Colored microspheres for measuring and tracing fluid mixing and flow

Abstract

Microspheres labeled with a dye for which the absorption spectra is known permit the measurement of blood flows, particularly regional myocardial blood flow (RMBF), without radiation safety concerns and radioactive waste disposal problems. Polystyrene spheres, nominally of diameter 15.+-.0.1 [SD] um and density 1.09 g/ml, are dyed with a fixed quantity, nominally 30 picograms per microsphere, with one of several, nominally 5, colored dyes. The colored microspheres (CM) are injected into the left atrium or into a coronary perfusion. The CM are extracted from myocardium and blood by digestion with KOH and subsequent microfiltration. The dyes are then recovered from the CM within a defined volume of a solvent, and their concentrations are determined by spectrophotometry. The composite absorbance or emission spectra of several dyes are mathematically resolved using matrix inversion. Leaching of dye from the CM was less than 0.1% over a two months period in vitro, and did not occur during 8 hours in blood and myocardium of 4 anesthetized dogs in vivo. For further validation of this method, pairs of CM and RM (15.5.+-.0.1 [SD] um) were simultaneously injected under 5 different RMBF conditions (range: 0-10 ml/(min g)) into the left anterior descending coronary artery of 4 anesthetized pigs, with coronary inflow as a flow-reference, or into the left atrium of 4 anesthetized dogs using aortic blood withdrawal as a reference.