Pulsed & Continuous Wave Techniques

Question 1

What is the main difference between continuous wave US vs pulsed wave US?

Answer 1

CW = 2 elements; one for transmission, one for reception

PW = 1 element that simultaneously transmits/receives

Question 2

What is the frequency determined by in CW vs PW?

Answer 2

CW = voltage
PW = crystal thickness and propagation velocity

Question 3

What is the duty factor in CW vs PW?

Answer 3

CW = 100% (constant emission of waves)
PW = 0.1% average

Question 4

What are the 3 advantages of continuous wave ultrasound?

Answer 4

1: obtaining Doppler on deeper structures
2: no aliasing / depth limitation
3: narrow bandwidth ( high quality facotr + sensitivity)

Question 5

What is the main disadvantage with continuous wave?

Answer 5

range ambiguity; we’re unable to determmine the exact location of the highest veloctiy

Question 6

What are the 2 advantages of pulsed wave ultrasound?

Answer 6

1. useful for 2D imaging
2. range specificity

Question 7

What is pulse duration and its diagnostic average range of values?

Answer 7

time of it takes for a single pulse to be transmitted

0.3 - 2.0 microseconds

Question 7

How many cycles are there usually in 2D vs Doppler imaging?

Answer 7

2D = 2-3 cycles per pulse

Doppler = 5-20 cycles per pulse

Question 8

What is pulse duration determined by? Is it adjustable?

Answer 8

Sound source; no

Question 9

How do you calculate pulse duration?

Answer 9

PD = # cycles/frequency
PD = # cycles x period

Question 10

When there is a ________ frequency, the pulse duration shortens.

Answer 10

higher

Question 11

T/F: SPL does not remain constant at all depth and varies.

Answer 11

false; remains constant throughout all depths

Question 11

What does a shorter pulse duration lead to?

Answer 11

improved axial resolution
increased PRF
decreased duty factor

Question 12

What is spatial pulse length and its diagnostic average range?

Answer 12

length of one pulse from the beginning to end

0.1 mm - 1.0 mm

Question 13

What is the SPL determine by? Is it adjustable?

Answer 13

Sound source and medium; no

Question 14

How is SPL calculated?

Answer 14

cycles x wavelength

Question 15

When there are more cycles in a pulse, what happens to the SPL?

Answer 15

increases

Question 16

We ideally want a _________ SPL because it leads to better image quality.

Answer 16

shorter

Question 17

A shorter SPL is seen with what kind of transducers?

Answer 17

high frequency

Question 18

What is Pulse Repetition Frequency and its diagnostic average range?

Answer 18

pulses emitted per second

1-10 kHz

Question 18

What is the PRF determined by? Is it adjustable?

Answer 18

medium; adjustable via depth and velocity scale in Doppler

Question 19

Is PRF related to frequency?

Answer 19

no

Question 20

If the pulsers PRF = 5 kHz, what is the PRF of the ultrasound wave?

Answer 20

5 kHz; will always be the same

Question 21

How do you calculate PRF?

Answer 21

77,000 cm/s / depth (cm)

PRF = 1/PRP

Question 22

When depth increases, what happens to the PRF and DF? Why?

Answer 22

both decrease the # of pulses decrease to travel deeper into the body, so PRF decreases since the transducer is transmitting less and receiving more, DF decreases

Question 22

In Doppler, what does PRP correspond to?

Answer 22

the time of pulse transmission to the time of the 1st Doppler shift

Question 22

What is PRP determined by? Is it adjustable?

Answer 22

medium; yes via depth

Question 23

Wha tis pulse repetition period and its diagnostic average range?

Answer 23

time from the start of one pulse to the end of the next 100 microseconds = 1 millisecond

Question 24

How do you calculate PRP?

Answer 24

depth x 13 microseconds/cm 1/PRF

Question 25

When depth increases, PRP ____________.

Answer 25

increases

Question 26

What is duty factor?

Answer 26

the % time pulse transmission is occurring

Question 27

Is DF adjustable?

Answer 27

yes via depth

Question 28

How do you calculate DF?

Answer 28

(PD/PRP) x 100%

Question 29

When depth increases, what happens to the DF, PRF, PRP, and PD?

Answer 29

DF, PRF, and PD decrease PRP increases

Question 30

What happens to the risk of thermal bioeffects when duty factor increases? Why?

Answer 30

increases due to increased sound waves emitted and therefore increased absorption

Question 30

What is bandwidth and its average values?

Answer 30

range of highest to lowest frequencies in each pulse (MHz) usually printed on housing 5-7 MHz or 2-4 MHz

Question 31

What is bandwidth determined by? Is it adjustable?

Answer 31

source (specifically the transducer); no

Question 32

How is bandwidth calculated?

Answer 32

maximum frequency - minimum frequency

Question 33

Longer pulses = ___________ bandwidth

Answer 33

narrower

Question 34

When there is a damping/backing layer present, what happens to the number of cycles in a pulse and bandwidth?

Answer 34

of cycles decrease and bandwidth broadens

Question 35

What does a narrower bandwidth do to quality factor and SPL? What does this do to the image quality?

Answer 35

increases QF and SPL = poorer image quality

Question 36

What is Q factor?

Answer 36

unitless # representing amount of damping applied

Question 37

What are the general QF differences between imaging vs Doppler/therapeutic transducers?

Answer 37

2D = low QF Doppler/therapeutic = high QF

Question 37

What is the Q factor also known as?

Answer 37

damping factor

Question 38

How do you calculate QF?

Answer 38

transducer frequency / bandwidth in MHz

Question 38

Q factor is directly related to _______.

Answer 38

frequency

Question 39

What is a sector angle?

Answer 39

the field of view

Question 39

What improves with a low QF?

Answer 39

resolution

Question 40

When there are more scan lines present, what happens to the spatial resolution?

Answer 40

improves

Question 41

When the sector angle is decreased, what happens to the frame rate and temporal resolution?

Answer 41

faster FR and better temporal resolution

Question 42

What is the significance of line density in sector imaging vs rectangular?

Answer 42

sector: determines the # of scan lines per degree rectangular = # scan lines per cm

Question 43

When line density increases, what also increases along with it?

Answer 43

pulses per frame, therefore improves axial and lateral resolution

Question 44

When line density increases, what decreases with it?

Answer 44

frame rate and temporal resolution

Question 45

If the sector angle contains 100 scan lines and the sector size is halved, what happens to the new sector angle?

Answer 45

it will now contain 50 scan lines

Question 46

What is fill-in interpolation?

Answer 46

preprocessing technique that fills gaps between scan lines with averaged information

Question 47

What does fill-in interpolation improve?

Answer 47

spatial and temporal resolution, frame rate