A new formulation of Tc-99m minimicroaggregated albumin for marrow imaging: comparison with other colloids, In-111 and Fe-59.

The biodistributions of five Tc-99m colloids were compared with the 24-hr distributions of Fe-59 and In-111 in dogs by direct radioassay 1 hr after intravenous injection. One formulation of Tc-99m minmicroaggregated albumin (particle size 30-100 mn), produced the highest marrow concentration, approximately six times that of Tc-99m sulfur colloid, with similar blood, and liver concentrations and a lower splenic uptake. Nevertheless, the best colloid marrow uptake was lower than the 24-hr value for In-11 and much lower than that for Fe-59. The marrow concentration of minimicroaggregated albumin was also higher than that of sulfur colloid in rats at 30 min after injection. The principal disadvantage of Tc-99m antimony sulfide colloid was its slow blood clearance. Clinical evaluation of Tc-99m minimicroaggregated albumin for marrow imaging appears warranted, although its hepatic activity will obscure overlying and immediately adjacent marrow.