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Echo Physics > Chap. 5 And 6 Level 1 > Flashcards

Chap. 5 And 6 Level 1 Flashcards

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1
Q

What is a transducer in ultrasound

A

A device that converts electrical energy into acoustic energy and back to electrical energy

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2
Q

What is the piezoelectric effect

A

An electric field is created by certain crystal materials getting mechanically deformed through vibrations

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3
Q

What material is commonly used in ultrasound transducers?

A

Lead zirconate titanate (PZT)

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4
Q

What is poling

A

Poling is placing the crystal materials into a specialized oven at high temperatures. These high temperatures allow the positive poles to align in one direction and the negative poles the opposite direction

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5
Q

What is the curie point

A

The temperature at which a crystal loses its poling and efficiency as a piezoelectric material

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6
Q

What is the curie temperature for PZT

A

300 degrees Celsius

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7
Q

Formula for operating frequency in PW

A

Fo (mhz) = C(mm/sec)/2 x thickness (mm)

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8
Q

The thickness of the crystal determines what?

A
  • A thinner crystal will imply a shorter period (higher frequency)
  • A thicker crystal will imply a longer period (lower frequency)
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9
Q

What determines the frequency in CW?

A
  • The drive voltage frequency of the pulser
  • Fo = drive voltage frequency = transmit signal
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10
Q

What is the crystals impulse response

A

How a crystal responds to a single, short electrical impulse

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11
Q

A long vs short crystal impulse response

A
  • Long, many cycles leading to a long spl
  • short, few cycles leading to a short spl
  • shorter spl, better axial resolution
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12
Q

What are the 2 physical dimensions of a transducer

A

Diameter and thickness

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13
Q

What do diameter and thickness determine in terms of a transducer

A
  • diameter determines beam width
  • thickness determines operating frequency
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14
Q

What is the beam shape view

A

The region in the patient that the sound wave propagates

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15
Q

Attenuation occurs at deeper or shallower depths?

A

Greater attenuation at Deeper depths

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16
Q

What is the shape of an ultrasound beam during CW?

A

The beam begins at the crystal and gets narrower as it reaches the center then diverges as it increases in depth

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17
Q

What is the natural focus

A
  • The depth at which the beam reaches its narrowest beamwidth.
  • the center of the beam
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18
Q

What is the “focal depth” or “near zone length”

A

The distance from the surface of the transducer to the natural focus

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19
Q

Formula for near zone length

A

NZL = D^2 x operating frequency/6

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20
Q

NZL is proportional and inverse to what?

A

-NZL is proportional to diameter squared and operating frequency
- NZL is inversely proportional to 4(wavelength)

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21
Q

What crystals are good for superficial and deeper focus

A
  • Smaller crystals are good for superficial imaging
  • large crystals are good for deep imaging
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22
Q

What beams produce better lateral resolution

A

Narrow beams

23
Q

Formula for axial resolution

A

Axial resolution = Spl/2

24
Q

Why do we have a matching layer

A

To minimize the acoustic impedance mismatch between the high impedance of the crystal and the low impedance of tissue

25
Q

What is the matching layer

A

A thin layer of material attaches to the front of the crystal

26
Q

Why is the matching layer a 1/4 wavelength

A

It prevents reverberation artifacts from energy ping ponging within the crystal

27
Q

What are the 3 imaging planes

A

Axial, lateral, and elevation

28
Q

What is lateral resolution

A

The ability to resolve 2 structures in the lateral dimension

29
Q

How to identify to separate structures side by side

A

If the beam is narrower, you can identify each structure individually

30
Q

What are the techniques for changing focus of the transducer

A

1) mirrors
2) lenses
3) curved elements
4) electronic focusing
5) retrospective gating

31
Q

What is elevation resolution

A
  • The elevation resolution is determined by the beamwidth
  • the elevation resolution is best where the beam is narrowest
32
Q

Define transmit power

A

The amplitude or gain

33
Q

What is the dynamic range

A
  • Dynamic range is the ratio of the maximum to the minimum amplitude
  • also known as the ratio of the biggest signal/smallest signal
34
Q

What are the 4 types of dynamic range

A
  • input dynamic range: max/min input signal
  • output dynamic range: max/min output signal
  • display dynamic range: max/min display signal
  • gain dynamic range: max/min applicable gain
35
Q

Difference between receiver gain and transmit power

A

Both control gain, but transmit power affects the amplitude going into the patient where receiver gain affects the amplitude after it has returned to the receiver

36
Q

Define signal and noise

A
  • Signal: any phenomenon desired to be measured
  • noise: any unwanted signals
37
Q

Define noise floor and signal-noise-ratio (SNR)

A
  • noise floor: the amplitude level where no signals are visible because of the presence of noise
  • SNR: the amplitude of the signal/amplitude of noise
38
Q

What are the signals for Doppler and ultrasound

A
  • The reflections from the tissues that are converted into images
  • signals for spectral Doppler are the Doppler shifts
39
Q

What is the SNR

A

SNR is what specifies the signal quality. A higher SNR gives better imaging while lower SNR gives poor imaging

40
Q

Give an ex: of a good signal to noise ratio and a bad

A
  • Good: a high amplitude and low noise floor
  • bad: high amplitude and high noise floor
41
Q

In terms of SNR, what does increasing amplitude do

A

Increasing amplitude increases both signal and noise evenly. The true SNR may not change. But the apparent SNR could

42
Q

Define clutter

A

Large returning echoes from structures that obliterate weaker signals

43
Q

Pre processing vs post processing

A
  • pre processing: a real time signal
  • post processing: imaging that can be changed after captured
44
Q

What can be changed in post processing?

A

Compression, colorization, and reject

45
Q

What are examples of analog in ultrasound?

A

Blood flow, EKG’s, pressure waveforms

46
Q

What is the NyQuist criterion

A

The minimum rate at which you must sample for an accurate reconstruction of an analog signal

47
Q

Equation for NyQuist criterion

A

NyQuist: F(max) = F (sampling)/2

48
Q

Basic system function

A
  • transducer converts electrical to acoustic and acoustic to electric signals
  • receiver receives the echo
  • processor converts echo into images
  • displays real time image
  • image is stored and can perform required measurements
49
Q

What are the 5 operations the receiver performs

A
  • amplification
  • compensation
  • compression
  • demodulation
  • rejection
50
Q

What is the job of the receiver

A

To receive signals from the transducer and apply the necessary processing before converting the signals into an image

51
Q

Compression in dynamic range

A

The dynamic range must be compressed in order for the human eye to be able to see it.

52
Q

What is demodulation

A

The process by which the modulations of the wave are removed or detected (signal detection)

53
Q

What is rectification

A

Converts the negative components of a signal into positive components (bipolar to unipolar)

Echo Physics (5 decks)

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