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HomeStretch/Numbers > HomeStretch CRACK Physics US > Flashcards

HomeStretch CRACK Physics US Flashcards

1
Q

What speed does the US machine assume sound travels?

A

1540 m/s in tissue

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2
Q

Speed’s effect on frequency?

A

Nothing! wavelength changes in media

frequency is chosen by what probe you use.

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3
Q

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?

A

log 10 scale

loss of 3dB = 50% loss of signal intensity

HVL = thickness that reduces the US intensity by 3dB

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4
Q

What 2 things influence refraction?

A

Speed change (based on tissue compression)

angle of incidence

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5
Q

Higher frequency probes have more or less scatter?

A

MORE (it’ll be non-specular scatter)

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6
Q

What is the unit for impedence?!

A

Rahl!

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7
Q

The operating frequency of US is dependent on what?

A

determined from the speed of sound in and the thickness of the piezoelectric material

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8
Q

The thickness of the transducer = what fraction of the wavelength?

A

1/2 the wavelength

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9
Q

What is the optimal matchin layer thickness?

A

1/4 the wavelength

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10
Q

Thin dampening block:

light/heavy damping?

high/low Q?

Long/short pulse length?

Wide/Narrow Bandwidth?

A

Light damping

High Q

Long SPL

Narrow bandwidth

Best for doppler (narrow bandwidth) which preserves the velocity infor

(tall/high and skinny)

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11
Q

Thick dampening block:

light/heavy damping?

high/low Q?

Long/short pulse length?

Wide/Narrow Bandwidth?

A

Heavy

Low Q

Short SPL (therefore improves axial resolution)

Broad

(short/low and fat)

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12
Q

Fresnel zone

A

near field zone

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13
Q

the fresnel zone length is dependent on what?

What happens if you increase these things?

A

transducer frequency and transducer diameter

Higher transducer frequency and larger diameter element = longer near field

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14
Q

Frauhofer Zone

A

Far field zone

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15
Q

Where do you get the best lateral resolution?

A

focal zone

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16
Q

What is the minimum required separation between two reflectors to resolve them as two objects?

A

1/2 spatial pulse length

17
Q

Is lateral resolution constant at different depths?

how about axial?

A

No

Yes

18
Q

Higher freqeuncy = higher/lower lateral resolution

A

higher

19
Q

Elevation resolution is which plane? what does it depend on?

A
20
Q

Side-Lobe Artifact

A

pSeduo sLudge

seen more with linear array transducers

21
Q

beam width artifact

A

something coming back that was reflected from something out of the actual width of the beam (in far far far zone spread sound waves)

22
Q

Reverberation artifact

Comet tail artifact

Ring doWn artifact

mirror image artifact

A
  • 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
23
Q

speed-displacement artifact

refraction artifact

A

speed discplacement = looks like a discontinuity of a surface like liver

refraction artifact = looks like double

24
Q

doppler angle should be?

A

< 60

25
Q

Output power (transmit gain) increase does what to lateral resolution?

A

degrades it

26
Q

What do you need to know about compounding?

A

Sharpens edges, loss of posterior shadowing (makes cystic things looks solid)

27
Q

Some things to know about harmonics

A

shadowing tends to be increased (solid things can look cystic)

blurry margins stay

reverberation, side lobe / grating and “speckle” artifact are GONE

28
Q

What is amplitude?

What is intensity?

If you square the amplitude, what happens to intensity?

The smaller the beam the smaller/greater the intensity?

A

amplitude = difference between peak and average value of waveform

Intensity = power / area

Amplitude2 = intensity X 4

GREATER!

29
Q

relative intensity of modes

A

B-mode < M-mode << Color/Power << Doppler

30
Q

per NCRP, a risk-benefit decision should be made when thermal index hit what number? What about mechanical index?

A

TI = 1.0

MI = 0.5

31
Q

Thermal indexes

<0.7

between 1.0 and 1.5

between 2.5 and 3.0

>3.0

A
  • <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

HomeStretch/Numbers (24 decks)

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