Monitoring brain repair in stroke using advanced magnetic resonance imaging

Thrombolysis and endovascular interventions have revolutionized stroke treatment, but many patients are excluded from such therapies, and residual disability is common.1 Emerging approaches to enhance poststroke brain repair may have no time constraints and are applicable to most stroke patients. Novel interventions to enhance brain repair include electromagnetic or robotic techniques, brain–computer interface, and restorative cell-based and pharmacological therapies.2–4 A major impediment to translation to patient care, however, is the lack of robust in vivo techniques to monitor the effects of such interventions in humans.3 Noninvasive imaging of the human brain for multiparametric in vivo monitoring of poststroke recovery presents challenges. The clinical application of certain techniques such as positron emission tomography is frequently restricted by radiation exposure, limited resolution, high cost, or difficult access.5–7 Magnetic resonance imaging (MRI), however, is accessible, noninvasive, safe, and versatile, with high resolution, making this an ideal modality for multiparametric in vivo monitoring of stroke recovery. This review concentrates on MRI markers of stroke recovery in experimental models and, when available, in humans (Table). View this table: Table. Magnetic Resonance Options for Imaging Poststroke Recovery ### Angiogenesis The peri-infarct cortex is a unique neurovascular niche, within which angiogenesis is closely and causally linked to neurogenesis through vascular growth factors and chemokines.2 Together with parenchymal astrocytes, angiogenic vessels facilitate synaptogenesis and axonal sprouting.2 Angiogenesis stimulated by cell-based or pharmacological interventions correlates with improved behavioral outcome.2 In rodents, capillary sprouting at the ischemic boundary leads to new vessel development between 2 and 28 days.8 Angiogenesis has been observed in the ischemic penumbra of humans 3 to 4 days after stroke, and higher cerebral blood vessel density has been associated with improved survival.9 Angiogenic vessels are permeable during the early stages of development and become less leaky as they …