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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
Edge Enhancement
Increase contrast (sharpness); useful for cysts
26
Smoothing
Filtering technique to reduce noise w/ averaging
27
Fill in Interpolation
Fills in mixing pixels due to diverging scan lines
28
Postprocessing (4 examples)
Changes in image after frame is frozen | Ex. Caliper placement, black/white inversion, read magnification, postprocessing curve
29
Read Magnification
Regular zoom
30
Raster Scan
Beam sweeps from left to right, then top to bottom
31
Interlaced display
525 closely spaced horizontal lines; odd lines written first, even written second Lines take 1/60th of a second; 30 frames per second
32
Non-interlaced display
Lines written in sequence; 30 frames per second
33
HD Resolution
Over 1,000 horizontal lines, better spatial res.
34
Bernouili's Principle
Inverse relationship between pressure (potential energy) and velocity (kinetic energy)
35
Pressure & velocity in stenosis
Before stenosis: High pressure, low velocity At stenosis: Low pressure, high velocity After stenosis: In between; pressure increase and velocity drops
36
Pressure difference & blood flow
Greater difference = greater flow = high velocity
37
Plug flow
Uniform velocity across the vessel, blunted profile | Occurs at entrance of great vessels
38
Laminar Flow
Ideal flow | Blood flows in concentric layers, velocity is fast at the center; bullet shaped profile
39
Disturbed Flow
Occurs a bifurcations, changes vessel size from small to big | Reynold's number ~ 1500
40
Turbulent Flow
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
Pulsatile Flow
Arterial system, delivers high blood pressure from heart to capillaries. Controlled by changing resistance (vasodilation/vasoconstriction)
42
Sources of pressure in arteries
Heart & gravity
43
Systole
Contraction of heart, arteries expand & act as reservoir
44
Diastole
Relaxation phase of heart, flow dependent on resistance in capillaries
45
Dicrotic Notch
Separates systole from diastole, closing of the aortic valve
46
Phasic Flow
Returns venous blood back to heart, dependent on inspiration/expiration
47
Inspiration
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
Expiration
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
Transmural Pressure
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
Calf Muscle Pump
Provides increased venous pressure in the legs; blood drains into venous sinuses
51
Hydrostatic Pressure
Weight of a column of blood from the heart to the point where the pressure is measured, mainly affected by body position
52
Color Doppler determines: (4)
1. Presence of flow 2. Direction of flow 3. Qualitative data on reflector velocity 4. Reflector variance
53
Reflector Variance
Differences in speed & direction between reflectors
54
Packet Size
of pulses per line of color; typically 8-30 pulses per packet
55
Larger packet size vs. smaller packet size
Larger: Accurate velocity measurements, increased sensitivity, worse temporal resolution Smaller: Inaccurate velocity measurements, decreased sensitivity, better temporal resolution
56
Advantages of Color Doppler
1. 2D info 2. Facilitates the examination 3. Provides info about flow direction, character of flow, relative (avg.) velocities, flow amplitude
57
Disadvantages of Color Doppler
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
Qualitative Assessment
Color
59
Quantitative Assessment
Spectral analysis

Ultrasound Physics (11 decks)

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