Sound and Waves Flashcards
Properties of Sound
- Travel in waves
- Elastic
- Periodic Motions
Periodic motion
Defined as motion which repeats itself at regular time intervals
(also called: Vibration, Oscillation, and Cycle)
Period of Motion (T)
Time required to complete one full cycle
Frequency
The number of vibrations per unit of time. The higher the frequency, the less time each vibration takes.
- Hertz (Hz)
- Mega Hertz (MHz)
Amplitide
The maximum distance moved from the equilibrium point.
Transverse wave
A wave in which the particles of the medium are oscillating back and forth PERPENDICULAR to the direction of the propagation of the wave.
Longitudinal Wave
Waves in which the periodic motion of the particles is PARALLEL to the propagation directions
Ultrasonic Sound (US)
Consist of Frequencies above the range of human hearing
- used for diagnosis (creates images), and treatment (localized increased in temperature)
- US is a high frequency sound wave that can enter the body and pass through it while attenuating (Down in density), due to absorption of the sound waves into tissue
Ultrasound
Sound waves above the level of detecting sound by the human ear
- Greater than 20,000 Hz
- Generally, measured in Megahertz
term for US increasing tissue temperature
Thermal
term for US altering cellular activity
Non-thermal (Athermal)
Description of US
A high frequency sound wave that can enter the body and pass through it while attenuating (Down in Density), due to absorption of the sound waves into tissue
High attenuation coefficient
Tendon, ligaments, cartilage, scar tissue, joint capsule, ect. (sound waves absorbed well)
Low attenuation coefficient
Material with water (muscle)
(not absorbed well)
3 Reasons for Attenuation
1) Refraction
2) Reflection
3) Absorption (main reason for Attenuation)
Transducer
sound head – crystal that converts electrical energy into sound
Intensity
Power per unit area of sound head (average or peak)
– Wcm^2
- Generally, the intensity is the important number for level of warmth
Power
watts (W)
The amount of WATTS given out of the transducer
Absorption
Conversion of mechanical energy into heat and how much is absorbed by tissue – absorption coefficient
Crystal Piezoelectric Properties
- Able to respond to electrical current by contracting and expanding as the electrical current alternates
- When the crystal expands, it COMPRESSES the material in front of it; when the crystal contracts it RAREFIES the material in front of it = US WAVE
- So basically this crystal changes shape due to electrical current coming out of wall into machine = US wave
- The frequency of the US waves depends on the thickness of the crystal
Acoustic Streaming
Steady, circular flow of cell material caused by US waves
Attenuation
Decrease in US intensity as travels through tissue
Cavitation
Gas bubbles in tissue are made smaller during compression phase of US and expand during rarefaction phase
Microstreaming
- very small flow of material (gas bubbles from cavitation)
- If these implode can cause tissue damage (lithotripsy)
Rarefaction
Down in density of material as US waves pass through it
Piezoelectric
Able to change shape in response to electrical current
Reflection
- Redirection of US wave opposite to angle of incident
- Mostly occurs between tissue interfaces (air-skin, soft tissue bone)
Effective Radiating Area
- The area of transducer from which US energy radiates
- 1/2 the size of the transducer head
Thermal effects of US
- Reduction of pain
- Extensibility of tissue
- Increase circulation
- Reduce muscles spasms
- Alter nerve conduction
Nonthermal effects of US
- Micro streaming , acoustic streaming, and cavitation cause mechanical changes in biological tissue and processes
- these changes can help increase cell healing due to damage
- effective for inflammation phase of healing, wound healing , blood flow (local area), increase skin permeability to topical medications
Absorption coefficient of the tissue
Higher coefficient (collagen) better absorption = higher temperature changes (tendons , ligaments, fascia, capsules)
Lower coefficient (water, muscle, fat) less absorption = less temperature changes in that tissue
Absorption accounts for the most of attenuation, but reflection and refraction occur as US waves penetrate through tissue
frequency (influence temperature change)
Higher frequency (3MHz) = higher temps of tissue
Average intensity (influence temperature change)
Need less intensity with higher frequencies (3-4 time less)
Duration of treatment
Allow more total energy to be delivered
Clinical uses of US
- Soft tissue shortening
- Pain control
- Dermal ulcers
- Surgical Skin incisions
- Tendon/Ligament injuries
- Resorption of calcium deposits
- Bone fractures
- Carpal Tunnel syndrome
- Phonophoresis
Frequency Selection
1 MHz for tissue 5 cm deep
3 MHz for tissue 1-2 cm deep (superficial)
