Therapeutic ultrasound refers generally to the use of ultrasound for the treatment of a medical condition or for therapeutic benefit. Physiotherapeutic ultrasound was introduced into clinical practice in the 1950s, with lithotripsy introduced in the 1980s. Other uses of ultrasound for therapeutic benefit are at various stages in transitioning from research to clinical use and include: high-intensity focused ultrasound (HIFU), targeted ultrasound drug delivery, trans-dermal ultrasound drug delivery, ultrasound hemostasis, cancer therapy, and ultrasound assisted thrombolysis Ultrasound used for therapeutic benefit often use focused ultrasound waves, however, unfocused ultrasound waves may also be used.
In the above applications, the ultrasound passes through human tissue where it is the main source of the observed biological effect (the oscillation of abrasive dental tools at ultrasonic frequencies therefore do not belong to this class). The ultrasound within tissue consists of very high frequency sound waves, between 800,000 Hz and 20,000,000 Hz, which cannot be heard by humans. Some of the advantages of ultrasound as a diagnostic and therapeutic tool include its safety profile, lack of radiation, portability, and low cost. Therapeutic ultrasound in medicine ranges from extracorporeal shockwave therapy for the breaking of renal calculi to HIFU in which tumors are ablated. In the research field, use of ultrasound is being explored as a mechanism of enhancing drug delivery, sorting particles, and measuring properties of tissue. In physical therapy, there is some evidence that ultrasound is more effective than placebo treatment for treating patients with arthritis pain, a range of musculoskeletal injuries and for promoting tissue healing.
Medical uses Relatively high-energy ultrasound can break up stony deposits, ablate tissue, accelerate the effect of drugs in a targeted area, assist in the measurement of the elastic properties of tissue, and sort cells or small particles for research.
Extracorporeal Shockwave Therapy
Extracorporeal shockwave therapy involves focused, high-energy ultrasound pulses that can be used to break solid masses into fragments. This is often utilized to break up calculi such as kidney stones and gallstones into pieces small enough to be passed from the body without undue difficulty, a procedure known as lithotripsy. The success of lithotripsy depends on the size and location of the stone, and the patient's age. Oncology
Ultrasound can ablate tumors or other tissue non-invasively. This is accomplished using a technique known as high intensity focused ultrasound (HIFU), also called focused ultrasound surgery. This procedure uses generally lower frequencies than medical diagnostic ultrasound (250–2000 kHz), but significantly higher time-averaged intensities. The treatment is often guided by magnetic resonance imaging (MRI); the combination is then referred to as magnetic resonance-guided focused ultrasound. In the clinical setting, HIFU techniques are currently being investigated to treat liver, kidney, and prostatic tumors. Ophthalmology
Focused ultrasound sources may be used for cataract treatment by phacoemulsification in which the internal lens of the eye is broken down into small pieces that may then be aspirated. HIFU can also be used in ophthalmology to treat glaucoma. This is accomplished by targeting the ultrasound beams to ablate the ciliary body.
Drug Delivery
Delivering chemotherapy to brain cancer cells and various drugs to other tissues is called acoustic targeted drug delivery. These procedures generally use high frequency ultrasound (1–10 MHz) and a range of intensities (0–20 W/cm2). The acoustic energy is focused on the tissue of interest to agitate the cellular matrix and make it more permeable for therapeutic drugs. Ultrasound has been used to trigger the release of anti-cancer drugs from delivery vectors including liposomes, polymeric microspheres and self-assembled polymeric. Phonophoresis is a form of soft tissue treatment that involves the use of ultrasound combined with medication gels to enhance drug delivery to the desired area.
Vascular Surgery
Ultrasound is essential to the procedures of ultrasound-guided sclerotherapy and endovenous laser treatment for the non-surgical treatment of varicose veins. Ultrasound-guided sclerotherapy techniques are also used to treat ovarian endometriomas, especially for patients who are pregnant. Plastic Surgery
Ultrasound-assisted lipectomy involves the use of ultrasound to aid in removal of subcutaneous fat during liposuction procedures. Highly focused ultrasound waves are used to emulsify fat cells and allow for easier removal with suction.
History The first large scale application of ultrasound was around World War II. Sonar systems were being built and used to navigate submarines. It was realized that the high intensity ultrasound waves that they were using were heating and killing fish. This led to research in tissue heating and healing effects. Since the 1940s, ultrasound has been used by physical and occupational therapists for therapeutic effects.
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