Intrinsic Parameters Measurable with MRI

Abstract

One of the specificities of magnetic resonance imaging (MRI) — and one of its major strengths — lies in the possibility it provides to modulate the image contrasts between various biological tissues. The MR image contrasts, due mainly to differences in intensity of MR signals from water protons from different tissues, depend on the interplay between certain instrumental parameters (radiofrequency (RF) pulse angles, delays between RF pulses, type of RF pulse sequences applied) and a large number of biophysical parameters characterizing the different tissues. Among the latter, water density as well as the longitudinal (T₁) and transverse (T₂) relaxation times of the water protons play an overwhelming role. Other biophysical parameters of particular importance include the magnetic susceptibility (either the bulk magnetic susceptibilities of the tissues or the magnetic susceptibilities of certain microscopic components within, such as the intra-and extracapillary spaces), the self-diffusion properties of water molecules, and the bulk tissue movements.