Biomedical Engineering Reference
In-Depth Information
5.3
MagA
Magnetotactic bacteria are motile prokaryotes that synthesize intracellular magnetic
structures and move in relation to the earth's magnetic field (Bazylinski and Frankel
2004
). The synthesized structures, magnetosomes, consist of multiple iron oxide
crystals surrounded by a lipid membrane. One of the genes identified to be involved
in magnetosome production is
magA
. When 293FT cells, a common human pack-
aging cell line, were transfected with
magA
, the cells produced sub-micron sized
magnetosomes that contained multiple iron oxide crystals each measuring 3-5 nm
in diameter (Zurkiya et al.
2008
). Induction of the gene
magA
increased intra-
cellular iron by 0.55 pg/cell and produced up to a fourfold change in measured
relaxation rate. The use of
magA
is in its infancy, but current results suggest that it
is a promising MR reporter.
6
Applications of Cellular MRI
The development of
in vivo
cellular tracking by MRI has generated much interest.
The balance between spatial resolution and sensitivity, as well as its lack of ionising
radiation, makes MRI a practical and translatable modality for cellular detection.
Not only has MRI been used to track the movement and incorporation of adminis-
tered cells in animal models of diseases, but also clinical trials of MR cellular
tracking have begun.
6.1
Animal Models of Diseases
Tissue engineering has progressed from early use of acellular artificial scaffolds to the
incorporation of cells or tissue onto biocompatible materials prior to their implan-
tation, improving tissue regeneration. With the integration of imaging techniques,
the participation of cells in tissue repair can be monitored. The approach by various
research groups is similar: label cells with a clinical iron oxide contrast agent,
seed the labelled cells on an engineered implant (the sequence of the first two
steps can be reversed) and introduce the cell-loaded implant into an animal model.
Ferumoxide-labelled MSC on collagen scaffolds have been imaged
in vitro
(Terrovitis
et al.
2006
), as have labelled MSC within gelatine sponges
in vivo
(Ko et al.
2007
).
By labelling aortic smooth muscle cells with USPIO prior to seeding them onto a
polymeric vascular graft, researchers were able to evaluate the graft performance
in vivo
(Nelson et al.
2008
). The cells were detected to have successfully remained in
the scaffold vicinity for up to several weeks. The success of MR monitoring, however,
may be limited by the MR properties of implants used. Ferrous metallic implants
and voluminous, water-impenetrable implants may cause susceptibility artefacts, and
may not provide sufficient contrast to identify hypo-intense cells (Nelson et al.
2008
).
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