Basic principles of magnetic resonance imaging.

Magnetic resonance imaging (MRI) is a noninvasive imaging technique that is becoming more and more important in clinical cardiology. Physicians must understand the basic principles of MRI before reliable use in practice is possible. Therefore, we will give an introduction to basic MRI principles necessary to understand the difficulties of cardiac MRI. First the generation of a signal by the combination of a strong magnetic field, radiofrequency pulses, and temporary changes in the magnetic field is explained. Then, the processes of localization of different points in an image, resolution, and signal-to-noise ratio are highlighted. Finally, the influence of tissue characteristics such as T1 and T2 on the contrast of an image are discussed.