# Pulsed Waves Flashcards

1
Q

What is an ultrasound pulse?

A

A collection of wave cycles that move together

2
Q

What is pulse duration?

A

Transmit time from the start to end of that pulse

3
Q

What is the equation for pulse duration?

A
```Pulse duration (us) = # cycles x period (us)
Pulse duration (us) = # cycles/ frequency (MHz)```
4
Q

What determines pulse duration?

A

Sound source

5
Q

A

No

6
Q

What is spatial pulse length? (SPL)

A

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

7
Q

What is the equation for SPL?

A

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

8
Q

What determines SPL?

A

Sound source and medium

9
Q

A

No

10
Q

What is pulse repetition period? (PRP)

A

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

One pulse duration and one listening time

11
Q

What determines PRP?

A

Sound source and imaging depth

12
Q

A

Yes

13
Q

How are period and PRP related?

A

Unrelated

14
Q

How does PRP change with depth?

A

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)

15
Q

What is pulse repetition frequency? (PRF)

A

The number of pulses that the ultrasound machine transmits each second

16
Q

What determines PRF?

A

Sound source and imaging depth

17
Q

Can PRF be changed?

A

Yes by adjusting depth of view

18
Q

How is PRF related to depth?

A

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

19
Q

How are frequency and PRF related?

A

Unrelated

20
Q

How are PRP and PRF related?

A

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

21
Q

What special relationship do PRP and PRF have?

A

Reciprocals
PRF = 1/PRP
PRP = 1/PRF

22
Q

What is duty factor?

A

Percentage of time that the system is transmitting a pulse

23
Q

What is the equation for duty factor?

A

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

24
Q

How is duty factor related to depth?

A

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

25
Q

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

A

No, it is continuous and cannot produce images

26
Q

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

A

PRP, PRF, and Duty Factor

27
Q

What is axial resolution?

A

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

28
Q

What are the other terms used to describe axial resolution?

A
```LARRD
Longitudinal
Axial
Range
Depth```
29
Q

Can the sonographer adust axial resolution?

A

No

It depends on SPL

30
Q

Does higher or lower frequency create better axial resolution?

A

Higher frequency

31
Q

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

A

Less ringing (cycles per second)

32
Q

How are axial resolution and SPL related?

A

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

33
Q

What is lateral resolution?

A

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

34
Q

What are other terms used to describe lateral resolution?

A
```LATA
Lateral
Angular
Transverse
Azimuthal```
35
Q

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

A

Best at the focal point, where the beam is narrowest

36
Q

Is axial or lateral resolution better?

A

Axial because the ultrasound pulses are shorter than they are wide

37
Q

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

A

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

38
Q

What clinical benefit is provided by lower frequency sound waves?

A

Provide deeper penetration

39
Q

What is external focusing?

A

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

40
Q

A

No

41
Q

What is internal focusing?

A

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

42
Q

A

No

43
Q

What is phased array focusing?

A

Narrowing beam width with electronics of US system

44
Q

A

Yes

45
Q

What is bandwidth?

A

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

46
Q

What is quality factor?

A
• A unitless number inversely related to bandwidth
47
Q

What is the equation for quality factor?

A

Quality Factor = main frequency/bandwidth