Lipid-Based Pharmaceutical Nanocarriers for Imaging Applications - Nanotechnology for Biomedical Imaging and Diagnostics - page 48

Consequently, chief objectives for successful biomedical imaging become to
accumulate a sufficient quantity of the contrast moiety in the area of interest and keep
its presence in normal tissues on the most minimal level possible.
A very attractive approach is the application of contrast-loaded pharmaceutical
nanocarriers as contrast materials providing an enhanced accumulation of reporter
moieties in pathological areas. for almost three decades now, liposomes have been
identified as promising vehicles to deliver a wide range of encapsulated and/or
membrane-associated therapeutic or diagnostic agents into the required areas [1-
3], and in more recent years, micelle-loaded imaging agents have also shown great
clinical promise. in particular, these nanocarriers have been utilized for carrying
the diagnostic moieties used with all imaging modalities: gamma-scintigraphy,
magnetic resonance imaging (mri), computed tomography (CT) imaging, and
sonography [4, 5]. in the last case, acoustic characterization of echogenic systems,
such as liposomes, becomes especially important as well as the choice of the
optimal frequency to obtain a required signal [6]. in several important recent review
papers, the use of magnetoliposomes for molecular imaging and cancer theranos-
tics is described [7], as well as the development of liposomes from drug delivery
vehicles to the leading platform in diagnostic and theranostic nanomedicine [8],
and general problems of using liposomes in molecular imaging [9] are analyzed.
some of those reviews concentrate on specific problems, such as liposomal contrast
agents for brain tumor imaging [10] or for cardiovascular diseases [11] or the use
of liposomal contrast agents in specific imaging modalities, such as positron
emission tomography (pET) [12].
Now, the combination of advanced imaging methods and equipments, providing
high sensitivity and spatial resolution, and the use of nanoscale devices to deliver
diagnostic agents with high target specificity allow for more accurate detection and
staging, leading to more accurate therapy planning of the disease state.
Among the current pharmaceutical nanoscale drug vehicles, lipid-based nanoves-
icles, such as liposomes (predominantly, for water-soluble drugs) and micelles (prin-
cipally, for water-insoluble drugs), are considered the most extensively studied,
demonstrating marked advantages over other delivery systems, and possess the most
suitable characteristics for encapsulation of many drugs, genes, and diagnostic
(imaging) agents [13, 14]. simply, possibility to easily control composition, size, and
in vivo stability of a nanoreservoir is a major advantage. more importantly, these
nanovesicular systems retain remarkable loading capacity of various imaging and
contrast agents, of either hydrophilic or lipophilic nature or both [15].
Liposomes are bilayered phospholipid vesicles of size ranging from 50 to 1000 nm
in most cases, which can be loaded with a variety of water-soluble cargos (into their
inner aqueous compartment) and water-insoluble molecules (into the hydrophobic
compartment of their phospholipid membrane), and are considered as promising
drug carriers for well over three decades [15]. The use of targeted liposomes, that is,
liposomal carriers specifically accumulating inside the affected organ or tissue,
would increase the efficacy of the liposome-incorporated drug and decrease the loss
of their contents in the reticuloendothelial system (rEs) [15]. several successful
protocols have been employed to actively and passively target liposomal nanocarriers