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Fall '23 Echo > Physics Final Exam > Flashcards

Physics Final Exam Flashcards

1
Q

Detail resolution is a combo of

A

axial and lateral rez

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2
Q

ANY FACTOR THAT LOWERS FRAME RATE, lowers THIS form of resolution

A

TEMPORAL resolution

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3
Q

factors that lower temporal resolution are (4)

A

imaging depth, imaging frame, sector size, how man foci, line density/# of acoustic lines per display line

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4
Q

what parameter determines the “excellent movie” analogy

A

frame rate

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5
Q

frame rate unit

A

hertz or per second

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6
Q

velocity of sound in soft tissue is

A

1540 m/s

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7
Q

In soft tissue it takes how long per cm for sound to travel to area of interest AND BACK?

A

per 1 cm, it takes 13 microseconds (round trip)

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8
Q

frame determined by 3 things

A
  1. speed of sound in media
  2. imaging depth
  3. number of lines in sight
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9
Q

more lines (higher line density) = better _______ resolution

A

spatial

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10
Q

FR = c / 2dN

A

Frame rate = speed of sound in medium divided by 2x (the depth of interest x number of lines per sight)

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11
Q

x and y axis in a-mode represent

A

x axis: depth from time of flight
y axis: represents amplitude

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12
Q

what’s dynamic receive focusing?

A

when US receiver sets time delays to some electric signals during reception - much more accurate image

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13
Q

A “channel” is the combo of these 3 things

A

active element, wire, system electronics

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14
Q

what does the curie temp do?

A

temp which frees the microscopic crystals, allowing them to move… the element can lose its special properties if heated above the curie temp (300 degrees C)

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15
Q

resonance frequency determined mainly by

A

piezoelectric element THICKNESS

most effective thickness is 1/2 the wavelength

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16
Q

the thicker the crystal…

A

the longer the wavelength, the lower the frequency…

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17
Q

the most effective crystal thickness for a 2.5 MHz transducer with a 0.6mm wavelength would be

A

0.3 mm thickness!

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18
Q

purpose of the matching layer

A

to reduce reverb, decreases reflections at PZT/skin boundary as to increase % of transmitted sound

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19
Q

thickness of the matching element and active element

A

active element: 1/2 wavelength thick
matching element: 1/4 wavelength thick

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20
Q

backing/damping material purpose is to

A

reduce ringing… directly related to high or low Q value. More backing = lower Q value (short ring down time)

decreased sensitivity
wide bandwidth
low q-factor

Think of a damp pedal on a piano

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21
Q

damping improves

A

axial resolution and shortens pulse/reduces. pulse duration

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22
Q

Continuous wave has a _______bandwidth and ________ frequencies while pulsed wave has a _________ bandwidth and ________ frequencies

A

CW: narrow bandwidth, higher frequencies
PW: wider bandwidth, more frequencies

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23
Q

If the bandwidth increases, the ________ decreases

A

Q factor

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24
Q

A low Q factor indicates

A
  1. A broad bandwidth
  2. A low operating frequency
  3. Shortened pulse length
  4. Uniform near field
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25
Q

2 dimensions of crystal

A

diameter and crystal thickness

26
Q

length of the near field and the far field determined by

A

transducer diameter and ultrasound frequency

27
Q

if you’re imaging shallow structures, should image using

A

small diameter, high frequency transducer

28
Q

beam width at the focus is what width compared to when it left the transducer?

A

half

29
Q

distance from transducer to focus

A

focal length

30
Q

diameter and _________ are directly related

A
31
Q

2 transducers have the same diameter… the one with the HIGHER frequency will have a _________ foci.

A

deeper

32
Q

2 factors of beam divergence

A

beam diameter, frequency of sound

33
Q

_________ crystals produce beams that spread out more in the far field

A

Smaller

34
Q

_______frequency sound diverge less in the far field

A

high

35
Q

axial resolution is determined by the

A

pulse duration or spatial pulse length

36
Q

axial rez depends on 3 things

A
  1. SPL
  2. ultrasound frequency
  3. damping factor
37
Q

SPL measure in ____ and determined by the

A

PD = pulse duration

38
Q

shorter pulses create more accurate images so for axial Rez,

A

LOWER NUMBERS ARE BETTER

39
Q

pulse of 3 cycles and a pulse of 6 cycles… which has better axial rez

A

3 cycle pulse

40
Q

higher frequencies there is better axial rez but decreased

A

depth penetration

41
Q

lateral rez, ability to resolve objets in a direction _____ to the beam

A

perpendicular to beam

42
Q

axial rez, ability to resolve objects in a direction ______ to the beam

A

parallel to beam

43
Q

Large PZT. crystal create waveforms that are _________ while tiny, tiny pieces of PZT create. waveforms that are _______ shaped.

A

hourglass, “V”

44
Q

the reason to focus the US beam is to increase _______rez

A

lateral

45
Q

transforms electrical energy into acoustic energy

A

transducer

46
Q

determines amplitude, PRF, PRP, creates the electrical signals that excites the PZT crystal

A

pulser

47
Q

evens out the bumps. aka “smoothing” - filtering process carried out after demodulation

A

enveloping

48
Q

demodulation

A

purpose is to change the form of the electrical signal so that it is appropriate for the systems display

49
Q

rectification is one of two parts of demodulation, the other being enveloping… what is rectification?

A

converts all the
negative voltages into positive
voltages. It corrects for or
eliminates negative voltages

50
Q

out of amplification, compression, rejection, demodulation, and compensation… the ONLY one NOT adjustable is

A

demodulation

51
Q

an ideal # for a duty factor is between

A

.1 and 1% (the rest of the time is spent listening*

52
Q

PRP is what plus what

A

PD + listening time

53
Q

the pulse repetition frequency is

A

the number of pulses occurring in one second (TIME) unit in hertz… all it is, it’s the reciprocal of PRP. PRF = 1 over PRP

54
Q

equation for PRF or pulse repetition frequency is

A

PRF = C divided by (2R) x D

the 2 accounts for the “round trip”

55
Q

Would PRF be high or low at a SHALLOW DEPTH

A

HIGH (takes only a short amount of time to create a new pulse… created rapidly over and over… resulting in a high pulse frequency)

56
Q

draw spatial pulse length

A
57
Q

SPL =

A

wavelength x number of cycles

SPL - directly proportional to # of cycles
SPL - directly proportional to wavelength
SPL - inversely related to frequency

58
Q

duty factor for continuous wave is always

A

1.0 or 100% because THE SYSTEM IS ALWAYS TRANSMITTING (pedoff probe for ex)

59
Q

Tricuspid Regurg velocity in Doppler typically has what defining identifier when looking at the spectral waveform

A

respiratory variation

60
Q

if you can’t obtain a continuity equation due to an inaccurate LVOT Diameter use the

A

dimensionless index!
DI = VTILVOT / VTIAO

61
Q
A

Fall '23 Echo (19 decks)

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