Chapter 10 Axial and Lateral Resolution

Question 0

The ability to distinguish two structures lying close together front-to-back or parallel to the sound beam is called?

Answer 0

Longitudinal, Axial, Range, Radial, or depth resolution

Question 1

Accuracy in imaging is called what?

Answer 1

Resolution

Question 2

What are the units of axial resolution?

Answer 2

Measured in mm or any other unit of distance

Question 3

Axial resolution is related to what?

Answer 3

Spatial pulse length

Question 4

Synonyms for axial resolution?

Answer 4

LARRD:
Longitudinal
Axial
Range
Radial
Depth

Question 5

The sonographer _________ change axial resolution?

Answer 5

Cannot

Question 6

In clinical imaging, axial resolution ranges from _____ to _____mm.

Answer 6

0.1 to 1.0 mm

Question 7

What is the relationship between the numerical value of the axial resolution and the image quality?

Answer 7

The image quality is better when axial resolution has a lower numerical value.

Question 8

Lower numerical values of axial resolution indicate?

Answer 8

Shorter pulse

Question 9

Shorter pulses create more ___________ images?

Answer 9

Accurate

Question 10

What is the mathematical description of axial resolution?

Answer 10

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

Axial resolution (mm) = (wavelength (mm) * # of cycles in pulse)/2

In soft tissue: 
Axial resolution (mm) = (0.77 * # of cycles in pulse)/ frequency (MHz)

Question 11

What allows some transducers to have better axial resolution than others?

Answer 11

Axial resolution is determined by the pulse length, with shorter pulses yielding improved axial resolution

Question 12

A short pulse is created in what two ways?

Answer 12

1. Less ringing

2. Higher frequency

Question 13

A pulse is short if there are few cycles in the pulse, just like a train is short if there are few cars in the train. This is known as?

Answer 13

Less ringing

Question 14

What is one way to reduce ringing?

Answer 14

Dampen the crystal after it has been excited by an electrical signal from the system

Question 15

A pulse is short if each cycle in the pulse has a __________ wavelength.

Answer 15

Short

Question 16

Shorter wavelengths are characteristics of _____________.

Answer 16

Higher frequency sound

Question 17

Pulses made of higher frequency cycles have ____________ axial resolution.

Answer 17

Superior

Question 18

Better axial resolution is associated with the following:

Answer 18

• shorter spatial pulse length
• shorter pulse duration
• higher frequencies (shorter wavelengths)
• fewer cycles per pulse (less ringing)
• lower numerical values

Question 19

Which of the following transducers has the poorest axial resolution? 
A. 1.7 MHz and 4 cycles/pulse
B. 2.6 MHz and 3 cycles/pulse
C. 1.7 MHz and 5 cycles/pulse
D. 2.6 MHz and 2 cycles/pulse

Answer 19

C. This is the longest pulse. It has the lowest frequency and the most ringing (more cycles/pulse)

Question 20

Axial resolution is ________ in transducers with the highest frequency and the fewest numbers of cycles per pulse.

Answer 20

Best

Question 21

The ability to distinctly identify two structures that are very close together when the structures are side-by-side, or perpendicular to the beams main axis

Answer 21

Lateral resolution

Question 22

This answers the question: what is the minimum distance that two structures, positioned side-by-side, can be apart and still produce two distinct echoes on an ultrasound image?

Answer 22

Lateral resolution

Question 23

What are the units for lateral resolution?

Answer 23

Units of mm, cm, or any unit of distance

Question 24

Lateral resolution is determined by?

Answer 24

Width of the sound beam

Question 25

Narrower beams have ______ resolution.

Answer 25

Better

Question 26

How does a sonographer improve image resolution?

Answer 26

Adjust depth; beam diameter varies with depth

Question 27

Synonyms for lateral resolution?

Answer 27

``` LATA: Lateral Angular Transverse Azimuthal ```

Question 28

Lateral resolution is best at the ______.

Answer 28

Focus

Question 29

The mathematical relationship for lateral resolution is?

Answer 29

Lateral resolution (mm) = beam diameter (mm)

Question 30

Which type of resolution is better in clinical imaging systems: lateral or axial resolution?

Answer 30

Axial resolution because pulses are shorter than they are wide

Question 31

When two reflectors are closer side-by-side than the beam width, what will be observed?

Answer 31

One reflector

Question 32

With regard to resolution, what are the advantages of using a high frequency transducer?

Answer 32

Axial resolution is improved due to its shorter pulses Lateral resolution is improved due to its pulses diverging less in the far field

Question 33

What are the three methods of focusing?

Answer 33

1. External focusing - with a lens 2. Internal focusing - with a curved active element 3. Phased array focusing - with the electronics of the ultrasound system

Question 34

Which focusing technique(s) can be used with single element transducers? Array transducers?

Answer 34

Single element transducers = external and internal focusing Array transducers = phased array focusing

Question 35

External and internal focusing techniques are both called what?

Answer 35

Fixed focusing Conventional focusing Mechanical focusing

Question 36

What is a limitation to fixed focusing?

Answer 36

Focal depth and the extent of focusing cannot be changed

Question 37

What four things happen to a beam when it is focused?

Answer 37

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

Question 38

In regards to sound beams, continuous wave frequency is determined by?

Answer 38

Electrical frequency from ultrasound system

Question 39

In regards to sound beams, pulsed wave frequency is determined by?

Answer 39

Thickness of ceramic and speed of sound in ceramic

Question 40

In regards to sound beams, focal length is determined by?

Answer 40

Diameter of ceramic and frequency of sound

Question 41

In regards to sound beams, beam divergence is determined by?

Answer 41

Diameter of ceramic and frequency of sound

Question 42

In regards to sound beams, lateral resolution is determined by?

Answer 42

Beam width