Perfusion imaging employs concepts that date back to the early 1830s, and it leverages hardware and software that emerged around the same time at multidetector helical CT scans. But it has only become popular in recent years for thrombectomy decision-making. If I'm being honest, I often never use it for this purpose. So what other purposes might it serve? And how does it work? This week, we review the fundamental concepts of perfusion CT, its utility in stroke care, and how it might prove useful for other neurologic conditions as well. ** IF YOU’RE TAKING YOUR NEUROLOGY BOARDS THIS SUMMER, CHECK OUT THE PENN NEUROLOGY BOARD REVIEW COURSE. FOR A DISCOUNTED RATE ON THE ONLINE OR STREAMING RESOURCES, USE PROMO CODE ‘WAVES2020’. ** Produced by James E. Siegler. Music courtesy of Julie Maxwell, John Bartmann, Kai Engel, and Pachyderm. Our theme song was composed by Jimothy Dalton. Sound effects by Mike Koenig and Daniel Simion. Some of the voices you heard throughout the program were those of Dr. Mathias Prokop, Radbound Medical Center, Netherlands; Terri Yeager, Comprehensive Stroke Program Coordinator at Cooper University Hospital; and a recording that was produced by GE Healthcare, which are freely available on YouTube. Unless otherwise mentioned in the podcast, no competing financial interests exist in the content of this episode. BrainWaves' podcasts and online content are intended for medical education only and should not be used for clinical decision making. Be sure to follow us on Twitter @brainwavesaudio for the latest updates to the podcast. REFERENCES Campbell BC, Christensen S, Levi CR, Desmond PM, Donnan GA, Davis SM and Parsons MW. Comparison of computed tomography perfusion and magnetic resonance imaging perfusion-diffusion mismatch in ischemic stroke. Stroke; a journal of cerebral circulation. 2012;43:2648-53. Boned S, Padroni M, Rubiera M, Tomasello A, Coscojuela P, Romero N, Muchada M, Rodriguez-Luna D, Flores A, Rodriguez N, Juega J, Pagola J, Alvarez-Sabin J, Molina CA and Ribo M. Admission CT perfusion may overestimate initial infarct core: the ghost infarct core concept. J Neurointerv Surg. 2017;9:66-69. Martins N, Aires A, Mendez B, Boned S, Rubiera M, Tomasello A, Coscojuela P, Hernandez D, Muchada M, Rodriguez-Luna D, Rodriguez N, Juega JM, Pagola J, Molina CA and Ribo M. Ghost Infarct Core and Admission Computed Tomography Perfusion: Redefining the Role of Neuroimaging in Acute Ischemic Stroke. Interv Neurol. 2018;7:513-521. Campbell BCV, Ma H, Ringleb PA, Parsons MW, Churilov L, Bendszus M, Levi CR, Hsu C, Kleinig TJ, Fatar M, Leys D, Molina C, Wijeratne T, Curtze S, Dewey HM, Barber PA, Butcher KS, De Silva DA, Bladin CF, Yassi N, Pfaff JAR, Sharma G, Bivard A, Desmond PM, Schwab S, Schellinger PD, Yan B, Mitchell PJ, Serena J, Toni D, Thijs V, Hacke W, Davis SM, Donnan GA, Extend E and Investigators E. Extending thrombolysis to 4.5-9 h and wake-up stroke using perfusion imaging: a systematic review and meta-analysis of individual patient data. Lancet. 2019;394:139-147. Siegler JE, Messe SR, Sucharew H, Kasner SE, Mehta T, Arora N, Starosciak AK, De Los Rios La Rosa F, Barnhill NR, Mistry AM, Patel K, Assad S, Tarboosh A, Dakay K, Wagner J, Bennett A, Jagadeesan B, Streib C, Weber SA, Chitale R, Volpi JJ, Mayer SA, Yaghi S, Jayaraman MV, Khatri P and Mistry EA. Noncontrast CT versus Perfusion-Based Core Estimation in Large Vessel Occlusion: The Blood Pressure after Endovascular Stroke Therapy Study. J Neuroimaging. 2019. Epub ahead of print. Barber PA, Demchuk AM, Zhang J and Buchan AM. Validity and reliability of a quantitative computed tomography score in predicting outcome of hyperacute stroke before thrombolytic therapy. ASPECTS Study Group. Alberta Stroke Programme Early CT Score. Lancet. 2000;355:1670-4. Wintermark M, Reichhart M, Thiran JP, Maeder P, Chalaron M, Schnyder P, Bogousslav