Image Formation and Echoes

Question 1

What resolution does the focus improve?

Answer 1

Lateral / beam width resolution

Question 2

What is known as the resistance to sound traveling within a medium?

Answer 2

Acoustic Impedence

Question 3

What is the formula of acoustic impedance and its units?

Answer 3

z (rayls) = p (density) x c (prop speed)

Question 4

Do greater differences in acoustic impedances create produce a stronger or weaker reflection?

Answer 4

STRONGER

Question 5

When reflection increases, what happens to transmission?

Answer 5

Decreases

Question 6

% reflection equation?

Answer 6

((z2-z1/z2+z1))^2 x 100

Question 7

What occurs when there is NO acoustic mismatch between mediums?

Answer 7

100% transmission of the beam = anechoic structures

Question 8

What occurs when z2 is close to z1?

Answer 8

Hypoechoic structures - lower reflection

Question 9

The more acoustic impedance mismatch = more or less reflection?

Answer 9

MORE reflection

Question 10

When medium 2 has a higher propagation speed than medium 1, will the transmission or incident angle be larger?

Answer 10

Transmission

Question 11

Why might refraction occur?

Answer 11

1. Oblique incidence angle
2. Different propagation speeds of media

Question 12

What artifacts does refraction contribute to?

Answer 12

1. Lateral position artifact
2. Refractive shadowing

Question 13

In what type of reflection does the angle of incidence = angle of reflection?

Answer 13

Specular reflector

Question 14

What kind of reflector is ANGLE dependent and NOT frequency dependant?

Answer 14

Specular reflectors

Question 15

What is the reflector size compared to its transmitted wavelength in a specular reflector?

Answer 15

Large size compared to wavelength

Question 16

What type of reflector has a similar or smaller size compared to transmitted wavelength?

Answer 16

Scattering

Question 17

What type of reflector is frequency dependant and NOT angle dependant?

Answer 17

Scatter

Question 18

What artifact is seen with scatter reflectors?

Answer 18

Speckle

Question 19

Does high frequency produce a more fine or coarse speckle?

Answer 19

fine speckle

Question 20

Most echoes in US arise from what type of reflectors?

Answer 20

Scatter - comprises parenchyma/tissues

Question 21

What gives us the impression of “tissue texture”?

Answer 21

Speckle

Question 22

What is speckle appearance based on?

Answer 22

Constructive and destructive interference

Question 23

Irregular speckle pattern will create what kind of pattern in the tissues?

Answer 23

Heterogenous

Question 24

When is rayleigh scatter angle dependant?

Answer 24

In colour doppler

Question 25

What is the size of reflector in Rayleigh scatter compared to transmitted wavelength?

Answer 25

Very small

Question 26

What is rayleigh scatter proportional to?

Answer 26

f^4

Question 27

Appearance of rayleigh scatter?

Answer 27

Dark, anechoic

Question 28

What is known as the distance from the transducer to an echo-generating structure?

Answer 28

Range

Question 29

What information is required to determine Range?

Answer 29

Direction
Distance

Question 30

In soft tissue, what is the ROUND TRIP travel time for each cm of depth?

Answer 30

13 micro seconds

Question 31

In soft tissue, what is the travel time from transducer to imaged structure?

Answer 31

6.5 micro seconds

Question 32

In speed-error artifact, if propagation speed is GREATER than soft tissue, where will the image be placed?

Answer 32

Too shallow due to echoes returning to the transducer faster

Question 33

In speed-error artifact, if propagation speed is LESS than soft tissue, where will the image be placed?

Answer 33

Too deep

Question 34

What type of artifact is seen in “bayonet sign” ?

Answer 34

Speed error artifact