Module 1 Physics

Question 1

What is the equation for medium impedance? (and measurement)

Answer 1

AI = density x velocity (raylz)

Question 2

What is the speed of EM waves?

Answer 2

3.0x10^8 m/s = FAST

Question 3

What does it mean to be ionizing?

Answer 3

it can knock of electrons from atoms resulting in free radicals in the body which is not good

Question 4

EM waves from short wavelength/high freq –> long wavelength/lowfreq

Answer 4

gamma ray, x-ray, UV, visible, infrared, microwave, radio

Question 5

What are the acoustic variables?

Answer 5

1. Pressure
2. Density
3. distance

Question 6

Diagnostic Ultrasound Hz levels

Answer 6

1-15 MHz

Question 7

What are the 4 sound wave parameters

Answer 7

1. Freq and period
2. Wavelength
3. Amplitude (power/intensity)
4. Prop. velocity

Question 8

Define stress and strain

Answer 8

Stress - a change in pressure applied

Strain - % of change in volume from the stress

Question 9

What is an acoustic variable

Answer 9

A mechanical change in a medium

Question 10

What happens when we increase our overall gain?

Answer 10

we are increasing the voltage of already returned echoes that have been converted back into the electrical signal = increased amplitude = increased brightness and contrast

Question 11

What is the measurement of attenuation? Why?

Answer 11

dB - large non linear energy changes occur

Question 12

Relationship between frequency and amplitude?

Answer 12

No direct relationship but related through attenuation. Increase freq = increase attenuation = decrease amplitude

Question 13

What has the longest pulse duration?

Answer 13

Continuous wave - continuous never stops

Question 14

Smallest FOV

Answer 14

Sector

Question 15

Lowest DF vs Highest DF

Answer 15

Lowest - B mode

Highest - Continuous wave, has a DF of 100

Question 16

What is duty factors relations to bioeffects

Answer 16

Increased DF = increased bioeffects

Question 17

Why wont we lose a lot of energy when going through skin even though it has a high attenuation?

Answer 17

because its so thin

Question 18

What is the attenuation calculation

Answer 18

medium coefficient x frequency x distance (2)

Question 19

What does 3dB of intensity attenuation represent?

Answer 19

1/2

Question 20

What does 6dB of amplitude attenuation represent?

Answer 20

1/2

Question 21

3 types of reflectors

Answer 21

Specular - large, flat, and smooth
Scatter - small and rough
Rayleigh scatter - very small

Question 22

Specular reflections are highly dependent on what? And therefore independent from what?

Answer 22

highly angular dependent, and frequency independent

Question 23

What could cause a loss of the bright reflection in a specular reflector?

Answer 23

loss of the perpindicular angle (angular dependent)

Question 24

Scatter reflectors are dependent on what?

Answer 24

frequency dependent - increase freq = smaller wavelength = smoother reflector

Question 25

degree of rayleigh scatter =

Answer 25

f^4

Question 26

What kind of frequency does Doppler use?

Answer 26

Very low frequency to scan blood as an increased freq would increase friction and therefore loss of energy to heat and absorption so wouldnt be able to see rayleigh

Question 27

Impedence formula

Answer 27

impedence = density x prop speed

Question 28

What is the Z value of Crystals

Answer 28

38 MRayls

Question 29

Z value of tissue?

Answer 29

2 MRayls

Question 30

In what cases will retraction occur

Answer 30

- an oblique angle of incidence | - when the speeds at the boundary are different on either side

Question 31

What is the unit of amplitude

Answer 31

Pascals (Pa)

Question 32

What is the unit of power

Answer 32

Watts (W) or mW

Question 33

Relationship between power and amplitude

Answer 33

Power= amplitude squared

Question 34

Relationship of power and intensity

Answer 34

equal Power = intensity therefore intensity also = amplitude squared

Question 35

What is the Duty Factor

Answer 35

Displays the % of time the ultrasound system is producing sound Its is the reinging period over the ringing and listening period PD/PRP

Question 36

what does dampening the sound beam do?

Answer 36

it reduces the length of the "ring" therefore decreases the SPL

Question 37

What is the unit of density

Answer 37

kg/cm3

Question 38

What is snells law?

Answer 38

describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media (refraction)

Question 39

What is the total attenuation equation? How do you get this to amplitude form

Answer 39

medium coefficient (dB/cm-Mhz) X freq (MHz) X Distance (2) (cm) Amplitude form - dB (attenuation amount) X 20 X log (Af/Ai)