Flashcards in Chapters 12-13 Deck (86):
Define mechanical transducer
contains a single, circular, disc-shaped active element that is physically moved
How many active elements/crystals are in mechanical transducers?
What is the image shape for a mechanical transducer?
fan or sector shaped
How is the scan plane of a mechanical transducer created?
through mechanical steering
Mechanical transducer have a ___ focal depth
Other terms used for fixed focal depth?
conventional, mechanical, or fixed focusing
What are two methods of fixed focusing?
internal-curved active element
external-with an acoustic lens
What happens with the PZT crystal is damaged in a mechanical transducer?
since they only have one single crystal; the entire image is lost when the crystal malfunctions
What type of transducers contain multiply active elements?
What is the arrangement of active elements in a linear array transducer?
active elements are arranged in a straight line
What is the arrangement of active elements in a annular array transducer?
elements are arranged as circular rings with a common center
What is the arrangement of active elements in a convex array transducer?
active elements are arranged in a bowed or arched line. the transducer may also be called a curve
When the beam is steered and focused using an electrical technique what is this called?
What is the image shape of a linear phased array?
fan or sector shaped
What is the beam steering in a linear phased array?
electronic steering process called phasing
How is the beam focused with a linear phased array?
What is the main advantage of phased arrays?
the electronically controlled, adjustable focusing
What happens to the PZT crystal in a damage phased transducer?
results in inconsistent or erratic beam steering and focusing
When is the sound beam steered?
if the spike line has a slope
What happens when a spike pattern is a straight line?
an unfocused sound beam is created
When is the the sound beam focused in a linear phased array?
the sound beam is focused if tge spike pattern is curved
In a linear phased array, the electronic pattern is a slope, what happens to the beam?
it is steered
In a linear phased array, the electronic pattern is a curvature, What happens to the sound beam?
What shape crystals do annular phased arrays have?
bulls eye target/ disc shaped
How is beam steering achieved with annular phased arrays?
What is the primary advantage with annular phased arrays?
multiply transmit focal zones
Smaller diameter PZT crystals create a ___focus beam
Larger diameter crystals create ___focus beams
What is the image shape for a annular array transducer?
fan or sector shaped
What happens when there is damage to a PZT crystal for an annular array transducer?
a horizontal or side to side band of dropout
What the linear sequential array have a small or large footprint?
What is the beam steering for linear sequential arrays?
a small group of the crystals are fired simultaneously
How is beam focusing achieved in a linear seq array?
electronic transmit focusing
How is receive focusing achieved in a linear seq array?
dynamically by introducing electrical delays in the signal returning from the transducer
What is the image shape for a linear seq array?
What happens if damage happens to a linear seq array?
if damage is done, then the portion of the image extending directly below the damage element is affected
Can linear sequential array transducer steer the sound beams electronically?
yes and this creates parallelogram shaped images
What shape do curved transducers have?
a bowed or curved shape
What is the beam steering for a convex seq array?
some, but not all the crystals are fired simultaneously to create each sound beam
How is focused achieved in a convex seq array?
How is transmit focusing achieved in a convex array?
by exciting the active elements in the fired group with a curved spike line pattern
How is dynamic receive focusing achieved in a convex array?
by introducing varying phase delays in the signal returning from the transducer to the US system during echo reception
What is the image shape for a convex array?
blunted sector shaped
What are vector arrays?
a combo of linear seques and linear phased arrays
what is the beam steering for vector arrays?
combo of linear and phased array so some but not all the crystals are fired sim to create a single sound beam
What is the beam focusing for vector arrays?
What is the image shape for vector arrays?
What shape of the active element creates the best elevational resolution?
active elements that are disc shaped (mechanical and annular phased array) provide thinnest slices
What is another term for slice thickness
What transducers create thinner beams with improved slice thickness?
1.5 D array which have multiply crystals in the up and down direction
What array creates a 3D image?
What does rendering do?
it creates an image from 3D data acquired during the US exam
Define side lobes
sound beams created by single element transducers are hour glass shaped. these off axis sound beams are side lobes
What do side lobes do?
reflections arising form within the side lobes degrade lateral resolution
What transducers create grating lobes?
What do grating lobes do?
degrade lateral resolution, reduce image quality, and create artifacts
reducing the strength of side and grating lobes
What are some methods to reduce grating lobes?
subdicing- in a linear array transducer
Define dynamic aperture
is used to make a sound beam narrow over a greater range of depth and this optimizing lateral resolution
What resolution is improved with dynamic aperture?
In a linear phased array, what is the firing pattern that steers a beam to the left or right?
In a linear phased array, what is the firing pattern that focuses a sound beam?
A machine that displays Doppler and 2D images is called?
Images that were displayed one frame at a time where called?
Define frame rate
ability to create numerous frames each second
What is frame rate determined by?
sounds speed in the medium
the depth of imaging
What are the units for frame rate?
Define temporal resolution
the ability to precisely position moving structures from instant to instant
Is temporal resolution better with higher or lower frame rate?
What is temporal resolution determined by?
What are units for temporal resolution?
What is the relationship between frame rate and time required to make a single image?
inversely and they are reciprocals
What are the system setting that affect frame rate?
number of pulsed per frame
What is the relationship between imaging depth and frame rate?
What is the formula for T frame?
=#pulses x PRP
how are pulses per frame and frame rate related?
What factors affect the number of pulses per frame?
number of pulses per scan line (multi-focus vs single focus)
liner per angle of sector (line density)
Multi focusing improves or degrades temporal resolution?
What improves with multi focusing?
Another name for sector size?
field of view
Which is better a narrow sector or a wide sector for temporal resolution?
Which is better low line density or high?
What is the main advantage of high line density?
improved spatial resolution
What are the systems two major functions?
1. the preparation and transmission of electrical signal to the transducer, which creates a sound beam
2. the reception of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sounds
What does the pulser determine?
the amplitude, PRP and PRF.