Physics Ch 8 US

Question 1

loss of 3 dB (-3 dB) –> signal intensity (power) –> dec/inc/no change? by how much?

Answer 1

dec by 50%

Question 2

what is “half-value” thickness (HVT)?

Answer 2

tissue thickness that reduce/attenuate US intensity by 3 dB

Question 3

US –> higher freq –> scatter –> dec/inc/no change?

Answer 3

inc

Question 4

higher freq –> half value thickness (HVT) –> dec/inc/no change?

Answer 4

dec

Question 5

attenuation –> loss of intensity of US beam (d/t absorption/scattering) –> what is rate of attenuation in soft tissue?

Answer 5

0.5 (dB/cm)/MHz

Question 6

what factors determine strength of echoes? (2)

Answer 6

• angle

- impedance

Question 7

higher freq US probe –> has thinner or thicker xl?

Answer 7

thinner

Question 8

which component of the US probe contributes to spatial resolution (axial resolution)?

Answer 8

dampening block

Question 9

thin dampening block:

• light vs heavy damping?
• low vs high Q?
• short vs long spatial pulse length?
• narrow vs broad bandwith?

Answer 9

• light damping
• high Q
• long spatial pulse length
• narrow bandwidth

Question 10

thick dampening block:

• light vs heavy damping?
• low vs high Q?
• short vs long spatial pulse length?
• narrow vs broad bandwith?

Answer 10

• heavy damping
• low Q
• short spatial pulse length
• broad bandwidth

Question 11

light damping (high Q) –> used for what kind of US study? why?

Answer 11

Doppler –> preserve velocity data

Question 12

heavy damping (low Q) –> pro? (1)

Answer 12

high spatial resolution (axial resolution)

Question 13

US probe –> matching layer –> fx?

Answer 13

minimize acoustic impedance differences bw transducer & pt

Question 14

US probe –> matching layer –> optimal thickness (relative to wavelength)?

Answer 14

1/4 wavelength

Question 15

higher freq –> near field (Fresnel zone) –> inc/dec/no change?

Answer 15

inc

Question 16

larger US probe –> near field (Fresnel zone) –> inc/dec/no change?

Answer 16

inc

Question 17

higher freq –> far field (Fraunhofer zone) –> divergence –> inc/dec/no change?

Answer 17

dec

Question 18

US beam –> what is focal zone (focal depth)? what is its significance?

Answer 18

spot bw converging & diverging beams:

• narrowest beam
• area of max intensity

==> best lat resolution

Question 19

what are the 3 dimensions in US?

Answer 19

• axial
• lat
• elevation (slice thickness)

Question 20

2 objects need to be what distance apart to be seen as 2 separate objects?

Answer 20

1/2 spatial pulse length

Question 21

US –> what is axial resolution?

Answer 21

ability to tell apart 2 closely spaced objects in the direction of the beam

Question 22

US –> what is lateral resolution?

Answer 22

ability to resolve objects in a direction perpendicular to beam direction

Question 23

axial resolution –> constant at different depths –> T/F?

Answer 23

T

Question 24

higher freq –> lat resolution –> dec/inc/no change?

Answer 24

inc

Question 25

US probe --> larger diameter --> lat resolution --> dec/inc/no change?

Answer 25

inc

Question 26

US probe --> higher scan line density --> lat resolution --> dec/inc/no change?

Answer 26

inc

Question 27

side lobe artifact --> occur more w linear vs phased array transducer vs no effect?

Answer 27

linear

Question 28

power doppler --> Doppler angle does not matter --> T/F?

Answer 28

T

Question 29

Power doppler --> produces aliasing artifact --> T/F?

Answer 29

F (color & spectral doppler do produce aliasing artifact. Power does not)

Question 30

doppler --> aliasing --> occur when velocity is higher than what?

Answer 30

Nyquist freq

Question 31

doppler --> aliasing artifact --> remedy? (2)

Answer 31

- inc pulse repetition freq (PRF) | - inc scale

Question 32

can adjust what control to brighten or darken image? (2)

Answer 32

- output power (transmit gain) | - receiver gain

Question 33

dark image --> want to brighten it up --> how do the following brighten image? - output power (transmit gain) - receiver gain

Answer 33

- output power (transmit gain): inc power of US beam | - receiver gain: inc strength of sound that returned to transducer

Question 34

dark image --> want to brighten it up --> adjust output power (transmit gain) vs receiver gain --> which is optimal? why?

Answer 34

receiver gain inc output power (transmit gain) --> degrade lat resolution

Question 35

time gain compensation --> fx?

Answer 35

compensate for loss of echo strength caused by depth of reflector --> uniform brightness from top to bottom

Question 36

how does pulse length relate to bandwidth?

Answer 36

pulse length = 1/Bw

Question 37

harmonics --> pros? (3)

Answer 37

- improve lat resolution - dec side lobe artifact (grating lobe artifact) - dec superficial reverberation artifact

Question 38

harmonics --> generated in superficial or deep tissue?

Answer 38

deep

Question 39

what is compound imaging? clinical significance?

Answer 39

transducer --> US beams in mult directions --> sharpen edges of object

Question 40

compound imaging --> cyst --> post shadowing --> dec/inc/no change?

Answer 40

no more post shadowing

Question 41

harmonic vs normal US --> what happens to... - comet tail - reverberation - through transmission - acoustic shadowing - speckle noise - side lobe/grating

Answer 41

- comet tail: inc - reverberation: dec - through transmission: inc - acoustic shadowing: inc - speckle noise: dec - side lobe/grating: dec

Question 42

what is "intensity"?

Answer 42

power/area

Question 43

amplitude --> squared --> what happen to intensity?

Answer 43

square amplitude --> 4x intensity

Question 44

cavitation --> more likely to occur with... - low vs high freq - low vs high pressure

Answer 44

- low freq | - high pressure

Question 45

NCRP --> risk-benefit decision at? - thermal index (TI) of?? - mechanical index (MI) of??

Answer 45

- TI >1.0 | - MI >0.5

Question 46

pulse repetition freq (PRF) ---> formula?

Answer 46

PRF = c/2D ``` c = 1540 m/s D = depth ```

Question 47

soft tissue --> attenuation coefficient?

Answer 47

0.5 dB/cm/MHz

Question 48

How does mechanical index depend on transducer frequency?

Answer 48

Inversely proportional to the square root

Question 49

What is the wavelength of a 1.5 MHz wave?

Answer 49

~1mm 1.5 MHz / 1540 m/s = 0.00097 m = 0.001 m = 1mm