Brain and vascular imaging in acute ischemic stroke

Imaging in patients presenting with the symptoms of acute ischemic stroke has two objectives: assessment of the immediate pathophysiologic state of the cerebral circulation and tissue and assessment of the underlying disease. Diagnosis of the underlying disease will help in the choice of adequate secondary prophylaxis. Assessment of the brain's current pathophysiologic state is a prerequisite to choosing adequate treatment and is the more urgent of the two objectives. The imaging tool has to be available and employed quickly within the first hours after stroke onset. The imaging modality should reliably differentiate cerebral ischemia from other causes of a sudden central neural deficit. In addition, it should be able at an early stage to differentiate normal brain tissue from tissue at risk and from tissue that is already dying. Historically, vascular imaging was developed first and provided the rationale for surgery in cases of high-grade carotid stenoses and for prophylaxis with antiplatelet agents. Brain tissue imaging with CT was developed later and this technique allowed the diagnosis of ischemic stroke and thus thrombolytic treatment, which recently has been shown to be beneficial.1,2 A variety of new tools are now available for vascular and tissue imaging: ultrasound, CT angiography (CTA), MRI and MR spectroscopy (MRS), single photon emission tomography, and positron emission tomography. Computed tomography and MRI/MRS are most promising for meeting the above-mentioned objectives in the clinical setting of acute stroke. Magnetic resonance perfusion imaging directly shows ischemic areas and magnetic resonance diffusion imaging immediately shows its sequelae with high sensitivity. However, the prospective value of MRI for treatment is not yet determined. Although CT is considered relatively insensitive in acute ischemic stroke by some authors, all major clinical trials are using CT before the randomization of patients. This is explained by the wide availability and high practicability of …