Test 1 Flashcards
Diagnostic ultrasound systems are:
- pulse echo systems
- it determines echo strength and location of echo-generating site
echo strength=
brightness
what is the location determined by?
- arrival time
- direction of returning echoes
what are the 4 main sections of an ultrasound instrument?
- beam former
- signal processor
- image processor
- display
what does the beam former work with?
the transducer
are we dealing with sound or voltage with the beam former?
voltage
transmission channels
each path to each individual element is a channel
reception channels
each path from each individual element is a reception channel
what are the components of the transmitter?
- master synchronizer
- pulser
- pulse delays
- transmit/receive switch
what are the components of the receiver?
- amplifier
- analog-to-digital converters
- echo delays
- summer
what is the master synchronizer?
- coordinates the entire system
- tells the pulser when to fire
why does the master synchronizer wait for the echo to come back before firing the next pulse?
prevents range ambiguity
AKA echo-misplacement
what is range ambiguity?
incorrect placement of echo along scan line
what is the pulser?
produces electric voltages that drive the transducer
-in response transducer produces ultrasound pulse
Fvoltage=
Fpulse, Fo
what does Fo range from for most applications?
2-20 MHz
PRFvoltage=
PRFpulse
why does the PRF voltage equal the PRF pulse?
for each voltage pulse one ultrasound pulse is generated
what are the units for f?
MHz
what are the units for PRF?
KHz
what are the typical values for PRFvoltage? (2D)
4-15 KHz
what are the typical values for PRF pulse? (doppler)
5-30 KHz
when is PRF operator controlled?
doppler
Why is PRF not operator controlled in grayscale?
it is automatic
-depth of image will determine PRF (indirect control)
what happens for deeper images?
- echoes take longer to return
- PRF goes down
- Frame rate goes down
instrument automatically achieves the highest ____
PRF
what happens if we go over 77 cm/ms?
an artifact will occur
what happens to the PRF in 2D if depth is increased by 4x?
decrease by 4x
what does 2D/grayscale automatically do?
accommodates depth
the power or strength of the beam entering the tissue is __________
closely related to intensity
stronger voltage =
stronger pulse
can the pulser be controlled?
yes
how do we control pulser?
“output” dial on some machines
-displayed in dB/%
what are pulse delays?
- decide how many elements/crystals are involved
- decide which ones to fire and when
what are pulse delays involved in?
- sequencing arrays
- phasing and steering
- electronic focusing
- dynamic aperture control
- apodization
- coded excitation
what are sequencing arrays?
multiple blocks of sound, each producing a scan line
what is phasing and steering?
microsecond delays between element firings
what is electronic focusing?
- Curved delay pattern send sound beam to a focal point
- Adjusting the delay places focus closer or farther away
what is dynamic aperture control?
pulser+pulse delays
decides the width of our aperture
what is apodization?
pulser+pulse delays
- Decreasing the strength to outer elements
- Reduction of grating lobes in arrays
what is coded excitation?
normally send one pulse per scan line (ensemble length=1) or can send multiple pulses per scan line (esemble length=3-30)
what is another way coded excitation can be used?
send 1 pulse, wait, then 2 cycle pulse, wait, e.t.c
what does coded excitation involve?
decoder in beam former
what helps in avoiding range ambiguity?
decoder in coded excitation
what does coded excitation allow for?
- multiple foci
- spatial compounding
- increased penetration
- increasing contrast resolution
- B-flow imaging
what is B flow imaging?
multiple pulses are sent down the same scan line and decoder stacks the received echoes (constructive interference)
what does constructive interference do?
- overall higher intensity echo
- makes weak echoes seem brighter
what does increased sensitivity do?
able to pick up weaker echoes
how is B flow different than B mode?
picking up very weak echoes (the blood cells themselves)
what is the purpose of the pulser?
provides the voltage
what is the purpose of pulse delays?
decides how many elements are involved and which ones to fire and when (linear sequencing, phasing, e.t.c)
what type of signals are amplifiers used to receiving?
weaker signals
what will happen if the amplifier receives a high signal?
receiving the stronger voltage from the pulser/pulse delays results in the overload of the amplifier
what is the purpose of the T/R regards to amplifiers?
it protects the amplifiers from the outgoing voltage
what does an amplifier do?
returning echo is a mechanical wave and the transducer converts it into an electrical signal and voltage travels to the amplifier
what does the power ratio equal?
gain (dB)
what is amplification opposite of?
attenuation
what do amplifiers allow for?
- amplification (gain)
- compensation (TCG)
what is the attenuation in soft tissue?
0.5 dB/cm MHz (one way)
lateral gain compensation
for adjacent structures that have different attenuation
what is a drawback to amplification?
weaker echoes from the electric current result in a grainier signal
analog-to-digital converters
voltage to numbers
echo delays
same as pulse delays
THESE ARE DIGITAL DELAT LINES NOW
summer (adder)
signals added together as a scan line
reception apodization
reducing the returning voltages on the peripheral of the transducer
what are the functions of the beam former?
- generating pulses that drive the transducer
- determining PRF
- coding
- frequency and intensity
- scanning, focusing and apodizing the transmitting beam
- amplifying the returning echo voltages
- compensating for attenuation
- digitizing the echo voltage stream
- directing, focusing, and apodizong the reception beam
Which part of the beam former function does the Pulser perform?
- generates voltage pulses
- sets the PRF
- controls power
How many cycles are produced by the electric voltages?
2/3 cycles per pulse
What determines the frequency of the resulting ultrasound pulse?
The frequency of the voltage pulse/transducer element thickness
why is a transmission channel required?
for a more precise control over the beam characteristics
What does the Transmit/ Receive switch do?
Directs voltage pulses and the delays to the transducer during transmission and then directs echo voltages from the transducer to the amplifier during reception
The ultrasound PRF is equal to the __________PRF of the pulser.
voltage
TGC
Corrects for tissue attenuation
gain
Increases all amplitudes
analog
porportional
digital
discrete (numbers)
what does TGC compensate for?
attenuation
