THE RELATION BETWEEN BRAIN IRON AND NMR RELAXATION-TIMES - AN IN-VITRO STUDY

T-1 and T-2 relaxation times and iron concentrations were measured in 24 specimens of gray matter from fresh human and monkey brains at magn etic fields from 0.05 to 1.5 Tesla, Three different effects were found that correlate with iron content: a T-1-shortening that falls off som ewhat at high fields, a T-2-shortening that is field-independent and t hus important at low fields, and a contribution to 1/T-2 that increase s linearly with field strength, This linear field dependence has been seen only in ferritin and other ferric oxyhydroxide particles, Our res ults are in agreement with in vivo MRI studies and are generally consi stent with values for ferritin solution, except for differences such a s clustering of ferritin in tissue, A cerebral cavernous hemangioma sp ecimen showed similar T-2-shortening, but with a 2.7 times larger magn itude, attributed to larger clusters of hemosiderin in macrophages, Th e dependence on interecho time 2 tau was measured in three brains; 1/T -2 increased significantly for tau up to 32 ms, as expected from the s ize of the ferritin clusters, These findings support the theory that f erritin iron is the primary determinant of MRI contrast in normal gray matter.