Basics

Question 0

Define the term period (include units, formula)

Answer 0

The time per cycle. Time it takes for one compression and one rarefaction to occur.
May be expressed in any unit of time. Often millisecond (ms) or microsecond (µs).
Formula: T (us) = 1/frequency (MHz)

Question 1

Define the term frequency (include units, ranges).

Answer 1

Number of cycles (compressions and rarefactions) per second.
Cycles per second may be written as Hertz (Hz).
Infrasound 20 kHz
Clinical imaging ultrasound 2-10 MHz

Question 2

List the four acoustic variables

Answer 2

Acoustic pressure
Density
Temperature
Particle motion

Question 3

Define acoustic pressure.

Answer 3

Force/area

Units are Pascals (Pa)

Question 4

Define density.

Answer 4

Mass/volume

Units are grams(g)/cm^3

Question 5

Define temperature.

Answer 5

The degree of heat or cold measured on a definite scale

Units are Kelvin (K), Centigrade (C), or Farenheit (F)

Question 6

Define particle motion.

Answer 6

The displacement or movement of a particle by a wave

Units are length or distance (e.g. millimeters (mm), meters (m)

Question 7

What is sound?

Answer 7

A mechanical, longitudinal wave.

Does not travel as a transverse (particles of the medium move perpendicular to the direction of sound travel) wave

Question 8

Mechanical

Answer 8

Infers motion and a transfer of energy

Question 9

Longitudinal

Answer 9

The particles of the medium are vibrating parallel to the direction of sound travel

Question 10

Wave

Answer 10

Vibration which travels from one location to another

Question 11

Define acoustic impedance

Answer 11

The opposition to sound propagation through a medium
Units are rayl
Formula: Z(Rayls) = p(kg/m^3) * c(m/s)

Question 12

What is a decibel (dB)?

Answer 12

A qualitative method of expressing the difference between two sound intensities or amplitudes

Question 13

Define intensity. (include units, formula)

Answer 13

The amount of energy transferred (power) to a particular area.
Units are Watts (W)/cm^2 or milliwatts (mW)/cm^2
Formula: Intensity (W/cm^2 or mW/cm^2) = power (W or mW) / area (cm^2)

Question 14

Is intensity controlled by the sonographer?

Answer 14

Yes, via the transmit gain control. Increasing the transmit gain causes the pulser to strike the piezoelectric element with a greater voltage thus increasing the amplitude, power and intensity of sound to the patient

Question 15

Define power (include units)

Answer 15

The amount of energy transferred from the source.

Units are Watts (W) or milliwatts (mW)

Question 16

Is power controlled by the sonographer?

Answer 16

Yes, through the transmit gain control

Question 17

Define amplitude (include units)

Answer 17

One way to express the strength (loudness) of a sound wave.
Maximum variation of an acoustic variable minus the mean value.
Units depend on the acoustic variable being measured

Question 18

Define the term propagation speed (include units, average value for soft tissue)

Answer 18

The rate at which a vibration (sound) travels through a medium.
Units are distance/time (m/s or mm/µs)
Soft tissue = 1540 m/s

Question 19

Define the term wavelength (include units, formula)

Answer 19

The length of one cycle. The distance covered by one compression and one rarefaction.
Units are length or distance, usually meters (m) or millimeters (mm)
Formula: λ = propagation speed (mm/µs) / frequency (MHz)

Question 20

List the 6 “R’s” of ultrasound physics

Answer 20

Rarefaction
Reflection
Refraction
Reverberation
Range Ambiguity
Range Discrimination (Resolution)

Question 21

Define rarefaction

Answer 21

The area of low pressure, low density of a sound wave

Question 22

Define reflection

Answer 22

The sound energy returned back to the sound source

Question 23

Define refraction

Answer 23

The change in the direction of sound as it crosses a boundary.
Occurs when there is oblique incidence and the propagation speeds of the two media are not equal

Question 24

Define reverberation

Answer 24

An ultrasound artifact involving two highly reflective structures (e.g. transducer and skin surface) which results in the display of multiple echoes equally spaced

Question 25

Define range ambiguity

Answer 25

A disadvantage of CW Doppler. Since CW Doppler collects Doppler shift information all along the ultrasound beam, the precise location or depth of the returning Doppler shift is unknown

Question 26

Define range discrimination (resolution)

Answer 26

The advantage of pulsed wave Doppler in that Doppler shift information is determined and displayed only from a particular depth or location chosen by the sonographer