Page 192 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

8.2 Approved modes for ultrasound therapy 191

8.2.2.2 Intracorporeal lithotripsy
Intracorporeal lithotripsy to treat urolithiasis means the fragmentation and removal
of urinary calculi. These procedures are performed through endoscopes in the urinary
tract. Endoscopic lithotripsy refers to the visualization of a calculus in the urinary tract
and the simultaneous application of energy to fragment the stone or stones into either
extractable or passable pieces. Many calculi in the upper urinary tract are treated with
ESWL. However, for stones that are poor candidates for this modality, endoscopic ther-
apy is indicated. Intracorporeal lithotripsy is the favored treatment for many patients,
for example, for very large stones, and many different methods and techniques have
been reported. The stone may be imaged for guidance by external ultrasound or fluoros-
copy, or by ureteroscopic, endoscopic or laparoscopic methods. The number of stones,
the size and the composition of the stones and their location are certainly the most
important factors in deciding the appropriate treatment for a patient with kidney stones.
Different probes may be used in this method. Electrohydraulic probes which gen-
erate a vaporous cavity at the tip have been used in the past (similar to the spark gap
external lithotripter but without focusing. The rigid probes may be manipulated per-
cutaneously, but some flexible probes can be applied via the ureter. Rigid ultrasonic
probes can utilize both pneumatic action at a few Hz to 1000 Hz, and ultrasonic
action at about 25 kHz [31, 32]. Some of bioeffects of intracorporeal lithotripsy are
as follows: carries risk of hemorrhage, ureteral perforation, urinary tract trauma, and
infection due to the invasive nature of the procedures.
8.2.2.3 Other ultrasound devices (kilohertz-frequency)
A) Harmonic scalpel
The Harmonic scalpel is a surgical ultrasonic instrument used to simultaneously cut
and cauterize tissue. It has a 40–80 kHz vibrating titanium rod with a static clamp
member, between which the tissue (and blood vessels) is rapidly coagulated due to
localized frictional heating [12]. The high-frequency vibration of tissue molecules
generates stress and friction in tissue, which generates heat and causes protein dena-
turation. Also, Harmonic scalpel is widely used in cosmetic surgery for the purpose
of removing excessive fat tissue [33]. The mechanism of this invasive method (ultra-
sound-assisted liposuction), involves cavitational fat cell break up with removal of
the fat emulsion by suction through the probe. Unlike electrosurgery, the harmonic
uses ultrasonic vibrations instead of electric current to cut and cauterize tissue
B) Sonicators
Sonicators are ultrasonic systems operating in the kHz-frequency regime (20–90 kHz).
They are used routinely in biological research to break up cells and tissues, as well
as in general and advanced surgical procedures for tissue cutting and hemostasis for
tissue removal.

C) Microbubbles and cavitation
Another new technic of ultrasound low frequency therapeutic is microbubble-based
therapeutic strategy. In this method, the external ultrasound exposure activates