Ch 10: Axial & Lateral Resolution Flashcards
Define ‘resolution’.
The ability to create accurate images
Define ‘axial resolution’.
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.
Axial resolution is measured in units of…
distance, mm.
Axial resolution is determined by…
both the sound source and the medium (like spatial pulse length).
T/F? Longer pulses improve axial resolution.
FALSE, *shorter
The synonyms of axial resolution are…
longitudinal, range, radial, or depth resolution.
Is axial resolution adjustable?
No
In clinical imaging, axial resolution ranges from…
0.1 to 1.0 mm.
___ numerical values indicate shorter ___ and improved image quality.
Lower, pulses
Spatial pulse length (mm) divided by 2 =
axial resolution (mm)
Wavelength (mm) times # cycles in pulse divided by 2 =
axial resolution (mm)
A short pulse is created in what two ways?
- less ringing
2. higher frequency
Better axial resolution is associated with ___ spatial pulse length, ___ pulse duration, and ___ frequencies.
shorter, shorter, higher
Better axial resolution is associated with ___ cycles per pulse and ___ numerical values.
fewer, lower
Define ‘lateral resolution’.
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.
Lateral resolution is measured in units of…
distance, mm.
Lateral resultion is determined by…
the width of the sound beam.
Narrower beams have ___ resolution.
better
Lateral resolution is also called…
angular, transverse, or azimuthal resolution.
Lateral resolution is best at the focus where the beam is…
narrowest.
lateral resolution (mm) =
beam diameter (mm)
Which type of resolution is better in clinical imaging systems?
axial resoltution
The numerical value for axial resolution is ___ the value for lateral resolution.
less than
When using a high frequency transducer, axial resolution is improved in the ___ because ___ pulses are associated with higher frequency sound.
entire image, shorter
When using a high frequency transducer, lateral resolution is improved in the ___ because high frequency beams are ___ lower frequency beams.
far field only, narrower than
Name three methods of focusing.
- external
- interal
- phased array
What type of focusing uses a lens?
external
What type of focusing uses a curved active element?
internal
What type of focusing uses the electronics of the u/s system?
phased array
___ includes borth external and internal techniques.
Fixed focusing
As the arc of the acoustic lens becomes more prominent, the degree of focusing ___ and the beam ___ in the focal zone.
increases, narrows
As the curvature of the PZT becomes more pronounced, the degree of focusing ___.
increases
There is no lens with ___ focusing.
internal
Phased array focusing may only be used on ___ transducers, never on ___ transducers.
multi-element, single crystal
When a sound beam focuses, the diameter in the near field and the focal zone…
narrows.
When a sound beam focuses, the focus is moved ___ to the transducer.
closer
When a sound beam focuses, the near zone length is…
reduced.
When a sound beam focuses, the diameter beyond the focal zone…
widens.
When a sound beam focuses, lateral resolution in the near and focal zones ___ and lateral resolution beyond the focal zone ___.
improves, degrades
When a sound beam focuses, the size of the focal zone is…
reduced.
