Chapter 10 Flashcards
_ is the ability to create
accurate images.
Resolution
_ measures 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. (one in front of the other)
Axial resolution
_ answers the question: What is 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
Axial resolution is usually measured in
units of distance such as mm
Axial resolution is related to
SPL and pulse duration
_ pulse improve axial resolution
Shorter
Is axial resolution adjustable? Why/why not?
No, SPL for a transducer is fixed, you cannot change the axial resolution.
Typical value for axial resolution
- 1-1mm (for class)
0. 05-0.5mm (for SPI)
For axial resolution, _ numerical values indicated shorter pulses and _ image accuracy
Lower
Improve
Axial resolution AKA
LARRD Longitudinal Axial Range Radial Depth
Image quality is better when axial
resolution has a _ numerical value.
Lower
The mathematical description of axial
resolution is:
Axial resolution= SPL/2
Axial resolution= wavelength x # of cycles in pulse/2
Axial resolution is determined by
Pulse length
_ pulses yield improved axial resolution
Shorter
A short pulse is created in 2 ways:
- Less ringing
2. Higher frequency
A pulse is _ if there are few cycles in the
pulse.
Short
Crystal dampening creates shorter pulses by
reducing the ringing of the crystal after it has
been excited by an electrical signal.
A pulse is _ if each cycle in the pulse has a short
wavelength.
Short
Shorter wavelengths are characteristic of
Higher frequency sound
Pulses made of _ frequency cycles have better axial resolution
Higher
Better axial resolution is associated with:
Shorter SPL Shorter pulse duration Higher frequencies (shorter wavelength) Fewer cycles per pulse (less ringing) lower numerical values
Which is the best and worst axial resolution: A. 12 MHz; 6 cycles/pulse B. 12 MHz; 3 cycles/pulse C. 4 MHz; 8 cycles/pulse D. 4 MHz; 2 cycles/pulse
Best: B
Worst: C
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
_ resolution 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?
Lateral
Lateral resolution is measured in units of
Distance
mm, cm
Lateral resolution: _ numbers are preferable since they
indicate more accurate images
Smaller
Lateral resolution is determined by
The width of the sound beam
_ beams have better lateral resolution
Narrow
Beam diameter varies with _; lateral resolution varies with
Depth
Depth
Lateral resolution AKA
LATABP Lateral Angular Transverse Azimuthal Beam width variation Point spread artifact
Lateral Resolution is best at
the focus
where the beam is the narrowest.
Lateral resolution=
beam diameter
When two side-by-side reflectors are
closer to each other than the width of
the beam, _ reflection is observed on the image
only one
Lateral resolution is degraded/worse in
the far field
