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Dipoles to Images Main Field – B0 µ Magnetic Moment M z M xy S (t) ⇥ S k I ( x) Bulk Magnetization Transverse Magnetization Received Signal k-space signal Image } B 0 } B 1 } Coil } Gradients } FFT Radiology Main Field (B0) - Principles Magnetic Dipoles & Larmor • B0 is a strong magnetic field – 1.5T, 3.0T, 7.0T, etc. – Z-oriented B 0 = B 0 k • B0 forces M to precess – Larmor Equation • B0 generates M – More B0, more M ⇥ = M = B NX total n=1 µ n Radiology Radiology Movie from Don Plewes
Bulk Magnetization Zeeman Splitting M = NX total n=1 µ n N S N S S N S N N S N S N N S S N N S N S N S S N N N E =+ 1 N N N 2 B 0 E = 1 2 B 0 N S S N N S S S N S N S N S S S N S N S B 0 is o B 0 is on } } Radiology Ntotal=0.24x10 23 spins in a 2x2x10mm voxel Radiology N = Spin-Up State, Low Energy N = Spin-Down State, High Energy N S N S Zeeman Splitting N N ⇥ ⇥ hB 0 N total 2KT = 42.58 ⇤ 10 6 Hz/T h = 6.6 ⇤ 10 34 J · s [Planck’ Constant] T = 300K (room temperature) K = 1.38 ⇤ 10 23 J/K [Boltzmann Constant] B 0 = 1.5T RF Pulses – B1 N ⇥ N ⇤ ⌅ 42.58 ⇤ 106 · 6.6 ⇤ 10 34 · 1.5 N total 2 · 1.38 ⇤ 10 23 · 300 Radiology ⌅ 4.5 ⇤ 10 6 ~4.5ppm @ 1.5T 09
Page 1: Introduction to MRI Daniel B. Ennis
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 and 16: T2 Relaxation • Transverse or spi
Page 17 and 18: What are echoes What are echoes •
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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