الفهرس 
• Principles of high intensity focused ultrasoundOnly 14 pages are availabe for public view
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Abstract
Summary:
One of the medical field’s aspirations is to provide patients with minimally
invasive therapy. With such therapy, infection and blood loss is minimized,
procedure and recovery time is shortened, and procedures can be offered on an
outpatient basis. HIFU is an extracorporeal non invasive method for tumor
ablation.
Ultrasound beam can travel through the body and reach area of targeted
tissue which is deep within the body. Focusing this beam makes the acoustic
energy at the focal region much higher compared with the region outside the focus.
As a result, the energy deposition in the tissue along the US beam path which
locates outside the focal region is so low that be difficult to induce the tissue
damage. Accordingly, the tissues including tumors at the focal region would
absorb enough energy of US beam causing heat generation and inducing tissues
damage by producing coagulation necrosis if the temperature in the tissue is raised
to 60°C or higher for 1 second or longer.
Cooling intervals are needed between each sonication so that the tissue
anterior and, to a lesser extent, posterior to the focal spot cool between sonications,
allowing further sonications to be placed closer to the first one without any damage
to the intervening tissues.
Advanced imaging modalities as MRI, US and elasticity imaging make the
potential of HIFU for clinical use greatly enhanced by combining HIFU treatment
with imaging guidance allowing accurate HIFU dose delivery to the target tissue
with minimal damage to the surrounding normal tissue and to evaluate the tissue
response to HIFU treatment.
HIFU is approved for treatment of many solid tumors. Transrectal HIFU
ablation has become a reasonable option for the treatment of localized prostate
cancer in non-surgical patients, with 5-year disease-free survival similar to that of
radiation therapy. It is also a promising salvage therapy of local recurrence after
radiation therapy. HIFU is performed as an outpatient procedure, usually
under epidural anesthesia.
Several studies have indicated that HIFU treatment and magnetic resonance–
guided focused ultrasound surgery (MRgFUS) are safe, effective, and feasible in
clinical applications for treatment of uterine fibroids. MRgFUS allows a patient to
return to normal everyday life 1–2 days after treatment. When compared with
hysterectomy (which reports a 6 to 8 week return), or uterine artery embolization
(8 days after which patients return to normal activity).
HIFU has the potential of eliminating the invasiveness of current ablative
treatment of hepatic masses and the complications of placing needles and probes
into an oftentimes more widely diseased liver. It is reported that HIFU can achieve
complete tumor necrosis even when the lesion is located adjacent to the major
hepatic blood vessels. The main advantage of HIFU over other conventional
thermal ablation techniques such as RFA is that it does not require puncturing the
tumor, thereby avoiding the risk of bleeding or seeding of tumor cells along the
needle tract
HIFU ablation of renal tumors in humans remains in the early stages of
clinical trials.
In brain two mechanisms underlying HIFU-induced cell destruction were
proposed: direct effect by ultrasound and indirect effect by drugs delivered through
ultrasound-modified blood-brain barrier.
In breast cancer using HIFU treatment is attempting to try to replace
conventional surgery with a completely noninvasive procedure maintaining
efficacy and reducing the cosmetic impact of surgery with allowing patients to
have an outpatient treatment.
HIFU insonation in bone rapidly heats the targeted bone cortex, and
subsequently the adjacent periosteum and the tumor tissue. In addition, the high
absorption and the low conductivity of bone tissue lead to a localized effect within
the targeted ultrasound beam. HIFU ablation results in fewer complications and
well-preserved limb function because there were no surgical traumas and blood
vessels > 2 mm in diameter were retained, which could be beneficial to
revascularization and the repair of inactivated tumor bones.
Because of most of the patients with pancreatic cancer are not suitable for
surgery when the diagnosis is made therefore HIFU ablation may be used to extend
the life expectancy and improve the quality of life. HIFU treatment of pancreatic
tumors indeed relieves pancreatic adenocarcinoma- related pain and focally ablates
malignant tissue.