ULTRASOUND

Question 1

US matrix size

Answer 1

512x512, 1 byte/pixel, 0.25 MB

Question 2

hypoechoic and hyperechoic image

Answer 2

Question 3

mirror artifact image

Answer 3

causing the appearance of “liver” or “spleen” inside the lung

Question 4

shadowing artifact image

Answer 4

-hard things like bone, stones

Question 5

enhanceent artifact image

Answer 5

-liquid filled things like bladder, cyst

Question 6

ring down artifact image

Answer 6

when fluid is trapped in a tetrahedron of air bubbles, the ultrasound waves reflect infinitely and result in an infinitely long vertical echogenic line.

Question 7

comet tail artifact

Answer 7

Comet tail artifact is a form of reverberation artifact. In comet tail artifact the two reflective surfaces are closely spaced together (such as the bevel of a metallic needle). The reflective surfaces are so close that it is difficult to distinguish between each reflected echo.

Comet tail artifact is different from ring down artifact (described next) because the comet tail artifact dissipates with depth

Question 8

lateral resolution compared to axial

Answer 8

4X worse than axial and becomes worse as distance from transudcer increases

Question 9

what is lateral resolution determined by

Answer 9

US beam width
increasing lines per frame also increases resilution

Question 10

assumptions in US

Answer 10

-echo depth ~ echo time
-sound travels in straight lines
-attenuation is uniform

Question 11

Doppler effect- what objects have higher f?

Answer 11

-objects going toward detector

Question 12

doppler shift formula

Answer 12

delta f = 2 v cos(theta) f/c

Question 13

PFR for Doppler

Answer 13

must be 2X max expected doppler shift
PFR ~ 8 kHz

Question 14

length of near field

Answer 14

D^2/4 lambda
D is transducer diameter

Question 15

formula for PFR

Answer 15

frame rate * lines per image
each pulse is a line of sight

Question 16

intensities for B mode vs M mode vs Doppler

Answer 16

B mode 10 mW/cm2
M mode 4X higher
Doppler 50x higher

Question 17

duration of pulse

Answer 17

1 us

Question 18

cavitation

Answer 18

creation and collapse of microscopic bubbles

Question 19

thermal index of 1

Answer 19

increase in temperature of 1 degree celcius

Question 20

what uses A ode imaging

Answer 20

ophthalmology
-depth on horizontal axis, echo intensity on vert

Question 21

how many lines of sight in US image

Answer 21

100

Question 22

PRF typical rate

Answer 22

4000 pulses/s, listening interval of 250 us

Question 23

what corrects for attenuation at depth

Answer 23

depth gain compensation

Question 24

T-M imaging

Answer 24

time on horizontal axis and depth on vertical axis

Question 25

how many frames per second is typical

Answer 25

30

Question 26

what does temporal resolution depend on?

Answer 26

PRF line density FOV independent of pulse length

Question 27

mechanical index

Answer 27

estimates change of inducing cavitation

Question 28

what is line density

Answer 28

of lines per image/FOV

Question 29

how to increase line density

Answer 29

reduce frame rate but this reduces temporal resolution it improves lateral resolution

Question 30

harmonic imaging receives signals at what frequency

Answer 30

2X transmit frequency

Question 31

elevational resolution

Answer 31

refers to planes perpendicular to the image plane aka slice thickness depends on height of transducer elements can improve using 1.5D arrays

Question 32

what can make something appear as reverse flow?

Answer 32

aliasing

Question 33

reflected US intensity

Answer 33

((Z2-Z1)/(Z2+Z1))^2 Z is impedance

Question 34

Impedance of air, tissue, bone, PZT

Answer 34

0.01 1, 5, 20

Question 35

what organs scatter vs don't scatter

Answer 35

-get scatter when object is smaller than wavelength -kdiney, pancrease, spleen, and liver scatter -bladder and cysts show black

Question 36

does axial resolution vary with depth?

Answer 36

no, but lateral does

Question 37

US spectral shift

Answer 37

plot Doppler frequency shift as a function of time -gives info on blood flow

Question 38

sound velocity in bone

Answer 38

4100 m/s

Question 39

pulse duration and frequency relationship

Answer 39

delta f * delta t = 1/(2pi)

Question 40

attenuation through tissue vs through bone

Answer 40

f*0.5dB/cm/MHz for tissue, musle f^2*0.5dB/cm/MHz

Question 41

equation for lateral resolution

Answer 41

lambda * F/2a F is focal length 2a is aperture of transducer

Question 42

impedance of matching layer

Answer 42

Zmatching layer = root(Ztransducer*Zskin)

Question 43

frequency where mechanical energy is best converted into electrical enerrgy

Answer 43

Q= (sound velocity in crystal)/(2*crystal thickness)

Question 44

time it takes crystal to decay from resonant to unexcited

Answer 44

Q/(2*pi*fres)

Question 45

divergence of far zone

Answer 45

phi= arcsin(1.2lambda/D) D=aperture diameter

Question 46

types of averaged US intensity

Answer 46

temporal pulse averaged

Question 47

focused transducer

Answer 47

use curved crystal- get constructive interference at a point

Question 48

phased array

Answer 48

-crystals can be excited independently -by exciting crystals with certain time delays, can do depth focusing and steering

Question 49

size of object versus lambda- effect on US image

Answer 49

d>>> lambda- strong echoes d<< lambda- scattering (speckle) d~ lambda- graininess (structure)

Question 50

time gain amplification is log or linear?

Answer 50

usually log

Question 51

can sound waves travel in vaccuum?

Answer 51

no

Question 52

how to get final attenuation in US

Answer 52

add up DBs

Question 53

divergence of the far field

Answer 53

sin(theta)=1.22lambda/D

Question 54

harmful US power

Answer 54

0.1W/cm2

Question 55

narrow bandwidth

Answer 55

light damping, high Q