Pulsed Echo Instrumentation- Ch 13 Flashcards
what is an ultrasound system?
the entire device that produces sound beams, retrieves the echoes and produces visual images and audio signals
what info is processed by the US system? (4)
time of flight, strength of reflection, direction, frequency (for doppler)
what is the us system made up of? what are the names of these?
six interconnected components - info is transferred to and from each; master synchronizer, pulser, transducer, receiver, display, storage.
what is the master synchronizer’s role in the system?
communicates with all of the individual components of the system; organizes, synchronizes and times their functions so as to operate as a single integrated system
what is the pulser’s role in the US system?
(controls, determines, create) controls the electrical signals sent to the active elements for sound pulse generation; determines the pulse repetition period, PRF, and pulse amplitude; creates the firing pattern for phased array systems, called the “beam former”
what is the transducer’s role in the system?
(converts) converts electrical into acoustic energy during transmission. and converts returning acoustic into electrical energy during reception
what is the receiver’s role in the system?
the electronics associated with processing the electronic signal produced by the transducer during reception and producing a pic on a display device
what is the display’s role in the system?
the device associated with the presentation of processed data for interpretation»_space;> monitor, audio speakers, a paper record
what is storage’s role in the system?
any number of devices and “media” that are used to permanently archive the US data.»_space; computer memory, hard drives, (aka NAS/ network attached storage)
what is the function of the pulser? what does it do?
receives timing signal from the synchronizer; produces electrical voltage, up to 100 volts, that excites PZE crystal during transmission
what do pulser signals depend on? what happens when sonographer increases output power?
system and transducer; higher electrical voltages are created that strike the PZT crystal, this increases the sound intensity created by the transducer and sent into the pt
what happens if you use a transducer with a crack?
can shock the pt
what are the 3 diff pulser modes?
continuous wave; pulsed wave (single crystal); pulsed wave, arrays
what is a continuous wave? (pulser modes)
continuous electrical signal int he form of a sine wave elec frequency = sound’s frequency
what is a pulsed wave (single crystal)? (pulser modes)
short duration electrical “spike” one electrical spike per US pulse
what is a pulse wave (arrays)? (pulser modes)
many elements fired for each US pulse. So for each sound pulse, many short duration electrical spiked are required. one electrical spike per fired element (or per channel) here also called the “beam former”
what does output power do? specifically what does it change? can this be changed by the sonographer?
all reflections from anatomic structures change, changing the brightness of the entire image; signal-to-noise ratio changes; yes
how does changing output power affect the pulse? what determines this?
when changed the strength of every transmitted pulse to the body changes; determined by the excitation voltage from the pulser. PZT crystal vibrates w a magnitude related to pulser voltage.
what does each component mean in the signal to noise ratio?
signal - meaningful portion of the data, good. noise - inaccurate portion of the data which degrades the quality of our information, bad.
what happens with a high signal to noise ratio?
the meaningful part of our data is much stronger than the inaccurate portion = high quality image created
what happens with a low signal to noise ratio?
the inaccurate part of out data is much stronger that the meaningful part. Noise contaminates the good data and degrades the image
how can you improve signal to noise ratio? how does it do this?
increasing output power is the primary way to improve s/n ratio. meaningful signal strength is increased while the noise level remains unchanged
what is the overall function of the receiver?
signals returning from the transducer are extremely weak. Receiver boosts the strength of these signals, processes them and prepares them for display.
in what order does the receiver function?
gain (amplification), compensation (TGC), dynamic range, reject
what is the purpose of gain (amplification)? can it be adjusted?
increases the strength of all electrical signals in the receiver prior to further processing. yes
what units is gain measured in? why is this?
dB. the ratio of the output elec signal strength to the input elec signal strength of the amplifier.
what is the effect of gain on the image?
every signal is treated identically (uniform amplification). thus, gain changes the brightness of the entire image
how does gain change the s/n ratio? why is that?
ratio remains the same bc the signal and noise are both changed equally.
what does preamplification do? where does this occur?
alters the signal before gain is applied, often performed in the probe
what is the relationship bw gain and resolution?
gain kills resolution; bc receiver gain doesn’t improve resolution
what is the purpose of compensation/ TGC? how does this work?
used to create image of uniform brightness from top to bottom. since deeper pulses undergo more attenuation, echoes returning from greater depths have lower amplitudes than those returning from shallow depths.
how does compensation/TGC affect the image? can it be adjusted?
compensation makes all echoes from similar reflectors appear identical regardless of their depth (makes image bright regardless of depth) “uniform brightness from top to bottom”; yes
what does compensation depend on?
compensation treats echoes differently depending upon the depth at which they arise.
what is the relationship be compensation/TGC and high frequency?
higher frequency requires more compensation bc it attenuates more.
what is the relationship be compensation/TGC and low frequency?
requires less compensation bc it attenuates less
what will you adjust if you cannot see reflectors of the near or far field of your image?
adjust the TGC (compensation)
what is the purpose of dynamic range/ compression? does this change anything specifically?
adjusts the gray scale range within the image. allows us to see all gray shades and differentiate tissues; done w/o altering the relative relationships; brightest stays brightest, darkest remains dark
how does dynamic range (compression) affect the image? can it be changed?
changes the gray scale mapping; yes
how do you determine if dynamic range has been changed?
if the gray scale maps on the image are different
what is the purpose of reject (suppression) ? can it be changed?
displays low level echoes only when they are clinically meaningful, very low echoes are not always important. =eliminates low-level noise in our images; yes can be changed by sonographer
what are the effects of reject (suppression) on the image?
affects only low level signals everywhere on the image, but does not affect bright echoes. fewer shades of gray.
what are contrast agents? what is special about these and why?
aka “micro-bubbles” of gas entrapped in a shell; these have a diff acoustic fingerprint than blood or tissue, bc there is a large impedance difference bw contrast agents and biologic tissues (this creates strong reflections)
how are contrast agents used and administered?
injected into the circulation (intravenously). these agents create strong reflections that “light up” blood chambers or vessels
what are the 4 requirements for contrast agents?
safe, strong reflector of ultrasound, long persistence, metabolically inert
visually, how do the contrast agents affect the image?
make a “negative contrast” effect
what do outpower and gain have in common? how do they differ?
adjustments to either of these alter the brightness of the entire image; output power affects pt exposure = more bioeffects, where gain does not
how does output power work?
affects brightness by adjusting the strength of the sound waves sent to the body from the transducer. output power affects pt exposure
how does adjusting the strength of the sound waves produce a brighter image?
when the pulse is more powerful, all of the returning echoes from the body are stronger, and the image is brighter.
what is another downside to using output power?
when the image is too bright due to high output power, the lateral and longitudinal resolution degrade.
what happens when adjusting the gain? (step by step how it affects signals and receiver)
affects the brightness by changing the amplification of the electronic signals after returning to the receiver. the electronic signals are boosted, making the image brighter, while not affecting pt exposure
how do you determine whether a control affects output power or gain?
if term suggests “outgoing” = output power, if it indicates “reception or incoming” = gain
what is the alara principle?
as low as reasonably achievable
if following alara principles, what do you do when an entire image is too bright or too dark?
as a first option, always choose the option that will minimize pt exposure.
-too dark = first increase gain
-too bright = first reduce output power
when following alara principles, how would it be better to image deep?
better to use a lower frequency transducer than to increase output power
