  Infarcted brain tissue resulting from acute stroke readily shows up as
hyperintense regions within diffusion-weighted magnetic resonance imaging
(DWI). It has also been proposed that computed tomography perfusion (CTP) could
alternatively be used to triage stroke patients, given improvements in speed
and availability, as well as reduced cost. However, CTP has a lower signal to
noise ratio compared to MR. In this work, we investigate whether a conditional
mapping can be learned by a generative adversarial network to map CTP inputs to
generated MR DWI that more clearly delineates hyperintense regions due to
ischemic stroke. We detail the architectures of the generator and discriminator
and describe the training process used to perform image-to-image translation
from multi-modal CT perfusion maps to diffusion weighted MR outputs. We
evaluate the results both qualitatively by visual comparison of generated MR to
ground truth, as well as quantitatively by training fully convolutional neural
networks that make use of generated MR data inputs to perform ischemic stroke
lesion segmentation. Segmentation networks trained using generated CT-to-MR
inputs result in at least some improvement on all metrics used for evaluation,
compared with networks that only use CT perfusion input.
