Chapter 4 Flashcards
A mode
mode of operation in which the display presents echo amplitude versus depth (used in ophthalmology).
Amplification
the process by which small voltages are increased to larger ones.
Amplifier
a device that accomplishes amplification.
Analog
related to a procedure or system in which data are represented by proportional, continuously variable, physical quantities (e.g. electric voltage).
Analog-to-digital converter
a device that converts voltage amplitude to a number. Abbreviated ADC.
B mode
mode of operation in which the display presents a spot of appropriate brightness for each echo received by the transducer.
B scan
a B-mode image that represents an anatomic cross section through the scanning plane.
Beam former
the part of an instruement that accomplishes electronic beam scanning, apodization, steering, focusing,, and aperture with arrays.
Bistable
having two possible states (e.g. on or off, white or black, one or zero).
Bit
binary digit; one or zero.
Chanel
a single one or two-way path for transmitting electric signals, in distinction from other parallel paths; an independent transmission delay line and transducer element path; an independent reception transducer lement, amplifier, analog-to-digital converter, and delay line path.
Cine loop
sequential display of all the frames stored in memory at a controllable frame rate.
Coded excitation
a sophisticated form of transmission in which the driving voltage pulses have intrapulse variations in amplitude, frequency, and/or phase.
bandpass filter
f
Compensation
equalization of received echo amplitude differences caused by different attenuations for different reflector depths; also called depth gain compensation or time gain compensation.
Compression
reduction in differences between small and large amplitudes. Region of high density and pressure in a compressional wave.
Contrast resolution
ability of a gray-scale display to distinguish between echoes of slightly different intensities.
depends on the number of bits per pixel in the image memory
more bits per pixel = more gray
dynamic range, pre and post processing are functions that the operator can change to optimize the contrast resolution
Demodulation
detection.
Depth gain compensation
compensation. Abbreviated DGC.
Detection
conversion of voltage pulses from radio frequency to video form. Also called demodulation, amplitude detection, and envelop detection.
Digital
related to a procedure or system in which data are represented by numeric digits.
Digital-to-analog converter
a device that converts a number to a proportional voltage amplitude. Abbreviated DAC.
Display
a device that presents a visual image derived from voltages received from an image processor.
Dynamic range
ratio (in decibels) of largest to smallest power that a system can handle; ratio of the largest to smallest intensity of echoes encountered.
Elastography
imaging tissue stiffness by tracking movement under mechanical stress.
Flat-panel display
a backlighted rectangular matrix of thousands of liquid-crystal display elements.
Frame
a single image produced by one complete scan of the sound beam.
Frame rate
number of frames of echo information stored each second.
Freeze
constant display of one of the frames in memory.
Gain
ratio (in decibels) of amplifier output to input electric power.
Gray scale
range of brightnesses (gray levels) between white and black
Image memory
the part of the image processor where echo information is stored in image format.
Image processor
an electronic device that manipulates and prepares images for visual presentation.
Lateral gain control
gain controls that enable different gain values to be applied laterally across an image to compensate for differing attenuation values in different anatomic regions.
M mode
a B-mode presentation of changing reflector position (motion) versus time (used in echocardiography).
Panoramic imaging
the extension of the field of view beyond the normal limits of a transducer scan plane.
Persistence
averaging sequential frames together.
Physical beam
s
Picture archiving and communications systems
the system provides means for electronically communicating images and associated information to workstations and devices external to the sonographic instrument, the examining room, and even the building in which the scanning is done. Abbreviated PACS.
Pixel
picture element; the unit into which imaging information is divided for storage and display in a digital instrument.
Postprocessing
image processing done after storage in the memory.
Preprocessing
signal and image processing accomplished before storage in the memory.
Pulse-echo principle
pulse-echo technique.
Radio frequency
voltages representing echoes in cyclic form. Abbreviated RF.
Real-time
imaging with a rapid frame sequence display.
Real-time display
a display that, with a sufficient frame rate, appears to image moving structures or a changing scan plane continuously.
Refresh rate
the number of times each second that information is sent from the image memory to the display. The number of times per second that computer monitor redraws the information found in the memory.
Scan line
a line produced on a display that represents ultrasonic echoes returning from the body. A sonographic image is composed of many such lines.
Scanning
the sweeping of a sound beam through the anatomy to produce an image.
Shear wave
transverse wave.
Signal
information-bearing voltages in an electric circuit; an acoustic, visual, electric, or other conveyance of information. The physical representation of a message or information.
Signal processor
an electronic device that manipulates electric signals in preparation for appropriate presentation of information contained in them.
Spatial compounding
averaging of frames that view the anatomy from different angles.
Strain
the increase or decrease of the length of a segment of a material, subjected to as tress, divided by its original length
Stress
a force per unit area applied to a material that compresses or stretches it,
Temporal resolution
ability to distinguish closely spaced events in time; improves with increased frame rate.
time required to generate one frame
units are ms
depends on FR, depth, LPF, and foci
improves with higher FR
Time gain compensation
equalization of echo amplitude differences caused by different attenuations for different reflector depths; also called depth gain compensation. Abbreviated TGC.
Virtual beam
an imaginary beam (as opposed to aa physical ultrasound beam ) that describes the result of retrospective, computed beam forming, the virtual beam can be imagined in transmission or reception form.
Volume imaging
3D imaging.
Young’s modulus
a measure of the hardness (stiffness) of a material.
stress/strain
transmit power
controls the amplitude of excitation voltage which drives the crystals
a higher voltage = a higher amplitude sound wave
dynamic range
the ratio of the max to the min amplitude
signal
any phenomenon desired to be measured
noise
any unwanted signals
primarily from the electronics
noise floor
the amplitude level below which no signals are visible because of the presence of noise
SNR
amplitude of the signal/amplitude of the noise
specifies signal quality
in ultrasound the signals are
the reflections and doppler shifts
OP1 instruments are composed of what?
beam former
signal processor
image processor
display
beam former
where the action originates
consists of: pulser pulse delays channels T/R switch amplifiers digitizer echo delays summer
pulser
generates the voltages that drive the transducer
its frequency determines the frequency of the resulting ultrasound pulse
its PRF and PRP = the ultrasound’s PRF and PRP
1 ultrasound puls eis produced from each voltage pulse
to avoid misplacement, the following formula must hold true
penetration x PRF =< 77
pulse delays
along with the pulser carry out sequencing, phase delays, and variations in pulse amplitude
Transmit/receive switch
directs the driving voltages from pulse delays to the probe during transmission
and directs the returning echo voltages to the amplifiers during reception
amplifiers
increase voltage amplitude (called gain)
TGC
attenuation and max amplifier gain determines the max imaging depth
max amplifier is determined by noise
lateral gain controls are available in some systems
TGC compensates for what?
attenuation as depth increases
power (amplitude) ratio=
output power/input power
digitizer
aka ADC (analog to digital converter)
echo voltages are digitized here
echo voltages are replaced by a series of numbers
interrogation rate must be 2x the highest frequency involved to persevere all harmonics
eg if the highest frequency is 5 mhz, the digitizing rate must be at least 10 mhz
echo delays
digital delay lines that digitized echoes pass through to accomplish reception dynamic focus and steering
summer
aka adder
combines all signals from all channels to create a scan line
reception apodization and dynamic aperture occur here
transmission channels
pulser -> delay -> element
reception channels
element -> amplifier -> ADC -> delay -> summer
signal processor consists of
filtering/rejection
detection/demodulation
compression
filter
tuned amplifiers reduce noise
eleminates frequencies outside the echo bandwidth while retaining the useful ones
uses a bandpass filter
detection
aka demodulation
converts echo voltages from radio frequency to video form
the video retains the amplitudes of the echo voltages
compression
reduces the dynamic range with selective amplification
reduces the difference between the smallest and largest amplitudes
image processor
converts the serial scan line data into iimages that are stored in the image memory
preprocessing
occurs before the echo data is stored in the image memory
pixel interpolation
fills in missing pixels
assigns brightness value based on the average brightness of adjacent pixels
common in sector images
uncommon in linear images
persistance
is the averaging of sequential frames to provide a smoother image and to reduce noise
speckle reduction, increases dynamic range and contrast resolution
decreases frame rate
not used for rapidly moving structures
volume imaging (3D)
acquired by assembling 2D scans into a 3D volume of echo information in the image memory
4D imaging is 3D imaging in real-time
the 4th dimension is time
image memory
after the echo data is preprocessed, the image frames are stored here
freeze
displaying one frame out of a sequence
cine loop
aka cine review, clip, loop, cine
last several frames stored before freezing
pixels and bits
sonography memories are stored in numbers (binary)
the image is divided into pixels like a checkerboard
in a bit memory there’s 4 checkerboards back to back
each pixel has 4 bits
allows for numbers from 0-15
is a 16 shade memory
ultrasound systems usuall have a ______ bit memory.
6, 7, or 8-bit memory
the ___ the binary number, the ___ the pixel will be displayed
higher, brighter
write zoom
occurs in preprocessing
uses all the pixels on a smaller region
read zoom
occurs in postprocessing
enlarges pixels
postprocessing
image processing done after the echoes are stored in the scan converter
determines how the echo data stored in the memory will appear on the display
white echo display is the one we use
B color
ability to colorize echoes in different shades other than gray
volume presentation
3D can be displayed in 2D slices, surface renderings, transparent view (x-ray view), etc.
DAC
aka digital to analog converter
converts the digital data received from the image memory to analog voltages that are fed to the display to determine echo brightness
display
the brightness is proportional to the echo strength
flat -panel display: presents image in horizontal lines from top to bottom
3 types:
B mode
A mode
M mode
B - mode
brightness mode, gray scale, B scan
M - mode
motion
used to show motion of cardiac
presents depth vs time
A - mode
shows the amplitude in echoes
used in ophthalmology
presents depth vs amplitude
temporal resolution
ability of a display to distinguish closely spaced events in time and to present rapidly moving structures correctly
improves when the FR increases because less time elapses between one frame to the next
frame rate
the number of images stored in the image memory per second
for each focus on each scan line in each frame a ___ is required.
pulse
n x LPF x FR =
PRF
to increase the number of foci, the number of lines per frame, and the FR, the PRF must increase
to avoid echo misplacement, all echoes from one pulse must
be received before the next pulse is emitted
wider images and multiple foci reduce
the FR
echo misplacement will occur if this equation doesn’t hold true
pen x n x LPF x FR =< 77,000 cm/s
77,000 is half of the average speed 1.54
harmonic imaging
filtering in which the fundamental frequency echoes are filtered out and the second harmonic frequencies are accepted
harmonic beam is narrower (improves LR)
grating lobe artifacts are eliminated
AR is kept high by sending two pulses per scan line and inversing the second (pulse inversion)
FR decreases
panoramic imaging
wider field of view like a panoramic photo
adds new info
done by sliding the probe
spatial compounding
is the averaging of frames to view anatomy in different angles
reduces speckle and clutter
specular surfaces are presented more completely
structures previously hidden can be visualized
elastography
presents qualitative or quantitative information regarding the stiffness of the tissue
displayed as color red = soft
blue = hard
cardiac strain imaging
presents info regarding contraction and relaxation strain and strain rate information for the myocardium
fusing imaging
combo of sonography imaging and another imaging like CT or MRI
Major parts of the system
beam former
signal processor
image processor
display
Beam former
found in array systems
consists of: pulser pulse delays T/R switch amplifier ADCs echo delays sum
pulser
produces electric voltages that drive the probe
forms the beam that goes into the tissue
informs receiver and memory when ultrasound pulses are made (for accurate display echo placement)
ultrasound PRF is determine by what?
the voltage PRF of the pulser
to avoid echo misplacement
all echoes from one pulse must be recieved before the next pulse is emitted
PRF must be adjusted
pen (cm) x PRF =< 77 cm/ms
what determines the max A of the ultrasound pulse?
the pulser
the higher the voltage, the higher the max
which allows for higher system sensitivity
pulse delays
assist the pulser
carry out sequencing, phasing, and amplitude variations
what does pulse delays make possible?
scanning steering transmission focusing aperture variation apodization
coded excitation
when a series of pulses and gaps is used
allows multiple foci and separated harmonic bandwidth from frequency pulse bandwidth
increases penatration and contrast resolution
decreases speckle
allows B flow (gray scale imaging of blood flow)
the more channels, the more ___ of the beam
control
there’s separate transmit and receive channels
usually 64-192 channels in modern equipment
usually no more channels than the number of elements
T/R switch
transmit/receive switch
directs voltages from pulse delay to probe
directs echo voltages from probe to amplifiers
protects amplifiers from the large driving voltages of the pulser
amplifiers
increase voltage amplitude
pre-amplifiers
boosts strength of all voltages to prevent them from being lost and sends them to the receiver
can be located in scanner or probe assembly
receiver gain
the ratio of amplifier output to electric power input
units are dB
overall gain
the ratio of ooutput signal strength to input signal strength
controlled by us
compensation
allows graded amplification according to depth of the echoes within the image
controlled by us
later GC exists (compensates for outer edges)
LIKE TISSUES SHOULD APPEAR LIKE REGARDLESS OF DEPTH
compensation is also called
TGC transmit gain compensation, DGC depth gain compensation, SGC swept gain compensation
SNR
signal to noise ratio
you want the signal to have high amplitude and the noise to have low amplitude
we want the difference in A between the two to be large
does increasing reciever gain improve SNR
NO
because both signals and noise are being boost equally
apparent SNR
how it looks to our eyes
how to improve SNR
increase transmit power
decrease frequency for deeper depths
use different imaging plane
maneuvers to remove attenuation
move transmit focus deeper
use larger aperture for deeper focus
use semi-invasive techniques like endoprobes
HID formula
6/f
or
3/attenuation coefficient
depth determines what and why?
the PRF because of the time it takes echoes to return
CRT
cathode ray tube
type of monitor
old times
Digitizer
aka ADC
converts analog (proportional) signal to digital (discrete numbers)
the rate at which sampling occurs can affect the digital signal accurateness representing the analog signal
digital output is in binary (bits)
faster signals need ___ sampling
faster
what does it mean when something is aliased?
when we lose info bc of sampling rate made the (reconstructed) output signal different from the (original) input signal
nyquist criterion
to avoid aliasing, the sample frequency must be AT LEAST twice as fast as the highest frequency in the signal
sampling frequency (min) = 2 x signal frequency (max
echo delays
digital delay lines which accomplish reception dynamic focus and steering
summer
aka adder
last component of the beam former
is where all the channels signals are combined to form a scan line
reception apodization and dynamic aperture are accomplished here
Signal processor
filtering, demodulation (detection), and compression happen here
filter
tuned amplifiers are used to reduce noise in electronics by using a bandpass filter
keeps most signal frequencies and rejects noise frequencies outside of it
tuned amplifier
amplifier which has an electronic bandpass filter
bandpass filter
passes a range of frequencies and rejects those outside the acceptance bandwidth
compression
reduces dynamic range to the dynamic range of the monitor and our eyes
the echo amplitudes undergo compression in which they’re logarithmically amplified
weaker echoes are amplified more than stronger ones
compression reduces the difference between the smallest and the largest echo voltage amplitudes
can result in loss of info/signals
dynamic range
is the ratio of the largest amplitude to the smallest amplitude signal that a system can process
max dynamic range is determined by the electrical capacity of the system
detection/demodulation
is the process of converting the radio frequency signal to video form
amplitude remains the same
includes rectification and smoothing
when sound goes into the body, the body changes/modulates the signal
these changes are detected by detection/demodluation
echo voltages from the probe are in radio frequency form which are too big and difficult to store and display
rectification
converts the negative components of a signal into positive components so that all components are positive (unipolar)
smoothing
aka envelope detection or amplitude detection
is the conversion of voltage pulses from radio frequency to video form
retains signal amplitudes
traces the signal peaks and valleys while applying some averaging/smoothing
rejection is part of this
rejection
aka suppression or threshold
eliminates voltage pulses with an amplitude below the rejection level
these low echoes are produced by side and grating lobes
can be adjusted by operator
image processor
converts the serial scan line data into images which are processed before and after storage in the image memory in order to prepare the images for display
consists of: preprocessor scan converter image memory postprocessor DAC
preprocessing
any processing done to echoes before they are stored in the scan converter
includes: edge enhancement pixel interpolation persistence volume imaging (3D)
can be changed only in real-time, not on freeze mode
postprocessing
can be applied in real-time and freeze mode
tissue texture preprocessing
done preprocessing
different gray-scale assignments result in subtle texture changes in the image
edge enhancement
sharpens boundaries of reflectors to make them more detectable and for measurements to be more accurate
pixel interpolation
filling in of missing pixels to increase the image quality
assigned brightness value is determined by averaging adjacent values
performed more commonly in sector formats
persistance
averaging of sequential frames (temporal averaging) to provide a smoother image
reduces noise (primarily speckle because it’s random)
decreases FR and temporal resolution
improves SNR
volume imaging
slices reformatted into 3D
when performed at rates of 30 per sec, it is real time imaging aka 4D imaging
scan converter
is the memory of the system
formats echo data into image form for processing, storage, and display
modern ultrasound machines use digital scan converters (DSC) which allows the info to be displayed in linear or sector format
produces the framers for storage and display
digital memory operates in what kind of system?
binary numbers
digital scan converter
obtains 2 quantities for each echo signal
obtains the echo signal’s memory storage address
obtains the echo signal’s amplitude value in binary number form.
address
is the signal location
signal is placed in a location in the computer memory matrix according to its address
address is determined by round trip time of the echo (calculated by the range equation)
to determine distance from source to reflector, the propagation speed in the medium must be known or assumed and round trip time is measured
image memory
each frame is stored in the memory after the data has been converted into image form by the scan converter
when freeze is on there’s no transmission or reception
digital memory
only the distance to reflector is needed, that’s why the range equation has the o.5
after the distance is calculated, the voltage level of each echo amplitude is given a value and placed at its address
multiple layers of matrices exist in the memory and is used to create different shades of gray
binary number combo allotted to each pixel location corresponds to echo amplitude received for that address
the higher the binary number, the higher the amplitude stored in the matrix
each bit combo is assigned a corresponding display brightness level
most systems display 64 shades (dynamic range of human eye)
memory-bit depth
aka multiple layers of matrices or memory resolution
6-8 bit depth memory is most common for ultrasound systems
the DSC stores ___ of image data in ___ format
the DSC stores bits of image data in matrix format
typically consists of 512 x 512 pixels
__ bits = 1 byte
8 bits
__ bytes = 1 kilobyte
1024 bytes
color tints can be differentiated by our eyes more than ___?
grays
3D representations vs acquisition
acquisition is preprocessing
representations is postprocessing
DAC
digital to analog converter
after the images are stored in memory and postprocessed
digital numbers are retrieved and converted into voltages that determine the brightness of echoes on display
CRT
cathode ray tube
old times
very large
made a display with an electron beam that painted horizontal lines which corresponded to rows of echo information
had a phosphor-coated face and a bright spot
flat panel
modern
uses backlit LCD
SVGA
super video graphics array
pixel matrix is 1024 x 768 and refresh rate is 60 Hz
LCD
liquid crystal display
composed of rectangular matrix with thousands of LCD elements which be turned on or off individually to pass or block light
each element can be turned on to a certain degree to allow a measured amount of light to pass through
256 levels of luminance (displayed grays)
1024x768 matrix pixels
PRF
a pulse is requried for each focus on each scan line in each frame
PRF=nxLPFxFR
decreases as pen increases
pen=nxLPFxFR=<77,000 cm/s
frame rate
decreases with increasing depth or multiple foci since it requires more time to make each frame
increase as field of view is narrowed, requiring fewer scan lines per frame
output devices
vcrs
printers
digital devices like hard drives and usbs
storage formats
JPEG Joint Photographic Experts Groups
TIFF Tagged Image File Format
AVI audio-video interweaver
MPEG Moving Picture Experts Group
if file size increase, quality increases and vice versa
DICOM
standardized protocol
digital imaging and communications in Medicine
included in PACS
