ABSTRACT
Magnetic resonance imaging (MRI) is a powerful noninvasive technique that provides high-quality 3D images of so£ tissues, including information on anatomy, function, and metabolism of tissue in vivo [1]. An important attribute of magnetic resonance imaging is that numerous clinically important applications do not require the use of exogenous materials to generate su—cient contrast for routine diagnostic purposes. In the context of medical imaging, contrast is the di›erence in visual properties that renders structures or §uids within a body (or representation image thereof) distinguishable from other objects and the background. šis is possible because adjacent tissues of varying structure and chemical composition tend to possess inherently unique nuclear magnetic resonance (NMR) properties such as relaxation times and proton density. As described in greater detail in Chapter 5, appropriate selection of pulse sequences allows one to exploit these unique properties and thus, in many cases, generate satisfactory contrast between neighboring tissues of interest. še lack of a need for contrast agents in many MRI applications represents a fundamental advantage over other clinical imaging modalities such as nuclear imaging methods (PET/SPECT) and certain X-ray techniques. Despite this advantage, non-contrastenhanced MRI has important limitations, and a growing number of clinically relevant MRI applications require the application of exogenous contrast agents. šese applications include, but are not limited to, di›erentiation of tissue phenotypes that otherwise cannot be di›erentiated with non-contrast-enhanced MRI, providing speciœcity to regions of abnormal signal and/or depiction of tissue vascularity and perfusion [2].
