An introduction to the series, followed by an introductory video courtesy of Sir Paul Callaghan: What is NMR and how does it work?
Further videos explaining the principles of nuclear magnetic resonance - how the intrinsic spin of certain atomic nuclei interacts with applied magnetic fields to yield useful information.
Videos showing the anatomy of a miniature scanner, a basic NMR experiment, why shimming is important for NMR (and MRI), how and why a spin echo works, and the relaxation of spins back towards their ground state.
Mathematics of oscillations: an introduction to imaginary and complex numbers, and frequency and phase.
An introduction to the Fourier transform - what it does and how it works. Includes a description of Fourier analysis, and explains conjugate variables and (Fourier) domains.
Practical issues arising from the use of the Fourier transform in MRI:
- Fourier pairs
- Convolution in pictures
- Time-decaying signals
- Finite acquisition periods and signal clipping
- The Nyquist frequency
Magnetic field gradients and one-dimensional MRI:
- A magnetic field alters the local resonance frequency
- Acquiring an MR signal in the presence of a gradient
- One-dimensional imaging in pictures
- An explanation of how GRE works
- The benefits of acquiring a gradient echo
- How slice selection works
- Using a GRE with slice selection
K-space - conjugate variables redefined:
- Conjugate variables revisited
- Representing pictures in reciprocal space
- One-dimensional imaging as seen in k-space
- Tracing kx through time
- Getting off axis (into 2D)
K-space in two dimensions:
- A useful pictorial representation of imaging pulse sequences
- The goal revisited
- Gradients along the x direction (again)
- Gradients along the y axis
- The equivalence of frequency and phase encoding
- Gaining an intuitive understanding of phase encoding
Resolution and field-of-view as seen in k-space:
- Spatial frequencies in k-space: what lives where?
- Why does the signal level change across k-space?
- Defining parameters in k-space to yield the image you want
- Image field-of-view
- Image resolution
The echo planar imaging (EPI) pulse sequence:
- Gradient echo EPI pulse sequence
- Processing 2D k-space for EPI
- Signal dropout
A tour through a real EPI pulse sequence:
- Interpreting what you see
- Fat saturation
- Crusher gradients for fat suppression
- Crusher gradients to eliminate signal from prior slice excitations
- Slice selection
- N/2 ghost correction echoes
- Phase encode dephasing gradient
- Readout gradient echoes
- Relative duration of functional modules in the EPI sequence
Partial Fourier EPI.
To come: Ramp sampling for EPI.
To come: Eddy currents.
To come: Crusher/spoiler gradients in EPI.