Module 4 : Resolution Flashcards
resolution
- most important thing to consider
- 3 aspects
3 aspects of resolution
- detail (spatial)
- contrast
- temporal
detailed resolution types
- axial (y)
- lateral (x)
- elevational (z)
axial resolution
- ability to separate reflectors along the path of the beam
- dependant of the SPL and is calculated by 1/2 SPL
axial resolution equation
AR = 1/2 SPL
SPL decreases axial resolution improves
high frequency probes + axial
- increased frequency = decreased wavelength = decreased SPL = increased AR
wide bandwidth + axial
- wider bandwidth = shorter pulse = increased AR
decreased wavelength + axial
- decreased wavelength = decreased SPL = increased AR
increased dampening + axial
- increased dampening = decreased RD = decreased SPL = increased AR
low Q factor + axial
- lower Q = increased AR
axial resolution names
- LARD \+ longitudinal \+ axial \+ range \+ depth
lateral resolution
- ability to separate reflectors perpendicular to path of beam
- dependent on width of beam
- not constant with depth
beam width and lateral resolution
- beam width decreases lateral resolution improves
distance form probe + lateral
- beam shape changes with depth
- wider = worse lateral
amount of focusing + lateral
- lateral resolution increases at the focus but worse everywhere else especially far field
size of aperture + lateral
- shortens NZL so improves at focus but worse everywhere else
NZL = lateral
- pushed deeper get better lateral resolution deeper
higher frequency + lateral
- pushes near zone length deeper improving lateral resolution
lateral resolution names
- LATA
- latera
- angular
- transverse
- azimuthal
elevational resolution
- also known as slice thickness ability to separate reflectors perpendicular to image plane beam
- just like lateral resolution dependent on width of beam in Z axis
- fixed
- beam width in z axis decreases elevational resolution increases
higher the frequency + elevational
- pushed near zone length not penetrating deeper but better resolution
amount of focusing in z plane + elevational
- external mechanical focusing
- cannot be controlled but more focusing is better
NZL + elevational plane
- longer = better
- shorter = worse
distance from probe + elevational
- gets worse deeper without focusing
contrast resolution
- ability to distinguish subtle differences in tissue gray scale
- related to bit depth
- higher bit depth more shade of gray more stuff to do with dynamic range
temporal resolution
- ability to appreciate moving structures in real time
- related to frame rate
- frame rate increases temporal resolution increase
temporal resolution formula
PRF = n x LPF x FR
n = number of foci LPF = lines per Frame FR = frame rate
temporal resolution formula with penetration
penetration (cm) x n x LPF x FR
= 77000 cm/s
- 77000 used because it represents Hal the average speed of sound in soft tissue
- if you exceed this you get range ambiguity
depth of penetration + temporal
- have to go deeper takes longer for it to come back = less FR = less TR
number of foci + temporal
- hard to look at more than one thing
- have to add scan lines for every focus
- decrease FR = decrease TR
sector width + temporal
- sector down = less lines per scan = less FR = less TR
number of lines per frame
- increase lines per Frame = decrease FR = decrease TR
- want not a lot of interpolation
frame rate + temporal
- increase FR = increase TR
