Ultrasound Physics - 12\2D Imaging

Front 1

What two sound characteristics make it difficult to create 2D images?

Back 1

1) sound travels only in a straight line
2) sound beams must be narrow (to optimize lateral resolution)

Front 2

How do modern ultrasound systems overcome the two difficult characteristics of sound?

Back 2

Multiple Sound Pulses

Front 3

This transducer has:
- 1 circular, disc-shaped crystal
- sector shaped image
- mechanical steering
- fixed focusing (internal or external)

Back 3

Mechanical Transducer

Front 4

This transducer has:
- 100-300 crystals, arranged in a straight line
- sector shaped image
- electronic steering (phased)
- compact, no moving parts
- electronic focusing

Back 4

Linear Phased Array Transducer

Front 5

What happens to the 2D image when a single-crystal or mechanical transducer malfunctions?

Back 5

The entire image is lost

Front 6

What happens to the 2D image when a crystal in a phased array transducer malfunctions?

Back 6

It varies - erratic beam steering & focusing is common

Front 7

How many elements in a phased array transducer are excited to create a single sound pulse?

Back 7

Each active element creates a small sound wavelet, and all the wavelets combine (interference) to form a single sound beam

Front 8

In a phased array system, how does the pattern of electrical signals steer the sound beam in various directions?

Back 8

Sound beams are steered in the direction perpendicular to the spike line's slope

Front 9

When the spike line is straight, what kind of sound beam is produced?

Back 9

Unfocused Sound Beam

Front 10

The electronics within the ultrasound system that create electrical patters which stear sound beams is called what?

Back 10

Beam Former

Front 11

When the spike line is curved, what kind of sound beam is produced?

Back 11

Focused Sound Beam

Front 12

To create a shallower focus, the beam former's pattern should have (more|less) curvature

Back 12

More

Front 13

When using linear phased arrays, (slope|curvature) controls (steering|focusing)

Back 13

Slope controls Steering
Curvature controls Focusing

Front 14

How does a phased array system create images with multiple focal points?

Back 14

Three distinct sound pulses are transmitted down each plane: each with a different degree of curvature to specifiy a different focal point

Front 15

Can signals being received be focused?

Back 15

Yes. Dynamic Receive Focusing occurs when the ultrasound receiver applies time delays to incoming signals (depending on their depth).

Front 16

Is dynamic receive focusing controlled by the sonographer?

Back 16

No

Front 17

This transducer has:
- multiple, ring-shaped crystals around one central crystal (bullseye)
- sector shaped image
- mechanical steering
- multiple transmit focal zones
- electronic focusing

Back 17

Annular Phased Array Transducer

Front 18

What happens to the 2D image when a n annular phased array transducer malfunctions?

Back 18

Only a horizontal, side-to-side band is lost at a specific depth

Front 19

This transducer has:
- 120-250 crystals, arranged side-by-side
- rectangular shaped image
- electronic steering (via some, but not all, crystals firing simultaneously)
- large acoustic footprint
- electronic focusing

Back 19

Linear Sequential Array Transducer

Front 20

What happens to the 2D image when a linear sequential array transducer malfunctions?

Back 20

Only the portion of the image directly below the damaged element is lost (vertical band)

Front 21

What type of image is produced when a linear array transducer steers its beams electronically?

Back 21

Parallelogram-shaped images

Front 22

This transducer has:
- 120-250 crystals, arranged side-by-side in a bowed line
- blunted sector shaped image
- electronic steering (some, but not all, crystals firing simultaneously
- curved tip
- electronic focusing

Back 22

Convex, Curved, or Curvilinear Array Transducers

Front 23

What happens to the 2D image when a convex array transducer malfunctions?

Back 23

Only the portion of the image directly below the damaged element is lost (vertical band)

Front 24

This transducer has:
- 120-250 crystals, arranged side-by-side
- trapezoidal shaped image
- electronic steering (combination of linear and phased array)
- electronic focusing

Back 24

Vector Array Transducer

Front 25

Accuracy in imaging is called what?

Back 25

Resolution

Front 26

In addition to axial resolution and lateral resolution, what third factor affects resolution?

Back 26

Slice Thickness or Elevational Resolution (shallow-to-deep)

Front 27

A crystal shaped in what manner provides the best elevational resolution?

Back 27

Disc-shaped crystals

Front 28

Can elevational resolution be adjusted when using phased array, linear array, and convex array transducers?

Back 28

Not really since these transducers use tall & narrow crystals side-by-side, so while lateral resolution can be improved, elevational resolution cannot be

Front 29

What type of transducer has been developed to overcome the elevational resolution problem of phased, linear, and convex array transducers?

Back 29

1 1/2 dimensional array transducers, composed of multiple crystals in both directions, thus improving elevational resolution

Front 30

Accuracy in imaging is called what?

Back 30

Resolution

Front 31

In addition to axial resolution and lateral resolution, what third factor affects resolution?

Back 31

Slice Thickness or Elevational Resolution (shallow-to-deep)

Front 32

A crystal shaped in what manner provides the best elevational resolution?

Back 32

Disc-shaped crystals

Front 33

Can elevational resolution be adjusted when using phased array, linear array, and convex array transducers?

Back 33

Not really since these transducers use tall & narrow crystals side-by-side, so while lateral resolution can be improved, elevational resolution cannot be

Front 34

What type of transducer has been developed to overcome the elevational resolution problem of phased, linear, and convex array transducers?

Back 34

1 1/2 dimensional array transducers, composed of multiple crystals in both directions, thus improving elevational resolution

Front 35

Sound beams created by single element transducers create additional areas of sound energy at depths equal to and greater than the focal zone, outside of the main beam. What are these called?

Back 35

Side Lobes

Front 36

What effect do side lobes have on image quality?

Back 36

They degrade lateral resolution

Front 37

Sound beams created by array transducers create extra, off-axis beams outside of the main beam. What are these called?

Back 37

Grating Lobes

Front 38

How do modern transducers reduce the strength of side and grating lobes?

Back 38

Apodization: stronger electrical signals excite the inner crystals and progressively weaker signals excite the outer crystals

Front 39

How do modern transducers keep the sound beam narrow over a substantial depth range?

Back 39

Dynamic Aperture: the array transducer will change the number of crystals used to transmit and receive

Front 40

T/F: Mechanical scanning produces pictures that are similar in shape to linear phased array images.

Back 40

True. Mechanical scanning and linear phased arrays create sector-shaped images

Front 41

T/F: Many active elements fire at almost the same time in a mechanical scanner

Back 41

False. There is only one active element in a mechanical scanner

Front 42

T/F: Many active elements fire at almost the same time in a phased array scanner

Back 42

True. Many active elements fire at almost the same time in a phased array scanner

Front 43

Which transducer is best described as mechanically steered and fixed, single focused?

Back 43

Mechanical Transducer

Front 44

Which transducer is best described as mechanically steered and multi-focus?

Back 44

Annular Phased Array Transducers

Front 45

Which transducer creates a rectangular shaped image?

Back 45

Linear Sequential Array Transducer

Front 46

A linear phased array transducer has 128 crystals. How many of these crystals are fired to create a single beam of sound?

Back 46

128 - all of the active elements are fired to create each sound pulse

Front 47

A linear sequential array transducer has 128 crystals. How many are fired to create a single sound beam?

Back 47

A small group of active elements are fired to create each sound pulse

Front 48

In a linear phased array, what is the firing pattern that steers a beam up or down called?

Back 48

Electronic Slope

Front 49

In linear phased arrays, what is the firing pattern that focuses a sound beam?

Back 49

Electronic Curvature

Front 50

T/F: There are large time delays in the firing pattern of a linear phased array transducer

Back 50

False. There are tiny time delays in the firing pattern of a linear phased array transducer

Front 51

T/F: A machine that displays A-mode and 2D images is called a duplex scanner

Back 51

False. A machine that displays doppler and 2D images is called a duplex scanner