Dr. Tarzwell has dual certification in psychiatry and nuclear medicine, and he has a cross-appointment in the Department of Radiology. He is the Chief Medical Officer and medical director of INITIO, a PET/CT imaging clinic. His main clinical and research interest is imaging brain function, particularly glucose metabolism with PET (positron emission tomography) and perfusion with SPECT (single-photon emission computed tomography) in the diagnosis and treatment of psychiatric disorders. He has published work in the use of SPECT to diagnose TBI (traumatic brain injury) and to separate TBI from PTSD (posttraumatic stress disorder). His current work involves the use of neural networks to discover brain activity biomarkers in major depressive disorder and bipolar disorder. He regularly consults in complex injury cases where there are psychiatric consequences or head injury. His research appeared 19th on the 2015 list of Top 100 Science Stories of the Year in Discover Magazine. He is the content creator for the YouTube medical educational channel One Minute Medical School.