Principles of Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy

The wide range of contrast that can be obtained using magnetic resonance imaging (MRI) has made it the modality of choice for the imaging of soft tissues. The mechanisms underlying the wide range of contrast depend on numerous intrinsic and extrinsic parameters. The inherent intrinsic parameters include, but are not limited to, proton density, spin-lattice (T1) relaxation times, spin-spin (T2) relaxation times, chemical environment, velocity, temperature, and the rate at which the protons diffuse. Extrinsic parameters, on the other hand, are those parameters that can be utilized to select which of the intrinsic parameters will be the primary contributor to image contrast. Such parameters include the choice of pulse sequence, the timing parameters for a given sequence, that is, the echo time (TE) and the repetition time (TR), various types of preparation pulses, and, for gradient-echo sequences, the flip angle.