Week 9 Axial and Lateral Resolution Flashcards
Axial and Lateral Resolution
Resolution
The ability to create accurate images.
What is Axial Resolution?
The ability of a system to display 2 structures that are close together when structures are parallel to the sound beams main axis.
What is axial resolution measured in?
distance, mm
What is axial resolution determined by?
It is determined by spatial pulse length.
What is the typical value of axial resolution?
0.1 to 1.0 mm
Other names for axial resolution
LARRD:
Longitudinal
Axial
Range
Radial
Depth
Is axial resolution adjustable by the sonographer?
No, because the spatial pulse length for a transducer is fixed.
Which is better for axial resolution, short or long pulses?
Short pulses improve axial resolution.
Shorter pulse lengths Improves what?
The ability to accurately portray structures.
Pulse duration
Is related to axial resolution.
axial resolution formula in soft tissue:
AR = 0.77 x # of cycles/ frequency
Better axial resolution is associated with:
- shorter spatial pulse length
- shorter pulse duration
- Higher frequencies (shorter wavelength)
- fewer cycles per pulse (less ringing)
- lower numerical values
How is a shorter pulse created?
- Less ringing
- Higher frequency
If there are more cycles in a pulse, the numerical value of range resolution is
greater, lesser or same?
greater
If a new pulsed transducer has many more cycles in its pulse, the image accuracy improves, degrades or remains the same?
it Degrades
High/ Low frequency transducers generally have the best range resolution?
High
Axial resolution formula:
spatial pulse length (mm) / 2
In soft tissue, a 3 cycle 1 MHz pulse has a pulse length equal to 4.5 mm. what is the axial resolution?
2.25
Axial resolution is 1/2 of the spatial pulse length.
4.5 / 2 = 2.25
Which of the following transducers have the best axial resolution?
A. 1.7 MHz & 4 cycles/ pulses
B. 2.6 MHz & 3 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses
High frequency
Low ringing ( fewest cycles/ pulses)
Which of the following transducers has the poorest axial resolution?
A. 1.7 MHz & 4 cycles/ pulses
B. 2.6 MHz & 3 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
Low frequency
Long ringing ( longest cycles/ pulses)
What is Lateral resolution?
The ability to identify 2 structures that are close together when they are side by side or perpendicular to the sound beam.
What is lateral resolution determined by?
It is determined by the width of the beam.
What are other names for Lateral resolution?
LATA:
Lateral
Angular
Transverse
Azimuthal
What area of the beam produce the best lateral resolution?
The focal zone, or the narrowest part of the beam.
Axial numbers will be bigger or smaller than lateral resolution?
smaller than lateral resolution.
Lateral resolution improves or degrades in the far field?
Improves in the far field.
Why does lateral resolution improve in the far field?
High frequency creates a deeper focus than low frequency.
Does lateral resolution change or stay the same with depth?
Changes with depth, best at focus.
In the near field, lateral resolution is best with?
smallest diameter crystal
In the far field, lateral resolution is best with?
Large diameter and highest frequency.
( least divergence)
What are the effects of focusing?
- beam diameter in near field and focal zone is reduced.
- Focal depth is shallow
- Beam diameter in the far zone increases.
- Focal zone is smaller
Focusing improves what?
Lateral resolution
What are the three methods of focusing?
- External focusing
- Internal
- Phased Array
What method of focusing do we use in ultrasound?
Phased Array
External focusing
lens is placed in front of the PZT.
fixed, conventional, or mechanical.
Curved element
internal lens
Fixed, conventional, or mechanical
Phased Array
Electronic Focusing
Is Phased array able to be adjusted by the sonographer?
Yes
In regard to axial resolution, lower numerical values indicate what?
shorter pulses and improved axial resolution.
Two different transducers create pulses. both transducers create sound with a freq. of 4MHz. One transducer creates a pulse that comprises 6 cycles and the other, 3 cycles. Which transducer is more likely to create a more accurate image with respect to axial resolution? Which transducer has a lower numerical value of axial resolution?
3 cycle pulse is more likely to create an image with better axial resolution. Less ringing, or fewer cycles in a pulse, generally implies shorter pulses and improved axial resolution.
Two different transducers create sound pulses. One transducer is labeled 5 MHz and the other, 3 MHz. Which transducer is more likely to create a more accurate image with respect to axial resolution? Which transducer probably has a lower numerical value of axial resolution?
The 5 MHz transducer is more likely to create an image with better axial resolution. The Higher frequency transducer creates a shorter pulse and thus has a lower numerical value of axial res.
what is the mathematical relationship that describes this beam diameter and lateral resolution?
lateral resolution = beam diameter
What type of focusing includes both external and internal techniques?
Fixed focusing
A lens is placed where on the transducer with external focusing? What type of focusing is this?
In front of the PZT, a fixed focusing technique for external focusing.
What does a curved PZT do to the beam? What type of focusing is this?
Concentrates the sound energy into a narrower or tighter beam. Internal focusing.
