SPI 4 Flashcards
What creates side lobes?
mechanical transducers create these. (p. 162)
What creates grating lobes?
Arrays create these (p. 162)
What can reduce grating lobes?
subdicing and apodization (p.162)
What is lobe artifact?
second copy of a true reflector side by side with true anatomic structure. (p. 162)
What resolution does lobe artifacts degrade?
lateral resolution (p.162)
When does slice thickness occur?
when beam has a greater width than the reflector. (p.163)
What is another name for slice thickness?
elevational resolution (p. 163)
What is Speckle artifact created by?
interference effects (p.163)
Characteristics of Speckle artifact
grainy appearance. (p. 163)
Range ambiguity artifact is created how?
- by reflector that is located deeper than that of the display.
- time of flight is underestimated and artifact appears too shallow on display. (p.164)
How is Range Ambiguity artifact cured?
by lowering the PRF (imaging deeper) or by using coded excitation. (p.164)
Cross talk is found-
in spectral Doppler only (p.165-166)
What is cross talk?
special form of mirror image where Doppler spectrum appears above and below the baseline. (p. 166)
What are the two causes of cross talk?
- Doppler gain set too high
- incident angle near 90 degrees when flow is at focus
(p. 166)
How to correct cross talk?
lower Doppler gain. (p.166)
Clutter
Doppler artifact. reflections of blood cells are weak, reflections from stationary anatomic structures such as muscle tissue and vessel walls are much stronger. The strong reflections are called clutter (p.166)
Clutter must be suppressed for what?
to get reliable estimates of blood cell velocities. (p.166)
Quality Assurance is?
routine periodic evaluation of an Ultrasound system. (p.167)
Requirements of Quality Assurance
- multiple evaluations of system’s components
- repairs
- preventative maintenance
- record keeping
(p. 167)
Goals of Quality Assurance
- proper equipment operation
- detect gradual changes
- minimize downtime
- reduces # of repeat scans
(p. 167)
Methods of Quality Assurance
- test under known, defined conditions
- constant instrument settings
- use phantom with measurable characteristics
- image in identical environment
(p. 167)
Devices used in QA
- AIUM 100mm test object ( water-filled phantom)
- Tissue Equivalent Phantom
- Doppler Phantom
AIUM phantom
- array of strategically located pins
- prop. speed of soft tissue
- no attenuation properties, cannot evaluate gray scale
(p. 168)
Tissue Equivalent Phantom
- Contains medium similar to soft tissue
- strategically placed pins, structures that mimic cysts and solid masses embedded in phantom.
- attenuation coeff. similar to soft tissue
- eval gray scale since phantom atteunates
(p. 169)
Doppler Phantom
- contains static simulated vessels as well as dynamic simulated vessels at a variety of angles
- pump forces echogenic fluid through vessels at known velocities
- constriction is found in one of the vessels
- used to assess accuracy of pulsed, CW and color flow systems
- vibrating string and moving belt phantom (p. 169)
What is the Gold Standard?
“perfect” technique- deems 100% accurate
p. 171
Informed Consent must be obtained?
- prior to sedation
- in language understood by patient
(p. 172)
a patient may revoke consent when?
at any time (p.172)
What should you do when you enter a patient’s room?
- identify yourself, the procedure, and your role in procedure
- identify patient (check wristband)
- if no wristband ask patient for last name and DOB
(p. 172)
Safety measures used
- Use standard/universal precautions
- wash hands before and after exam
- wear gloves
(p. 172)
To ensure patient dignity what should you do?
- be kind and respectful
- provide privacy
(p. 172)
Ergonomic devices
- wrist support
- transducer design
- control panel and monitor
- chairs
- beds
- support cushions
(p. 173)
What is a hydrophone?
small needle with PZT crystal at its end. (p. 175)
What does a hydrophone do?
- measures pressure in a sound beam.
- can quantitate amplitude, period, pulse duration, and PRP
(p. 175)
What is a Calorimeter?
transducer which turns acoustic energy into heat. (p.175)
What is a Thermocouple
small device embedded in absorbing material. (p.175)
What does a Thermocouple measure?
-temperature change.
intensity at specific locations are measured by this.) (p. 175
In-vivo
-living
difficult to study because of absorption (most) scattering and reflection) (p.176
In-vitro
non-living
What is Dosimetry?
Science of identifying and measuring those characteristics of US field which are especially relevant to its potential for producing bioeffects. (p.176)
American Institute of Ultrasound in Medicine (AIUM) does what?
evaluates research (p.176)
FDA regulates what?
system and transducer outputs (p.176)
Bioeffects intensity limit =
SPTA (p.176)
Exam duration has the greatest effect on what?
patient exposure
p.176
highest output intensity is what?
pulsed Doppler (p.176)
lowest output intensity is what?
gray scale imaging (p.176)
What is the mechanistic approach?
-Propose specific physical mechanism that could produce bioeffects
-Theoretical analysis to estimate scope of bioeffects at various exposures
Identify “cause-effect” relationship
(p.176)
What is the Empirical Approach?
- Acquire/Review data from patients or animals
- correlate exposure and effects
- Identify “exposure-response” relationship
(p. 176)
Thermal Mechanism
Temp elevation via absorption resulting from interaction of biologic tissue and US.
(p.177)
Thermal Index
Theoretical calc related to possible temp elevation, measured in degrees centigrade, that could/ may be produced by the sound beam.
(p. 177)
What is a non thermal cavitation mechanism?
gaseous nuclei- microbubbles may be excited by US
this takes form of shrinking and expanding of bubble
(p. 178)
What is the Mechanical Index?
proposed by AIUM that relates to cavitation. (p. 178)
A high mechanical index is more likely to produce cavitation with?
- Peak rarefaction pressure
- lower frequency sound
(p. 178)
What happens with stable cavitation?
- bubbles tend to oscillate when exposed to acoustic waves of small amp.
- bubbles do not burst
What effects does stable cavitation have?
shear stresses and microstreaming in surrounding fluid.
p. 178
What happens with transient cavitation?
- aka normal or inertial cavitation
- bubbles expand during rarefactions and bubbles burst
(p. 178)
What effect does transient cavitation have?
- highly localized violent effects
- enormous pressure
- colossal temps (not clinically significant)
(p. 178)
What is Epidemiology?
population studies
best study is prospective and randomized
(p. 179)
What are the limitations of Epidemiology?
often retrospective
ambiguities justification for exam, gest. age, # of exams etc.
other risk factors- maternal age, nutriton, smoking, etc
(p. 179)
What does AIUM suggest?
Potential benefits should outweigh the risks
Don't preform without reason Don't prolong studies without reason minimize exposure time use min output power and highest receiver gain ALARA (p.180)
