2-D Imaging Flashcards
What are the 3 methods of focusing?
- external
- internal
- phased array
What is conventional/mechanical/fixed focus?
Focal depth can’t be changed & isn’t user adjustable
What methods of focusing are considered fixed?
- external
- internal
What is phased array focusing?
This is user adjustable – multi-focusing
What is an array?
PZT that’s cut into separate elements
What is a channel?
An active element, wire, and system electronics
What are the 3 types of array transducers?
- linear
- annular
- convex
What is phasing?
An electronic steering process when sound beams are transmitted in different directions without mechanical (motor) parts
What is aperture?
An opening or hole – in U/S, it’s a group of crystals that make a sound beam
What is dynamic aperture?
Controlling the number of crystals to maintain beam diameter at different depths
Which type of resolution does dynamic aperture affect?
Lateral resolution (LR=beam diameter)
What is dynamic receive focusing?
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
What is apodization? What is it used for?
Reducing electrical energy towards the ends of the probe to reduce grating lobes
What is subdicing? What is it for?
Cutting up a crystal into sub-elements and putting it back together to reduce grating lobes
What are the two types of accessory lobes?
- Side lobes
- Grating lobes
What causes side lobes and what can reduce them?
Caused by large crystals (older probes). They can be reduced by harmonics
What causes grating lobes and what can reduce them?
Caused by array transducers. They can be reduced by apodization, subdicing, and harmonics.
What is electronic focusing?
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
What is electronic steering?
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.
What is electronic steering?
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.
