Physics Principles of Diagnostic Ultrasound

Question 1

Describe attenuation

Answer 1

As ultrasound waves travel through tissue it becomes progressively weaker

Question 2

How do we calculate attenuation?

Answer 2

a=(db/cm)xd

Question 3

As amplitude is decreased, what happens to intensity?

Answer 3

It decreases

Question 4

If there is an increase in frequency, what happens to attenuation?

Answer 4

It increases

Question 5

What is transverse?

Answer 5

Medium moves perpendicular to direction of the wave

Question 6

What is longitudinal?

Answer 6

Medium moves parallel to the wave

Question 7

What is compression?

Answer 7

Transducer moves towards the body and compresses tissue
*highest pressure of soundwave

Question 8

What is rarefaction?

Answer 8

Transducer moves away from the body and decompresses tissue
*smallest point of pressure of soundwave

Question 9

What is propagation speed?

Answer 9

The speed of the ultrasound waves through tissue

Question 10

What speed does the machine think soft tissue is?

Answer 10

1540m/s

Question 11

What is the frequency of sound waves?

Answer 11

Number of times per second

Question 12

What is amplitude?

Answer 12

Peak pressure

Question 13

What is intensity?

Answer 13

Power per unit in the wave

Question 14

As frequency increases what happens to the wavelength?

Answer 14

It decreases

Question 15

As the wavelength decreases what happens to the resolution?

Answer 15

It is enhanced

Question 16

What is the wavelength?

Answer 16

The wavelength is the distance between one peak of the wave and the next peak

Question 17

What is absorption?

Answer 17

Acoustic energy lost in the medium because it is converted into heat

Question 18

What 3 things is absorption determined by?

Answer 18

1) viscosity of the medium
2) relaxation time of the medium
3) frequency of the sound

Question 19

What is propagation speed?

Answer 19

Speed of sound affected by the density and elasticity of the medium it is travelling through

Question 20

Is propagation speed higher in bone or air?

Answer 20

Bone

Question 21

What is reflection?

Answer 21

Interaction of ultrasound with relatively large and smooth surfaces

Question 22

What 3 things does reflection depend on?

Answer 22

1) acoustic properties of two tissues
2) angle of incidence
3) reflecting surface

Question 23

What is specular reflector?

Answer 23

strong echoes

Question 24

What is non-specular reflector?

Answer 24

Weak echoes

Question 25

What is the reflection coefficient equation?

Answer 25

R=reflected intensity/incident intensity

Question 26

What type of reflect occurs at a perpendicular incidence?

Answer 26

No reflection

Question 27

What reflection occurs at tissues with a large impedance difference?

Answer 27

Full reflection

Question 28

When does scattering occur?

Answer 28

At interaction of small structures such as RBC & capillaries

Question 29

What is Rayleigh scatters?

Answer 29

Reflection of energy equally in all directions

Question 30

If frequency is increased, what happens to scatter?

Answer 30

It increases

Question 31

Describe acoustic impedance

Answer 31

Density of the medium and speed at which sound travels through the medium

Question 32

What is a Rayls?

Answer 32

kg/m2s
The unit of specific acoustic impedance

Question 33

What is the equation of acoustic impedance?

Answer 33

z=pxc
(tissue density x propagation speed)

Question 34

Define amplitude?

Answer 34

Strength, peak pressure

Question 35

What is the equation for amplitude reflection coefficient?

Answer 35

R=Z2-Z1 / Z2+Z1
(z1=acoustic impedance on proximal side of interface)
(z2=acoustic impedance on distal side of interface)

Question 36

What is refraction?

Answer 36

Bending of the soundwave

Question 37

What are the two conditions required for refraction?

Answer 37

1)incident sound wave must not be perpendicular
2)speed of sound must be different on the two sides of the interface

Question 38

What is snell’s law equation and what does it predict?

Answer 38

predicts the direction of a transmitted sound beam when refraction occurs.

Sin01/c1=sin0t/C2

Question 39

If there is a critical angle, what angle is the transmitted angle?

Answer 39

90 degrees

Question 40

If the transmitted angle is bigger than the critical angle what happens?

Answer 40

Total reflection

Question 41

What is diffraction?

Answer 41

Occurs when a wave passes through an opening or around a barrier

Question 42

What is penetration depth?

Answer 42

At some depth the attenuation is so great the returning US echoes are too weak to be detected

Question 43

What is the round trip attenuation equation?

Answer 43

(ax2pxf)

Question 44

What is the equation for calculating the attenuation when there is a reduction in the intensity?

Answer 44

dB=10 log I/I0

Question 45

What is the difference between speed and velocity?

Answer 45

Speed refers to an object’s change in distance with respect to time, whereas velocity refers to an object’s change in displacement with respect to time.

Question 46

What is compression and rarefaction?

Answer 46

compressions are regions of high pressure due to particles being close together. rarefactions are regions of low pressure due to particles being spread further apart

Question 47

What does the following equation show?
λ = c/f

Answer 47

the wavelength of the
ultrasound (λ) can be calculated by dividing the ultrasound propagation
speed (c) by the ultrasound frequency (f).