Sound and Waves

Question 1

Properties of Sound

Answer 1

• Travel in waves
• Elastic
• Periodic Motions

Question 2

Periodic motion

Answer 2

Defined as motion which repeats itself at regular time intervals
(also called: Vibration, Oscillation, and Cycle)

Question 3

Period of Motion (T)

Answer 3

Time required to complete one full cycle

Question 4

Frequency

Answer 4

The number of vibrations per unit of time. The higher the frequency, the less time each vibration takes.
- Hertz (Hz)
- Mega Hertz (MHz)

Question 5

Amplitide

Answer 5

The maximum distance moved from the equilibrium point.

Question 6

Transverse wave

Answer 6

A wave in which the particles of the medium are oscillating back and forth PERPENDICULAR to the direction of the propagation of the wave.

Question 7

Longitudinal Wave

Answer 7

Waves in which the periodic motion of the particles is PARALLEL to the propagation directions

Question 8

Ultrasonic Sound (US)

Answer 8

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

Question 9

Ultrasound

Answer 9

Sound waves above the level of detecting sound by the human ear
- Greater than 20,000 Hz
- Generally, measured in Megahertz

Question 10

term for US increasing tissue temperature

Answer 10

Thermal

Question 11

term for US altering cellular activity

Answer 11

Non-thermal (Athermal)

Question 12

Description of US

Answer 12

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

Question 13

High attenuation coefficient

Answer 13

Tendon, ligaments, cartilage, scar tissue, joint capsule, ect. (sound waves absorbed well)

Question 14

Low attenuation coefficient

Answer 14

Material with water (muscle)
(not absorbed well)

Question 15

3 Reasons for Attenuation

Answer 15

1) Refraction
2) Reflection
3) Absorption (main reason for Attenuation)

Question 16

Transducer

Answer 16

sound head – crystal that converts electrical energy into sound

Question 17

Intensity

Answer 17

Power per unit area of sound head (average or peak)
– Wcm^2

• Generally, the intensity is the important number for level of warmth

Question 18

Power

Answer 18

watts (W)
The amount of WATTS given out of the transducer

Question 19

Absorption

Answer 19

Conversion of mechanical energy into heat and how much is absorbed by tissue – absorption coefficient

Question 20

Crystal Piezoelectric Properties

Answer 20

• 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

Question 21

Acoustic Streaming

Answer 21

Steady, circular flow of cell material caused by US waves

Question 22

Attenuation

Answer 22

Decrease in US intensity as travels through tissue

Question 23

Cavitation

Answer 23

Gas bubbles in tissue are made smaller during compression phase of US and expand during rarefaction phase

Question 24

Microstreaming

Answer 24

• very small flow of material (gas bubbles from cavitation)
• If these implode can cause tissue damage (lithotripsy)

Question 25

Rarefaction

Answer 25

Down in density of material as US waves pass through it

Question 26

Piezoelectric

Answer 26

Able to change shape in response to electrical current

Question 27

Reflection

Answer 27

• Redirection of US wave opposite to angle of incident
• Mostly occurs between tissue interfaces (air-skin, soft tissue bone)

Question 28

Effective Radiating Area

Answer 28

• The area of transducer from which US energy radiates
• 1/2 the size of the transducer head

Question 29

Thermal effects of US

Answer 29

• Reduction of pain
• Extensibility of tissue
• Increase circulation
• Reduce muscles spasms
• Alter nerve conduction

Question 30

Nonthermal effects of US

Answer 30

• 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

Question 31

Absorption coefficient of the tissue

Answer 31

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

Question 32

frequency (influence temperature change)

Answer 32

Higher frequency (3MHz) = higher temps of tissue

Question 33

Average intensity (influence temperature change)

Answer 33

Need less intensity with higher frequencies (3-4 time less)

Question 34

Duration of treatment

Answer 34

Allow more total energy to be delivered

Question 35

Clinical uses of US

Answer 35

• Soft tissue shortening
• Pain control
• Dermal ulcers
• Surgical Skin incisions
• Tendon/Ligament injuries
• Resorption of calcium deposits
• Bone fractures
• Carpal Tunnel syndrome
• Phonophoresis

Question 36

Frequency Selection

Answer 36

1 MHz for tissue 5 cm deep

3 MHz for tissue 1-2 cm deep (superficial)