Abstract
In this review we discuss the development of paramagnetic liposomes incorporating MRI contrast agents and show how these are utilized in cellular imaging in vitro. Bi-functional, bi-modal imaging paramagnetic liposome systems are also described. Next we discuss the upgrading of paramagnetic liposomes into bi-modal imaging neutral nanoparticles for in vivo imaging applications. We discuss the development of such systems and show how paramagnetic liposomes and imaging nanoparticles could be developed as platforms for future multi-functional, multi-modal imaging theranostic nanodevices tailor-made for the combined imaging of early stage disease pathology and functional drug delivery.
Highlights
Cellular imaging has been defined as “the visualization of specific cells in an intact animal” but this is a collective term for the visualisation of any type of whole cell under a variety of circumstances [1]
Similar to cellular bilayers, liposomes or lipid-based nanoparticles represent a very useful alternative to macromolecular polymeric structures as carriers of contrast agents, because they can be adapted to meet the specific requirements of cell labelling vectors, and to meet the general criteria for the development of novel potential magnetic resonance imaging (MRI) contrast agents that can be summarized as: an increased thermodynamic stability, favourable rate of excretion, lowered toxicity, lipophilicity, target specific biodistribution and an increase in relaxivity
In the case of paramagnetic liposomes, these effects need to be considered alongside other factors such as liposome rigidity that leads to limited water flux between the liposome aqueous cavity and outer bulk water, and can impair the overall impact of the contrast agents on local tissue water relaxivity [44]
Summary
Cellular imaging has been defined as “the visualization of specific cells in an intact animal” but this is a collective term for the visualisation of any type of whole cell under a variety of circumstances [1]. 2010, 11 visualise molecules and sub-cellular components within individual cells [2]. Sci. 2010, 11 visualise molecules and sub-cellular components within individual cells [2] Both cellular and molecular imaging requires the use of molecular probes (or imaging agents) to facilitate the use and applications of either technique. Have limitations due to short lived radioisotopes and poor spatial resolution This is not the case for magnetic resonance imaging (MRI) which is capable of producing three-dimensional images of tissues containing water with a high degree of spatial resolution. The improvement in image quality that arises with these contrast agents, derives from the modulating effects of the coordinated metal ions on longitudinal (T1) or transverse (T2) relaxation times associated with proton resonance signals emanating from bulk water molecules surrounding the coordinated metal ions (see below). We shall look at contrast agents in more detail, focusing on Gd3+based systems
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