Indicator dilution theory and densitometric blood flow measurements

The indicator dilution theory is often thought to be the appropriate fundamental of most blood flow measurement techniques used daily in cardiac catheterization laboratories. By considering a simple theoretical flow system, the authors show that this theory is actually not applicable when the detector used to record the concentration-time curves is of the "trans-illumination" type, as is the case for instance in many videodensitometric applications (in these applications, pixels or groups of pixels play the role of detectors).