Wednesday 4 January 2012

Role of T2*GRE

T2* pronounced "T 2 star"
GRE stands for GRadient Echo sequence.

Due to its clinical implications this has became a non  omissible sequence in our stroke protocol.
Paramagnetic effect of substances like deoxyhemoglobin, methemoglobin and hemosiderin give rise to T2* based contrast, which is used to depict hemorrhage, calcification and iron deposition in various tissues and lesions.
I won't go in much technical details of the sequence like flip angle, TR TE and all.

Clinical applications of T2*GRE sequence:
Vessel thrombosis:
On left side serpigenous or cord like low signal intensity in the region of right parietal cortical sulci going towards superior sagittal sinus are the para sagittal cortical veins which are thrombosed depicted only on this GRE sequence where ax FLAIR study of this patient was showing only a focal vasogenic odema in right parietal sub cortical white matter. MR Venogram particularly the superior sagittal sinus was normal which is expected as it depicts only the dural venous sinuses.

On right side thrombosed right vertebral show abnormal high signal on FLAIR,  low signal on T2*GRE due to thrombus in it. Corresponding portion of right vertebral show a focal flow loss on MR Angio.

Infarct with hemorrhage : Arterial infarcts with hemorrhagic transformation or hemorrhagic venous infarcts will show low signal intensity areas of bleed in the region of infarct.

On right side ax FLAIR image show a sub acute right MCA inferior division terriory infarct. Hemorrhagic transformation seen as an area of low signal intensity on T2*GRE.

Axonal shearing injury and petechial bleed.
A case of head injury with poor Glass glow coma scale. On admission CT brain normal. MRI Ax FLAIR study show focal T2 hyperintensity in the region of corpus callosum with low signal intensity hemosiderin staining on GRE. Multiple punctate low signal intenisity foci in left frontal sub cortical white matter attributed petechial bleeds as a part of axonal shearing injury.

Microbleeds seen as multiple punctate low signal intensity foci in bilateral cerebral cortical white matter. Platelet aggregation inhibitor drugs to be used cautiously in this patients.

Vascular malformation, high flow vs slow flow: 
On left side T2 w image show multiple serpiginous flow voids clustered in right temporo parietal lobe suggestive of a vascular malformation. High signal on T2*GRE supports a high flow vascular malformation like AVM.

Bleed in a lesion : 
This is a case of multiple parenchymal metastasis with fluid fluid levels. In that the dependent portion show low signal on GRE attributed to a sedimentation of blood degradation product supports hemorrhagic metastasis.

Calcification in a lesion: 
Evaluation of calcification in a neoplastic lesion like meningioma, craniopharyngioma or an infective lesion like Granuloma.

Gliosis secondary to a chronic resolved hematoma vs infarct:
In this case a focal Gliotic cavity seen in left corona radiata can be a chronic resolved hematoma or chronic infarct. Low signal intensity hemosiderin staining along the lesion on GRE goes in favor of a chronic resolved hematoma.

Lesions with hemosiderin staining: Hemosiderin staining is pathognomic of certain leisons or pathologies.

On right side a bubbly heterogeneously T2 hyper intense Cavernoma with typical low signal intensity hemosiderin staining on GRE.
On right side a case of superficial siderosis with low signal intensity hemosiderin staining along tentorium.

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