Midterm Flashcards
what are we dealing with at the signal processor?
digital signals
what does the reception channel of the beam former do?
amplifies and combines echo voltages from individual elements and sends them to the signal processor
what are the functions of the signal processor?
- filtering
- detection
- compression
what is bandwidth?
range of frequencies contained in a pulse
what does pulsed wave ultrasound produce?
a bandwidth of transmitted frequencies
what is the strongest frequency?
fundamental frequency
do we have a bandwidth of returning echo frequencies?
yes
filtering
getting rid of frequencies we don’t want
what does filtering reject?
frequencies above or below bandwidth
how does filtering happen?
done with BANDPASS filters
what are the 2 filters?
tuned amplifier
dynamic filter
tuned amplifier
involves an amplifier with a filter attached
dynamic filter
a filter that can be adjusted
ex. harmonic frequencies
harmonics
modification of the sinusoidal waveform as it propagates through tissue
in harmonics what are multiple frequencies produced by
fundamental frequency (odd and even multiples)
If we have a fo of 5MHz what are the odd harmonic frequencies?
15 MHZ
25 MHZ
If we have a fo of 5MHz what are the even harmonic frequencies?
10 MHz
20 MHz
30 MHz
what is your first harmonic named?
fundamental frequency
what is the 2nd harmonic frequency?
will produce echoes that will allow for better resolution
what function do filters in signal processor preform?
harmonics
in harmonics, what echoes are received?
echoes from fo and 2fo
what happens to the fundamental frequency at the signal processor?
it is filtered out (this happens when we press THI)
what are the benefits of harmonics with a narrower beam?
- better lateral resolution
- better elevational resolution (thinner)
what are benefits of harmonics?
- narrower beam
- side/grading lobes eliminated
- reduction in anterior reverberation
anterior reverberation (AKA. main bang)
reflections between the transducer face and skin surface cause multiple horizontal lines of echoes to appear in near field
where can anterior reverberation also occur?
ribs
harmonics cause beam to be generated further into the tissue, what does it have a less chance of?
anterior reverb-main bang echoes are filtered out
summarizing all the points, what are the benefits of harmonics?
- better detail resolution (lateral and elevational)
- reduced artifacts (grading lobes and anterior reverberation)
what are the drawbacks of harmonics?
- decreased penetration
- worse axial resolution
why is there a decrease in penetration in harmonics?
higher frequency means more attenuation
what must the transducer fit into?
the bandwidths of both fo and 2fo
harmonics allow for better ________ overall
resolution
what do narrower bandwidths for harmonic frequenxy?
- longer SPL
- larger (worse) AR
- worse resolution
what helps with the drawbacks narrow bandwidth?
pulse inversion harmonic imaging
what is pulse inversion harmonic imaging?
2 pulses are sent out back to back
- regular pulse
- inverted pulse
where are harmonic signals produced?
In the tissue
what happens to the echo of the fundamental signal?
destructive interference
what happens to the echo of the harmonic signal?
sinusoidal signal
what happens to the fundamental signal in pulse inversion harmonic imaging?
does not make it back
-transducer can use its entire bandwidth for 2 fo
what is the wider bandwidth for harmonic frequency?
- shorter SPL
- smaller (better) AR
- better resolution
what does sending multiple pulses decrease?
Frame Rate
what is another name for detection?
demodulation
what is video form/amplitude form more useful for?
processing
what is detection?
radio frequency form to video form/ amplitude form
what is not an operator controlled function?
detection
what is voltage amplitudes proportional to?
intensity of returning echoes
what are the 2 steps to detection?
- rectification
2. smoothing
reactivation
turns negative voltages into positive voltages
smoothing
warps an envelope around the signal to make it less bumpy
video form
we only require the maximum values of the signal
what preforms dynamic range function?
compression
dynamic range
power ratio of largest to smallest amplitude that system can handle
what does dynamic range equal?
power ratio
what does 60 dB DR mean?
means the strongest echo is 10’6 stronger than the weakest echo
power ratio=
voltage ratio’2
what can amplifiers handle?
DR 100-170 dB
what can the display handle?
30 dB
what can our human vision handle?
20 dB
for us to view the highest brightness how much higher must the DR be?
can only be 100 times the lowest
compression
the process of decreasing the differences between the smallest and the largest echo amplitudes to a useable range
which signals are more amplified?
weaker signals
what does compression do?
reduces dynamic range with selective amplification
what does compression mean for us?
contribute to contrast resolution
contrast resolution
being able to separate 2 different echoes as 2 different shades of grey
what does compression effect?
our contrast
is compression operator controlled/
yes, DR button
what does the decrease in DR do to contrast?
more contrast=grainer
what does the increase in DR to do contrast?
less contrast=smoother
what are the functions of the signal processor?
- bandpass filtering
- amplitude detection
- compression (dynamic range reduction)
what are the components if the image processor?
- preprocessor
- scan converter
- image memory
- postprocessor
- digital-to-analog converter
scan line information is:
- built into frames of information
- pre-processed
what is stored in the image memory?
frames
frames can be pulled out of memory and:
- post-processed
- sent to display as an analog signal
what is scan conversion done by?
scan converter
scan conversion
building a frame
Echo information-scan lines (digital) to image form-frames (digital)
how many scan lines are in a frame?
96-256 lines in a frame
pixels
each frame is made up of a ‘matrix’ of tiny blocks called pixels
more pixels=
better resolution
what are common matrix?
- 1024 x 768 matrix
- 512 x 384 matrix
3D=
voxels
what do frames require?
processing
pre processing
- Done while echo data is being stored in the memory
- The frame is still being built during this time
post-processing
done on image retrieved from image memory
when does pre processing function?
before (while) the data is stored in image memory
when does post processing function?
after the data is stored in the image
preprocessing info
- persistence
- panoramic
- 3D & 4D
- spatial compounding
- write magnification
post processing info
- B colour
- Freeze Frame
- Black/white image inversion
- read magnification
- contrast variation
what does pre/post depend on?
the manufacturer
what does pre-processing do to the edges?
edge enhancement-sharpens boundaries to make them more detectable and make measurements more precise
pixel interpolation
filling in missed pixels
-Average the brightness of the adjacent pixels and fill in the missing pixel accordingly
Panoramic Imaging
compilation of frames as transducer is moved
what does panoramic imaging result in?
an image with a wider field of view
spatial compounding
hit the same object from different angles and average the images (trying to hit at 90 degrees)
what does spatial compounding do?
clear out cysts
sharpen borders
persistence (frame averaging)
- averaging of sequential frames (in times)
- reduces noise (speckle) and random content
what does persistence do to frame rate?
decrease
operator controlled
3D imaging
multiple parallel 2D frames obtained and built into 3D volume
elastography
imaging method that presents qualitative tissue stiffness information on the anatomic display and in some cases, presents quantitative stiffness information
what is used when presenting elastogrpahy?
split screen
what does colour side of electrography display?
compressibility
what does compressibility have a correlation with?
malignancy potential
what is pre-processing summary?
-all processing functions involved before frames are placed in memory
-they are all live-scanning options
CANNOT BE DONE AFTER PRESSING FREEZE
post processing summary?
-involves processing done to an image after it is pulled from the image memory
CAN BE DONE ON A FROZEN IMAGE
how many shades of grey and shades of colour can human eye see?
100 shades of grey
256 shades of colour
Read Magnifaction (read zoom)
pulls out specific pixels from the frame from memory and displays them using the entire display
what is the drawback of read magnification?
pixelization-enlargement of pixels
Write Magnification (write zoom)
smaller field of view is written using the pixels for the entire frame
-better resolution
what is another adjustment to write zoom?
changing depth
what is scan line information built into?
frames of information
describe scan line info process
- buildt into frames of information
- pre-processed
- frames are stored in image memory
- pulled out of memory
- post-processed
- sent to display as analog signal
what is each image stored as?
a frame of information (this is a continuous process)
what is another term for image memory?
digital memory
freeze frame
displays latest image stored in memory
cineloop
displays last 100-130 images
what information does each pixel conatin?
brightness (intensity/amplitude) at a particular anatomical postition
numbers are stores in the memory elements (pixels) according to what?
the intensity of the echoes received from corresponding anatomic location
how many shades of grey can one matrix (checkerboard) show?
2 shades (on and off)
what do more shades of grey require?
more matrixes (more bits)
how many options would you have with a 1-bit pixel?
2 options (0/1)
bistable
1-bit pixel
what is represented when memory element is off?
0 so the picture is black (on would be 1 and white)
multiple bits
binary digit
bit depth/capacity
how many options for black/white/grey
what is the bit depth for a 3 bit pixel?
8 possible shades of grey
2’8
256 possible shades of grey
if you have a 7 bit pixel (128 shades) how many options does each pixel have?
0-127
how many bit memories does a majority of ultrasound machines currently use?
6-8
how many shades of grey can humans see in?
100 shades
more pixels=
more shades of grey
what is the binary number system?
alternative to the decimal (Arabic) number system
CR=
dB/shade
contrast resolution
being able to separate 2 different echoes as 2 different shades of grey
what affects our DR?
compression reduces the DR for us so we wouldn’t have as many different amplitudes to deal with
what is the next step after compression?
group those intensities into the available shades of grey
if we have more bits what does that do to our contrast resolution?
better contrast resolution
what affects our contrast?
bits/pixels
is contrast operator controlled?
no it is manufacturer dependant
less shades=
- more contrast
- grainier
- lower DR
more shades=
- less contrast
- smoother
- higher DR
contrast reolution=
DR/bits-per-pixel
more bits/pixels=
more pixels/frame=
better CONTRAST resolution
better DETAIL resolution
1 byte=
8 bits
1 kilobyte
1024 bytes
when is a frame ready to be sent to the display?
once it is pre-processed, stored in the image memory, pulled from the image memory, and post-processed
digital memory (#’s)=
voltages for display
