Skeletal uptake of ⁹⁹Tc(m) diphosphonate in relation to local bone blood flow

The right/left ratios of tibial uptake of ⁹⁹(m)Tc diphosphonate (EHDP) and relative blood flow (based on microsphere distribution) were determined in control rats and rats with a ligated right femoral artery or a healing right tibial fracture. Correlation between ⁹⁹(m)Tc EHDP uptake and relative blood flow was highly significant (r = 0.917; P<0.0001) for relative flow ratios less than 1.7. When the ratio was greater than 1.7, there was little further increase in ⁹⁹(m)Tc EHDP uptake. Ligation of the femoral artery in rats with healing fractures resulted in a more marked reduction of blood flow than of ⁹⁹(m)Tc EHDP uptake. These results suggest that regional bone blood flow is a major determinant of ⁹⁹(m)Tc EHDP uptake, though changes in regional tracer extraction efficiency are also important.