2 Ch 10: Axial & Lateral Resolution

Question 1

Define ‘resolution’.

Answer 1

The ability to create accurate images

Question 2

Define ‘axial resolution’.

Answer 2

The ability of a system to display two structures that are very close together when the structures are parallel to the sound beam’s main axis.

Question 3

Axial resolution is measured in units of…

Answer 3

distance, mm.

Question 4

Axial resolution is determined by…

Answer 4

both the sound source and the medium (like spatial pulse length).

Question 5

T/F? Longer pulses improve axial resolution.

Answer 5

FALSE, *shorter

Question 6

The synonyms of axial resolution are…

Answer 6

longitudinal, range, radial, or depth resolution.

Question 7

Is axial resolution adjustable?

Answer 7

No

Question 8

___ numerical values indicate shorter ___ and improved image quality.

Answer 8

Lower, pulses

Question 9

Spatial pulse length (mm) divided by 2 =

Answer 9

axial resolution (mm)

Question 10

Wavelength (mm) times # cycles in pulse divided by 2 =

Answer 10

axial resolution (mm)

Question 11

A short pulse is created in what two ways?

Answer 11

1. less ringing

2. higher frequency

Question 12

Better axial resolution is associated with ___ spatial pulse length, ___ pulse duration, and ___ frequencies.

Answer 12

shorter, shorter, higher

Question 13

Better axial resolution is associated with ___ cycles per pulse and ___ numerical values.

Answer 13

fewer, lower

Question 14

Define ‘lateral resolution’.

Answer 14

The ability to distinctly identify two structures that are very close together when they are side by side, or perpendicular, to the sound beam’s main axis.

Question 15

Lateral resolution is measured in units of…

Answer 15

distance, mm.

Question 16

Lateral resultion is determined by…

Answer 16

the width of the sound beam.

Question 17

Narrower beams have ___ resolution.

Answer 17

better

Question 18

Lateral resolution is also called…

Answer 18

angular, transverse, or azimuthal resolution.

Question 19

Lateral resolution is best at the focus where the beam is…

Answer 19

narrowest.

Question 20

lateral resolution (mm) =

Answer 20

beam diameter (mm)

Question 21

Which type of resolution is better in clinical imaging systems?

Answer 21

axial resoltution

Question 22

The numerical value for axial resolution is ___ the value for lateral resolution.

Answer 22

less than

Question 23

When using a high frequency transducer, axial resolution is improved in the ___ because ___ pulses are associated with higher frequency sound.

Answer 23

entire image, shorter

Question 24

When using a high frequency transducer, lateral resolution is improved in the ___ because high frequency beams are ___ lower frequency beams.

Answer 24

far field only, narrower than

Question 25

Name three methods of focusing.

Answer 25

1. external
2. interal
3. phased array

Question 26

What type of focusing uses a lens?

Answer 26

external

Question 27

What type of focusing uses a curved active element?

Answer 27

internal

Question 28

What type of focusing uses the electronics of the u/s system?

Answer 28

phased array

Question 29

___ includes borth external and internal techniques.

Answer 29

Fixed focusing

Question 30

As the arc of the acoustic lens becomes more prominent, the degree of focusing ___ and the beam ___ in the focal zone.

Answer 30

increases, narrows

Question 31

As the curvature of the PZT becomes more pronounced, the degree of focusing ___.

Answer 31

increases

Question 32

There is no lens with ___ focusing.

Answer 32

internal

Question 33

Phased array focusing may only be used on ___ transducers, never on ___ transducers.

Answer 33

multi-element, single crystal

Question 34

When a sound beam focuses, the diameter in the near field and the focal zone…

Answer 34

narrows.

Question 35

When a sound beam focuses, the focus is moved ___ to the transducer.

Answer 35

closer

Question 36

When a sound beam focuses, the near zone length is…

Answer 36

reduced.

Question 37

When a sound beam focuses, the diameter beyond the focal zone…

Answer 37

widens.

Question 38

When a sound beam focuses, lateral resolution in the near and focal zones ___ and lateral resolution beyond the focal zone ___.

Answer 38

improves, degrades

Question 39

When a sound beam focuses, the size of the focal zone is…

Answer 39

reduced.