The Role of Magnetic Nanoparticle-Based Contrast Agents in MRI

8 The Role of Magnetic Nanoparticle-Based Contrast Agents in MRI A basic 

In an image, a region of high signal intensity appears bright, whereas a region of low intensity appears dark. In general, MRI has the ability to manipulate the tissue 

M RI contrast agents consist not only of superparamagnetic nanoparticles, but also of particular types of paramagnetic complexes. In general, MRI contrast agents are divided into two major types  

In order to describe, quantitatively, the effectiveness of a contrast agent, the relaxivity coefficients q are introduced [290]. The relaxivities describe the shortening of a certain relaxation time per millimole of contrast agent. They are, therefore, concentration-independent values, as the inverse relaxation time (R = 1/Ti) - that is, the relaxation rate - increases linearly with the contrast agent concentration  

The size and shape of nanoparticles must be adjusted for the desired application since, on the nanometer scale, magnetic properties such as saturation magnetization and magnetic anisotropy strongly size- and shape-dependent. In particular, Ms is greatly decreased with decreasing size of a superparamagnetic nanoparticle. As Ms directly determines the rj relaxivity, size control for the crystalline core is the key requirement. 

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