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Paramagnetic chemical exchange saturation transfer (PARACEST) agents
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Paramagnetic chemical exchange saturation transfer (PARACEST) agents offer a potential new paradigm in MR imaging. An advantage to this class of agents is the ability to switch each agent on or off through selective RF irradiation applied at the frequency of either its bound water resonance or an exchanging NH group. This feature means that multiple, different PARACEST agents can be injected together and their effects imaged either sequentially or simultaneously. In their “off” state, i.e., when not specifically irradiated, PARACEST agents will not interfere with conventional MR imaging sequences, with or without gadolinium. Consider two exchanging water pools, A and B, with different NMR chemical shifts. Here pool B will mean a water molecule bound to the agent, while pool A will mean bulk water.
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