On the validity of blood flow measurement using colored microspheres

The aim of this study was 1) to investigate the validity of repeated estima tions of blood flow using colored microspheres (CMS) and 2) to develop and validate a method that permits four consecutive estimations in the same ani mal using nonradiolabeled microspheres (NRMS). Several mixtures of differen t types of microspheres were injected in dogs, with each mixture containing the radiolabeled microspheres (RMS; labeled with Sn-113) with either three CMS, four CMS, or three CMS and one type of fluorescent (crimson labeled) microsphere (FMS). The blood flows estimated with the use of any of the inj ected microspheres were compared with those measured using the RMS as the " gold standard." The results were analyzed by 1) regression analysis, 2) var iance analysis (ANOVA I), and 3) estimation of the limits of agreement betw een RMS and NRMS flow rates. The results indicate that simultaneous estimat ions of blood flow obtained with the use of more than three CMS lack accura cy and reliability. A combination of three types of CMS with crimson-labele d FMS, however, offers the possibility to estimate consecutively four diffe rent flow rates in the same animal in an accurate way and with relatively h igh precision.