MRI Basic Principles

Study Notes

MRI uses strong magnetic fields and radio waves to generate images of the body's internal structures.
The presentation outlines the fundamental concepts of MRI, including atomic structure, motion of atoms, MR-active nuclei, Faraday's Law, proton alignment, and the Larmor equation.

All matter is composed of atoms.
Atoms combine to create molecules.
Key elements in the human body include hydrogen, oxygen, carbon, and nitrogen.
Atoms have a central nucleus surrounded by orbiting electrons.
The nucleus contains protons (positive charge) and neutrons (no charge).
Electrons (negative charge) orbit the nucleus.
The nucleus is tiny but contains most of the atom's mass.
It is composed of protons and neutrons.
The nucleus occupies a small fraction of an atom's volume.
Atoms have three types of motion: electrons spinning, electrons orbiting the nucleus, and the nucleus itself spinning.

Specific isotopes of certain elements are MR-active.
Hydrogen (1H) is abundant and crucial in MRI due to its high natural abundance and large magnetic moment from a single proton in its nucleus.
Other MR-active nuclei include 13C, 15N, 17O, and 19F.
Each nucleus has specific properties, such as nuclear spin.
Different nuclei have different gyromagnetic ratios and frequencies.

In the absence of a magnetic field, the magnetic moments of hydrogen nuclei are randomly oriented.
When placed in a strong external magnetic field (BO), hydrogen nuclei align parallel or anti-parallel to the field.
Parallel alignment has low energy and is favoured.
Anti-parallel alignment has high energy.
The excess of nuclei aligned parallel to BO results in a net magnetic vector (NMV).

The speed at which nuclei precess around the external magnetic field is called precession frequency.
The frequency (wO) is proportional to the strength of the external magnetic field (BO) and the nucleus' gyromagnetic ratio (γ).
Larmor equation: w0 = γBO.
Precessional frequencies are relevant for different nuclei and field strengths.