The method for the preparation of LC Bead® (Biocompatibles UK Ltd., Farnham, UK) has been described in detail elsewhere 24 . Briefly, the beads were produced using a PVA-based macromer. The macromer was synthesized by the acid-catalyzed reaction of N-acryloyl-aminoacetaldehyde dimethylacetal (NAAADA) with the 1,3 diol units on the PVA backbone to form a stable cyclic acetal structures with pendent reactive acrylamide groups. The macromer was used in an inverse suspension free-radical copolymerization with 2-acrylamido-2-methylpropanesulfonate sodium salt (AMPS). The aqueous macromer/monomer mixture was suspended in butyl acetate and stabilised by cellulose acetate butyrate to prevent coagulation. Potassium persulfate was used as one half of a redox initiator couple, which is present in the aqueous phase. The stirred mixture was heated to 60°C and then tetramethylethylenediamine (TMEDA, the other component of the redox couple) was added to the oil phase, where upon polymerization was initiated and a water-swollen crosslinked network formed. After the polymerization was complete the beads were dried by washing in acetone and drying in an oven at 40°C overnight to form a free-flowing powder 24 . PVA-AMPS beads were originally developed from contact lens technology and are thus inherently optically transparent and biocompatible. These beads are tinted blue using a reactive dye (Reactive Blue 4, RB4) to enable visualization of the bead suspension to make for easier handling (Figure 1). A novel process was developed in which the blue tinting step was replaced by an alternative reaction to attach a radiopaque moiety (triiodonated benzyl) to the preformed hydrogel (Figure 1). In order to couple the radiopaque compound to the polymer backbone, the beads in dimethyl sulfoxide (DMSO) were reacted with 2,3,5-triiodobenzaldehyde in an acid-catalyzed reaction under nitrogen with stirring, to form stable cyclic acetal linkages with pendent triiodobenzyl moieties. Consumption of the aldehyde was monitored using high-performance liquid chromatography (HPLC) and once complete, the reaction was filtered. The cake of beads was washed thoroughly with copious amounts of DMSO and then water, until free of unreacted aldehyde as determined by HPLC.