Ultrasound Therapy
Ultrasound is a therapeutic modality that has been used by physical therapists since the 1940s. Ultrasound is applied using a round-headed wand or probe that is put in direct contact with the patient’s skin. Ultrasound gel is used on all surfaces of the head in order to reduce friction and assist in the transmission of the ultrasonic waves. Therapeutic ultrasound is in the frequency range of about 0.8-3.0 MHz.
The 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.
Ultrasound in Sports Medicine
One of the most widely used therapeutic modalities
Primary use is for stimulating the repair of soft tissue injuries and pain relief
Background
Acoustic energy
Produces thermal or non-thermal physiological effects
Deep heat
Basic Physics of US
Ultrasound unit construction
Transducer
¡Sound head
¢Piezoelectric crystal
Piezoelectric effect
Transmission of Acoustical Energy in Biological Tissue
Acoustic energy requires molecular collision for transmission
“Stone in a pool of water”
US 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
Frequency of Wave Transmission
US has frequency greater than 20 kHz
¡0.75 – 3 MHz
¡Audible sound (16 – 20 kHz)
The lower the frequency, the greater the depth of penetration
US penetrates tissues high in H2O content
Absorbed in dense tissues high in protein
Ultrasound Beam
Larger diameter and higher frequency = more focused beam
Smaller diameter and lower frequency = more divergent beam
Wave Reflection
Some of the wave may be reflected or refracted as it encounters various tissue
Effective Radiating Area
Portion of the transducer that actually produces the sound wave
Frequency of Ultrasound
3 MHz = superficial heat
1 MHz = deep heat
Amplitude, Power, & Intensity
Amplitude – Magnitude of the vibration in a wave
Power – Total amount of US energy in the beam (Watts)
Intensity – Measure of the rate at which energy is being delivered per unit area (Watts/cm2)
Pulsed vs. Continuous Wave US
Continuous wave – sound intensity remains constant
¡Thermal effect
Pulsed wave – intensity is periodically interrupted with no US energy being produced during the off period
¡Duty cycle
¡Nonthermal effect
PULSE RATIO
¡Ultra sound on : Ultra sound off
¡1:1,1:4,1:7 (vary depends on machines)
Physiological Effects of Ultrasound
US may cause clinically significant responses in cells, tissues, and organs through both thermal and nonthermal mechanisms
Thermal Effects
Increase in the extensibility of collagen
Decrease in joint stiffness
Reduction of muscle spasm
Modulation of pain
Increased blood flow
Mild inflammatory response
¡May help in the resolution of chronic inflammation
Thermal Effects
Tissue must be raised to a level of 40 to 45° C for 5 minutes.
Temperature rise above base line is key factor
¡increases of 1° C increases metabolism and healing
¡Increases of 2 – 3° C decreases pain and muscle spasm
¡Increases of 4° C and greater increase extensibility of collagen and decrease joint stiffness
Nonthermal Effects
Cavitation – Formation of gas-filled bubbles that expand and compress due to ultrasonically induced pressure changes in tissue fluids
Acoustic streaming – Unidirectional movement of fluids along the boundaries of cell membranes resulting from the mechanical pressure in an ultrasonic field
Cavitation
Results in increased flow in the fluid around the vibrating bubbles
Acoustic Streaming
Produces high viscous stresses that can alter cell membrane structure and function
¡Changes in cell permeability to sodium and calcium ions occurs
Nonthermal Effects
Increased cell membrane permeability
Altered rate of diffusion across cell membrane
Increased vascular permeability
Secretion of cytokines
Increased blood flow
Stimulation of phagocytosis
Production of healthy granulation tissue
Synthesis of protein
Synthesis of collagen
Reduction of edema
Diffusion of ions
Tissue regeneration
Formation of stronger, more deformable scar
Techniques of Application
Frequency of treatment
¡Acute vs. chronic
¡How many treatments should be given?
Duration of treatment
¡Dependent on treatment goal
Keep the transducer moving!!!
Coupling Methods
Direct contact
Immersion
¡Watch for bubbles
COUPLING MEDIA
¡To avoid the impedance(Z) by air
¡Best is Aqua sonic gel(water based gel)
TECHNIQUES OF APPLICATION Of Ultrasound
Note : check equipment before application
DIRECT CONTACT
¡Should move concentric circles
¡Turn off and on in contact with patients
¡Three times the size of treatment head
WATER BATH
¡Immerse treatment part in water (without bubbles)
¡Keep the head 1cm from treatment part
WATER BAG
¡Rubber bag filled with water
¡Apply coupling media on bag and treatment area
¡Move the US head same like direct method
DOSAGE
ACUTE
¡Intensity – 0.25 Wcm-2 – 0.5 Wcm-2
¡Duration 2-3 Minutes
¡Use pulsed mode (Very acute – 1:7 , Acute – 1:1)
CHRONIC
¡Intensity 0.8 Wcm-2 – 2 Wcm-2
¡Duration upto 4 – 8 Minutes
¡Use continuous mode
¡
phonophoresis
Ultrasound 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
Clinical Applications of US
Soft tissue healing and repair
Scar tissue and joint contracture
Stretching of connective tissue
Chronic inflammation
Bone healing
Pain reduction
Contraindications
Areas of decreased temperature sensation
Areas of decreased circulation
Vascular insufficiencies
Eyes
Reproductive organs
Pelvis immediately following menses
Pregnancy
Pacemaker
Epiphyseal areas in developing individuals
Total joint replacements
Infections
Over spinal column
cancer
