Gadolinium and Ferumoxytol MRI in Diagnosing Patients With Abnormalities in the Central Nervous System

This study is comparing two different contrast agents (dyes used to improve MRI images) — gadolinium (the standard) and ferumoxytol (an iron-based alternative) — to see which provides better, more detailed images of the brain and nervous system in patients with neurological conditions or brain tumors. **You may be eligible if...** - You are at least 10 years old - You have neurological symptoms (such as headaches, seizures, weakness, or nerve problems), a brain abnormality seen on imaging, or a cancer elsewhere that may have spread to the brain - You are able to have an MRI without sedation **You may NOT be eligible if...** - You are pregnant or breastfeeding - You have a pacemaker, metal implants in your body, or are severely claustrophobic - You have an allergy to gadolinium, iron-based products, or dextran - You have a condition called iron overload (hemochromatosis) - You have three or more drug allergies from different drug classes Talk to your doctor to see if this trial is right for you.