Microwave imaging

Question 1

What is the wavelength range of microwaves?

Answer 1

1 mm - 1 m

Question 2

What is the Rayleigh Jeans law?

Answer 2

Low frequency approximation of Planck’s law for black body radiation intensity as a function of frequency and temperature.

I~ (2 f^2 kT ) / c^2

Question 3

What are the two types of medical microwave imaging?

Answer 3

Passive - measure black body radiation

Active - Irradiate and measure scattered radiation

Question 4

How does passive microwave imaging work?

Answer 4

Measure intensity of radiation emitted by tissue.

I = e_eff * I_Rayleigh Jeans

Effective emissivity is a function of tissue dielectric constant, which provides contrast

Question 5

What is the effective emissivity a function of?

Answer 5

frequency
size of antenna
antenna permittivity
tissue permittivity

Question 6

What is the microwave waveband used in medical imaging?

Answer 6

microwaves:
300 MHz - 300 GHz
medical imaging:
500 MHz - 100 GHz

Question 7

Two use cases for medical microwave imaging in the research literature?

Answer 7

breast imaging
brain imaging

Question 8

Why is a lower wavelength used for brain imaging compared to breast imaging?

Answer 8

brain tissue is more attenuating

Question 9

Two challenges associated with medical microwave imaging?

Answer 9

Intensity drop-off at low frequency on black-body spectrum => low SNR

Impedance matching - coupling fluid can be used, but difficult to match tissue permittivity across wide spectrum