Chapter 12 Flashcards
what 2 characteristics of sound make it challenging to make two-dimentional images?
sound travels in a straight line and sound beams must be narrow to optimize lateral resolution
a modern ultrasound system sends a ______ sound pulse into the body, receives reflections, processes, and stores the data
narrow- sound beams are redirected into the body at different angles
to create a 10 centimeter deep image with 90 individual ultrasound pulses takes more than ______ of a second
1/100th
the mechanical transducer contains a _____,_____,_____ active element that is physically moved, this movement creates a scan plane
single, circular, disc-shaped
how many active elements does the mechanical transducer contain?
one- resembles a coin
the image created by a mechanical transducer is ______, similar to the sweeping of a wiper blade across a cars window. What does the pulse created look like?
fan or sector-shape
spokes of a bicycle wheel as it rotates around a single point
In mechanical with ______ depths, gaps of ever increasing size exist between the scan lines in mechanical transducers
greater
In mechanical transducer the two-dimentional image is built up by rotating the crystal with a motor, sound beams are emitted as the crystal moves, the scan plane is created through ______
mechanical steering
Mechanical transducers have a fixed depth called______
conventional, mechanical, or fixed focusing
What happens when a mechanical transducer’s PZT gets damaged?
They only have one so the entire image is lost
An array comprises a single slab of PZT cut into a collection of separate pieces called ______
Elements-each one is acoustically isolated from its neighboring crystals
A ______ is the combination of the active element, wire, and system electronics
Channel
What is the size of the footprint on a linear phased array?
1 centimeter on each side
In linear phased array the beam is steered and focused using an electrical technique called _____, it also builds up the 2 dimensional images
Phasing
How many elements does a linear phased array have?
Between 100 to 300- they are rectangular and narrow, a width of 1/4 to 1/2 of the sounds wavelength
What shape does a phased array make?
Fan or sector-shaped
In linear phased array, the pulses re directed in a pattern similar to that of the sweeping of a ______
Windshield wiper
With phased array systems what can the sonographer modify?
The depth and amount of focusing of the sound beam
The phased array can transmit multiple beams down the same scan line, each with a different focal depth, thus providing ______ capability
Multi-focusing
What happens to a linear phased array if a Crystal gets damaged?
Inconsistent or erratic beam steering and focusing
how many active elements in a phases array probe are used to create a single sound?
all the active elements are fired, they all create small sound wavelets. they interfere constructively and destructively creating a single sound pulse with perpendicular characteristics, the patten determines the beams direction and focus
in phased array, how does the pattern of electrical spikes from the US system steer the sound beam in different directions?
the spikes travel down the wire and excite the active elements at the end of the wires, the electrical signals are lined up and will arrive at each of their respective PZTs at exactly the same time. their wavelets interfere forming a single sound beam
what are the 2 steps to determine the direction that the sound beam will transmit?
- draw a line that connects the electrical spikes
2. draw another line extending out of the transducer that is perpendicular to the solid line
the electrical signals are separated by ______ of a second
one billionths (10 nanoseconds)
the infinitesimal time differences between many wavelets create a single unified sound beam that is directed, these time differences are called______
phased delay
beam steering is achieved ______ without any moving parts in the transducer
electronically
the electronics within the ultrasound system that create the beam steering patterns is called the ______
beam former
what will happen if the spike pattern is a straight line?
on unfocused sound beam is created
how does the pattern of electrical spikes from the beam former focus the sound beam during transmission?
the outer crystals are excited earlier than the inner crystals, the curved pattern creates a focused sound beam during transmission
what happens when the electrical spikes pattern is convex with an outward or D-shape?
it creates a defocused beam, has no use
how does a phased array system create images with multiple transmit foci?
the US system sends multiple sound beams down each scan line, each electrical spike pattern has a different degree of curvature
with multi focus the pattern with the greatest curvature creates the beam with the ______ focus, the pattern with the least curved produces the beam with the ______ focus
shallowest, deepest
During receptions, when reflected sound arrives at the transducer, multiple neighboring elements in the probe are excited; these elements create electrical signals that return to the systems receiver via ______.
multiple channels
a more accurate images can be created when the US receiver introduces ______ to some of these electrical signals during reception
variable time delays; the delay patterns during receive-focusing changes continuously as the transducer listens for reflections
with ______ focusing, the reflected sound is focused at many depths
dynamic receives (preformed automatically by system)
the active elements of annular array transducers appear ______.
disc-like; comprises multiple ring-shaped elements with a common center
with annular transducers, ______ creates the two-dimenstional image
mechanical steering- a motor physically moves the ringed element array so that the sound beams are transmitted in different directions
what is the primary advantage of annular phased arrays?
multiple transmit focal zones create each scan line of the image
the inner crystal of an annular phased array transducer creates a ______ focus beam and information only from the shallowest depths is collected
shallow-imformation is stored only from the respective focal zone, which gets progressively deeper with every ring
what is the image shape of a annular phased array transducer?
fan or sector shaped
what happens if an annular phased array transducer PZT gets damaged?
a horizontal line or side-to-side band of dropout at a particular depth is seen
what does the linear sequential arrays transducer look like?
it has a large acoustic footprint and creates rectangular images
a linear sequential array has ______ rectangular-shaped strips of piezoelectric material arranged side by side in a line
120 to 250; each crystal is about 1 wavelength in width and up to 10 cm long
how does the beam steer in the linear sequential arrays?
a small group of the crystals are fired simultaneously to create each sound beam, the sound beams are parallel to each other and are typically directed straight ahead
How does the linear sequential arrays focus?
they preform both transmit and receive focusing using electronic phase delays
transmit focusing-curved excitation pattern of the active element (outer PZT are fired earlier than inner)
receive focusing- electrical delays in the signals returning from the transducer
what is the shape of the linear sequential arrays?
rectangular shaped, the image is never wider than the transducer
what happens when a linear sequential PZT is damaged?
only a portion of the image is non visible (from top to bottom)
what would happen if only a single crystal was fired instead of groups?
the beam would quickly diverge and result in poor lateral resolution
what happens to a linear sequential array if you use beam steering?
creates a parallelogram-shaped image
what is the number and shape of the crystals in a curved array transducer?
120 to 250 rectangular shaped strips of PZT material arranged side by side in a bowed line, the array is large, the foot print can be as long as 10 cm and 1 wavelength wide
in curved array the beam is directed straight out of the crystals, but since the crystals are arranged in an arc, the pulses travel in ______ as they radiate out from the transducer
different directions (not parallel)
what is the image shape of the curved array?
blunted sector-shaped
what happens if a PZT is damaged in a curved array?
a section from top to bottom is non visible
what is a vector array a combination of?
linear sequential and linear phased array; sloped phased delay patterns can electronically steer the sound beam in different directions
what is the number and shape of the crystals in vector arrays?
there are 120-250 rectangular shaped strips of PZT, the footprint is small
the electrical signals from the beam former are delayed in a ______ pattern as they excite a group of elements in a vector array, as a result the beam radiates out in different directions from the face of the transducer
sloped spike-line
______ is used in vector arrays, both transmit focusing and dynamic receive focusing improve lateral resolution over a great range of depths
electronic focusing
what image shape does the vector array make?
a trapezoidal image
what are the 3 dimensional space that resolution deals with?
shallow-to-deep, side-to-side, and above-to-below
______ is measured in a direction perpendicular to the imaging plane or above-to-below the imaging plane
slice thickness- the the slice is thick, structures above and below the plane create reflections that appear in the image
what shape of active element creates the best elevational resolution?
disc shaped PZT provide the thinnest US slices and best elevational resolution within the focal zone (found in mechanical and annular phased array)
the elevational resolution is identical to the ______ resolution with disc-shaped active elements
lateral
what determines elevational resolution in phased array, linear, and curved array transducers?
on acoustic lens is used to create a thinner slice, with these axial resolution is best then lateral then elevational
a 2-D array with thousands of elements arranged in a checkerboard pattern, creates ______ images
3-D
with 2-D array transducers, the sound beams are electronically focused in both the ______ and ______ planes
lateral and thickness
______ is simply a trendy way of describing real-time 3-D imaging
4-D (also uses 2-D array probes)
______ creates an image from three-dimensional data acquired during the ultrasound exam, uses color shadows, texture, and optical effects
rendering- provides an element of realism to the image, usually on an off line stand alone computer system
______ is on off axis sound beam, outside of the main beam in the far zone
side lobe- reflections arising within the side lobe degrade lateral resolution
______ is the same as side lobe, but they are created by array transducers
grating lobe
reducing the strength of a side lobe or grating lobe can be done through a process called ______
apodization- stronger signals are used to excite the inner crystals, and progressively weaker electrical spikes excite the out crystals
______ of each element in a linear array transducer also reduces grating lobes
subdicing- a crystal is divided into a group of smaller crystals called sub-elements (join to act as a single crystal)
a technique called ______ can be used to make a sound beam narrow over a greater range of depths and thus optimize lateral resolution
dynamic aperture (also known as changing aperture or variable aperture)- when a array transducer is used, the US system may change the number of crystals along the face used to transmit and receive reflections
the aperture may be thought of as the ______ or the ______ that is, the number of elements used to create sound beams or to receive reflected echoes
“transmit hole”, “listening hole”
