Blood flow measurements with radionuclide-labeled particles.

When appropriately and correctly applied, the microsphere technique is relatively simple and extremely accurate. Distribution patterns, both of total systemic arterial blood flow or venous return as well as within specific organs, can be measured. Several techniques have been applied to quantitate flow using microspheres; the reference sample method is extremely simple and by far the most accurate of all. Collection of venous effluent is perhaps more accurate but requires extensive surgery and is almost certainly the least physiologic. Other methods used for quantitation, such as bolus injections of indocyanine green dye or in fusions of diffusable indicators, are considerably less accurate and therefore significantly reduce the reliability of the microsphere technique. Selection of the appropriate size microspheres allows for definition of arteriovenous anastomoses as well as the measurement of organ blood flows and distribution of blood flow within those organs. In most instances, smaller microspheres (15mu diameter or 8-10mu diameter) have significant advantages over larger ones. They are distributed more like red cells, obstruct less of the vascular bed, are less variable in size, and can be given in significantly greater numbers. This latter point is important, since the statistical criteria need to be satisfied and the use of small spheres allows for the more reliable measurement of blood flow to small organs or to small regions of organs.