Biomedical Engineering Reference
In-Depth Information
The resulting accumulation of these particles may then be detected by MRI
(Zhang et al. , 2008).
While lacking the advantages of targeted nanoparticles, non-targeted
nanoparticles can be easier to produce and may still be of benefi t in MRI.
They can be combined with other novel techniques such as inversion recov-
ery with on resonant water suppression (IRON). IRON causes dispersion
of the resonant frequency of the protons in proximity to the contrast agents.
Since contrast agents are localised in the blood this leads to higher intra-
vascular contrast (Riederer, 2008). Employing IRON with the long circulat-
ing monocrystalline iron oxide particle (MION)-47, in a rabbit model, led
to an increase in intravascular contrast whilst suppressing background
tissue (mean contrast to noise ratio after injection was 61.9
±
12.4 vs. a
baseline of 1.1
0.001) and was also higher when compared with
conventional magnetic resonance angiograms. The combination of these
two technologies may result in an improvement in clinical MRI use
(Korosoglou et al. , 2008).
There are other applications of nanotechnology in tissue engineering.
Human aortic smooth muscle cells loaded with ultra-small superparamag-
netic iron oxide nanoparticles were seeded into tissue engineered vascular
grafts and subsequently implanted as aortic interposition grafts in mice. The
nanoparticles were retained for three weeks during which MRI was used
for real time non-invasive monitoring of smooth muscle cell retention
(Nelson et al. , 2008). This technology could be used to improve current
tissue engineering of vascular conduits and validate engineered grafts in the
future. Nanoparticles have also been used to improve experimental tech-
niques. In the laboratory setting iron oxide nanoparticle-loaded vascular
smooth muscle cells were delivered endovascularly to abdominal aortic
aneurysms in a rat model. The presence of these nanoparticles could be
confi rmed on MRI (Corot et al. , 2006; Deux et al. , 2008).
Non-iron-based magnetic nanoparticles are being developed. These
include magnetoliposomes, which are magnetite cores encapsulated in a
phospholipid bilayer. Such phospholipid vesicles containing phosphatidyl-
ethanolamine-diethylenetriaminepentaacetic acid can be complexed with
gadolinium ions (Gd 3+ ) to produce an agent which may have potential in
MRI contrast, though in vivo data are awaited (Ito et al. , 2005b; De Cuyper
et al. , 2007).
Another family of nanoparticles showing promise in MRI are dendrimers.
Different generations of gadolinium (Gd 3+ ) diethylenetriaminepentaacetic
acid (DTPA)-terminated poly(propylene) dendrimers have been devel-
oped as contrast agents in MRI. These Gd 3+ -based complexes provided
prolonged intravascular duration with improved contrast. Each generation
is defi ned according to the number of Gd 3+ ions per molecule (G1 - 4 ions
per molecule, G3 - 16 ions per molecule, G5 - 64 ions per molecule, etc.).
±
0.4 p
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