A Selection of Slides on MRI Basics

Mark S. Cohen, Ph.D.

Feel free to reprint these slides for educational purposes. For commercial use, please contact Mark Cohen.

Thanks for your interest.

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The Slides:

The slides are organized rather loosely by topic. In some cases the title and contents are a weak match.

Basic MR Principles
The Larmor Relation Magnetic Field Gradients Magnetic Susceptibility (1) Magnetic Susceptibility (2)
The Resonance Phenomenon RF Pulses convert between longitudinal & transverse magnetization Partial Saturation Sequence In-Phase precession
Out of Phase Precession Sampling Time and Gradient Requirements Signal Losses in Inhomogeneous Fields Signal Losses from Spin Dephasing
The Spin Echo Sequence T1 and TR What is T1? T2 and TE
What is T2? Making an MR Image Some Fourier Transform Pairs
Fourier transform Pairs The Transverse Relaxation Rate Proton Responses to Magnetic Fields Free Proton Orientations
Protons in an Applied Field The Spin Property of Protons The Hahn Echo (1) The Hahn Echo (2)
Imaging System Components Calculating Imaging Time Effects of a 90 degree pulse Magnetization after a 90 degree pulse
The Chemical Shift Artfifact Contrast Emphasis Contrast vs. TR and TE Contrast vs. T1/TR
Contrast vs. T2/TE Conventional MRI Determinants of MR Imaging Time Fourier Transform of a Square Wave
The Slice Selection Process Spatial Encoding Summary Spin Decay



Image Quality
Factors affecting MR image quality Determinants of MR Imaging Time The Chemical Shift Artfifact Contrast to Noise Ratio vs. TE
Contrast to Noise Ratio vs. TR Contrast to Noise Ratio Field of View vs. SNR Effects of FOV reduction
TE and SNR TR and SNR Effects of Longer TE Effects of Longer TR
Longitudinal Relaxation Matrix Size Noise in MR Images The MR Signal is Refractory
The MR Signal is Transient Averaging (NEX) vs. SNR Origin of the Chemical Shift Artifact Image Quality Outline
Effects of Reduced Voxel Volume Pickup of signal and noise Optimal Slice Order Slice Thickness vs. SNR
SNR and Voxel Size Determinants of SNR T1 and T2 are Correlated Interslice Crosstalk
TR and Image Quality (1)



K-Space
K-Space Properties of K-Space Slice Selection in K-Space K-Space Filling Strategies
K-Space Trajectory (1) K-Space Trajectory (2) Low k values encode large features High k-space values encode small features
Regular Sampling of k-space Equivalent k-space Strategies (1) Equivalent k-space Strategies (2) Spin Echo Slice Selection



Fast Imaging
Why does MRI Take so long? Calculating Imaging Time Signal and Flip Angle Magnetization Loss vs RF Flip Angle
Flip Angles and Contrast Flip Angle vs. TR and T1 contrast SNR vs. TR/T1 The FLASH Sequence
The FLASH magnetization cycle FLASH Timing Diagram The Gradient Echo Sequence Magnetic Susceptibility (1)
Magnetic Susceptibility (2) T2 and T2* The is no 180 degree pulse in FLASH Sequences TR and Flip Angle Combinations
Turbo FLASH Sampling time and Gradient Requirements FISP timing diagram The GRASS (FISP) magnetization cycle
The CE-FAST Sequence The Instascan (EPI) k-space trajectory The Instascan Pulse Sequence The RARE sequence
Spin Echo Instascan (EPI) The Spin Echo Sequence The SSFP Sequence Fast Imaging Outline



Surface Coils
Surface Coil Sensitivity (1) Surface Coil Sensitivity (1) What is a Surface Coil? Surface Coil Advantages
Disadvantages of Surface Coils



Functional MRI
Consequences of Brain Activation Deoxyhemoglobin Effects of Increased Flow

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