Chapter 18 Flashcards
Resolution
The ability to image fine detail
____ resolution is better
Smaller
Tinier details can be discerned
If two reflectors are not seperated sufficiently they produce
Overlapping echoes
Axial resolution aka
Longitudinal, radial, depth and range
Axial resolution is
Minimum reflector seperation along scan line to produce separate echoes
Axial resolution = ____ mm
2mm
Structures place 1 mm apart will be seen as a
Single structure
Axial resolution equation
AR= SPL/2
The smaller the AR the
Better
To improve AR we need to
Reduce SPL
Lateral resolution aka
Angular, transverse, azimuthal
Lateral resolution is
Minimum reflector seperation perpendicular to scan line to produce separate echoes
Lateral resolution occurs when _____=____
LR=Wb
Lateral resolution = width of beam
LR=3mm
Reflector seperation is less than Wb
LR=1mm
BEAM IS NARROWER THAN REFLECTOR SEPERATION
WHAT IS BETTER SMALL OR LARGE LR
Smaller
LR is improved by
Reducing the wb
Elevation resolution
Minimum reflector separation perpendicular to scan plane to produce separate echoes
Operates in 3 dimension
Elevational resolution has ____
Slice thickness aka section thickness / elevational plane
Elevational resolution can preoduce
Section thickness artifact aka partial volume artifact
Can fill in cysts or other anechoic structures
Poor elevation resolution will show
Echoes from outside the intended scan plane
Especially within anechoic structures
HOW DO WE FIX elevational resolution artifact
THI—> narrower and thinner beam
Less likely to pick up echoes from other plane
Spatial compounding
AR is less than _____mm to distinguish two seperate objects
1mm
Temporal resolution
Being able to separate echoes in time
Poor temporal resolution is visualized as lag
Contrast resolution
Being able to separate two different shades of grey
Usefull frequency range
2 to 20 MHz
Higher freq increase _____ and decrease ________
Resolution
Max imaging depth
Up to _____ Mhz can be used for ophthalmologic, dermatologic, and intravascular imaging
50 MHz
Focus can be achieved in the third dimension by
Lens or curved elements
What is third dimension
Perpendicular to the scanning plane
How many rows of elements needed for phasing to be applied to focus the third dimension electronically
At least three
Electronic focusing eliminates the need for
A lens or curved elements
2D arrays have the ability to _____ and _____ in two dimensions
Steer and focus
1D array =
2D imaging
2D array ->
3D imaging
3D imaging aka
Volume imaging
Volumetric scanning
3D imaging mainly used for
OBSTETRICS AND BREAT
4D imaging =
3D imaging + time
Echoes arriving to the transducer can be ________ as well
Delayed or phased
Reception steering
Listening from a particular direction
Dynamic focusing
Continual change of the focus with increasing depth
Dynamic aperture
As the focus continues to change during echo reception, the aperture will increase to maintain a constant focus with
Annular arrays
Concentric rings
Piezoelectric material carved out in rings
Go from smallest to largest
Not used anymore
