Introduction and Physics Flashcards
what is an ultrasound?
sound with a frequency higher than human hearing can detect
what is velocity in soft tissue?
1540 m/s
constant
what is used to produce ultrasound?
piezoelectric crystals
electric charge
what is axial resolution useful for?
differentiating structures parallel to ultrasound beam
what is lateral resolution useful for?
differentiating structures perpendicular to ultrasound beam
what is elevational resolution?
third dimension of ultrasound beam
slice thickness
what happens to the wave the deeper it travels?
it becomes weaker
0.5 dB/cm/MHz
what is the ultrasound image formed by?
returning echos
what does the angle of incidence between the ultrasound beam and the direction of flow need to be?
<60 degrees
does power doppler provide direction or velocity?
no
what is power doppler best for?
small vessels
amount and presence of flow
what are the doppler modes?
power doppler
color doppler
spectral doppler
what are the basic ultrasound machine controls?
gain
frequency
depth
beam size
focal point
what does increasing the frequency do?
decreases depth
increases resolution
what is the focal point for?
maximal lateral resolution
what is anechoic?
black echogenicity
what are the options for echotexture?
heterogenous
homogenous
what is a comet tail?
special form of reverberation artifact
with gas
what is acoustic shadowing?
ultrasound beam almost completely reflected or absorbed
mineral or gas
what is posterior enhancement?
behind pure fluid
almost no ultrasound beam attenuation through fluid
what is edge-shadowing?
form of refraction artifact
rounded structures
what is the frequency of ultrasound?
> 20,000 cycles/sec
20 kHz
what is frequency?
cycles/sec
Hz
what is the equation for velocity?
velocity = frequency x wavelength
what does an increase in frequency lead to?
decrease in wavelength
less depth, more resolution
what determines axial resolution?
pulse length
what determines lateral resolution?
beam width
adjusting focal point
what determines elevational resolution?
beam thickness
what is the equation for acoustic impedance?
acoustic impedance = velocity (1540m/s) x tissue density
what happens to the majority of ultrasound transmitted through tissue?
it is absorbed
convert into heat
what do the colors in color doppler signify?
direction of flow
what is gain?
increase signal of returning echoes
what happens when you increase the frequency?
depth is decreased
resolution is increased
how is the probe marker oriented when scanning a dog?
cranial in longitudinal plane
to the right in transverse plane
what is reverberation artifact from?
gas
when is a mirror image seen?
strong reflector
diaphragm
