The basic principles

Magnetic resonance imaging (MRI) makes use of the magnetic properties of certain atomic nuclei. An example is the hydrogen nucleus (a single proton) being present in water molecules, and therefore in all body tissues. The hydrogen nuclei behave like compass needles that are partially aligned by a strong magnetic field in the scanner. The nuclei can be rotated by the use of radio waves, and they subsequently return to equilibrium. While the nuclei still oscillate in the magnetic field, they emit a radio signal. This is detected using antennas (coils) and can be used for making detailed images of the body tissues. Unlike some other medical imaging techniques, MRI does not involve radioactivity or ionising radiation. The frequencies used (40-130 MHz) are in the normal radiofrequency range, and there are no known effects on the human body. Very detailed images can be made of soft tissues such as muscle and brain.The MR signal is sensitive to a broad range of influences, such as nuclear mobility, molecular structure, proton density, flow, diffusion and magnetic environment. MRI is consequently a very flexible technique, that allows for the measurement of both structure and function.

Further information on MRI techniques

Illustration from the course notes: MR Image formation using k-space description. Images are reconstructed by adding phase-roll patters in proportion to their similarity with the subject in the scanner.

A thorough introduction to many magnetic resonance techniques written in connection with teaching is available (~45 pages) as well as corresponding handouts for tutorials given at the Technical University of Denmark.  A locally developed graphical Bloch simulator made for demonstrating basic concepts of NMR/MRI also plays an important role in the lectures. The software and movies illustrating its use can be found at http://www.drcmr.dk/bloch. Additional educational material is provided at http://www.drcmr.dk/MR

Information in Danish

The DRCMR is located in Denmark, and some additional material is provided in Danish:

• Brief introduction to  Magnetic Resonance Imaging with examples.
• A longer text introducing MRI basics.