Patients with acute cerebral ischemia represent with hemiparesis, hemianopia, speech disturbance, or impairment of consciousness. The differential diagnosis is intracranial hemorrhage, cerebral venous thrombosis, focal encephalitis, demyelination disorder or tumour. Brain imaging is necessary to assess the exact diagnosis and the acute pathophysiological state of the brain. Both pieces of information will guide treatment and will finally determine the clinical outcome of the patient.

Kent and Larson proposed five levels of clinical efficacy for assessing diagnostic technology: (i) technical capacity; (ii) diagnostic accuracy; (iii) diagnostic impact; (iv) therapeutic impact; and (v) patient outcome. In this chapter, I will study the question what unenhanced CT is able to assess in patients with acute stroke; how accurate this information is; and whether imaging with CT has any impact on stroke diagnosis, stroke treatment and, finally, on the clinical outcome of patients.

Level 1 of clinical efficacy: technical capacity of CT in acute cerebral ischemia

Technical capacity is the capability of CT to reproducibly display recognizable images that demonstrate pathology with good intra- and interobserver reliability. Based on changes in X-ray attenuation, CT is capable of detecting intracranial hemorrhage, thrombo-embolic occlusion of major brain arteries, brain tissue swelling without edema, and ischemic brain edema. Intra- and interobserver reliability was not studied for all of these findings. Generally, it seems as if hyperattenuating lesions are easier to detect than hypoattenuating lesions.