Physics Flashcards
Specular reflectors are strong/weak? Scatterers are strong/weak reflectors?
Specular= strong Scatteres= weak
Does high frequency go with increased scatter?
Yes
another term for axial
longitudinal
what are the main variables affecting the following resolutions: 1) Longitudinal/axial- ? 2) Lateral-?
Longitudinal/axial = frequency (wavelength) Lateral= Beam width & Focus
what maneuver is helpful to eliminate near field (“Bang”) artifact?
contrast
if you see arcuate things on the echo, what artifact is it? (Physics II)
side-lobe
which variable determines the max depth imaged?
PRP (Pulse Repetition Period)
- floats over the cardiac structures, won’t move with cardiac structures, due to PRP NAME THE ARTIFACT
Range Ambiguity Artifact
if the go-return time is 13 microseconds, what was the reflector depth? total distance travelled?
1cm deep in the body 2cm
in the artifact with the pleural effusion looking like it is floating in the middle of the LV, what was its name?
range ambiguity artifact. (change the depth to bring the effusion into the window and the LV then looks normal.)
name the artifact caused by mech valve that looks like a comet tail
reverberation artifact
are artifacts from low pressure gas bubbles better see with fundamental or harmonic imaging?
harmonic
v = f x ?
wavelength
wavelength of 3 MHz sound wave = ? in soft tissue
0.5 mm
a 3 dB change does what to intensity? how about 30dB?
doubles 1000 fold change (10^3): 30–> 10^3
what happens with high MI (>1) and low MI (
> 1 –> bubbles destroyed weak harmonic signals
eq’n for Acoustic Impedance (Z) what happens if Z very different b/w mediums (e.g. bone and soft tissue)?
Z = density x V - sound gets reflected (proportional to difference of Z’s SQUARED), not transmitted (V = velocity of sound)
What is relationship b/w acoustic impedance (Z) and % beam that is reflected?
difference of Z’s SQUARED
relationship b/w frequency and scattering
directly proportional
is diffraction greater with larger or smaller transducer?
smaller
the summation of losses due to reflection, scattering and absorption = ?
attenuation
what is the amount of attenuation in dB/cm/MHz in soft tissue?
1 dB/cm/MHz
most common Piezoelectric crystal used
PZT (lead zirconate titrate)
purpose of backing block in transducer
absorbs sound wave and limits ringing of crystal to allow for more discrete U/S pulse
purpose of matching layer in transducer
matches crystal to skin acoustic impedance to improve U/S transmission into tissues
name the type of transducer that has CRYSTAL IMPURITIES, a BACKING BLOCK, and HARMONIC IMAGING
Wide Bandwidth transducer (Low Q-factor)
for CW, would you use wide or narrow bandwidth transducer?
narrow
time b/w transducer pulses = ?
PRP
PRP’s relation to depth?
directly proportional
PRF = ?
1/PRP
definition of duty factor and values for CW and PW
- fraction of PRP that emits sound CW = 1 , PW .001
resolution along the length of the beam =?
axial resolution
a 3MHz trasnducer has how much wavelength?
.5mm
which resolution is determined by spatial pulse length?
axial
(cycles x wavelength)/2 = ?
resolution
how can you better separate fundamental and harmonic signal?
use longer pulse
does a wider or narower beam improve lateral resolution?
narrow
does higher frequency mean higher lateral resolution?
yes
does higher frequency improve lateral AND axial resolution?
yes
does amplification (“increasing gain”) effect the signal to npise ratio or contrast bubbles
no
modified doppler eq’n
nyquist limit (delta f) = ?
PRF/2
the highest doppler shift that can be measured w/ pulsed doppler is called?
nyquist limit
at what relative depths and frequencies can you measure higher velocities?
shallower depth, lower frequencies
is COlor Flow Imaging CW or PW?
PW
what will more pulses with color flow imaging do to frame rate?
make it slower
Z/PRP = ?
(Z = distance)
velocity
Eq’n for Duty Factor
Pulse Duration/PRP = DF
for every 3dB attenuation, how much reduciton in intensity is there? what about for 10dB attenuation?
3dB–> 1/2
10dB–> 1/10
D
the frequency range for audible sound? U/S?
20Hz-20kHz
(U/S > 20kHz)
B: Frame rate
4 ways to improve temporal resolution
DECREASE: depth, width, #focal points, line density
D- speed of sound always 1540 m/s
will increasing gain increase output power? what will inc output power?
no. M.I.
In soft tissue, every 13 microsecond of go-return time means the reflector is _cm deep in body?
1
recite the 13 microsecond table
lateral resolution is dependent on the ___ of the ultrasound beam?
width
PRF =?
PRF = 77,000/depth
modified doppler velocity equation from physics lecture
