HomeStretch CRACK Physics US Flashcards
What speed does the US machine assume sound travels?
1540 m/s in tissue
Speed’s effect on frequency?
Nothing! wavelength changes in media
frequency is chosen by what probe you use.
the dB is based on what scale?
a loss of 3dB represents what perfect loss of a signal intensity?
what tissue thickness is the HVL for US?
log 10 scale
loss of 3dB = 50% loss of signal intensity
HVL = thickness that reduces the US intensity by 3dB
What 2 things influence refraction?
Speed change (based on tissue compression)
angle of incidence
Higher frequency probes have more or less scatter?
MORE (it’ll be non-specular scatter)
What is the unit for impedence?!
Rahl!
The operating frequency of US is dependent on what?
determined from the speed of sound in and the thickness of the piezoelectric material
The thickness of the transducer = what fraction of the wavelength?
1/2 the wavelength
What is the optimal matchin layer thickness?
1/4 the wavelength
Thin dampening block:
light/heavy damping?
high/low Q?
Long/short pulse length?
Wide/Narrow Bandwidth?
Light damping
High Q
Long SPL
Narrow bandwidth
Best for doppler (narrow bandwidth) which preserves the velocity infor
(tall/high and skinny)
Thick dampening block:
light/heavy damping?
high/low Q?
Long/short pulse length?
Wide/Narrow Bandwidth?
Heavy
Low Q
Short SPL (therefore improves axial resolution)
Broad
(short/low and fat)
Fresnel zone
near field zone
the fresnel zone length is dependent on what?
What happens if you increase these things?
transducer frequency and transducer diameter
Higher transducer frequency and larger diameter element = longer near field
Frauhofer Zone
Far field zone
Where do you get the best lateral resolution?
focal zone
What is the minimum required separation between two reflectors to resolve them as two objects?
1/2 spatial pulse length
Is lateral resolution constant at different depths?
how about axial?
No
Yes
Higher freqeuncy = higher/lower lateral resolution
higher
Elevation resolution is which plane? what does it depend on?
Side-Lobe Artifact
pSeduo sLudge
seen more with linear array transducers
beam width artifact
something coming back that was reflected from something out of the actual width of the beam (in far far far zone spread sound waves)
Reverberation artifact
Comet tail artifact
Ring doWn artifact
mirror image artifact
- reverberation = wave encounteres two parallel highly reflective surfaces = multiple equadistant spaced linear reflections
- comet tail = reverberation artifact with something smaller than the 1/2 the SPL
- Seen in thyroid colloid, adenomyomatosis, small gallstones, renal stones, pancreatic calc
- ring-down = sound waves encounter fluid trapped in a tetrahedron of air bubbles = parallel bands extending POSTERIOR TO A GAS COLLECTION
- mirror image = trapped behind a strong reflector, seen in liver or lung
speed-displacement artifact
refraction artifact
speed discplacement = looks like a discontinuity of a surface like liver
refraction artifact = looks like double
doppler angle should be?
< 60
Output power (transmit gain) increase does what to lateral resolution?
degrades it
What do you need to know about compounding?
Sharpens edges, loss of posterior shadowing (makes cystic things looks solid)
Some things to know about harmonics
shadowing tends to be increased (solid things can look cystic)
blurry margins stay
reverberation, side lobe / grating and “speckle” artifact are GONE
What is amplitude?
What is intensity?
If you square the amplitude, what happens to intensity?
The smaller the beam the smaller/greater the intensity?
amplitude = difference between peak and average value of waveform
Intensity = power / area
Amplitude2 = intensity X 4
GREATER!
relative intensity of modes
B-mode < M-mode << Color/Power << Doppler
per NCRP, a risk-benefit decision should be made when thermal index hit what number? What about mechanical index?
TI = 1.0
MI = 0.5
Thermal indexes
<0.7
between 1.0 and 1.5
between 2.5 and 3.0
>3.0
- <0.7 = for OB
- between 1.0 and 1.5 = don’t scan for > 30 min
- between 2.5 and 3.0 = don’t scan for > 1 min
- > 3.0 = don’t fucking do it
