High field MRI: what's different?

High magnetic field strength is the basic precondition for high signal-to-noise-ratio (SNR) in magnetic resonance imaging (MRI) and thus also for good image quality, for detailed spatial resolution, and for fast image acquisition. With increasing magnetic field strength numerous physical parameters and effects also change and may have a positive (e.g. contrast enhancing) or negative (e.g. artifact increasing) impact on MR imaging. This article provides a description of these physical effects in MRI - for example the signal-to-noise-ratio, the specific absorption rate, the relaxation times, chemical shift, magnetic susceptibility - and explains their differences at magnetic field strengths of 1,5, 3,0, and 7,0 Tesla. (orig.)