ABSTRACT

Magnetic resonance imaging has radically modified the practice of medicine in general and radiology in particular. It is a computer-based imaging modality that displays the body in thin tomographic slices, based on the interaction between radio waves and nuclei composing the object being scanned (whether an inanimate sample or a living subject, often called sample), in the presence of a static magnetic field. Physical characteristics of a volume element or voxel of tissue are translated by the computer into a two-dimensional image composed of picture elements, or pixels. Pixel intensity in MRI reflects spin density, generally as the hydrogen of water, weighted by some parameters such as chemical shift, relaxation times, magnetic susceptibility, motion, etc. MRI can produce images of very good morphological quality and/or very high functional interest. This reflects not only the contrast between different tissues, due to physicochemical properties of the tissues, but also the ability to display changes in contrast over time. Moreover, MRI allows images to be collected directly in any plane, that is, the usual axial, sagittal, coronal, or any degree of obliquity. This chapter contains some basic concepts regarding MR signal formation and conventional imaging techniques. In this setting, the

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MR signal arises in the time domain, and the image occupies the frequency domain.