Iron Oxide-Based Magnetic Nanoparticles Synthesized from THE Organic Solution Phase for Advanced Biological Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 41

(MaT B III) indicated the advantages of bimodal imaging [55]. Since the injected
NPs tended to accumulate in tumor due to enhanced permeability and retention
(EPR) effect, 3d cT images gave the enhanced signals from tumor-associated areas,
especially those contrast from newly formed blood vessel to tumors, which are the
main targets in practical clinical treatment to tumors (Fig. 2.9b) [55]. Simultaneously,
MRI with higher sensitivity than cT was used to reveal the more precise shape and
structure of the tumor (Fig. 2.9c). as the multimodality imaging probe, the Fe 3 O 4 /
TaO x NPs show no obvious toxicity to rats.

2.5.3 simultaneous T 1 − T 2 Images in MrI
considering requirements in toxicity, sensitivity, and spatial/time resolutions, MRI is
a unique multimodality imaging technique as it provides two independent imaging
modalities, T 1 -weighted image and T 2 -weighted image, to generate “brighter” and
“darker” images. Therefore, the preferential combination of T 1 and T 2 contrast effect
in a single NP will enable the so-called “self-confirming” imaging under a single
instrument [56]. as Figure 2.10a demonstrates, the fringe field created by superpara-
magnetic NP T 2 contrast agent perturbs the relaxation process of paramagnetic
T 1 contrast agent when two probes are in proximity, dramatically quenching the T 1
signal. To magnetically decouple the T 1 and T 2 contrast effect in a single agent, a
dual-mode nanoparticle contrast agent (dMca) was designed and synthesized
through fabricating multilayer core-shell NPs. Figure 2.10b shows the structure and
TEM image of this hybrid NPs [56]. The inner core is 15 nm MnFe 2 O 4 NPs acting as
T 2 contrast agent, while the outer shell of 1.5 nm gd 2 O(cO 3 ) 2 is used to enhance T 1
contrast. a separating SiO 2 layer is inserted between these two layers and is con-
trolled from 4 to 20 nm to study the decoupling effect (Fig. 2.10c and d). With the
16 nm layer of SiO 2 employed, the dMSa shows a three times higher r 1 (33.1 mM −1 ·s −1 )
than the conventional gd-dTPa T 1 contrast agent (9.6 mM −1 ·s −1 ) and a two times
higher r 2 (274 mM −1 ·s −1 ) than the conventional Ferridex T 2 contrast agent
(108 mM −1 ·s −1 ) (Fig. 2.10c and d) [56]. In vivo tests among gd-dTPa, Ferridex, and
dMca implanted in mice, only dMca displayed both brighter T 1 and darker T 2
responses (Fig. 2.10e). On the contrary, gd-dTPa and Ferridex were only effective
in one specific imaging mode. This study provides a new pathway to the multimodal-
ity imaging contrast agent with a higher level of accuracy and self-confirming
capability in one instrumental system.

2.6 conclusIon and perspectIve

Recent advance in synthetic methodology in organic solution phase allows for the
desirable control of IOMNPs' size, composition, crystallinity, and structures, leading
to the optimal magnetic property of IOMNPs. Superparamagnetic Fe 3 O 4 and ferrite
NPs with high magnetizations were used as advanced MRI contrast agent to enhance