Presentation
Right hemiplegia and aphasia three days ago.
Patient Data
Middle cerebral artery territory petechial hemorrhagic infarct.
The patient had presented early with an ischemic stroke, and underwent successful endovascular clot retrieval and recanalization 3 days prior to the CT shown above.
Selected images demonstrating a large left MCA distribution infarct with a large area of low signal on DWI and ADC imaging in keeping with associated petechial cortical hemorrhage. Loss of signal on DWI is due to T2 blackout, best seen on B=0 (GE EPI) image, which is of course a T2* weighted image and thus suffers from significant signal loss due to blood products.
Case Discussion
T2 blackout is essentially the opposite effect to T2 shine through, namely the extremely low signal on T2* images results in loss of signal on DWI and ADC. This clearly does not reflect actual diffusion characteristics of the tissue.
With no signal in a voxel on B=0 images, the DWI value will also be 0 (black) and ADC will be undefined (manipulating the DWI equation with B=0 results in a natural logarithm of 0/0, which is undefined - twice in fact).