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T2 * Relaxation T2 * Relaxation 1 T ⇤ 2 1 T ⇤ 2 = 1 T 2 + 1 T 0 2 Irreversible Losses Reversible Losses Irreversible Losses Reversible Losses Radiology = 1 T 2 + B 0 Radiology 1 T ⇤ 2 T2 * Relaxation = 1 T 2 + 1 T 0 2 Irreversible Losses Reversible Losses + 1 T D 2 Irreversible Losses + ··· Percent Signal [a.u.] 100 75 50 25 T2 * vs T2 T2 – 125ms T2 * – 90ms T2*
What are echoes What are echoes • Two-sided NMR signals – First half from re-focusing – Second half from de-phasing • Spin Echoes – Arise from multiple RF-pulses • Gradient Echoes – Arise from magnetic field gradient reversal • Line of k-space 48 Radiology Why echoes Pulse Sequences • Free Induction Decay – NMR signal immediate after an RF pulse – Signal decays rapidly • T2 * (
Page 1 and 2: Introduction to MRI Daniel B. Ennis
Page 3 and 4: Bulk Magnetization Zeeman Splitting
Page 5 and 6: Dipoles to Images Coils µ Magnetic
Page 7 and 8: Gradients MRI Instrumentation • G
Page 9 and 10: What is k-space 1D k-space • Spat
Page 11 and 12: Center What is k-space Contrast Wha
Page 13 and 14: 1952 Nobel Prize in Physics “for
Page 15: T2 Relaxation • Transverse or spi
Page 19 and 20: Spin Echo Spin Echo RF 90° 180° R
Page 21 and 22: Spin Echo - Contrast Spin Echo - Va
Page 23 and 24: Radiology 180° Inversion Recovery
Page 25 and 26: Basic Gradient Echo Sequence TR TE
Page 27 and 28: Spoiled GRE & Ernst Angle 90° 180

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