Thermography

Question 1

A black body is

Answer 1

is a theoretical perfect absorber, which absorbs radiation of all wavelengths falling on it.
It reflects no light at normal temperatures and thus appears black. (Both an absorber and a reflector)

Question 2

Explain temperature radiation

Answer 2

The radiation is absorbed in the walls of the cavity
This causes a heating of the cavity walls
Atoms in the walls of the cavity will vibrate at frequencies characteristic of the temperature of the walls
These atoms then re-radiate the energy at this new characteristic frequency
the best radiation emitter of all wavelengths
It is also known as “temperature radiation”.

Question 3

The intensities of the various wavelengths of radiation emitted is…

Answer 3

temperature dependent

Question 4

Wien’s Displacement Law talks about how…

Answer 4

when the temperature of a black body radiator (surface) increases, the overall radiated energy increases, and the peak of the radiation curve moves to shorter wavelengths.

The peak wave-length of the curve varies with the temperature of the radiating surface. The lower the temperature the longer the peak wavelength.

Question 5

The mid IR region…

Answer 5

radiates most heat and areas of elevated temperature will radiate at a different peak wavelength than those areas at normal temperature.

Question 6

For a surface area A maintained at a temperature T, the Stefan-Boltzmann Law states:

Answer 6

H=eoAT^4

Question 7

Emissitivity describes

Answer 7

how near the surface is to being a perfect “black body radiator”.

Question 8

What does e =1 mean?

Answer 8

e = 1 means perfect heat radiating surface (black matt surface)

Question 9

What does e = 0 mean?

Answer 9

e = 0 means poor heat radiating surface (highly polished, silvered surface)

Question 10

True or False: e = 0.97 for human skin (regardless of ethnicity) in the mid IR region.
The amount of heat radiated depends sensitively on the T4 term.

Answer 10

True

Question 11

How can you monitor surface temperature?

Answer 11

Can monitor surface temperature by measuring :
1. Variations in peak wavelength across the surface of the patient. (Spectral Measurement)
2. Variations in the rate of heat radiation across the body (Bolometric Measurement)

Question 12

Thermography results are disappointing when it comes to

Answer 12

screening for breast tumours due to the increased metabolic activity within the rapidly dividing cells.

Question 13

What is a false positive?

Answer 13

is where you receive a positive result for a test, when you should have received a negative results.

Question 14

What is a false negative?

Answer 14

is where you receive a negative result for a test, when you should have received a positive results.