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Ultrasound (Therapeutic)

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Therapeutic ultrasound refers generally to any type of procedure that uses ultrasound for therapeutic benefit. This includes HIFU, lithotripsy, targeted ultrasound drug delivery, trans-dermal ultrasound drug delivery, ultrasound hemostasis, and ultrasound assisted thrombolysis.[1]

Physical Therapy

Therapeutic ultrasound in physical therapy is alternating compression and rarefaction of sound waves with a frequency of >20,000 cycles/second. Therapeutic ultrasound frequency used is 0.7 to 3.3.MHz.Maximum energy absorption in soft tissue is 2 to 5 cm. Intensity decreases as the waves penetrate deeper. They are absorbed primarily by connective tissue: ligaments, tendons, and fascia (and also by scar tissue).[2]

Therapeutic ultrasound may have two types of benefit: Thermal effects and non thermal effects. Thermal effects are due to the absorption of the sound waves. Non thermal effects are from cavitation, microstreaming and acoustic streaming. Cavitational effects result from the vibration of the tissue causing microscopic air 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.[3]

Therapeutic ultrasound is sometimes recommended for muscle as well as joint pain, although some evidence suggests it may not be effective for this purpose.

Ultrasound drug delivery

Ultrasound has been used in various drug delivery applications to enhance the delivery of pharmaceuticals to target tissues (Acoustic Targeted Drug Delivery). Ultrasound been shown to facilitate the delivery of drugs across the skin, promote gene therapy to specific tissues, deliver chemotherapeutic drugs into tumours and deliver thrombolytic drugs into blood clots. In addition, ultrasound has also been shown to facilitate the healing of wounds and bone fractures.[4]

Therapeutic ultrasound convection enhanced delivery

Effects of exposure to 1.58MHz focused ultrasound on transport of drug in soft tissues are enhanced when an external pressure gradient is applied to induce convective flow through the tissue. Drug uptake and transport have been measured in equine brain, avian muscle and agarose brain-mimicking phantoms. Results show that ultrasound enhances drug uptake and transport, and the greatest enhancement occurs when the external pressure gradient is applied. One theory, currently being tested at Cornell, is that exposure of the brain parenchyma to ultrasound enhances penetration of material infused into the brain during convection enhanced delivery therapy.[5]

Therapeutic ultrasound assisted drug delivery to the brain and brain tumours

Medical treatment for brain tumours may combine radiation therapy with the surgical removal of part of the skull and the excision of the tumour. After resecting the tumour, before replacing the skull section, the surgeon may implant a thin, drug-encapsulated wafer that diffuses chemotherapy agent over time to help ensure that no remaining tumour cells survive.[6]

This approach is too often unsuccessful, and brain cancers like neuroblastomas and neurofibromatosis remain the leading cause of cancer-related death in people under the age of 35. Part of the problem may be that cancerous cells migrate beyond the range of the slowly diffusing drugs.[7]

Therapeutic ultrasound assisted brain drug delivery or Acoustic Targeted Drug Delivery is currently being studied to enhance the success of chemotherapy treatments to brain cancer cells. Scientists are using Therapeutic Ultrasound to increase the distribution of chemical dye agents into brain tissue, to help brain tissue absorb chemotherapy drugs faster. Researchers have found that the use of Therapeutic Ultrasound enhances the chemotherapy delivery and also reduces the time necessary for the drug to work.[8]

It is believed that when focused ultrasound is applied to the brain it agitates the tissues matrices causing enhanced permeability for the drug, and by mechanically pushing it with radiation forces where the acoustical waves are focused. The drugs can then spread further and faster into the tissues than by unassisted diffusion alone. Doctors and scientists hope to use these techniques to increase the effectiveness of chemotherapy as well as reduce the time it takes for the drugs to work in a given patient (e.g., to reach the cancerous brain tissue quickly and before the cells can migrate and regenerate).[9]


  1. Therapeutic Ultrasound: A Promising Future in Clinical Medicine
  2. Watson, T. (2006). "Therapeutic Ultrasound". (see here for a pdf version with the author and date information)
  3. Wilkin, H. D., et al. (2004). Influence of Therapeutic Ultrasound on Skeletal Muscle Regeneration Following Blunt Contusion. International Journal of Sports Medicine, 25, 73-77.
  4. Healing sound: the use of ultrasound in drug delivery and other therapeutic applications. -Mitragotri S.
  5. [ Ultrasound Enhancement of Drug Delivery to Soft Tissues- George Lewis Jr. et al.]
  6. Acoustic chemotherapy delivery for brain cancer - Lewis Jr. et al.
  7. Acoustics and brain cancer - Acoustical Society of America
  8. A phantom feasibility study of acoustic enhanced drug perfusion in neurological tissue- Lewis Jr. et al.
  9. Acoustic targeted drug delivery in neurological tissue - Lewis Jr. et al.

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