Ultrasound physics

Question 1

which transducer to use

Answer 1

highest frequency

Question 2

temporal resolution

Answer 2

frame rate

Question 3

improved axial resolution

Answer 3

higher frequencies

along the axis of US beam

90 degrees to skin

Y-axis

depth resolution

Question 4

improved lateral resolution

Answer 4

adjust focal zone

x axis - right left aspect of image

better with higher frequencies

Question 5

improve temporal resolution

Answer 5

minimize depth

adjust frame rate

use narrow sector

Question 6

benefits of compound imaging

Answer 6

reduces speckle

increases frame rate due to longer scan time

Question 7

effect of harmonic imaging

Answer 7

decreases frame rate

Question 8

acoustic power units

Answer 8

watts

Question 9

watts =

Answer 9

joules/sec

Question 10

intensity (thermal index/mechanical index)

Answer 10

power/beam area MW/cm2

Question 11

mechanical index

Answer 11

likelihood of a non thermal bioeffect such as cavitation (compression and decompression of tissue)

17 mW/cm2 ophthalmic related to intensity of pulse max

value of peak negative pressure/sq root of acoustic center frequency

Question 12

thermal index

Answer 12

ratio of the emitted acoustic power to the power to raise the temperature by 1 degree

acoustic power at depth of interest/ estimated power to elevate temp 1 degree

larger TI means larger heating potential

Question 13

application specific exposure limits in mW/cm2 peripheral vascular cardiac fetal ophthalmic

Answer 13

720 mW/cm2 peripheral vascular

430 mW/cm2 cardiac

94 mW/cm2 fetal

17 mW/cm2 ophthalmic

Question 14

according to J of US

0.23 W/cm2 (versus 1.9 for other organs)

ISPPA = spatial-peak pulse-average intensity

Answer 14

mechanical index

Question 15

specular reflection

Answer 15

at smooth surfaces such as bone, diaphragm, tendons calcifications, valves, needles

angle dependent

Question 16

mirror image artifact

Answer 16

90 degrees duplication at site of a strong reflector

far image is false image

1 reflector send it back to the other delay in sending back leads to duplicate

Question 17

back scattering

Answer 17

associated with most tissues

less angle dependent

rough surface

Question 18

Rayleigh scatter

Answer 18

blood - RBC’s smaller than wavelength

Question 19

shadowing

Answer 19

decreased echoes behind strong reflector

Question 20

refraction

Answer 20

reflector placed improperly

displaced laterally

greater change in impedance, greater bending

Question 21

range ambiguity

Answer 21

echo received at different interval

Question 22

reverberation

Answer 22

bouncing between 2 strong reflectors looks like multiple equally spaced lines

ex: comet tail artifact, ring down artifact

Question 23

pencil probe Doppler

Answer 23

CW - no angle correction

Question 24

duplex

Answer 24

B mode and Doppler

Question 25

Doppler equation: change in frequency

Answer 25

(2 x transmitted frequency x velocity x cosine theta)/ speed of sound = 1540 m/s

Question 26

Doppler equation: velocity

Answer 26

change in frequency x 1540 m/sec/ 2 x frequency x cosine theta cosine theta is smaller greater than 60 degrees making the velocity greater when dividing otherwise 1 at angle 0

Question 27

cosine 0

Answer 27

1

Question 28

cosine 30

Answer 28

.86

Question 29

cosine 60

Answer 29

0.50

Question 30

cosine 90

Answer 30

0

Question 31

benefit pulsed wave

Answer 31

measure from depth

Question 32

disadvantage pulsed wave

Answer 32

aliasing can't record super high velocities

Question 33

number of crystals with Doppler

Answer 33

pulsed - 1 CW - 2 (can detect higher velocities)

Question 34

advantage CW

Answer 34

picks up everything better signal to noise not range gated higher velocities (2 crystals)

Question 35

PRF (pulse repetition frequency)

Answer 35

SCALE

Question 36

PRF to elicit aliasing tips to decrease aliasing

Answer 36

1/2 PRF = Nyquist frequency to avoid aliasing, PRF must be 2X frequency of signal detected \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* adjust baseline and scale try lower frequency

Question 37

type of Doppler for color Doppler

Answer 37

pulsed wave

Question 38

decreased angle

Answer 38

decreased velocity

Question 39

to ascertain angle correctly look at which vessel wall

Answer 39

back wall

Question 40

p 21 of physics

Answer 40

drop image of MI and TI

Question 41

tips to decrease aliasing

Answer 41

adjust scale and baseline try lower frequency

Question 42

contributors for aliasing

Answer 42

deeper vessels higher velocities

Question 43

volume flow rate

Answer 43

pressure difference x radius 4/ 8 (PI) viscosity x length

Question 44

volume flow rate

Answer 44

P1-P2/R = pi (pressure difference) x radius 4/ 8 x (viscosity) x (length)

Question 45

Pouseille's law volume flow = pressure/resistance

Answer 45

as radius decreases, resistance increases (P1-P2) π r4/ 8 N L N- viscosity L - length