Tc-99m Nanocoll: Size changing effects of serum albumin particles and possible influence for sentinel lymph node detection

Objectives Labeling and visualization of the sentinel lymph node required a significant nodal tracer uptake. In this context the amount and particle size play a crucial role. The size changing effect after the labeling with Tc-99m and Ga-68 of serum albumin particles and the possible influence for sentinel lymph node detection were reported.

Methods The preparation of Tc-99m Nanocoll was carried out according the product information of the manufacture. The kit was reconstituted with 1-5 ml Na[99mTc]TcO4, containing 185 - 5550 MBq and incubated for 30 min at room temperature. The labelling with Ga-68 was performed analogue the procedure described by (Maus et al., 2011). RCP was determined by radio TLC. Size distribution was visualized after membrane filtration over a 100 nm filter via transmission electron microscopy using standard methods. Animal studies were carried out on Wistar rats anesthetized with Isoflurane and the biodistribution was visualized and quantificated using the micro PET scanner after i.v. application.

Results Labeling, both with Ga-68 and TC-99m result in a significant agglomeration.A subsequent filtering process takes about 2-3 minutes. The average radioactivity retained in the filter was 13 % ±2 of total activity. Radiochemical purity difference between the pre- and post-filtration for the Tc-99m labeled compound show no significant differences and was always > 97 %. Electron microscopic and digital image analyses rendered for the unfiltered particle an average size between 33-49 nm and for the filtered between 16- 24 nm. The analysis of the animal pet images showed depositions in lung and liver after i.v. application, a indicator for significant in vivo agglomeration.

Conclusions The results of this pilot study give evidence that particle size is influenced due to agglomeration and has effects on the physiochemical and surface properties