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ultrasound Flashcards

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1
Q

4 ways ultrasound can be attenuated

A

reflection
refraction
scatter
absorption

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2
Q

equation for velocity

A

velocity = frequency x wavelength

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3
Q

range of sound frequencies in medical ultrasound

A

2 MHz - 20 MHz

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4
Q

human hearing range

A

50 Hz - 20 kHz

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5
Q

low frequency sound waves in relation to penetration

A

they can penetrate deeper into the human body compared to high frequency

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6
Q

low frequency waves in relation to resolution

A

has lower anatomical resolution

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7
Q

abdomen ultrasound frequency

A

3-5 MHz - good penetration, but poor resolution

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8
Q

small and superficial parts

A

5-10 MHz

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9
Q

skin, eyes ultrasound frequency

A

10-20 MHz

- poor penetration, but good resolution

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10
Q

x-ray vs ultrasound oscillation

A

x-rays - transverse waves and oscillation in their amplitude is at right angles to the direction of travel.

ultrasound - longitudinal wave and oscillation in its amplitude is in the same direction of travel

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11
Q

sound waves need to pass through a…..

A

Medium such as air, water or solids

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12
Q

acoustic impedance

A

is the resistance that the sound waves experience when passing through matter/tissue

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13
Q

practical significance of acoustic impedance

A
  • impedance is high in bone, but less in soft tissue
  • allows us to see a range of structures
  • sound reflection is stronger at boundaries with different impedance values.
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14
Q

How can a sonographer improve the visualisation of deep structures in the body

A
  • use a lower frequency to increase penetration - however, this decreases the resolution
  • perhaps the use of different probes - adjusts beam focus
  • time gain compensation
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15
Q

time gain compensation

A
  • reduces the impact of wave attenuation by tissues through the increased intensity of the received signal in proportion to the depth
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16
Q

acoustic shadowing

A

occurs at boundaries between significantly different tissue impedances - which leads to signal loss and a dark appearance.

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17
Q

an example of acoustic shadowing

A
  • decreased signal behind calcifications. e.g. a gull stone in the gall bladder, as the gull bladder is fluid-filled and a gull stone is dense -high difference in acoustic impedances
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18
Q

useful artefacts

A
  • stones/ calcifications

- fluid structures like cysts can have acoustic enhancement behind them - brighter image response

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19
Q

how are ultrasound waves produced in a transducer

A
  • piezoelectric effect - when an electrical current is passed through the crystals, they vibrate to a set frequency and emit sound
    crystals in the probe acts as a transducer and emits and receives sound waves.
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20
Q

how are ultrasound waves received in a transducer

A
  • when sound waves return back from the body, the crystals start to vibrate too - giving us an electrical return signal
  • the changes in sound waves sent and received gives us the differences on our image.
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21
Q

Why do sound waves travel faster through denser materials

A

because the vibrations of sound pass faster through molecules that are packed close together

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22
Q

acoustic impedance and sound reflection

A
  • if the acoustic impedance is between tissues is large, then a lot of sound is reflected and not much sound penetrates deeper
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23
Q

when does reflection work best?

A

when the tissue boundary is at right angles to the probe

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24
Q

what happens when the tissue boundary is not at right angles to the probe

A

the refelcted sound is not received by a simple probe

some sound is refracted

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25
what is refraction
- where the angleof incident sound is not at 90 degrees to the boundary - sound velocity changes between the tissues and therefore the direction of travel changes
26
ultrasound scatter
reflectors such as Blood cells and non-smooth tissue interfaces vase sound to fan out in all directions - this causes speckle or irregularity in the image
27
a bleed will show up with
multiple small echoes that come from the blood cells and platelets - may look grainy
28
what happens as ultrasound passes through the body
The ultrasound is attenuated (reduction in beam intensity) with increasing depth in the body
29
what do decibels measure
the relative difference between 2 sound intensities e.g. intensity between a produced sound beam and a returning echo
30
types of image resolution
lateral resolution and axial resolution
31
lateral resolution (at right angles to the beam)
depends on the diameter of the ultrasound beam - best with narrow beam
32
axial resolution (in direction of the beam)
depends on the sound frequency - high frequency = good resolution
33
types of ultrasound scan
- A Mode - B Mode - M Mode - 3D and 4D - Doppler
33
types of ultrasound scan
- A Mode - B Mode - M Mode - 3D and 4D - Doppler
33
types of ultrasound scan
- A Mode - B Mode - M Mode - 3D and 4D - Doppler
34
types of ultrasound scan
- A Mode - B Mode - M Mode - 3D and 4D - Doppler
35
The piezoelectric effect
- when an electrical current is applied across the crystal, it resonates sending out a sound wave - when a force is applied perpendicular to the crystal, an electrical charge is produced - the frequency of the sound is determined by the thickness of the crystal
36
A mode scan - Amplitude modulated
- produces a graph whose height shows the strength of reflection over time time
37
B Mode scan - brightness modulated
this produces a 2D greyscale image based on the strength of reflected sound echos, according to depth - most common scan
38
M Mode
Shows motion (e.g. heart valves), over time
39
3D and 4D scan
- volume and video images
40
Doppler scan
- change in sound frequency shows the speed and direction of blood flow -
41
Duplex ultrasound
- Combines Doppler colour-coded blood flow direction - red towards the probe and blue away from the probe - flow speed with a 2D B-mode anatomical scan
42
rotating transducer
- produces an arc or fan shaped image section
43
linear array transducer
- consists of row elements and produces a straight sided image section
44
Array transducers
can be focused to either examine either shallow or deep tissues
45
Anechoic
no echoes
46
Exhogenic
- Brighter than (compared to something next to it) | - E.g. Bone is echogenic
47
hypoechoic
less echoes than surroung structures
48
Hyperechoic
higher level of echoes then surrounding structures
49
cystic
no echoes with echo enhancement behind
50
complex mass
components of solid/cystic tissue
51
solid mass
internal echoes, no enhancement behind
52
homogenous
same appearances/texture, smooth throughout .I.e liver/uterus
53
heterogeneous
different irregular pattern, different echo characteristics
54
biological effects of ultrasound
Thermal effects mechanical effects
55
factors affecting temperature increases
frequency of the ultrasound beam - heating increases with F power in watts Attenuuation (acoustic impedance) of tissue - heating is greatest at bone scan time
56
factors affecting mechanical indices
peak ultrasound beam pressure - related to power frequency of the ultrasound beam - mechanical effects decrease with F Beam focus depth - mechanical effects decrease with focus depth
57
Ultrasound ALARA
- use minimum power output keep scanning time to a minimum do not rest the transducer on the skin surface when not scanning
58
Artefacts -- misleading or incorrect information
- caused by: - the nature if the tissue - the operator Equipment malfunction
59
Artefacts: Assumptions made by the machine
- the beam being infinitely thin propagation being in a straight line the speed of sound being exactly 1540 m/s the brightness of the echo being directly related to the reflectivity of the target
60
propagation
- the speed at which a sound wave travels through a medium

Image science principles (12 decks)

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