Nonacute subdural hematoma: fundamental interpretation of MR images based on biochemical and in vitro MR analysis.

Few reports have described the nature of the appearance of nonacute subdural hematoma on magnetic resonance (MR) images. The authors analyzed MR images in 39 cases of nonacute subdural hematoma and subdural effusion by measuring in vitro proton relaxation times and the biochemical variables of hematoma fluids. T1 became proportionally shorter than T2 with an increase in hematocrit but the direct cause of the variation in T1 and T2 was the amount of methemoglobin. The free iron content, not the bound iron content, was another main cause for shortened T1 and T2. Paradoxical findings in the correlation between the total protein or albumin concentration and relaxation times were noted. It is possible that as the protein level in the supernatant increased, more free iron was bound to the protein, decreasing the influence of the free iron on the relaxation times.