Final answer:
Dynamic enhanced MRA sequences of the mesenteric arteries utilize MRI contrast agents, most notably a stable complex form of the paramagnetic metal ion Gd³+, to produce detailed images of soft tissues by altering the magnetic properties of water in cells.
Step-by-step explanation:
Dynamic enhanced Magnetic Resonance Angiography (MRA) sequences of the mesenteric arteries are performed using a MRI contrast agent. These contrast agents often contain a paramagnetic metal cation in the form of a stable complex to alter the magnetic properties of water in cells. By doing this, the different environments within various types of cells respond distinctly, allowing for detailed imaging of soft tissues. Among the important metal ions used in MRI contrast agents is Gd³+ (gadolinium), which is highly paramagnetic due to its seven unpaired electrons. However, gadolinium is toxic as a free ion, hence it is used as a stable complex such as DTPA³ˍ (diethylene triamine pentaacetic acid), which does not dissociate in the body and can be safely excreted by the kidneys.