Lipid-Based Pharmaceutical Nanocarriers for Imaging Applications - Nanotechnology for Biomedical Imaging and Diagnostics - page 61

3.4 diagNostic appLicatioNs of LiposomaL imagiNg ageNts

The main body of experimental data on lipidic nanocarrier contrast agents relates to
liposomal formulations. some key examples of in vivo imaging utilizing contrast
liposomal vehicles are presented here (additional information can be found in
reference [19]).

3.4.1 Liver and spleen imaging

The imaging of the most macrophage-rich organs of rEs, liver and spleen, is the
easiest to perform, as rEs organs are the natural targets for intravenously adminis-
tered nanovesicles. The diagnostic imaging of liver and spleen is usually aimed at
discovering tumors and metastases in those organs, as well as certain blood flow
irregularities and inflammatory processes. The use of at least three different imaging
modalities for this purpose was described, namely, gamma-imaging, mri, and CT
imaging.
gamma-scintigraphy of the liver and spleen with liposomal contrast is used rather
rarely. However, suVs loaded with 99m Tc-glucoheptonate were found to accumulate
well in the liver of mice and rabbits and provide good scintigraphic images 90 min
upon iV administration of the liposomal contrast [87].
Currently, mri and CT imaging of the liver and spleen with diagnostic nanocar-
riers are well developed. Nanocarriers containing a soluble gd-dTpA complex
were demonstrated to be effective contrast agents for mri of liver, spleen, and
hepatic metastases [88-90]. Besides, gd-dTpA in 70 nm vesicles showed better
enhancement of rat liver and major blood vessels than the equivalent dose of free
gd-dTpA [35, 91].
Liposomes containing X-ray contrast agents (such as verografin, ioxaglate,
iohexol, iopromide, different nonionic contrast media, etc.) were used for CT imaging
[81]. iopromide-containing nanocarriers were even obtained in the lyophilized state
and then used for effective detection of liver tumors in mice and demonstrated good
storage longevity [55, 56]. iodine-containing interdigitation/fusion vesicles [92] with
high iodine content and a size of more than 1 µm were shown to provide sufficient
parenchyma enhancement at a dose of 0.1 g of iodine/kg. recently, the application of
serine- and mannose-modified liposomes loaded with a nonionic X-ray contrast
media, iohexol, for the parenchymal enhancement in rabbit liver VX-2 tumor model
was described, since Kupffer cell imaging is important for the detection of the liver
cancer [93]. similar model was also used for tumor CT imaging with iopromide
liposomes [94].

3.4.2 tumor imaging with contrast Nanocarriers

The main mechanism of nanocarrier accumulation in tumors is via extravasation
through leaky tumor capillaries into the interstitial space [95]. As in many other cases,
the efficacy of such accumulation can be sharply increased by using long-circulating
pEg-coated nanocarriers [96]. Nanocarrier-based imaging agents were already