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

In clinical imaging, axial resolution ranges from…

Answer 8

0.1 to 1.0 mm.

Question 9

___ numerical values indicate shorter ___ and improved image quality.

Answer 9

Lower, pulses

Question 10

Spatial pulse length (mm) divided by 2 =

Answer 10

axial resolution (mm)

Question 11

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

Answer 11

axial resolution (mm)

Question 12

A short pulse is created in what two ways?

Answer 12

1. less ringing

2. higher frequency

Question 13

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

Answer 13

shorter, shorter, higher

Question 14

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

Answer 14

fewer, lower

Question 15

Define ‘lateral resolution’.

Answer 15

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 16

Lateral resolution is measured in units of…

Answer 16

distance, mm.

Question 17

Lateral resultion is determined by…

Answer 17

the width of the sound beam.

Question 18

Narrower beams have ___ resolution.

Answer 18

better

Question 19

Lateral resolution is also called…

Answer 19

angular, transverse, or azimuthal resolution.

Question 20

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

Answer 20

narrowest.

Question 21

lateral resolution (mm) =

Answer 21

beam diameter (mm)

Question 22

Which type of resolution is better in clinical imaging systems?

Answer 22

axial resoltution

Question 23

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

Answer 23

less than

Question 24

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

Answer 24

entire image, shorter

Question 25

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

Answer 25

far field only, narrower than

Question 26

Name three methods of focusing.

Answer 26

1. external 2. interal 3. phased array

Question 27

What type of focusing uses a lens?

Answer 27

external

Question 28

What type of focusing uses a curved active element?

Answer 28

internal

Question 29

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

Answer 29

phased array

Question 30

___ includes borth external and internal techniques.

Answer 30

Fixed focusing

Question 31

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

Answer 31

increases, narrows

Question 32

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

Answer 32

increases

Question 33

There is no lens with ___ focusing.

Answer 33

internal

Question 34

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

Answer 34

multi-element, single crystal

Question 35

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

Answer 35

narrows.

Question 36

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

Answer 36

closer

Question 37

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

Answer 37

reduced.

Question 38

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

Answer 38

widens.

Question 39

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

Answer 39

improves, degrades

Question 40

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

Answer 40

reduced.