AJP - Heart and Circulatory Physiology, Vol 243, Issue 3 371-H378, Copyright © 1982 by American Physiological Society
Relative error and variability in blood flow measurements with radiolabeled microspheres
W. P. Dole, D. L. Jackson, J. I. Rosenblatt and W. L. Thompson
The validity of blood flow measurements made using radiolabeled
microspheres (reference sample technique) has been well established in a
variety of experimental models. Previous studies of the variability of the
method emphasize tissue sphere number as the principle source of random
variation. However, blood flow measurements depend on sphere distribution
to both tissue and reference samples as well as on quantitation of
different isotopes in a single tissue sample. In this study we examined the
major determinants of relative error and variability in flow rate
measurements inherent in the reference sample technique. Error magnitude
was predicted from a statistical model, simulated with numerical analogs,
and measured in anesthetized dogs with 15-micrometers microspheres.
Theoretically, with 2,000 spheres in the reference sample and greater than
or equal to 475 spheres in a tissue sample, blood flow can be measured with
10% accuracy at the 95% confidence level and with duplicate variability of
14%. Random errors in isotope quantitation were influenced by the specific
activity of the isotope and the fractional distribution of a given isotope
over the various energy windows. Suspension of tissue and reference sample
spheres at different heights (0.2 cm) resulted in systematic flow errors of
up to 13%. When errors due to separation of isotopes and differences in
sample height were minimized, the major determinant of variability in flow
measurements during simultaneous injection of differently labeled
microspheres was the number of spheres in both tissue and reference
samples.
