Introducton

Functional neuroimaging in the form of cerebral blood flow (CBF) measurement continues to be a rapidly expanding tool in the care of patients with cerebrovascular disease, head trauma, seizure disorders and many other disease states involving the central nervous system. Computerized tomographic (CT)-based assessment of cerebral blood flow (CBF) offers many advantages in the care of patients with disorders of the central nervous system. CT-based technology capable of evaluating CBF can be readily combined with routine CT scanning equipment thus increasing the availability and decreasing the costs of this technology. Monitoring of patients with respiratory and hemodynamic instability is also more easily done using CT based technology. In addition, patients with mechanical heart valves, permanent cardiac pacemakers and other ferromagnetic devices can be safely studied. Two primary CT-based imaging techniques are clinically available to evaluate CBF; stable xenon enhanced CT (XeCT) and dynamic CT perfusion imaging (CTP). These techniques are based upon two entirely different mathematical models. XeCT is based upon the well-established diffusable tracer model, while CTP is based upon a non-diffusable tracer kinetic model that can be applied to both CTP and magnetic resonance perfusion (MRP).

Xenon CT cerebral blood flow

Xenon (Xe) is a naturally occurring element that is an inert gas at room temperatures. Like iodine, Xe is effective in attenuating X-rays and can therefore be employed as a contrast agent.