A review of MRI pulse sequences and techniques in neuroimaging

BACKGROUND: The unmatched soft tissue contrast provided by magnetic resonance imaging (MRI) has made it the modality of choice for many neuroimaging examinations. The fact that signal intensity in MRI depends on many parameters, including spin-lattice and spin-spin relaxation times, proton density, and velocity, makes it possible to highlight various pathologies by appropriate choice of pulse sequences and pulse sequence parameters. It is somewhat overwhelming, however, to filter through various pulse sequences and parameters in order to understand how their selection affects image contrast. This brief review is intended to highlight common pulse sequences and parameters as well as introduce new techniques currently being released for clinical use. MATERIALS: Basic pulse sequences are described and the influence of the acquisition parameters on image contrast are illustrated. Such basic sequences include the ubiquitous spin echo, fast spin echo, and gradient echo sequences. Specialized techniques for fat suppression and magnetic resonance angiography are also presented. Currently approved contrast agents for use in MRI are briefly reviewed, and various advanced pulse sequences, such as those for diffusion and magnetization transfer contrast imaging, are briefly outlined. RESULTS: The utility of basic and advanced pulse sequences are demonstrated by clinical examples and images of normal brain and spine. New sequences and techniques are briefly outlined with regard to their potential for improving neuroimaging examinations. CONCLUSIONS: This brief review outlines how the choice of pulse sequence and acquisition parameters influences the resulting image contrast for a variety of basic and advanced imaging techniques.