【Q&A in MRI】9.1.5 Bolus Gadolinium Effect 团注锇剂的效应

Dynamic Susceptibility Contrast (DSC) T2*-weighted source images acquired before, during, and after passage of the gadolinium bolus. At peak (middle image) note decreased signal throughout the brain, especially in blood vessels. Advanced Discussion (show/hide)»As you might expect, the relationship between the presence of Gd in a vessel and its T2(*) effects are more complex than the simple discussion above suggests. First, standard Gd contrast agents are confined to the plasma and do not enter red blood cells. Accordingly, there are susceptibility effects within the intravascular space itself as well as those due to intravascular-extravascular space compartmentalization. The extent of compartmentalization varies with hematocrit. Hematocrit, in turn, differs between larger blood vessels and capillaries. Field strength is important, as susceptibility effects generally scale with B0². The pulse sequence used will also determine the relative contributions of susceptibility from different vessels. GRE sequences will be sensitive to T2* dephasing from all vessels, but especially the larger ones; SE sequences will be more sensitive to T2 effects in small arterioles, venules and capillaries.Finally, the orientation of blood vessels with respect to B0 affects both intravascular and extravascular susceptibility phenomena. For example, blood vessels oriented parallel to B0 will have no extravascular susceptibility changes while those oriented perpendicularly will exhibit a maximal effect. This curious phenomenon results from the angular dependence of dipole-dipole relaxation described in a prior Q&A.

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