Chapter 16 and 17 Flashcards
______ is a method of reporting the extent to which a signal can vary and still be accurately measured “number of available choices “
dynamic range
what are the units of dynamic range?
decibels
the dynamic range information ______ the more it is processed
deceases; components earliest in the imaging has chain process data with the widest dynamic range (transducer), components farther along in the imaging process data with narrower dynamic range (display and storage)
the process of ______ eliminates a problem with components with different dynamic ranges
compression (reduces dynamic range) (adjustable)
what are the requirements of compression?
the largest signal remains the largest
the smallest signal remains the smallest
the range of signals is reduced
______ dynamic range means fewer gray scale, they are also called high contrast (few choices and black and white)
narrow
______ dynamic range means many shades of gray, also called low contrast (many choices and gray scale)
wide
The frequency of sound created by the transducer and transmitted into the body is?
Fundamental frequency
Twice the fundamental frequency is?
Harmonics frequency
Harmonic frequency sound waves arise from ______
Nonlinear behavior
The image created by processing reflections that have the same frequency as the transmitted sound
Fundamental image
The image created by precessing reflections that are twice the fundamental frequency
Harmonic image
Harmonic imaging is most useful in improving poor quality images because harmonic frequency waves undergo less ______ than fundamental sound waves
Distortion
What are the two forms of harmonics that is important in US?
Tissue harmonics and contrast harmonics
Linear means ______ or symmetrical, linear systems response in an even manner
Proportional
Nonlinear means ____ or disproportionate, a system is nonlinear when it behaves unevenly
Irregular
Harmonic frequency sound arises from _____ behavior
Nonlinear
As a sound wave travels in the body, a minuscule amount of energy is converted from the fundamental frequency to the harmonic frequency- this creates ______ during transmission
Tissue harmonics
The ______ variation in speed creates tissue harmonics in the biologic media
Nonlinear
The strength of the harmonics wave ______ as sound travels in tissue
Grows
During fundamental imaging significant amounts of artifact arise within the first few centimeters of tissue, why?
The beam is very strong and the many different superficial anatomical layers distort the sound beam
Tissue harmonics develop _____ in tissue
Deeper; they do not exist in extremely superficial depths
Harmonics get at ______ through the superficial tissue, remaining distortion free with less noise (but increases signal-to-noise ratio)
“Free ride”
______ sound beams create significant tissue harmonic signals (nonlinear)
strong
since harmonics arise only in the non-distored main beam, the harmonic image has less distortion, very few harmonics are created in the ______ because they are so weak
side lobes; beams that are most likely to create harmonics are least likely to create artifact
sound in ______ travels faster than sound in rarefaction
compression
______ harmonics is an imaging technique specifically designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections
pulse inversion
______ imaging creates images from the portion of the reflected sound that has the same frequency as the transmitted sound
fundamental
______ imaging creates images only from harmonic, which is twice the frequency of the transmitted sound
harmonic
with pulse inversion harmonics, two ______ ultrasound pulses are transmitted down each scan line
consecutive
the first is a _____ pulse, the second pulse inversion is an _____ copy that is out-of-phase with the first: compression exists in the first pulse, a rarefaction exists in the second
typical, inverted
the reflections from these pulses are combined in the _____
receiver
since fundamental portions of the reflections exhibit _____ behavior, the two inverse fundamental signals destructively interfere and completely cancel each other out
linear
since the harmonic portion of the reflections are in-phased and interfere constructively, they remain while the fundamental portions ______
disappear
the time required to create a frame is ______ in pulse inversion harmonics, the frame rate is halved and temporal resolution is reduced
doubled
______ harmonics is another imaging technique specially designed to augment harmonic reflections, which contain less distortion, while eliminating distorted fundamental reflections
power modulation; it achieves the same goals as pulse inversion but uses a different engineering approach
two constructive US pulses are sent down the same line; the second pulse is ______ the strength of the first one
twice; the stronger second reflection contains harmonics
in power modulation, during reception the reflection from the first pulses are doubled and then ______ from the second reflection
subtracted
the fundamental potions cancel each other out in power modulation harmonics, leaving only the harmonic portion of the _____ reflection
second
contrast agents, also called ______, are gas bubbles encapsulated in a shell; they are injected in the circulation or ingested
microbubbles
contrast agents have different ______ fingerprint than blood or tissue, they are designed to create strong reflections that accurately “light up” blood chambers, vessels, or other anatomic regions
acoustic
what are the five requirements for contrast agents?
safe, metabolically inert, long lasting, strong reflector of US, and small enough to pass through capillaries
as sound pulses interacts with contrast agents, much ______ harmonics are generated, contrast agents are created because microbubbles act in a nonlinear manner when struck by sound waves
stronger
contrast harmonics are created during ______ as energy is converted from the fundamental frequency to the harmonic frequency
reflection
when a microbubble is within a sound beam, the bubble grows and shrinks in relation to the ______ variations in sound
pressure
when exposed to sound beams of adequate strength, contrast harmonics are created because of the nonlinear changes in bubble size, this is called ______
resonance
during compression the bubbles ______ and the pressure inside the bubble increased, the bubble stabilizes which limits how small the bubble will become
shrinks
during rarefaction the bubbles ______, a small amount of energy is transferred from the fundamental frequency to the harmonic frequency
expands (bubbles expand to a greater extent then they shrink)
the amount of contrast harmonics produced may be estimated by a number called the _____
mechanical index
what does mechanical index depend on?
frequency of the transmitted sound and the rarefaction pressure of the sound wave
what is the mechanical index equation?
MI= peak rarefaction pressure/ square root of frequency
small pressure and higher frequency is?
lower mechanical index
large pressure variation and lower frequency is?
higher mechanical index
microbubbles are the size of red blood cells and resonate when exposed to sound in the ______ MHz range, this range is right in the middle of the frequencies used in diagnostic US
2 to 4
the relationship between the mechanical index and harmonic creation is ______
nonlinear
______ mechanical sound beams do not create harmonics because the microbubbles expand and contrast evenly in a linear fashion
low; when the MI is less than 0.1 bubbles create only backscatter
between 0.1 to 1 create a relatively small amount of harmonics
greater than 1 creates substantial signals
with ______ mechanical index sound beams the bubbles may expand and break apart
high
what are the two important characteristics of contrast agents?
the nature of the shell and the gas that fills the microbubble
what does the relationship of the shell and the internally trapped gas determine?
stability and longevity while circulating in blood
shells trap the gas and increase the effective life of a microbubble
the gas trapped in the interior of the shell also determines the stability of the microbubble
larger gas molecules find the shell less permeable and remain trapped within the bubble
contrast harmonics created by microbubbles are much ______ than tissue harmonics
stronger
