Ultrasound

Question 1

what is the velocity of the wave

Answer 1

Velocity of the wave = wave frequency x wavelength

Question 2

what type of wave is ultrasound?

Answer 2

ultrasound is a longitudinal wave

Question 3

ultrasound requires a medium. T/F?

Answer 3

True

Question 4

what are the two components of the wave as it prorogates through tissue?

Answer 4

the wave undergoes a series of compressions and rarefractions.

Question 5

is ultrasound higher or lower frequency than what the human ear can detect

Answer 5

it is higher than what we can hear (x1000)

Question 6

what is the difference between doppler and normal ultrasound?

Answer 6

Doppler has much higher pressure than normal ultrasound

Question 7

what is young’s modulus?

Answer 7

young’s modulus is a measure of the elasticity of a medium

Question 8

what is young’s modulus equation?

Answer 8

c = ⎷E/⍴
⍴ = density of medium
E = youngs modulus

Question 9

what needs to be matched for passing of ultrasound from one medium to another

Answer 9

you need to match the acoustic impedance

Question 10

what is acoustic impedance

Answer 10

a measure of how “easy” it is for sound to pass through a medium

Question 11

what is high power ultrasound used for?

Answer 11

lithotripsy

Question 12

is the intensity of the ultrasound beam uniform?

Answer 12

no

Question 13

write down equation used to compare intensities of the beam

Answer 13

dB = 10log10 I2 / I1

Question 14

what unit is the loss of power of the US beam

Answer 14

1Db/cm/MHz

Question 15

what is the effect when acoustic impedance difference is very big?

Answer 15

there is a lot of reflection when the acoustic impedance difference is large

Question 16

what are the different fates of US beam

Answer 16

refraction, reflection, scatter

Question 17

what is the angle of incidence?

Answer 17

the angle of incidence is the angle of reflection

Question 18

what happens to the beam as it passes through one medium to another

Answer 18

the beam bends

Question 19

what is diffraction?

Answer 19

the bending of the US beam into the shadow of a strong absorber

Question 20

where does diffraction commonly occur?

Answer 20

absorber edge, ie: gallstone

Question 21

how are images constructed?

Answer 21

images are constructed by computing the time is takes for the beam to travel from the transducer and return from a reflecting surface. this is our depth data

Question 22

what dictates the brightness of the display

Answer 22

the magnitude of the echo

Question 23

what is a transducer?

Answer 23

a device that converts one form of energy into another form

Question 24

what happens to the piezoelectric crystal when an electric current is applied?

Answer 24

the crystal alters shape, this is because the molecular dipoles change direction

Question 25

name components of the transducer and their basic function

Answer 25

acoustic insulation acoustic lens backing block - absorbs US going backwards, attenuates stray beam matching layer - allows 100% transmission of beam into tissues, minimising reflection due to traversing mediums (acoustic impedance) piezoelectric crystals - converts electrical to mechanical energy and forces the ceramic plate to move

Question 26

what is the function of the crystal in receive mode?

Answer 26

the small voltage generated by deformation of the crystal is detected and amplified, crystal compresses and expands, wave sent into patient and backwards into the probe, bounces back to the crystal and registered as an impulse

Question 27

what does the matching layer improve?

Answer 27

improves sound transmission by compensating for large acoustic impedances

Question 28

what does the US gel do?

Answer 28

it eliminates the air layer

Question 29

what is continuous wave be used for

Answer 29

measuring femur length in utero

Question 30

are higher or lower frequency waves absorbed more?

Answer 30

Higher frequency waves are absorbed more

Question 31

when SPL changes, what is also effected?

Answer 31

the spatial resolution

Question 32

what is meant by the term dispersion

Answer 32

the filtering out of the higher frequencies

Question 33

when SPL is longer, what can happen to two adjacent objects

Answer 33

when the SPL is longer, two adjacent objects can be seen as overlapping objects

Question 34

what is the pulse repetition frequency?

Answer 34

the number of pulses per second

Question 35

image depth

Answer 35

the time between two pulses must be greater than the time for the "return trip" which is equivalent to twice the image depth

Question 36

what determines the imaging depth

Answer 36

the PRF

Question 37

what is the bandwidth

Answer 37

the number of frequencies within a pulse

Question 38

what effect does increasing spatial pulse length have on bandwidth

Answer 38

increasing SPL will decrease the bandwidth

Question 39

short pulses have greater or lesser mixtures of frequencies?

Answer 39

short pulses have a greater mixture of frequencies

Question 40

SPL in imaging vs doppler

Answer 40

SPL shorter in regular US, longer in doppler

Question 41

what is specular reflection

Answer 41

occurs when the boundaries of two structures are smooth, generates echoes that define organ boundaries like liver.

Question 42

what happens when sound waves encounter structures much smaller than their frequencies

Answer 42

they are scattered in all directions, happens with RBCs for example

Question 43

what do scattered waves produce on the image

Answer 43

a speckle appearance, does not correspond to anatomical detail

Question 44

what is the mirror artefact?

Answer 44

when reflecting surface meets the beam at a large angle of incidence, such as the diaphragm, part of the beam not reflected directly back to the transducer, produces a secondary reflection

Question 45

effect of higher frequency on near & far fields

Answer 45

higher frequency, longer near field

Question 46

what is lateral resolution?

Answer 46

spatial resolution in a plane perpendicular to the beam

Question 47

another term for the near field

Answer 47

fresnel zone

Question 48

another term for far field

Answer 48

Fraunhoffer zone

Question 49

in which field is lateral res preserved

Answer 49

lateral resolution is preserved in the near field/fresnel zone

Question 50

what happens to the beam after the fresnel zone

Answer 50

the beam diverges

Question 51

what optimises lateral resolution at depth

Answer 51

a wide transducer of high frequency as divergence decreases with wider transducer or increasing frequency

Question 52

what does the acoustic lens do

Answer 52

narrow the beam to improve lateral resolution