IMPORTANCE OF CLOT STRUCTURE IN GRADIENT-ECHO MAGNETIC-RESONANCE-IMAGING OF HEMATOMA

The MR appearance of clots with different internal structures was comp ared on gradient-echo (GE) and spin-echo (SE) images. After MR imaging , clots were submitted for histological analysis to allow direct corre lation of clot structure with MR image intensity. Normal heterogeneous clots (containing entrapped serum) were hypointense compared to both unclotted blood (Hct 45) and brain on GE MR images. Homogeneous (serum -poor) clots and settled blood were hyperintense to unclotted blood an d isointense or hyperintense to brain. These results indicate that the GE technique is quite sensitive to the physical inhomogeneity created (at the voxel level) when blood forms an inhomogeneous clot containin g relatively large islands of red blood cells (RBCs) surrounded by lak es of serum. The effect of the different possible clot structures on G E signal intensity thus provides an etiology for the previously unexpl ained observations of hemorrhage with high signal intensity on GE MR i mages.