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I./3.3.: Magnetic resonance imaging – MR
I./3.3.1.: MR detection in certain phases of hemorrhages
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According to the below described processes, signal changes turn in cerebral hematomas by the time as follows:
I./3.3.1.1.: Hyperacute phase
Duration is 1-3 hours after the onset of hemorrhage. In this phase, signaling of hematoma is moderate, isointensive compared to cerebral parenchyma on T1 weighted, high on T2 weighted sequences. Based on the adaptation of these sequences there is no difference between tumorous or inflammatory processes. Bleeding can be differentiated by T2* (haem) sequence successfully, because its rim will be signal free such as „drawn out by clack ink”.
I./3.3.1.2.: Acute phase
Duration lasts from several hours after the onset of hemorrhage until the 3rd posthemorrhagic day. The blood can be already distinguished better based on its signal course – intracellular deoxyhemoglobin is isointense with cerebral parenchyma on T1 weighted, or lower, and hypointense on T2 weighted sequences. In this case, hyperintense zone appears around the blood as sign of perifocal edema.
I./3.3.1.3.: Subacute phase
Duration lasts from the second day after the onset of hemorrhage appr. until the 7-10th posthemorrhagic days. Namely, until this time stays the methemoglobin, the denaturated product of hemoglobin intracellularly which has very high signal intensity on T1 weighted, and very low signal intensity on T2 weighted images. High signal intense zone indicating the perifocal edema is still visible.
I./3.3.1.4.: Late subacute phase
Duration lasts from the second posthemorrhagic week after the onset of hemorrhage appr. until one month. Methemoglobin, which becomes extracellular due to the disintegration of red blood cells, gives very high signal both on T1 and T2 weighted sequences.
I./3.3.1.5.: Chronic phase
This phase lasts for months, years. The end products in the chronic hematoma are hypointense on T1 sequence, but hypointense to signalfree on T2 weighted image (hyperintense rim is possible). Nevertheless, not only the transformation of hemoglobin comes off in hematomas but also the colliquation of the original structures and accumulated cells. Accordingly, signal intensity will be identical to liquor in the center of these areas.
I./3.3.2.: Additional techniques, other characteristics
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Gradient echo sequences indicate the environmental magnetic inhomogeneity (susceptibility) very sensitively so that signal loss is generated on the course of the entire hemoglobin degradation process. This is how to „reveal” a previous hematoma if it looks a small lacuna or plain slot by CT, since hemosiderin deposition is demonstrated in the wall by T2 and Gradient echo sequences.
Diffusion weighted imaging demonstrated a high signal in hyperacute phase in hemorrhage. Low signal is present in acute and subacute phases, which signal will be high in late subacute phase. Finally, low signal is present in chronic hematoma.
Please note that this process does not occur at the sime time in hematomas. The change proceeds usually inward from outside (areas rather affected by tissue impacts). Therefore, transformation from intracellular methemoglobin to excellular one can be already come off in the peripheral areas of hematomas according to the related signal intensity changes (T1 high, T2 low), whiles methemoglobin is located still intracellularly in the center of hematoma (T1 high, T2 low). Posthemorrhagic lesions show high signal on T2 weighted images due to gliosis, as fibrosis of any other origin in the brain (white matter, basal ganglia, thalamus, cortex). Thus multiple signal can be combined inside according to the grade of gliosis, the encephalomalacia caused by the destruction and the decomposition product of the blood cells. However, no enhancement can be observed in late phasic lesions.
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