system operations ultrasound DMS 110 acoustic physics
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| what are the 6 core functions an US system must perform | transmit beams
receive beams
process returned data
perform measurements
display processed data
store processed data
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| synonyms for transmit power (7) | acoustic power
transmit gain
power gain
acoustic gain
output intensity
transmit voltage
output voltage
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| increasing transmit power results in two effects | more intense beam, hence, stronger echoes
risk of bioeffects
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| the maximum or minimum of any quantity | dynamic range
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| the range of signal amplitudes a system can receive and process without causing harmonic distortion | input dynamic range
system default
there are many dynamic ranges, have to specify which one
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| the amplitude level below which no signals are visible because of noise | noise floor
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| amplitude of signal divided by amplitude of noise | S/N ratio, or, SNR
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| increasing amplification usually _____ the signal and ____ the noise | increases, increases
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| a mistaken observation related to the S/N ratio usually caused by low gain | apparent SNR
SNR is fine, gain is set low and operator things there's bad SNR
more gain is required to drive the signal into visual range
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| types of noise (4) | electronic noise
electronic interference
clutter
haze
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| noise from larger signals obliterating smaller ones | clutter
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| noise that can be cause by poor interface contact | haze
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| noise that can show up as bright flashes of light | electrical interference
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| noise that shows up as random speckles or random color pixels | electrical noise
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| all receiver functions are pre/post processing | pre
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| pre/post processing can be performed on saved and live data | post
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| pre/post processing is usually performed by the scan converter | post
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| which part of an US machine conditions the signals for conversion, measurement and display | receiver
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| the ___ ____ is part of an US machine that converts streamed data into a format where it can be measured, stored and displayed | scan converter
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| which component of an US machine performs these functions | transmitter
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| produce pulses also changes amplitude and produces small time delays | also called 'pulser' and 'transmit beam former'
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| increasing the ____ ____ control increases the amplitude of the voltage driving the transducer | output power
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| two effects when increasing power | bioeffects
increased acoustic power resulting in greater penetration
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| what are the functions of the receiver (5) | compression
compensation
amplification
rejection
demodulation
Memory aid: All Cars Can Drag Race
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| this function of the receiver is necessary because the signals returning from tissue are too small to process | amplification
also called receiver gain
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| synonyms for amplification (2) | gain, receiver gain
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| synonyms for TGC (3) | DGC, depth gain compensation
SGC, swept gain compensation
pots, potentiometers
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| the application of extra amplification to adjust for the increasing attenuation with depth | compensation (what TGC does)
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| this function of the receiver is necessary because the dynamic range of the returning echoes is much larger than the dynamic range of the display | compression
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| it is possible to compress signal levels into brightness levels visible to the human eye (Y/N) | N
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| can clinically significant signals be compressed out of visibility (Y/N) | Y
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| the process by which modulations of the reflected wave are removed or detected | demodulation
often called 'signal detection'
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| the two things that demodulation does to the US signal | rectification
smoothing
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| the process that converts negative components of a signal into positive | rectification
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| the process that essentially averages the signal taking out bumps | smoothing
also called envelope detection
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| this function of the receiver effectively sets a threshold below which signals will not be visible on the screen | rejection
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| imaging modality affects power because what two things | duty factor, scanned vs non-scanned modality
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| when duty factor increases, the transmit power must _____ | decrease
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| what happens to the transmit power when image size decreases | decrease
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| what happens to the transmit power when pulse length increases | decrease
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| what happens to the transmit power with shallower focus | decrease
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| what happens to the transmit power with a lower image depth | decrease
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| reasons (2) why the system internally applies approximately 30dB of compensation before TGC | make TGC more responsive
so TGC is not too sensitive
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| TGC is operative under color (T/F) | F, TGC control is entirely internal for color
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| since TGC is entirely internal, what can the sonographer do to mask incorrect TGC | use gain
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| what's it called when the system uses an algorithm to make a 'best guess' at TGC settings | pre-compensated TGC
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| how is the amplification in each TGC zone calculated | overall gain + TGC
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| name the two functions of the beam former (front end process) | creates sequencing and phase delays for transmit and receive
apodization, limiting which elements are active
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| the data output format from the front end is _____ | digital
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| all post processing in the system takes place on the data in ____ format | digital
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| what are the two core functions of the scan converted (back end process) | converting A-mode into B-mode lines
organizing lines into formatted image
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| the precise definition of a pre-process function is any process that is performed before the ___ ___ and ___ ___ | scan conversion, data storage
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| the precise definition of a post-process function is any process that can be performed on ___ ___ after ____ | stored data, conversion
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| the disparity between the 80dB dynamic range of the returning signal and the 36dB dynamic range of the eye is the reason why ___ ____ is required | logarithmic compression
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| the primary clinical concern of compression techniques | could loose important clinical data
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| compression takes place in the __ __ and the ___ ___ | front end, back end
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| compression that takes place in the front end is under user control (Y/N) | N
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| compression that takes place in the back end is under user control (Y/N) | Y
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| what's the primary purpose of using tissue colorization | using color hues extends the dynamic range of the eye
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| monitor formats standards (3) | NTSC, United States, 525 lines, 29.97 fps color
PAL, Europe, 625 lines, 25fps
SECAM, France, 819 lines, 25 fps
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| interlaced monitors are divided into ___ and ___ groupings | even, odd
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| interlaced monitors display __ frames per second | 30
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| non-interlaced monitors display ___ frames per second | 60
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| no motivation exists to improve the line frequency of monitors > 60 fps because | 60 fps is the limit the eye can perceive
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| what's the smallest division of a monitor | pixel
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| the human eye can only see __ shades of gray | 64
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| the number of shades of gray is calculated by taking 2 to the power of the ___ __ ____ | number of bits
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| since the eye can only see 64 shades of gray, only ___ bits are required for gray scale | 6, 26 = 64
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| most systems store gray scale to at least 8 or 10 bits even though only 6 is needed. The reason for this is because of ___ ____ | ambient light
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| what's one of the benefits of using cine loop | the acoustic frame rate is higher than the monitor frame rate allowing more 'real' time frames to be examined
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| data from cine loop is stored in ___ | memory
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| synonyms for zooming | res, magnification
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| what are the two techniques used for zooming | acoustic and non-acoustic
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| what zooming technique essentially 'stretches' the area of interest | non-acoustic zooming
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| what's the zooming technique called where the system changes the beam profile to improve resolution | acoustic zooming
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| another name for non-acoustic zoom | read zoom, implies reading it from memory, like digital zoom on cameras
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| another name for acoustic zoom | write zoom, implies new data is written to memory post-conversion, like optical zoom on cameras
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| what's a technique to improve lateral focus for a longer depth | multiple transmit foci
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| what's the drawback of using multiple transmit foci | degraded temporal resolution
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| a change in the maximum transmit power during multiple transmit foci causes what kind of artifact | banding
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| the system is allowed to change parameters during receive time. This ability is used as an alternative to B-mode for _____ | dynamic (continuous) receive focus
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| dynamic (continuous) receive focus uses the technique of _____ which changes the focus and delay profile | apodization
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| parallel processing, which improves temporal resolution, works by sending a ___ transmit beam and processing ___ receive beams | large, smaller
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| averaging techniques rely on the fact that the desired image remains _____ over time and noise is ____ | constant, random
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| SNR equation | sqrt(n), where n is the number lines averaged
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| compound (spatial) imaging besides benefiting from averaging has the advantage of reducing _____ ____ | specular reflection
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| the compound image technique that has these two features angle is not changed between frames a weighted average is applied to each frame making newer frames count for more | image persistence
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| image improvements made by making the center pixel the average of its neighbors | spatial averaging
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| short name for constant depth mode | C-mode, listening for echoes at a specific depth
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| an imaging mode where a single acoustic line is repeatedly transmitted, results plotted against time | M-Mode
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| what are the three categories of resolution | detail
contrast
temporal
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| this type of resolution is highly dependent on the transducer characteristics. It’s the combination of axial, lateral and elevation | detail resolution
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| this type of resolution is the ability to distinguish structures based on variations of brightness | contrast resolution
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| this type of resolution is the ability to distinguish dynamics or changes over time | temporal resolution
any factor that lowers frame rate lowers temporal resolution
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| name two averaging techniques commonly used that degrade temporal resolution | persistence, compound imaging
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| what are the three components of resolution | detail, contrast, temporal
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| elevation beam dimension affects which component of resolution? | detail
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| SPL/2 affects which component of resolution? | detail
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| lateral beam dimension affects which component of resolution? | detail
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| the scan converter affects which component of resolution? | contrast
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| the #bits/pixel affects which component of resolution? | contrast
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| post processing curves affects which component of resolution? | contrast
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| the monitor settings (contrast/brightness) affects which component of resolution? | contrast
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| ambient light affects which component of resolution? | contrast
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| acoustic impedance mismatch affects which component of resolution? | contrast
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| depth affects which component of resolution? | temporal
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| packet size (color) affects which component of resolution? | temporal
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| image size affects which component of resolution? | temporal
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| line density affects which component of resolution? | temporal
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| parallel processing affects which component of resolution? | temporal
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| # foci/line affects which component of resolution? | temporal
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| persistence affects which component of resolution? | temporal
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| compound imaging affects which component of resolution? | temporal
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