“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Multifunctional Nanomaterials for Cancer Theranostics 249
5.5. Magnetic Resonance Imaging
MRI is a noninvasive diagnostic method, which is the most com
monly used in current medical examination for getting highresolution
and 3D anatomical images in the body through differing relaxation
times between physiological tissues. The parameters of longitudinal
(T 1) or transverse (T 2) represent the differences in these relaxation
times with the use of image contrasts. DTPA–Gd (Magnevist®) is a
commercial MRI Gdbased contrast agent. In order to develop more
efficient contrast agents, more and more attention is focused on
nanotechnology. Currently the most studied nanosized contrast
agents mainly include, Fe 3 O 4 based T 2 contrast agent, manganese
oxide nanoparticlesbased T 1 contrast agent.302–304 For example, Xu
et al. developed a premix membrane emulsification method to pre
pare uniform PEGylated PLGA microcapsules with superparamag
netic Fe 3 O 4 nanoparticles embedded in the shell for ultrasound/
magnetic resonance bimodal imaging.^305 However, spherical super
paramagnetic Fe 3 O 4 nanoparticles exhibit relatively low transverse
relaxivity. In order to solve this deficiency, Zhao et al. reported a
new strategy to achieve high transverse relaxivity by controlling the
morphology of iron oxide nanoparticles.^306 Sizecontrollable octa
pod Fe 3 O 4 nanoparticles with an ultrahigh transverse relaxivity value
were successfully fabricated. These octapod Fe 3 O 4 nanoparticles
were much more effective T 2 contrast agents for in vivo imaging and
small tumor detection in comparison with conventional Fe 3 O 4 nano
particles. Detection of brain gliomas at the earliest stage is of great
importance to improve outcomes, but it remains a most challenging
task. Chen et al. prepared folic acid modified manganese oxide
nanoparticles for the early diagnosis of brain gliomas.^307 T 1 – T 2 dual
modal MRI can offer complementary diagnostic information, lead
ing to more precise diagnosis. Li et al. reported novel hybrids of
nanocubes with both iron and Gd elements as T 1 – T 2 dual modal
contrast agents.^308 In vivo MRI of rats showed both T 1 positive and
T 2 negative contrast enhancements in the livers, which were about
two folds of those of Gd 2 O 3 nanoparticles and Fe 3 O 4 nanocubes,
respectively.
