MIRA2015 Lecture Notes - Lecture 4: Free Induction Decay, Larmor Precession, Spin Echo

• School: Curtin University
• Department: Medical Imaging, Radiology & Radiography
• Course: MIRA2015
• Professor: Cat Kealley

Document Summary

Transmits to the nuclei: produces oscillating field in resonance with nuclei, causes the torque that tips the magnetisation out of equilibrium into the transverse plane. Same coil receives the signal: detects electromotive force/oscillating voltage as nuclear magnetisation precesses around in the coil, with signal gradually decaying away with time (free induction decay) as spins come back to thermal equilibrium. Main field (b0) coils: principal magnet windings plus superconducting shim and shield coil. Patient coils: detect mr signal or transmit/receive. Cross-section of a superconducting scanner showing position of superconducting and resistive shim coils. Also, two different patient coils: a receive only spine coil array, and a transmit/receive knee coil. Rf coils may serve as transmitters, receivers, or both. Rf coils generate oscillating/rotating magnetic field (b1) perpendicular to static main magnetic field (b0). If b1 oscillation matches natural precession of nuclear spins near larmor frequency, energy is deposited into spin system -> change in net alignment.