Nanomaterials for Medical Imaging …
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size, the interaction behavior of MR signals produces high relaxivity properties [174].
Paramagnetic gadolinium oxide nanoclusters with size ~1 nm showed a larger relaxivity of 9.9 s
−1 mM
−1 , after injection of these nanoclusters with high positive contrast
enhancement at various time points. This clearly shows that the injected particles with
more positive contrast enhancement of nanoparticles.
The high longitudinal relaxivity of paramagnetic Gd 2 O 3 NPs size of 1 nm was
observed when refluxing the precursors of Gadolinium ions under an oxygen environment. The relaxivity of the 1 nm Gd 2 O 3 NPs of water was around 9.9 s
−1 mM
−1 .
The large relaxivity of these NPs depends on the direct coupling effect and interaction with Gd ions and the size of nanomaterials. From the above literature, we could
narrow down that particle size with less than ~5 nm possesses high longitudinal
relaxivity, and are suitable for in vivo imaging. But the biodistribution and compatibility have to study to understand the use of Gd based NPs as clinical contrast.
Recent studies have shown the biodistribution of nanosized Gd 2 O 3 NPs has shown
less toxicity similar to chelated gadolinium. Tilement and his coworkers studied the
in vivo biodistribution analysis of Gd 2 O 3 NPs of a size range of 3–5 nm encapsulated
with polysiloxane shell conjugated with cyanine dye. Intravenous injection of these
NPs can be studied with optical imaging techniques. Initially, a small number of
particles was uptake through RES from the systemic circulation with less retention
time in RES. They suggested that the significant excretion was through the renal
system, which was evident from both the optical and MR imaging methods. Large
chelates of the Gd ions were accumulated from the liver and spleen. Hybrid imaging
with Gd 2 O 3 NPs is possible with the results given by the same group and further
developments of contrast agents with other imaging modalities [175].
Despite Gd 2 O 3 NPs, different nano compositions of Gadolinium have reported
modifying MR relaxivity of the contrast agents, combined therapeutic effects, and
image-guided surgery [176–178]. Capping and targeting agents of Gd 2 O 3 NPs are
essential to improvise the T 1 relaxivity in MRI. Polyacrylic acid capped Gd 2 O 3 NPs
were studied by Miao et al. with high positive contrast enhancement in liver, kidneys,
and bladder observed in 10 min duration. On increasing the time up to 2 h, the gradual
decrease in the contrast in the MR signals was due to the clearance from the bladder
[179]. Mekuria et al. encapsulated Gd 2 O 3 NPs with PAMAM dendrimer (G4.5Gd 2 O 3 NPs) and capped with polyethylene glycol. T 1 and T 2 images were acquired
by injecting these NPs in vivo at a concentration of 0.5 uM per kg. In general, NPs
with size, more than 20 nm would be uptake by RES in the body. But they were able
to circulate for a while and accumulated in the organs with high positive T 1 contrast
MR signals. These signals were observed in the kidney after 30 min of post-injection
and decrease after an hour. This is due to the circulation in enterohepatic circulation.
A similar effect of these G4.5-Gd 2 O 3 NPs with higher negative contrast in T 2 or
dark region in kidneys [180]. Navon and group showed a higher accumulation of
PET agents in tumor regions when linked with glucosamine compared to glucose
molecules [181]. Glucosamine linked with poly-cyclodextrin capped with Gd 2 O 3
NPs were used as a better targeting moiety for early diagnosis of cancer. Compared
to control Gd-DOTA (T 1 = 2.79 mM
−1 s
−1 ), glucosamine functionalized nanoparticles show better contrast with a relaxivity with T 1 = 4.86 mM
−1 s
−1 . The metastasis
365
size, the interaction behavior of MR signals produces high relaxivity properties [174].
Paramagnetic gadolinium oxide nanoclusters with size ~1 nm showed a larger relaxivity of 9.9 s
−1 mM
−1 , after injection of these nanoclusters with high positive contrast
enhancement at various time points. This clearly shows that the injected particles with
more positive contrast enhancement of nanoparticles.
The high longitudinal relaxivity of paramagnetic Gd 2 O 3 NPs size of 1 nm was
observed when refluxing the precursors of Gadolinium ions under an oxygen environment. The relaxivity of the 1 nm Gd 2 O 3 NPs of water was around 9.9 s
−1 mM
−1 .
The large relaxivity of these NPs depends on the direct coupling effect and interaction with Gd ions and the size of nanomaterials. From the above literature, we could
narrow down that particle size with less than ~5 nm possesses high longitudinal
relaxivity, and are suitable for in vivo imaging. But the biodistribution and compatibility have to study to understand the use of Gd based NPs as clinical contrast.
Recent studies have shown the biodistribution of nanosized Gd 2 O 3 NPs has shown
less toxicity similar to chelated gadolinium. Tilement and his coworkers studied the
in vivo biodistribution analysis of Gd 2 O 3 NPs of a size range of 3–5 nm encapsulated
with polysiloxane shell conjugated with cyanine dye. Intravenous injection of these
NPs can be studied with optical imaging techniques. Initially, a small number of
particles was uptake through RES from the systemic circulation with less retention
time in RES. They suggested that the significant excretion was through the renal
system, which was evident from both the optical and MR imaging methods. Large
chelates of the Gd ions were accumulated from the liver and spleen. Hybrid imaging
with Gd 2 O 3 NPs is possible with the results given by the same group and further
developments of contrast agents with other imaging modalities [175].
Despite Gd 2 O 3 NPs, different nano compositions of Gadolinium have reported
modifying MR relaxivity of the contrast agents, combined therapeutic effects, and
image-guided surgery [176–178]. Capping and targeting agents of Gd 2 O 3 NPs are
essential to improvise the T 1 relaxivity in MRI. Polyacrylic acid capped Gd 2 O 3 NPs
were studied by Miao et al. with high positive contrast enhancement in liver, kidneys,
and bladder observed in 10 min duration. On increasing the time up to 2 h, the gradual
decrease in the contrast in the MR signals was due to the clearance from the bladder
[179]. Mekuria et al. encapsulated Gd 2 O 3 NPs with PAMAM dendrimer (G4.5Gd 2 O 3 NPs) and capped with polyethylene glycol. T 1 and T 2 images were acquired
by injecting these NPs in vivo at a concentration of 0.5 uM per kg. In general, NPs
with size, more than 20 nm would be uptake by RES in the body. But they were able
to circulate for a while and accumulated in the organs with high positive T 1 contrast
MR signals. These signals were observed in the kidney after 30 min of post-injection
and decrease after an hour. This is due to the circulation in enterohepatic circulation.
A similar effect of these G4.5-Gd 2 O 3 NPs with higher negative contrast in T 2 or
dark region in kidneys [180]. Navon and group showed a higher accumulation of
PET agents in tumor regions when linked with glucosamine compared to glucose
molecules [181]. Glucosamine linked with poly-cyclodextrin capped with Gd 2 O 3
NPs were used as a better targeting moiety for early diagnosis of cancer. Compared
to control Gd-DOTA (T 1 = 2.79 mM
−1 s
−1 ), glucosamine functionalized nanoparticles show better contrast with a relaxivity with T 1 = 4.86 mM
−1 s
−1 . The metastasis