2-D Imaging

Question 1

What are the 3 methods of focusing?

Answer 1

1. external
2. internal
3. phased array

Question 2

What is conventional/mechanical/fixed focus?

Answer 2

Focal depth can’t be changed & isn’t user adjustable

Question 3

What methods of focusing are considered fixed?

Answer 3

1. external
2. internal

Question 4

What is phased array focusing?

Answer 4

This is user adjustable – multi-focusing

Question 5

What is an array?

Answer 5

PZT that’s cut into separate elements

Question 6

What is a channel?

Answer 6

An active element, wire, and system electronics

Question 7

What are the 3 types of array transducers?

Answer 7

1. linear
2. annular
3. convex

Question 8

What is phasing?

Answer 8

An electronic steering process when sound beams are transmitted in different directions without mechanical (motor) parts

Question 9

What is aperture?

Answer 9

An opening or hole – in U/S, it’s a group of crystals that make a sound beam

Question 10

What is dynamic aperture?

Answer 10

Controlling the number of crystals to maintain beam diameter at different depths

Question 11

Which type of resolution does dynamic aperture affect?

Answer 11

Lateral resolution (LR=beam diameter)

Question 12

What is dynamic receive focusing?

Answer 12

Improves image resolution at a range of imaging depths by adding variable time delays to some electrical signals (mainly to the middle sound beams) during reception

Question 13

What is apodization? What is it used for?

Answer 13

Reducing electrical energy towards the ends of the probe to reduce grating lobes

Question 14

What is subdicing? What is it for?

Answer 14

Cutting up a crystal into sub-elements and putting it back together to reduce grating lobes

Question 15

What are the two types of accessory lobes?

Answer 15

1. Side lobes
2. Grating lobes

Question 16

What causes side lobes and what can reduce them?

Answer 16

Caused by large crystals (older probes). They can be reduced by harmonics

Question 17

What causes grating lobes and what can reduce them?

Answer 17

Caused by array transducers. They can be reduced by apodization, subdicing, and harmonics.

Question 18

What is electronic focusing?

Answer 18

AKA electronic curvature. A beam former adjusts the firing sequence by adding small time delays. Outer PZTs are fired before inner PZTs, which curves the wavefront

Question 19

What is electronic steering?

Answer 19

AKA electronic slope. The sound beam’s firing pattern is adjusted to go from L -> R or R-> L. This firing sequence puts the wavefront on a slope, steering the slop in a direction.

Question 19

What is electronic steering?

Answer 19

AKA electronic slope. The sound beam’s firing pattern is adjusted to go from L -> R or R-> L. This firing sequence puts the wavefront on a slope, steering the slop in a direction.