Therapeutic ultrasound refers generally to any type of ultrasonic procedure that uses

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

for

therapeutic A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health problem, usually following a medical diagnosis. As a rule, each therapy has indications and contraindications. There are many different ...

benefit. Physiotherapeutic ultrasound was introduced into clinical practice in the 1950s, with

lithotripsy Lithotripsy is a non-invasive procedure involving the physical destruction of hardened masses like kidney stones, bezoars or gallstones. The term is derived from the Greek words meaning "breaking (or pulverizing) stones" ( litho- + τρίψω r ...

introduced in the 1980s. Others are at various stages in transitioning from research to clinical use:

HIFU High-intensity focused ultrasound (HIFU) is a non-invasive therapeutic technique that uses non-ionizing ultrasonic waves to heat or ablate tissue. HIFU can be used to increase the flow of blood or lymph or to destroy tissue, such as tumors, via ...

, targeted ultrasound drug delivery, trans-dermal ultrasound drug delivery, ultrasound

hemostasis In biology, hemostasis or haemostasis is a process to prevent and stop bleeding, meaning to keep blood within a damaged blood vessel (the opposite of hemostasis is hemorrhage). It is the first stage of wound healing. This involves coagulation, whi ...

cancer therapy Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

, and ultrasound assisted

thrombolysis Thrombolysis, also called fibrinolytic therapy, is the breakdown (lysis) of blood clots formed in blood vessels, using medication. It is used in ST elevation myocardial infarction, stroke, and in cases of severe venous thromboembolism (massive p ...

It may use focused ultrasound (FUS) or unfocused ultrasound. 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. 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 power ultrasound can break up stony deposits or tissue, accelerate the effect of drugs in a targeted area, assist in the measurement of the elastic properties of tissue, and can be used to sort cells or small particles for research. * Focused high-energy ultrasound pulses can be used to break calculi such as kidney stones and gallstones into fragments small enough to be passed from the body without undue difficulty, a process known as

. * Focused ultrasound sources may be used for

cataract A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...

treatment by

phacoemulsification Phacoemulsification is a modern cataract surgery method in which the eye's internal lens is emulsified with an ultrasonic handpiece and aspirated from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution to maintain ...

. * Ultrasound can

ablate Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft material for ...

tumors or other tissue non-invasively. This is accomplished using a technique known as High Intensity Focused Ultrasound (HIFU), also called ''focused ultrasound surgery'' (FUS 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'' (MRgFUS). ATDD Topical Application

* Delivering chemotherapy to brain cancer cells and various drugs to other tissues is called acoustic targeted drug delivery (ATDD). 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 its 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. * Ultrasound is essential to the procedures of ultrasound-guided

sclerotherapy Sclerotherapy (the word reflects the Greek ''skleros'', meaning ''hard'') is a procedure used to treat blood vessel malformations (vascular malformations) and also malformations of the lymphatic system. A medicine is injected into the vessels, wh ...

and

endovenous laser treatment Endovenous laser treatment (ELT) is a minimally invasive ultrasound-guided technique used for treating varicose veins using laser energy commonly performed by a phlebologist, interventional radiologist or vascular surgeon. Methods Endovenous las ...

for the non-surgical treatment of varicose veins. * Ultrasound-assisted lipectomy is Liposuction assisted by ultrasound. There are three potential effects of ultrasound. The first is the increase in blood flow in the treated area. The second is the decrease in pain from the reduction of swelling and edema. The third is the gentle massage of muscle tendons and/ or ligaments in the treated area because no strain is added and any scar tissue is softened. These three benefits are achieved by two main effects of therapeutic ultrasound. The two types of effects are: thermal and non thermal effects. Thermal effects are due to the absorption of the sound waves. Non thermal effects are from

cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...

, microstreaming and

acoustic streaming Acoustic streaming is a steady flow in a fluid driven by the absorption of high amplitude acoustic oscillations. This phenomenon can be observed near sound emitters, or in the standing waves within a Kundt's tube. Acoustic streaming was explaine ...

. Cavitational effects result from the vibration of the tissue causing microscopic bubbles to form, which transmit the vibrations in a way that directly stimulates cell membranes. This physical stimulation appears to enhance the cell-repair effects of the inflammatory response.

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.

Physical therapy

Ultrasound is applied using a transducer or applicator that is in direct contact with the patient's skin. Gel is used on all surfaces of the head to reduce friction and assist transmission of the ultrasonic waves. Therapeutic ultrasound in physical therapy is alternating

compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...

and rarefaction of sound waves with a

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

of 0.7 to 3.3

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

. Maximum energy absorption in

soft tissue Soft tissue is all the tissue in the body that is not hardened by the processes of ossification or calcification such as bones and teeth. Soft tissue connects, surrounds or supports internal organs and bones, and includes muscle, tendons, ligam ...

occurs from 2 to 5 cm. Intensity decreases as the waves penetrate deeper. They are absorbed primarily by

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal li ...

tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

s, and fascia (and also by

scar tissue Scar tissue may refer to: Medicine * Scar, an area of fibrous tissue that replaces normal skin after injury * Granulation tissue, a product of healing in major wounds Film and television * ''Scar Tissue'' (1975 film), or ''Wanted: Babysitter'' ...

). Conditions for which ultrasound may be used for treatment include the following examples: ligament

sprain A sprain, also known as a torn ligament, is an acute soft tissue injury of the ligaments within a joint, often caused by a sudden movement abruptly forcing the joint to exceed its functional range of motion. Ligaments are tough, inelastic fibers ...

s, muscle strains,

tendonitis Tendinopathy, a type of tendon disorder that results in pain, swelling, and impaired function. The pain is typically worse with movement. It most commonly occurs around the shoulder ( rotator cuff tendinitis, biceps tendinitis), elbow ( tennis e ...

, joint inflammation,

plantar fasciitis Plantar fasciitis or plantar heel pain (PHP) is a disorder of the plantar fascia, which is the connective tissue which supports the arch of the foot. It results in pain in the heel and bottom of the foot that is usually most severe with the f ...

metatarsalgia Metatarsalgia, literally metatarsal pain and colloquially known as a stone bruise, is any painful foot condition affecting the metatarsal region of the foot. This is a common problem that can affect the joints and bones of the metatarsals. Meta ...

, facet irritation,

impingement syndrome Shoulder impingement syndrome is a syndrome involving tendonitis (inflammation of tendons) of the rotator cuff muscles as they pass through the subacromial space, the passage beneath the acromion. It is particularly associated with tendonitis of t ...

, bursitis,

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...

osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...

, and scar tissue adhesion. There is no evidence to support the use of ultrasound for the treatment of low back pain, and current clinical guidelines recommend that ultrasound is not used for this condition. Ultrasound used for calcific tendonitis had a positive short term effect. For the long term, there was no significant difference with ultrasound use. This shows that for pain relief and short-term treatment ultrasound can be an effective treatment for Calcific Tendonitis A review with five small placebo‐controlled trials from 2011, did not support the use of ultrasound in the treatment of acute ankle sprains and the potential treatment effects of ultrasound appear to be generally small and of probably of limited clinical importance, especially in the context of the usually short‐term recovery period for these injuries. A meta-analysis found that ultrasound therapy is effective in reducing pain, increasing ROM, and reducing WOMAC functional scores in patients with knee osteoarthritis.

Research tools

Acoustic tweezers Acoustic tweezers (or acoustical tweezers) are used to manipulate the position and movement of very small objects with sound waves. Strictly speaking, only a single-beam based configuration can be called acoustical tweezers. However, the broad con ...

is an emerging tool for contactless separation, concentration and manipulation of microparticles and

biological cells The cell is the basic structural and functional unit of life forms. Every cell consists of a cytoplasm enclosed within a membrane, and contains many biomolecules such as proteins, DNA and RNA, as well as many small molecules of nutrients an ...

, using ultrasound in the low MHz range to form standing waves. This is based on the acoustic radiation force which causes particles to be attracted to either the

nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two ...

or anti-nodes of the standing wave depending on the

acoustic contrast factor The acoustic contrast factor is a number used to describe the relationship between the densities and the sound velocities (or, equivalently because of the form of the expression, the densities and compressibilities) of two media. It is most ofte ...

, which is a

function Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

of the sound velocities and

densities Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek language, Greek letter Rho (letter), rho), although the Latin letter ''D'' ca ...

of the particle and of the medium in which the particle is immersed. * Application of focused ultrasound in conjunction with microbubbles has been shown to enable non-invasive delivery of

epirubicin Epirubicin is an anthracycline drug used for chemotherapy. It can be used in combination with other medications to treat breast cancer in patients who have had surgery to remove the tumor. It is marketed by Pfizer under the trade name Ellence in ...

across the

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of ...

in mouse models and non invasive delivery of GABA in non human primates.

Research

* Using ultrasound to generate cellular effects in soft tissue has fallen out of favor as research has shown a lack of efficacy and a lack of scientific basis for proposed biophysical effects. * According to a 2017 meta-analysis and associated practice guideline, Low intensity pulsed ultrasound should no longer been used for bone regeneration because high quality clinical studies failed to demonstrate a clinical benefit. * An additional effect of low-intensity ultrasound could be its potential to disrupt the

for drug delivery. * Transcranial ultrasound is being tested for use in aiding

tissue plasminogen activator Tissue plasminogen activator (abbreviated tPA or PLAT) is a protein involved in the breakdown of blood clots. It is a serine protease () found on endothelial cells, the cells that line the blood vessels. As an enzyme, it catalyzes the conversion ...

treatment in

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

patients in the procedure called ultrasound-enhanced systemic thrombolysis. * Ultrasound has been shown to act synergistically with antibiotics in killing bacteria. * Ultrasound has been postulated to allow thicker eukaryotic cell tissue cultures by promoting nutrient penetration. * Long-duration therapeutic ultrasound called sustained acoustic medicine is a daily slow-release therapy that can be applied to increase local circulation and theoretically accelerates healing of musculoskeletal tissues after an injury. However, there is some evidence to suggest this may not be effective.

References

External links

* * * {{cite web , url = http://www.istu.org/ , title = International Society for Therapeutic Ultrasound Medical ultrasonography Athletic training