Therapeutic ultrasound delivers mechanical vibration above the upper threshold of human hearing. Studies have demonstrated its biological effects at a cellular level, including angiogenesis and leukocyte adhesion.
Ultrasound has grown far beyond its diagnostic roots to become an adaptable therapeutic technology used by physicians across many specialties. Physical therapists frequently utilize low-intensity therapeutic ultrasound for injuries to muscles and bones.
1. 1. 3 MHz
Therapeutic ultrasound (US) falls within the umbrella of Physiotherapy Modalities; however it should not technically be considered electro therapy. US is a form of mechanical energy and produces sound waves beyond normal hearing range (16Hz-20kHz), at frequencies from one to three MHz (1MHz = Million cycles per second).
US can not only be used to interact with tissues in the presence of water or body fluids, but can also be employed to manipulate particles of matter using its ability to cause molecular vibrations. Acoustic tweezers use this principle for example in order to separate, concentrate and manipulate microparticles or biological cells.
Therapeutic ultrasound treatment of soft tissue structures typically entails using a metallic probe that contacts the skin, along with application of gel that enables sound waves to penetrate evenly across the treatment area. Once placed, it may then be moved over the area of interest for approximately 10 minutes before repeated this process again.
Acoustic energy can stimulate physiological processes within tissues. Mechanical stimulation of tissue may result in increased proliferative activity of cells and an accelerated healing response, possibly as a result of effects such as cell permeability enhancement and increasing membrane potentials.
Other effects are due to the thermal properties of acoustic energy. When applied for short duration (2-5 minutes) this form of therapy can produce localized increases in tissue temperature; however, at higher intensities or longer durations this effect is less likely to take place.
Acoustic energy may also be directed at specific parts of the body where there is injury or dysfunction, such as extracorporeal shockwave lithotripsy for treating kidney stones; ultrasound can also be used for muscle spasms such as Piriformis syndrome treatment.
Studies have demonstrated the therapeutic effects of ultrasound are dependent on its intensity and duration of application, with clear dose-response relationships for human muscle heating using 1 MHz and 3 MHz therapeutic ultrasound treatments, measured by tissue temperature increases after 10 minute treatment sessions. Below is a table displaying these rates of heating using both therapeutic ultrasound frequency bands.
2. 1. 1 MHz
Physiotherapists utilize therapeutic ultrasound for various indications, including acute injuries, sports medicine injuries and chronic pain. Ultrasound therapy uses mechanical vibration to stimulate tissue acuity while simultaneously encouraging the release of anti-inflammatory mediators which reduce pain while increasing metabolism and blood flow. Furthermore, ultrasound may facilitate micro cellular repair through cavitation or sono-echo effects on micro level repair processes.
Therapeutic ultrasound typically operates between three and one megahertz (millions of cycles per second). As frequency increases, more energy can penetrate deeply. Conversely, lower frequencies provide superficial energy delivery.
Physiotherapists must select an appropriate frequency and intensity level for treatment in their treatment area, in order to achieve desired physiological or therapeutic effects without overheating the tissue.
Before applying therapeutic ultrasound treatment on a wound, the area must be free of dressing residue or debris that might block its absorption by ultrasound waves. A physiotherapist must always check for signs of infection, rash or active bleeding as well as ensure there are no medical devices like pacemakers in its vicinity.
An ultrasound therapeutic session typically begins with the patient lying on a treatment table in a darkened room and being treated by their therapist, who applies ultrasound gel directly onto their transducer and positions it over their target area, before adjusting intensity levels as needed and treating for approximately 10 minutes.
If a physiotherapist wants to treat an area that is deeper, they should use a one megahertz setting in order to avoid overheating of superficial tissues. For more superficial settings they may wish to switch up and use three megahertz instead.
Physiotherapists must also understand that when soundwaves hit tissue, a process called attenuation occurs which reduces the intensity of energy that reflects back off its surface due to differences in density and permeability of body tissues. Because this may vary for every patient depending on his/her diagnosis and pathology, as well as whether therapeutic ultrasound should be considered diagnostic ultrasound, planning sessions with therapeutic ultrasound is crucial to ensure all therapeutic outcomes are being reached successfully.
3. 1. 3 MHz
Ultrasound has long been used as a diagnostic modality to assess tissue status. Recently, however, technological advancements have enabled ultrasound to also serve as a therapy modality for treating musculoskeletal injuries and conditions. Therapeutic ultrasound differs significantly from diagnostic ultrasound in that its purpose is stimulating physiological processes rather than simply imaging tissue status.
Therapeutic ultrasound works by applying mechanical vibration through an acoustic wave to tissue, altering its cell structure by oscillating water molecules within it and stimulating collagen tissue production and increasing blood circulation in an area.
Therapeutic ultrasound requires the use of an additional coupling medium in order to transmit waves from the transducer to target tissues, usually in the form of a gel that can be easily and safely applied onto skin surfaces. Though various types of gels have been tried out for clinical applications, most physicians advise selecting non-greasy hypoallergenic gel as an ideal medium to ensure efficient transmission of acoustic energy.
Acoustic waves may be targeted to specific tissue structures without impacting surrounding tissues and organs, for instance targeting an abnormal growth in the uterus to kill cancer cells without harming any nearby tissues or organs – this therapeutic ultrasound treatment method is known as high-intensity focused ultrasound (HIFU).
For most musculoskeletal injuries, therapeutic ultrasound should be applied at frequencies between 0.5 and 2.5 W/cm squared and up to 1 megahertz for continuous or pulsed mode use for up to 10 minutes in either mode; studies have also revealed that higher intensities and longer therapy sessions may enhance healing by increasing collagen deposition and wound breaking strength.
4. 1. 1 MHz
Therapeutic ultrasound employs mechanical vibration to initiate healing at a cellular level, helping reduce pain, promote circulation and mobilize soft tissue. Physical therapists utilize this non-invasive form of therapy in order to decrease discomfort levels, promote blood flow and mobilize soft tissues more effectively. Furthermore, ultrasound has shown promise as an anti-inflammatory treatment and speed up healing time in certain conditions – making it suitable for sports medicine, surgery augmentation as well as treating acute and chronic pain conditions.
Frequency is of vital importance in ultrasound waves because it determines their depth of penetration and thermal effects, as well as providing a measurement of mechanical vibration speed. Low frequencies may provide shear waves which cause faster evaporation of water molecules in skin tissues and deeper tissues.
Therapeutic ultrasound has long been recognized for its use in manipulating soft tissues, such as joint mobilization. Additionally, ultrasound can also be employed for atrial ablation, extracorporeal shockwave lithotripsy, fracture healing, limited rhytidectomy and to speed the release of thrombolytic agents during stroke recovery (Ultrasound-enhanced systemic thrombolysis or uEST).
Most ultrasound machines are handheld devices that use piezoelectric crystals to emit sound energy and a hypoallergenic contact gel to transmit it into tissues of the body. A therapist holds the transducer over an area requiring treatment, applying gentle circular movements with it.
Ultrasound frequency of 1 MHz is widely utilized and has been found effective for producing thermal changes and producing desired treatment responses in various clinical studies.
Studies suggest it is ideal to treat an area of tissue that is two times the size of the ultrasound probe’s soundhead, ensuring most of its surface area is exposed to ultrasound waves for maximum thermal effects.
Another indicator of ultrasound intensity is pulse ratio. A pulse ratio between 10ms and 40ms total pulse duration is considered high intensity; lower pulse ratios (1-3mHz) indicate lower intensities.
