2-D imaging - chapter 11 Flashcards
what are 2-D images aka? why?
B-scans or B-modes bc they are gray scale
what do 2-D images do?
construct a 2-D image from multiple US pulses transmitted into the body in diff directions.
what do narrow beams provide?
better lateral resolution, more accurate images
in mechanical scanning, how many crystals are found? shape? what happens with a defective crystal here?
one disc-shaped element, destroys entire image
what kind of steering is found in mechanical scanning? How does this work?
mechanical, the active element is moved by a motor, oscillating crystal or mirror thru a pathway, automatically creating a scan plane.
what kind of focusing is found in mechanical scanning? how does this work? where does focusing occur? how can you change the depth?
conventional or fixed; curvature (internal) of the PZT or an acoustic lens (external) focuses the beam at a specific depth. focusing occurs in the the horizontal and vertical planes. changing focal depth = changing transducer
describe image shape when using mechanical scanning
sector-shaped (fan), starts as a point, scan lines spread apart creating gaps at greater depths.
what is an array?
a collection of active elements in a single transducer
what is an element in a transducer?
a single slab of PZT cut into separate pieces called elements
what is a channel in a transducer?
combination of electronic circuitry, the wire and the element
what is a linear array? what are the 2 types?
a collection of elements in a line. linear switched array (sequential) or linear phased array
what is an annular array?
a group of ringed elements (bull’s eye) with a common center
what is a curvilinear array? what are the two types?
elements arranged in an arc. curvilinear switched array (sequential) or curvilinear phased array
describe number of crystals and shape found in switched/sequential linear array transducers
large transducers with about 200 rectangular elements arranged in a line
in a switched/sequential linear array transducer how does steering work? what does the image shape look like? what happens when there’s a defective crystal?
no steering, pulses sent down parallel lines. the scan lines are parallel, remain equally spaced at all depths, and there is no gaps bw lines; rectangular image shape, no wider than transducer; dropout extending from superficial to deep
describe how the elements work in a switched/sequential linear array transducer. what does it do?
a few elements (3-10) but not all are fired at exactly the same time to create a narrow directional beam. This improves lateral resolution.
what does a linear phased array transducer do?
adjustable focus or multi-focus, achieved electronically.
describe crystal shape and number in a linear phased array transducer
about 200 rectangular shaped elements arranged in a line
how does steering and focusing work in a linear phased array transducer? (what powers it and when does it occur?)
a collection of electric pulses are delivered to many or all of the transducer’s elements in various patterns for each sound pulse (creating phasing patterns). Thus, focusing and steering are electronic. These phasing patterns steer and focus the sound beam during transmission.
what is the image shape in a linear phased array transducer? what happens when there is a defective crystal?
image is sector-shaped; if one element malfunctions, the steering and focusing become erratic
what are phase delays? where do they occur? in which transducer does this occur?
miniscule time delays (10 nsec); bw electronic pulses delivered to the individual array elements. The elements are fired nearly simultaneously. linear phased array transducer
which electrical patterns are found in linear phased array transducers? what do each of them do?
electronic slope (creates beam steering) and electronic curvature (creates beam transmit focusing)
what does a beam former do? in which transducer array is it found?
creates the electronic patterns, delays are about 10 nsecs. linear phased array transducer
linear phased array transducers also have dynamic receive focusing. what is this and what does it provide?
phase delays during reception can be applied to the elec signals from the transducer to the US system. this provides focusing at many depths during reception.
describe number and shape of crystals in an annular phased array transducer
concentric rings cut from the same circular slab of PZT, array looks like a bull’s eye target; small #
how do annular phased array transducers work to create an image?
selected focal zones use inner crystals for shallow regions and outer crystals for deep regions. small diameter = shallow focus but diverge rapidly. large diameter = deep focal length
what is the image shape when using an annular phased array transducer? what happens with a defective crystal?
image is pointed, fan or sector-shaped; defective crystal causes horizontal band of dropout.
what kind of focusing is found in an annular phased array transducer? what does this kind of focusing create?
multi-focusing provides electronic focusing in all planes at all depths; a core sample. this provides optimal lateral resolution at all depths throughout the image; makes a thin slice where the beam is small, known as improved elevational resolution.
what kind of steering is performed in annular phased array transducers?
steering is performed mechanically (unlike other phased array transducers)
what does transmitting multiple pulses down a single scan line indicate?
- multiple-focusing or
2.m-mode (depth vs time)
what is a curvilinear array transducer? are there different types?
piezoelectric crystals arranged in a curve to provide a natural sector image. yes, this may also be sequential or phased array.
what is number and shape of the crystals found in curvilinear array transducer? image shape?
about 200 rectangular shaped elements; blunted-sector, fan-shaped image
what are the characteristics of a large curvilinear array transducer?
curvilinear sequential arrays place a large acoustic footprint on the pt (area of contact bw the transducer and the skin)
what are the characteristics of a small curvilinear array transducer?
typically a curvilinear phased array
what do multidimensional array transducers create?
2-D arrays create 3-D or 4-D images
when is 3-D imaging used? what determines the quality of this?
more accurately measures volumes of structures like cysts; quality is determined by the number of slices.
what is 4-D imaging?
real time 3-D imaging
how are elements set up in 2-D arrays?
may contain 1000s of elements; 2-D arrays have the same number of elements up and down and side-to-side
how are elements set up in 1 1/2-D arrays?
contains more elements side-to-side
1 1/2-D arrays allow focusing in the _______ of the image. what does this make and what does it do?
plane; this makes a thinner slice which improves elevational resolution.
how do vector array transducers work?
combine linear sequential and linear phased array. phasing is applied to a linear sequential array.
what is the image shape created by a vector array transducer? aka?
trapezoidal, a sector with a flat top. aka expanded view
when is expanded view useful?
when imaging superficial structures and large organs.
