US Physics Wk4 Quiz

intensity is the US beam's ______ divided by its _____

power

area

- spatial

- peak

- average

- temporal

- pulsed

key words related to the intensities of pulsed waves

refers to distance or space

spatial

refers to all time, both transmit and receive

temporal

the maximum value of intensity

peak

the mathematical middle value of intensity

average

refers to only the transmit time

pulsed

transmit time, AKA

pulse duration

the beams intensity at the location where it's maximum

spatial peak intensity

the average intensity across the beams entire cross-section area

spatial average intensity

there are ___ different methods for measuring temporal intensity in pulsed US

4

the intensity of the beam at the instant in time of its maximal value

temporal peak intensity

the time-averaged intensity over the largest half cycle in the pulse at the spatial peak

maximum intensity

the average intensity during the pulse duration (during transmit time)

pulse average intensity

the average intensity during the entire PRP (both transmit and receive times)

temporal average intensity

largest value of temporal intensity

temporal peak intensity

smallest value of temporal intensity

temporal average intensity

1. temporal peak intensity

2. maximum intensity

3. pulse average intensity

4. temporal average intensity

temporal intensities from largest to smallest

temporal average intensity is _____ times lower than TPI because it includes listening time

500

measured at the location where intensity is maximum and the instant in time when the most powerful part of the pulse passes

spatial peak temporal peak

measured at the location where intensity is maximum, averaged over the transmit time only

spatial peak pulse average

measured at the location where intensity is maximum and averaged over all time, both transmit and receive times

spatial peak temporal average

measured over the entire cross sectional area of the sound beam, and over all time

spatial average temporal average

highest value of intensity measurements

Spatial peak temporal peak

**SPTP**

intensity measurement that is most important for thermal bioeffects

spatial peak, temporal average

**SPTA**

lowest value of intensity measurements

spatial average, temporal average

**SATA**

the ratio of the center intensity to the average spatial intensity; describes the spread of a beam in space

beam uniformity coefficient

beam uniformity coefficient, AKA

SP/SA Factor

for continuous wave US, the beam is always on, so the pulse average and temporal average will be ___________

the same

SPTA = SPPA

SATA = SAPA

when pulsed and continuous wave sound beams have the same peak intensity values (SPTP), the __________ wave intensity has the higher SPTA intensity value

continuous

sound waves weaken, or _______, as they travel in the body

attenuate

the sound that comes back to the transducer is converted to an electrical signal, this signal is sent to the US system where it is strengthened, or _________

amplified

weakened =

attenuated

strengthened =

amplified

in dx US, we are interested in the degree of ______ and the extent of ______

attenuation

amplification

if the logarithm increases by 1, the actual number increases by

10

unit used for measuring the signal strength in diagnostic US

decibels

decibels does not measure absolute numbers, but rather reports relative _______

changes

two intensities required for decibels:

1. the reference/starting level

2. the actual level at the time of measurement

the reference/starting level is when the signal ____ the US machine

leaves

the actual level at the time of measurement is when the signal ______ to the US machine

comes back

if asked what the relative measurement of something is, you will use

decibels

when a waves intensity doubles, the relative change is

+ 3 dB

when a waves intensity increases ten-fold, the relative change is

+ 10 dB

when a waves intensity is reduced to 1/2 its original value, the relative change is

-3 dB

when a waves intensity is reduced to 1/10 its original value, the relative change is

- 10 dB

+ 3 dB =

doubled

+ 10 dB =

ten times larger

- 3 dB =

1/2

- 10 dB =

1/10

the decrease in intensity, power, and amplitude as sound travels through a medium

attenuation

attenuation is determined by 2 factors :

- path length

- frequency of sound

distance and attenuation are ______ related

directly

frequency and attenuation are ______ related

directly

if distance increases, attenuation will

increase

if frequency gets higher, attenuation will

increase

- reflection

- scattering

- absorption

3 processes that contribute to attenuation

as sound strikes a boundary and a portion of the waves energy may reflect back to the sound source

reflection

there are ____ forms of reflection in soft tissue

2

- specular

- diffuse

the two forms of reflection

type of reflection that occurs when sound strikes a smooth boundary and the sound is only reflected in one direction, in an organized manner

specular reflection

type of reflection that occurs when a wave hits an irregular surface and sound radiates in more than one direction

diffuse reflection

diffuse reflection, AKA

backscatter

backscattered signals have _______ strength than specular

lower

sound scatters when the tissue interface is ______ or equal to/less than the wavelength

small

______ frequency sound beams scatter much more

higher

scattering is ______ related to frequency

directly

special form of scattering that occurs when the structures dimensions are much smaller than the beams wavelength

Rayleigh scattering

rayleigh scattering redirects the sound wave equally in _____ directions

all

type of scattering seen exclusively with red blood cells

Rayleigh scattering

rayleigh scattering is proportional to the frequency ____

to the 4th power

rayleigh scattering increases ______ with increasing frequency

dramatically

most sizeable component of attenuation

absorption

occurs when US energy is converted into another form of energy like heat

absorption

absorption is _____ related to frequency

directly

the number of decibels of attenuation that occurs when the sound travels one cm

attenuation coefficient

the value of attenuation coefficient remains _______ regardless of how far the sound travels

constant

total attenuation (dB) =

attenuation coefficient (dB/cm) x distance (cm)

if sound travels to a depth of 5 cm and the coefficient is 2 dB/cm, what is the total attenuation?

10 dB

in soft tissue, the attenuation coefficient and the frequency are _______ related

directly

attenuation coefficient is _____ the frequency

one half

attenuation coefficient (dB/cm) =

frequency (MHz)/2

bone absorbs US energy to a ______ extent

large

______ attenuates dramatically due to scattering and absorption

lung

main mechanism of attenuation in air is

absorption

sound with frequencies above 1 MHz attenuate _______ in air

entirely

the distance sound travels in a tissue that reduces its intensity to one half the original value

half-value layer thickness

units for half-value layer thickness

cm, or unit of length

typical values of half-value layer thickness

0.25 - 1 cm

- penetration depth

- depth of penetration

- half-boundary layer

AKAs for half-value layer thickness

half-value layer thickness depends on 2 factors :

the medium

the frequency of sound

half-value layer thickness is ______ proportional to frequency

inversely

a thin HVLT will have a ______ frequency of sound

high

as attenuation increases, propagation speed will

remain unchanged

the ________ produced as sound moves from one medium to another forms the basis for US imaging

reflection

________ is critical to US's ability to image structures located deep in the body

transmission

the acoustic resistance to sound traveling in a medium

acoustic impedance

acoustic impedance is calculated by multiplying the _______ of a medium by the _____ at which sound travels in the medium

density

speed of sound

impedance (Z) =

density x propagation speed (m/s)

units for acoustic impedance

Rayls (Z)