Ch. 10 physics: Axial and Lateral Resolution Flashcards
A systems ability to distinguish between two structures that are lying close together.
Resolution
The ability of a system to accurately display two very close structures that are parallel to the axis of the sound beam.
Axial Resolution
Represents the minimum distance that two structures, positioned front-to-back, can be apart and still produce two distinct echoes on an ultrasound image.
Axial Resolution
LARRD
Longitudinal
Axial
Range
Radial
Depth
Shorter pulses have __________ axial resolution
Improved
How are shorter pulses are created?
Less ringing
Higher frequency
Is the axial resolution adjustable or non adjustable?
Not adjustable
Pulse length is fixed
What is the clinical range of axial resolution?
0.1 - 1.0mm
The ability to separate structures parallel to the ultrasound beam.
Axial Resolution
Formula for axial resolution and spatial pulse length.
axial resolution (mm) = spatial pulse length (mm) / 2
formula for axial resolution and wavelength.
Axial resolution (mm) = wavelength (mm) x # cycles in pulse / 2
Formula for axial resolution in soft tissue.
Axial resolution (mm) = 0.77 x # cycles in pulse / frequency (MHz)
True or false:
A pulse is longer if there are fewer cycles in the pulse
false
the pulse is shorter
If a pulse is shorter with fewer cycles, this is known as…
Less ringing
With fewer cycles in the pulse length, axial resolution …..
improves
A pulse is short if each cycle in the pulse has a …..
Short wavelength
High frequency and having shorter wavelengths =
Better axial resolution
Better Axial Resolution is Associated with:
Shorter spatial pulse length
Shorter pulse duration
Higher Frequencies (shorter wavelengths)
Fewer cycles per pulse (less ringing)
Lower numerical values
With axial resolution, Wavelength = ½ the PZT thickness, which means ….
thinner crystals equal shorter wavelengths resulting in higher frequency
Thinner crystals means
Fast
Thicker crystals means
Slow
True or False:
Higher frequency is associated with shorter pulse length.
True
True or False:
Fewer pulses per cycle will improve axial resolution.
True
Which of the following choices would have the best axial resolution?
12 MHz, 2 cycles per pulse
6 MHz, 2 cycles per pulse
12 MHz, 4 cycles per pulse
6 MHz, 4 cycles per pulse
6 MHz, 2 cycles per pulse
The ability to distinctly identify two structures that are very close together when they are perpendicular to the sound beams main axis.
Lateral Resolution
Lateral resolution is also known as LATA, which means….
Lateral
Angular
Transverse
Azimuthal resolution
Lateral resolution is measured in …..
Distance (mm, cm)
Lateral resolution is determined by
Beam width
Lateral resolution changes with ______ due to _____
Depth
divergence of the sound beam
When two side-by-side reflectors are closer together than the beam’s diameter, only ______ reflection is seen on the image
one
For lateral resolution, image is accuracy is best at _________
the focus
the beam in lateral resolution is the narrowest at ________
The focus
The structures located closer together than the beams diameter at the depth they are located, appear as one structure instead of ________
two
Higher frequencies improve both _______ and _____________
axial
Lateral resolution
Axial is improved in the entire image with
shorter pulses
Lateral is improved in the far field with
Less divergence
Results in a narrower beam, improving lateral resolution
focusing the beam
What are the types of focusing?
Fixed, Conventional, or Mechanical
How do you focus externally?
with a lens
How do you focus internally?
with a curved active element
How is Phased array focused?
with the electronics of the ultrasound system
Phased array is adjustable or not adjustable?
adjustable
A fixed focusing technique where a lens is placed in front of the PZT
External focusing
As the arc of the lens becomes more prominent in external focusing, ……
the degree of focusing increases and the beam narrows
The PZT is curved, concentrating its energy and creating a narrow beam, improving the beams focus and is the most common form of fixed focusing used. Is this internal focusing or external focusing?
Internal focusing
What type of focus is achieved through phased array transducers?
Electrical focusing
What does phased array mean?
Adjustable or multiple focusing
What kind of transducers use phased array?
Multi-element transducers only
True or false:
Electronic focusing allows the sonographer the ability to alter the beams focus.
True
How can the Sonographer alter the electronic focus?
By beam steering
What are the 4 modifications a sound beam goes through to be electronically focused?
The beam diameter in the near field and the focal zone narrows
Near zone length is reduced
The beam diameter beyond the focal zone widens
Size of the focal zone is reduced
Where is the lateral resolution better in the beam?
Where it is narrow
If the transducer crystal diameter is 10 cm, what is the lateral resolution at the focus?
5cm
remember the lateral resolution = beam diameter
The beam diameter is ½ the crystal diameter at the focus.
Which of the following transducers have the poorest axial resolution?
2.5 MHz and 2 cycles/pulse
3 MHz and 4 cycles/pulse
2.5 MHz and 4 cycles/pulse
3 MHz and 2 cycles/pulse
2.5 MHz and 4 cycles/pulse
In soft tissue, a 4 cycle, 2MHz pulse has a pulse length equal to 6 mm. What is the axial resolution?
3 mm
the axial resolution = ½ the spatial pulse length
A transducer with more cycles per pulse will have greater/lower axial resolution?
Lower
Which of the following terms does not belong with the others?
Longitudinal
Range
Azimuthal
Radial
Range
What is the most common form of fixed focusing?
internal
What is electronic beam focusing called?
Phased
Single crystal transducers are always (fixed/phased) focusing?
Fixed
