![]() When high concentrations of contrast are present, low-T2 effects may predominate. In routine MR imaging, the mild T2-shortening effects of low doses of gadolinium (which decrease signal intensity) are usually overwhelmed by the more dominant T1-shortening effects (which increase signal intensity) and are therefore not normally observed. In which of the following scenarios would the T2-shortening effects of gadolinium not be expected to be seen?.Since ΔT1 and ΔT2 are given in seconds and is measured in millimoles per liter, r 1 and r 2 have units of L/mmol-s. Since a contrast agent may affect the two relaxation rates (1/T1 and 1/T2) individually, there are two corresponding relaxivities, denoted r 1 and r 2. The relaxivity of an MR contrast agent reflects how the relaxation rates of a solution change as a function of concentration. The T1- and T2-relaxivities of a contrast agent are given in what units?.In all MR contrast agents now commercially available, a ligand group occupies eight of these sites while the ninth is available for transient bonding by a solvent water molecule for an inner sphere effect to occur. Most gadolinium contrast agents have multiple coordination sites available for inner sphere relaxation to take place.Ī consequence of its electron structure is that the Gd +3 ion typically exhibits nine coordination sites for bonding and chemical interactions.Although weaker on a per molecule basis, outer sphere effects are important because they involve larger numbers of water molecules.Inner sphere relaxation requires very close approach of a water molecules to the gadolinium metallic center. ![]()
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