Week 9 Axial and Lateral Resolution

Question 1

Resolution

Answer 1

The ability to create accurate images.

Question 2

What is Axial Resolution?

Answer 2

The ability of a system to display 2 structures that are close together when structures are parallel to the sound beams main axis.

Question 3

What is axial resolution measured in?

Answer 3

distance, mm

Question 4

What is axial resolution determined by?

Answer 4

It is determined by spatial pulse length.

Question 5

What is the typical value of axial resolution?

Answer 5

0.1 to 1.0 mm

Question 6

Other names for axial resolution

Answer 6

LARRD:
Longitudinal
Axial
Range
Radial
Depth

Question 7

Is axial resolution adjustable by the sonographer?

Answer 7

No, because the spatial pulse length for a transducer is fixed.

Question 8

Which is better for axial resolution, short or long pulses?

Answer 8

Short pulses improve axial resolution.

Question 9

Shorter pulse lengths Improves what?

Answer 9

The ability to accurately portray structures.

Question 10

Pulse duration

Answer 10

Is related to axial resolution.

Question 11

axial resolution formula in soft tissue:

Answer 11

AR = 0.77 x # of cycles/ frequency

Question 12

Better axial resolution is associated with:

Answer 12

1. shorter spatial pulse length
2. shorter pulse duration
3. Higher frequencies (shorter wavelength)
4. fewer cycles per pulse (less ringing)
5. lower numerical values

Question 12

How is a shorter pulse created?

Answer 12

1. Less ringing
2. Higher frequency

Question 13

If there are more cycles in a pulse, the numerical value of range resolution is
greater, lesser or same?

Answer 13

greater

Question 14

If a new pulsed transducer has many more cycles in its pulse, the image accuracy improves, degrades or remains the same?

Answer 14

it Degrades

Question 15

High/ Low frequency transducers generally have the best range resolution?

Answer 15

High

Question 16

Axial resolution formula:

Answer 16

spatial pulse length (mm) / 2

Question 17

In soft tissue, a 3 cycle 1 MHz pulse has a pulse length equal to 4.5 mm. what is the axial resolution?

Answer 17

2.25

Axial resolution is 1/2 of the spatial pulse length.
4.5 / 2 = 2.25

Question 18

Which of the following transducers have the best axial resolution?

A. 1.7 MHz & 4 cycles/ pulses
B. 2.6 MHz & 3 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses

Answer 18

D. 2.6 MHz & 2 cycles/ pulses

High frequency
Low ringing ( fewest cycles/ pulses)

Question 19

Which of the following transducers has the poorest axial resolution?

A. 1.7 MHz & 4 cycles/ pulses
B. 2.6 MHz & 3 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses

Answer 19

C. 1.7 MHz & 5 cycles/ pulses

Low frequency
Long ringing ( longest cycles/ pulses)

Question 20

What is Lateral resolution?

Answer 20

The ability to identify 2 structures that are close together when they are side by side or perpendicular to the sound beam.

Question 21

What is lateral resolution determined by?

Answer 21

It is determined by the width of the beam.

Question 22

What are other names for Lateral resolution?

Answer 22

LATA:
Lateral
Angular
Transverse
Azimuthal

Question 23

What area of the beam produce the best lateral resolution?

Answer 23

The focal zone, or the narrowest part of the beam.

Question 24

Axial numbers will be bigger or smaller than lateral resolution?

Answer 24

smaller than lateral resolution.

Question 25

Lateral resolution improves or degrades in the far field?

Answer 25

Improves in the far field.

Question 26

Why does lateral resolution improve in the far field?

Answer 26

High frequency creates a deeper focus than low frequency.

Question 27

Does lateral resolution change or stay the same with depth?

Answer 27

Changes with depth, best at focus.

Question 28

In the near field, lateral resolution is best with?

Answer 28

smallest diameter crystal

Question 29

In the far field, lateral resolution is best with?

Answer 29

Large diameter and highest frequency. ( least divergence)

Question 30

What are the effects of focusing?

Answer 30

1. beam diameter in near field and focal zone is reduced. 2. Focal depth is shallow 3. Beam diameter in the far zone increases. 4. Focal zone is smaller

Question 31

Focusing improves what?

Answer 31

Lateral resolution

Question 32

What are the three methods of focusing?

Answer 32

1. External focusing 2. Internal 3. Phased Array

Question 33

What method of focusing do we use in ultrasound?

Answer 33

Phased Array

Question 34

External focusing

Answer 34

lens is placed in front of the PZT. fixed, conventional, or mechanical.

Question 35

Curved element

Answer 35

internal lens Fixed, conventional, or mechanical

Question 36

Phased Array

Answer 36

Electronic Focusing

Question 37

Is Phased array able to be adjusted by the sonographer?

Answer 37

Yes

Question 38

In regard to axial resolution, lower numerical values indicate what?

Answer 38

shorter pulses and improved axial resolution.

Question 39

Two different transducers create pulses. both transducers create sound with a freq. of 4MHz. One transducer creates a pulse that comprises 6 cycles and the other, 3 cycles. Which transducer is more likely to create a more accurate image with respect to axial resolution? Which transducer has a lower numerical value of axial resolution?

Answer 39

3 cycle pulse is more likely to create an image with better axial resolution. Less ringing, or fewer cycles in a pulse, generally implies shorter pulses and improved axial resolution.

Question 40

Two different transducers create sound pulses. One transducer is labeled 5 MHz and the other, 3 MHz. Which transducer is more likely to create a more accurate image with respect to axial resolution? Which transducer probably has a lower numerical value of axial resolution?

Answer 40

The 5 MHz transducer is more likely to create an image with better axial resolution. The Higher frequency transducer creates a shorter pulse and thus has a lower numerical value of axial res.

Question 41

what is the mathematical relationship that describes this beam diameter and lateral resolution?

Answer 41

lateral resolution = beam diameter

Question 42

What type of focusing includes both external and internal techniques?

Answer 42

Fixed focusing

Question 43

A lens is placed where on the transducer with external focusing? What type of focusing is this?

Answer 43

In front of the PZT, a fixed focusing technique for external focusing.

Question 44

What does a curved PZT do to the beam? What type of focusing is this?

Answer 44

Concentrates the sound energy into a narrower or tighter beam. Internal focusing.