Chapters 18-20

Question 1

speed errors appear as?

Answer 1

a step-off, split or cut

Question 2

propagation speed error aka?

Answer 2

range error artifact

Question 3

what happens to the reflector when the propagation speed is greater than 1,540 m/s?

Answer 3

it will be placed to shallow on the display

Question 4

what happens to the reflector when the propagation speed is less than 1,540 m/s?

Answer 4

it will be placed too deep in the display

Question 5

what happens when we have enhancement artifact?

Answer 5

the correct # of anatomic reflectors appear on the image

Question 6

what do ultrasound systems assume when we have mirror image artifact?

Answer 6

that sound travels directly to a reflector and back to the transducer

Question 7

refraction @ the edge of a circular structure is aka?

Answer 7

shadowing by refraction or edge shadow

Question 8

when does shadowing artifact happen?

Answer 8

when sound is unable to pass through a structure with higher than usual attenuation

Question 9

refraction artifact occurs when?

Answer 9

• sound strikes a boundary obliquely

- the media have different propagation speeds

Question 10

side lobes

Answer 10

are created by mechanical tranducers

Question 11

grating lobes

Answer 11

are created by array transducers

Question 12

what is subdizing?

Answer 12

divides each element into small, miniature pieces

Question 13

what is apodization and what does it reduce?

Answer 13

exciting the subdized elements with different voltages, it reduces lobes

Question 14

what does lobe artifact degrade?

Answer 14

lateral resolution

Question 15

what assumption is violated with lobe artifact?

Answer 15

that reflections arise from the beams main axis

Question 16

when does slice thickness occur?

Answer 16

when a beam has a greater width than the reflector

Question 17

linear array transducers have….

Answer 17

poor elevational resolution

Question 18

how is speckle created?

Answer 18

by interference effects of scattered sound, both constructive and destructive from the many tissue reflectors.

Question 19

how can range ambiguity artifact be corrected?

Answer 19

by lowering the PRF

Question 20

what does a hydrophone do?

Answer 20

measures the pressure in a sound beam

Question 21

what is measured by a thermocouple?

Answer 21

the intensity @ specific locations

Question 22

what is dosimetry?

Answer 22

the science of measuring those characteristics of an US field which are specially relevant to producing biological effects

Question 23

Bioeffects intensity limit: SPTA

Answer 23

• 100 mW/cm^2 unfocused

- 1 W/cm^2 or 1000 mW/cm^2 focused

Question 24

it’s difficult to study in vivo because?

Answer 24

due to absorption, scattering and reflection

Question 25

what is most likely @ a bone tissue interface?

Answer 25

temperature elevation

Question 26

what temperature elevation is considered potentially harmful to a fetus?

Answer 26

anything greater than 41 degrees celcius

Question 27

What is thermal index?

Answer 27

a theoretical calculation related to possible temperature elevation, measured in degrees centigrade

Question 28

TIS

Answer 28

TI calculated assuming that the sound beam travels in soft tissue

Question 29

TIB

Answer 29

TI calculated assuming the bone is @ the beam’s focus, usually a higher number than TIS

Question 30

TIC

Answer 30

TI calculated assuming that cranial bone is @ or near the skin’s suface

Question 31

Mechanical Index is higher with?

Answer 31

• peak rarefaction pressure

- lower frequency

Question 32

M =

Answer 32

peak rarefaction pressure/ frequency

Question 33

what are the effects of stable cavitation?

Answer 33

shear stresses and microstreaming

Question 34

what is transient cavitation aka?

Answer 34

normal or inertial (TIN)

Question 35

when do microbubbles get bigger?

Answer 35

during rarefactions, this expansion shears bubble apart and creates cavitation

Question 36

Nonthermal (cavitation) mechanism…..

Answer 36

microbubbles may be excited by US, this takes the form of shrinking and expanding the bubble; potential or near total energy absorption where the nuclei exist may lead to thermal injury

Question 37

the best study is

Answer 37

• prospective

- randomized

Question 38

limitations of epidemiologic studies are:

Answer 38

• often retrospective
• ambiguities
• other risk factors