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Ultrasound Physics > Test 3 > Flashcards

Test 3 Flashcards

1
Q

What are the 7 components of an imaging system?

A

Pulser, Beam Former, Transducer, Receiver, Display, Memory, Master Synchronizer

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2
Q

Beam Former

A

Calculates all phasing (time delays for electronic steering/focusing)

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3
Q

Pulser

A

Distributes electrical voltage to transducer to produce an echo

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4
Q

Pulser & scan converter

A

Tells scan converter that contact has been made, time of flight timer starts

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5
Q

Pulser & CW

A

Sets frequency, controls PRP, PRF, amplitude of pulse

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6
Q

Pulser & PW

A

Freq. dependent on thickness & speed of crystal

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7
Q

Acoustic Power aka

A

Output power, transmit, output, energy output, output gain

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8
Q

Receiver Functions

A

Amplification, Compensation, Compression, Demodulation, Rejection

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9
Q

Amplification

A

Small voltages boosted to be stronger, controlled by gain

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10
Q

Preamplification

A

Clips large voltage spikes or amplifies very weak signals

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11
Q

Compensation

A

aka TGC, swept gain, depth gain

Compensates for attenuation due to depth; helps create uniform echogenicity

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12
Q

Compression

A

aka log compression, dynamic range

Ratio of the greatest to smallest amplitude the instrument can handle. Squeeze signal amplitudes into a narrower range

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13
Q

Dynamic range relationships

A

Inverse to compression. More compression = lower dynamic range = less shades of grey; less compression = higher dynamic rance = more shades of grey

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14
Q

Dynamic range of instruments

A

Transducer/receiver: 100-200
Memory: 40-45
Display/printer: 20-30

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15
Q

Demodulation

A

Change voltages into another form

  1. Rectification: Turn negative amplitudes to positive
  2. Smoothing: Avg. of signals

NOT user adjustable!

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16
Q

Rejection

A

aka suppression, threshold, filter, wall filter

Suppress/eliminate small voltage amplitudes to reduce noise. Filter key

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17
Q

Scan Converter

A

aka memory

Storage of memory from receiver; analog/digital

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18
Q

Analog

A

Infinitely variable; Great resolution but unstable

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19
Q

Digital

A

Discreet binary numbers stored in RAM; stable storage

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20
Q

Bit

A

Smallest form of memory; on/off
8 bits = 1 byte
More bits increase contrast resolution (more shades of grey)

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21
Q

Pixel

A

Picture element, smallest form of picture.
Voxel in 3D
More pixels increase spatial resolution

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22
Q

Preprocessing (7 examples)

A

Available as image is live, before storage in memory

Ex. TGC, dynamic range, RES/Write Zoom, persistence, edge enhancement, smoothing, fill in interpolation

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23
Q

RES/Write Zoom

A

Rescans the ROI w/ more scan lines to improve spatial resolution

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24
Q

Persistence

A

Frame averaging for a smoother image & lower frame rate

25
Q

Edge Enhancement

A

Increase contrast (sharpness); useful for cysts

26
Q

Smoothing

A

Filtering technique to reduce noise w/ averaging

27
Q

Fill in Interpolation

A

Fills in mixing pixels due to diverging scan lines

28
Q

Postprocessing (4 examples)

A

Changes in image after frame is frozen

Ex. Caliper placement, black/white inversion, read magnification, postprocessing curve

29
Q

Read Magnification

A

Regular zoom

30
Q

Raster Scan

A

Beam sweeps from left to right, then top to bottom

31
Q

Interlaced display

A

525 closely spaced horizontal lines; odd lines written first, even written second
Lines take 1/60th of a second; 30 frames per second

32
Q

Non-interlaced display

A

Lines written in sequence; 30 frames per second

33
Q

HD Resolution

A

Over 1,000 horizontal lines, better spatial res.

34
Q

Bernouili’s Principle

A

Inverse relationship between pressure (potential energy) and velocity (kinetic energy)

35
Q

Pressure & velocity in stenosis

A

Before stenosis: High pressure, low velocity
At stenosis: Low pressure, high velocity
After stenosis: In between; pressure increase and velocity drops

36
Q

Pressure difference & blood flow

A

Greater difference = greater flow = high velocity

37
Q

Plug flow

A

Uniform velocity across the vessel, blunted profile

Occurs at entrance of great vessels

38
Q

Laminar Flow

A

Ideal flow

Blood flows in concentric layers, velocity is fast at the center; bullet shaped profile

39
Q

Disturbed Flow

A

Occurs a bifurcations, changes vessel size from small to big

Reynold’s number ~ 1500

40
Q

Turbulent Flow

A

Chaotic, erratic flow pattern caused by stenosis or abrupt changes in vessel lumen
Reynold’s number ~ 2000
Spectral analysis = spectral broadening, color Doppler = mosaic, variance map = green

41
Q

Pulsatile Flow

A

Arterial system, delivers high blood pressure from heart to capillaries. Controlled by changing resistance (vasodilation/vasoconstriction)

42
Q

Sources of pressure in arteries

A

Heart & gravity

43
Q

Systole

A

Contraction of heart, arteries expand & act as reservoir

44
Q

Diastole

A

Relaxation phase of heart, flow dependent on resistance in capillaries

45
Q

Dicrotic Notch

A

Separates systole from diastole, closing of the aortic valve

46
Q

Phasic Flow

A

Returns venous blood back to heart, dependent on inspiration/expiration

47
Q

Inspiration

A

Diaphragm descends, intra-abdominal pressure increases (stops flow of lower extremities to heart), intra-thoracic pressure decreases (allows flow of upper extremities to heart)

48
Q

Expiration

A

Diaphragm ascends, intra-abdominal pressure decreases (allows lower extremities to flow to heart), intra-thoracic pressure increases (stops flow from upper extremities to heart)

49
Q

Transmural Pressure

A

Difference in pressure between the inside & outside of the vessel; determines vein shape, changes vein shape from dog bone to round
Higher pressure = rounder vein

50
Q

Calf Muscle Pump

A

Provides increased venous pressure in the legs; blood drains into venous sinuses

51
Q

Hydrostatic Pressure

A

Weight of a column of blood from the heart to the point where the pressure is measured, mainly affected by body position

52
Q

Color Doppler determines: (4)

A
  1. Presence of flow
  2. Direction of flow
  3. Qualitative data on reflector velocity
  4. Reflector variance
53
Q

Reflector Variance

A

Differences in speed & direction between reflectors

54
Q

Packet Size

A

of pulses per line of color; typically 8-30 pulses per packet

55
Q

Larger packet size vs. smaller packet size

A

Larger: Accurate velocity measurements, increased sensitivity, worse temporal resolution
Smaller: Inaccurate velocity measurements, decreased sensitivity, better temporal resolution

56
Q

Advantages of Color Doppler

A
  1. 2D info
  2. Facilitates the examination
  3. Provides info about flow direction, character of flow, relative (avg.) velocities, flow amplitude
57
Q

Disadvantages of Color Doppler

A
  1. Poor temporal resolution (lower frame rate)
  2. Subject to aliasing (b/c of high velocities or low scale)
  3. Unable to measure exact velocity of flow
58
Q

Qualitative Assessment

59
Q

Quantitative Assessment

A

Spectral analysis

Ultrasound Physics (11 decks)

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