3. How do contrast agents work?

3.1 Contrast agents and relaxation

The effectiveness of a paramagnetic chelate used as a contrast agent is expressed as relaxivityér ₁ or r ₂ , with reference to the 1/T ₁ or 1/T ₂ relaxation velocities of protons in water molecules. The relaxivity of a contrast agent is defined as the paramagnetic increase in the relaxation velocity of water protons normalized by the concentration of this agent