Nanoprobes for hybrid SPECT/MR molecular imaging

Advances in superparamagnetic iron oxide nanoparticles modified with branched polyethyleneimine for multimodal imaging

Multimodal imaging are approaches which combines multiple imaging techniques to obtain multi-aspect information of a target through different imaging modalities, thereby greatly improve the accuracy and comprehensiveness of imaging. Superparamagnetic iron oxide nanoparticles (SPIONs) modified with branched polyethyleneimine have revealed good biocompatibility and stability, high drug loading capacity and nucleic acid transfection efficiency. SPIONs have been developed as functionalized platforms which can be further modified to enhance their functionalities. Those further modifications facilitate the application of SPIONs in multimodal imaging. In this review, we discuss the methods, advantages, applications, and prospects of BPEI-modified SPIONs in multimodal imaging.

Microfluidic Fabrication of Gadolinium-Doped Hydroxyapatite for Theragnostic Applications

Among the several possible uses of nanoparticulated systems in biomedicine, their potential as theragnostic agents has received significant interest in recent times. In this work, we have taken advantage of the medical applications of Gadolinium as a contrast agent with the versatility and huge array of possibilities that microfluidics can help to create doped Hydroxyapatite nanoparticles with magnetic properties in an efficient and functional way. First, with the help of Computational Fluid Dynamics (CFD), we performed a complete and precise study of all the elements and phases of our device to guarantee that our microfluidic system worked in the laminar regime and was not affected by the presence of nanoparticles through the flow requisite that is essential to guarantee homogeneous diffusion between the elements or phases in play. Then the obtained biomaterials were physiochemically characterized by means of XRD, FE-SEM, EDX, confocal Raman microscopy, and FT-IR, confirming the successful incorporation of the lanthanide element Gadolinium in part of the Ca (II) binding sites. Finally, the magnetic characterization confirmed the paramagnetic behaviour of the nanoparticles, demonstrating that, with a simple and automatized system, it is possible to obtain advanced nanomaterials that can offer a promising and innovative solution in theragnostic applications.

Nanoconfinement-mediated cancer theranostics

Despite various therapeutic or diagnostic developments, cancer is still one of the most lethal diseases due to insufficiently adequate treatments and the delay of the early stage of disease detection. An image-guided drug delivery system (IGDDS), as a real-time noninvasive imaging assessment of therapeutic response, has the strong potential to improve the diagnosis and treatment of cancer because its imaging property offers the quantification of nanomedicine at the intended disease sites, the possible assurance of adequate treatment and elimination of undesirable delay of early-stage diagnosis due to low resolution. One of potential modality that overcomes these challenges could be the nanoconfinement of gold (Au) nanoparticles within other nanoparticles called "Particle-in-Particle (PIP)", which is a strong candidate of cancer treatment because of its "theranostic (therapy + diagnostics)" advantages including imaging (e.g., CT) and therapeutic hyperthermia application. In this review, we will elaborate on the current application of theranostic by nanoconfinement. Then, we will narrow down the gold nanoparticle-mediated theranostic application and its nanoconfinement advantages. Finally, the future direction for maximum nanoconfinement mediated cancer therapy will be included.

Tomographic magnetic particle imaging of cancer targeted nanoparticles

Magnetic Particle Imaging (MPI) is an emerging, whole body biomedical imaging technique, with sub-millimeter spatial resolution and high sensitivity to a biocompatible contrast agent consisting of an iron oxide nanoparticle core and a biofunctionalized shell. Successful application of MPI for imaging of cancer depends on the nanoparticles (NPs) accumulating at tumors at sufficient levels relative to other sites. NPs' physiochemical properties such as size, crystallographic structure and uniformity, surface coating, stability, blood circulation time and magnetization determine the efficacy of their tumor accumulation and MPI signal generation. Here, we address these criteria by presenting strategies for the synthesis and surface functionalization of efficient MPI tracers, that can target a typical murine brain cancer model and generate three dimensional images of these tumors with very high signal-to-noise ratios (SNR). Our results showed high contrast agent sensitivities that enabled us to detect 1.1 ng of iron (SNR ∼ 3.9) and enhance the spatial resolution to about 600 μm. The biodistribution of these NPs was also studied using near-infrared fluorescence (NIRF) and single-photon emission computed tomography (SPECT) imaging. NPs were mainly accumulated in the liver and spleen and did not show any renal clearance. This first pre-clinical study of cancer targeted NPs imaged using a tomographic MPI system in an animal model paves the way to explore new nanomedicine strategies for cancer diagnosis and therapy, using clinically safe magnetic iron oxide nanoparticles and MPI.

99mTc-conjugated manganese-based mesoporous silica nanoparticles for SPECT, pH-responsive MRI and anti-cancer drug delivery

In recent decades, hybrid imaging techniques that exploit the advantages of multiple imaging technologies have aroused extensive attention due to the deficiencies of single imaging modes. Along with the development of single photon emission computed tomography-magnetic resonance imaging (SPECT-MRI), it is currently necessary to develop a series of dual probes that can combine the outstanding sensitivity of SPECT with the high spatial resolution of MRI. Herein, the commonly used technetium-99 (^99mTc) was labelled on the surface of manganese oxide-based mesoporous silica nanoparticles (MnO_x-MSNs) for use in SPECT-MRI dual-modal imaging. The radiolabelling yield was as high as 99.1 ± 0.6%, and the r₁ value of the nanoprobes was able to reach 6.60 mM^-1 s^-1 due to the pH-responsive properties of the MnO_x-MSNs. The high-performance SPECT-MRI dual-modal imaging was confirmed in vivo in tumour-bearing mice, which could also provide semi-quantitative information for tumour detection. Importantly, these nanoprobes can deliver anti-cancer drugs in cancer therapy due to their unique mesoporous structures. Thus, nanotheranostics combining dual-modal imaging with anti-cancer therapeutic properties were achieved.

Preclinical models of atherosclerosis. The future of Hybrid PET/MR technology for the early detection of vulnerable plaque

Cardiovascular diseases are the leading cause of death in developed countries. The aetiology is currently multifactorial, thus making them very difficult to prevent. Preclinical models of atherothrombotic diseases, including vulnerable plaque-associated complications, are now providing significant insights into pathologies like atherosclerosis, and in combination with the most recent advances in new non-invasive imaging technologies, they have become essential tools to evaluate new therapeutic strategies, with which can forecast and prevent plaque rupture. Positron emission tomography (PET)/computed tomography imaging is currently used for plaque visualisation in clinical and pre-clinical cardiovascular research, albeit with significant limitations. However, the combination of PET and magnetic resonance imaging (MRI) technologies is still the best option available today, as combined PET/MRI scans provide simultaneous data acquisition together with high quality anatomical information, sensitivity and lower radiation exposure for the patient. The coming years may represent a new era for the implementation of PET/MRI in clinical practice, but first, clinically efficient attenuation correction algorithms and research towards multimodal reagents and safety issues should be validated at the preclinical level.

The design of a multifunctional dendrimer-based nanoplatform for targeted dual mode SPECT/MR imaging of tumors

A multifunctional dendrimer-based nanoplatform labeled with ^99mTc can be synthesized for targeted SPECT/MR dual mode imaging of tumors.

Gadolinium-based nanoparticles for theranostic MRI-radiosensitization

A rapid development of gadolinium-based nanoparticles is observed due to their attractive properties as MRI-positive contrast agents. Indeed, they display high relaxivity, adapted biodistribution and passive uptake in the tumor thanks to enhanced permeability and retention effect. In addition to these imaging properties, it has been recently shown that they can act as effective radiosensitizers under different types of irradiation (radiotherapy, neutron therapy or hadron therapy). These new therapeutic modalities pave the way to therapy guided by imaging and to personalized medicine.

Utilization of nanoparticles as X-ray contrast agents for diagnostic imaging applications

Among all the diagnostic imaging modalities, X-ray imaging techniques are the most commonly used owing to their high resolution and low cost. The improvement of these techniques relies heavily on the development of novel X-ray contrast agents, which are molecules that enhance the visibility of internal structures within the body in X-ray imaging. To date, clinically used X-ray contrast agents consist mainly of small iodinated molecules that might cause severe adverse effects (e.g. allergies, cardiovascular diseases and nephrotoxicity) in some patients owing to the large and repeated doses that are required to achieve good contrast. For this reason, there is an increasing interest in the development of alternative X-ray contrast agents utilizing elements with high atomic numbers (e.g. gold, bismuth, ytterbium and tantalum), which are well known for exhibiting high absorption of X-rays. Nanoparticles (NPs) made from these elements have been reported to have better imaging properties, longer blood circulation times and lower toxicity than conventional iodinated X-ray contrast agents. Additionally, the combination of two or more of these elements into a single carrier allows for the development of multimodal and hybrid contrast agents. Herein, the limitations of iodinated X-ray contrast agents are discussed and the parameters that influence the efficacy of X-ray contrast agents are summarized. Several examples of the design and production of both iodinated and iodine-free NP-based X-ray contrast agents are then provided, emphasizing the studies performed to evaluate their X-ray attenuation capabilities and their toxicity in vitro and in vivo.

Development of a Hybrid Nanoprobe for Triple-Modality MR/SPECT/Optical Fluorescence Imaging

Hybrid clinical imaging is an emerging technology, which improves disease diagnosis by combining already existing technologies. With the combination of high-resolution morphological imaging, i.e., MRI/CT, and high-sensitive molecular detection offered by SPECT/PET/Optical, physicians can detect disease progression at an early stage and design patient-specific treatments. To fully exploit the possibilities of hybrid imaging a hybrid probe compatible with each imaging technology is required. Here, we present a hybrid nanoprobe for triple modality MR/SPECT/Fluorescence imaging. Our imaging agent is comprised of superparamagnetic iron oxide nanoparticles (SPIONs), labeled with ^99mTc and an Alexa fluorophore (AF), together forming ^99mTc-AF-SPIONs. The agent was stable in human serum, and, after subcutaneous injection in the hind paw of Wistar rats, showed to be highly specific by accumulating in the sentinel lymph node. All three modalities clearly visualized the imaging agent. Our results show that a single imaging agent can be used for hybrid imaging. The use of a single hybrid contrast agent permits simultaneous hybrid imaging and, more conventionally, allow for single modality imaging at different time points. For example, a hybrid contrast agent enables pre-operative planning, intra-operative guidance, and post-operative evaluation with the same contrast agent.

Multimodality imaging using SPECT/CT and MRI and ligand functionalized 99mTc-labeled magnetic microbubbles

Background

In the present study, we used multimodal imaging to investigate biodistribution in rats after intravenous administration of a new ^99mTc-labeled delivery system consisting of polymer-shelled microbubbles (MBs) functionalized with diethylenetriaminepentaacetic acid (DTPA), thiolated poly(methacrylic acid) (PMAA), chitosan, 1,4,7-triacyclononane-1,4,7-triacetic acid (NOTA), NOTA-super paramagnetic iron oxide nanoparticles (SPION), or DTPA-SPION.

Methods

Examinations utilizing planar dynamic scintigraphy and hybrid imaging were performed using a commercially available single-photon emission computed tomography (SPECT)/computed tomography (CT) system. For SPION containing MBs, the biodistribution pattern of ^99mTc-labeled NOTA-SPION and DTPA-SPION MBs was investigated and co-registered using fusion SPECT/CT and magnetic resonance imaging (MRI). Moreover, to evaluate the biodistribution, organs were removed and radioactivity was measured and calculated as percentage of injected dose.

Results

SPECT/CT and MRI showed that the distribution of ^99mTc-labeled ligand-functionalized MBs varied with the type of ligand as well as with the presence of SPION. The highest uptake was observed in the lungs 1 h post injection of ^99mTc-labeled DTPA and chitosan MBs, while a similar distribution to the lungs and the liver was seen after the administration of PMAA MBs. The highest counts of ^99mTc-labeled NOTA-SPION and DTPA-SPION MBs were observed in the lungs, liver, and kidneys 1 h post injection. The highest counts were observed in the liver, spleen, and kidneys as confirmed by MRI 24 h post injection. Furthermore, the results obtained from organ measurements were in good agreement with those obtained from SPECT/CT.

Conclusions

In conclusion, microbubbles functionalized by different ligands can be labeled with radiotracers and utilized for SPECT/CT imaging, while the incorporation of SPION in MB shells enables imaging using MR. Our investigation revealed that biodistribution may be modified using different ligands. Furthermore, using a single contrast agent with fusion SPECT/CT/MR multimodal imaging enables visualization of functional and anatomical information in one image, thus improving the diagnostic benefit for patients.

Bisphosphonate-anchored PEGylation and radiolabeling of superparamagnetic iron oxide: long-circulating nanoparticles for in vivo multimodal (T1 MRI-SPECT) imaging

The efficient delivery of nanomaterials to specific targets for in vivo biomedical imaging is hindered by rapid sequestration by the reticuloendothelial system (RES) and consequent short circulation times. To overcome these two problems, we have prepared a new stealth PEG polymer conjugate containing a terminal 1,1-bisphosphonate (BP) group for strong and stable binding to the surface of ultrasmall-superparamagnetic oxide nanomaterials (USPIOs). This polymer, PEG(5)-BP, can be used to exchange the hydrophobic surfactants commonly used in the synthesis of USPIOs very efficiently and at room temperature using a simple method in 1 h. The resulting nanoparticles, PEG(5)-BP-USPIOs are stable in water or saline for at least 7 months and display a near-zero ζ-potential at neutral pH. The longitudinal (r(1)) and transverse (r(2)) relaxivities were measured at a clinically relevant magnetic field (3 T), revealing a high r(1) of 9.5 mM(-1) s(-1) and low r(2)/r(1) ratio of 2.97, making these USPIOs attractive as T1-weighted MRI contrast agents at high magnetic fields. The strong T1-effect was demonstrated in vivo, revealing that PEG(5)-BP-USPIOs remain in the bloodstream and enhance its signal 6-fold, allowing the visualization of blood vessels and vascular organs with high spatial definition. Furthermore, the optimal relaxivity properties allow us to inject a dose 4 times lower than with other USPIOs. PEG(5)-BP-USPIOs can also be labeled using a radiolabeled-BP for visualization with single photon emission computed tomography (SPECT), and thus affording dual-modality contrast. The SPECT studies confirmed low RES uptake and long blood circulation times (t(1/2) = 2.97 h). These results demonstrate the potential of PEG(5)-BP-USPIOs for the development of targeted multimodal imaging agents for molecular imaging.