Nano-sized CT contrast agents

Chemistry and engineering of cyclodextrins for molecular imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides bearing a basket-shaped topology with an "inner-outer" amphiphilic character. The abundance of hydroxyl groups enables CDs to be functionalized with multiple targeting ligands and imaging elements. The imaging time, and the payload of different imaging elements, can be tuned by taking advantage of the commercial availability of CDs with different sizes of the cavity. This review aims to offer an outlook of the chemistry and engineering of CDs for the development of molecular probes. Complexation thermodynamics of CDs, and the corresponding implications for probe design, are also presented with examples demonstrating the structural and physiochemical roles played by CDs in the full ambit of molecular imaging. We hope that this review not only offers a synopsis of the current development of CD-based molecular probes, but can also facilitate translation of the incremental advancements from the laboratory to real biomedical applications by illuminating opportunities and challenges for future research.

Recent Development of Inorganic Nanoparticles for Biomedical Imaging

Inorganic nanoparticle-based biomedical imaging probes have been studied extensively as a potential alternative to conventional molecular imaging probes. Not only can they provide better imaging performance but they can also offer greater versatility of multimodal, stimuli-responsive, and targeted imaging. However, inorganic nanoparticle-based probes are still far from practical use in clinics due to safety concerns and less-optimized efficiency. In this context, it would be valuable to look over the underlying issues. This outlook highlights the recent advances in the development of inorganic nanoparticle-based probes for MRI, CT, and anti-Stokes shift-based optical imaging. Various issues and possibilities regarding the construction of imaging probes are discussed, and future research directions are suggested.

Three-Dimensional Printing Antimicrobial and Radiopaque Constructs

Three-dimensional (3D) printing holds tremendous potential as a tool for patient-specific devices. This proof-of- concept study demonstrated the feasibility, antimicrobial properties, and computed tomography(CT) imaging characteristics of iodine/polyvinyl alcohol (PVA) 3D meshes and stents. Under scanning electron microscopy, cross-linked PVA displays smoother and more compacted filament arrangements. X-ray and transaxial CT images of iodized PVA vascular stents show excellent visibility and significantly higher Hounsfield units of radiopacity than control prints. Three-dimensional PVA prints stabilized by glutaraldehyde cross-linking and loaded with iodine through sublimation significantly suppressed Escherichia coli and Staphylococcus aureus growth in human blood agar disk diffusion assays. It is suggested that PVA 3D printing with iodine represents an important new synthetic platform for generating a wide variety of antimicrobial and high-visibility devices.

99mTc-Labeled RGD-Polyethylenimine Conjugates with Entrapped Gold Nanoparticles in the Cavities for Dual-Mode SPECT/CT Imaging of Hepatic Carcinoma

We report the construction and characterization of ^99mTc-labeled arginine-glycine-aspartic acid (RGD)-polyethylenimine (PEI) conjugates with entrapped gold nanoparticles in the cavities (RGD-^99mTc-Au PENPs) for dual-mode single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging of an orthotopic hepatic carcinoma model. In this study, PEI was successively decorated with diethylenetriaminepentaacetic acid, poly(ethylene glycol) (PEG), and PEGylated RGD segments, and was utilized as an effective nanoplatform to entrap Au NPs and to be labeled with ^99mTc. We showed that the designed RGD-^99mTc-Au PENPs displayed desirable colloidal stability and radiostability, and cytocompatibility in the investigated concentration range, and could be specifically uptaken by α_vβ₃ integrin-overexpressing liver cancer cells in vitro. In vivo CT and SPECT imaging results indicated that the particles were able to be accumulated within an orthotopic hepatic carcinoma and displayed both CT and SPECT contrast enhancement in the tumor tissue. With the proven biocompatibility in vivo via histological examinations, the designed RGD-^99mTc-Au PENPs may be potentially employed as an effective nanoprobe for a highly efficient dual-mode SPECT/CT imaging of various α_vβ₃ integrin-overexpressing tumors.

2D Superparamagnetic Tantalum Carbide Composite MXenes for Efficient Breast-Cancer Theranostics

Background: The emergence of two-dimensional MXenes has spurred their versatile applications in broad fields, but the exploring of novel MXene-based family members and their potential applications in theranostic nanomedicine (concurrent diagnostic imaging and therapy) have been rarely explored. In this work, we report the construction of a novel superparamagnetic MXene-based theranostic nanoplatform for efficient breast-cancer theranostics, which was based on intriguing tantalum carbide (Ta₄C₃) MXene and its further rational surface-superparamagnetic iron-oxide functionalization (Ta₄C₃-IONP-SPs composite MXenes) for efficient breast-cancer theranostic. Methods: The fabrication of ultrathin Ta₄C₃ nanosheets was based on an exfoliation strategy and superparamagnetic iron oxide nanoparticles were in-situ grown onto the surface of Ta₄C₃ MXene according to the redox reaction of MXene. Ta₄C₃-IONP MXenes were modified with soybean phospholipid (SP) to guarantee high stability in physiological conditions. The photothermal therapy, contrast-enhanced CT, T₂-weighted magnetic resonance imaging and the high biocompatibility of these composite nanosheets have also been evaluated in vitro at cellular level and in vivo on mice breast tumor allograft tumor model. Results: The Ta component of Ta₄C₃-IONP-SPs exhibits high performance for contrast-enhanced CT imaging because of its high atomic number and high X-ray attenuation coefficient, and the integrated superparamagnetic IONPs act as excellent contrast agents for T₂-weighted magnetic resonance imaging. Especially, these Ta₄C₃-IONP-SPs composite nanosheets with high photothermal-conversion efficiency (η: 32.5%) has achieved complete tumor eradication without reoccurrence, verifying their highly efficient breast-tumor photo-ablation performance. Conclusion: This work not only significantly broadens the biomedical applications of MXene-based nanoplatforms (Ta₄C₃ MXene) by exploring their novel family members and further functionalization strategies (magnetic functionalization in this work), but also provides a novel and efficient theranostic nanoplatform for efficient breast-cancer theranostics.

Few-Layered Black Phosphorus: From Fabrication and Customization to Biomedical Applications

As a new kind of 2D material, black phosphorus has gained increased attention in the past three years. Although few-layered black phosphorus nanosheets (BPs) degrade quickly under ambient conditions to phosphate anions, which greatly hampers their optical and electronic applications, this property also makes BPs highly biocompatible and biodegradable, and is regarded as an advantage for various biomedical applications. This Concept summarizes the state-of-art progresses of BPs, from fabrication and surface modification to biomedical applications. It is expected that BPs with such fascinating properties will encourage more scientists to engage in expanding its biomedical applications by tackling the scientific challenges involved in their development.

Tailoring the morphology of AIEgen fluorescent nanoparticles for optimal cellular uptake and imaging efficacy

The rational design of robust fluorescent organic materials for long-term cell tracing is still challenging, and aggregation-caused quenching of emission is a big limitation of this strategy. Organic dyes with aggregation-induced emission (AIE) can effectively address this problem. Herein, AIEgen-containing nanoparticles, with different morphologies and emission, were prepared by assembling amphiphilic copolymers with an AIEgen. We compared the physical and chemical properties of rod-like and spherical nanoparticles, particularly investigating the effects of the shape on internalization and the imaging effect. The formulated nanoparticles exhibit advantageous features, such as a large Stokes shift, robust stability in physiological conditions, strong fluorescent emission, and photobleaching resistance. Interestingly, the rod-like nanoparticles were internalized more efficiently than their spherical counterparts, and their strong green fluorescence can still be clearly observed even after 15 days in vitro and in vivo. This work demonstrates the great potential of regulating the morphology of nanoparticles to obtain an ideal biological function.

A new formulation of poly(MAOTIB) nanoparticles as an efficient contrast agent for in vivo X-ray imaging

Polymeric nanoparticles (PNPs) are gaining increasing importance as nanocarriers or contrasting material for preclinical diagnosis by micro-CT scanner. Here, we investigated a straightforward approach to produce a biocompatible, radiopaque, and stable polymer-based nanoparticle contrast agent, which was evaluated on mice. To this end, we used a nanoprecipitation dropping technique to obtain PEGylated PNPs from a preformed iodinated homopolymer, poly(MAOTIB), synthesized by radical polymerization of 2-methacryloyloxyethyl(2,3,5-triiodobenzoate) monomer (MAOTIB). The process developed allows an accurate control of the nanoparticle properties (mean size can range from 140 nm to 200 nm, tuned according to the formulation parameters) along with unprecedented important X-ray attenuation properties (concentration of iodine around 59 mg I/mL) compatible with a follow-up in vivo study. Routine characterizations such as FTIR, DSC, GPC, TGA, ¹H and ¹³C NMR, and finally SEM were accomplished to obtain the main properties of the optimal contrast agent. Owing to excellent colloidal stability against physiological conditions evaluated in the presence of fetal bovine serum, the selected PNPs suspension was administered to mice. Monitoring and quantification by micro-CT showed that iodinated PNPs are endowed strong X-ray attenuation capacity toward blood pool and underwent a rapid and passive accumulation in the liver and spleen.

STATEMENT OF SIGNIFICANCE

The design of X-ray contrast agents for preclinical imaging is still highly challenging. To date, the best contrast agents reported are based on iodinated lipids or inorganic materials such as gold. In literature, several attempts were undertaken to create polymer-based X-ray contrast agents, but their applicability in vivo was limited to their low contrasting properties. Polymer-based contrast agents present the advantages of an easy surface modification for future application in targeting. Herein, we develop a novel approach to design polymer-based nanoparticle X-ray contrast agent (polymerization of a highly iodine-loaded monomer (MAOTIB)), leading to an iodine concentration of 59 mg/mL. We showed their high efficiency in vivo in mice, in terms of providing a strong signal in blood and then accumulating in the liver and spleen.

Dendrimer as a multifunctional capping agent for metal nanoparticles for use in bioimaging, drug delivery and sensor applications

Various strategies (single & multi-pot) to synthesize dendrimer-coated metal nanoparticles and their exploration in various biomedical applications.

Iodinated Echogenic Glycol Chitosan Nanoparticles for X-ray CT/US Dual Imaging of Tumor

Development of biopolymer-based imaging agents which can access rapidly and provide detailed information about the diseases has received much attention as an alternative to conventional imaging agents. However, development of biopolymer-based nanomaterials for tumor imaging still remains challenging due to their low sensitivity and image resolution. To surmount of these limitations, multimodal imaging agents have been developed, and they were widely utilized for theranostic applications. Herein, iodine containing echogenic glycol chitosan nanoparticles are developed for x-ray computed tomography (CT) and ultrasound (US) imaging of tumor diagnosis. X-ray CT/US dual-modal imaging probe was prepared by following below two steps. First, iodine-contained diatrizoic acid (DTA) was chemically conjugated to the glycol chitosan (GC) for the CT imaging. DTA conjugated GC (GC-DTA NPs) formed stable nanoparticles with an average diameter of 315 nm. Second, perfluoropentane (PFP), a US imaging agent, was physically encapsulated into GC-DTA NPs by O/W emulsion method yielding GC-DTA-PFP nanoparticles (GC-DTA-PFP NPs). The GC-DTA-PFP NPs formed nanoparticles in physiological condition, and they presented the strong x-ray CT, and US signals in phantom test in vitro. Importantly, GC-DTA-PFP NPs were effectively accumulated on the tumor site by enhanced permeation and retention (EPR) effects. Moreover, GC-DTA-PFP NPs showed x-ray CT, and US signals in tumor tissues after intratumoral and intravenous injection, respectively. Therefore, GC-DTA-PFP NPs indicated that x-ray CT/US dual-modal imaging using iodinated echogenic nanoparticles could be provided more comprehensive and accurate diagnostic information to diagnosis of tumor.

Polymerization-induced self-assembly of large-scale iohexol nanoparticles as contrast agents for X-ray computed tomography imaging

Fundamental research for CT imaging, in which iohexol nanoparticles (INPs) were synthesised using a one-pot strategy via polymerization-induced self-assembly (PISA).

Two-Dimensional Tantalum Carbide (MXenes) Composite Nanosheets for Multiple Imaging-Guided Photothermal Tumor Ablation

MXenes, an emerging family of graphene-analogues two-dimensional (2D) materials, have attracted continuous and tremendous attention in many application fields because of their intrinsic physiochemical properties and high performance in versatile applications. In this work, we report on the construction of tantalum carbide (Ta₄C₃) MXene-based composite nanosheets for multiple imaging-guided photothermal tumor ablation, which has been achieved by rational choice of the composition of MXenes and their surface functionalization. A redox reaction was activated on the surface of tantalum carbide (Ta₄C₃) MXene for in situ growth of manganese oxide nanoparticles (MnO_x/Ta₄C₃) based on the reducing surface of the nanosheets. The tantalum components of MnO_x/Ta₄C₃ acted as the high-performance contrast agents for contrast-enhanced computed tomography, and the integrated MnO_x component functionalized as the tumor microenvironment-responsive contrast agents for T₁-weighted magnetic resonance imaging. The photothermal-conversion performance of MnO_x/Ta₄C₃ composite nanosheets not only has achieved contrast-enhanced photoacoustic imaging, but also realized the significant tumor-growth suppression by photothermal hyperthermia. This work broadens the biomedical applications of MXenes, not only by the fabrication of family members of biocompatible MXenes, but also by the development of functionalization strategies of MXenes for cancer-theranostic applications.

Osteoinductive superparamagnetic Fe nanocrystal/calcium phosphate heterostructured microspheres

Functional magnetic and biocompatible particles are of great interest because of their potential use in various bioapplications such as hyperthermia for cancer treatment, magnetic resonance imaging (MRI) contrast agents and drug delivery. Herein, we introduce a facile method for synthesizing magnetic Fe nanocrystal/Fe-substituted calcium phosphate (Fe/FeCaP) heterostructured microspheres using a two-step procedure: (1) one-pot hydrothermal synthesis to prepare uniform-sized FeCaP microspheres and (2) post-reduction annealing at 600 °C for Fe extraction from FeCaP. This approach results in the fabrication of Fe/FeCaP heterostructured microspheres that exhibit superparamagnetism with a saturation magnetization of 10.77 emu g^-1. The Fe/FeCaP particles annealed at 600 °C show a much higher magnetic moment compared with the non-annealed FeCaP particles. Moreover, T2-weighted MRI phantom images reveal that the Fe/FeCaP heterostructured microspheres possess higher relaxivity than paramagnetic FeCaP, demonstrating their potential as superior and biocompatible MRI contrast agents. Moreover, the enhancement in osteoconductivity for Fe/FeCaP microspheres without any evidence of cytotoxicity was verified. Our results demonstrate the great potential of multi-functional Fe/FeCaP microspheres for use as biocompatible bone regeneration agents as well as MRI contrast agents.

In Vivo Computed Tomography/Photoacoustic Imaging and NIR-Triggered Chemo-Photothermal Combined Therapy Based on a Gold Nanostar-, Mesoporous Silica-, and Thermosensitive Liposome-Composited Nanoprobe

Safe multifunctional nanoplatforms that have multiple therapeutic functions integrated with imaging capabilities are highly desired for biomedical applications. In this paper, targeted chemo-photothermal synergistic therapy and photoacoustic/computed tomography imaging of tumors were achieved by one novel multifunctional nanoprobe (GMS/DOX@SLB-FA); it was composed of a gold nanostar core and a doxorubicin (DOX)-loaded mesoporous silica shell (GMS), which was coated with a folic acid (FA)-modified thermosensitively supported lipid bilayer (SLB-FA) as a gatekeeper. The multifunctional probe had perfect dispersion and stability; 2.1 nm mesoporous pores and 208 nm hydration particle sizes were obtained. In vitro studies indicated that the drug-loaded probe had excellent ability to control the release of DOX, with 71.98 ± 2.52% cumulative release after laser irradiation, which was significantly higher than that of unirradiated control group. A survival rate of 72.75 ± 4.37% of HeLa cells at 57.75 μg/mL probe also demonstrated the low cytotoxicity of the targeted probe. Both in vitro and in vivo results showed that the probe could achieve targeted photoacoustic imaging of tumors because of the fact that the FA-modified probe could specifically recognize the overexpressed FA receptors on tumor cells; meanwhile, the probe could also achieve the chemo-photothermal synergistic therapy of tumors through controlling the drug release from mesoporous channels by a near-infrared laser. Therefore, the probe had great potential in the early diagnosis and treatment of cancer.

Recent development of nanoparticles for molecular imaging

Molecular imaging enables us to non-invasively visualize cellular functions and biological processes in living subjects, allowing accurate diagnosis of diseases at early stages. For successful molecular imaging, a suitable contrast agent with high sensitivity is required. To date, various nanoparticles have been developed as contrast agents for medical imaging modalities. In comparison with conventional probes, nanoparticles offer several advantages, including controllable physical properties, facile surface modification and long circulation time. In addition, they can be integrated with various combinations for multimodal imaging and therapy. In this opinion piece, we highlight recent advances and future perspectives of nanomaterials for molecular imaging.This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.

A Proposed Computed Tomography Contrast Agent Using Carboxybetaine Zwitterionic Tantalum Oxide Nanoparticles: Imaging, Biological, and Physicochemical Performance

OBJECTIVES

The aim of this study was to produce and evaluate a proposed computed tomography (CT) contrast agent based on carboxybetaine zwitterionic (CZ)-coated soluble tantalum oxide (TaO) nanoparticles (NPs). We chose tantalum to provide superior imaging performance compared with current iodine-based clinical CT contrast agents. We developed the CZ coating to provide biological and physical performance similar to that of current iodinated contrast agents. In addition, the aim of this study was to evaluate the imaging, biological, and physicochemical performance of this proposed contrast agent compared with clinically used iodinated agents.

MATERIALS AND METHODS

We evaluated CT imaging performance of our CZ-TaO NPs compared with that of an iodinated agent in live rats, imaged centrally located within a tissue-equivalent plastic phantom that simulated a large patient. To evaluate vascular contrast enhancement, we scanned the rats' great vessels at high temporal resolution during and after contrast agent injection. We performed several in vivo CZ-TaO NP studies in healthy rats to evaluate tolerability. These studies included injecting the agent at the anticipated clinical dose (ACD) and at 3 times and 6 times the ACD, followed by longitudinal hematology to assess impact to blood cells and organ function (from 4 hours to 1 week). Kidney histological analysis was performed 48 hours after injection at 3 times the ACD. We measured the elimination half-life of CZ-TaO NPs from blood, and we monitored acute kidney injury biomarkers with a kidney injury assay using urine collected from 4 hours to 1 week. We measured tantalum retention in individual organs and in the whole carcass 48 hours after injection at ACD. Carboxybetaine zwitterionic TaO NPs were synthesized and analyzed in detail. We used multidimensional nuclear magnetic resonance to determine surface functionality of the NPs. We measured NP size and solution properties (osmolality and viscosity) of the agent over a range of tantalum concentrations, including the high concentrations required for standard clinical CT imaging.

RESULTS

Computed tomography imaging studies demonstrated image contrast improvement of approximately 40% to 50% using CZ-TaO NPs compared with an iodinated agent injected at the same mass concentration. Blood and organ analyses showed no adverse effects after injection in healthy naive rats at 3 times the ACD. Retention of tantalum at 48 hours after injection was less than 2% of the injected dose in the whole carcass, which very closely matched the reported retention of existing commercial iodine-based contrast agents. Urine analysis of sensitive markers for acute kidney injury showed no responses at 1 week after injection at 3 times the ACD; however, a moderate response in the neutrophil gelatinase-associated lipocalin biomarker was measured at 24 and 48 hours. Compared with other TaO NPs reported in the literature, CZ-TaO NPs had relatively low osmolality and viscosity at concentrations greater than 200 mg Ta/mL and were similar in these physical properties to dimeric iodine-based contrast agents.

CONCLUSIONS

We found that a CZ-TaO NP-based contrast agent is potentially viable for general-purpose clinical CT imaging. Our results suggest that such an agent can be formulated with clinically viable physicochemical properties, can be biologically safe and cleared rapidly in urine, and can provide substantially improved image contrast at CT compared with current iodinated agents.

Novel Biocompatible Au Nanostars@PEG Nanoparticles for In Vivo CT Imaging and Renal Clearance Properties

Nanoprobes are rapidly becoming potentially transformative tools on disease diagnostics for a wide range of in vivo computed tomography (CT) imaging. Compared with conventional molecular-scale contrast agents, nanoparticles (NPs) promise improved abilities for in vivo detection. In this study, novel polyethylene glycol (PEG)-functionalized Au nanoparticles with star shape (AuNS@PEG) with strong X-ray mass absorption coefficient were synthesized as CT imaging contrast agents. Experimental results revealed that AuNS@PEG nanoparticles are well constructed with ultrasmall sizes, effective metabolisability, high computed tomography value, and outstanding biocompatibility. In vivo imaging also showed that the obtained AuNS@PEG nanoparticles can be efficiently used in CT-enhanced imaging. Therefore, the synthesized contrast agent AuNS@PEG nanoparticles as a great potential candidate can be widely used for CT imaging.

Optimization of the composition and dosage of PEGylated polyethylenimine-entrapped gold nanoparticles for blood pool, tumor, and lymph node CT imaging

Gold nanoparticles (Au NPs) with a high X-ray attenuation coefficient have a good potential in CT imaging applications. Here, we report the design and synthesis of Au NPs entrapped within polyethylene glycol (PEG)-modified branched polyethyleneimine (PEI) with varying the initial Au salt/PEI molar ratios and with the remaining PEI surface amines being acetylated for blood pool, lung tumor and lymph node CT imaging. The formed unacetylated and acetylated PEGylated PEI-entrapped Au NPs (Au PENPs) were characterized via different methods. We show that the PEGylated PEI is an effective template to entrap Au NPs having a uniform size ranging from 1.7nm to 4.4nm depending on the Au salt/PEI molar ratio. After optimization of the composition-dependent X-ray attenuation effect, we then selected {(Au⁰)₁₀₀-PEI·NHAc-mPEG} NPs for biological testing and show that the particles have good cytocompatibility in the given concentration range and can be used as a contrast agent for effective CT imaging of the blood pool of rats, lung cancer model of nude mice and lymph node of rabbits after intravenous injection. For each application, the injected dosage of the particles was optimized. In addition, the {(Au⁰)₁₀₀-PEI·NHAc-mPEG} NPs could be excreted out of the body with time. Our results indicate that the formed Au PENPs with an appropriate composition and dosage hold a great promise to be used for CT imaging of various biosystems.

An update on nanoparticle-based contrast agents in medical imaging

Despite the great value of current exogenous contrast agents for providing main diagnostic information, they still have certain drawbacks such as short blood half life, nonspecific biodistribution, fast clearance, slight renal toxicity and poor contrast in fat patients. Nanoparticles (NPs) are used as novel contrast agents that represent a promising strategy for the non invasive diagnosis. As a platform, nanoparticulates are compatible for developing targeted contrast agents. Advances in nanotechnology will provide enhanced sensitivity and specificity for tumor imaging enabling earlier detection of metastases. This article focuses on fundamental issue such as biological interactions, clearance routes, coating of NPs and presents a wide discussion about most recent category of NPs that are used as contrast agents and thebenefits/concerns issues associated with their use in clinical procedures.

Unique Roles of Gold Nanoparticles in Drug Delivery, Targeting and Imaging Applications

Nanotechnology has become more and more potentially used in diagnosis or treatment of diseases. Advances in nanotechnology have led to new and improved nanomaterials in biomedical applications. Common nanomaterials applicable in biomedical applications include liposomes, polymeric micelles, graphene, carbon nanotubes, quantum dots, ferroferric oxide nanoparticles, gold nanoparticles (Au NPs), and so on. Among them, Au NPs have been considered as the most interesting nanomaterial because of its unique optical, electronic, sensing and biochemical properties. Au NPs have been potentially applied for medical imaging, drug delivery, and tumor therapy in the early detection, diagnosis, and treatment of diseases. This review focuses on some recent advances in the use of Au NPs as drug carriers for the intracellular delivery of therapeutics and as molecular nanoprobes for the detection and monitoring of target molecules.

Simultaneous Enhancement of Photoluminescence, MRI Relaxivity, and CT Contrast by Tuning the Interfacial Layer of Lanthanide Heteroepitaxial Nanoparticles

Nanoparticle (NP) based exogenous contrast agents assist biomedical imaging by enhancing the target visibility against the background. However, it is challenging to design a single type of contrast agents that are simultaneously suitable for various imaging modalities. The simple integration of different components into a single NP contrast agent does not guarantee the optimized properties of each individual components. Herein, we describe lanthanide-based core-shell-shell (CSS) NPs as triple-modal contrast agents that have concurrently enhanced performance compared to their individual components in photoluminescence (PL) imaging, magnetic resonance imaging (MRI), and computed tomography (CT). The key to simultaneous enhancement of PL intensity, MRI r1 relaxivity, and X-ray attenuation capability in CT is tuning the interfacial layer in the CSS NP architecture. By increasing the thickness of the interfacial layer, we show that (i) PL intensity is enhanced from completely quenched/dark state to brightly emissive state of both upconversion and downshifting luminescence at different excitation wavelengths (980 and 808 nm), (ii) MRI r1 relaxivity is enhanced by 5-fold from 11.4 to 52.9 mM-1 s-1 (per Gd3+) at clinically relevant field strength 1.5 T, and (iii) the CT Hounsfield Unit gain is 70% higher than the conventional iodine-based agents at the same mass concentration. Our results demonstrate that judiciously designed contrast agents for multimodal imaging can achieve simultaneously enhanced performance compared to their individual stand-alone structures and highlight that multimodality can be achieved without compromising on individual modality performance.

The Effect of Patient Diameter on the Dual-Energy Ratio of Selected Contrast-Producing Elements

OBJECTIVES

The aim of this study was to assess whether the low- to high-kVp computed tomography (CT) number ratio at dual-energy CT is affected by changes in patient diameter.

METHODS

Seven contrast-producing elements were housed sequentially within an abdomen phantom. Fat rings enlarged the phantom diameter from 26 to 44 cm. The phantom was scanned using single-energy CT at tube potentials of 80 and 140 kVp and rapid-kVp-switching dual-energy CT.

RESULTS

CT numbers decreased proportionally (∼20% CT number reduction for smallest to largest phantom diameters) for low- and high-energy acquisitions but resulted in consistent dual-energy ratios for each contrast element. For 17 of 21 material pair combinations, the dual-energy ratio ranges of the two elements did not overlap, implying that discrimination should remain possible for these material pairs at all patient sizes.

CONCLUSIONS

The dual-energy ratio for different contrast materials is largely unaffected by changes in phantom diameter. This should allow for robust separation of most contrast material combinations irrespective of patient size.

Multifunctional nanoparticles as a tissue adhesive and an injectable marker for image-guided procedures

Tissue adhesives have emerged as an alternative to sutures and staples for wound closure and reconnection of injured tissues after surgery or trauma. Owing to their convenience and effectiveness, these adhesives have received growing attention particularly in minimally invasive procedures. For safe and accurate applications, tissue adhesives should be detectable via clinical imaging modalities and be highly biocompatible for intracorporeal procedures. However, few adhesives meet all these requirements. Herein, we show that biocompatible tantalum oxide/silica core/shell nanoparticles (TSNs) exhibit not only high contrast effects for real-time imaging but also strong adhesive properties. Furthermore, the biocompatible TSNs cause much less cellular toxicity and less inflammation than a clinically used, imageable tissue adhesive (that is, a mixture of cyanoacrylate and Lipiodol). Because of their multifunctional imaging and adhesive property, the TSNs are successfully applied as a hemostatic adhesive for minimally invasive procedures and as an immobilized marker for image-guided procedures.

Synthesis and Preclinical Characterization of a Cationic Iodinated Imaging Contrast Agent (CA4+) and Its Use for Quantitative Computed Tomography of Ex Vivo Human Hip Cartilage

Contrast agents that go beyond qualitative visualization and enable quantitative assessments of functional tissue performance represent the next generation of clinically useful imaging tools. An optimized and efficient large-scale synthesis of a cationic iodinated contrast agent (CA4+) is described for imaging articular cartilage. Contrast-enhanced CT (CECT) using CA4+ reveals significantly greater agent uptake of CA4+ in articular cartilage compared to that of similar anionic or nonionic agents, and CA4+ uptake follows Donnan equilibrium theory. The CA4+ CECT attenuation obtained from imaging ex vivo human hip cartilage correlates with the glycosaminoglycan content, equilibrium modulus, and coefficient of friction, which are key indicators of cartilage functional performance and osteoarthritis stage. Finally, preliminary toxicity studies in a rat model show no adverse events, and a pharmacokinetics study documents a peak plasma concentration 30 min after dosing, with the agent no longer present in vivo at 96 h via excretion in the urine.

Perfluorocarbon/Gold Loading for Noninvasive in Vivo Assessment of Bone Fillers Using 19F Magnetic Resonance Imaging and Computed Tomography

Calcium phosphate cement (CPC) is used in bone repair because of its biocompatibility. However, high similarity between CPC and the natural osseous phase results in poor image contrast in most of the available in vivo imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI). For accurate identification and localization during and after implantation in vivo, a composition with enhanced image contrast is needed. In this study, we labeled CPC with perfluoro-15-crown-5-ether-loaded (PFCE) poly(latic-co-glycolic acid) nanoparticles (hydrodynamic radius 100 nm) and gold nanoparticles (diameter 40 nm), as 19F MRI and CT contrast agents, respectively. The resulting CPC/PFCE/gold composite is implanted in a rat model for in vivo longitudinal imaging. Our findings show that the incorporation of the two types of different nanoparticles did result in adequate handling properties of the cement. Qualitative and quantitative long-term assessment of CPC/PFCE/gold degradation was achieved in vivo and correlated to the new bone formation. Finally, no adverse biological effects on the bone tissue are observed via histology. In conclusion, an easy and efficient strategy for following CPC implantation and degradation in vivo is developed. As all materials used are biocompatible, this CPC/PFCE/gold composite is clinically applicable.

Ultrasmall Magnetic CuFeSe2 Ternary Nanocrystals for Multimodal Imaging Guided Photothermal Therapy of Cancer

Nanoscale ternary chalcogenides have attracted intense research interest due to their wealth of tunable properties and diverse applications in energy and environmental and biomedical fields. In this article, ultrasmall magnetic CuFeSe₂ ternary nanocrystals (<5.0 nm) were fabricated in the presence of thiol-functionalized poly(methacrylic acid) by an environmentally friendly aqueous method under ambient conditions. The small band gap and the existence of intermediate bands lead to a broad NIR absorbance in the range of 500-1100 nm and high photothermal conversion efficiency (82%) of CuFeSe₂ nanocrystals. The resultant CuFeSe₂ nanocrystals show superparamagnetism and effective attenuation for X-rays. In addition, they also exhibit excellent water solubility, colloidal stability, biocompatibility, and multifunctional groups. These properties enable them to be an ideal nanotheranostic agent for multimodal imaging [e.g., photoacoustic imaging (PAI), magnetic resonance imaging (MRI), computed tomography (CT) imaging] guided photothermal therapy of cancer.

Nanoparticle design strategies for enhanced anticancer therapy by exploiting the tumour microenvironment

Nanovehicles can efficiently carry and deliver anticancer agents to tumour sites. Compared with normal tissue, the tumour microenvironment has some unique properties, such as vascular abnormalities, hypoxia and acidic pH. There are many types of cells, including tumour cells, macrophages, immune and fibroblast cells, fed by defective blood vessels in the solid tumour. Exploiting the tumour microenvironment can benefit the design of nanoparticles for enhanced therapeutic effectiveness. In this review article, we summarized the recent progress in various nanoformulations for cancer therapy, with a special emphasis on tumour microenvironment stimuli-responsive ones. Numerous tumour microenvironment modulation strategies with promising cancer therapeutic efficacy have also been highlighted. Future challenges and opportunities of design consideration are also discussed in detail. We believe that these tumour microenvironment modulation strategies offer a good chance for the practical translation of nanoparticle formulas into clinic.

Cancer-Associated, Stimuli-Driven, Turn on Theranostics for Multimodality Imaging and Therapy

Advances in bioinformatics, genomics, proteomics, and metabolomics have facilitated the development of novel anticancer agents that have decreased side effects and increased safety. Theranostics, systems that have combined therapeutic effects and diagnostic capabilities, have garnered increasing attention recently because of their potential use in personalized medicine, including cancer-targeting treatments for patients. One interesting approach to achieving this potential involves the development of cancer-associated, stimuli-driven, turn on theranostics. Multicomponent constructs of this type would have the capability of selectively delivering therapeutic reagents into cancer cells or tumor tissues while simultaneously generating unique signals that can be readily monitored under both in vitro and in vivo conditions. Specifically, their combined anticancer activities and selective visual signal respond to cancer-associated stimuli, would make these theranostic agents more highly efficient and specific for cancer treatment and diagnosis. This article focuses on the progress of stimuli-responsive turn on theranostics that activate diagnostic signals and release therapeutic reagents in response to the cancer-associated stimuli. The present article not only provides the fundamental backgrounds of diagnostic and therapeutic tools that have been widely utilized for developing theranostic agents, but also discusses the current approaches for developing stimuli-responsive turn on theranostics.

Highly water-stable rare ternary Ag-Au-Se nanocomposites as long blood circulation time X-ray computed tomography contrast agents

X-ray computed tomography (CT) is a powerful and widely used medical non-invasive technique that often requires intravenous administration of contrast agents (CAs) to better visualize soft tissues. In this work, we have developed a novel CT contrast agent based on ternary Ag-Au-Se chalcogenide nanoparticles (NP). A facile ligand exchange by using a 3 kDa PEGylated ligand with a dithiol dihydrolipoic acid as an anchor group resulted in highly water-soluble and monodisperse nanoparticles. These PEGylated ternary NPs were tested in vivo in mice, showing slow uptake by the mononuclear phagocyte system, long blood circulation times, low toxicity, and very good X-ray contrast, thus being promising candidates as CT contrast agents for clinical applications.

Non-invasive monitoring of in vivo degradation of a radiopaque thermoreversible hydrogel and its efficacy in preventing post-operative adhesions

In vivo behavior of hydrogel-based biomaterials is very important for rational design of hydrogels for various biomedical applications. Herein, we developed a facile method for in situ fabrication of radiopaque hydrogel. An iodinated functional diblock copolymer of poly(ethylene glycol) and aliphatic polyester was first synthesized by coupling the hydroxyl end of the diblock copolymer with 2,3,5-triiodobenzoic acid (TIB) and then a radiopaque thermoreversible hydrogel was obtained by mixing it with the virgin diblock copolymer. A concentrated aqueous solution of the copolymer blend was injectable at room temperature and spontaneously turned into an in situ hydrogel at body temperature after injection. The introduction of TIB moieties affords the capacity of X-ray opacity, enabling in vivo visualization of the hydrogel using Micro-CT. A rat model with cecum and abdominal defects was utilized to evaluate the efficacy of the radiopaque hydrogel in the prevention of post-operative adhesions, and a significant reduction of the post-operative adhesion formation was confirmed. Meanwhile, the maintenance of the radiopaque hydrogel in the abdomen after administration was non-destructively detected via Micro-CT scanning. The reconstructed three-dimensional images showed that the radiopaque hydrogel with an irregular morphology was located on the injured abdominal wall. The time-dependent profile of the volume of the radiopaque hydrogel determined by Micro-CT imaging was well consistent with the trend obtained from the dissection observation. Therefore, the radiopaque thermoreversible hydrogel can serve as a potential visualized biomedical implant and this practical mixing approach is also useful for further extension into the in vivo monitoring of other biomaterials.

STATEMENT OF SIGNIFICANCE

While a variety of biomaterials have been extensively studied, it is rare to monitor in vivo degradation and medical efficacy of a material after being implanted deeply into the body. Herein, the radiopaque thermoreversible hydrogel developed by us not only holds desirable performance on the prevention of post-operative abdominal adhesions, but also allows non-invasive monitoring of its in vivo degradation with CT imaging in a real-time, quantitative and three-dimensional manner. The methodology based on CT imaging provides important insights into the in vivo fate of the hydrogel after being deeply implanted into mammals for different biomedical applications and significantly reduces the amount of animals sacrificed.

Radiopaque Resorbable Inferior Vena Cava Filter Infused with Gold Nanoparticles

Failure to remove a retrievable inferior vena cava (IVC) filter can cause severe complications with high treatment costs. Polydioxanone (PPDO) has been shown to be a good candidate material for resorbable IVC filters. However, PPDO is radioluscent under conventional imaging modalities. Thus, the positioning and integrity of these PPDO filters cannot be monitored by computed tomography (CT) or x-ray. Here we report the development of radiopaque PPDO IVC filters based on gold nanoparticles (AuNPs). Commercially available PPDO sutures were infused with AuNPs. Scanning electron microscopy analysis confirmed the presence of AuNP on the surface of PPDO. Micro-CT and x-ray images of the AuNP-infused PPDO sutures showed significant signal enhancement compared to untreated PPDO sutures. Elemental analysis showed that gold loading exceeded 2000 ppm. Tensile strength and in vitro cytotoxicity showed no significant difference between AuNP-infused and untreated PPDO. In a 10-week stability study, neither the gold content nor the radiopacity of the infused PPDO sutures significantly changed in the first 6 weeks. The increased attenuation of AuNP-infused PPDO sutures indicates their major advantage as a radiopaque resorbable filter material, as the radiopacity allows monitoring of the position and integrity of the filter, thereby increasing its safety and efficacy.

Use of Nanoparticle Contrast Agents for Cell Tracking with Computed Tomography

Efforts to develop novel cell-based therapies originated with the first bone marrow transplant on a leukemia patient in 1956. Preclinical and clinical examples of cell-based treatment strategies have shown promising results across many disciplines in medicine, with recent advances in immune cell therapies for cancer producing remarkable response rates, even in patients with multiple treatment failures. However, cell-based therapies suffer from inconsistent outcomes, motivating the search for tools that allow monitoring of cell delivery and behavior in vivo. Noninvasive cell imaging techniques, also known as cell tracking, have been developed to address this issue. These tools can allow real-time, quantitative, and long-term monitoring of transplanted cells in the recipient, providing insight on cell migration, distribution, viability, differentiation, and fate, all of which play crucial roles in treatment efficacy. Understanding these parameters allows the optimization of cell choice, delivery route, and dosage for therapy and advances cell-based therapy for specific clinical uses. To date, most cell tracking work has centered on imaging modalities such as MRI, radionuclide imaging, and optical imaging. However, X-ray computed tomography (CT) is an emerging method for cell tracking that has several strengths such as high spatial and temporal resolution, and excellent quantitative capabilities. The advantages of CT for cell tracking are enhanced by its wide availability and cost effectiveness, allowing CT to become one of the most popular clinical imaging modalities and a key asset in disease diagnosis. In this review, we will discuss recent advances in cell tracking methods using X-ray CT in various applications, in addition to predictions on how the field will progress.

A biomimetic Au@BSA-DTA nanocomposites-based contrast agent for computed tomography imaging

Early detection of cancer is increasingly important for being considered to increase the survival rate in the treatment process. The past decades years have witnessed the great progress in the biological detection application of gold nanoparticles. Herein, we reported a facile one-pot synthesis process to obtain gold nanoparticles (Au@BSA) with bovine serum albumin (BSA) as a biotemplate following with conjugation of diatrizoic acid (DTA) for a potential X-ray computed tomography (CT) imaging contrast agent (Au@BSA-DTA). The as-prepared biomimetic material was characterized systematically by several techniques. It was shown that the prepared biomaterial is colloid stable under the tested range of pH and temperature. The cell cytotoxicity assay, hemolytic assay and cell morphology observation showed that Au@BSA-DTA has good biocompatibility and hemocompatibility at a concentration of Au even up to 80μg/mL. Besides, the biomimetic material Au@BSA-DTA with double radiodense elements of Au and iodine displayed much stronger CT imaging effect compared with the traditional small molecule contrast agents, which paves the potential clinical application in cancer early diagnosis.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

pH-sensitive Au-BSA-DOX-FA nanocomposites for combined CT imaging and targeted drug delivery

Albumin-based nanoparticles (NPs) as a drug delivery system have attracted much attention owing to their nontoxicity, non-immunogenicity, great stability and ability to bind to many therapeutic drugs. Herein, bovine serum albumin (BSA) was utilized as a template to prepare Au–BSA core/shell NPs. The outer layer BSA was subsequently conjugated with cis-aconityl doxorubicin (DOX) and folic acid (FA) to create Au–BSA–DOX–FA nanocomposites. A list of characterizations was undertaken to identify the successful conjugation of drug molecules and targeted agents. In vitro cytotoxicity using a cell counting kit-8 (CCK-8) assay indicated that Au–BSA NPs did not display obvious cytotoxicity to MGC-803 and GES-1 cells in the concentration range of 0–100 μg/mL, which can therefore be used as a safe drug delivery carrier. Furthermore, compared with free DOX, Au–BSA–DOX–FA nanocomposites exhibited a pH-sensitive drug release ability and superior antitumor activity in a drug concentration-dependent manner. In vivo computed tomography (CT) imaging experiments showed that Au–BSA–DOX–FA nanocomposites could be used as an efficient and durable CT contrast agent for targeted CT imaging of the folate receptor (FR) overexpressed in cancer tissues. In vivo antitumor experiments demonstrated that Au–BSA–DOX–FA nanocomposites have selective antitumor activity effects on FR-overexpressing tumors and no adverse effects on normal tissues and organs. In conclusion, the Au–BSA–DOX–FA nanocomposite exhibits selective targeting activity, X-ray attenuation activity and pH-sensitive drug release activity. Therefore, it can enhance CT imaging and improve the targeting therapeutic efficacy of FR-overexpressing gastric cancers. Our findings suggest that Au–BSA–DOX–FA nanocomposite is a novel drug delivery carrier and a promising candidate for cancer theranostic applications.

Opportunities for new CT contrast agents to maximize the diagnostic potential of emerging spectral CT technologies

The introduction of spectral CT imaging in the form of fast clinical dual-energy CT enabled contrast material to be differentiated from other radiodense materials, improved lesion detection in contrast-enhanced scans, and changed the way that existing iodine and barium contrast materials are used in clinical practice. More profoundly, spectral CT can differentiate between individual contrast materials that have different reporter elements such that high-resolution CT imaging of multiple contrast agents can be obtained in a single pass of the CT scanner. These spectral CT capabilities would be even more impactful with the development of contrast materials designed to complement the existing clinical iodine- and barium-based agents. New biocompatible high-atomic number contrast materials with different biodistribution and X-ray attenuation properties than existing agents will expand the diagnostic power of spectral CT imaging without penalties in radiation dose or scan time.

A study on the imaging characteristics of Gold nanoparticles as a contrast agent in X-ray computed tomography

Aim: In the current study, some imaging characteristics of AuNPs were quantitatively analyzed and compared with two conventional contrast media (CM) including Iodine and Gadolinium by using of a cylindrical phantom.

Methods: AuNPs were synthesized with the mean diameter of 16 nm and were equalized to the concentration of 0.5, 1, 2 and 4 mg/mL in the same volumes. A cylindrical phantom resembling the head and neck was fabricated and drilled to contain small tubes filled with Iodine, Gadolinium, and AuNPs as contrast media. The phantom was scanned in different exposure techniques and CT numbers of three studied contrast media inside test tubes were measured in terms of Hounsfield Unit (HU). The imaging parameters of the noise and contrast to noise ratios (CNR) were calculated for all studied CMs.

Results: AuNPs showed 128% and 166% higher CT number in comparison with Iodine and Gadolinium respectively. Also, Iodine had a greater CT number than Gadolinium for the same exposure techniques and concentration. The maximum CT number for AuNPs and studied contrast materials was obtained at the highest mAs and the lowest tube potential. The maximum CT number were 1033±11 (HU) for AuNP, 565±10 (HU) for Iodine, 458±11 for Gadolinium. Moreover, the maximum CNRs of 433±117, 203±53, 145±37 were found for AuNPs, Iodine and Gadolinium respectively.

Conclusion: The contrast agent based on AuNPs showed higher imaging quality in terms of contrast and noise relative to other iodine and gadolinium based contrast media in X-ray computed tomography. Application of the AuNPs as a contrast medium in x-ray CT is recommended.

Ultrasmall Silica-Based Bismuth Gadolinium Nanoparticles for Dual Magnetic Resonance-Computed Tomography Image Guided Radiation Therapy

Selective killing of cancer cells while minimizing damage to healthy tissues is the goal of clinical radiation therapy. This therapeutic ratio can be improved by image-guided radiation delivery and selective radiosensitization of cancer cells. Here, we have designed and tested a novel trimodal theranostic nanoparticle made of bismuth and gadolinium for on-site radiosensitization and image contrast enhancement to improve the efficacy and accuracy of radiation therapy. We demonstrate in vivo magnetic resonance (MR), computed tomography (CT) contrast enhancement, and tumor suppression with prolonged survival in a non-small cell lung carcinoma model during clinical radiation therapy. Histological studies show minimal off-target toxicities due to the nanoparticles or radiation. By mimicking existing clinical workflows, we show that the bismuth-gadolinium nanoparticles are highly compatible with current CT-guided radiation therapy and emerging MR-guided approaches. This study reports the first in vivo proof-of-principle for image-guided radiation therapy with a new class of theranostic nanoparticles.

Nanopolymersomes with an Ultrahigh Iodine Content for High-Performance X-Ray Computed Tomography Imaging In Vivo

Biocompatible and biodegradable nanopolymersomes with an unprecedented iodine content, low viscosity, and iso-osmolality achieve significantly enhanced CT imaging of blood pool and the reticuloendothelial system. Moreover, in subcutaneous and orthotopic tumor models in mice, they show enhanced in vivo imaging when compared to iohexol, a clinically used small-molecule contrast agent.

Photoacoustic-Based Multimodal Nanoprobes: from Constructing to Biological Applications

Multimodal nanoprobes have attracted intensive attentions since they can integrate various imaging modalities to obtain complementary merits of single modality. Meanwhile, recent interest in laser-induced photoacoustic imaging is rapidly growing due to its unique advantages in visualizing tissue structure and function with high spatial resolution and satisfactory imaging depth. In this review, we summarize multimodal nanoprobes involving photoacoustic imaging. In particular, we focus on the method to construct multimodal nanoprobes. We have divided the synthetic methods into two types. First, we call it “one for all” concept, which involves intrinsic properties of the element in a single particle. Second, “all in one” concept, which means integrating different functional blocks in one particle. Then, we simply introduce the applications of the multifunctional nanoprobes for in vivo imaging and imaging-guided tumor therapy. At last, we discuss the advantages and disadvantages of the present methods to construct the multimodal nanoprobes and share our viewpoints in this area.

Future of the Renal Biopsy: Time to Change the Conventional Modality Using Nanotechnology

At the present time, imaging guided renal biopsy is used to provide diagnoses in most types of primary and secondary renal diseases. It has been claimed that renal biopsy can provide a link between diagnosis of renal disease and its pathological conditions. However, sometimes there is a considerable mismatch between patient renal outcome and pathological findings in renal biopsy. This is the time to address some new diagnostic methods to resolve the insufficiency of conventional percutaneous guided renal biopsy. Nanotechnology is still in its infancy in renal imaging; however, it seems that it is the next step in renal biopsy, providing solutions to the limitations of conventional modalities.