Influence of colloid particle profile on sentinel lymph node uptake

IntroductionParticle size of colloids employed for sentinel lymph node (LN) detection is not well studied. This investigation aimed to correlate particle size and distribution of different products with LN uptake.MethodsAll agents (colloidal tin, dextran, phytate and colloidal rhenium sulfide) were labeled with 99mTc according to manufacturer's instructions. Sizing of particles was carried out on electron micrographs using Image Tool for Windows (Version 2.0). Biodistribution studies in main excretion organs as well as in popliteal LN were performed in male Wistar rats [30 and 90 min post injection (p.i.)]. The injected dose was 0.1 ml (37 MBq) in the footpad of the left posterior limb. Dynamic images (0–15 min p.i.) as well as static ones (30 and 90 min) were acquired in gamma camera.ResultsPopliteal LN was clearly reached by all products. Nevertheless, particle size remarkably influenced node uptake. Colloidal rhenium sulfide, with the smallest diameter (5.1×10-3±3.9×10-3 μm), permitted the best result [2.72±0.64 percent injected dose (%ID) at 90 min]. Phytate displayed small particles (<15 μm) with favorable uptake (1.02±0.14%ID). Dextran (21.4±12.8 μm) and colloidal tin (39.0±8.3 μm) were less effective (0.55±0.14 and 0.06±0.03%ID respectively). Particle distribution also tended to influence results. When asymmetric, it was associated with biphasic uptake which increased over time; conversely, symmetric distribution (colloidal tin) was consistent with a constant pattern.ConclusionThe results are suggesting that particle size and symmetry may interfere with LN radiopharmaceutical uptake.