intro

Question 1

Why is MRI important

Answer 1

MRI does not use x-rays.

MRI can lead to early detection and treatment of disease.

The MRI images are extremely precise.

Is sensitive for a variety of diseases, cancers, tumours, injuries and other abnormalities.

Question 2

How does MRI work

Answer 2

A Large Magnet
Radio waves
Special Receiver Coils
A powerful Computer

Question 3

The Receiver Coils

Answer 3

Specific coil for each region.
The coil measures the energy released by the protons as well as the time it takes to return to their aligned positions.
Different coils with different elements/receivers.

Question 4

The fundamentals of MRI can be explained via

Answer 4

quantum physics as well as classical physics.

Question 5

3 Forces:

Answer 5

Motion
Magnetism
Charge

Question 6

Quantum Theory

Answer 6

Describes discrete quantities of energy.
Hydrogen nuclei possess discrete quantities of energy of populations termed high and low.

Low-energy nuclei align their nuclei to the external magnetic field (spin-up) nuclei.

High-energy nuclei go in the opposite direction and are called (spin-down) nuclei.

Question 7

NMV

Answer 7

The Net Magnetic Moment of hydrogen

Question 8

Precession

Answer 8

Each hydrogen nucleus is spinning on its own axis.

Bo has got an influence on this spin, in that it produces an addition spin or wobble of the magnetic moments of hydrogen around the external applied magnetic field.

This secondary spin is called precession and it follows a circular path around Bo.

Question 9

The Larmor equation

Answer 9

ω = Bo x γ
Gyro-magnetic ratio is constant and expresses the relationship between the angular momentum and the magnetic moment of each MR active nucleus.

Question 10

Resonance

Answer 10

“Resonance is an energy transition that occurs when an object is subjected to a frequency the same as its own” MRI at a glance (2010)

When this process happens to a nucleus, it gains energy from the external force. The frequency delivered must be exactly the same as the precessional frequency of the nucleus otherwise resonance does not occur.

The energy (precessional frequency of hydrogen) at all field strengths in clinical MRI corresponds to (RF) radio frequency band of the electromagnetic spectrum.

Question 11

Excitation

Answer 11

Excitation is the term used when resonance occur if an RF pulse is applied that causes resonance.

There is an increase in spin-up nuclei because of the absorption of energy and if the field strength increases the energy difference between the two populations (spin-up and spin-down) also increases.
Example of excitation

Question 12

What needs to happen for resonance of hydrogen to occur?

Answer 12

RF must be applied at exactly the Larmor frequency of hydrogen.

Question 13

What is the result of resonance?

Answer 13

Magnetism in the transverse plane that is

in phase and precesses at the Larmor frequency.

Question 14

The Free Induction Decay (FID) Signal

Answer 14

Recovery = when the amount of magnetization in the longitudinal plane gradually increases.

Decay = when at the same time, but independently the amount of magnetization in the transverse plane gradually decreases.

Question 15

Relaxation

Answer 15

During this process the hydrogen give up their absorbed RF energy and their NMV returns toB0.
Independently, but at the same time the magnetic moments of hydrogen lose coherency due to dephasing.

Question 16

T1 Recovery

Answer 16

When nuclei give up their energy to the surrounding environment (lattice) it is called: spin lattice relaxation.

It is the time it takes for 63% of the longitudinal magnetization to recover in the tissue.

Question 17

T2 Decay

Answer 17

When nuclei exchange their energy with their neighboring nuclei it is termed spin-spin relaxation and results in the loss of coherent transverse magnetization in the transverse plane.

It is the time it takes 63% of the transverse magnetization to be lost.