Ultrasound physics Ch 3 (Describing Sound Waves)

The source of a sound wave is the

ultrasound system and transducer

The tissue through which sound is traveling through is also called the

medium

The following describes:

. the time it takes a wave to vibrate a single cycle

. the time from the start of one cycle to the start of the next cycle

Period

period is reported in units of

time, such as microseconds, seconds, hours, or days.

The typical value of period in diagnostic ultrasound is ________.

0.06 to 0.5 microseconds

6x10^-8 to 5x10^-7

Is period determined by the sound source or the medium?

determined by the sound source only

Can the sonographer the period?

no

The following describes:

. the number of particular events that occur in a specific duration

. the number of cycles that occurs in one second

frequency

Frequency is reported in units of

per second, 1/second, hertz, or Hz

1 cycle/second is

1 hertz

1,000 cycles/second is

1 kHz

1,000,000 cycles/second is

1 MHz

frequency ranges from approximately

2 MHz to 15 MHz (2 million to 15 million per second)

What is frequency of a sound wave determined by?

Sound source only

Can a sonographer change the frequency?

No

infrasound, which is below human hearing, is

less than 20 Hz

Audible, sound humans can hear, is

between 20 Hz and 20 kHz

Ultrasound, frequencies so high humans can't hear it, is

greater than 20 kHz (20,000 Hz)

What type of relationship do period and frequency have?

inverse relationship

These 3 parameters describe the size, magnitude, or strength of a sound wave

1. amplitude

2. power

3. intensity

The following describes:

. difference between the maximum value and average or undisturbed value of an acoustic variable

. the difference between the minimum value and average value of the acoustic variable

amplitude

amplitude can have units of any of the acoustic variables

pressure- pascals

density- kg/cm^3

particle motion/distance- cm, inches

temperature- Fahrenheit, Celsius

decibels, dB

pressure amplitude ranges from

1 million pascals (1 MPa) to 3 million pascals (3 MPa)

Initially, amplitude is determined only by

sound source

Can the initial amplitude of a wave be changed by a sonographer?

yes

Amplitude is measured from....

the middle value to the maximum value

peak to peak amplitude is

the difference between maximum and minimum values, it is twice the value of the amplitude

The following describes:

the rate of energy transfer or the rate at which work is performed

Power

The units of power is

watts

Power ranges from

0.004 to 0.090 watts

Initial power is determined by

sound source

Can the sonographer change the initial power of a wave?

yes

How is power related to amplitude?

power is proportional to amplitude squared

The following describes:

. the concentration of energy in a sound beam

. relates to power in a wave spreads or is distributed in space

. depends on both the power in a beam and the area over which the power is applied

Intensity

The units of intensity are

watts/square centimeter

The equation used to calculate intensity is

power divided by area

Power is initially determined by

sound source

Can the sonographer change the initial intensity of a wave?

yes

What is the relationship between power and intensity?

power is proportional to intensity

What is the relationship between intensity and amplitude?

Intensity is proportional to amplitude squared

The following describes:

. the distance or length of one complete cycle

wavelength

What are the units of wavelength?

mm, meters, any units of length

Wavelength in soft tissue ranges from _______.

0.1 to 0.8 mm

Is wavelength determined by the sound source or the medium?

Wavelength is determined by both the sound source and the medium

Can the sonographer change wavelength?

no

As long as a wave remains in one medium, what is the relationship between wavelength and frequency?

Wavelength and frequency are inversely related

What is the wavelength of 1MHz sound in soft tissue?

Sound with a frequency of 1MHz has a wavelength of 1.54mm

What is the equation used to find wavelength?

1.54mm/ microseconds divided by frequency (MHz)

Why is wavelength important in Image quality?

Shorter wavelengths from high frequency, producing higher quality images

The following describes:

. the rate at which a sound wave travels through a medium

propagation speed

Speed is measured in units of

meters per second or any distance divided by time

Depending on the tissue it is traveling through the speed of sound ranges from ________.

500 m/s to 4000 m/s

What is speed determined by?

medium only

Regardless of frequency, does all sound travel at the same speed through any specific medium if the medium is the same?

yes

Can speed be changed by the sonographer?

no

What is the speed of sound in soft tissue?

1540 m/s or 1.54 mm/microseconds or 1.54 km/s. (A mile a second).

The speed of sound in the lung tissue is?

500 m/s

The speed of sound in fat tissue is ?

1,450 m/s

the speed of sound in soft tissue (average) is?

1,540 m/s

The speed of sound in liver tissue is?

1,560 m/s

The speed of sound in blood is

1560 m/s

The speed of sound in muscle tissue is?

1,600 m/s

The speed of sound in tendon tissue is?

1,700 m/s

The speed of sound in bone tissue is?

3,500 m/s

the speed of sound in air is?

330 m/s

the speed of sound in water is?

1,480 m/s

the speed of sound in metals is?

2,000 to 7,000

What is the equation used to find speed is?

frequency times wavelength

What 2 characteristics of a medium affect the speed of sound?

stiffness and density

The following describes:

. the ability of an object to resist compression

stiffness

How are stiffness and speed related?

directly related

increased stiffness equals increased speed

What is another term for stiffness?

bulk modulus

What terms are the opposite of stiffness?

elasticity and compressibility

The following describes:

. the relative weight of a material

Density

How are density and speed related?

inversely related

increase density equals decreased speed

Does density or stiffness have a greater influence on speed?

stiffness