Chapter 5, 21, 24 Flashcards
What is an artifact?
Anything that is not real or an error in imaging.
What are the 6 assumptions of imaging systems?
- sound travels in a straight line. 2. sound travels directly to reflector and back. 3. it is exactly 1540m/s. 4.reflections only arise if structure is positioned in the beam’s main axis. 5. imaging plane is thin. 6. strength of reflection is related to tissue’s characteristics.
what causes reverberation
The bouncing of the sound waves
between two strong reflectors positioned parallel to the beam
which of the echoes are real during reverberation? Which are artifact?
The first two are real. Any others are artifact.
What are characteristics of reverberation?
It appears in multiples, equally spaced, parallel to main axis, and at increasing depth.
What is Spacial Average Intensity
the average intensity across the
beams whole cross section. This average is less intense than a peak.
What is spacial peak intensity?
The beams intensity at the location where it is at its maximum. Will always have a higher intensity than an average.
Does an ultrasound beam have the same intensity at different depths?
No. Intensity weakens with depth
Which is stronger? Average or Peak
Peaks are stronger
What is Time Average (TA)
The average measurement of intensity over the whole pulse
What is pulse average
Pulse average is the average intensity over the whole pulse (not a cycle)
What is temporal peak (TP?)
the peak intensity over the very highest cycle in the pulse.
List the temporal intensities from strongest to weakest
TP, PA, TA
When we combine the temporal intensities with the part of the beam we are measuring, what are the possibilities from strongest to weakest?
SPTP, SPPA, SPTA
SATP, SAPA, SATA
How is SPTA relevant in DMS?
The most relevant intensity measurement with respect to tissue heating
How is SPSA relavant in DMS? Why is this importamt?
It describes the spread of a beam in a particular space. It’s important because an unfocused beam is more harmful than focused.
What tool is used to measure the characteristics of a sound beam?
A hydrometer or hydrophone
What does a calorimeter measure?
measures total power in a a
beam through absorption
What does a thermocouple measure?
measures temperature of the
sound beam
What do Liquid Crystals measure?
measures temperature by
liquid crystals that change color based on the temperature
Which is more important: The risk of doing an exam or the benefit to a patient’s health? Explain.
The benefit must outweigh the risk. Ultrasounds are very safe, but that doesn’t mean we should be doing them when they aren’t medically necessary.
What is dosimetry?
The science of identifying and measuring the characteristics of an ultrasound beam that are relevant
to its potential for producing biological effects.
What two methods of research are used with dosimetry?
In-vivo (within the living body) or In-vitro (outside the living body)
What does the American Institute of Ultrasound in Medicine (AIUM) say in their statement?
Even though ultrasound imaging is currently identified as safe, we should never uszse ultrasound for non-medical purposes.
What are thermal mechanisms of bioeffects?
Bioeffects from tissue temperature elevation
What are cavitation mechanisms of bioeffects?
the interaction of ultrasound waves with microbubbles which are
stabilized gas bubbles in tissue
What is the thermal index?
a predictor of maximum temperature increase under most
clinically relevant conditions
What do TIS, TIB, and TIC stand for?
Thermal index in soft tissue, bone, and cranial bone respecively.
Which is safer: Focused or Unfocused beams?
Focused beams are safer.
At what temperature elevation might begin to present harm to an embryo? What could reach these levels?
1.5 C or higher may cause harm. Spectral pulsed Doppler and COlor Doppler might reach these levels.
What are factors of stable caviation?
Oscillating bubbles, lower MI, no bursting
What are factors of transient (normal or inertial) caviation?
bursting bubbles, shock waves, high temp, high MI
MI is directly related to the potential for Caviation. What is MI inversely related to?
Frequency
What is epidemiology?
studies of population
What is a prospective study?
hypothesis first and then set up
and collect info for the study
What is a retrospective study?
having a hypothesis and then
going and looking for date to support. A less desirable option.
What is a randomized study?
a control group and a study
group- compare the two for differences
What are two possible causes of Comet Tail artifact?
- sound bouncing between two closely spaced objects. 2. resonance of gas bubbles vibrated by the beam
What assumption is violated to cause Comet Tail?
The assumption that sound travels
directly to a reflector and back
What is the cause of Ring Down artifact? What diagnosis could this indicate?
The sound bounces between bubbles. It could indicate infection.
What happens with reflection when shadowing occurs? What assumption is being violated?
100% reflection and 0% transmission is occuring. The assumption that the intensity of a
reflection is related to the tissue creating the reflection.
What assumption is being violated with edge shadowing?
Intensity of a reflection is related to the characteristics of the tissue creating the reflection
What assumption is being violated with enhancement?
the intensity of a reflection is related to the characteristics of the tissue
What is focal enhancement
Hyperechoic side-to-side
region that results from increased
intensity at the focus
Which mirror artifact is real?
The top is real, the bottom is artifact
What assumptions are broken with mirror images?
Sound travels in a straight line, to the reflector and back.
What happens when sound travels at a speed other than 1540m/s?
A speed error. The correct number of reflectors appear at incorrect depths and may appear split or cut off.
What happens when the speed in a tissue is faster than expected
Go-return time is too short and the system writes the reflection too shallow on the screen.
What happens when the speed in a tissue is slower than expected
Go-return time is too long and the system writes the reflection too deep on the screen.
What is a lobe artifact
An extra or multiple copies of the reflector. All are side by side at the same depth.
what assumption is broken by lobe artifacts?
Reflections arise from structures along the beam’s main axis
Lobe artifacts are reduced through subdicing and apodization. What do these terms mean?
Subdicing- dividing each element into small pieces.
Apodization- central elements are excited with higher voltages than the outermost elements
What reduces lobe artifacts
Apodization and Subdicing
What assumption
