Pulsed Waves

Question 1

What is an ultrasound pulse?

Answer 1

A collection of wave cycles that move together

Question 2

What is pulse duration?

Answer 2

Transmit time from the start to end of that pulse

Question 3

What is the equation for pulse duration?

Answer 3

Pulse duration (us) = # cycles x period (us) 
Pulse duration (us) = # cycles/ frequency (MHz)

Question 4

What determines pulse duration?

Answer 4

Sound source

Question 5

Can pulse duration be adjusted?

Answer 5

No

Question 6

What is spatial pulse length? (SPL)

Answer 6

The distance a pulse goes from the start to end of that pulse

Question 7

What is the equation for SPL?

Answer 7

SPL (mm) = # cycles x wavelength (mm)

Question 8

What determines SPL?

Answer 8

Sound source and medium

Question 9

Can SPL be adjusted?

Answer 9

No

Question 10

What is pulse repetition period? (PRP)

Answer 10

Time from the start of one pulse to the start of the next

One pulse duration and one listening time

Question 11

What determines PRP?

Answer 11

Sound source and imaging depth

Question 12

Can PRP be adjusted?

Answer 12

Yes

Question 13

How are period and PRP related?

Answer 13

Unrelated

Question 14

How does PRP change with depth?

Answer 14

Directly
When depth is decreased, time from one pulse to the next is shorter (Decreases PRP)
When depth is increased, time from one pulse to the next is longer (Increases PRP)

Question 15

What is pulse repetition frequency? (PRF)

Answer 15

The number of pulses that the ultrasound machine transmits each second

Question 16

What determines PRF?

Answer 16

Sound source and imaging depth

Question 17

Can PRF be changed?

Answer 17

Yes by adjusting depth of view

Question 18

How is PRF related to depth?

Answer 18

Inversely
When depth of view increases, PRF decreases
When depth of view decreases, PRF increases

Question 19

How are frequency and PRF related?

Answer 19

Unrelated

Question 20

How are PRP and PRF related?

Answer 20

Inversely
A longer PRP results in lower PRF
A shorter PRP results in higher PRF

Question 21

What special relationship do PRP and PRF have?

Answer 21

Reciprocals
PRF = 1/PRP
PRP = 1/PRF

Question 22

What is duty factor?

Answer 22

Percentage of time that the system is transmitting a pulse

Question 23

What is the equation for duty factor?

Answer 23

Duty Factor (%) = (pulse duration/ PRP) x 100

Question 24

How is duty factor related to depth?

Answer 24

Inversely
As depth increases, duty factor decreases
As depth decreases, duty factor increases

Question 25

Can you have a duty factor of 1 or 100% in ultrasound imaging?

Answer 25

No, it is continuous and cannot produce images

Question 26

What three properties change when the sonographer adjusts the depth of the image?

Answer 26

PRP, PRF, and Duty Factor

Question 27

What is axial resolution?

Answer 27

Ability of the system to distinguish between two structures very close together and parallel to the sound beam

Question 28

What are the other terms used to describe axial resolution?

Answer 28

``` LARRD Longitudinal Axial Range Radial Depth ```

Question 29

Can the sonographer adust axial resolution?

Answer 29

No | It depends on SPL

Question 30

Does higher or lower frequency create better axial resolution?

Answer 30

Higher frequency

Question 31

Does more or less ringing (cycles per pulse) create better axial resolution?

Answer 31

Less ringing (cycles per second)

Question 32

How are axial resolution and SPL related?

Answer 32

Axial resolution (mm) = spatial pulse length (mm)/2

Question 33

What is lateral resolution?

Answer 33

The ability to identify two structures very close together and perpendicular to the sound beam main axis

Question 34

What are other terms used to describe lateral resolution?

Answer 34

``` LATA Lateral Angular Transverse Azimuthal ```

Question 35

At what point in the beam is lateral resolution the best?

Answer 35

Best at the focal point, where the beam is narrowest

Question 36

Is axial or lateral resolution better?

Answer 36

Axial because the ultrasound pulses are shorter than they are wide

Question 37

Is lateral resolution better in the far-field with high or low frequencies?

Answer 37

Lateral resolution because high frequency pulses diverge less in the far field than low frequency pulses.

Question 38

What clinical benefit is provided by lower frequency sound waves?

Answer 38

Provide deeper penetration

Question 39

What is external focusing?

Answer 39

When a lens is placed in front of piezoelectric material to narrow beam width

Question 40

Is external focusing adjustable?

Answer 40

No

Question 41

What is internal focusing?

Answer 41

When a curved piezoelectric crystal is used to concentrate sound energy into a narrower beam

Question 42

Is internal focusing adjustable?

Answer 42

No

Question 43

What is phased array focusing?

Answer 43

Narrowing beam width with electronics of US system

Question 44

Is phased array focusing adjustable?

Answer 44

Yes

Question 45

What is bandwidth?

Answer 45

Range of frequencies in the pulse. The difference between the highest and lowest frequencies.

Question 46

What is quality factor?

Answer 46

- A unitless number inversely related to bandwidth

Question 47

What is the equation for quality factor?

Answer 47

Quality Factor = main frequency/bandwidth