Transfer function through regional cerebral cortex evaluated by a photoelectric method.

A new technique is reported for obtaining the transfer function through the regional cerebral cortex. Tissue carbon-black (CB) dilution curves were recorded with a photoelectric apparatus used as a densitometer head in cat cortex in situ following intracarotid injection of 0.2 ml of 1/40 diluted CB solution. The linearity and stationarity of the vascular system, reproducibility of the curve, and recirculation were tested. The tissue CB dilution curve, a cumulative distribution function, was first differentiated yielding two curves comprising the inlet and outlet curves. The error due to "overlapping" was corrected for by extrapolation using the gamma-density function. The transfer function through the cortex was then calculated by numerical deconvolution of the inlet and outlet curves. The validity of the calculated transfer function was verified by comparison with that obtained from actual CB dilution curves recorded simultaneously from the pial artery and superior sagittal sinus. The transfer function was further subjected to moment analysis for determining the intraparenchymal circulatory parameters of the cerebral cortex. Some examples demonstrating the applicability of technique are given.