Ch.3 Describing Sound Waves

Question 1

What are the 7 parameters that describe sound waves?

Answer 1

Period
Frequency
Amplitude
Power
Intensity
Wavelength
Speed

Question 2

Define period

Answer 2

Time it take a wave to vibrate a single cycle. Units in time. 0.06-0.5 microseconds. Determined by source. Not adjustable by sonographer.

Question 3

Define frequency

Answer 3

Number of events in a specific amount of time. Affects penetration and image quality. Units are hertz. Typical values are 2MHz-15 MHz. Determined by sound source. Not adjustable by sonographer.

Question 4

Period x frequency=

Answer 4

1. They are reciprocals of each other.

Question 5

What are the 3 bigness parameters?

Answer 5

Amplitude, power, intensity

Question 6

Define amplitude

Answer 6

Bigness of a wave. Units are pressure, density, or distance. Typical values are 1MPa-3MPa. Determined by sounds source, but decreases with propagation through body. Can be controlled by sonographer

Question 7

Define power

Answer 7

Rate of energy transferred or rate which work is performed. Units are in watts. Typical values are 4-90 mW. Initially sound source but decreases as it goes through the body. Relies on medium and wave. Controlled by sonographer.

Question 8

How are power and amplitude related?

Answer 8

Proportional to each other. Power is proportional to amplitude squared.

Question 9

Define intensity

Answer 9

Concentration of energy in a sound beam. I=P/area
Units are W/cm^2
Typical values are 0.01-300 W/cm^2
Determined by sound source but changes as sound propagates in body. Sonographer can adjust.
Intensity proportional to amplitude ^2

Question 10

Define wavelength

Answer 10

Distance of one complete cycle. Units mm/cm length. 0.1-0.8mm where 1MHz=1.54mm.
Determined by source and medium.
No controlled by sonographer.Affects image quality.
Inversely related to frequency.

Question 11

What role does wavelength perform in image quality?

Answer 11

Shorter wavelengths create higher frequency sound therefore more detail.

Question 12

Define propagation speed

Answer 12

Rate at which sound wave travels. meters per second. Typically mm/microsecond, 500-4000 m/s.
Determined by medium.
All sound travels at same speed through any medium. Not adjustable by sonographer.

Question 13

Speed=

Answer 13

Frequency* wavelength

Question 14

What is the speed of sound in soft tissue ?

Answer 14

1,540 m/s

Question 15

Sound travels fastest in ____, slower in ___, and slowest in _____.

Answer 15

Solids, liquids, gases

Question 16

What two characteristics of a medium affect speed of sound?

Answer 16

Stiffness and density

Question 17

Define stiffness

Answer 17

Ability of an object to resist compression.

Question 18

How does stiffness affect speed?

Answer 18

Directly related.

Question 19

Other terms that describe stiffness?

Answer 19

Bulk modulus is the same as stiffness.
Elasticity and compressibility are opposites of stiffness.
Ex: Marshmallows low bulk modulus that are highly compressible and highly elastic.

Question 20

Density define

Answer 20

Weight of a material.

Question 21

How does density affect speed?

Answer 21

Inversely related. Sound traveled faster in media with low density.

Question 22

What has the greatest influence on speed?

Answer 22

Stiffness.
Ex: air has low stiffness, therefore travels slowly in air

Question 23

What is the source of a sound wave in an ultrasound?

Answer 23

The ultrasound system and transducer