Components of the MRI Machine
📌 The main coil generates the B₀ (main magnetic field) along the longitudinal (Z) axis, determined by the number of coils and current flow, requiring superconductors like Niobium-Titanium alloys cooled by liquid helium (below 4 K).
⚙️ Shims (passive or active) are used to manipulate the main magnetic field, aiming for perfect homogeneity along the Z-axis to ensure accurate signal localization.
⚡ Gradient coils (X, Y, and Z planes) create differential magnetic field strengths along the axes by superimposing fields onto B₀, which varies the precessional frequency of hydrogen protons—a foundation for spatial encoding.

The Role of the Radio Frequency (RF) Coil
📡 The RF coil generates a magnetic field perpendicular (transverse/XY plane) to the main field, designed to match the precessional frequency of specific hydrogen protons.
🧲 When the RF pulse frequency matches the proton's precessional frequency, protons gain energy, fan out, and become in phase, creating a net magnetization vector that flips into the transverse plane (e.g., a 90-degree flip angle).
📶 This movement of the net magnetization vector into the transverse plane allows the measurement of the signal used to ultimately generate the MRI image, enabling techniques like slice selection.

Superconductivity and Quenching
🌡️ Superconductivity occurs when certain materials are cooled below their critical temperature (around 4 K), causing an abrupt drop in resistance, allowing for massive current flow to sustain strong magnetic fields.
⚠️ If the temperature exceeds 4 K, resistance reappears, generating heat; the liquid helium vaporizes, expands, and is released into the room in a controlled safety process called quenching.

Key Points & Insights
➡️ The strength of the B₀ field directly influences the precession frequency of hydrogen protons; a stronger field means faster precession.
➡️ Gradient coils change the magnetic field strength along the Cartesian axes (not direction), causing differing precessional frequencies necessary for spatial encoding.
➡️ The RF pulse is crucial for flipping the net magnetization vector from the longitudinal to the transverse plane to measure the MR signal.

📸 Video summarized with SummaryTube.com on Dec 25, 2025, 17:59 UTC