day 4

Question 1

denotes a direction of travel of the ultrasound wave perpendicular to the boundary between two media.The incident sound may be reflected into the first medium or transmitted into the second medium; most often, both occur.

Answer 1

perpendicular incidence

Question 2

determines how much of an incident sound wave is reflected back into the first medium and how much is transmitted into the second medium

Answer 2

impedance

Question 3

Impedance increases if density ____ or if propagation speed ___

Answer 3

increases

Question 4

Dividing the reflected (echo) intensity by the incident intensity yields thecfraction of the incident intensity that is reflected. This fraction is called the

Answer 4

intensity reflection coefficient (IRC)

Question 5

Dividing the transmitted intensity (It) by the incident intensity yields the fraction of the incident intensity that is transmitted into the second medium. This fraction is called the

Answer 5

intensity transmission coefficient (ITC)

Question 6

greater the difference between the impedances, the ___ the echo

Answer 6

stronger

Question 7

e greater the similarity of the impedances, the ___ the echo

Answer 7

weaker

Question 8

difference between the impedances increases, the
intensity reflection coefficient (and echo intensity) ___

Answer 8

increases

Question 9

intensity reflection coefficient increases, the intensity
transmission coefficient _____

Answer 9

decreases

Question 10

used to provide a good sound path from the transducer to the skin (eliminating the thin layer of air that would reflect the sound, preventing entrance of the sound into the body).

Answer 10

gel coupling medium

Question 11

denotes a direction of travel of the incident ultrasound that is not perpendicular to the boundary between two media. common in diagnostic ultrasound.

Answer 11

Oblique Incidence

Question 12

For perpendicular incidence, the ___ angle is zero

Answer 12

incidence angle

Question 13

direction of sound changes when it crosses a boundary, it means that the transmission angle is different from the incidence angle. A change in the direction of sound when it crosses a boundary is called

Answer 13

refraction

Question 14

Two requirements for refraction to occur are as follows:

Answer 14

1. Oblique incidence
2. Different propagation speed on
   either side of the boundary

Question 15

the resulting reflections are called

Answer 15

specular

Question 16

redirection of sound in many directions by rough surfaces or by
heterogeneous media such as (cellular) tissues, or particle suspensions, such as blood.

Answer 16

scattering

Question 17

(sound scattered back in the direction from which it originally came) intensities from rough surfaces and heterogeneous media vary with frequency and scatterer size.

Answer 17

backscatter

Question 18

While the ultrasound beam is scanned through the tissues, with scatterers moving into and out of the beam, the interference alternates between being constructive and being destructive, resulting in a displayed dot patter —a grainy appearance—that does not directly represent scatterers but, rather, represents the interference pattern of the scatterer distribution scanned. This phenomenon is called

Answer 18

acoustic speckle

Question 19

form of acoustic noise in sonographic imaging.

Answer 19

speckle

Question 20

Because bubbles generate stronger harmonics than tissue, detecting harmonic frequency echoes increases the contrast between the contrast agent and the surrounding tissue. This is called

Answer 20

contrast harmonic imaging or harmonic contrast imaging