Physical Principles/Duplex Imaging

Question 1

ultrasound is a ___ wave that is directed through the tissues

Answer 1

mechanical

Question 2

grayscale imaging

strength of the return wave is dependent upon (2)

Answer 2

tissue interfaces
angle of insonation

Question 3

grayscale imaging

the strongest reflection = beam strikes an interface at a ___ angle

Answer 3

90° angle

Question 4

grayscale imaging

average speed of ultrasound through soft tissue is ___

Answer 4

1540 m/sec

Question 5

what is the 13 microsecond rule?

Answer 5

13 microsecond rule (roundtrip)

signal obtained at 13 microseconds is from 1cm deep

Question 6

duplex imaging combines (2)

Answer 6

grayscale (B-mode)
Doppler

Question 7

Doppler

frequency of reflected sound waves depends upon (2)

Answer 7

speed
direction

Question 8

Doppler shift is the difference between ___

Answer 8

wave frequency directed into the tissues and what returns

Question 9

2 forms of the Doppler equation

Answer 9

Df (Hertz) = (2 fo V cos θ) / C
solves for Doppler-shifted frequency

V = (Df C) / 2 fo cos θ
solves for velocity

Df = Doppler shift frequency
fo = carrier frequency
V = velocity
cos θ = angle of incidence (60° or less for vascular)
C = speed of sound through tissue

Question 10

2 techniques for Doppler analysis

Answer 10

continuous wave (CW)
pulsed wave (PW)

Question 11

CW Doppler has no ___ and does not ___

Answer 11

no range or depth resolution
does not alias

Question 12

2 types of CW Doppler velocimetry (signal processing)

Answer 12

analog
digital

Question 13

analog uses ___ frequency detector

Answer 13

zero-crossing frequency detector

estimates and displays the frequencies present in the reflected wave

high frequency waves = many oscillations
low frequency waves = fewer oscillations

(analog - average)

Question 14

drawbacks of analog processing (2)

Answer 14

noise
decreased sensitivity

Question 15

digital - spectral analysis uses ___

Answer 15

fast fourier transfer (FFT)

analyzes and displays ALL frequencies moving through the sample area

(digital - detail)

Question 16

analog or digital

which is more accurate?

Answer 16

digital

better sensitivity, less noise

Question 17

CW Doppler or PW Doppler

which is the primary technique used in duplex scanning?

Answer 17

PW Doppler

Question 18

PW Doppler determines the returning signal’s ___

Answer 18

precise location (depth)

Question 19

PW Doppler

what is pulse repetition frequency? (PRF)

Answer 19

number of pulses per unit of time sent into the tissue

Question 20

PW Doppler may alias if ___

Answer 20

the Doppler-shifted frequency is greater than ½ the PRF (Nyquist limit)

Question 21

PW Doppler signals are processed using ___

Answer 21

fast fourier transfer (FFT)

Question 22

what is a limitation of PW Doppler?

Answer 22

unable to see what is occurring outside the small sample volume

Question 23

___ is able to sample thousands of sample volumes throughout the image

Answer 23

color Doppler

Question 24

color Doppler displays a ___ frequency

Answer 24

mean frequency

Question 25

color Doppler low resolution compared to ___

Answer 25

spectral analysis

Question 26

color Doppler color bar displays flow direction relative to the ___

Answer 26

transducer

Question 27

color Doppler flow towards the transducer is always on ___

Answer 27

top

Question 28

CW Doppler ___ sample displays ___ frequencies no ___

Answer 28

one large displays ALL frequencies no depth resolution

Question 29

spectral Doppler or color Doppler uses PW on one sample to distinguish flow at different depths

Answer 29

spectral Doppler

Question 30

spectral Doppler or color Doppler uses PW on thousands of sample volumes

Answer 30

color Doppler

Question 31

3 transducers used in vascular testing

Answer 31

linear* curvilinear sector

Question 32

linear transducer ___ footprint ___ beam ___ beam steering ___ MHz

Answer 32

large footprint rectangular beam can beam steer 5-10 MHz

Question 33

curvilinear transducer ___ footprint ___ beam ___ beam steering ___ MHz

Answer 33

large footprint trapezoidal beam cannot beam steer 2-5 MHz

Question 34

sector transducer ___ footprint ___ beam ___ beam steering ___ MHz

Answer 34

small footprint triangular beam cannot beam steer 1-5 MHz

Question 35

what is frequency?

Answer 35

number of cycles (vibrations) per second

Question 36

yes or no frequency is user adjustable

Answer 36

frequency is NOT user adjustable transducer crystal determines frequency

Question 37

typical values for diagnostic ultrasound range between ___ MHz

Answer 37

2-15 MHz

Question 38

higher frequency = ___ resolution ___ penetration

Answer 38

better resolution less penetration

Question 39

when flow is normal and organized, the spectral window is ___

Answer 39

narrow - clear spectral window

Question 40

as flow becomes more disorganized, the spectral will ___

Answer 40

broaden, no spectral window

Question 41

yes or no sample volume size is user adjustable

Answer 41

yes - sample volume size is user adjustable

Question 42

smaller sample volumes ___ signal ___ spectral waveform

Answer 42

weaker signal narrow spectral waveform

Question 43

large sample volumes ___ signal may include ___

Answer 43

stronger signal but more spectral broadening may include multiple small vessels

Question 44

sample volume size 1. dependent upon ___ 2. most arterial applications ___ mm 3. venous applications may increase size to ___ 4. ___ will nearly always have a filled in spectral window

Answer 44

1. dependent upon the size of the vessel 2. most arterial applications 1.5-2.5mm 3. venous applications may increase the size to increase detection of small Doppler shifts 4. CW will nearly always have a filled in spectral window because the sample volume is large

Question 45

deeper vessel = ___ pulse/cycle ___ frequency ___ frame rate

Answer 45

longer pulse/cycle more accurate frequency decreased frame rate

Question 46

slow frame rates are unable to view ___

Answer 46

transient flow events

Question 47

frame rate is related to ___

Answer 47

temporal resolution = rate at which images are acquired

Question 48

what is Nyquist limit/frequency?

Answer 48

ability of the system to properly display flow events

Question 49

what is aliasing?

Answer 49

improper display of flow due to the sampling rate

Question 50

6 ways to fix aliasing

Answer 50

1. increase scale (PRF) 2. adjust baseline - better display 3. adjust angle of insonation 4. decrease depth 5. lower frequency 6. use CW Doppler

Question 51

___ artifact often occurs with a strong Doppler signal and using a high Doppler gain

Answer 51

mirroring artifact

Question 52

yes or no can color Doppler display mirror artifact?

Answer 52

yes - flow will be displayed where it is not

Question 53

how do you fix mirroring artifact?

Answer 53

decrease gain

Question 54

blood vessels may exhibit a helical flow pattern common in the ___ spectral waveforms are ___ above and below the baseline

Answer 54

common in the carotid bifurcation spectral waveforms are different above and below the baseline