[The effectiveness of dynamic CT as a tool for the analysis of cerebral hemodynamics].

It is generally accepted that dynamic CT is one of the best way to evaluate cerebral hemodynamics. Employing our original computer simulation method, the present study was undergone to examine the theoretical background of dynamic CT. When a single bolus injection of non-diffusable indicator is intravenously performed, the time density curve of a cerebral tissue consists of the following two components: the time density curve of a carotid artery (g(x)) and the dispersion curve through the cerebral tissue (f(x)). A mean transit time (MTT) of the latter curve can be mathematically calculated by height-over area method. The concept gave us an interesting idea that a computer simulation could produce the time density curve implying an MTT. Convolution technique was applied to synthesize it from f(x) and g(x). The latter curve (g(x)) is influenced by several conditions such as a dispersion through a lung, a cardiac output and systemic arterial pressure. Therefore, it is not essential to measure the definite parameter from the time density curve obtained by dynamic CT. Dynamic CT should be considered as a qualitative method rather than a quantitative one. Several parameters were given by the analysis of a simulated curve. A time to peak (PT), above all, was most linearly correlated to MTT. A prolongation of PT in the insulted area, which means a prolongation of MTT, leads to a decrease of cerebral blood flow. In addition, we examined if Gamma variate fitting curve could apply a substitute for an original time density curve.(ABSTRACT TRUNCATED AT 250 WORDS)