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CHAPTER
Ultrasound applications in 8
cancer therapy
Chapter outline
8.1 Ultrasound in biomedical engineering ................................................................ 181
8.2 Approved modes for ultrasound therapy .............................................................. 186
8.2.1 Thermal ultrasound therapeutic applications ....................................186
8.2.2 Non-thermal ultrasound therapeutic applications ..............................190
8.2.3 Effects of ultrasonic waves on tissues and blood ...............................192
8.3 Governing equations .......................................................................................... 198
8.3.1 Linear ultrasonic relationships .........................................................198
8.3.2 Westervelt equation ........................................................................199
8.3.3 Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation .............................200
8.3.4 Kuznetsov equation ........................................................................200
8.4 Ultrasonic-activated drug delivery ..................................................................... 201
8.4.1 Drug carriers for ultrasound drug delivery .........................................201
8.4.2 Sonodynamic therapy (SDT) ............................................................202
8.4.3 Chemotherapy combination with ultrasound......................................203
8.4.4 Ultrasound-mediated gene transfection ............................................205
8.4.5 Transdermal drug delivery ...............................................................206
8.4.6 Cardiovascular disease ...................................................................206
8.5 Application of HIFU on thermal ablation ............................................................. 207
References .............................................................................................................. 214
8.1 Ultrasound in biomedical engineering
Ultrasound is a form of mechanical energy. Mechanical vibration at increasing fre-
quencies is known as sound energy. The normal human sound range is from 16 Hz to
something approaching 15–20,000 Hz. Sound waves are longitudinal waves consist-
ing of areas of compression and rarefaction. As the energy within the sound wave
is passed to the material, it will cause oscillation of the particles of that material.
The mechanical vibration sounds with frequency higher than the level of human
hearing is ultrasound. The frequencies used in therapy are typically between 1.0
and 3.0 MHz. Three important factors in ultrasound are frequency, wavelength, and
velocity. Ultrasound wave frequency (f) is typically 1 or 3 MHz. In an “average
tissue” the wavelength (l) would be 1.5 and 0.5 mm at 1 and 3 MHz, respectively.
In a saline solution, the velocity of US (v) is approximately 1500 m/s compared
with approximately 350 m/s in air. The velocity of US in most tissues is thought to
Bio-Engineering Approaches to Cancer Diagnosis and Treatment. http://dx.doi.org/10.1016/B978-0-12-817809-6.00008-X 181
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