Physics Final Ch. 13-24 Flashcards
Accuracy in time. Describes the ability to accurately show structures from instant to instant
temporal resolution
Temporal resolution is determined by
frame rate
System settings that affect frame rate
imaging depth, number of pulses per scan
Multiple focal zones ______ the frame rate and _______ temporal resolution but has improved ______
decrease, diminishes, lateral resolution
More pulses per scan line creates multiple focal zones
multi focus
Allows the sonographer to control whether the low-level gray scale information within the data will appear on the displayed image
Reject
Another name for reject
threshold or suppression
Reject effect on the image
affects all low level signals on the image, regardless of their location
Reject does not affect
bright echoes
Made up of a single PZT element in the transducer, the electronics in the beam former/pulser, and the wire that connects them
channel
6 major components of an ultrasound system
transducer, pulser/beam former, receiver, display, master synchronizer
During transmission, transforms electrical energy into acoustic energy and during reception, transforms acoustic energy into electrical energy
transducer
Creates and controls the electrical signal sent to the transducer that generates sound pulses
pulser/beam former
The pulser determines the
amplitude, PRP, PRF
The beam former determines the
firing delay patterns for phased array systems
Transforms the electrical signals from the transducer (produced by the reflected sound) into an image to display
receiver
Presents processed data-screen
display
Archival of data
storage
Maintains and organizes the systems components
master synchronizer
Spatial resolution is also called
detailed resolution
Spatial resolution is determined by
pixel density
How to calculate number of gray shades
multiply 2 by itself the same number of times as there are bits
Determines the range of brilliancies within the displayed image
contrast
Bistable images are _____ contrast (black and white)
high
Gray scale is ______ contrast
low
Composed of two shades, black and white
bistable images
Gray scale displays _____ levels of brightness
multiple
Many shades of gray have better
contrast resolution
With sector shaped images, the scan lines separate at increasing depths. “Gaps” or “missing information” exists between the scan lines, especially as the lines spread apart
fill-in interpolation
Fill-in interpolation is form of
preprocessing
Fill-in interpolation improves
spatial resolution
Creation of an image from sound reflections at twice the frequency of the transmitted sound
harmonic imaging
Harmonic frequency sound waves arise from _______ behavior
non-linear
As sound waves travel in the bod, a miniscule amount of energy is converted from the fundamental frequency to the harmonic frequency
tissue harmonics
Tissue harmonics occurs during
transmission
Tissue harmonics are
non-linear
Series of compressions and rarefactions
sound
Sound travels at an _______ speed through soft tissue
uneven
Sound is ______ through compression and ______ through rarefaction
faster, slower
As an ultrasound pulse interacts with contrast agents, _______ harmonics are generated
much stronger
Contrast harmonics are created because the microbubbles act in a _____ manner when struck by sound waves
non-linear
Contrast harmonics are created during
reflection
Occurs when blood moves with variable velocity
pulsatile
In pulsatile flow, blood accelerates and decelerates as a result of
cardiac contraction
Pulsatile flow commonly appears in
arterial circulation
Occurs when blood moves at variable velocity
phasic
In phasic flow, blood accelerates and decelerates as a result of
respiration
Phasic flow commonly appears in
venous circulation
Occurs when a fluid moves at a constant speed or velocity
steady
Steady is present in
venous circulation with held inspiration/expiration
Characterized by chaotic flow patterns in many different directions and at many velocities
turbulent flow
Sound associated with turbulence is called a
murmur or bruit
A narrowing in the lumen of a vessel
stenosis
Effects stenosis has on blood flow
changes in direction, increase in velocity, post stenotic turbulence, pressure gradient
Velocity is highest where the vessel is
narrowest
The streamlines are destroyed and turbulence in the form of
eddy currents/vortices
Tissue vibration is called a
thrill
Pressure downstream from the stenosis is _____ than the pressure upstream
lower
Describes the relationship between velocity and pressure in a moving fluid
bernoulli’s principle
Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level
hydrostatic pressure
If blood pressure measurement is made at the level of the heart, the hydrostatic pressure is ______, no error in measured pressure
0mmHg
If the blood pressure measurement is made below the level of the heart, the measured blood pressure is
erroneously high
If the blood pressure measurement is made above the level of the heart, the measured blood pressure is
erroneously low
Change in frequency from motion between the sound source and the receiver
doppler shift/doppler frequency
The frequency of sound changes when the sound source and the receiver move
closer together or farther apart
Doppler shift is a principle used to measure the
velocity of blood in the circulation
Doppler Shift (Hz)=
reflected frequency-transmitted frequency
Doppler shifts are in the ______ range of frequencies
audible
Doppler shifts are created when transmitted sound wave strikes
moving red blood cells
Blood flow is moving toward the transducer
positive doppler shift
Blood flow is moving away from the transducer
negative doppler shift
Simultaneous anatomic imaging and doppler is called
duplex imaging
Advantage of PW doppler
being able to select the exact location where velocities are measured
PW doppler exact location is called
range resolution, range specicity, range specific
Most common error associated with doppler ultrasound
aliasing
An alias is a
false identity
The false identity in PW doppler is that very high velocities in one direction are
incorrectly displayed as going in the opposite direction
Does aliasing happen with CW doppler
no
Aliasing occurs when the doppler sampling rate (PRF) is
too low in comparison to the measured blood velocities
Two ways to avoid aliasing
raise PRF (nyquist limit), reduce doppler shift
Color doppler reports/measures
average or mean velocities
Color doppler is angle
dependent
If the angle between the sound beam and blood flow is 90 degrees
no doppler shift is created or measured, no color will appear in the vessel
To correct aliasing on color doppler is to
increase scale/PRF/nyquist limit
Increasing the color doppler scale
decreases the sensitivity to low velocity flow
Identifies only the presence of a doppler shift
power doppler
Power doppler does not evaluate
velocity or direction
Power doppler mode is
non-directional color doppler
Advantages of power doppler mode
increases sensitivity to low flow/low velocity flow, unaffected by doppler angles, no aliasing
Disadvantages/limitations of power doppler mode
no velocity or flow direction, low frame rate
Appears as a hyperechoic region beneath tissue with abnormally LOW attenuation
enhancement
Enhancement is completely unrelated to
speed of sound in soft tissue
What assumption is not true with enhancement
6 the strength of a reflection is related to the characteristics of the tissue creating the reflection
Appears when the sound energy is transmitted in a direction other than along the beams main axis
lobes
Lobe artifacts degrade
lateral resolution
What assumption is not true with lobes
4 reflections arise from structures located along the beams main axis
Lobe artifact and true reflector are located ______ and ______
side by side, at the same depth
Created when sound reflects off a strong reflector and is redirected toward a second structure
mirror image
Mirror artifact is located
deeper than the real structure
Slice thickness artifact is related to dimension of the beam that is
perpendicular to the imaging plane
Small amplitude echoes and results from many sources
noise
Noise is more likely to affect ______ regions rather than ______
low level hypoechoic regions, bright echogenic areas
Phantoms are an
objective standard
Have ultrasonic features similar to soft tissue, used to evaluate gray scale, tissue texture, multi focus
tissue equivalent phantom
Tissue equivalent phantom is similar to soft tissue in what 4 ways
speed of sound in phantom is 1540 m/sec, attenuation, scattering characteristics, echogenicity
Region close to the transducer where images are inaccurate
dead zone
In dead zone, it extends from the transducer to
shallowest depth where reflection appears
Dead zone is assessed with the
shallowest pins in a test phantom
What can be used for help with dead zone for superficial structures
acoustic standoff (or gel pad)
Minimum distance at which two side by side pinds are displayed as two distinct images, PERPENDICULAR TO SOUND BEAM
lateral resolution
Smallest distance at which two pins positioned PARALLEL to the sound beam are displayed as two distinct echos
axial resolution
Quality of being worthy, honored or esteemed
dignity
Factors that make a patient vulnerable to a loss of dignity include
advanced age, infirmity, lack of privacy
A primary mandate regarding clinical ultrasound is that the
benefit to the patient must outweigh the risk of the exam
Maximal heating is related to the beams
SPTA intensity
Interaction of sound waves with microscopic, stabalized, gas bubbles (gaseous nuclei) in the tissues
cavitation
Proposed that bioeffects result from tissue temperature elevation
thermal mechanism
It is ______ to use diagnostic ultrasound in a non-medical setting for entertainment
inappropriate