Unit 1 Exam Review Flashcards
Another name for image on the screen
Frame
What technique is used for U/S?
Pulse-Echo Technique
What is a B-scan?
Gray-scale scan that scans in an anatomic cross-section.
How is Doppler produced?
Echoes from moving objects have different frequencies.
What frequencies can humans hear?
20kHz or 20,000Hz
What is the propagation speed of sound in soft tissue?
1.54 mm/us
What affects propagation speed in a medium?
Stiffness and less by the density of the medium.
What can determine period and frequency?
The source only.
Which results in better resolution: pulsed U/S or continuous U/S?
Pulse U/S
How are PRP and Depth of View (DOV) related?
Directly; PRP inc./DOV inc.
What is the typical DF for sonography?
0.1 - 1.0%
What is the typical DF for Doppler?
0.5 - 5.0%
How are DF and DOV related?
Inversely
What kind of bandwidth do U/S pulses have?
Broadband- short pulses & low Q-factor
What kind of events have narrow bandwidth?
Non-imaging transducers (therapeutic probes) with continuous wave or long duration pulses.
Amplitude is always squared. What does this mean?
If amp is doubled, it’s inc. by a factor of 4.
What’s true about U/S beam intensity?
Intensity varies at different depths and at different side to side locations.
What button allows you to compensate for attenuation?
TGC (Time gain compensation)
Does the propagation speed change after leaving the transducer?
NO
What happens to attenuation as Frequency increases?
Attenuation dB increase: 0.5dB of atten/cm for each MHz of freq.
Range Equation (mm)=
1/2 x [prop speed (mm/us) x pulse round trip travel time (us)]
What does positive and negative dB mean?
positive the signal strengthens / negative means the signal is less than original.
Relate positive decibels and intensity:
3 dB (Double); 10 dB (ten times)
Relate negative decibels and intensity:
-3 dB (halved); -10 dB (1/10)
What happens to PD if the number of cycles in a pulse is reduced?
PD is decreased.
What happens to intensity if beam area decreases (focusing)?
Intensity increases.
Compare attenuation in the lung and soft tissue.
Atten. high in lung than S.T. because of air.
Compare attenuation in bone and soft tissue.
Atten. higher in bone than S.T.
What happens to attenuation with longer distances?
It increases, limiting imaging depth.
Relate frequency and attenuation.
Freq. inc. / atten. inc. (directly)
What has pulses with short duration and length (wide bandwidth)?
Imaging transducers
How are impedance, density, and prop speed of the medium related?
Directly proportional
What if impedance of 2 media is equal?
No reflection.
What affect does the difference in impedance have on IRC and echo intensity?
If the difference increases, the IRC and echo intensity increases.
Why do we use coupling medium (gel)?
The large difference in impedance (air/tissue) = nearly total reflection.
How does density affect prop speed?
Density inc. / Prop speed dec.
What media has highest prop speed?
Bone then liquid then air (gases are lowest).
What part of PRP changes with altered DOV?
Only the listening time, not the pulse itself!
