Detection and Description of Tissue Disease: Advances in the Use of Nanomedicine for Medical Imaging - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 248

water-soluble iodine contrast agent, in liposomes (giving an iodine
concentration of 13.8 mg/ml in the formulation) resulted in a
relatively small improvement in contrast. However, loading the
liposomes with both iopamidol and lipiodol, an iodinated oil, resulted
in iodine concentrations as high as 49.2 mg/ml in the combined
formulation, and the lipiodol did not disrupt the liposomal structure.
A limitation of this approach is that increasing the amount of lipiodol
in the liposome resulted in a mixture that was too viscous to produce
a liposomal dispersion. This formulation included cholesterol in
addition to 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC),
which increased the rigidity of the liposomal structure, reducing
leakage of entrapped iopamidol and increasing its concentration
within the liposomes by 1.6-fold. The in vivo performance of these
liposomes was encouraging, with an increase of 30 HU, and the
material also showed delayed clearance from the circulation. For
comparison, iopamidol, which is commonly used as a contrast agent
by itself, produces an increase of <7 HU when used at the same iodine
concentration.
8.2.1.3 Dendrimers
Dendrimers are large, synthetic, branched molecules made from
repeats of chemical units built around an inner core. The attraction
of these materials as imaging agents is that the structure is highly
defined and the size can be precisely controlled by controlling the
number of repeats (generations). The outer face of these molecules
can be chemically modified, so they can be targeted relatively simply.
One of the drawbacks of the dendrimers is the synthesis, which can
require up to several days depending on the formulation.
u et al. [16] reported the synthesis, characterization, and initial
imaging studies with a dendrimer-based CT contrast agent. This
compound was composed of a PEG core derivatized at each end
with polylysine dendrimers. Diff erent lengths of PEG and numbers
of generations of polylysine were used to construct molecules of
diff ering sizes with a large number of sites available for iodination.
The resulting compounds had molecular weights ranging from 21.7
kDa to 66.4 kDa (compared with 0.82 kDa for iodohexol). An initial
imaging study with PEG12000-carbamate-Gen4-IOB showed good
contrast in the liver of a rat, including the visualization of the blood
vessels. The 35 min blood half-life of this compound meant that
contrast was still evident 30+ min after intravenous injection, much