Medical Physics

Question 1

Explain the main principles behind the use if nuclear magnetic resonance imaging (NMRI) to obtain diagnostic information about the internal body structures.

Answer 1

1. A strong uniform magnetic field is used that causes the nuclei to precess and rotate about the field.
2. Radiofrequency pulses are emitted at the Larmor frequency which causes resonance.
3. As the nuclei deexcite, they release pulses which are detected and processed.
4. A non-uniform magnetic field is used that allows the position of the nuclei to be located and it also allows for the location of detection to be changed.

Question 2

Suggest the causes as to why there can be a lack of sharpness in an X-ray image.

Answer 2

Scattering of the X-ray beam/ no lead grid
lack of collimation of beam/ aperture is large
anode area is large
beam PD is low/ low photon energy

Question 3

What is the formula for Intensity attenuation?

Answer 3

I = Io * e^(-lamba*X)

Question 4

What does the contrast of an X-ray image mean?

Answer 4

The difference in degrees of blackening between structures.