Chapter 3 Kremkau Flashcards
size of a transducer element (for a single-element transducer) or a group of elements (for an array)
aperture
nonuniform driving of elements in an array to reduce grating lobes
apodization
a transducer assembly containing several piezoelectric elements
array
in the direction of the transducer axis
axial
the minimum reflector separation along the sound path that is required to produce separate echoes
axial resolution
region containing continuous wave sound; region through which a sound pulse propagates
beam
capactitative micromachined ultrasonic transducer that contains miniature elements that are comprised of two electrically conducting layers facing each other; one of which is fixed and the other of which is a flexible membrane
CMUT
combination of a piezoelectric ceramic and a nonpiezoelectric polymer
composite
curved linear array
convex array
element
crystal
temperature at which an element material loses its piezoelectric properties
curie point
material attached to the rear face of a transducer element to reduce pulse duration; the process of pulse duration reduction
damping
the ability to image fine detail and to distinguish closely spaced reflectors
detail resolution
a thin, flat, circular object
disk
aperture that increases with increasing focal length (to maintain constant focal width)
dynamic aperture
continuously variable reception focusing that follows the increasing depth of the transmitted pulse as it travels
dynamic focusing
the piezoelectric component of a transducer assembly
element
the detail resolution in the direction perpendicular to the scan plane. It is equal to the section thickness artifact.
elevational resolution
the region of a sound beam in which the beam diameter increases as the distance from the transducer increases; also called the far field
far zone
distance from a focused transducer to the center of a focal region or to the location of the spatial peak intensity
focal length
region of minimum beam diameter and area
focal region
length of the focal region
focal zone
the concentration of the sound beam into a smaller beam area than would exist otherwise
focus
additional weaker beams of sound traveling out in directions different from the primary beam as a result of the multielement structure of transducer arrays
grating lobes
perpendicular to the direction of sound travel
lateral
minimum reflector separation perpendicular to the sound path that is required to produce separate echoes
lateral resolution
a ceramic piezoelectric material
lead zirconate titanate
a curved material that focuses a sound or beam
lens
adjectival form of line
linear
array made of rectangular elements arranged in a straight line
linear array
linear array operated by applying voltage pulses to all elements, but with small time differences (phasing) to direct ultrasound pulses out in various directions
linear phased array
linear array operated by applying voltage pulses to groups of elements sequentially
linear sequenced array
material attached to the front face of a transducer element to reduce the reflections at the transducer surface
matching layer
the narrowing of a sound beam that occurs with an unfocused flat transducer element
natural focus
the region of a sound beam in which the beam diameter decreases as the distance from the transducer increases; also called near field
near zone
preferred (maximum efficiency) frequency of operation of a transducer
operating frequency
an array that steers and focuses the beam electronically (with short time delays)
phased array
linear sequenced array with phased focusing added; linear sequenced array with phased steering of pulses to produce a parallelogram-shaped display
phased linear array
conversion of pressure to electric voltage
piezoelectricity
transducer assembly
probe
the ability to distinguish echoes in terms of space, time, or strength (called detail, temporal, and contrast resolutions
resolution
operating frequency
resonance frequency
transducer assembly
scanhead
a geometric figure bounded by two radii and the arc of the circle included between them
sector
ability of an imaging system to detect weak echoes
sensitivity
weaker beams of sound traveling out from a single element in directions different from those of the primary beam
side lobes
the region of a medium that contains virtually all of the sound produced by a transducer
sound beam
an emitter of ultrasound; transducer
source
a device that converts energy from one form to another
transducer
transducer elements with damping and matching materials assembled in a case
transducer assembly
a device that converts electric energy to ultrasound energy, and vice versa
ultrasound transducer
linear sequenced array that emits pulses from different starting points and (by phasing) in different directions
vector array
Composites have lower impedance and improved _______, ________, _________.
bandwidth
sensitivity
resolution
sonographic imaging produces a __-__ cycle ultrasound pulse
2-3
Doppler ultrasound is typically __-__ cycles
5-30
typical thickness of diagnostic ultrasound elements
.2-1mm thick
Fo = c / 2 x thickness
operating frequency
provides electronic control of location of focus
phasing
______, ________, and ______ determine the beam width at the focus.
aperture, focal length, wavelength
imaging resolution has three aspects:
detail, contrast, temporal
AR = 1/2SPL
axial resolution
decrease in wavelength = _______ frequency
increased
increase in frequency, _______ penetration
reduces
attenuation increases while frequency ________.
increases
Lateral resolution is equal to
beam width
Beam width can be reduced by focusing to improve _______.
lateral resolution
Types of array construction
linear and covex
types of array scanning operations
sequenced, phased, vector
thinner elements operate at ____ frequencies
higher
The beam diameter is ____ the diameter of the transducer element at a distance of two near zone lengths
equal to
Linear phased array transducer, the elements measure the width of about
one quarter the wavelength
Focusing of the sound beam is achieved within
the freesnel zone
utilizing multiple focal zone simultaneously increases image detail resolution and degrades
temporal resolution
What happens to the near zone length if the aperture decreases?
decreases
In the linear array transducer the pulses travel in
straight lines
What is the impendance of the matching layer
an intermediate value between the transducer element and tissue
The ability to display moving structures in real time is termed
temportal resolution
What is the material of the transducer that reduces the number of cycles produced in a pulse?
backing or damping material
If the sector width is increased by a factor of 2, what happens to the frame rate?
decreases by a factor of 2
The sonographer is most likely to miss something changing quickly in time when
using five focal zones
What are the three aspects of imaging resolution?
detail
contrast
temporal
What is the cause of poor elevation resolution?
too large of a beam width in the elevation plane
Where should the focal zone be located for the best lateral resolution?
at or just deep to the reflectors to be resolved
What is elevational resolution?
the ability to accurately differentiate between two structures in the slice thickness plane
How can radial resolution of a transducer be maximized?
By using the thickest possible damping layer during transducer construction
what is the best angular resolution
at the natural focus
What are the major limiting factors of temporal resolution?
depth
sweep angle
line density
pulse repetition frequency
what is the main disadvantage of continuous (pedoff) transducers?
depth ambiguity
What does the term phased excitation mean
the electrical impulse to each element in the crystal array is excited as a slightly different time, resulting in summated wave that has a wave front with varied direction and focal depth
____ transducers do not utilitize electronic steering
mechanical sector
what is the shape of the footprint produced by a curved sequential array transducer?
smaller convex near field and larger convex far field
In a linear array transducer, what function utilizes electronic steering
color Doppler
Which type of transducer can produce a vector or trapezoid shaped image
linear array
How does a linear sequential array transducer produce its characteristic image shape
by sequencing
What is the effect of increasing the thickness of the damping material in transducer design?
it acts to decrease the spatial pulse length, increasing bandwidth, resulting in better axial resolution
What is considered a disadvantage of the damping material in a pulsed wave transducer?
decreased sensitivity
What is the purpose of damping material in a pulsed wave transducer?
It decreases the spatial pulse length of the pulse, leading to improved axial resolution
What are two things that contribute to the efficient transmission of sound from the transducer into the patient
matching layer
gel
What part of the transducer provides protection from electric shock and reduces the effects of electrical interference?
transducer housing
What is the formula for the quality factor?
operating frequency/bandwidth
What is constructive interference?
It occurs when in phase waves meet; the amplitude of the two waves are added to form one large wave
What happens to the signal strength of an ultrasound wave during constructive interference?
It increases
What type of interference pattern will result in the resultant wave having an amplitude of 0?
out of phase, destructive interference
How is the piezoelectric property instilled in a man-made crystal material?
The crystal is heated to 328 to 365 degrees C in the presence of a magnetic field and then cooled
Coupling medium is applied to the transducer tissue boundary to
increase transmission of the sound wave
Arrays are operated in two ways called
sequencing
phasing
The transducer element converts ____ to ____ and vice versa
electricity; ultrasound
The transducer has an impedance ____ times that of tissue
20
The linear image consist of ____ scan lines
vertical
Another name for the Fresnel zeon
the near zone
In a single element transducer, additional beams not included in the ultrasound beam are called
side lobes
Lateral resolution is equal to
Beam width
The useful frequency range for most diagnostic applications is
2-20 MHz
Factors that determine axial resolution
number of cycles in the pulse and wavelength
What is the purpose of the matching layer?
Reduces reflection of ultrasound at the element
What principle states that some materials produce a voltage when deformed by an applied pressure
Piezoelectric principle
Electric ____ applied to the transducer are converted to ultrasound
voltages
Sequenced, phased, and vector are types of
operations
_____ resolution relates more directly to transducers
detail
The critical temperature an ultrasound transducer cannot exceed is called
the curie point
_____ is attached to the rear face of the transducer element
Damping
Ultrasound transducers operating according to
the piezoelectric principle
Shortening the pulses in diagnostic ultrasound
broadens the bandwidth
Which image format would be similar to that of convex array except that the footprint is smaller?
vector
Partial-volume artifact is also called
section thickness artifact
The near zone length is determined by the size and the _____ of the element
operating frequency
Intravascular imaging generally utilizes a frequency range
up to 50 MHz
Linear and convex are types of ____ arrays
assembly
Increasing the transducer frequency _____ the maximum imaging depth
decreases
The purpose of the coupling medium is to
facilitate passage of ultrasound into human tissue
Invasive transducers utilize ____ wavelengths
smaller
Without compensation the ultrasound transducer would cause about _____ of the emitted intensity to be reflected at the skin boundary
80%
In the curved array, the pulses travel
out in different directions
Electronic scanning is performed by
array transducers
phasing can
focus the beam
improve the image quality
steer the beam
The dimension perpendicular to the scan plane is called the
section thickness
Arrays have additional beams resulting from their multi-element structure called
grating lobes
______ is a combination of linear and phased array operations
vector
With phasing, the reception beam is _____ and dynamically _____
steered; focused
If the aperture increases, the near zone length
increases
What is axial resolution?
the minimum separation necessary to resolve reflectors along the scan line
The distance from the transducer to the center of the focal region is called the
focal length
What determines the beam width at the focus>
aperture, focal length, and wavelength
What is achieved within the Fresnel zone?
Focusing of the sound beam
Improvements in Principle 2 virtual beam forming include reduced section thickness, which improves ______
elevational resolution
Continuous wave transducers have ______ because energy is not lost to damping material
Higher efficiencies
Axial resolution is often normally _____ that lateral resolution
better
Focusing in the section thickness place reduces
section thickness artifact
Various formulations of ______ are commonly used in modern day transducers
lead zirconate titanate
Beam width can be reduced by focusing to improve
lateral resolution
A transducer converts one form of _____ to another.
energy
Ultrasound transducers convert _____ energy into ______ energy, and vice versa.
electric, ultrasound
Ultrasound transducers operate on the _____ principle.
piezoelectric
Single element transducers are in the form of ______
disks
The ______ of a transducer element changes when voltage is applied to its faces.
thickness
The term transducer is used to refer to a transducer ______ or to a transducer _______.
element, assembly
A transdcuer _______ is part of a transducer _______.
element, assembly
An electric voltage pulse, when applied to a transducer, produces an ultrasound _____ of a(n) _______ that is equal to that of the voltage pulse.
pulse, frequency
The resonance frequency of an element is determined by its _______.
thickness
Operating frequency _____ when transducer element thickness is increased
decreases
The addition of damping material to a transducer reduces the number of _______ in the pulse, thus improving _______. It increases _______.
cycles, axial resolution, bandwidth
Damping material reduces the ______ of the transducer and ______ of the diagnostic system.
efficiency, sensitivity
Ultrasound transducers typically generate pulses of ______ or ______ cycles.
two, three
For a particular transducer element material, if a thickness of 0.4 mm yields an operating frequency of 5 MHz, the thickness required for an operating frequency of 10 MHz is _____ mm.
0.2
Which of the following transdcuer frequencies would have the thinnest elements?
a. 2 MHz
b. 3 MHz
c. 5 MHz
d. 7 MHz
e. 10 MHz
e
The matching layer on the transducer surface reduces _____ caused by impedance differences.
reflection
A coupling medium on the skin surface eliminates reflection caused by ______.
air
Damping lengthens the pulse.
false
Damping increases efficiency.
false
The damping layer is in ____ of the element.
back
The matching layer is in ____ of the element.
front
The matching layer has _____ impedance.
intermediate
Elements in linear arrays are in the form of _______.
rectangles
Transducer assemblies are also called _____.
a. transducers
b. probes
c. scanheads
d. scan converters
e. more than one of the above
e
Operating frequency is also called ____.
resonance frequency
Mixtures of a piezoelectric ceramic and a nonpiezoelectric polymer are called _____.
composites
To operate a transducer at more than one frequency requires ______.
broad bandwidth
Is it practical to attempt to operate a 5 MHz transducer with a bandwidth of 1 MHz at 6 MHz.
No
Is it practical to attempt to operate a 5 MHz transducer with a bandwidth of 2.5 at 3 and 7 MHz.
No
A focused beam is divided into three regions, called the _______ zone, the _______ zone, and the _______ zone.
near, focal, far
The region between the transducer and the focal region is the _____ length.
near zone
Transducer size is also called ____.
aperture
Near-zone length increases with increasing source _____ and _____.
aperture, frequency
Which transducer element has the longest near zone?
a. 6mm, 5 MHz
b. 6mm, 7 MHz
c. 8mm, 7 MHz
c
A higher-frequency transducer produces a ____ near-zone length
longer
A smaller aperture produces a(n) near-zone length
shorter
A transducer with a near-zone length of 10 cm can be focused at 12 cm.
false
Which of the following transducer(s) can focus at 6 cm?
a. 5 MHz, near-zone length of 5 cm
b. 4 MHz, near-zone length of 6 cm
c. 4 MHz, near-zone length of 10 cm
d. b and c
e. none of the above
c
Sound may be focused by using a ______.
a. curved element
b. lens
c. phased array
d. more than one of the above
d
Focusing reduces the beam diameter at all distances from the transducer.
false
The distance from a transducer to the location of the narrowest beam width produced by a focused transducer called focal _____
length
Transducer arrays are transducer assemblies with several transducer _____
elements
Linear arrays scan beams by ______ element groups.
sequencing
