Ultrasound Flashcards
Acoustic Dependance
Property of material that determines amount of sound reflected back
What’s acoustic dependance affected by?
Density and Speed of sound
Do we want a small difference of acoustic Dependance or a large difference?
Ultrasound is reflected more if AD difference of material is high
Acoustic Dependance equation?
Z=PV
Z- AD (kgms-1)
P-Density (Kgm-3)
V- velocity (ms-1)
Velocity Equations?
V=(k/P)^1/2
K- bulk elastic modulus of material
P- density (Kgm-3)
V=1/2mv^2
Reflection coefficient of material equations
Ir/Ii
Ir= reflected intensity of beam
Ii- incident intensity of beam
(Z2-Z1)^2/(Z2+Z1)^2
Z1- AD of incident material
Z2- AD of material light being reflected off of
Advantages Ultrasound
- cheap
- portable
- In real time/ moving image
- Non- Invasive
- No known hazards
Ultrasound disadvantages
- low resolution
- Can’t be used on some parts of the body e.g. BRAIN, LUNGS, BONES
Coupling gel where used?
Between probe and skin
Why use coupling gel??
Gel have similar AD to skin and tissue so US absorbed by skin otherwise won’t happen.
Also excludes air from maximum sound transmission
Producing Ultra sounds
- Connect piezoelectric crystals to high emf or alternating current
- Causes crystals to expand and contract at emf frequency
- Vibration produces an ultrasound wave
- Backing material around crystals dampen oscillations so not oscillating between end of transmission and start of received pulse
Why pulses of piezoelectric crystals short?
Crystals acts as transmitter and receiver can’t be oscillating whilst receiving US
Properties of Amplitude scan and where used
Got one plane of pulsing light hence measure depth
Used In eye
Properties of Brightness Scan and where used??
Whole array of transducers creates a 2D image
Used for foetus scans
Intensity definition
Power per unit cross sectional area
