Therapeutic ultrasound
Encyclopedia
Therapeutic ultrasound refers generally to any type of procedure that uses ultrasound
for therapeutic benefit. This includes HIFU, lithotripsy
, targeted ultrasounddrug delivery, trans-dermal ultrasound drug delivery, ultrasound hemostasis
, and ultrasound assisted thrombolysis
.
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
: ligament
s, tendon
s, and fascia
(and also by scar tissue
).
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.
Therapeutic ultrasound is sometimes recommended for muscle as well as joint pain.
). Ultrasound has 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.
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.
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.
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).
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
for therapeutic benefit. This includes HIFU, lithotripsy
Lithotripsy
Lithotripsy refers to the physical destruction of gallstones or kidney stones. The term is derived from the Greek words meaning "breaking stones" .Forms include:* Extracorporeal shock wave lithotripsy...
, targeted ultrasounddrug delivery, trans-dermal ultrasound drug delivery, ultrasound hemostasis
Hemostasis
Hemostasis or haemostasis is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel . Most of the time this includes blood changing from a liquid to a solid state. Intact blood vessels are central to moderating blood's tendency to clot...
, and ultrasound assisted thrombolysis
Thrombolysis
Thrombolysis is the breakdown of blood clots by pharmacological means. It is colloquially referred to as clot busting for this reason...
.
Physical Therapy
Therapeutic ultrasound in physical therapy is alternating compression and rarefactionRarefaction
Rarefaction is the reduction of a medium's density, or the opposite of compression.A natural example of this is as a phase in a sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.Another...
of sound waves with a frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of >20,000 cycles/second. Therapeutic ultrasound frequency used is 0.7 to 3.3 MHz. Maximum energy absorption in soft tissue
Soft tissue
In anatomy, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body, not being bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes...
is 2 to 5 cm. Intensity decreases as the waves penetrate deeper. They are absorbed primarily by connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
: ligament
Ligament
In anatomy, the term ligament is used to denote any of three types of structures. Most commonly, it refers to fibrous tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.Ligament can also refer to:* Peritoneal...
s, tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
s, and fascia
Fascia
A fascia is a layer of fibrous tissue that permeates the human body. A fascia is a connective tissue that surrounds muscles, groups of muscles, blood vessels, and nerves, binding those structures together in much the same manner as plastic wrap can be used to hold the contents of sandwiches...
(and also by scar tissue
Granulation tissue
Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...
).
Therapeutic ultrasound may have two types of benefit: Thermal effects and non thermal effects. Thermal effects are due to the absorption
Absorption (acoustics)
Acoustic absorption is that property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to that sound energy that material reflects or conducts. Acoustic absorption is represented by the symbol A in calculations...
of the sound waves. Non thermal effects are from cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
, microstreaming and acoustic streaming
Acoustic streaming
Acoustic streaming is a steady current 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....
. 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.
Therapeutic ultrasound is sometimes recommended for muscle as well as joint pain.
Ultrasound Research at University California Santa Barbara
In 1975-1977, the first positive results of osteoblast stimulation were discovered by Harry Rabin while doing research under Dr. Stephen Horvath and Dr. JB Borgia of University of California Santa Barbara's Institute of Environmental Stress. Rabin was working on his Bachelors of Science degree in Biomedical Engineering. The concept was to vibrate a piezoelectric crystal which had similar properties to bone, at a given frequency and at low intensity, to help stimulate the growth of new bone cells. This study was done under a grant from the EPA. The experiment was performed on several rats whose femur had been deliberately fractured. Eight lab rats, including six principals and two controls, were subjected to water baths, with the former group receiving ultrasound in the baths. By subjecting all the rats to water baths, the physical stress levels in both groups remained the same irrespective of whether they actually received ultrasound. After the study data had been analyzed, it was found that the subjects receiving ultrasound showed a remarkable gain in the amount of newly generated bone cells (known as osteoblasts), versus the non-treated subjects, of over 157%. The study can be downloaded from UCSB IES archive number IES3426728836393.ucsb.77.PDFUltrasound drug delivery
Ultrasound has been used in various drug delivery applications to enhance the delivery of pharmaceuticals to target tissues (Acoustic Targeted Drug DeliveryAcoustic Targeted Drug Delivery
Acoustic targeted drug delivery is a method that uses ultrasound energy to enhance the transport of molecules into and/or across specific tissues...
). Ultrasound has 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.
Therapeutic ultrasound convection enhanced delivery
Effects of exposure to 1.58 MHz 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.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.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.
Therapeutic ultrasound assisted brain drug delivery or Acoustic Targeted Drug Delivery
Acoustic Targeted Drug Delivery
Acoustic targeted drug delivery is a method that uses ultrasound energy to enhance the transport of molecules into and/or across specific tissues...
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.
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).
External links
- Watson, T. (2006). "Therapeutic Ultrasound". (see here for a pdf version with the author and date information)
- International Society for Therapeutic Ultrasound
- Ultrasound Use in Physiotherapy