TH521: MACHINES PT 3
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84 Terms
What is therapeutic ultrasound?
The generation of sound waves that produce mechanical energy and heat in tissues.
What physical effect generates ultrasound?
The reverse piezoelectric effect.
What is piezoelectricity?
The ability of crystals to convert electrical energy into mechanical energy or vice versa.
Energy conversion in therapeutic ultrasound
Electricity → crystals → sound waves → vibration → heat.
Do ultrasound waves require a medium?
Yes.
What type of wave is ultrasound?
Longitudinal mechanical wave.
Normal human hearing range
18 Hz-20 kHz.
Therapeutic ultrasound frequency range
1-3 MHz.
Diagnostic ultrasound frequency
Greater than 16 MHz.
Which ultrasound frequency penetrates deeper?
1 MHz.
Which ultrasound frequency is absorbed more superficially?
3 MHz.
Why does 3 MHz heat superficial tissues more?
It is absorbed more rapidly.
Air has what effect on ultrasound?
Disperses the sound waves.
Water has what effect on ultrasound?
Efficiently transmits ultrasound.
Dense tissues have what effect on ultrasound?
Reflect and absorb more energy.
What is attenuation?
Absorption of ultrasound energy by tissue.
What happens when ultrasound energy is absorbed?
Mechanical energy is converted into heat.
Which tissue absorbs the most ultrasound energy?
Bone.
Approximate ultrasound absorption by bone
96%.
Approximate ultrasound absorption by cartilage
68%.
Approximate ultrasound absorption by tendon
59%.
Approximate ultrasound absorption by skin
39%.
Approximate ultrasound absorption by muscle
24%.
Approximate ultrasound absorption by fat
13%.
Approximate ultrasound absorption by blood
3%.
Why do dense tissues heat more with ultrasound?
They absorb and reflect more energy.
What produces ultrasound waves in the transducer?
Piezoelectric crystals.
What are the two ultrasound delivery modes?
Continuous and pulsed.
Continuous ultrasound primarily produces what effect?
Thermal effects.
Pulsed ultrasound primarily produces what effect?
Mechanical/nonthermal effects.
What is duty cycle?
The percentage of time ultrasound is actively transmitting.
Duty cycle of continuous ultrasound
100%.
Duty cycle of 50% pulsed ultrasound
Half the machine is on and half is off.
What does a 20% duty cycle mean?
The machine is on 20% of the time and off 80%.
What is Beam Nonuniformity Ratio (BNR)?
The ratio of peak intensity to average intensity.
Lower BNR means what?
More uniform energy delivery.
Higher BNR increases the risk of what?
Hot spots.
Why should ultrasound machines be serviced regularly?
To reduce BNR and improve safety.
Thermal effect of ultrasound
Increases tissue temperature.
How does ultrasound increase tissue temperature?
Molecular vibration creates friction.
Physiological effects of ultrasound heat
Increased circulation, metabolism, inflammation, decreased pain, decreased muscle tone.
What is cavitation?
Formation of microscopic gas bubbles during ultrasound.
What is acoustic streaming?
Movement of fluid around vibrating gas bubbles.
What is acoustic vibration?
Mechanical movement of tissue fluids.
Mechanical effects of ultrasound
Increased membrane permeability, vascular permeability, protein synthesis, macrophage activity.
How does ultrasound affect fibroblasts?
Increases protein synthesis.
How does ultrasound affect macrophages?
Increases responsiveness.
What is phonophoresis?
Using ultrasound to enhance medication delivery through the skin.
Purpose of phonophoresis
Deliver medication without injections.
What two substances are needed for phonophoresis?
A therapeutic medication and a coupling medium.
Common medications used in phonophoresis
Hydrocortisone, dexamethasone, lidocaine, methyl salicylate.
Why is coupling gel required with ultrasound?
It removes air and transmits sound efficiently.
What does diathermy mean?
"Through heat."
What is diathermy?
A deep-heating modality using electromagnetic energy.
What forms of electromagnetic energy are commonly used in diathermy?
Shortwave and microwave.
Can ultrasound be considered a form of diathermy?
Yes, because it produces deep heating through a different mechanism.
What type of waves are used in shortwave diathermy?
High-frequency radio waves.
Primary therapeutic effect of diathermy
Deep tissue heating.
Why has diathermy become less common?
Concerns about safety and side effects.
What is low-level laser therapy (LLLT)?
Photobiomodulation using low-energy light.
Primary goal of LLLT
Stimulate cellular activity rather than destroy tissue.
How does LLLT differ from surgical lasers?
It uses much lower energy and does not cut tissue.
What is photobiomodulation?
Using light energy to influence cellular metabolism.
Typical baseline LLLT dose
12 J/cm².
When should lower laser doses be used?
Superficial tissue or lighter skin.
When should higher laser doses be used?
Deeper tissue, more muscle, or darker skin.
How does cryotherapy before laser affect treatment?
Increases penetration.
How does thermotherapy before laser affect treatment?
Increases superficial absorption.
Typical laser wavelength in the lecture
780-860 nm.
Recommended laser treatment frequency
Daily for about 2 weeks or every other day for 3-4 weeks.
Minimum laser energy for many tendon points
4 Joules.
Minimum laser energy for hip treatment
6 Joules.
Recommended cervical spine laser dose
16 Joules.
Recommended lumbar spine laser dose
16 Joules.
Recommended plantar fasciitis laser dose
8 Joules.
Recommended Achilles tendon laser dose
8 Joules.
Recommended supraspinatus laser dose
8 Joules.
What is an LED?
A semiconductor producing light through spontaneous emission.
How does an LED differ from a laser?
It is not stimulated emission.
What is a Super Luminous Diode (SLD)?
An amplified array of LEDs with laser-like properties.
Main difference between LED and laser
Lasers produce coherent stimulated light; LEDs produce spontaneous light.
General purpose of therapeutic modalities
Reduce pain and improve function.
Clinical reminder from the lecture
Most therapeutic modalities have limited high-quality evidence.
What should guide treatment decisions?
Clinical reasoning and patient goals rather than machine claims.