The axial, coronal and sagittal projections are all considered standard for Magnetic Resonance Imaging (MRI) and a variety of signal sequences are used, usually T1 weighted,T2 weighted and balanced (proton density) images. The MRI picture of hemorrhage depends on the sequence and the age of the hemorrhage, further on this non invasive method can detect smaller hemorrhages than computed tomography (CT).
According to the age of hemorrhage there are six phases: the hipreacute phase ( till six hours of evolution ), the acute phase ( from six hours to three days ); the early subacute phase (three days to six days ) ; the late subacute phase ( six days to one or two months ); the early cronic phase (one or two to four months ); and the late chronic phase (years ).
At the hiperacute phase, the red blood cell are spherical with oxihemoglobin. Coagulation and retraction occur and there is little oedema. It is difficult to distinguish from infarction on T1 weigthed in this early stage , as the lesion has the same signal as normal tissue, with a halo of lower siganal, because of the clot retraction. On T2 weighted image, the lesion appears higher in signal.
At the acute phase , the red cells become altered in shape with predominance of deoxihemoglobin, and accentuation of the oedema occurs . On T1 weighted images may still have the same signal then the normal tissue or may appear lower in signal, as it happens on T2 weighted images. The red blood cells become crenated, at the early subacute phase , with predominance of methemoglobin. This alteration are always well noted from periphery to centre , because of the contact with oxigen .The oedema is more accentuated and reach the maximum qf its expansive effect. On T1 weighted images of this phase appears with higher signal while it is lower on the T2 weighted images.
When the crenated red blood cells break out at the late subacute phase, the methemoglobin empties and the oedema starts diminishing .At this phase the lesion appears higher in signal on both T1 and T2 weighted images, which makes easier the diagnostic, because a few number of structures have this pattern.
At the early chronic phase , all red blood cells are broken out and there is a lot of methemoglobin . Then it occurs intense vascular proliferation and macrophages migrates to form a capsula. At this stage the lesion appears higher in signal with a halo of lower signal.
At the late chronic phase , there are a few materials and an empty space which were before occupied by the clot. At this phase the lesion appears lower in signal the T1 and T2 weighted images .
As we can observe the hemorrhage lesions change the picture rapid and radically on MRI, which is more sensitive and provide earlier measure than CT. MRI , however , is more cortly, besides the need of exclude ferromagnetic materials and the difficult in monitoring patients in the scanner, making it unsuitable for many acutly ill patients.
Go back to RADIOLOGY
Go back to MEDSTUDENTS HOMEPAGE