a method for measuring organ blood flow by indicator dilution, but more importantly, a method for measuring the distribution of cardiac output or the intraorgan distribution of blood flow. To measure distribution of flow, neutrally buoyant, chemically inert microspheres that have an indicator property (for example, radioactivity) are injected into a cardiac chamber or arterial blood. They are presumed to distribute in proportion to the distribution of arterial blood flow. Injected sphere size is selected to be large enough to embolize the vessels of interest. Injected quantity is selected to be large enough to provide statistically meaningful samples and small enough not to alter the organ blood flow under investigation. Organ samples are taken to quantify the distribution of the microspheres and hence the flow. See: Fick method, Stewart-Hamilton method.