Manufacturing process to control particle size

A process for preparing a sterile injectable suspension of radiolabeled macroaggregated serum albumin suitable for use in scanning a mammalian patient consisting of: 1) purifying serum albumin with a saline solution; 2) buffering the purified serum albumin; 3) adding stannous halide in HCl solution to the buffered mixture to obtain a reaction mixture; 4) gradually heating and cooling the reaction mixture to form macroaggregate particles; 5) separating the macroaggregates from the reaction mixture; 6) suspending the macroaggregates in sterile water for injection; 7) adding purified serum albumin; 8) lyophilizing the suspension; and 9) reconstituting the radiolabeled lyophilizate with 99mTc. The invention also includes a process for preparing a stable, sterile lyophilizate of macroaggregate particles of human serum albumin consisting of steps 1-7.