Regional blood flow with first circulation time-indicator curves: a simplified, physiologic method of interpretation.

Dynamic computed tomography, digital subtraction angiography, and radionuclide angiography can all be used to evaluate regional blood flow noninvasively. In each case an indicator is injected intravenously and time-indicator curves are generated from regions of interest during the first circulation. Although regional blood flow cannot be determined uniquely from first circulation time-indicator curves, relative transit time to and through the regions of interest and relative regional blood volume in the regions of interest can be measured and related to relative regional blood flow using a modified Stewart-Hamilton equation. However, for precise mathematical calculation, extrapolation of the first circulation data beyond the point of recirculation is required. This extrapolation is inconvenient and difficult to perform accurately and reproducibly. Indices of transit time and regional volume that do not require extrapolation were evaluated in an experimental model. The correlation coefficients between the indices of transit time and volume and the more mathematically precise measurements were 0.99 and 0.95, respectively (p less than 0.01). It is suggested that these indices, which can also be evaluated visually, are useful in interpreting first circulation time-indicator curves in a physiologic manner.