Week 11 and 12 quiz!

Nuclear magnetic resonance and relaxation + MRI instrumentation and safety

Magnetic Resonance Imaging

• Principle of nuclear magnetic resonance

• Produces cross-sectional image

• visualises and analyses variety of tissue characteristics, blood flow and metabolic functions

• scans image without using ionising radiation but using interactions between magnetic fields, radio waves and atomic nuclei in the body

Nuclear Magnetic Resonance

• nuclei in a magnetic field absorb and re-emit electromagnetic radiation at radiofrequency energy called Larmor or resonance frequency

Why is MRI primarily applied to hydrogen?

1. One unpaired proton - able to interact to cause a magnetic moment

2. High sensitivity for NMR signal

3. High natural abundance in the body

Solenoid

current runs down solenoid and produces B0

B0

main static magnetic field

What does the strength of B0 determine?

determines the amount of magnetisation we have

Magnetic moment μ

process of seeking to align with an externally applied magnetic field (B0)

Spin

intrinsic angular momentum of a particle

• e.g., protons, neutrons, electrons and unpaired protons all have spin value of 1/2

Magnetic fields B0

precession → spin magnetic moments move around the field on a cone (around and around)

spin behaves in this way because they possess angular momentum with magnetic moment

Torque by B0

vector force, acting on an object to twist it to align along the direction of the magnetic field

• generated by forcing the material to align with magnetic field lines

Larmor precession

angular momentum resists change instead of twisting, it traces out a circle

MRI scanner schematic

intense magnetic field generated by superconductive magnet that doesn’t vary with time and nearly has the same field strength throughout the anatomical region to the examined

Shimming

make magnetic field (b0) more homogenous