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Physics Flashcards

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1
Q

What is frequency measured in?

A

Hertz. Number of cycle per second.

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2
Q

Equation for velocity?

A

Velocity (m/sec) = Frequency (cycles/sec) x wavelength (m)

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3
Q

What is the assumed speed of sound in soft tissue?

A

1540 m/s

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4
Q

What is the speed of sound in bone vs air?

A

Bone: 4080 m/s
Air: 331 m/s

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5
Q

Acoustic impedance is calculated how?

A

AI (Z) = velocity x tissue density

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6
Q

What really counts when discussing acoustic impedance when talking about US penetration?

A

The difference in acoustic impedance between two tissues.

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7
Q

What is a specular reflector?

A

It is a surface that is larger than the sound beam. Reflection depends on angle of incidence.

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8
Q

What is diffuse or non-specular reflectors

A

The surface is smaller than the sound beam. This creates scatter and echotexture. DOES NOT depend on angle of the beam. It is called speckle and increases with higher freq.

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9
Q

What is refraction and what artifact does it create?

A

It is the bending of the sound wave as it enters a different medium. Causes edge shadowing

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10
Q

What is sound attenuation measured in?

A

dB

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11
Q

How much dB are lost per increase in MHz on the US probe?

A

0.5 dB/cm/MHz

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12
Q

What is responsible for axial resolution in US?

A

Pulse frequencey - how fast a pulse (around three waves) is transmitted after the first one

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13
Q

What is power?

A

Volume - FDA controls this

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14
Q

What is the pulse repetition frequency?

A

How fast one pulse comes after another… you can control this.

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15
Q

New transducers have a broad bandwidth and what does that mean?

A

A large MHz range

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16
Q

How many grays can the human eye see?

A

10-12

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17
Q

What is the mode used in eye exams?

A

A-mode

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18
Q

What is a sector scanner?

A

It has a triangle shape beam… so the normal look that we normally see

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19
Q

What is the disadvantage of sector scanner?

A

small FOV in the shallow tissues

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20
Q

What are mechanical transducer?

A

A transducer that mechanically moves an array… still used in high freq eyeball transducer

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21
Q

What type of arrays are there?

A
  1. Phased
  2. Linear
  3. Curvillinear
  4. Annular
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22
Q

How do linear arrays fire?

A

Sequentially - in a line

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23
Q

Advantages of the curvillinear array probe?

A

Small foot print
Good freq.
Large deep FOV

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24
Q

What probe is used for cardiac imaging?

A

Phased.

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25
How are the arrays arranged in annular arrays?
In a circle
26
What is the disadvantage of annular array?
It must be rotated manually. No used often.
27
What controls the pulse length and thus controls the axial resolution?
Frequency.
28
Stand off pads help resolution of the near field by?
Allowing the focal zone to be in the near field.
29
What influences elevation (azimuth) resolution?
Beam thickness - based off factory design
30
What are the three types of resolution?
Axial Elevation Lateral
31
What type of resolution is the most important?
Axial
32
Harmonics is useful with what type of patient?
Big patients - increases depth.
33
What artifacts does harmonics limit?
1. Reverberation 2. Scatter 3. Slice thickness/side lobe
34
What does harmonics increase in respect to image quality?
spatial resolution
35
Spatial compounding reduces what artifact?
1. Speckle - therefore increases contrast. 2. Edge shadowing 3. Acoustic shadowing
36
What effect does spatial compounding have on acoustic enhancement?
None
37
What is ring-down and how does it differ from reverberation?
Ring-down is the diffuse echoes between each reverberation
38
What is the difference between comet-tails and ring-down?
Comet-tails are from metal Ring-down is from air They look identical
39
What are other names for side-lobe artifact?
Grating lobe or secondary lobe
40
What is side-lobe artifact?
It is where secondary beams traveling off-axis of the primary beam pick up signal and erroneously put it in the image as if it came from the primary beam
41
What artifact produces pseudosludge in the bladder?
Side-lobe artifact
42
What is the difference between side-lobe artfiact and grating lobe artifact---even though they are pretty much the same?
Side lobe can occur from any transducer (single or array) and is just slightly off axis. Grating lobe - just occurs in array transducers and can have more extreme angles.
43
How can you tell the difference between pseudosludge and real sediment?
Pseudosludge has a curved margin Real sediment has a flat interface.
44
Another name for mirror artifact?
Multipath
45
Propagation of speed artifact is what?
When sound goes through two different types of tissue in the near field that have different speed and therefore the tissue under it can be irregular. Ex. spleen and fat overlying the kidney. Sound travels slower through the fat and therefore that part of the kidney is deeper than the part of the kidney under the spleen giving the kidney an irregular margin.
46
What is the difference between gas and bone when it comes to shadowing and why does this happen?
Dirty- due to 99% of the sound beam being reflected Clean - Due to most of the beam being absorbed
47
Edge shadowing is created by?
Refraction of sound through a cystic structure. This can be seen in the medulla diverticulum interface
48
What is doppler classified into? Two classifications
Spectral | Color
49
What are the four types of Doppler?
Pulsed wave Continuous wave Color Power
50
Which two types of Doppler are spectral doppler?
Continuous | Pulsed
51
Which two types of Doppler are color doppler?
Color | Power
52
What is the difference between spectral and color?
Spectral gives you information of the time-velocity
53
What is a positive shift vs a negative shift when discussing Doppler?
Positive shift - motion towards the transducer and therefore the waves are higher frequency Negative: Motion away from the transducer and therefore waves are lower frequency.
54
What is the doppler shift?
The difference between incoming and transmitted waves due to flow of a substance
55
The principle objective of Doppler evaluation is to orient the incident beam how?
Parallel to flow or as minimal of an angle Rule is 60 degrees or less. This reduces the effect of the angle on the calculation.
56
What is the advantage of pulsed waved Doppler?
It is range gated or it can accept frequency from a certain depth and can tell you what the velocity of that structure at that depth is.
57
What is the limitation of pulsed wave Doppler?
Cannot accurately assess very high blood flow (aliasing)
58
Continuous wave doppler does not possess what?
The ability to calculate high flow... no aliasing.
59
Continuous wave doppler is essential for what imaging?
Cardiac
60
What does the width of a spectral trace indicate?
The range of velocities
61
What does the brightness of a spectral trace indicate?
The amount of RBCs running
62
What is spectral broadening?
Where there is a large range of velocities....normally seen at areas of stenosis
63
What is the color red/yellow represent in color doppler?
Fluid coming towards the transducer
64
Velocity sample area of a color Doppler bar is based off what?
Pulse repetition frequency. Higher pulse freq. the higher the ability to sample higher velocity.
65
What are three big disadvantages of color doppler?
1. Low sensitivity 2. Aliasing artifact can happen 3. Angle flow dependence These are all the advantages for Power doppler
66
What are two disadvantages of Power Doppler?
1. No velocity 2. No direction 3. Very sensitive to motion artifact These are all advantages of Color doppler.
67
What does the size of the gate affect?
Large gate - more sensitive | Smaller gate - more precise
68
What is the recommended size of the gate?
1/3 the size of the vessel
69
What will happen if you are perpendicular to the vessel flow in doppler?
The doppler signal will be smaller or zero.
70
When does aliasing occur mostly in doppler imaging?
``` High velocity blood flow Deep vessel (PRF has to be reduced to allow signal to return to probe). ```

Utlrasound (10 decks)

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