Physics Test Ch 21 Flashcards Preview

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Flashcards in Physics Test Ch 21 Deck (73)
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1

Causes of artifacts

Violation of assumptions
Equipment malfunction/poor design
Physics of ultrasound
Operator error pg. 355

2

Types of artifacts

Not real
Not seen on image
Incorrect shape or size
Incorrect position
Incorrect brightness pg. 355

3

Characteristics of artifacts

Hyperechoic
Hypoechoic
Anechoic
Isoechoic
Homogenous
Heterogenous

4

Assumptions of artifacts

1. Sound travels in a straight line
2. Sound travels directly to a reflector and back
3. Sound travels in soft tissue at exactly 1540 m/s
4. Reflections arise only from structures positioned in the beam's main axis
5. The imaging plane is very thin
6. The strength of a reflection is related to the characteristics of the tissue creating the reflection pg. 356

5

Characteristics of reverberation

Appear in multiples
Appear equally spaced
Located parallel to sound beam's main axis
Located at ever-increasing depths pg. 357

6

What artifact appears as multiple, equally spaced echoes caused by the bouncing of the sound wave between 2 strong reflectors positioned parallel to the ultrasound beam?

Reverberation pg. 357

*only the first and second reflections, closest to the transducer are real, but the remaining echoes do not correspond to true anatomic structures

7

What artifact appears as a solid hyperechoic line directed downward?

Comet tail aka Ring down artifact pg. 358

8

What are the characteristics of comet tail?

Single long hyperechoic echo
Located parallel to sound beam's main axis pg. 358

9

What artifact appears as a hypoechoic or anechoic region extending downward from a highly attenuating structure?

Shadow pg. 359

10

What are the characteristics of shadowing?

Hypo- or anechoic background
Result of too much attenuation
Located beneath the structure with abnormally high attenuation
Prevents visualization of true anatomy on the scan pg. 359

11

What artifact is a special form of shadowing that appears as a hypoechoic region extending down from the edge of a curved reflector?

Edge shadow pg. 360
AKA shadowing by refraction

12

What artifact appears as a hyperechoic region beneath tissues with abnormally low attenuation?

Enhancement pg. 361

*opposite of shadowing

13

What are the characteristics of enhancement?

Hyperechoic
Result of too little attenuation
Located beneath a structure with abnormally low attenuation pg. 361

14

What artifact is a special form of enhancement in which a side-to-side region of an image appears brighter than tissues at other depths?

Focal enhancement aka Focal banding pg. 362

15

What artifact is created when sound reflects off a strong reflector and is redirected toward a second structure?

Mirror image pg. 363

16

What are the characteristics of mirror image?

A second copy of a true reflector
Located deeper than true reflector
The mirror lies on a straight line between the artifact and transducer
True reflector and artifact are equal distances from mirror pg. 363

17

What is crosstalk?

Mirror image on a spectral Doppler display pg. 363

18

What artifact is created when a sound wave propagates through a medium at a speed other than soft tissue?

Speed error pg. 364

19

What are the characteristics of speed error?

Correct number of reflections
Improper depth
Appears as a step-off ("split" or "cut") pg. 365

20

What artifact appears when sound energy is transmitted in a direction other than along the beam's main axis?

Lobes pg. 366

21

What resolution is degraded with lobe artifact?

Lateral resolution pg. 366

22

What are the characteristics of lobe artifact?

Second copy of the true reflector
The artifact and true reflector are located side-by-side at the same depth pg. 366

23

Which transducer creates side lobes?

Mechanical probe pg. 367

24

What transducer creates grating lobes?

Array transducers pg. 367

25

What artifact is created when a sound pulse changes direction during transmission?

Refraction pg. 368

*Remember- refraction is transmission with a bend

26

What are the characteristics of refraction?

Second copy of the reflector
The copy is side-by-side and the same depth of the true reflector pg. 368

27

What is an artifact?

It is an error in imaging

28

Reverberations resembles..

a ladder or Venetian blind

29

"Reverberation with the spaces squeezed out"

Comet tail

30

_________ appears when a sound wave bounces back and forth between two very closed spaced objects.

Comet tail