Particle size analysis of (99m)Tc-labeled and unlabeled antimony trisulfide and rhenium sulfide colloids intended for lymphoscintigraphic application.

Colloidal particle size is an important characteristic to consider when choosing a radiopharmaceutical for mapping sentinel nodes in lymphoscintigraphy. Photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) were used to determine the particle size of antimony trisulfide and rhenium sulfide colloids, and membrane filtration (MF) was used to determine the radioactive particle size distribution of the corresponding (99m)Tc-labeled colloids. Antimony trisulfide was found to have a diameter of 9.3 +/- 3.6 nm by TEM and 18.7 +/- 0.2 nm by PCS. Rhenium sulfide colloid was found to exist as an essentially trimodal sample with a d(v(max1)) of 40.3 nm, a d(v(max2)) of 438.6 nm, and a d(v) of 650-2200 nm, where d(v) is volume diameter. (99m)Tc-antimony trisulfide by MF showed that more than 96% of radioactive particles were smaller than 100 nm; however, (99m)Tc-rhenium sulfide showed that more than 21% were smaller than 100 nm. These radioactive colloids were used with seven different membrane compositions and found not to adsorb significantly to any of them. MF was validated as a simple and reliable technique to estimate the percentage radioactive particle size distribution.