Physics Final Exam Flashcards
Detail resolution is a combo of
axial and lateral rez
ANY FACTOR THAT LOWERS FRAME RATE, lowers THIS form of resolution
TEMPORAL resolution
factors that lower temporal resolution are (4)
imaging depth, imaging frame, sector size, how man foci, line density/# of acoustic lines per display line
what parameter determines the “excellent movie” analogy
frame rate
frame rate unit
hertz or per second
velocity of sound in soft tissue is
1540 m/s
In soft tissue it takes how long per cm for sound to travel to area of interest AND BACK?
per 1 cm, it takes 13 microseconds (round trip)
frame determined by 3 things
- speed of sound in media
- imaging depth
- number of lines in sight
more lines (higher line density) = better _______ resolution
spatial
FR = c / 2dN
Frame rate = speed of sound in medium divided by 2x (the depth of interest x number of lines per sight)
x and y axis in a-mode represent
x axis: depth from time of flight
y axis: represents amplitude
what’s dynamic receive focusing?
when US receiver sets time delays to some electric signals during reception - much more accurate image
A “channel” is the combo of these 3 things
active element, wire, system electronics
what does the curie temp do?
temp which frees the microscopic crystals, allowing them to move… the element can lose its special properties if heated above the curie temp (300 degrees C)
resonance frequency determined mainly by
piezoelectric element THICKNESS
most effective thickness is 1/2 the wavelength
the thicker the crystal…
the longer the wavelength, the lower the frequency…
the most effective crystal thickness for a 2.5 MHz transducer with a 0.6mm wavelength would be
0.3 mm thickness!
purpose of the matching layer
to reduce reverb, decreases reflections at PZT/skin boundary as to increase % of transmitted sound
thickness of the matching element and active element
active element: 1/2 wavelength thick
matching element: 1/4 wavelength thick
backing/damping material purpose is to
reduce ringing… directly related to high or low Q value. More backing = lower Q value (short ring down time)
decreased sensitivity
wide bandwidth
low q-factor
Think of a damp pedal on a piano
damping improves
axial resolution and shortens pulse/reduces. pulse duration
Continuous wave has a _______bandwidth and ________ frequencies while pulsed wave has a _________ bandwidth and ________ frequencies
CW: narrow bandwidth, higher frequencies
PW: wider bandwidth, more frequencies
If the bandwidth increases, the ________ decreases
Q factor
A low Q factor indicates
- A broad bandwidth
- A low operating frequency
- Shortened pulse length
- Uniform near field
2 dimensions of crystal
diameter and crystal thickness
length of the near field and the far field determined by
transducer diameter and ultrasound frequency
if you’re imaging shallow structures, should image using
small diameter, high frequency transducer
beam width at the focus is what width compared to when it left the transducer?
half
distance from transducer to focus
focal length
diameter and _________ are directly related
2 transducers have the same diameter… the one with the HIGHER frequency will have a _________ foci.
deeper
2 factors of beam divergence
beam diameter, frequency of sound
_________ crystals produce beams that spread out more in the far field
Smaller
_______frequency sound diverge less in the far field
high
axial resolution is determined by the
pulse duration or spatial pulse length
axial rez depends on 3 things
- SPL
- ultrasound frequency
- damping factor
SPL measure in ____ and determined by the
PD = pulse duration
shorter pulses create more accurate images so for axial Rez,
LOWER NUMBERS ARE BETTER
pulse of 3 cycles and a pulse of 6 cycles… which has better axial rez
3 cycle pulse
higher frequencies there is better axial rez but decreased
depth penetration
lateral rez, ability to resolve objets in a direction _____ to the beam
perpendicular to beam
axial rez, ability to resolve objects in a direction ______ to the beam
parallel to beam
Large PZT. crystal create waveforms that are _________ while tiny, tiny pieces of PZT create. waveforms that are _______ shaped.
hourglass, “V”
the reason to focus the US beam is to increase _______rez
lateral
transforms electrical energy into acoustic energy
transducer
determines amplitude, PRF, PRP, creates the electrical signals that excites the PZT crystal
pulser
evens out the bumps. aka “smoothing” - filtering process carried out after demodulation
enveloping
demodulation
purpose is to change the form of the electrical signal so that it is appropriate for the systems display
rectification is one of two parts of demodulation, the other being enveloping… what is rectification?
converts all the
negative voltages into positive
voltages. It corrects for or
eliminates negative voltages
out of amplification, compression, rejection, demodulation, and compensation… the ONLY one NOT adjustable is
demodulation
an ideal # for a duty factor is between
.1 and 1% (the rest of the time is spent listening*
PRP is what plus what
PD + listening time
the pulse repetition frequency is
the number of pulses occurring in one second (TIME) unit in hertz… all it is, it’s the reciprocal of PRP. PRF = 1 over PRP
equation for PRF or pulse repetition frequency is
PRF = C divided by (2R) x D
the 2 accounts for the “round trip”
Would PRF be high or low at a SHALLOW DEPTH
HIGH (takes only a short amount of time to create a new pulse… created rapidly over and over… resulting in a high pulse frequency)
draw spatial pulse length
SPL =
wavelength x number of cycles
SPL - directly proportional to # of cycles
SPL - directly proportional to wavelength
SPL - inversely related to frequency
duty factor for continuous wave is always
1.0 or 100% because THE SYSTEM IS ALWAYS TRANSMITTING (pedoff probe for ex)
Tricuspid Regurg velocity in Doppler typically has what defining identifier when looking at the spectral waveform
respiratory variation
if you can’t obtain a continuity equation due to an inaccurate LVOT Diameter use the
dimensionless index!
DI = VTILVOT / VTIAO
