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Flashcards in Ultrasound Deck (18)
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1

Acoustic Dependance

Property of material that determines amount of sound reflected back

2

What's acoustic dependance affected by?

Density and Speed of sound

3

Do we want a small difference of acoustic Dependance or a large difference?

Ultrasound is reflected more if AD difference of material is high

4

Acoustic Dependance equation?

Z=PV
Z- AD (kgms-1)
P-Density (Kgm-3)
V- velocity (ms-1)

5

Velocity Equations?

V=(k/P)^1/2
K- bulk elastic modulus of material
P- density (Kgm-3)

V=1/2mv^2

6

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

7

Advantages Ultrasound

-cheap
-portable
-In real time/ moving image
-Non- Invasive
-No known hazards

8

Ultrasound disadvantages

-low resolution
- Can't be used on some parts of the body e.g. BRAIN, LUNGS, BONES

9

Coupling gel where used?

Between probe and skin

10

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

11

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

12

Why pulses of piezoelectric crystals short?

Crystals acts as transmitter and receiver can't be oscillating whilst receiving US

13

Properties of Amplitude scan and where used

Got one plane of pulsing light hence measure depth
Used In eye

14

Properties of Brightness Scan and where used??

Whole array of transducers creates a 2D image
Used for foetus scans

15

Intensity definition

Power per unit cross sectional area

16

Attenuation definition

Reduction in intensity through a medium

17

What causes attenuation?

-Absorption/ scattering of sound before reaches desired area
-Diffraction of sound

18

Equation for attenuation

10logI/I0

I- intensity left over
I0- intensity started with