Quiz 6 Ch 12 (steering focusing)

linear phased array beam steering?

electronic - without the use of moving parts - done by PHASING

phased array means

electronic focusing

vector arrays beam focusing

electronic in both transmit and receive focusing

Annular phased array beam focusing

electronic, can achieve multiple focal zones

Linear sequential array focusing

electronic, uses both transmit and receive focusing

convex sequential array focusing

electronic, uses dynamic receive and transmit focusing

vector arrays steering

electronic, uses linear segments and the whole beam in the slope pattern

Linear sequential array beam steering

electronically, using sequential firing

Annular array

elements are arranged as circular rings with a common center

Mechanical transducer PZT damage?

entire image is lost

Whenever the crystal in any SINGLE crystal transducer breaks the __________!!

entire image is lost!!

phased array effect on image

erratic steering and focusing, the extent to which the image is affected is variable

Annular phased array image shape

fan or sector shaped

Linear phased array image shape

fan or sector shaped

Mechanical transducer image shape

fan or sector shaped

Linear sequential arrays are fired...

in a sequence of groups of crystals

Linear phased array means the crystals are ..

in a straight line (linear)

phase delays

infinitesimal time differences between many wavelets that create a single unified beam -- the time differences

Does the sonographer control the dynamic receive focusing?

no, the imager automatically does this and sonographer has no way to control it (no buttons)

Mechanical transducers have how many crystals

one or very few (coin shaped)

phasing means

order in which crystals can be altered

The order in which the crystals can be altered is...

phasing

Linear sequential array crystals

120-250 rectangular-shaped

Dynamic receive focusing uses?

Time delays before echo signals from array elements are combined

T frame

# pulses x PRP

Linear phased array transducers have how many crystals

100 to 300

Curvilinear sequential array has how many crystals

120 to 250 large rectangle crystals

Why fire in a sequence?

-improve frame rate -individual beams have excellent AR, each segment has its own beam -no divergence = good LR in far field!!

Linear sequential list

-large footprint -larger crystals -each crystal about 1 wavelength -rectangular format -can be changed into parallelogram

Linear phased list

-small footprint -smaller crystals -each crystal 1/4 to 1/2 wavelength -sector format

3 components of a sound wave

1. mechanical energy 2. longitudinal wave 3. must have a medium

Vector array has how many crystals

120 to 250 large rectangular crystals

Apodization

Alters the electrical spike voltages and reduces lobe strength, anything under a certain strength we can ignore (imager ignores)

convex sequential array image shape

BLUNTED sector shaped

linear and convex arrays effect on image

Dropout of image information from the top to the bottom of the image. The location of the line corresponds to the broken crystal.

Sound beams must be ____ to optimize lateral resolution

narrow

steering means...

SLOPE of electronic pattern (t)

Use ____ to determine the direction of the beam

T !!!

frame rate

The number of frames recorded per second - time it takes to create one picture or frame

annular phased arrays effect on image

a horizontal or side to side band of dropout at a particular depth

receive focusing

achieved dynamically by introducing electrical delays in the signals returning from the transducer

electronic transmit focusing

achieved with a curved excitation pattern of the active elements

Convex, curved, curvilinear array

active elements are arranged in a bowed or arched line

Linear array

active elements are arranged in a straight line

Phased array always means..

adjustable or multi-focus, or electronic focusing!

elevational resolution

another name for slice thickness

Side lobes can be fixed with

apodization

Grating lobes are basically side lobes, and can be improved with

apodization and subdicing

linear sequential array size of crystal

approx 1 wavelength

slice thickness resolution answers the following question:

are the reflections on the image created from the structures directly in the imaging plane, or from structures lying above or beneath the imaging plane?

Grating lobes are created by

array transducers

If electronic signals are not sent in a straight line, what happens?

beam becomes focused

the electronics of the transducer that allow the phasing of the beam pattern is....

beam former

in a beam that is focused, the slice thickness can ____

change

Annular phased array crystals

concentric rings (donut shaped) cut from the same circular slab of PZT, the array looks like a bull's eye target - multiple ring-shaped elements with common center

the sound beam is focused if the spike pattern has a

curve

Focusing means...

curving of the electronic pattern

1 1/2 - Dimensional Arrays

decrease slice thickness, by decreasing transducer thickness

Linear phased array transducer crystal measurement

each crystal is 1/4 to 1/2 of the sound's wavelength

linear phased array focusing

electronic

Subdicing

is placing tiny matching layers between the crystals to keep them from hitting each other

Side lobes create extra lobes off to the side, degrading ____ resolution

lateral

Multiple focus zones is good for ____ ___ but really bad for ___ ____

lateral resolution; frame rate

vector arrays are a combination of

linear phased and linear sequential

Convex, curved, curvilinear, linear array

linear sequential array whose crystals have curved shape

mechanical effect on image

loss of the entire image

Annular phased array beam steering

mechanical - due to shape of transducer

Disc shaped crystals are found in

mechanical and annular array transducers

Mechanical transducer beam steering

mechanical, (2D imaging is built up by rotating the crystal with a motor)

Mechanical transducer focusing

mechanical, using curved lens or crystal (fixed focusing with internal and external focusing)

convex sequential array beam steering

minimal, but electronic

interference or crashing of waves into each other causes ___

problems

What type of exams use an annular phased array?

prostate

Linear sequential array image shape

rectangular (can be changed to parallelogram)

Side lobes happen with ___ element transducers

single

the sound beam is always steered if the spike line has a

slope

In convex sequential arrays ________ of the crystals are fired simultaneously to create a single sound beam.

some, not all

The slope of the electrical spike line will determine the direction of the sound beam ____

steering

slope =

steering

If they are fired together, the beam goes...

straight

sound travels in a

straight line

steering

the beam will go to the direction in which the crystals are pulsed, or fired

Slice thickness

thickness of the section in the patient that contributes to echo signals on any one image -- the image slice is as thick as the transducer

Array means

transducer with multiple active elements (crystals)

array means

transducer with multiple active elements or PZTs or crystals

a curved pattern on the beam creates a focused sound beam during...

transmission

dynamic receive focusing uses the same concept as ____ focusing, but in reverse

transmit

curvature =

transmit focusing

vector array image shape

trapezoidal - or flat top sector

linear phased array damaged PZT

unpredictable

Linear sequential array damaged PZT

vertical drop out

curvilinear sequential array damaged PZT

vertical drop out

Transmit focusing

when we focus the beam by using electronic means to send out the beam using an array transducer

Dynamic receive focusing explained

•The beam hits the transducer and the information is processed using the electronic spike lines. The information is virtually focused using "delay patterns"