Lecture 17

Question 1

Linear phased array is a ____ line of elements

Answer 1

Straight

Question 2

In Linear phased array elements are fired with

Answer 2

A small time difference —> phasing

Question 3

______us of time delay between each firing

Answer 3

<1us

Question 4

Wave front created by the

Answer 4

Differing distances of the waves do to phasing

Question 5

A wave always travels ______ to its wave front

Answer 5

Perpendicular

Question 6

The new waveform created by secondary wavelets happens according to

Answer 6

Huygens principle

Question 7

How do we stear a beam to the right

Answer 7

Phase the fire with the left side firing first

Question 8

If all elerments are energized simultaneously then

Answer 8

There are no delays

Question 9

The shorter the the delay between firing in elements than

Answer 9

The more horizontal the wavefront

Question 10

How do we change the focus

Answer 10

Increase intensity —> improves intensity

Question 11

Where is the beam width the smallest

Answer 11

At the focus

Question 12

In electronic focusing the phased arry can also

Answer 12

Focus the beam

Question 13

In electronic focusing greater durvature places the focus

Answer 13

Closer to the transducer

Question 14

In electronic focusing less curvature moves focus

Answer 14

Deeper

Question 15

In electronic focusing can move focus depth up or down based on the

Answer 15

Time delay

Question 16

Greater time delay = _____ focus

Answer 16

Closer to the surface

Question 17

How do we achieve curvature

Answer 17

Fire outside crystals first and fire the middle ones the last

Question 18

an unfocused sound beam has

Answer 18

Natural focusing

Question 19

Focus sound beam has

Answer 19

Electronic focussing

Question 20

Multiple foci

Answer 20

They require multiple pulses, each focused at a different depth

Montage of overlaid images, better resolution at each depth

Decrease frame rate is lag

Question 21

What is a further application for phasing

Answer 21

Spatial compounding

Question 22

What is the purpose of spatial compounding

Answer 22

Hit the same object from different angles

Question 23

Spatial compounding has more

Answer 23

Pulses per image

Allows to sharpen boarders, smoother image, clears out cysts

Question 24

Phasing of a very small group of elements =

Answer 24

Sector image

Question 25

Phased array can be used to assess

Answer 25

Large ares through very small windows

Question 26

Phasing can be applied to each element group in a linear sequenced array to do the following :

Answer 26

Steer pulses in various directions

Initiate pulses at various starting points across the array

Question 27

Vector aray is _____+ _____

Answer 27

Linear array + phased array

Question 28

Vector array has a _____ top

Answer 28

Flat

Question 29

Widescreen =

Answer 29

Sector

Question 30

Vector array used to measure

Answer 30

Larger organs

Question 31

In vector arrays, phasing applie to linear sequence array….

Answer 31

Keep delays the same for each group

Beams sent out in an angled direction

Parallelogram shaped display

Used in doppler ultrasound

Question 32

Variable aperture

Answer 32

Not all elements of a phased array are used to generate all pulses

Smaller groups are used for short focal lengths

Larger groups for foci located at increasing depths

Question 33

Two types of grating lobes

Answer 33

Sides lobes

Grating lobes

Question 34

Side/grating lobes are ______ beams

Answer 34

Weaker

Question 35

Grating lobes are from _________ interactions

Answer 35

Interelement

Question 36

If side lobes/ grating lobes hit a strong reflector, they produce

Answer 36

Strong echoes

Examples of strong reflectors (diaphragm, gas, fetal bone)

Question 37

Side lobe and grating lobes show as ____ that look like ______

Answer 37

Artifacts

Amniotic bands

Question 38

How do we fix grating lobes? (3)

Answer 38

Apodization
Subdicing
THI

Question 39

Apodization

Answer 39

Grating lobes come from the edges of the elements

We can reduce the amplitude of the voltage to the outside elements

The weaker beam going out results in weaker echo, allowing for less artifacts to be created