, is a board-certified vascular neurologist. His expertise includes caring for patients with stroke, cerebrovascular diseases, and those who require neurological critical care. Hemmen directs the Comprehensive Stroke Center at UC San Diego Health and was instrumental in establishing the center as the first certified Stroke Center of Excellence in San Diego County.
As a professor at the University of California School of Medicine Department of Neurosciences, Hemmen directs the Stroke Fellowship Program and provides leadership and education to medical students, residents and fellows.
Hemmen is the lead investigator for numerous clinical trials in cerebrovascular disease. He investigates the use of neuroprotection and reperfusion therapies after acute ischemic stroke, as well as stroke prevention, recovery and research in intracerebral hemorrhage. He also leads the cerebrovascular research and trial coordination center that conducts national and international collaborative trials and researches new cures in all areas of cerebrovascular medicine.