High spatial resolution measurements of organ blood flow in small laboratory animals

With the use of a newly developed Imaging Cryomicrotome to determine the sp atial location of fluorescent microspheres in organs, we validate and repor t our processing algorithms for measuring regional blood flow in small labo ratory animals. Microspheres (15-mum diameter) of four different fluorescen t colors and one radioactive label were simultaneously injected into the le ft ventricle of a pig. The heart and kidneys were dissected, and the number s of fluorescent and radioactive microspheres were determined in 10 randoml y selected pieces. All microsphere counts fell well within the 95% expected confidence limits as determined from the radioactive counts. Fluorescent m icrospheres (15-mum diameter) of four different colors were also injected i nto the tail vein of a rat and the left ventricle of a rabbit. After correc tion for Poisson noise, correlation coefficients between the colors were 0. 99 +/- 0.02 (means +/- SD) for the rabbit heart and 0.99 +/- 0.02 for the r at lung. Mathematical dissection algorithms, statistics to analyze the spat ial data, and methods to visualize blood flow distributions in small animal organs are presented.