Nano-sized CT contrast agents

An overview of current practice in external beam radiation oncology with consideration to potential benefits and challenges for nanotechnology

Over the past two decades, there has been a significant evolution in the technologies and techniques employed within the radiation oncology environment. Over the same period, extensive research into the use of nanotechnology in medicine has highlighted a range of potential benefits to its incorporation into clinical radiation oncology. This short communication describes key tools and techniques that have recently been introduced into specific stages of a patient’s radiotherapy pathway, including diagnosis, external beam treatment and subsequent follow-up. At each pathway stage, consideration is given towards how nanotechnology may be combined with clinical developments to further enhance their benefit, with some potential opportunities for future research also highlighted. Prospective challenges that may influence the introduction of nanotechnology into clinical radiotherapy are also discussed, indicating the need for close collaboration between academic and clinical staff to realise the full clinical benefit of this exciting technology.

In Vivo Micro-CT Imaging of Human Mesenchymal Stem Cells Labeled with Gold-Poly-L-Lysine Nanocomplexes

Developing in vivo cell tracking is an important prerequisite for further development of cell-based therapy. So far, few computed tomography (CT) cell tracking studies have been described due to its notoriously low sensitivity and lack of efficient labeling protocols. We present a simple method to render human mesenchymal stem cells (hMSCs) sufficiently radiopaque by complexing 40 nm citrate-stabilized gold nanoparticles (AuNPs) with poly-L-lysine (PLL) and rhodamine B isothiocyanate (RITC). AuNP-PLL-RITC labeling did not affect cellular viability, proliferation, or downstream cell differentiation into adipocytes and osteocytes. Labeled hMSCs could be clearly visualized in vitro and in vivo with a micro-CT scanner, with a detection limit of approximately 2×104 cells/μl in vivo. Calculated HU values were 2.27 /pg of intracellular Au as measured with inductively coupled plasma mass spectrophotometry (ICP-MS), and were linear over a wide range of cell concentrations. This linear CT attenuation was observed for both naked AuNPs and those that were taken up by hMSCs, indicating that the number of labeled cells can be quantified similar to the use of radioactive or fluorine tracers. This approach for CT cell tracking may find applications in CT image-guided interventions and fluoroscopic procedures commonly used for the injection of cellular therapeutics.

PB@Au Core-Satellite Multifunctional Nanotheranostics for Magnetic Resonance and Computed Tomography Imaging in Vivo and Synergetic Photothermal and Radiosensitive Therapy

To integrate multiple diagnostic and therapeutic strategies on a single particle through simple and effective methods is still challenging for nanotheranostics. Herein, we develop multifunctional nanotheranostic PB@Au core-satellite nanoparticles (CSNPs) based on Prussian blue nanoparticles (PBNPs) and gold nanoparticles (AuNPs), which are two kinds of intrinsic theranostic nanomaterials, for magnetic resonance (MR)-computed tomography (CT) imaging and synergistic photothermal and radiosensitive therapy (PTT-RT). PBNPs as cores enable T₁- and T₂-weighted MR contrast and strong photothermal effect, while AuNPs as satellites offer CT enhancement and radiosensitization. As revealed by both MR and CT imaging, CSNPs realized efficient tumor localization by passively targeted accumulation after intravenous injection. In vivo studies showed that CSNPs resulted in synergistic PTT-RT action to achieve almost entirely suppression of tumor growth without observable recurrence. Moreover, no obvious systemic toxicity of mice confirmed good biocompatibility of CSNPs. These results raise new possibilities for clinical nanotheranostics with multimodal diagnostic and therapeutic coalescent design.

Effect of Gold Nanoparticle Size and Coating on Labeling Monocytes for CT Tracking

With advances in cell therapies, interest in cell tracking techniques to monitor the migration, localization, and viability of these cells continues to grow. X-ray computed tomography (CT) is a cornerstone of medical imaging but has been limited in cell tracking applications due to its low sensitivity toward contrast media. In this study, we investigate the role of size and surface functionality of gold nanoparticles for monocyte uptake to optimize the labeling of these cells for tracking in CT. We synthesized gold nanoparticles (AuNP) that range from 15 to 150 nm in diameter and examined several capping ligands, generating 44 distinct AuNP formulations. In vitro cytotoxicity and uptake experiments were performed with the RAW 264.7 monocyte cell line. The majority of formulations at each size were found to be biocompatible, with only certain 150 nm PEG functionalized particles reducing viability at high concentrations. High uptake of AuNP was found using small capping ligands with distal carboxylic acids (11-MUA and 16-MHA). Similar uptake values were found with intermediate sizes (50 and 75 nm) of AuNP when coated with 2000 MW poly(ethylene-glycol) carboxylic acid ligands (PCOOH). Low uptake values were observed with 15, 25, 100, and 150 nm PCOOH AuNP, revealing interplay between size and surface functionality. Transmission electron microscopy (TEM) and CT performed on cells revealed similar patterns of high gold uptake for 50 nm PCOOH and 75 nm PCOOH AuNP. These results demonstrate that highly negatively charged carboxylic acid coatings for AuNP provide the greatest internalization of AuNP in monocytes, with a complex dependency on size.

Development of magneto-plasmonic nanoparticles for multimodal image-guided therapy to the brain

Magneto-plasmonic nanoparticles are one of the emerging multi-functional materials in the field of nanomedicine. Their potential for targeting and multi-modal imaging is highly attractive. In this study, magnetic core/gold shell (MNP@Au) magneto-plasmonic nanoparticles were synthesized by citrate reduction of Au ions on magnetic nanoparticle seeds. Hydrodynamic size and optical properties of magneto-plasmonic nanoparticles synthesized with the variation of Au ions and reducing agent concentrations were evaluated. The synthesized magneto-plasmonic nanoparticles exhibited superparamagnetic properties, and their magnetic properties contributed to the concentration-dependent contrast in magnetic resonance imaging (MRI). The imaging contrast from the gold shell part of the magneto-plasmonic nanoparticles was also confirmed by X-ray computed tomography (CT). The transmigration study of the magneto-plasmonic nanoparticles using an in vitro blood-brain barrier (BBB) model proved enhanced transmigration efficiency without disrupting the integrity of the BBB, and showed potential to be used for brain diseases and neurological disorders.

Nanomaterials for In Vivo Imaging

In vivo imaging, which enables us to peer deeply within living subjects, is producing tremendous opportunities both for clinical diagnostics and as a research tool. Contrast material is often required to clearly visualize the functional architecture of physiological structures. Recent advances in nanomaterials are becoming pivotal to generate the high-resolution, high-contrast images needed for accurate, precision diagnostics. Nanomaterials are playing major roles in imaging by delivering large imaging payloads, yielding improved sensitivity, multiplexing capacity, and modularity of design. Indeed, for several imaging modalities, nanomaterials are now not simply ancillary contrast entities, but are instead the original and sole source of image signal that make possible the modality's existence. We address the physicochemical makeup/design of nanomaterials through the lens of the physical properties that produce contrast signal for the cognate imaging modality-we stratify nanomaterials on the basis of their (i) magnetic, (ii) optical, (iii) acoustic, and/or (iv) nuclear properties. We evaluate them for their ability to provide relevant information under preclinical and clinical circumstances, their in vivo safety profiles (which are being incorporated into their chemical design), their modularity in being fused to create multimodal nanomaterials (spanning multiple different physical imaging modalities and therapeutic/theranostic capabilities), their key properties, and critically their likelihood to be clinically translated.

Protein-directed synthesis of Bi2S3 nanoparticles as an efficient contrast agent for visualizing the gastrointestinal tract

BSA@Bi₂S₃ nanoparticles can be applied for CT imaging of the gastrointestinal tract, realizing the visualization of gastrointestinal structures.

Temperature sensitive p(N-isopropylacrylamide-co-acrylic acid) modified gold nanoparticles for trans-arterial embolization and angiography

Temperature-sensitive in situ hydrogels of GNP@PNA nanomedicine achieve good blood-vessel embolization and X-ray imaging on rabbits.

Lanthanide-doped bismuth oxobromide nanosheets for self-activated photodynamic therapy

Low tissue penetration depth of the excited light and complicated synthetic procedures greatly hinder the clinical application of photodynamic therapy (PDT).

Ultrasmall Biocompatible Bi2Se3 Nanodots for Multimodal Imaging-Guided Synergistic Radiophotothermal Therapy against Cancer

Sub-3 nm ultrasmall Bi₂Se₃ nanodots stabilized with bovine serum albumin were successfully synthesized through a reaction of hydroxyethylthioselenide with bismuth chloride in aqueous solution under ambient conditions. These nanodots exhibit a high photothermal conversion efficiency (η = 50.7%) due to their strong broad absorbance in the near-infrared (NIR) window and serve as a nanotheranostic agent for photoacoustic imaging and photothermal cancer therapy. In addition, they also display radioenhancement with a ratio of 6% due to their sensitivity to X-rays, which makes them a potential sensitizer for radiotherapy. These nanodots were also labled with radioactive ^99mTc for quantification of their biodistribution by single-photon-emission computed tomography (SPECT)/computed tomography (CT) imaging. Our work demonstrates the potential of ultrasmall Bi₂Se₃ nanodots in multimodal imaging-guided synergetic radiophotothermal therapy of cancer.

Gold Nanoparticles as a Potential Cellular Probe for Tracking of Stem Cells in Bone Regeneration Using Dual-Energy Computed Tomography

Transplant of bone marrow mesenchymal stem cells (BMSCs) has attracted considerable interest for bone regeneration. However, noninvasive and real-time tracking of location and concentration of the implanted BMSCs remains a big challenge. Herein we designed a novel approach involving the surface modification of gold nanoparticles (AuNPs) with silica layers and DNA Transfectin 3000 (TS) to improve biocompatibility and to enhance the uptake by BMSCs, hence rendering the ability of tracking BMSCs with dual-energy computer tomography (DECT). Results showed that the endocytosis of AuNPs@SiO₂-TS by BMSCs was as high as ∼255 pg/cell after one-day incubation and did not obviously decrease after 14 days. Meanwhile, the AuNPs@SiO₂-TS had no influence on the viability, cell cycle, and capabilities on osteogenic, chondrogenic, and adipogenic differentiation of BMSCs. Under a bone-defect rabbit model, the DECT images showed the migration of BMSCs toward a cortical bone defect without variation in volume. This study demonstrated that AuNPs@SiO₂-TS could be a potential cellular probe for noninvasive and real-time tracking of BMSCs in bone tissue repairs using clinical CT or DECT techniques. It provided a novel and intuitive methodology for observing and investigating the bone regeneration in clinic.

Cancer Diagnosis and Imaging-Guided Photothermal Therapy Using a Dual-Modality Nanoparticle

To improve patient outcome and decrease overall health-care costs, highly sensitive and precise detection of a tumor is required for its accurate diagnosis and efficient therapy; however, this remains a challenge when using conventional single mode imaging. Here, we successfully designed a near-infrared (NIR)-response photothermal therapy (PTT) platform (Au@MSNs-ICG) for the location, diagnosis, and NIR/computer tomography (CT) bimodal imaging-guided PTT of tumor tissues, using gold (Au) nanospheres coated with indocyanine green (ICG)-loaded mesoporous silica nanoparticles (MSNs), which would have high sensitivity and precision. The nanoparticles (NPs) exhibited good monodispersity, fluorescence stability, biocompatibility, and NIR/CT signaling and had a preferable temperature response under NIR laser irradiation in vitro or in vivo. Using a combination of NIR/CT imaging and PTT treatment, the tumor could be accurately positioned and thoroughly eradicated in vivo by Au@MSNs-ICG injection. Hence, the multifunctional NPs could play an important role in facilitating the accurate treatment of tumors in future clinical applications.

PGMA-Based Cationic Nanoparticles with Polyhydric Iodine Units for Advanced Gene Vectors

It is crucial for successful gene delivery to develop safe, effective, and multifunctional polycations. Iodine-based small molecules are widely used as contrast agents for CT imaging. Herein, a series of star-like poly(glycidyl methacrylate) (PGMA)-based cationic vectors (II-PGEA/II) with abundant flanking polyhydric iodine units are prepared for multifunctional gene delivery systems. The proposed II-PGEA/II star vector is composed of one iohexol intermediate (II) core and five ethanolamine (EA) and II-difunctionalized PGMA arms. The amphipathic II-PGEA/II vectors readily self-assemble into well-defined cationic nanoparticles, where massive hydroxyl groups can establish a hydration shell to stabilize the nanoparticles. The II introduction improves cell viabilities of polycations. Moreover, by controlling the suitable amount of introduced II units, the resultant II-PGEA/II nanoparticles can produce fairly good transfection performances in different cell lines. Particularly, the II-PGEA/II nanoparticles induce much better in vitro CT imaging abilities in tumor cells than iohexol (one commonly used commercial CT contrast agent). The present design of amphipathic PGMA-based nanoparticles with CT contrast agents would provide useful information for the development of new multifunctional gene delivery systems.

Optimization of Bi3+ in Upconversion Nanoparticles Induced Simultaneous Enhancement of Near-Infrared Optical and X-ray Computed Tomography Imaging Capability

Bioimaging probes have been extensive studied for many years, while it is still a challenge to further improve the image quality for precise diagnosis in clinical medicine. Here, monodisperse NaGdF₄:Yb³⁺,Tm³⁺,x% Bi³⁺ (abbreviated as GYT-x% Bi³⁺, x = 0, 5, 10, 15, 20, 25, 30) upconversion nanoparticles (UCNPs) have been prepared through the solvothermal method. The near-infrared upconversion emission intensity of GYT-25% Bi³⁺ has been enhanced remarkably than that of NaGdF₄:Yb³⁺,Tm³⁺ (GYT) with a factor of ∼60. Especially, the near-infrared upconversion emission band centered at 802 nm is 150 times stronger than the blue emission band of GYT-25% Bi³⁺ UCNPs. Such high ratio of NIR/blue UCL intensity could reduce the damage to tissues in the bioimaging process. The possibility of using GYT-25% Bi³⁺ UCNPs with strong near-infrared upconversion emission for optical imaging in vitro and in vivo was performed. Encouragingly, the UCL imaging penetration depth can be achieved as deep as 20 mm. Importantly, GYT-25% Bi³⁺ UCNPs exhibit a much higher X-ray computed tomography (CT) contrast efficiency than GYT and iodine-based contrast agent under the same clinical conditions, due to the high X-ray attenuation coefficient of bismuth. Hence, simultaneous remarkable enhancement of NIR emission and X-ray CT signal in upconversion nanoparticles could be achieved by optimizing the doping concentration of Bi³⁺ ions. Additionally, Gd³⁺ ions in the UCNPs endow GYT-25% Bi³⁺ UCNPs with T₁-weighted magnetic resonance (MR) imaging capability.

Hyaluronic Acid Stabilized Iodine-Containing Nanoparticles with Au Nanoshell Coating for X-ray CT Imaging and Photothermal Therapy of Tumors

In recent years, considerable efforts have been made for the development of multifunctional nanoparticles with diagnosis and therapy functions. To achieve enhanced CT imaging and photothermal therapy on the tumor, we employed iodinated nanoparticles as template to construct Au nanoshell structure and demonstrated a facile but effective approach to synthesize biocompatible and well-dispersed multifunctional nanoparticles by coating iodinated nanoparticles with Au nanoshell and subsequent surface modification by hyaluronic acid. The resultant poly(2-methacryl(3-amide-2,4,6-triiodobenzoic acid))/polyethylenimine/Au nanoshell/hyaluronic acid (PMATIB/PEI/Au nanoshell/HA) nanoparticles had relatively high X-ray attenuation coefficient and photothermal efficiency. After intravenous injection into MCF-7 tumor-bearing mice, PMATIB/PEI/Au nanoshell/HA nanoparticles were efficiently accumulated in the tumor, remarkably enhanced the tumor CT imaging, and selectively ablated the tumor through the thermal treatment of lesions under the NIR irradiation. Thus, PMATIB/PEI/Au nanoshell/HA nanoparticles displayed a great potential for CT diagnosis and CT-guided, focused photothermal tumor therapy.

Gd-Hybridized Plasmonic Au-Nanocomposites Enhanced Tumor-Interior Drug Permeability in Multimodal Imaging-Guided Therapy

An original gadolinium-hybridized plasmonic gold nanocomposite is fabricated to provide an insightful and attractive strategy to overcome both the physiological and pathological barriers of tumor, and increase the transportation and permeability of imaging agents and drugs in tumor interior for achieving high-sensitive multimodal imaging and simultaneously improving the therapeutic efficacy of cancer.

Ambient Aqueous Synthesis of Ultrasmall PEGylated Cu2-x Se Nanoparticles as a Multifunctional Theranostic Agent for Multimodal Imaging Guided Photothermal Therapy of Cancer

Ultrasmall PEGylated Cu_2-x Se nanoparticles with strong near-infrared absorption have been prepared by an ambient aqueous method. The resultant water-soluble and biocompatible nanoparticles are demonstrated to be a novel nanotheranostic agent for effective deep-tissue photoacoustic imaging, computed tomography imaging, single-photon emission computed tomography imaging, and photothermal therapy of cancer.

Structural-Engineering Rationales of Gold Nanoparticles for Cancer Theranostics

Personalized theranostics of cancer is increasingly desired, and can be realized by virtue of multifunctional nanomaterials with possible high performances. Gold nanoparticles (GNPs) are a type of especially promising candidate for cancer theranostics, because their synthesis and modification are facile, their structures and physicochemical properties are flexibly controlled, and they are also biocompatible. Especially, the localized surface plasmon resonance and multivalent coordination effects on the surface endow them with NIR light-triggered photothermal imaging and therapy, controlled drug release, and targeted drug delivery. Although the structure, properties, and theranostic application of GNPs are considerably plentiful, no expert review systematically explains the relationships among their structure, property. and application and induces the engineering rationales of GNPs for cancer theranostics. Hence, there are no clear rules to guide the facile construction of optimal GNP structures aiming at a specific theranostic application. A series of structural-engineering rationales of GNPs for cancer theranostics is proposed through digging out the deep relationships between the structure and properties of GNPs. These rationales will be inspiring for guiding the engineering of specific and advanced GNPs for personalized cancer theranostics.

Graphene-based nanomaterials for bioimaging

Graphene-based nanomaterials, due to their unique physicochemical properties, versatile surface functionalization, ultra-high surface area, and good biocompatibility, have attracted considerable interest in biomedical applications such as biosensors, drug delivery, bioimaging, theranostics, and so on. In this review, we will summarize the current advances in bioimaging of graphene-based nanomaterials, including graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene quantum dots (GQDs), and their derivatives. There are two methods to synthesize graphene-based nanomaterials: in situ synthesis and binding method. We will highlight the molecular imaging modalities including optical imaging (fluorescence (FL), two-photon FL, and Raman imaging), PET/SPECT (positron emission tomography/single photon emission computed tomography), MRI (magnetic resonance imaging), PAI (photoacoustic imaging), CT (computed tomography), and multimodal imaging. In the end, we will elaborate on the prospects and challenges of their future bioimaging applications.

Ligand Layer Engineering To Control Stability and Interfacial Properties of Nanoparticles

The use of mixed ligand layers including poly(ethylene glycol)-based ligands for the functionalization of nanoparticles is a very popular strategy in the context of nanomedicine. However, it is challenging to control the composition of the ligand layer and maintain high colloidal and chemical stability of the conjugates. A high level of control and stability are crucial for reproducibility, upscaling, and safe application. In this study, gold nanoparticles with well-defined mixed ligand layers of α-methoxypoly(ethylene glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) and 11-mercaptoundecanoic acid (MUA) were synthesized and characterized by ATR-FTIR spectroscopy and gel electrophoresis. The colloidal and chemical stability of the conjugates was tested by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and UV/vis spectroscopy based experiments, and their interactions with cells were analyzed by elemental analysis. We demonstrate that the alkylene spacer in PEGMUA is the key feature for the controlled synthesis of mixed layer conjugates with very high colloidal and chemical stability and that a controlled synthesis is not possible using regular PEG ligands without the alkylene spacer. With the results of our stability tests, the molecular structure of the ligands can be clearly linked to the colloidal and chemical stabilization. We expect that the underlying design principle can be generalized to improve the level of control in nanoparticle surface chemistry.

Surface engineering of bismuth nanocrystals to counter dissolution

Rapid dissolution of Bi Nanocrystals (NCs) in lysosomal conditions results in poor biocompatibility. We report that an in situ surface coating of Bi nanocrystals with Ganex® V216, a cosmetic dispersant, limits its dissolution under physiological conditions. These Bi Ganex (BiG) NCs are readily encapsulated in FDA approved polymer poly(dl-lactic-co-glycolic acid) (PLGA) by an oil-in-water emulsion technique and also undergo facile SiO2 coating. BiG NCs in BiG@PLGA and BiG@SiO2 nanoparticles dissolve slowly under physiological conditions and exhibit excellent biocompatibility, as opposed to uncoated Bi NCs. Finally, these Bi nanoconstructs are shown to be strong CT CAs, even at relatively low Bi concentrations.

Multimodal Imaging of Nanocomposite Microspheres for Transcatheter Intra-Arterial Drug Delivery to Liver Tumors

A modern multi-functional drug carrier is critically needed to improve the efficacy of image-guided catheter-directed approaches for the treatment of hepatic malignancies. For this purpose, a nanocomposite microsphere platform was developed for selective intra-arterial transcatheter drug delivery to liver tumors. In our study, continuous microfluidic methods were used to fabricate drug-loaded multimodal MRI/CT visible microspheres that included both gold nanorods and magnetic clusters. The resulting hydrophilic, deformable, and non-aggregated microspheres were mono-disperse and roughly 25 um in size. Sustained drug release and strong MRI T₂ and CT contrast effects were achieved with the embedded magnetic nano-clusters and radiopaque gold nanorods. The microspheres were successfully infused through catheters selectively placed within the hepatic artery in rodent models and subsequent distribution in the targeted liver tissues and hepatic tumors confirmed with MRI and CT imaging. These multimodal nanocomposite drug carriers should be ideal for selective intra-arterial catheter-directed administration to liver tumors while permitting MRI/CT visualization for patient-specific confirmation of tumor-targeted delivery.

Clinical advances of nanocarrier-based cancer therapy and diagnostics

INTRODUCTION

Cancer is a leading cause of death worldwide and efficient new strategies are urgently needed to combat its high mortality and morbidity statistics. Fortunately, over the years, nanotechnology has evolved as a frontrunner in the areas of imaging, diagnostics and therapy, giving the possibility of monitoring, evaluating and individualizing cancer treatments in real-time. Areas covered: Polymer-based nanocarriers have been extensively studied to maximize cancer treatment efficacy and minimize the adverse effects of standard therapeutics. Regarding diagnosis, nanomaterials like quantum dots, iron oxide nanoparticles or gold nanoparticles have been developed to provide rapid, sensitive detection of cancer and, therefore, facilitate early treatment and monitoring of the disease. Therefore, multifunctional nanosystems with both imaging and therapy functionalities bring us a step closer to delivering precision/personalized medicine in the cancer setting. Expert opinion: There are multiple barriers for these new nanosystems to enter the clinic, but it is expected that in the near future, nanocarriers, together with new 'targeted drugs', could replace our current treatments and cancer could become a nonfatal disease with good recovery rates. Joint efforts between scientists, clinicians, the pharmaceutical industry and legislative bodies are needed to bring to fruition the application of nanosystems in the clinical management of cancer.

PEGylated polyethylenimine-entrapped gold nanoparticles loaded with gadolinium for dual-mode CT/MR imaging applications

Aim: To synthesize and characterize cost-efficient polyethylenimine-entrapped gold nanoparticles loaded with gadolinium (Gd@Au PENPs) for dual-mode computed tomography (CT)/magnetic resonance (MR) imaging applications. Materials & methods: PEGylated PEI modified with gadolinium (Gd) chelator (DOTA) was used as a template to synthesize the Gd@Au PENPs and the particles were well characterized in terms of their physicochemical properties, cytotoxicity and performances in CT and MR imaging in vitro and in vivo. Results: The formed Gd@Au PENPs with low cytotoxicity can be used as a highly efficient contrast agent for dual-mode CT/MR imaging of blood pool and major organs of animals. Conclusion: The designed Gd@Au PENPs may be used as a versatile nanoplatform for dual-mode CT/MR imaging of different biological systems.

Facile Synthesis of Uniform-Sized Bismuth Nanoparticles for CT Visualization of Gastrointestinal Tract in Vivo

High-performance and biocompatible contrast agents are the key to accurate diagnosis of various diseases in vivo via CT imaging. Fabrication of pure Bi nanoparticles is the best way to maximize X-ray absorption efficiency due to the ultrahigh X-ray attenuation ability of Bi and 100% content of Bi element. However, high-quality Bi nanoparticles prepared through a facile strategy are still lacking. Herein, we report a simple noninjection method to fabricate uniformly sized pure Bi nanoparticles using only two commercial reagents by simply heating the mixture of raw materials in a short time. The obtained Bi nanoparticles owned highly uniform size, excellent monodispersity, and impressive antioxidant capacity. After being modified with oligosaccharide, the "sweet" Bi nanoprobe with comfortable patient experience and favorable biocompatibility was successfully used in CT visualization of gastrointestinal tract in detail.

Rapid Degradation and High Renal Clearance of Cu3BiS3 Nanodots for Efficient Cancer Diagnosis and Photothermal Therapy in Vivo

A key challenge for the use of inorganic nanomedicines in clinical applications is their long-term accumulation in internal organs, which raises the common concern of the risk of adverse effects and inflammatory responses. It is thus necessary to rationally design inorganic nanomaterials with proper accumulation and clearance mechanism in vivo. Herein, we prepared ultrasmall Cu3BiS3 nanodots (NDs) as a single-phased ternary bimetal sulfide for photothermal cancer therapy guided by multispectral optoacoustic tomography (MSOT) and X-ray computed tomography (CT) due to bismuth's excellent X-ray attenuation coefficient. We then monitored and investigated their absorption, distribution, metabolism, and excretion. We also used CT imaging to demonstrate that Cu3BiS3 NDs can be quickly removed through renal clearance, which may be related to their small size, rapid chemical transformation, and degradation in an acidic lysosomal environment as characterized by synchrotron radiation-based X-ray absorption near-edge structure spectroscopy. These results reveal that Cu3BiS3 NDs act as a simple but powerful "theranostic" nanoplatform for MSOT/CT imaging-guided tumor ablation with excellent metabolism and rapid clearance that will improve safety for clinical applications in the future.

Targeted Imaging of Damaged Bone in Vivo with Gemstone Spectral Computed Tomography

Achieving high-resolution imaging of bone-cracks and even monitoring them in live organisms are of great significance for understanding their extreme biological effects but remain quite challenging, especially for adopting commercial imaging systems. Herein, we explore the use of the clinical gemstone spectral computed tomography (GSCT) technique as a powerful tool for targeted imaging of bone-cracks in rats via intramuscularly administrating crack-targeted ytterbium-based contrast agents (CAs). Material density images of GSCT reveal that bone-cracks targeted with CAs can be successfully differentiated from healthy bone based on their different X-ray attenuation characteristics, giving GSCT a distinct advantage over conventional CT. More importantly, the superior imaging capability of GSCT allows us to real-time monitor the targeting and accumulation of CAs toward bone-crack in vivo. These results highlight that clinical GSCT, combined with ytterbium-based CAs, provides a promising opportunity for understanding bone-related diseases in the future.

Energy Calibration of a CdTe Photon Counting Spectral Detector with Consideration of its Non-Convergent Behavior

Fast and accurate energy calibration of photon counting spectral detectors (PCSDs) is essential for their biomedical applications to identify and characterize bio-components or contrast agents in tissues. Using the x-ray tube voltage as a reference for energy calibration is known to be an efficient method, but there has been no consideration in the energy calibration of non-convergent behavior of PCSDs. We observed that a single pixel mode (SPM) CdTe PCSD based on Medipix-2 shows some non-convergent behaviors in turning off the detector elements when a high enough threshold is applied to the comparator that produces a binary photon count pulse. More specifically, the detector elements are supposed to stop producing photon count pulses once the threshold reaches a point of the highest photon energy determined by the tube voltage. However, as the x-ray exposure time increases, the threshold giving 50% of off pixels also increases without converging to a point. We established a method to take account of the non-convergent behavior in the energy calibration. With the threshold-to-photon energy mapping function established by the proposed method, we could better identify iodine component in a phantom consisting of iodine and other components.

Comparison of small animal CT contrast agents

Non-invasive in vivo small animal computed tomography (CT) imaging provides high resolution bone scans but cannot differentiate between soft tissues. For most applications injections of contrast agents (CAs) are necessary. Aim of this study was to uncover the advantages and disadvantages of commercially available CT CAs (ExiTron nano 12 000 and 6000, eXIA 160 and 160XL, Fenestra VC and LC) regarding their pharmacokinetics, toxicological side-effects and the influence of anesthesia on the biodistribution, based on an injection volume of 100 μL/25 g body weight. The pharmacokinetics of the CAs were determined for up to five days. The CA-induced toxicological/physiological side-effects were evaluated by determining blood counts, liver enzymes, thyroxine and total protein values, pro-inflammatory mediators (messenger ribonucleic acid (mRNA)), histology and immunohistochemistry. ExiTron nano 12 000 and 6000 yielded a long-term contrast enhancement (CE) in the liver and spleen for up to five days. Some of the evaluated CAs did not show any CE at all. Anesthesia did not impair the CAs' biodistribution. The CAs differentially affected the body weight, blood counts, liver enzymes, thyroxine and total protein values. ExiTron nano 12 000 and 6000 induced histiocytes in the liver and spleen. Moreover, ExiTron nano 12 000 and eXIA 160 enhanced tumor necrosis factor (TNF) mRNA expression levels in the kidneys. Thus, we recommend ExiTron nano 12 000 and 6000 when multiple injections should be avoided. We recommend careful selection of the employed CA in order to achieve an acceptable CE in the organs of interest and to avoid influences on the animal physiology. Copyright © 2016 John Wiley & Sons, Ltd.

Size-Tuning Ionization To Optimize Gold Nanoparticles for Simultaneous Enhanced CT Imaging and Radiotherapy

Computed tomography (CT) contrast and radiosensitization usually increase with particle sizes of gold nanoparticles (AuNPs), but there is a huge challenge to improve both by adjusting sizes under the requirements of in vivo application. Here, we report that AuNPs have great size-dependent enhancements on CT imaging as well as radiotherapy (RT) in the size range of 3-50 nm. It is demonstrated that AuNPs with a size of ∼13 nm could simultaneously possess superior CT contrast ability and significant radioactive disruption. The Monte Carlo method is further used to evaluate this phenomenon and indicates that the inhomogeneity of gold atom distributions caused by sizes may influence secondary ionization in whole X-ray interactions. In vivo studies further indicate that this optimally sized AuNP improves real-time CT imaging and radiotherapeutic inhibition of tumors in living mice by effective accumulation at tumors with prolonged in vivo circulation times compared to clinically used small-molecule agents. These results suggest that ∼13 nm AuNPs may serve as multifunctional adjuvants for clinical X-ray theranostic application.

Iodinated hyaluronic acid oligomer-based nanoassemblies for tumor-targeted drug delivery and cancer imaging

Nano-sized self-assemblies based on amphiphilic iodinated hyaluronic acid (HA) were developed for use in cancer diagnosis and therapy. 2,3,5-Triiodobenzoic acid (TIBA) was conjugated to an HA oligomer as a computed tomography (CT) imaging modality and a hydrophobic residue. Nanoassembly based on HA-TIBA was fabricated for tumor-targeted delivery of doxorubicin (DOX). Cellular uptake of DOX from nanoassembly, compared to a DOX solution group, was enhanced via an HA-CD44 receptor interaction, and subsequently, the in vitro antitumor efficacy of DOX-loaded nanoassembly was improved in SCC7 (CD44 receptor positive squamous cell carcinoma) cells. Cy5.5, a near-infrared fluorescence (NIRF) dye, was attached to the HA-TIBA conjugate and the in vivo tumor targetability of HA-TIBA nanoassembly, which is based on the interaction between HA and CD44 receptor, was demonstrated in a NIRF imaging study using an SCC7 tumor-xenografted mouse model. Tumor targeting and cancer diagnosis with HA-TIBA nanoassembly were verified in a CT imaging study using the SCC7 tumor-xenografted mouse model. In addition to efficient cancer diagnosis using NIRF and CT imaging modalities, improved antitumor efficacies were shown. HA and TIBA can be used to produce HA-TIBA nanoassembly that may be a promising theranostic nanosystem for cancers that express the CD44 receptor.

High-performance dendritic contrast agents for X-ray computed tomography imaging using potent tetraiodobenzene derivatives

The use of computed tomography (CT) for vascular imaging is critical in medical emergencies requiring urgent diagnostic decisions, such as cerebral ischemia and many cardiovascular diseases. Small-molecule iodinated contrast media are often injected intravenously as radiopaque agents during CT imaging to achieve high contrast enhancement of vascular systems. The rapid excretion rate of these agents is overcome by injecting a significantly high dose of iodine, which can have serious side effects. Here we report a simple method to prepare blood-pool contrast agents for CT based on dendrimers for the first time using tetraiodobenzene derivatives as potent radiopaque moieties. Excellent in vivo safety has been demonstrated for these small (13-22nm) unimolecular water-soluble dendritic contrast agents, which exhibit high contrast enhancement in the blood-pool and effectively extend their blood half-lives. Our method is applicable to virtually any scaffold with suitable surface groups and may fulfill the current need for safer, next-generation iodinated CT contrast agents.

NaYF4:Yb/Er@PPy core-shell nanoplates: an imaging-guided multimodal platform for photothermal therapy of cancers

Imaging guided photothermal agents have attracted great attention for accurate diagnosis and treatment of tumors. Herein, multifunctional NaYF4:Yb/Er@polypyrrole (PPy) core-shell nanoplates are developed by combining a thermal decomposition reaction and a chemical oxidative polymerization reaction. Within such a composite nanomaterial, the core of the NaYF4:Yb/Er nanoplate can serve as an efficient nanoprobe for upconversion luminescence (UCL)/X-ray computed tomography (CT) dual-modal imaging, the shell of the PPy shows strong near infrared (NIR) region absorption and makes it effective in photothermal ablation of cancer cells and infrared thermal imaging in vivo. Thus, this platform can be simultaneously used for cancer diagnosis and photothermal therapy, and compensates for the deficiencies of individual imaging modalities and satisfies the higher requirements on the efficiency and accuracy for diagnosis and therapy of cancer. The results further provide some insight into the exploration of multifunctional nanocomposites in the photothermal theragnosis therapy of cancers.

Microwave-assisted one-step rapid synthesis of near-infrared gold nanoclusters for NIRF/CT dual-modal bioimaging

Highly fluorescent lysozyme-capped gold nanoclusters have been prepared using a one-step rapid microwave-assisted approach for the application of NIRF/CT dual-modal bioimaging.

Overcoming the Achilles' heel of photodynamic therapy

This review summarizes the latest progress in deep photodynamic therapy (PDT), which overcomes the Achilles' heel of PDT.

Ultra-small and size tunable PVP-NaGdF4:Dy nanoparticles with high biocompatibility for multimodal tumor imaging

Ultra-small PVP-NaGdF₄:Dy nanoprobes were prepared and they could induce obvious signal enhancement in T₁/T₂-weighted MRI and CT imaging.

Radiopaque tantalum oxide coated persistent luminescent nanoparticles as multimodal probes for in vivo near-infrared luminescence and computed tomography bioimaging

The design and fabrication of multimodal imaging nanoparticles is of great importance in medical diagnosis. Here we report the fabrication of core-shell structured Zn2.94Ga1.96Ge2O10:Cr(3+),Pr(3+)@TaOx@SiO2 nanoparticles for persistent luminescence and X-ray computed tomography (CT) imaging. Persistent luminescent nanoparticles Zn2.94Ga1.96Ge2O10:Cr(3+),Pr(3+) were used as the core to provide near-infrared luminescence, and a TaOx layer was grown on the core to serve as the contrast agent for CT. The tenuous outermost SiO2 shell was fabricated on the TaOx layer to gain high biocompatibility and to facilitate post-modification with tumor-targeting peptides. The fabricated core-shell structured nanoparticle shows intense near-infrared luminescence and the CT contrast effect. No obvious mutual interference was found in these two modalities, which ensures that each imaging modality merits could be brought in a full play. Furthermore, covalent bonding of cyclic-Asn-Gly-Arg peptides makes the core-shell structured nanoparticles promising for in vivo targeted imaging of tumor-bearing mice.

Trifunctional Polymeric Nanocomposites Incorporated with Fe₃O₄/Iodine-Containing Rare Earth Complex for Computed X-ray Tomography, Magnetic Resonance, and Optical Imaging

In this study, a novel polymerizable CT contrast agent integrating iodine with europium(III) has been developed by a facile and universal coordination chemistry method. The Fe3O4 nanoparticles are then incorporated into this iodine-containing europium complex by seed-emulsifier-free polymerization. The nanocomposites combining the difunctional complex and superparamagnetic Fe3O4 nanoparticles, which have uniform size dispersion and high encapsulation rate, are suitable for computed X-ray tomography (CT), magnetic resonance imaging (MRI), and optical imaging. They possess good paramagnetic properties with a maximum saturation magnetization of 2.16 emu/g and a transverse relaxivity rate of 260 mM(-1) s(-1), and they exhibit obvious contrast effects with an iodine payload less than 4.8 mg I/mL. In the in vivo optical imaging assessment, vivid fluorescent dots can be observed in the liver and spleen by two-photon confocal scanning laser microscopy (CLSM). All the results showed that nanocomposites as polymeric trifunctional contrast agents have great clinical potential in CT, MR, and optical imaging.

Engineering iodine-doped carbon dots as dual-modal probes for fluorescence and X-ray CT imaging

X-ray computed tomography (CT) is the most commonly used imaging technique for noninvasive diagnosis of disease. In order to improve tissue specificity and prevent adverse effects, we report the design and synthesis of iodine-doped carbon dots (I-doped CDs) as efficient CT contrast agents and fluorescence probe by a facile bottom-up hydrothermal carbonization process. The as-prepared I-doped CDs are monodispersed spherical nanoparticles (a diameter of ~2.7 nm) with favorable dispersibility and colloidal stability in water. The aqueous solution of I-doped CDs showed wavelength-dependent excitation and stable photoluminescence similar to traditional carbon quantum dots. Importantly, I-doped CDs displayed superior X-ray attenuation properties in vitro and excellent biocompatibility. After intravenous injection, I-doped CDs were distributed throughout the body and excreted by renal clearance. These findings validated that I-doped CDs with high X-ray attenuation potency and favorable photoluminescence show great promise for biomedical research and disease diagnosis.

PEGylated NaHoF4 nanoparticles as contrast agents for both X-ray computed tomography and ultra-high field magnetic resonance imaging

It is well-known that multimodal imaging can integrate the advantages of different imaging modalities by overcoming their individual limitations. As ultra-high field magnetic resonance imaging (MRI) will be inevitably used in future MRI/X-ray computed tomography (CT) scanner, it is highly expected to develop high-performance nano-contrast agents for ultra-high field MR and CT dual-modality imaging, which has not been reported yet. Moreover, specific behavior of nano-contrast agents for ultra-high field MRI is a challenging work and still remains unknown. Herein, a novel type of NaHoF4 nanoparticles (NPs) with varied particle sizes were synthesized and explored as high-performance dual-modality contrast agents for ultra-high field MR and CT imaging. The specific X-ray absorption and MR relaxivity enhancements with varied nanoparticle diameters (3 nm, 7 nm, 13 nm and 29 nm) under different magnetic field (1.5/3.0/7.0 T) are investigated. Based on experimental results and theoretical analysis, the Curie and dipolar relaxation mechanisms of NaHoF4 NPs are firstly separated. Our results will greatly promote the future medical translational development of the NaHoF4 nano-contrast agents for ultra-high field MR/CT dual-modality imaging applications.

Fluorescence-Guided Probes of Aptamer-Targeted Gold Nanoparticles with Computed Tomography Imaging Accesses for in Vivo Tumor Resection

Recent development of molecular imaging probes for fluorescence-guided surgery has shown great progresses for determining tumor margin to execute the tissue resection. Here we synthesize the fluorescent gold nanoparticles conjugated with diatrizoic acid and nucleolin-targeted AS1411 aptamer. The nanoparticle conjugates exhibit high water-solubility, good biocompatibility, visible fluorescence and strong X-ray attenuation for computed tomography (CT) contrast enhancement. The fluorescent nanoparticle conjugates are applied as a molecular contrast agent to reveal the tumor location in CL1-5 tumor-bearing mice by CT imaging. Furthermore, the orange-red fluorescence emitting from the conjugates in the CL1-5 tumor can be easily visualized by the naked eyes. After the resection, the IVIS measurements show that the fluorescence signal of the nanoparticle conjugates in the tumor is greatly enhanced in comparison to that in the controlled experiment. Our work has shown potential application of functionalized nanoparticles as a dual-function imaging agent in clinical fluorescence-guided surgery.

Emerging therapeutic delivery capabilities and challenges utilizing enzyme/protein packaged bacterial vesicles

Nanoparticle-based therapeutics are poised to play a critical role in treating disease. These complex multifunctional drug delivery vehicles provide for the passive and active targeted delivery of numerous small molecule, peptide and protein-derived pharmaceuticals. This article will first discuss some of the current state of the art nanoparticle classes (dendrimers, lipid-based, polymeric and inorganic), highlighting benefits/drawbacks associated with their implementation. We will then discuss an emerging class of nanoparticle therapeutics, bacterial outer membrane vesicles, that can provide many of the nanoparticle benefits while simplifying assembly. Through molecular biology techniques; outer membrane vesicle hijacking potentially allows for stringent control over nanoparticle production allowing for targeted protein packaged nanoparticles to be fully synthesized by bacteria.