Ultrasound

Question 1

what are uses of ultrasound in medicine?

Answer 1

Imaging
Doppler (vascular and cardiology)
Therapeutic (lithotripsy)

Question 2

what are ultrasounds?

Answer 2

Sound energy that has frequencies higher than is detected by the human ear

Question 3

what are properties of sound waves?

Answer 3

longitudional waves
compression waves
needs a medium to propagate
has a low propagation speed compared to light

Question 4

what determines the speed of the soundwave?

Answer 4

frequency x wavelength

Question 5

what frequency are ultrasounds above?

Answer 5

20kHz

Question 6

what is the average speed of sound tissue?

Answer 6

1540m-1

Varies slightly in different tissues

Question 7

what are the different interactions ultrasound has with tissue?

Answer 7

Absorption
Reflection
Refraction
Scatter

Question 8

what is absorption?

Answer 8

Ultrasound energy is converted to heat which reduces amplitude

Question 9

what is reflection?

Answer 9

Energy reflected from a boundary (acoustic interface) The boundary is between two materials that have different acoustic impedances and some ultrasound will pass through the boundary and some will reflect.

The amount of reflection depends on the differences in acoustic impedence

Question 10

what is refraction?

Answer 10

some or all energy is diverted from its original path

Question 11

what is scatter?

Answer 11

energy is dispersed in all directions

Question 12

what is frequency?

Answer 12

how many cycles occur per second

Question 13

what is wavelength?

Answer 13

distance travelled by one cycle

Question 14

what does amplitude indicate?

Answer 14

how strong the ultrasound is represented by the height of the wave
*reduces with absorption

Question 15

what does absorption vary with?

Answer 15

tissue properties
frequency (the higher the frequency the more absorption)
distance travelled

Question 16

what determines acoustic impedence?

Answer 16

density x speed of sound

Question 17

what is the amount of reflection and transmission of an ultrasound depend on?

Answer 17

difference in acoustic impedance

the larger the difference in acoustic impedance the more energy is reflected and less transferred.

Question 18

what is gel used for ultrasound imaging?

Answer 18

The air acoustic impedance is very different to that of tissue.
Gel has an acoustic impedance that is more similar to that of tissue.

The air-fat interface has such a large difference in acoustic impedance that only 0.1% of energy is transferred and passes through the air layer and the rest reflected
With gel-fat interface there is less of a difference on acoustic impedance values so 99.5% of energy is transferred so this allows you to get an image.

Question 19

how does reflection effect the image?

Answer 19

the greater the reflection the brighter the image will appear on USS.

Question 20

what is the result of high frequency?

Answer 20

High resolution
HOWEVER
shorter wavelength
more attenuation

Question 21

what is attenuation?

Answer 21

loss of power or amplitude of the ultrasound signal as it passes through the tissue

Question 22

what makes up attenuation?

Answer 22

absorption
scatter
reflection

Question 23

what are biological effects of ultrasound?

Answer 23

1. Mechanical: cavitation and streaming.

2. Thermal

Question 24

what are the safety indicators of ultrasound?

Answer 24

mechanical index

thermal index

Question 25

what is mechanical index?

Answer 25

the likelihood of causing cavitation. The highest allowed is 1.9

Question 26

what is the relationship between frequency and wavelength?

Answer 26

The shorter the wavelength, the higher the frequency

Question 27

what frequency is best for deep structures?

Answer 27

A lower frequency and it has a longer wavelength and better penetration

Question 28

what is a sound wave?

Answer 28

a longitudional compression wave so it needs a medium to travel in

Question 29

what does the amount of refraction depend on?

Answer 29

speed of sound

Question 30

what is scatter?

Answer 30

where the energy goes in all directions. Scatter from both the surface and inside the tissue.

Question 31

what is attenuation?

Answer 31

how much power/amplitude is lost as it passes through the tissue.

Question 32

what makes up the transducer?

Answer 32

``` piezoelectic element electrodes backing block Matching layer housing ```

Question 33

what is the most common material for the piezoelectric element?

Answer 33

zirconate titanate

Question 34

what is good about continious waves on doppler?

Answer 34

can be used to measure higher velocities No aliasing artefact Good resolution

Question 35

what isn't good about continious waves on doppler?

Answer 35

no information about depth of vessel

Question 36

what is good about pulsed wave on doppler?

Answer 36

gives information about depth and can work out velocity

Question 37

what isn't good about pulsed wave on doppler?

Answer 37

aliasing when velocity is too high

Question 38

what is a linear array?

Answer 38

Produces a rectangular field of view with uniform beam density throughout useful for shallow structures and small parts

Question 39

what is linear array good for?

Answer 39

shallow structures

Question 40

what is curvilinear array good for?

Answer 40

deeper structures

Question 41

what is curvilinear array?

Answer 41

linear elements arranged along a curved transducer allowing a wider field of view

Question 42

what is a phased array?

Answer 42

A small footprint probe with a wide range of view

Question 43

what is phased array good for?

Answer 43

because it has a small footprint it's good for in between ribs etc as the arrays can change the direction of the us

Question 44

What is m mode?

Answer 44

Motion: uses short pulsed waves

Question 45

what is TGC Mode?

Answer 45

Time gain compensation Used for unified brightness so deeper structures aren't darker. Compensates for attenuation due to absorption

Question 46

what is bright on us imaging?

Answer 46

fatty structures as they have high reflectivity

Question 47

what are advantages of ultrasound?

Answer 47

allows for real time imaging no radiation can be used for biopsy relatively cheap

Question 48

what are disadvantages of US?

Answer 48

operator dependant | diagnostic errors

Question 49

what is microcavitation?

Answer 49

a biological mechanical effect of US. | Tiny bubbles that have been produce rapidly collapse and release energy.

Question 50

when do you get shadowing?

Answer 50

when there is high attenuation

Question 51

when do you get enhancement?

Answer 51

when there is low attenuation and the tissue behind it appears brighter than expected

Question 52

what is reverberation?

Answer 52

when sound waves bounce back and fourth between two reflective surfaces before returning to the transducer

Question 53

what are different forms of artefact?

Answer 53

shadowing enhancement repeat reflection reverberation