MRI Basic Principles and Atomic Structure

MRI Basic Principles

• MRI uses the magnetic properties of atomic nuclei to create images.
• The presentation outlines the principles, starting with atomic structure.
• The presentation includes information on atomic structure, motion of atoms, MR active nuclei, Faraday's law, proton alignment, net magnetization vector, precession, the Larmor equation, precessional phase, resonance, MRI signal, and FID (free induction decay).

Atomic Structure

• All matter consists of atoms.
• Atoms combine to form molecules.
• Key elements in the human body include hydrogen, oxygen, carbon, and nitrogen.

Composition of Atoms

• Atoms have a central nucleus with orbiting electrons.
• The nucleus contains protons (positive charge) and neutrons (no charge).
• Electrons (negative charge) orbit the nucleus.

Mass and Size of Nucleus

• The nucleus is small but contains most of the atom's mass.
• The nucleus is composed of protons and neutrons (nucleons).
• The nucleus occupies a tiny fraction of the atom's volume.

Motion in the Atom

• Atoms have electrons spinning on their axis, orbiting the nucleus, and the nucleus spinning on its own axis.
• Protons along with neutrons can have a net spin.

MR-Active Nuclei

• Certain atomic nuclei have a property called "spin", which can be aligned in the presence of a magnetic field.
• 1H (hydrogen), 13C (carbon), 15N (nitrogen), 17O (oxygen), 19F (fluorine), and 23Na (sodium) are examples of MR-active nuclei.
• They have specific gyromagnetic ratios for different nuclei which are relevant to imaging.

The Hydrogen Nucleus

• Protium, a hydrogen isotope, is the most commonly used MR-active nucleus in MRI.
• It has a single proton and no neutrons, leading to a relatively large magnetic moment, which is valuable for imaging purposes.

Faraday's Law of Electromagnetism

• A magnetic field is created by a moving charged particle. This principle is fundamental in MRI.
• A charged moving particle (proton) creates both an electric and magnetic field

Alignment

• In the absence of a magnetic field, the magnetic moments of hydrogen nuclei are randomly oriented.
• When in a strong magnetic field, the nuclei align either parallel or antiparallel to the field.
• Parallel alignment has lower energy; antiparallel alignment has higher energy.

Net Magnetic Vector (NMV)

• Parallel and antiparallel alignments cause an overall magnetization vector, also known as NMV.
• The NMV is proportional to the field strength.

Precession and Precessional (Larmor) Frequency

• The speed at which magnetic moments rotate around the main magnetic field (B0).
• The Larmor equation (WO = γB0) describes the precessional frequency in relation to field strength (B0) and gyromagnetic ratio(γ).

Precessional Phase

• "In-phase" describes coherent spins.
• "Out-of-phase" describes incoherent spins.

Resonance

• Resonance occurs when the oscillating frequency of external RF pulse is close to the nucleus's natural frequency (Larmor frequency).
• Nuclei gain energy from the RF pulse, causing them to generate measurable signals

MRI Signal

• RF pulse causes the magnetization vector to tilt and move into planes.
• Dephasing is a phenomenon where the signal loses coherence due to variations in the magnetic field.
• The free induction decay (FID) signal is the initial signal that decays over time.

The Free Induction Decay (FID) signal

• The decay of the magnetic signal after the removal of the RF pulse which shows the free precession of nuclei in the magnetic field.
• This signal is influenced by the magnetic field's inhomogeneities and interactions between spins.

This quiz explores the fundamental principles of MRI, focusing on atomic structure and the magnetic properties of atomic nuclei. Key topics include the motion of atoms, MR active nuclei, and the mechanics behind MRI signal generation. Test your understanding of how atomic structure relates to MRI technology.