Question | Answer |
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 |
synonyms for transmit power (7) | acoustic power
transmit gain
power gain
acoustic gain
output intensity
transmit voltage
output voltage |
increasing transmit power results in two effects | more intense beam, hence, stronger echoes
risk of bioeffects |
the maximum or minimum of any quantity | dynamic range |
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 |
the amplitude level below which no signals are visible because of noise | noise floor |
amplitude of signal divided by amplitude of noise | S/N ratio, or, SNR |
increasing amplification usually _____ the signal and ____ the noise | increases, increases |
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 |
types of noise (4) | electronic noise
electronic interference
clutter
haze |
noise from larger signals obliterating smaller ones | clutter |
noise that can be cause by poor interface contact | haze |
noise that can show up as bright flashes of light | electrical interference |
noise that shows up as random speckles or random color pixels | electrical noise |
all receiver functions are pre/post processing | pre |
pre/post processing can be performed on saved and live data | post |
pre/post processing is usually performed by the scan converter | post |
which part of an US machine conditions the signals for conversion, measurement and display | receiver |
the ___ ____ is part of an US machine that converts streamed data into a format where it can be measured, stored and displayed | scan converter |
which component of an US machine performs these functions | transmitter |
produce pulses
also changes amplitude and produces small time delays | also called 'pulser' and 'transmit beam former' |
increasing the ____ ____ control increases the amplitude of the voltage driving the transducer | output power |
two effects when increasing power | bioeffects
increased acoustic power resulting in greater penetration |
what are the functions of the receiver (5) | compression
compensation
amplification
rejection
demodulation
Memory aid: All Cars Can Drag Race |
this function of the receiver is necessary because the signals returning from tissue are too small to process | amplification
also called receiver gain |
synonyms for amplification (2) | gain, receiver gain |
synonyms for TGC (3) | DGC, depth gain compensation
SGC, swept gain compensation
pots, potentiometers |
the application of extra amplification to adjust for the increasing attenuation with depth | compensation (what TGC does) |
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 |
it is possible to compress signal levels into brightness levels visible to the human eye (Y/N) | N |
can clinically significant signals be compressed out of visibility (Y/N) | Y |
the process by which modulations of the reflected wave are removed or detected | demodulation
often called 'signal detection' |
the two things that demodulation does to the US signal | rectification
smoothing |
the process that converts negative components of a signal into positive | rectification |
the process that essentially averages the signal taking out bumps | smoothing
also called envelope detection |
this function of the receiver effectively sets a threshold below which signals will not be visible on the screen | rejection |
imaging modality affects power because what two things | duty factor, scanned vs non-scanned modality |
when duty factor increases, the transmit power must _____ | decrease |
what happens to the transmit power when image size decreases | decrease |
what happens to the transmit power when pulse length increases | decrease |
what happens to the transmit power with shallower focus | decrease |
what happens to the transmit power with a lower image depth | decrease |
reasons (2) why the system internally applies approximately 30dB of compensation before TGC | make TGC more responsive
so TGC is not too sensitive |
TGC is operative under color (T/F) | F, TGC control is entirely internal for color |
since TGC is entirely internal, what can the sonographer do to mask incorrect TGC | use gain |
what's it called when the system uses an algorithm to make a 'best guess' at TGC settings | pre-compensated TGC |
how is the amplification in each TGC zone calculated | overall gain + TGC |
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 |
the data output format from the front end is _____ | digital |
all post processing in the system takes place on the data in ____ format | digital |
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 |
the precise definition of a pre-process function is any process that is performed before the ___ ___ and ___ ___ | scan conversion, data storage |
the precise definition of a post-process function is any process that can be performed on ___ ___ after ____ | stored data, conversion |
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 |
the primary clinical concern of compression techniques | could loose important clinical data |
compression takes place in the __ __ and the ___ ___ | front end, back end |
compression that takes place in the front end is under user control (Y/N) | N |
compression that takes place in the back end is under user control (Y/N) | Y |
what's the primary purpose of using tissue colorization | using color hues extends the dynamic range of the eye |
monitor formats standards (3) | NTSC, United States, 525 lines, 29.97 fps color
PAL, Europe, 625 lines, 25fps
SECAM, France, 819 lines, 25 fps |
interlaced monitors are divided into ___ and ___ groupings | even, odd |
interlaced monitors display __ frames per second | 30 |
non-interlaced monitors display ___ frames per second | 60 |
no motivation exists to improve the line frequency of monitors > 60 fps because | 60 fps is the limit the eye can perceive |
what's the smallest division of a monitor | pixel |
the human eye can only see __ shades of gray | 64 |
the number of shades of gray is calculated by taking 2 to the power of the ___ __ ____ | number of bits |
since the eye can only see 64 shades of gray, only ___ bits are required for gray scale | 6, 26 = 64 |
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 |
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 |
data from cine loop is stored in ___ | memory |
synonyms for zooming | res, magnification |
what are the two techniques used for zooming | acoustic and non-acoustic |
what zooming technique essentially 'stretches' the area of interest | non-acoustic zooming |
what's the zooming technique called where the system changes the beam profile to improve resolution | acoustic zooming |
another name for non-acoustic zoom | read zoom, implies reading it from memory, like digital zoom on cameras |
another name for acoustic zoom | write zoom, implies new data is written to memory post-conversion, like optical zoom on cameras |
what's a technique to improve lateral focus for a longer depth | multiple transmit foci |
what's the drawback of using multiple transmit foci | degraded temporal resolution |
a change in the maximum transmit power during multiple transmit foci causes what kind of artifact | banding |
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 |
dynamic (continuous) receive focus uses the technique of _____ which changes the focus and delay profile | apodization |
parallel processing, which improves temporal resolution, works by sending a ___ transmit beam and processing ___ receive beams | large, smaller |
averaging techniques rely on the fact that the desired image remains _____ over time and noise is ____ | constant, random |
SNR equation | sqrt(n), where n is the number lines averaged |
compound (spatial) imaging besides benefiting from averaging has the advantage of reducing _____ ____ | specular reflection |
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 |
image improvements made by making the center pixel the average of its neighbors | spatial averaging |
short name for constant depth mode | C-mode, listening for echoes at a specific depth |
an imaging mode where a single acoustic line is repeatedly transmitted, results plotted against time | M-Mode |
what are the three categories of resolution | detail
contrast
temporal |
this type of resolution is highly dependent on the transducer characteristics. It’s the combination of axial, lateral and elevation | detail resolution |
this type of resolution is the ability to distinguish structures based on variations of brightness | contrast resolution |
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 |
name two averaging techniques commonly used that degrade temporal resolution | persistence, compound imaging |
what are the three components of resolution | detail, contrast, temporal |
elevation beam dimension affects which component of resolution? | detail |
SPL/2 affects which component of resolution? | detail |
lateral beam dimension affects which component of resolution? | detail |
the scan converter affects which component of resolution? | contrast |
the #bits/pixel affects which component of resolution? | contrast |
post processing curves affects which component of resolution? | contrast |
the monitor settings (contrast/brightness) affects which component of resolution? | contrast |
ambient light affects which component of resolution? | contrast |
acoustic impedance mismatch affects which component of resolution? | contrast |
depth affects which component of resolution? | temporal |
packet size (color) affects which component of resolution? | temporal |
image size affects which component of resolution? | temporal |
line density affects which component of resolution? | temporal |
parallel processing affects which component of resolution? | temporal |
# foci/line affects which component of resolution? | temporal |
persistence affects which component of resolution? | temporal |
compound imaging affects which component of resolution? | temporal |