EFFECT OF NON-STEADY-STATE PERFUSION ON XE-133 CEREBRAL BLOOD-FLOW MEASUREMENTS - AN ANALYTICAL STUDY

Activation studies employing the noninvasive xenon-133 technique are w idely used to investigate the cerebral circulation. Typical examples a re the investigation of hemispheral specialization of higher cortical function with cognitive activation or the assessment of the hemodynami c reserve in occlusive cerebrovascular disease by CO, inhalation. Trad itionally, in studies using this technique, there is the requirement o f a circulatory steady state during the measurement, Due to limitation s in the duration of the stimulus or habituation to the stimulus, the basic assumption is often violated. In this study we investigated with the aid of a computer model to what extent blood flow measurement res ults are affected by non-steady-state blood flow. The findings indicat e that cortical activation need not extend throughout the whole measur ement to be detectable. Maintenance of activation for at least 5 min i s sufficient for a successful measurement. In addition, the results sh ow that the activation should be fully established when the measuremen t starts to achieve maximal sensitivity. Delay in activating the circu lation will result in attenuated responses, especially if the stimulus is delayed beyond 2 min.