Beam former Flashcards
number of cycles per second is called?
Frequency
number of pulses per second?
PRF
Number of pulses per scan line?
ensenble length
ensemble length on dopper?
3-30
ensemble length on 2D?
1
of cycles in a pulse on 2D and doppler?
2D- 2-3
Doppler- 5-30
what affects PRF in B-mode?
penetration/ depth
grating lobes are produced by?
arrays
3 ways to fix grating lobes?
- apodization
- THI
- subcidy
what affects NZL?
- frequency
- aperture sizer/ diameter
U/S systems are what kind of system?
pulse-echo systems
u/s systems determine what?
strength and location of echo-generating site
the location of an echo is determined by? (2)
- arrival time (depth)
- direction of returning echoes
4 main sections of intrument?
1- beam former
2- signal processor
3. image processor
4. display
what 8 things are involved in the beam former?
1) Master Synchronizer*
2) Pulser
3) Pulse delays
4) Transmit/Receive Switch
5) Amplifiers
6) Analog-to-Digital Converters
7) Echo delays
8) Summer
beam former involves?
- transmission and reception
what are transmission channels?
- each path to each individual element is a channel
what are reception channels?
- each path from each individual element
beam former- components of transmitter? (4)
- master synchronizer
- pulser
- pulse delays
- T/R switch
beam former- components of receiver? (4)
- amplifier (TGC, overall gain)
- analog-to-digital converters
- echo delays
- summer
what is the master synchronizer?
- coordinated the entire system
- tells pulser when to fire
- T/R switch functions
master synchronizer prevents?
- range ambiguity (incorrect placement of echo along scan line)
AKA echo-misplacement
what is the pulser?
- produces electric voltages that drive the transducer
operating frequency range?
from 2-20 MHz
PRFvolt= PRFpulse what are the typical values for 2D?
4- 15 kHz
PRF?
- operator controlled in doppler
- automatic in grey scale
- depth of image will determine PRF
PRF is limited by?
depth
what is the pulser?
- all echoes from one pulse must be received before the next pulse is emitted
pulser- deeper images?
- echoes take longer to return
- decreased PRF and FR and Temp. res
Beam former- What happens if we go over 77 cm/ms?
- range ambiguity
What happens to the PRF in 2D if depth is increased by 4 x?
- PRF must drop 4x to prevent range ambiguity
Pulser can be controlled in terms of?
power output
transmission channels typically there are how many?
64, 128, 192
Pulse delays?
- involved in sequencing arrays
- multiple blocks of sound, each producing a scan line
what instument of the beam former is involved in phasing?
pulse delays
how much time is between element firings?
< 1 microsecond delays between element firings
what can pulse delays affect?
Can affect our near zone length (natural focus)
Can affect our beam width at the focus
How does this affect our image?
Lateral resolution
pulse delays are involved in?
- dynamic aperture control
- apodization
- coded excitation
pulse delays are involved in?
- dynamic aperture control
- apodization
- coded excitation
dynamic aperture control ?
pulser + pulse delays
- decided the width of our aperture
apodization?
Decreasing the strength to outer elements
Reduction of grating lobes in arrays
Coded excitation allows for? (5)
multiple foci spatial compounding increased penetration ↑ contrast resolution B-flow imaging
