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Ultrasound therapy

žUltrasound Therapy

ža therapeutic modality used physical therapists since the 1940s. Ultrasound applied using a round-headed wand or probe that put in direct contact with the patient’s skin. Ultrasound gel used on all surfaces of the head in order to reduce friction and assist in the transmission of the ultrasonic waves. Therapeutic ultrasound in the frequency range of about 0.8-3.0 MHz.


žThe waves are generated by a piezoelectric effect caused by the vibration of crystals within the head of the wand/probe. The sound waves that pass through the skin cause a vibration of the local tissues. This vibration can cause a deep heating locally though usually no sensation of heat will be felt by the patient. In situations where a heating effect is not desirable, such as a fresh injury with acute inflammation, the ultrasound can be pulsed rather than continuously transmitted.

žUltrasound in Sports Medicine

žOne of the most widely used therapeutic modalities

žPrimary use is for stimulating the repair of soft tissue injuries and pain relief


žAcoustic energy

žProduces thermal or non-thermal physiological effects

žDeep heat

žBasic Physics of US

žUltrasound unit construction


¡Sound head

¢Piezoelectric crystal

žPiezoelectric effect

žTransmission of Acoustical Energy in Biological Tissue

žAcoustic energy requires molecular collision for transmission

ž“Stone in a pool of water”

žUS is a mechanical wave in which energy is transmitted by the vibrations of the molecules of the biological medium through which the wave is traveling

žFrequency of Wave Transmission

žUS has frequency greater than 20 kHz

¡0.75 – 3 MHz

¡Audible sound (16 – 20 kHz)

žThe lower the frequency, the greater the depth of penetration


žUS penetrates tissues high in H2O content

žAbsorbed in dense tissues high in protein

žUltrasound Beam

žLarger diameter and higher frequency = more focused beam

žSmaller diameter and lower frequency = more divergent beam

žWave Reflection

žSome of the waves may be reflected or refracted as it encounters various tissue

žEffective Radiating Area

žPortion of the transducer that actually produces the sound wave


žFrequency of Ultrasound

ž3 MHz = superficial heat

ž1 MHz = deep heat


žAmplitude, Power, & Intensity

žAmplitude – Magnitude of the vibration in a wave

žPower – Total amount of US energy in the beam (Watts)

žIntensity – Measure of the rate at which energy is being delivered per unit area (Watts/cm2)

žPulsed vs. Continuous Wave US

žContinuous wave – sound intensity remains constant

¡Thermal effect

žPulsed wave – intensity is periodically interrupted with no US energy being produced during the off period

¡Duty cycle

¡Nonthermal effect


The ¡Ultra sound on Ultrasound off

¡1:1,1:4,1:7 (vary depends on machines)

žPhysiological Effects of Ultrasound

žThe US may cause clinically significant responses in cells, tissues, and organs through both thermal and nonthermal mechanisms

žThermal Effects

žIncrease in the extensibility of collagen

žDecrease in joint stiffness

žReduction of muscle spasm

žModulation of pain

žIncreased blood flow

žMild inflammatory response

¡May help in the resolution of chronic inflammation

žTemperature rise above baseline is a key factor


žNonthermal Effects

žCavitation – Formation of gas-filled bubbles that expand and compress due to ultrasonically induced pressure changes in tissue fluids

žAcoustic streaming – Unidirectional movement of fluids along the boundaries of cell membranes resulting from the mechanical pressure in an ultrasonic field


žResults in increased flow in the fluid around the vibrating bubbles

žAcoustic Streaming

žProduces high viscous stresses that can alter cell membrane structure and function

¡Changes in cell permeability to sodium and calcium ions occurs

žNonthermal Effects

žIncreased cell membrane permeability

žAltered rate of diffusion across the cell membrane

žIncreased vascular permeability

žSecretion of cytokines

žIncreased blood flow

žStimulation of phagocytosis

žProduction of healthy granulation tissue

žSynthesis of protein

žSynthesis of collagen

žReduction of edema

žDiffusion of ions

žTissue regeneration

žFormation of stronger, more deformable scar

žTechniques of Application

žFrequency of treatment

¡Acute vs. chronic

¡How many treatments should be given?

žDuration of treatment

¡Dependent on treatment goal

žKeep the transducer moving!!!

žCoupling Methods

žDirect contact


¡Watch for bubbles


¡To avoid the impedance(Z) by air

¡Best is Aqua sonic gel(water-based gel)



žNote : check equipment before application


¡Should move concentric circles

¡Turn off and on in contact with patients

¡Three times the size of treatment head


¡Immerse treatment part in water (without bubbles)

¡Keep the head 1cm from treatment part



¡Rubber bag filled with water

¡Apply coupling media on bag and treatment area

¡Move the US head same like direct method




¡Intensity – 0.25 Wcm-2 – 0.5 Wcm-2

¡Duration 2-3 Minutes

¡Use pulsed mode (Very acute – 1:7 , Acute – 1:1)


¡Intensity 0.8 Wcm-2 – 2 Wcm-2

¡Duration up to 4 – 8 Minutes

¡Use continuous mode



žUltrasound can also be used to achieve phonophoresis. This is a non-invasive way of administering medications to tissues below the skin; perfect for patients who are uncomfortable with injections. With this technique, the ultrasonic energy forces the medication through the skin

žClinical Applications of US

žSoft tissue healing and repair

žScar tissue and joint contracture

žStretching of connective tissue

žChronic inflammation

žBone healing

žPain reduction


žAreas of decreased temperature sensation

žAreas of decreased circulation

žVascular insufficiencies


žReproductive organs

žPelvis immediately following menses



žEpiphyseal areas in developing individuals

žTotal joint replacements


žOver spinal column