DWI and hemorrhage

The appearance of hemorrhage on DW MR images is complex and involves many factors, including the relative amounts of different hemorrhagic products and the pulse sequence used (Fig). Oxyhemoglobin is hyperintense on DW images and has a lower ADC than does normal brain tissue; this may indicate the relative restriction of water movement inside the red blood cell. 

Extracellular methemoglobin has a higher ADC than does normal brain tissue, which indicates that the mobility of water in the extracellular space is increased. The prolongation of the T2 component of fluid with extracellular methemoglobin results in hyperintensity on DW images.

Hemorrhage containing deoxyhemoglobin, intracellular methemoglobin, and hemosiderin are hypointense on DW images because of magnetic susceptibility effects. Because these products of hemorrhage have very low signal intensity on T2-weighted images, ADCs cannot be reliably calculated for them. 

Hematoma in a patient with a right hemisphere glioblastoma who had undergone prior resection and who had developed a hematoma in the right frontal lobe. The patient was hospitalized for progression of symptoms and development of fever. A ring-enhancing lesion at the site of the prior hematoma was seen on a gadolinium-enhanced T1-weighted MR image (not shown) in the right frontal lobe. Left: DW MR image( 6,000/108) demonstrates a hyperintense lesion (arrow) in the right frontal lobe. Right: On the ADC image, the lesion is hypointense (arrow), which is consistent with restricted diffusion. The lesion was drained, and old hemorrhage was demonstrated. There was no evidence of infection.