HomeStretch CRACK Physics US

Question 1

What speed does the US machine assume sound travels?

Answer 1

1540 m/s in tissue

Question 2

Speed’s effect on frequency?

Answer 2

Nothing! wavelength changes in media

frequency is chosen by what probe you use.

Question 3

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?

Answer 3

log 10 scale

loss of 3dB = 50% loss of signal intensity

HVL = thickness that reduces the US intensity by 3dB

Question 4

What 2 things influence refraction?

Answer 4

Speed change (based on tissue compression)

angle of incidence

Question 5

Higher frequency probes have more or less scatter?

Answer 5

MORE (it’ll be non-specular scatter)

Question 6

What is the unit for impedence?!

Answer 6

Rahl!

Question 7

The operating frequency of US is dependent on what?

Answer 7

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

Question 8

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

Answer 8

1/2 the wavelength

Question 9

What is the optimal matchin layer thickness?

Answer 9

1/4 the wavelength

Question 10

Thin dampening block:

light/heavy damping?

high/low Q?

Long/short pulse length?

Wide/Narrow Bandwidth?

Answer 10

Light damping

High Q

Long SPL

Narrow bandwidth

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

(tall/high and skinny)

Question 11

Thick dampening block:

light/heavy damping?

high/low Q?

Long/short pulse length?

Wide/Narrow Bandwidth?

Answer 11

Heavy

Low Q

Short SPL (therefore improves axial resolution)

Broad

(short/low and fat)

Question 12

Fresnel zone

Answer 12

near field zone

Question 13

the fresnel zone length is dependent on what?

What happens if you increase these things?

Answer 13

transducer frequency and transducer diameter

Higher transducer frequency and larger diameter element = longer near field

Question 14

Frauhofer Zone

Answer 14

Far field zone

Question 15

Where do you get the best lateral resolution?

Answer 15

focal zone

Question 16

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

Answer 16

1/2 spatial pulse length

Question 17

Is lateral resolution constant at different depths?

how about axial?

Answer 17

No

Yes

Question 18

Higher freqeuncy = higher/lower lateral resolution

Answer 18

higher

Question 19

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

Question 20

Side-Lobe Artifact

Answer 20

pSeduo sLudge

seen more with linear array transducers

Question 21

beam width artifact

Answer 21

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

Question 22

Reverberation artifact

Comet tail artifact

Ring doWn artifact

mirror image artifact

Answer 22

• 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

Question 23

speed-displacement artifact

refraction artifact

Answer 23

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

refraction artifact = looks like double

Question 24

doppler angle should be?

Answer 24

< 60

Question 25

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

Answer 25

degrades it

Question 26

What do you need to know about compounding?

Answer 26

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

Question 27

Some things to know about harmonics

Answer 27

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

blurry margins stay

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

Question 28

What is amplitude?

What is intensity?

If you square the amplitude, what happens to intensity?

The smaller the beam the smaller/greater the intensity?

Answer 28

amplitude = difference between peak and average value of waveform

Intensity = power / area

Amplitude² = intensity X 4

GREATER!

Question 29

relative intensity of modes

Answer 29

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

Question 30

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

Answer 30

TI = 1.0

MI = 0.5

Question 31

Thermal indexes

<0.7

between 1.0 and 1.5

between 2.5 and 3.0

>3.0

Answer 31

• <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