Week 1 - US Basics Flashcards
audible sound range
20 - 20k Hz
ultrasound range
> 20 kHz
Diagnostic Ultrasound range
1MHz - 20 MHz
what are waves
disturbance away from average condition which carries only energy
types of waves
mechanical & electromagnetic
mechanical waves ___
propagate through physical mediums like sound & water
electromagnetic waves ___
travel through space/vacuum without needing a physical medium such as heat & x-rays
types of mechanical waves
transverse + longitudinal
transverse wave particles move ___
perpendicular to direction of wave propagation
longitudinal wave particles move ___
parallel / anti-parallel to wave motion; oscillate back and forth in their resting positions
variables of sound
wave speed, frequency, wavelength
speed of sound is dependent on ___
media density & compressibility
speed of sound is constant for particular medium as long as temperature is ___
constant
the average speed of soft tissue using ultrasound is ___
1540m/s
the denser the medium, the ___ the sound wave propagation
slower
density refers to the __
number of particles per unit volume
compressibility refers to
how easy the volume of material can change
the more compressible the medium is, the __ sound waves propagate
faster
compressibility & density of a substance are ___
interdependent
1 kHz is ___ cycles per sec
1000
diagnostic ultrasound frequency
2 - 18 MHz
ultrasound wavelength ranges between ____
0.1 to 1.0mm
Attenuation
redirected energy that is lower in energy compared to incident wave
sound & matter interactions
SARR
Scattering, Attenuation, Reflection, Refraction
For attenuation, the deeper the wave travels in the body, the ___ it becomes
weaker
attenuation =
absorption + scattering
what happens to the tissue during absorption
tissue energy content increases while beam intensity decreases during transmission
intensity loss formula
intensity loss = μ x f x z
μ = intensity attenuation coefficient
z = distance travelled in cm
attenuation coefficient is the ___
loss of intensity in decibels per tissue cm traversed per megahertz
attenuation coefficient is ___ proportional to frequency
directly
attenuation coefficient unit is __
dB/cm
attenuation factors
tissue type, frequency, depth
low frequency = ____ depth of penetration
high
acoustic impedance is defined as the ____
medium resistance to sound transmission
acoustic impedance formula
Z (acoustic impedance) = p (density) x c (sound velocity)
acoustic impedance unit
rayl
if acoustic impedance in 2 mediusm are the same, sound will travel ___
readily from one to another
if acoustic impedance in 2 mediusm are not the same, a portion of the sound will be ___
reflected at interface
what allows for visualization of soft tissue structures within US beam
acoustic impedance
difference in acoustic impedance between 2 tissues causes ___
sound wave reflection
reflection is determined by ___ of interface
size & surface
reflections occur at ___ between 2 adjacent tissues
boundary / interface
reflection coefficient
amount of US beam reflected at interface
% reflection of fat/muscle
1.08
% reflection of fat/kidney
0.6
% reflection of soft tissue / water
0.2
% reflection of bone/fat
49
% reflection of soft tissue / air
99
specular reflection
US strikes smooth boundary = interface large & relatively smooth with max reflection at 90 degrees
non-specular reflection
US strikes boundary w/ irregular surface & multiple interfaces = sound deflects in multiple directions
refraction follows what law
snell’s law
greater diff of velocity = __ refraction
increased
critical angle is defined as __
incident angle for which refraction angle is 90 degrees
what happens to the beam at the critical angle
refracted beam travels along interface
common US artifacts
CARD
- reverberation
- dirty vs clean acoustic shadowing
- acoustic enhancements
- comet-tail artifacts
reverberation occurs when ___
beam encounters 2 highly reflective surfaces
acoustic shadowing occurs due to __
reduction in echo strength distal to high attenuating / reflective object
what benefit does acoustic shadowing offer
visualize calcifications; often seen with bone & calcifications
where does clean shadowing occur commonly
distal to larger calculi & bone as a dark anechoic band
where does dirty shadowing occur commonly
distal to highly reflecting surface as multiple secondary reflections of low level echos that appear within the shadow
comet tail artifacts appear as ___
multiple internal reflections within small reflective object producing many short tapered echoes
energy loss during reverberation process causes echoes to ___
decrease in width & brightness
