Ultrasound

Question 1

rarefraction

Answer 1

low pressure and density

Question 2

compression

Answer 2

high pressure and density

Question 3

what is a wavelenght made up of

Answer 3

1 cycle = 1 compresion and 1 rarefraction

Question 4

frequency

Answer 4

1 cycle per second = 1Hz

Question 5

propagation

Answer 5

speed at which a wave moves through a medium
metres/second
in soft tissue - approx 1540 m/s

Question 6

equation for propogation

Answer 6

propogation = frequency x wavelength

Question 7

what does propgation depend on

Answer 7

density
stiffness

gases - lower propagation speed
solids - higher propagation speed

Question 8

speed in imaging

bone

Answer 8

3000-5000m/s-1

Question 9

speed in imaging

soft tissue

Answer 9

1440-1640m/s-1

Question 10

speed in imaging

Fat

Answer 10

1440m/s-1

Question 11

speed in imaging

air

Answer 11

330m/s-1

Question 12

why can you not constantly put sound wave into tissue

Answer 12

will cause tissue to heat up

Question 13

why does reflection occur

Answer 13

because of various densities and stiffness = impedence between tissues
similar impedance = weak echo
identical impedance = no echo
different impedance = stong echo

Question 14

what is the range equation

Answer 14

t = 2d/c

t = echo time 
d = distance to reflective 
c = speed of sound

Question 15

what is impedance

Answer 15

relates acoustic pressure and speed of particle vibration

Question 16

impedance calculation

Answer 16

impedance = density of medium x propagation speed w

Question 17

what is intenisty transmission coefficient T

Answer 17

the fraction of the sound which is transmitted

Question 18

what is intensity reflection coefficient R

Answer 18

the fraction of the sound intensity which is reflected

Question 19

how are the sound waves generated

Answer 19

the probe (transducer) converts electrical signal to sound waves and vice versa
uses piezoelectric crystals

Question 20

what material is used in ultrasound probes

Answer 20

man made ceramin material PLT

lead Zirconate titante

Question 21

how do piezoelectric crystals work

Answer 21

electrodes on opposites sides
dioples aligned obliqely
change in current create pressure changes around the crystals causing them to rotate to create compression and rarefraction

Question 22

what is a dipole

Answer 22

closely spaced pair of electric charges

Question 23

describe the process of the transmitter

Answer 23

electrical drive signal
apply an electrical field
crystals change in physical dimesions
generates an ossiciating acoustic pressure

Question 24

desribe the process of the reciever

Answer 24

osicilating acoustic pressure
change in physical dimesions of the crystal
generates an electrical field
electrical signal to display electrons

Question 25

connections in the transducer

Answer 25

coacial cables deliver voltage pulses which drive the crystals two faces of the crystlas are coated with thin conducting films which contact the cable terminations front electrode is earthed to prevent patient from electric shock

Question 26

what is the baking block

Answer 26

absorbs ultrasound from back face | limits crystal vibrations to allow short pulse duration

Question 27

what is the acoustic insulator

Answer 27

cork/rubber | prevents ultrasound propagating into the plastic housing and operators hand

Question 28

what is the role of gel

Answer 28

elimates layer of air between patient and probe to prevent reflection prevents an impedance mismatch

Question 29

requirements of an image test

Answer 29

``` define normal anantomy detect variations from normal charactise abnormaility stage of the disease guide interventions monitor effects of treatment screening risk vs benefit ```

Question 30

requirements of an ultrasound

Answer 30

compact and portable cheap department based but can be moved range of appliactions

Question 31

describe a low frequency curvilinar imaging probe

Answer 31

able to penetrate deep into the tissues of image internal organs, sector shaped image suitable for imaging large areas but still not enough to image whole organ such as liver curved face

Question 32

describe a high frequency linear imaging probe

Answer 32

suitable for imaging surface structures only. rectanglar shaped image so limited field of view improves resolution but limits depth of penetration

Question 33

decribe a endo-cavaity/transaginal imaging probe

Answer 33

high frequency inserted into body cavity close to area of interest so high fequency can improve resolution invasive and uncomfortable

Question 34

doppler ultrasound

Answer 34

3 types colourflow power doppler pulsed wave

Question 35

what does a colour flow detect

Answer 35

presence of flow morphology of vasculature identification of flow abnormalities, turbulance

Question 36

what does a pulsed wave detect

Answer 36

quatitive flow information, velocity, pulsatility index, resistance index etc