Physics Chapter 7

Question 1

Doppler effect

Answer 1

change in frequency that occurs when there is relative motion between the transducer and the reflecting surface (RBCs) determines velocity of reflectors and direction of blood flow

Question 2

What frequency are the transmit sounds and receive sounds

Answer 2

Transmit in Mhz and recieve and process into audible range KHz

Question 3

Dopppler shift

Answer 3

doppler shift= reflected f - transmitted f this is the frequency of the moving blood cells

Question 4

postive and negative shift

Answer 4

positive flow is towards transducer
negative flow is away from transducer

Question 5

Insonation angle

Answer 5

Best doppler angle= 0 or 180
Vascular angle=60 most common range 30-60
echo= 0
90= no doppler shift

Question 6

cos values

Answer 6

cos 0=1
cos 60=0.5
cos90=0

Question 7

RBC Aggregation (Rouleau)

Answer 7

Low shear flow states BC form a rouleau formation like a roll of coins increasing the refelctibity often results in ability to visualize the blood (spontaneous contrast)

Question 8

obtain a good angle

Answer 8

Beam sterring- signal phasing process allows doppler to be steered left or right
heel toe trasnducer- decrease angle to flow
natural vessel angle
angle correction

Question 9

CW doppler

Answer 9

Continuous stream of sound waves, measures velocity of blood flow along a fixed line cant determine exact location, high sensitivity but limited range

Question 10

PW doppler

Answer 10

Short pursed of sound waves to measure flow velocities, allow to determine exact location and velocity, lower sensitivity but wider range.

Question 12

Nyquist limit

Answer 12

highest doppler freq accurately processed by pw ultrasound without aliasing= 1/2 PRF

Question 12

PRF

Answer 12

Number of echoe cycles per second determined by depth of sample volume increase sv decreae in max prf

Question 13

Aliasing

Answer 13

artifact that occurs when using pw doppler and the nyquist limit is exceeded. high velocitys reported in opposite direction they are in

Question 14

Spectral doppler aliasing

Answer 14

Only in pw not cw

Question 15

Bidirectional doppler intrument

Answer 15

distinguishes between pos and neg doppler shifts
can be pw or cw

Question 16

directional doppler

Answer 16

speed and direction of rbcs use stereo system to determine pos or neg shift

Question 17

unidirectional

Answer 17

presence of shift
inexpensive small units determine presence or absence of flow

Question 18

non directional

Answer 18

only speed not flow simple speaker

Question 19

spectral doppler

Answer 19

examines flow at one sire
detailed analysis of distribution of flow
good temp resolution
allow calc of velocity and indices
pos shift above baseline
neg shift below baseline

Question 20

Colour doppler

Answer 20

overall view of flow in region
limite flow info
poor temp resolution
determines velocity, direction and flow pattern
Colour flow map

Question 21

High PRF spectral doppler

Answer 21

used to measure high velocitys without aliasing exceed nyquist limit

Question 22

power doppler

Answer 22

assigns values to doppler shift
power determined by concentration of moving scatters producing doppler shifts
independent of doppler shift, freq and angle

Question 23

b mode imaging

Answer 23

Helps image diagnose vascular disease
image moving particles
flow plus b mode creates image

Question 24

vector flow imaging

Answer 24

uses multiple beams to create flow map assessment of flow direction velocity and patterns within blood vessels. enhances capabilities for conditions

Question 25

spectral analysis

Answer 25

study or interpretaation of collection allows visualization of doppler signal and provides quantitative data to evaluate doppler shift

Question 26

What happens to recieved echoes (very long 7 things)

Answer 26

-amplifier preforms amplification, mixer preforms doppler shift detection -wall filter-selectively decreases dynamic range by eliminating high amplitude low velocity echoes -gain- addition gain after dr reduce so weak signals are amplified -audio- stereo signal and one speaker for forward and one speaker for reverse flow -adc- start to prepare signal for visualization -fft -post processing- compression, reject, gray scale

Question 27

FFT fast fourier transform

Answer 27

mathmatical process that analyses returning doppler signals and sieplays on spectral display x axis time y axis doppler shift f an amplitude

Question 28

Quadrature phase detection

Answer 28

samples are separated into forward and reverse shifts to determine flow direction seperated by 90 one quadrant to detect flow

Question 29

spectral window

Answer 29

clear area under spectrum freq range narrow- large clear window freq range wide- window filled with echoes

Question 30

waveform magnitude or brightness

Answer 30

amplitude of signal changed by scanning technique of sonographer

Question 31

main factors affecting spectral doppler

Answer 31

power- transmitting power into tissue gain-overall sensitivity to flow signals (amplification of doppler signal recieved) velocity scale/prf- high prf high velocity low prf low velocity gate size beam steering- can allow improved beam flow angle for better accuracy of v calc live duplex/ triplex-scanning modes spectral resolution constrained by need for b mode/ color pulses

Question 32

wall filters and sweep speed

Answer 32

wf-eliminate unwanted blood flow signals high amplitude low freq signals ss- faster speed easier to measure slower more cardiac cycles

Question 33

Color doppler

Answer 33

superimpose colour code map of doppler shifts on b mode image pulses fewer and shorter mean velocities shown

Question 34

Packet

Answer 34

color of pulses per scan line of color bmode= 1 color 3-20 common 8-20 high number robust colour lower frame rate improved sensitivity to weak signals low number weak color oposite of high

Question 35

Autocorrelation provides

Answer 35

-flow direction -mean freq shift -power amplitude -variances

Question 36

colour frame rate variables

Answer 36

pulses per line packet size density scan lines color box width prf

Question 37

color persistence (smoothing)

Answer 37

averages frames over time improves signal to noise ratio, allows colour to remain on image longer

Question 38

Directional color power doppler

Answer 38

combines power (amplitude) of signal with direction info to encode direction and variation in blood flow

Question 39

HPRF

Answer 39

aliasing eliminated PW switched to HPRF increase number of active sample volume when operator wants to measure blood flow at certain depth where aliasing occurs with pw

Question 40

color box orientation

Answer 40

orientate color box so that its orientation aligns with orientation of blood vessels