Page 190 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

8.2 Approved modes for ultrasound therapy 189

FIGURE 8.3 High-intensity ultrasound emission in tissue.

of the more active areas of research and development among all the nonionizing-
energy modalities such as radiofrequency, lasers, and microwaves. One of the oldest
and possibly the most investigated area of HIFU, is the treatment of benign prostatic
hyperplasia and the treatment of prostate cancer. A number of research has estab-
lished the use of HIFU as available option for the management of prostate cancer
[21, 22]. The capability to focus energy several millimeters to centimeters away from
the transducer plane is available in HIFU system. Therefore, the location of the treat-
ment zone is accurately determined. The focused ultrasound beam can then be moved
to a different location to complete the treatment of the planned volume. MRI and
ultrasound imaging are used for image guidance and treatment monitoring. The uter-
ine fibroid treatment, breast cancer, and prostate cancer management have ultrasound
therapy sub-systems integrated into MR-imagers [12].
The ultrasound image monitoring of tissue changes during ultrasound therapy is
based on a combination of speed of sound, attenuation, stiffness, and vapor content
changes in the target region [23], including boiling detection and combined mea-
surement and modeling approaches [12]. In addition to external focused devices, a
number of other devices and systems are being developed for soft tissue coagula-
tion which are primarily used in noninvasive approaches, or through natural orifices
such as the transrectal approach for prostate treatments [24]. For example, trans-
urethral ultrasound has been proposed for heating the prostate [25], and endoscopic
treatment using an intraductal ultrasound probe has been used to treat bile duct
tumors. Treatment of hepatic and pancreatic cancer can also lead to serious compli-
cations, including fistula formation and rib necrosis with delayed rib fracture [26].
Depending on the device, as well as the cosmetic application, both thermal, as well
as nonthermal mechanisms within an ultrasound field are employed for these proce-
dures. Like other methods, HIFU applications have bioeffect complications can also
occur with unique risk-benefit considerations for each application, such as unwanted
burns and pain, cause vasospasm and hemorrhage under conditions which generate