Intro To Ultrasound Flashcards
Why can’t you scan brain
50% reflected and rest absorbed by bone
Speed of sound in soft tissue
1540m/s
If ultrasound probe is 5MHz what is the wavelength?
c=freqwavelength
Wave=c/f
Speed = 1540 m/s, freq 5MHz
1540/5000000(f in Hz) =0.000308
0.0003081000=0.308
Answer 0.3mm
Is ultrasound possible with continuous waves?
No wave pulses only to measure echoes
What is the appearance of blood on B mode images
Black
Which probe will produce sharper images? 3.5 MHz or 7 MHz
7MHz
If an echo takes 52 micro seconds to to return to the probe what is the depth of the structure? With a freq of 35Hz
Depth = ctime
15400.000052=0.0801
0.0801/2=0.0401 (/2 as depth just one way)
0.0401*100=4.01
Answer 4cm
What is the equation for depth
Depth=c*time pulse takes to travel
Remember time in seconds and divide by 2 as the depth is only waves going one way not back to probe
What is the equation for speed
C=f*wavelength
What is best probe for penetration
Lower freq = deeper penetration but less resolution
Best probe for resolution
High frequency = higher resolution but but less penetration
Unit for wavelengths
mm
Speed of sound through bone
4400 m/s
Speed of sound through soft tissue
1540 m/s
What plane are ultrasound waves on
Longitudinal vibration parallel to wave direction
What happens when ultrasound molecules vibrate
Cause pressure disturbances
How to determine strength of echo
Grey level with weak echoes appearing darker
What is characteristic impedance
Different acoustic properties of structures change echoes
How much echo is reflected in soft tissue
1%
How much echo reflected in bone
50% rest attenuated with depth bone absorbs ultrasound (heat)
How much does tissue next to gas reflect?
99%
Does high freq ultrasound have high or low attenuation?
High freq ultrasound has High attenuation
