Automatic interpretation of 4D computed tomography images in acute stroke

Strokes—caused by a disturbance of blood supply to the brain— are a leading cause of death and disability worldwide.1 In the majority of cases, strokes are caused by a blockage of the blood supply (known as an ischemic stroke), but another type of stroke (hemorrhagic stroke) is caused by the rupture of a vessel or aneurysm. Strokes can result in soft tissue damage and loss of brain function. Treatment for acute ischemia consists of administering thrombolytic drugs within four and a half hours of the onset of symptoms. However, this treatment can have disastrous consequences in hemorrhagic strokes. A fast neuroimagingbased patient triage is therefore required for appropriate treatment selection. Computed tomography (CT) is the first choice of imaging modality for the assessment of acute stroke.2 CT is widely available in emergency situations, and is a cheaper and faster method than magnetic resonance imaging. CT perfusion (CTP) is a 4D imaging technique in which a contrast agent is used to visualize cerebral hemodynamics over time. Hemodynamic measures, such as cerebral blood flow and cerebral volume, contain information about the extent and severity of an infarcted (oxygen-deprived) region. These measurements can be used to differentiate between brain tissue that is permanently damaged and tissue that is possibly salvageable by reperfusion therapy (restoring blood flow where blood vessels have become blocked).3 Despite the widespread use of CT, as well as advances in high spatialand temporal-resolution CT imaging, there has been little progress in the development of algorithms for the automated quantification and analysis of cranial CT exams in acute stroke. Isolation of all pertinent information and cerebral anatomy from 4D images for subsequent post-processing and Figure 1. Computed tomography (CT) axial view of a patient with a metallic foreign object surrounded by cerebral soft tissue. The presence of metal causes bright (high intensity) streaking artifacts that reduce the image quality.