C2: Basic Intrumentation Flashcards
What elements make up the beam former?
Pulser Pulse delays Transmit receive switch Amplifier Analog to digitall conversion Echo delays Sum
What’s the pulser?
Sends the voltage pulse to the probe determining the intensity, operating frequency and PRF
When you change the frequency, what are you telling the pulser?
What voltage to use
What does the pulse delay do?
Applies the necessary delays to accomplish focusing, beam steering and aperture size…. also responsible for dynamic apodization (gets rid of grading lobes)
What’s the function of the transmit-receive switch?
Directs the pulse in the correct direction to protect the sensitive components from the voltage
What’s the function of the amplifier?
Boots the voltage of the echos to make them stronger… this is needed in order to get the voltage through the circuit
What’s the function of the analog to digital converter?
It digitizes the voltages which is needed for memory storage and manipulation of the image later on
What’s the function of echo delays in the beam former?
This function delays the echos that it first receives if order to wait until it’s received all the echos to send the completed information at the same time… the early echos must be delayed in order to construct an image properly
What’s the function of the ‘sum’ portion of the beam former
Adds together the pulses from each element in the segment to for the scan line
What’s digitization and why do we do it?
Process of converting the voltage into a binary number
Important to maintain the integrity of the data…. its also more stable
When does digitization occur? What is the preference from when it occurs?
Can occur before or after the echo delay in the beam former
Preferable to occur early on to stabilize the signal
What’s considered late vs early digitization?
Late is after the echo delay
Early is before the echo delay
Signal processing involves what 2 processes?
ADC
The receiver
What do the dotes lines on the block diagrams represent?
The probe and pulser giving a heads up to the memory and receiver that a pulse was sent out and echos are coming back soon
What’s the function of the receiver and what steps is it made up of?
Function is to process the returned echos as analog voltages in preparation for display
Made up of 5 steps:
- Amplification
- Compensation
- Compression
- Rejection
- Demodulation (includes rectification and smoothing)
what control on the US machine is for amplification?
gain, usually expressed in dB…. or %
can amplification also decrease the amount of power in the returning echos?
yes
whats the function of compensation?
whats the US control for it?
compensates for attenuation…. makes the echos from similar reflector have a same brightness regardless of depth
TGCs, expressed in dB…
whats another term for TGCs and what does that term correct?
TCGs can also be called DGCs (depth gain compensation)
they can correct the main bang artifact and attenuation in the far field
in how many cm increments do TGCs/DGCs operate?
1cm
another term for compression
dynamic range
whats the function of compression and how is it accomplished?
process of decreasing the difference between the smallest and largest amplitudes/brightest and darkest shades of grey (expressed in dB)
accomplished with logarithmic amplification
define what logarithmic amplification is
the application of exponential gain as a function of the input signal level
(results in compression of dynamic range)
whats another term for the smallest amplitudes and largest amplitudes
small: reject level
large: saturation
whats the difference between the noise level and reject level?
noise lvl you cant control, reject lvl you can
noise level is usually made up of false echos that are being omitted, where as, reject level is composed of low level echos
what are 2 other terms for rejection?
threshold or suppression
whats the function of rejection?
eliminates or suppresses low level echos that may be noise, and improves signal to noise ratio
how does rejection effect dynamic range?
reduces it
what is demodulation?
process that converts the radio frequency signal (voltage/sine wave) to a video signal for monitor display
whats rectification?
process that converts all – parts of the signal into + ones (everything is above baseline)
whats smoothing and what are 2 other terms for it?
it filters the signal to smooth out bumps which helps create a distinct aide of grey
also called enveloping or signal filtering
what are the components of image processing?
scan converter pre processing memory post processing DAC display
where does the voltage travel after its passed the signal processor?
scan converter
whats the function of a scan converter?
rewrites vertically received info horizontally into the memory
when is the info we acquire naturally in a vertical format?
and when is it horizontal
when we acquire it from the sound returning to the probe… its horizontal when its displayed on the US screen
whats another term for scan converter?
memory
how is an analog scan converted similar to a CRT?
it functions in the same way but it has a silicon wafer called the dielectric matrix instead of a phosphorus face
describe how an analog scan converter works
electrons are admitted by the filament, pass through the deflection plates and hit the silicon wafer where they leave a + charge
the amount of + charge left by the electrons on the silicon wafer is proportional to what?
the amplitude of the signal
in an analog scan converter, how does the electron beam move across the dielectric matrix?
in raster format
what are the 6 pre processing functions we discussed?
receiver functions maps interpolation edge enhancement write zoom persistance
what are maps and why do we use them?
‘curves’ applied to the shades of grey, used to enhance visualization
how do we correct for gaps between scan lines?
interpolation…. accomplished by averaging pixel grey scale values to fill in the gaps
‘extrapolating’
what does too much interpolation cause?
a misrepresentation of the image
whats edge enhancement and how does it work?
edge enhancement sharpens boarders
functions by applying a ‘kernel’ to the pixels which makes the gap between the shades of grey along the edges larger and more distinct
does edge enhancement change the homogeneity of tissues?
no
whats another term for write zoom
regional expansion
whats the advantage of write zoom?
the area is rescanned and additional scan lines are aded which increases spatial resolution and pixel ratio
whats ROI
region of interest
what is persistence? how does it effect signal to noise ratio?
frame averaging
improves signal to noise ratio
how does persistence effect temporal resolution?
decreases it, so there must be minimal movement
is persistence used for echo and OB?
no
which instrumentation made grey scale possible?
scan converter
what are some post processing functions?
measuring annotation post processing curves read zoom colour doppler maping angle correct b colour
what are post processing curves?
curves that assign a display intensity to the image
what function controls post processing curves?
DAC
what type of curve is usually used when using post processing curves?
linear curve
what is B colour? what may it improve?
assigning shades of other colours to the image
may improve contrast resoltuion
what the function of DAC?
converts digital information to a voltage signal
can display systems accept digital information?
no, only voltage (video or analog)
How are dynamic range and rejection related?
Inversely
What is contrast resolution?
What happens when we have too little contrast or too much contrast?
The ability to distinguish between like shades of grey
Too little: hard to tell the shades from one another because they’re too similar
Too much: similar shades of grey are grouped together and we can’t tell them apartF
What controls contrast resolution?
Dynamic range
What’s the relationship between the voltage and the pressure of returning waves?
Directly proportional
When sampling incoming analog voltages, in order to convert them into digital format, how fast should the sampling rate be?
Must be at least 2 times the highest operating frequency used
Gains can be expressed as a ratio, what is this ratio?
Ratio of output to input of electrical power
TGC amplifiers compensate for approximately how many dB of attenuation?
60dB
In what order should the receiver functions be used?
Amplification, compensation, compression…… and then rejection and demodulation can be in any order
What’s another term for edge enhancement?
Sharpness
What is one con of edge enhancement?
Can increase the amount of noise in an image
