Ultrasound (Therapeutic machine)

Introduction

The term “ultrasound” describes mechanical vibrations that are fundamentally higher frequency versions of sound waves. Since these waves are inaudible to humans, they are referred as “ultrasonic”.
Ultrasonic frequencies range from 20kHz to 10GHz, Whereas normal sound waves ranges from 20Hz to 20,000Hz.
Despite being produced electrically, ultrasound is not precisely an electrotherapy because it is a mechanical vibration.

The use of ultrasound in tissues can result in both mechanical and thermal effects. It has been discovered that ultrasound heats tissues with high collagen content, including fascia, ligaments, and tendons.
It can change the tensile strength to allow for higher extensibility and separate the collagen fibers.

Definition

Wavelength

The distance between the two nearest points on a wave that are moving in the same direction at any given moment is known as the wavelength.

Frequency

The number of times a particle completes a cycle in a second is known as its frequency.

Velocity

The speed at which a wave travels through a medium is known as its velocity, and it varies according to the physical properties of the medium.
Water is an excellent sound-transmitter, whereas air is a poor transmitter.

The production of Ultrasound

A solid, liquid, or gaseous media is mechanically vibrated to create sound and ultrasonic waves.
In order to generate therapeutically useful high frequency ultrasonic waves, mechanical oscillation frequencies between 1MHz to 3MHz are required.

One million cycles per second of vibration is required for a machine to operate at 1 MHz. A crystal made of quartz or barium titanium is used to accomplish this.

Piezoelectrical crystals are crystalline solids with the unique ability to alter their thickness in response to an applied voltage.When a piezoelectric crystal is exposed to an alternating voltage, it will vibrate at the voltage’s frequency.

Either a quartz crystal or a barium titanium crystal is used to do this.
The term “Piezo-electric effect” refers to how these crystals change when exposed to a fluctuating potential differential.

The parts of a therapeutic ultrasound

Parts of therapeutic ultrasound

A transducer circuit or treatment head receives high frequency current from a source and receives it via coaxial wire.

A linking electrode within the transducer circuit applies high frequency current to the crystal, fusing it to the treatment’s metal front plate.

Any alteration in the crystal’s form results in movement of the metal front plate, which generates an ultrasonic wave.

Reflection of ultrasound

Sound travels according to the rules of reflection, and reflection occurs when an ultrasonic beam passing through one medium comes into contact with another that prevents it from passing through.

In order to minimize reflection during ultrasonic therapy, extreme caution should be taken to avoid leaving air between the treatment head and the patient. This is because air cannot transfer ultrasonic waves.

Attenuation (Reduction) of ultrasound

The gradual reduction in intensity of ultrasound after leaving the treatment head is known as attenuation.

There are two major factors contribute the attenuation :

• Absorption
• Scattering

Absorption : The energy of ultrasound is converted into heat by the tissues, through the absorption of the ultrasonic beam. Thus, these reduces the intensity of ultrasound.

Scattering : The air bubble that is present during interphase causes reflection and refraction, which lowers the ultrasound’s intensity within the tissue.

The ultrasound’s intensity is reduced by a constant fraction every cm due to these two factors, resulting in a reduction of the ultrasound’s intensity to “half” at a specific depth below the surface. This depth is called “half – value thickness”

Normally the half-value thickness varies for soft tissues. It is different for every machine, for 1MHz it is approx 4cm and for 3MHz it is approx 2.5cm.

Coupling medium

Since air cannot transmit ultrasonic waves, a couplant that can transmit ultrasonic waves should be positioned between the treatment head and the patient’s skin.

Even though when the most efficient couplant is applied the dose is reduced by quarter.

Since air transmits zero ultrasonic wave, the ultrasonic waves are reflected back to transducer which can damage the crystals inside the transducer.

pulse ultrasound

The majority of ultrasonic generators let users choose between an ultrasound output that is continuous or pulsed. An 8-millisecond pause occurs after 2 milliseconds of ultrasonic pulse, although certain devices may vary in this regard. 

Ultrasonic waves effects

Thermal (heat) effects

Heat is produced when the ultrasonic waves are absorbed and transformed into thermal energy.
The quantity of heat generated is depend upon many elements, including the frequency with which the transducer head passes over a portion and the space-averaged intensity used.

Mechanical effects

The pressure changes that the sound waves apply to the tissues results in a mechanical effects.

Mostly there are two types of mechanical effects:

• Cavitation
  • Stable cavitation
  • Transient cavitation .
• The micromassage effect.

Cavitation

Cavitation is a situation when insonation causes a gas bubble to form in the tissues.

Stable cavitation: As long as the gas bubbles remain intact and vibrate in the ultrasonic field without harming the tissues, stable cavitation is safe.

Transient cavitation: Because the bubble expands and collapses quickly in the ultrasonic beam and is believed to raise temperature dramatically, thus transient cavitation poses a risk to the tissues.

The micro massage effect.

Similar to massage, this is said to affect the fluids between cells, which in turn lowers oedema.

Biological and chemical effects

Acoustic streaming

The ultrasonic beam creates a phenomenon known as acoustic streaming. The flow of tissue components is unidirectional and mostly happens at the cell membrane. 
As streaming has been seen to alter the rate of protein synthesis, it is possible that streaming contributes to stimulation repair.

Applications (Uses) of Ultrasound

The course of treatment involves treating orthopedic injuries.

• Bursitis
• Frozen shoulder
• Tendonitis
• Tears and muscular strains
• Muscle spasm
• Osteoarthritis
• Myofascial Pain
• Rheumatoid arthritis.

Recent injuries and inflammation

Following soft tissue injuries, ultrasound is frequently employed because of its mechanical properties, which helps to eliminate traumatic exudate and lower the risk of adhesion development. Increased protein synthesis speeds up the process of mending injured tissues.

Scar tissue

There have been claims that using ultrasound makes scar tissue flexible, thereby enabling more successful stretching of constricted scars.
If the scar is tightly attached to underlying tissues, ultrasonography may be useful in releasing it.

Indurated chronic oedema

Ultrasound’s mechanical action affects it and helps in the treatment of chronic oedema. Moreover, it dissolves adhesions that have developed between nearby structures.

Dangers

Burns

Excess heat can build up in the tissues and eventually cause a burn if a continuous beam is used and kept stationary.
Still, by keeping the treatment head moving, using pulsed beams, and if at all possible avoiding bone prominences, the risk of burns is reduced.

Cavitation

Transient cavitation: Because the bubble expands and collapses quickly in the ultrasonic beam and is believed to raise temperature dramatically, thus transient cavitation poses a risk to the tissues.

Overdose

Symptoms may worsen as a result of overtreatment.

Damage to equipment

Holding the treatment head in midair while it is turned on might cause a standing wave that could harm the crystals within the head due to the reflection of the beam back into the treatment head.

Contraindications

Vascular Conditions

Ultrasound therapy is not used for conditions like thrombophlebitis, where insonation may result in the breaking off of emboli.

Acute sepsis

Due to the risk of infection spreading, ultrasound is not used to treat a spot that presents acute sepsis. 

Radiotherapy

Ultrasound is not applied to a radiated area for at least six months following irradiation due to the harmful effects of radiotherapy on tissues.

Tumors

Tumors are not insonated because they could initiate growing or cause metastases to occur.

Pregnancy

Because the insonation could harm the fetus, a pregnant uterus is not treated. (The use of ultrasound scanning for diagnostic purposes during pregnancy differs from that of therapeutic purposes.)

Testing the apparatus (components)

Testing must always be done before beginning any kind of treatment. Using a water bath to reflect an ultrasonic beam up to the surface, where it will cause ripples, is the easiest method to determine whether or not ultrasound is being produced. With the treatment head inside the water, the device is turned on and off to check ultrasound.

Techniques of application

Direct contact application

If the surface of the application is fairly regular, the coupling medium is applied to the skin to eliminate any air between the skin and the transducer head. Also, in order to transmit the ultrasonic beam to the skin from the transducer head, the coupling medium is applied.

Water Bath application

A bath filled with water, if possible use de-gassed water since ordinary tap water has gas which forms bubbles on both treatment head as well as on patient’s skin, due to which ultrasonic beam gets reflected. if one has to use tap water then gas bubbles should be wiped out frequently from patient’s skin as well as from treatment head.

Water Bag application

Water bag application is used on a irregular bony surfaces. Water bag is made up of rubber which is filled with de-gassed water.

Then coupling medium has to be applied between the treatment head and the water bag and as well as between the patient’s skin and the water bag.

Treatment head should be moved on water bag in small concentric circles.