Module 4: Resolution Flashcards
Resolution can be broken down into what three aspects?
- Detail
- Contrast
- Temporal
Detailed resolution can be further divided in what three aspects?
- Axial
- Lateral
- Elevational
What is axial resolution?
The ability to separate reflects along the path of the beam
Axial resolution is dependent of what? and is calculated how?
Dependent of SPL and is calculated by 1/2 the SPL
What is the formula for spatial resolution?
AR = (1/2) SPL
If SPL decreases what happens to axial resolution?
It improves
Axial resolution is known by what of the following names?
- Longitudinal
- Range
- Depth
Remember LARD
What is lateral resolution?
The ability to separate reflectors perpendicular to the path of the beam
Lateral resolution is dependent of what?
The width of the beam and therefore, is not constant with depth
What does this image represent?
Lateral resolution
Lateral resolution is directly related to what?
The width of the beam
If the beam width decreases then what?
Lateral resolution improves
Lateral resolution is known by what other names?
- Angular
- Transverse
- Azimuthal
Remember LATA
What is elevational resolution?
Also known as slice thickness this is the ability to separate reflectors perpendicular to the image plane of the beam
Elevational resolution is dependent on what aspect of the beam?
Width of the beam but in Z axis
Elevational resolution is directly related to what?
The width of the beam in the Z axis
If beam width in the Z axis decreases then what happens?
Elevational resolution improves
Elevational Resolution is also known as what?
Slice thickness
What is contrast resolution?
The ability to distinguish subtle differences in tissue gray scale
What is contrast resolution related to?
Bit depth
For contrast resolution, having a higher bit depth means what?
The more shades of tray the system is capable of displaying
More shades of gray gives the operator what?
More control over the dynamic range
By reducing the dynamic range the sonographer may increase the ability to do what?
Distinguish once subtle differences in grayscale
What is temporal resolution?
The ability to appreciate moving structures in real time
What is temporal resolution related to?
System frame rate
Temporal resolution is directly related to what?
Frame rate
If frame rate increases then what happens?
Temporal resolution improves
Since temporal resolution is defined by frame rate, what else is frame rate related to?
PRF
What is the formula for temporal resolution?
PRF(Hz) = n x LPF x FR(Hz)
n = number of foci
LPF = lines per frame
FR = frame rate or frames per second
Penetration of sound plays an important role in what?
PRF
What is the formula for sound penetration?
Penetration (cm) x n x LPF x FR < 77,000 cm/s
Why do we use 77,000 for penetration of sound?
Because it represents half the average speed of sound in soft tissue (154,000 cm/s)
What things relate to better axial resolution? 5
- Higher frequency probes
- Wide bandwidth
- Decreased wavelength
- Increased damping
- Low Q factor
What things relate to better lateral resolution?
- Distance from the probe
- Amount of focusing
- Size of aperture
- NZL
- Higher the frequency
What things relate to better elevational resolution?
- Distance from the probe
- Higher the frequency
- NZL
- Amount of focusing in the Z plane
What things relate to better temporal resolution? 5
- Depth of penetration
- The number of foci
- The sector width
- Frame rate
- The number of lines per frame
