The successful management of stroke patients requires the ability to confirm the diagnosis and determine underlying pathophysiology. Techniques such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT) provides a window onto the structural and functional changes that occur during stroke. This chapter focuses on the limitations of currently used brain imaging techniques. There has been a widespread belief that conventional MRI is less sensitive than CT in the detection of intracerebral hemorrhage. Ischemic changes may be seen in conventional MR studies within 1 to 2 hours of stroke onset. However, both CT and MRI have low sensitivities for acute ischemia in the hyper acute phase and neither imaging modality is able to identify hypoperfused but potentially salvageable ischemic tissue. SPECT and PET have added significantly to our knowledge of the pathophysiology of stroke.