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Ultrasound Physics > Ch. 12 (2D imaging) > Flashcards

Ch. 12 (2D imaging) Flashcards

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1
Q

two characteristics of sound make 2D images challenging to make… what are these 2 characteristics

A

sound travels in a straight line

sound beams must be narrow to optimize lateral resolution

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2
Q

how do we overcome these difficulties?

A

the use of multiple pulses to create a 2D image

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3
Q

why does the US system send multiple pulses?

A

each pulse sends back a line of reflections to eventually gather all stored pulses to create a 2D image
sonographers are usually unaware of this because it happens so rapidly

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4
Q

Mechanical Transducer characteristics

A 
one coin/disc shaped crystal (curved)
sector shaped image
mechanical steering
fixed focusing
loss of entire image if crystal malfunctions
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5
Q

linear sequential array

A

rectangular strips of crystals in a straight line [][][][][][][]
element groups are fired in a sequence to create an image
parallel scan lines
rectangular image shape - no wider than transducer
electronic steering
electronic focusing (transmit - curved pattern of crystals excitation, receive - electrical delays in returning signal)
vertical dropout

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6
Q

linear phased array

A 
arrangement of elements - line
sector image shape
electronic steering
electronic focusing
extent of image distortion is variable
small acoustic footprint
crystals fired at same time to create one sound pulse (phasing) small time delays to beam steer and focus
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7
Q

annular phased array

A 
crystal rings (inner crystals - shallow scanning, outer crystals - deeper scanning) creates multiple focal zones
sector image
mechanical steering
electronic focusing
horizontal dropout
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8
Q

convex / curvilinear transducers

A 
elements arranged in an arc
blunted sector
electronic steering
electronic focusing
vertical dropouts
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9
Q

vector transducers

A

combination of linear sequential and linear phased array
trapezoid image shape (flat topped sector)
electronic steering
electronic focusing

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10
Q

arrangement of crystals in linear array

A

straight line

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11
Q

arrangement of crystals in annular array

A

circular rings

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12
Q

arrangement of crystals in convex array

A

bowed / arched line

transducer may be called curved or curvilinear array

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13
Q

what does phased array mean

A

adjustable or multi focus

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14
Q

if there is a slope, there is __

A

steering

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15
Q

if there is a curve, there is __

A

focusing

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16
Q

what does resolution mean in imaging?

A

accuracy

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17
Q

image resolution deals with 3D space. name the 3 types of space

A

shallow to deep
side to side
above to below

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18
Q

slice thickness resolution is also called

A

elevational resolution

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19
Q

how to measure slice thickness

A

perpendicular to imaging plane or above to below the imaging plane

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20
Q

T or F

Slice thickness can vary with depth.

A

true

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21
Q

active element shape that creates the best (thinnest) elevational resolution

A

disc shaped

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22
Q

disc shaped crystals are found in what type of transducers

A

mechanical and annular phased array

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23
Q

the width of the circle (in a disc shaped element) indicates the

A

beam diameter (lateral resolution)

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24
Q

the height of the circle indicates

A

beam thickness (elevational resolution)

25
Q

the elevational resolution is identical to the ___ resolution with disc shaped elements

A

lateral

26
Q

what determines elevational resolution in phased array, linear array, and convex array transducers?

A

these array probes have rectangular elements placed side by side [] [] [] [] [] []
with phasing, the beam is focused / narrowed only side to side in the imaging plane
this narrowing improves lateral resolution but does not affect slice thickness

27
Q

Do all lenses have a fixed focal depth?

A

yes

28
Q

beam thickness is equal to the height of the _____

A

active element

29
Q

a limitation of linear arrays

A

inability to create thin slices

30
Q

newer types of transducers have improved slice thickness resolution, name one

A

1 1/2 dimension array transducer
checkerboard appearance
multiple crystals

31
Q

the 1 1/2 D array improves what type of resolution

A

elevational

32
Q

resolution from best to worst

A

axial, lateral, elevational

33
Q

what is rendering

A

creating an image from 3D data and providing a realistic view of the image

34
Q

sound beams created by single element transducers that are hourglass shaped

A

side lobes

35
Q

side lobes degrade what type of resolution

A

lateral

36
Q

side lobes are reflections arising outside of the main beam in the far zone, but show up where on images (when shown as artifact)

A

middle of image

37
Q

similar to side lobes but are created by array transducers

A

grating lobes

38
Q

grating lobes degrade ___ resolution

A

lateral

39
Q

Do grating lobes create artifact that reduce image quality?

A

yes

40
Q

how do we fix grading lobes

A

apodization
subdicing
aperture

41
Q

what is apodization

A

hitting inner crystals with stronger intensity than outer crystals reduces intensity of reflection and side lobes

42
Q

what is subdicing

A

dividing crystals into groups of smaller crystals, sub elements, not isolated

43
Q

what is aperture

A

diameter of beam

44
Q

frequency of an imaging transducer is based on what 2 things

A

thickness and speed

45
Q

what is a 3D pixel called

A

voxel

46
Q

no slope, but there is a curve

A

focused

47
Q

straight imaging line is focused or unfocused

A

unfocused

48
Q

time differences between many wavelets firing

A

phase delays

49
Q

electronics within ultrasound system that create patterns

A

beam former

50
Q

what is an array

A

single slab of crystal cut into a collection of elements

can ring a single element or group of elements in various ways

51
Q

what is a channel

A

the combination of the active element, wire, and system electronics

52
Q

can an US system excite a single or multiple elements in various ways during transmission?

A

yes

53
Q

In a linear array transducer (cardiac) returning echoes have time delays… this creates receive zone focus with optimal image quality. What is this termed?

A

dynamic receive focusing or

dynamic focusing

54
Q

axial resolution

A

top to bottom

55
Q

lateral resolution

A

side to side

56
Q

elevational resolution

A

front to back

beam thickness varies with depth

57
Q

which shape of crystals create best elevational resolution

A

disc shaped crystals

58
Q

how can we create a narrow sound beam over greater depths?

A

aperture
how? change # of crystals used to transmit & receive
aperture is an opening or hole
improves lateral resolution at a wide range of depths

59
Q

diameter of beam is referred to as ___ on ARDMS board exam

A

aperture

Ultrasound Physics (24 decks)

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