Ch. 12 (2D imaging)

Question 1

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

Answer 1

sound travels in a straight line

sound beams must be narrow to optimize lateral resolution

Question 2

how do we overcome these difficulties?

Answer 2

the use of multiple pulses to create a 2D image

Question 3

why does the US system send multiple pulses?

Answer 3

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

Question 4

Mechanical Transducer characteristics

Answer 4

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

Question 5

linear sequential array

Answer 5

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

Question 6

linear phased array

Answer 6

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

Question 7

annular phased array

Answer 7

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

Question 8

convex / curvilinear transducers

Answer 8

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

Question 9

vector transducers

Answer 9

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

Question 10

arrangement of crystals in linear array

Answer 10

straight line

Question 11

arrangement of crystals in annular array

Answer 11

circular rings

Question 12

arrangement of crystals in convex array

Answer 12

bowed / arched line

transducer may be called curved or curvilinear array

Question 13

what does phased array mean

Answer 13

adjustable or multi focus

Question 14

if there is a slope, there is __

Answer 14

steering

Question 15

if there is a curve, there is __

Answer 15

focusing

Question 16

what does resolution mean in imaging?

Answer 16

accuracy

Question 17

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

Answer 17

shallow to deep
side to side
above to below

Question 18

slice thickness resolution is also called

Answer 18

elevational resolution

Question 19

how to measure slice thickness

Answer 19

perpendicular to imaging plane or above to below the imaging plane

Question 20

T or F

Slice thickness can vary with depth.

Answer 20

true

Question 21

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

Answer 21

disc shaped

Question 22

disc shaped crystals are found in what type of transducers

Answer 22

mechanical and annular phased array

Question 23

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

Answer 23

beam diameter (lateral resolution)

Question 24

the height of the circle indicates

Answer 24

beam thickness (elevational resolution)

Question 25

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

Answer 25

lateral

Question 26

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

Answer 26

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

Question 27

Do all lenses have a fixed focal depth?

Answer 27

yes

Question 28

beam thickness is equal to the height of the _____

Answer 28

active element

Question 29

a limitation of linear arrays

Answer 29

inability to create thin slices

Question 30

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

Answer 30

1 1/2 dimension array transducer checkerboard appearance multiple crystals

Question 31

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

Answer 31

elevational

Question 32

resolution from best to worst

Answer 32

axial, lateral, elevational

Question 33

what is rendering

Answer 33

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

Question 34

sound beams created by single element transducers that are hourglass shaped

Answer 34

side lobes

Question 35

side lobes degrade what type of resolution

Answer 35

lateral

Question 36

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

Answer 36

middle of image

Question 37

similar to side lobes but are created by array transducers

Answer 37

grating lobes

Question 38

grating lobes degrade ___ resolution

Answer 38

lateral

Question 39

Do grating lobes create artifact that reduce image quality?

Answer 39

yes

Question 40

how do we fix grading lobes

Answer 40

apodization subdicing aperture

Question 41

what is apodization

Answer 41

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

Question 42

what is subdicing

Answer 42

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

Question 43

what is aperture

Answer 43

diameter of beam

Question 44

frequency of an imaging transducer is based on what 2 things

Answer 44

thickness and speed

Question 45

what is a 3D pixel called

Answer 45

voxel

Question 46

no slope, but there is a curve

Answer 46

focused

Question 47

straight imaging line is focused or unfocused

Answer 47

unfocused

Question 48

time differences between many wavelets firing

Answer 48

phase delays

Question 49

electronics within ultrasound system that create patterns

Answer 49

beam former

Question 50

what is an array

Answer 50

single slab of crystal cut into a collection of elements | can ring a single element or group of elements in various ways

Question 51

what is a channel

Answer 51

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

Question 52

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

Answer 52

yes

Question 53

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

Answer 53

dynamic receive focusing or | dynamic focusing

Question 54

axial resolution

Answer 54

top to bottom

Question 55

lateral resolution

Answer 55

side to side

Question 56

elevational resolution

Answer 56

front to back | beam thickness varies with depth

Question 57

which shape of crystals create best elevational resolution

Answer 57

disc shaped crystals

Question 58

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

Answer 58

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

Question 59

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

Answer 59

aperture