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ATTR 362: Principles and Application of Therapeutic Ultrasound
Transcript of ATTR 362: Principles and Application of Therapeutic Ultrasound
Acoustical Energy, Not Electromagnetic
Diagnostic Imaging: 0.5 - 50 W/cm2
Therapeutic Deep Heating: 1 - 3 W/cm2
Tissue Destruction: 0.5 - 100 W/cm2
We'll focus on this!
16,000 - 20,000 Hz
750,000 - 3,300,000 Hz
Most commonly used 1 or 3 MHz
Uses of Therapeutic Ultrasound
Increase rate of tissue healing
Increase blood flow
Increase tissue extensibility
Reduce calcium deposits
Reduce muscle spasm
Delivery of Rx Meds (phonophoresis)
Alternating Current >>> Piezoelectric Crystal >>> Expansion and Contraction >>> Vibration >>> High Frequency Sound Waves
High Frequency Sound Waves (US)
So how is it possible for US Energy to pass through tissue without displacing the molecules??
US Energy is Acoustical Energy!
The kinetic energy is transferred by molecules bumping into one another, but not changing position.
Think of it like a leaf in a pond. When you drop a rock in the pond, it creates ripples and the leaf bobs up and down, but the actual position doesn't change (or changes very little)
Important Principles and Parameters of Ultrasound!
Frensel Zone (near field) - area of non-uniform beam close to transducer head. This portion used for therapeutic purposes
Effective Radiating Area (ERA) - proportion of the transducer's surface area that produces energy. Described in terms of Squared Centimeters (cm2).
ALWAYS SMALLER THAN FACE OF THE TRANSDUCER
*Large ERAs produce a collimated, focused beam
*Small ERAs produce a divergent beam
So when treating a localized area, what type of transducer would you use? www.padlet.com/jedler/ATTR362004 or 003
Measured in MHz and describes the number of waves produced in 1 second.
Remember that the two most common frequencies for TUS are 1MHz and 3 MHz
Depth of Penetration
Max rate of heating
5 or more cm
Retains heat 2x longer than 3 MHz
0.8 - 3 cm
Retains heat half as long as 1 MHz
Power and Intensity
Power - The amount of energy produced (measured in Watts)
Intensity - The strength of the sound waves at a given location within the tissues being treated.
Relationship between ERA, Intensity, and Power
Total Power (W)
Ultrasound Beam Nonuniformity
Ultrasound output "cone" consists of peaks and valleys of high and low energy.
From imperfections in crystal.
BNR describes variation between peaks, intensity, and valleys
US Plot - Notice Peaks and Valleys
MAX Allowable BNR is 8:1. Listed on Transducer
Ultrasound Energy Transfer Through Tissues
Air is not dense enough to transfer US energy. So you ALWAYS need to us a coupling agent!! (water, gel, gel pads, etc)
Whenever an US beam strikes an acoustical interface, some energy is reflected or refracted.
Percent Reflection of US Energy at Various Interface
Bottom Line: DO NOT HAVE US HEAD ON WITHOUT COUPLING AGENT!!!
Biophysical Effects of US
Temperature Increases Required for Specific Therapeutic Effects
Used for Thermal Effects
Decreasing Muscle Spasm
Increasing Blood Flow
Reducing Chronic Inflammation
Tissue elongation, scar tissue red
Inhibition of sympathetic activity
Ultrasound's Effects on the Injury Process
1's - Cellular Response
2's - Inflammation
3's - Body and Fluid Dynamics
4's - Nerve Conduction and Pain Control
5's - Muscle Spasms
6's - Tissue Elasticity
7's - Muscle & Tendon Healing
8's - Wound Healing
9's - Fracture Healing
www.padlet.com/jedler/attr362004 or (003)
5 minutes to come together, read, and write responses on padlet
A Brief Word on Phonophoresis
Phonophoresis is the use of therapeutic ultrasound to assist in the diffusion of medication through the skin
Proposed Mechanism - US energy changes the tissue and/or the medication to allow the medication to diffuse across barriers (Skin) and be absorbed into the body
Why Phono? - No 1st pass effect, larger area of application
Only used approved medications that are specifically designed for US/Phono Use!!!
Contraindications to Therapeutic Ultrasound
Areas of Impaired Sensation
Tumors or Cancer
Use over eyes, heart, skull, genitals
Use over implanted medical devices
Over abdominal, pelvis, lumbar areas during pregnancy
Acute or stress fracture sites (except US bone stims)
Areas over implants or bone cement
US application over spine or nerve plexus**
Overview of the Evidence
Relatively large amounts of literature
Efficacy is still in question
What we know: Continuous US can increase tissue temperature, but the temperature increases may be dependent on US machine AND may vary between units of the same model!
No Evidence of Cavitation!!
Common Clinical Mistakes Also Make US Less Effective
Wrong Output Frequency
Output Intensity Too Low
Treating Too Large of Area
Using Wrong Coupling Agent
Moving the Sound Head Too Fast
DON'T MAKE THESE!