COMPARISON OF T2 RELAXATION IN BLOOD, BRAIN, AND FERRITIN

T2 was measured in samples of human blood and monkey brain over a held range of 0.02-1.5 Tesla, with variable interecho times, and was compa red with previous data on ferritin solutions [taken with the same appa ratu]. 1/T2 in deoxygenated blood increased quadratically with held st rength, as noted previously, but in brain gray matter the increase was linear, as also was the case in ferritin solution. In both deoxygenat ed blood and gray matter, 1/T2 increased with interecho time, but appe ared to level off at times around 50 msec, as expected from the theory of diffusion through magnetic gradients. Diffusion times estimated by using the chemical exchange approximation were 3.4 msec for deoxygena ted blood and 5.7 msec for the globus pallidus. The quadratic held dep endence in blood is consistent with this same theory, but the linear d ependence in brain tissue and in ferritin solutions remains unexplaine d.