Particle size analysis: 90Y and 99mTc‐labelled colloids

Colloidal particle size is an important characteristic to consider when choosing a radiopharmaceutical for diagnosis and therapeutic purposes in nuclear medicine. Photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) were used to determine the particle‐size distribution of ⁹⁰Y‐ and ^99mTc‐labelled antimony trisulfide (Sb₂S₃) and tin colloids (Sn‐colloid). ⁹⁰Y‐Sb₂S₃ and ^99mTc‐Sb₂S₃ were found to have a diameter of 28.92 ± 0.14 and 35.61 ± 0.11 nm, respectively, by PCS. By TEM, ⁹⁰Y‐Sb₂S₃ particles were measured to be 14.33 ± 0.09 nm. ⁹⁰Y‐labelled Sn colloid were found to exist with a d_v(max1) of 805 nm and a d_v(max2) of 2590 nm, by PCS, whereas ^99mTc‐Sn colloid was shown to have more than 80% of radioactive particles of approximately 910 nm by PCS. For ⁹⁰Y‐labelled Sb₂S₃ and Sn colloid, a comparison of TEM and PCS indicates that these techniques found significantly different mean diameters. TEM has an excellent resolution necessary for radiocolloid particle‐sizing analysis, and it is a desirable size‐measuring technique because it is more reliable than PCS.