MR detectability and appearance of small experimental intracranial hematomas at 1.5 T and 0.5 T. A 6-7-month follow-up study.

PURPOSE: To investigate the detectability and appearance of small experimental intracranial hemorrhages on MR at 0.5 T and 1.5 T in a long-term follow-up.
MATERIAL AND METHODS: Autologous blood (1 ml) was injected into the brain of 7 rabbits to create intraparenchymal hematomas. The injected blood leaked partially into the cerebrospinal fluid (CSF) spaces. MR imaging at 0.5 T and 1.5 T were performed immediately before and after hematoma creation, at 2 weeks and monthly up to 6 or 7 months using T1-, proton density- and T2-weighted (w) spin-echo (SE), FLAIR and T2*-w gradient echo (GE) pulse sequences.
RESULTS: Blood was detected both in the brain and in the CSF spaces of all animals during the first hours after hematoma creation at 1.5 T. In the last examination after 6-7 months, the T2*-w GE sequences still showed residues of the intraparenchymal hematomas in all the rabbits at 1.5 T, but the signal pattern was not specific for the age of the hematomas. SE and FLAIR sequences were insensitive. The histopathology revealed iron deposits in all brains.
CONCLUSION: Residues of small intraparenchymal hematomas can be seen for months with T2*-w GE sequences on brain MR imaging at 1.5 T. The age of the microhematomas cannot be estimated with MR imaging.