Pulsed Echo Instrumentation- Ch 13

Question 1

what is an ultrasound system?

Answer 1

the entire device that produces sound beams, retrieves the echoes and produces visual images and audio signals

Question 2

what info is processed by the US system? (4)

Answer 2

time of flight, strength of reflection, direction, frequency (for doppler)

Question 3

what is the us system made up of? what are the names of these?

Answer 3

six interconnected components - info is transferred to and from each; master synchronizer, pulser, transducer, receiver, display, storage.

Question 4

what is the master synchronizer’s role in the system?

Answer 4

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

Question 5

what is the pulser’s role in the US system?

Answer 5

(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”

Question 6

what is the transducer’s role in the system?

Answer 6

(converts) converts electrical into acoustic energy during transmission. and converts returning acoustic into electrical energy during reception

Question 7

what is the receiver’s role in the system?

Answer 7

the electronics associated with processing the electronic signal produced by the transducer during reception and producing a pic on a display device

Question 8

what is the display’s role in the system?

Answer 8

the device associated with the presentation of processed data for interpretation&raquo_space;> monitor, audio speakers, a paper record

Question 9

what is storage’s role in the system?

Answer 9

any number of devices and “media” that are used to permanently archive the US data.&raquo_space; computer memory, hard drives, (aka NAS/ network attached storage)

Question 10

what is the function of the pulser? what does it do?

Answer 10

receives timing signal from the synchronizer; produces electrical voltage, up to 100 volts, that excites PZE crystal during transmission

Question 11

what do pulser signals depend on? what happens when sonographer increases output power?

Answer 11

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

Question 12

what happens if you use a transducer with a crack?

Answer 12

can shock the pt

Question 13

what are the 3 diff pulser modes?

Answer 13

continuous wave; pulsed wave (single crystal); pulsed wave, arrays

Question 14

what is a continuous wave? (pulser modes)

Answer 14

continuous electrical signal int he form of a sine wave elec frequency = sound’s frequency

Question 15

what is a pulsed wave (single crystal)? (pulser modes)

Answer 15

short duration electrical “spike” one electrical spike per US pulse

Question 16

what is a pulse wave (arrays)? (pulser modes)

Answer 16

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”

Question 17

what does output power do? specifically what does it change? can this be changed by the sonographer?

Answer 17

all reflections from anatomic structures change, changing the brightness of the entire image; signal-to-noise ratio changes; yes

Question 18

how does changing output power affect the pulse? what determines this?

Answer 18

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.

Question 19

what does each component mean in the signal to noise ratio?

Answer 19

signal - meaningful portion of the data, good. noise - inaccurate portion of the data which degrades the quality of our information, bad.

Question 20

what happens with a high signal to noise ratio?

Answer 20

the meaningful part of our data is much stronger than the inaccurate portion = high quality image created

Question 21

what happens with a low signal to noise ratio?

Answer 21

the inaccurate part of out data is much stronger that the meaningful part. Noise contaminates the good data and degrades the image

Question 22

how can you improve signal to noise ratio? how does it do this?

Answer 22

increasing output power is the primary way to improve s/n ratio. meaningful signal strength is increased while the noise level remains unchanged

Question 23

what is the overall function of the receiver?

Answer 23

signals returning from the transducer are extremely weak. Receiver boosts the strength of these signals, processes them and prepares them for display.

Question 24

in what order does the receiver function?

Answer 24

gain (amplification), compensation (TGC), dynamic range, reject

Question 25

what is the purpose of gain (amplification)? can it be adjusted?

Answer 25

increases the strength of all electrical signals in the receiver prior to further processing. yes

Question 26

what units is gain measured in? why is this?

Answer 26

dB. the ratio of the output elec signal strength to the input elec signal strength of the amplifier.

Question 27

what is the effect of gain on the image?

Answer 27

every signal is treated identically (uniform amplification). thus, gain changes the brightness of the entire image

Question 28

how does gain change the s/n ratio? why is that?

Answer 28

ratio remains the same bc the signal and noise are both changed equally.

Question 29

what does preamplification do? where does this occur?

Answer 29

alters the signal **before** gain is applied, often performed in the probe

Question 30

what is the relationship bw gain and resolution?

Answer 30

gain kills resolution; bc receiver gain doesn't improve resolution

Question 31

what is the purpose of compensation/ TGC? how does this work?

Answer 31

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.

Question 32

how does compensation/TGC affect the image? can it be adjusted?

Answer 32

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

Question 33

what does compensation depend on?

Answer 33

compensation treats echoes differently depending upon the depth at which they arise.

Question 34

what is the relationship be compensation/TGC and high frequency?

Answer 34

higher frequency requires more compensation bc it attenuates more.

Question 35

what is the relationship be compensation/TGC and low frequency?

Answer 35

requires less compensation bc it attenuates less

Question 36

what will you adjust if you cannot see reflectors of the near or far field of your image?

Answer 36

adjust the TGC (compensation)

Question 37

what is the purpose of dynamic range/ compression? does this change anything specifically?

Answer 37

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

Question 38

how does dynamic range (compression) affect the image? can it be changed?

Answer 38

changes the gray scale mapping; yes

Question 39

how do you determine if dynamic range has been changed?

Answer 39

if the gray scale maps on the image are different

Question 40

what is the purpose of reject (suppression) ? can it be changed?

Answer 40

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

Question 41

what are the effects of reject (suppression) on the image?

Answer 41

affects only low level signals everywhere on the image, but does not affect bright echoes. fewer shades of gray.

Question 42

what are contrast agents? what is special about these and why?

Answer 42

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)

Question 43

how are contrast agents used and administered?

Answer 43

injected into the circulation (intravenously). these agents create strong reflections that "light up" blood chambers or vessels

Question 44

what are the 4 requirements for contrast agents?

Answer 44

safe, strong reflector of ultrasound, long persistence, metabolically inert

Question 45

visually, how do the contrast agents affect the image?

Answer 45

make a "negative contrast" effect

Question 46

what do outpower and gain have in common? how do they differ?

Answer 46

adjustments to either of these alter the brightness of the entire image; output power affects pt exposure = more bioeffects, where gain does not

Question 47

how does output power work?

Answer 47

affects brightness by adjusting the strength of the sound waves sent to the body from the transducer. **output power affects pt exposure**

Question 48

how does adjusting the strength of the sound waves produce a brighter image?

Answer 48

when the pulse is more powerful, all of the returning echoes from the body are stronger, and the image is brighter.

Question 49

what is another downside to using output power?

Answer 49

when the image is too bright due to high output power, the lateral and longitudinal resolution degrade.

Question 50

what happens when adjusting the gain? (step by step how it affects signals and receiver)

Answer 50

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

Question 51

how do you determine whether a control affects output power or gain?

Answer 51

if term suggests "outgoing" = output power, if it indicates "reception or incoming" = gain

Question 52

what is the alara principle?

Answer 52

as low as reasonably achievable

Question 53

if following alara principles, what do you do when an entire image is too bright or too dark?

Answer 53

as a first option, always choose the option that will minimize pt exposure. -too dark = first increase gain -too bright = first reduce output power

Question 54

when following alara principles, how would it be better to image deep?

Answer 54

better to use a lower frequency transducer than to increase output power