Chapter 18, 19 and 20 Study Guide

Question 1

Pulsed Doppler

Answer 1

range resolution
sample volume
limited maximum velocity-Nyquist
aliasing

Question 2

Continuous Wave Doppler

Answer 2

range ambiguity
region of overlap
unlimited maximum velocity
no aliasing

Question 3

Pulsed Doppler Transducer

Answer 3

at least one crystal 
dampened PZT 
low Q-factor 
wide bandwidth 
low sensitivity

Question 4

Continuous Doppler Transducer

Answer 4

at least two crystals 
undampened PZT 
high Q-factor 
narrow bandwidth 
higher sensitivity

Question 5

Imaging

Answer 5

normal incidence- 90 degrees
higher frequency- improves resolution
pulsed wave only
minimum of 1 crystal

Question 6

Doppler

Answer 6

0 to 180 degrees
lower frequency- avoids aliasing
minimum of 1 (pulsed) or 2 (continuous wave) crystals

Question 7

What is the movement of fluid from one location to another called?

Answer 7

velocity

Question 8

Fluid moving with a variable velocity when it accelerates and decelerates, what is that called?

Answer 8

Pulsatile Flow
accelerates and decelerates as a result of cardiac contraction
appears in the arterial circulation

Question 9

What is fluid moving from one location to another and it accelerates and decelerates with respiration?

Answer 9

Phasic Flow

appears in the venous circulation

Question 10

What type of flow pattern will be seen with normal physiological states?

Answer 10

Laminar Flow

Question 11

Frictional loss occurs when one object rubs against another, blood sliding along the vessel wall would be considered what?

Answer 11

Frictional loss

Question 12

The Reynolds number for turbulent flow is what?

Answer 12

greater than 2,000

Question 13

What are the effects of stenosis?

Answer 13

change in flow direction 
turbulence downstream from the stenosis 
increased velocity as vessel narrows 
pressure gradient across the stenosis 
loss of pulsatility

Question 14

What information is the Doppler shift providing?

Answer 14

velocities of blood cells

Question 15

What is a positive Doppler shift?

Answer 15

when blood cells move toward the transducer

the reflected frequency is higher than the transmitted frequency

Question 16

What is a negative Doppler shift?

Answer 16

when blood cells move away from the transducer

the reflected frequency is lower than the transmitted frequency

Question 17

Hydrostatic Pressure

Answer 17

pressure related to the weight of blood pressing on a vessel measured at a height above or below the heart level
units: mmHg (the same units used for blood pressure)
when supine: all parts of the body are at the level of the heart and hydrostatic pressure is 0

Question 18

Hydrostatic Pressure: Supine and Standing

Answer 18

supine: all parts of the body are at the level of the heart and hydrostatic pressure is 0
standing: hydrostatic pressure depends on if the measurement is taken above or below the heart
measurements below the heart: will be positive
measurements above the heart: will be negative

measured pressure = circulatory pressure + hydrostatic pressure

Question 19

What is the typical range of Doppler shift found in imaging exam?

Answer 19

20 Hz to 20,000 Hz (20 KHz)

audible range

Question 20

What are the 5 ways to eliminate aliasing?

Answer 20

adjust the scale to its maximum 
select a lower frequency transducer 
select a new ultrasound view with a shallower sample volume 
use a baseline shift 
use continuous wave Doppler

Question 21

What does the Y axis stand for on the Doppler spectrum?

Answer 21

Doppler shift or velocity

Question 22

What does the X axis stand for on the Doppler spectrum?

Answer 22

time

Question 23

What two things are the gray shades related to on the Doppler spectrum?

Answer 23

amplitude of the reflected signal

number of blood cells creating reflection

Question 24

When we look at our Doppler spectrum and see our waveform is high, are we using a higher or lower frequency?

Answer 24

higher frequency
the Doppler shift is directly proportional to the transducer frequency. When the transmitted frequency doubles, the Doppler frequency doubles.

Question 25

What is speed?

Answer 25

speed = distance/time

Question 26

What is velocity?

Answer 26

velocity = speed with direction

Question 27

What is the primary advantage for pulsed wave Doppler?

Answer 27

being able to select the exact location where velocities are measured

Question 28

What is the primary advantage for continuous wave?

Answer 28

to accurately measure very high velocities

Question 29

Bidirectional Doppler uses what kind of processing?

Answer 29

phase quadrature or quadrature detection

Question 30

What type of velocities does color flow measure?

Answer 30

average (mean) velocity

Question 31

Autocorrelation

Answer 31

is a digital technique used to analyze color flow Doppler uses color Doppler because of the enormous amount of data that is processed less accurate but faster to perform than FFT (fast fourier transform)

Question 32

Color Flow

Answer 32

a form of two-dimensional Doppler velocity is coded into colors (away and towards flow) black and white identifies anatomic structures color identifies blood flow

Question 33

What are the limitations to color flow imaging?

Answer 33

provides information on the location of flow: is a pulsed ultrasound technique has a range resolution (range specificity) is subject to aliasing

Question 34

What are the advantages of Doppler Packets?

Answer 34

more accurate velocity measurement | increased sensitivity to low flow

Question 35

What are the disadvantage of Doppler Packets?

Answer 35

more time needed to acquire data reduced frame rate decreased temporal resolution

Question 36

Inspiration

Answer 36

``` diaphragm moves downward toward the abdomen thoracic pressure decreases abdominal pressure increases venous return to the heart increases venous flow in legs decreases ```

Question 37

Expiration

Answer 37

``` diaphragm moves upward into thorax thoracic pressure increases abdominal pressure decreases venous return to the heart decreases venous flow in legs increases ```

Question 38

When venous pressure is low, what is the volume of blood in the veins?

Answer 38

when veins have low pressure, they are only partially filled with blood and only partially expanded

Question 39

What happens to the shape of the vein when the venous pressure increases?

Answer 39

the cross-sectional shape of a vein change from hourglass to oval and then to round hourglass > oval > round this allows veins to accommodate a large volume increase with a small increase in pressure

Question 40

What is Doppler shift inversely related to?

Answer 40

propagation speed

Question 41

What is Fast Fourier Transform used for?

Answer 41

to process both pulsed and continuous wave Doppler signals | distinguishes laminar flow from turbulent flow

Question 42

When the sample volume is deep the PRF is what? And the nyquist limit is what?

Answer 42

PRF is low and Nyquist is low | deeper sample volumes have a lower pulse repetition frequency and create aliasing