lower half of the perfusion chamber [91, 92]. The phantom material was
allowed to set for 30 min prior to evaluation. The RF ablation catheters eval-
uated were a 4-mm-tip Steerocath and a large-tip 8-mm catheter.
A catheter for microwave ablation was constructed with a 12-mm helical
antenna [16]. The microwave ablation catheter consists of a steerable 10F
catheter with a central flexible coaxial cable with an overall diameter of
2.413 mm (0.095 in.). At the tip of the catheter the coaxial cable terminates in
a helical antenna. The coaxial cable has an attenuation of approximately 29
dB/100 ft. Before the catheter was tested in the phantom material, it was eval-
uated on a network analyzer to confirm that the catheter radiated energy at
915 MHz.
Temperature measurements were obtained using a 12-channel Luxtron
fiber-optic thermometry system. The fiber-optic probes were inserted into the
fine glass capillary tubes at various positions to record the temperature. These
measurements were taken at depths of 0, 2.5, 5, and 7.5 mm; at lengths of
5,
0, 5, 10,15, 20, 25, and 30 mm from the tip along the length of the catheter; and
at distances of 0, 2.5, 5, 7.5, 10, 12.5, and 15 mm from the catheter at each side.
Data were recorded for a total of 90 s during each run: 30 s at baseline, 30 s
during power delivery, and 30 s during cooling.
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