In the early stage of a hyperacute hematoma (Figs. 6.1 and 6.2), oxygenated hemoglobin within intact red blood cells is dominant. Oxy-hemoglobin is a dia-magnetic substance and will, as such, generate an opposing magnetic field that reduces the applied magnetic field, as in most normal tissues in the body. Since there are no unpaired electrons in the iron of oxygenated hemoglobin, both longitudinal and transverse relaxation will be created by the so-called proton-proton, dipole-dipole interactions. At this stage, hematomas will have shorter relaxation times than water due to their protein content and will be slightly hypo- or iso-intense when compared with brain parenchyma on Tl-weighted images. On T2-weighted images, oxy-hemoglobin will be seen as a slightly hyperintense region because of the high water content [7,11,14,19,22,23,25,28,29,33,34].
Figure 6.1 a-f
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