Computed tomography in color: NanoK-enhanced spectral CT molecular imaging

Gold nanoparticles spectral CT imaging and limit of detectability in a new materials contrast-detail phantom

This study involves the synthesis, characterization, and spectral photon counting CT (SPCCT) imaging of gold nanoparticles tailored for enhancing the contrast of small cancer lesions. We used the modified Turkevich method to produce thiol-capped gold nanoparticles (AuNPs) at different concentrations (20, 15, 10, 5, 2.5, 1.25, 0.6 mg/ml). We thoroughly characterized the AuNPs using Transmission Electron Microscopy (TEM), X-ray diffraction spectroscopy (XRD), Dynamic Light Scattering (DLS), and UV-visible absorption spectroscopy. To assess the AuNPs contrast enhancing performance, we designed and built a new material contrast detail phantom for CT imaging and determined the minimum detectable concentrations of AuNPs in simulated lesions of small diameters (1, 2, 3, and 5 mm). The synthesized AuNPs are spherical with an average size of approximately 20 ± 4 nm, with maximum UV absorption occurring at 527 nm wavelength, and exhibit a face-centered cubic structure of gold according to XRD analysis. The synthesized gold nanoparticles demonstrated high contrast in SPCCT, suggesting their potential as contrast agents for imaging cancer tissues. The AuNPs image contrast was directly proportional to the AuNPs concentration. We are the first to determine that the lowest visually distinguishable contrast was achieved at a gold concentration of 5 mg/ml for a 2 mm simulated lesion. For 1 mm size lesion the smallest visible concentration was 10 mg/ml. This newly developed phantom can be used for determining the minimal concentration required for various high-Z nanoparticles to produce detectable contrast in X-ray imaging for small-size simulated lesions.

Device Design and Diagnostic Imaging of Radiopaque 3D Printed Tissue Engineering Scaffolds

3D printed biomaterial implants are revolutionizing personalized medicine for tissue repair, especially in orthopedics. In this study, a radiopaque Bi 2 O 3 doped polycaprolactone ( PCL ) composite is developed and implemented to enable the use of diagnostic X-ray technologies, especially photon counting X-ray computed tomography ( PCCT ), for comprehensive in vivo device monitoring. PCL filament with homogeneous Bi 2 O 3 nanoparticle ( NP ) dispersion (0.8 to 11.7 wt%) are first fabricated. Tissue engineered scaffolds ( TES ) are then 3D printed with the composite filament, optimizing printing parameters for small feature size and severely overhung geometries. These composite TES are characterized via micro-computed tomography ( µ CT ), tensile testing, and a cytocompatibility study, with Bi 2 O 3 mass fractions as low as 2 wt% providing excellent radiographic distinguishability, improved tensile properties, and equivalent cytocompatibility of neat PCL. The excellent radiographic distinguishability is validated in situ by imaging 4 and 7 wt% TES in a mouse model with µCT, showing excellent agreement with in vitro measurements. Subsequently, CT image-derived swine menisci are 3D printed with composite filament and re-implanted in their corresponding swine legs ex vivo . Re-imaging the swine legs via clinical CT allows facile identification of device location and alignment. Finally, the emergent technology of PCCT unambiguously distinguishes implanted menisci in situ.

Spindle Monitor: A Tool for Real-Time Assessment and Concurrent Treatment of Postoperative Tumor Prognosis

Cancer surgery remains a mainstay in clinical treatment. However, the efficacy of subsequent therapies largely depends on the precise evaluation of postoperative prognoses, underscoring the critical need for a comprehensive and accurate assessment of surgical outcomes. Nanoprobes targeting tumors offer a promising solution for visual prognostic assessment. In this study, we developed a "Spindle Monitor" system, designated as APPADs (Au NBPs@PDA-pep-AS1411-Dox), composed of core-shell nanoparticles. The core was made up of gold nanobipyramids (Au NBPs), coated with polydopamine (PDA), and subsequently loaded with peptide chains, AS1411, and doxorubicin (Dox). Upon deployment in the acidic tumor microenvironment (TME), APPADs released substantial amounts of Dox, initiating the apoptotic process. This triggered the activity of caspase-3, which is a crucial executor in the apoptotic pathway. Consequently, DEVD, a specific recognition site for caspase-3, was cleaved, enabling the disconnection of FITC-conjugated peptide chains and the recovery of fluorescence. Through assessing this fluorescence imaging effect, local laser irradiation could be precisely guided to the postoperative site, facilitating a synergistic combination of photothermal therapy and chemotherapy. Specifically, our "Spindle Monitor" APPADs had been validated to achieve accurate fluorescence imaging in vitro and in vivo, which demonstrated its potential value as a versatile tool for evaluating postoperative prognosis in surgical treatments, such as thyroid cancer, and assessing chemotherapy efficacy in difficult cases, like late-stage osteosarcoma. This promising tool lays a good foundation for development in visual prognosis evaluation after tumor surgery.

Achieving safe and high-performance gastrointestinal tract spectral CT imaging with small-molecule lanthanide complex

BACKGROUND

Non-intrusive imaging of gastrointestinal (GI) tract using computed tomography (CT) contrast agents is of the most significant issues in the diagnosis and treatment of GI diseases. Moreover, spectral CT, which can generate monochromatic images to display the X-ray attenuation characteristics of contrast agents, provides a better imaging sensitivity for diagnose inflammatory bowel disease (IBD) than convention CT imaging.

METHODS

Herein, a convenient and one-pot synthesis method is provided for the fabrication of small-molecule lanthanide complex Holmium-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (Ho-DOTA) as a biosafe and high-performance spectral CT contrast agent for GI imaging with IBD. In vivo CT imaging was administered with both healthy mice and colitis mice induced by dextran sodium sulfate.

RESULTS

We found that Ho-DOTA accumulated in inflammation sites of large intestines and produced high CT contrast compared with healthy mice. Both in vitro and in vivo experimental results also showed that Ho-DOTA provided much more diagnostic sensitivity and accuracy due to the excellent X-ray attenuation characteristics of Ho-DOTA compared with clinical iodinate agent. Furthermore, the proposed contrast media could be timely excreted from the body via the urinary and digestive system, keeping away from the potential side effects due to long-term retention in vivo.

CONCLUSION

Accordingly, Ho-DOTA with excellent biocompatibility can be useful as a potential high-performance spectral CT contrast agent for further clinical imaging of gastrointestinal tract and diagnosis of intestinal system diseases.

Clinical Applications of Photon-counting CT: A Review of Pioneer Studies and a Glimpse into the Future

CT systems equipped with photon-counting detectors (PCDs), referred to as photon-counting CT (PCCT), are beginning to change imaging in several subspecialties, such as cardiac, vascular, thoracic, and musculoskeletal radiology. Evidence has been building in the literature underpinning the many advantages of PCCT for different clinical applications. These benefits derive from the distinct features of PCDs, which are made of semiconductor materials capable of converting photons directly into electric signal. PCCT advancements include, among the most important, improved spatial resolution, noise reduction, and spectral properties. PCCT spatial resolution on the order of 0.25 mm allows for the improved visualization of small structures (eg, small vessels, arterial walls, distal bronchi, and bone trabeculations) and their pathologies, as well as the identification of previously undetectable anomalies. In addition, blooming artifacts from calcifications, stents, and other dense structures are reduced. The benefits of the spectral capabilities of PCCT are broad and include reducing radiation and contrast material dose for patients. In addition, multiple types of information can be extracted from a single data set (ie, multiparametric imaging), including quantitative data often regarded as surrogates of functional information (eg, lung perfusion). PCCT also allows for a novel type of CT imaging, K-edge imaging. This technique, combined with new contrast materials specifically designed for this modality, opens the door to new applications for imaging in the future.

Spectral computed tomography-guided radiotherapy of osteosarcoma utilizing BiOI nanosheets

As an aggressive malignant bone tumor, osteosarcoma (OS) is usually found in children and adolescents. Computed tomography (CT) is an important tool for the clinical evaluation of osteosarcoma, but limits to low diagnostic specificity due to single parameters of traditional CT and modest signal-to-noise ratio of clinical iodinated contrast agents. As one kind of spectral CT, dual-energy CT (DECT), with the advantage of a provision of multi-parameter information, makes it possible to acquire the best signal-to-noise ratio image, accurate detection, as well as imaging-guided therapy of bone tumors. Hereby, we synthesized BiOI nanosheets (BiOI NSs) as a DECT contrast agent with superior imaging capability compared to iodine agents for clinical detection of OS. Meanwhile, the synthesized BiOI NSs with great biocompatibility is able to achieve effective radiotherapy (RT) by enhancing X-ray dose deposition at the tumor site, leading to DNA damage, which in turn inhibits tumor growth. This study offers a promising new avenue for DECT imaging-guided treatment of OS. STATEMENT OF SIGNIFICANCE: Osteosarcoma (OS) is a common primary malignant bone tumor. Traditional surgical procedures and conventional CT scans are often used for the treatment and monitoring of OS, but the effects are generally unsatisfactory. In this work, BiOI nanosheets (NSs) was reported for dual-energy CT (DECT) imaging-guided OS radiotherapy. The powerful and constant X-ray absorption of BiOI NSs at any energy guarantees excellent enhanced DECT imaging performance, allowing detailed visualization of OS through images with a better signal-to-noise ratio and guiding radiotherapy process. The deposition of X-rays could be greatly enhanced by Bi atoms to induce serious DNA damage in radiotherapy. Taken together, the BiOI NSs for DECT-guided radiotherapy will greatly improve the current treatment status of OS.

Harnessing Hafnium-Based Nanomaterials for Cancer Diagnosis and Therapy

With the rapid development of nanotechnology and nanomedicine, there are great interests in employing nanomaterials to improve the efficiency of disease diagnosis and treatment. The clinical translation of hafnium oxide (HfO2 ), commercially namedas NBTXR3, as a new kind of nanoradiosensitizer for radiotherapy (RT) of cancers has aroused extensive interest in researches on Hf-based nanomaterials for biomedical application. In the past 20 years, Hf-based nanomaterials have emerged as potential and important nanomedicine for computed tomography (CT)-involved bioimaging and RT-associated cancer treatment due to their excellent electronic structures and intrinsic physiochemical properties. In this review, a bibliometric analysis method is employed to summarize the progress on the synthesis technology of various Hf-based nanomaterials, including HfO2 , HfO2 -based compounds, and Hf-organic ligand coordination hybrids, such as metal-organic frameworks or nanoscaled coordination polymers. Moreover, current states in the application of Hf-based CT-involved contrasts for tissue imaging or cancer diagnosis are reviewed in detail. Importantly, the recent advances in Hf-based nanomaterials-mediated radiosensitization and synergistic RT with other current mainstream treatments are also generalized. Finally, current challenges and future perspectives of Hf-based nanomaterials with a view to maximize their great potential in the research of translational medicine are also discussed.

Recent advances in targeted delivery of non-coding RNA-based therapeutics for atherosclerosis

Cardiovascular disease (CVD) has overtaken infectious illnesses as the leading cause of mortality and disability worldwide. The pathology that underpins CVD is atherosclerosis, characterized by chronic inflammation caused by the accumulation of plaques in the arteries. As our knowledge about the microenvironment of blood vessel walls deepens, there is an opportunity to fine-tune treatments to target the mechanisms driving atherosclerosis more directly. The application of non-coding RNAs (ncRNAs) as biomarkers or intervention targets is increasing. Although these ncRNAs play an important role in driving atherosclerosis and vascular dysfunction, the cellular and extracellular environments pose a challenge for targeted transmission and therapeutic regulation of ncRNAs. Specificity, delivery, and tolerance have hampered the clinical translation of ncRNA-based therapeutics. Nanomedicine is an emerging field that uses nanotechnology for targeted drug delivery and advanced imaging. Recently, nanoscale carriers have shown promising results and have introduced new possibilities for nucleic acid targeted drug delivery, particularly for atherosclerosis. In this review, we discuss the latest developments in nanoparticles to aid ncRNA-based drug development, particularly miRNA, and we analyze the current challenges in ncRNA targeted delivery. In particular, we highlight the emergence of various kinds of nanotherapeutic approaches based on ncRNAs, which can improve treatment options for atherosclerosis.

Spectral computed tomography with inorganic nanomaterials: State-of-the-art

Recently, spectral computed tomography (CT) technology has received great interest in the field of radiology. Spectral CT imaging utilizes the distinct, energy-dependent X-ray absorption properties of substances in order to provide additional imaging information. Dual-energy CT and multi-energy CT (Spectral CT) are capable of constructing monochromatic energy images, material separation images, energy spectrum curves, constructing effective atomic number maps, and more. However, poor contrast, due to neighboring X-ray attenuation of organs and tissues, is still a challenge to spectral CT. Hence, contrast agents (CAs) are applied for better differentiation of a given region of interest (ROI). Currently, many different kinds of inorganic nanoparticulate CAs for spectral CT have been developed due to the limitations of clinical iodine (I)-based contrast media, leading to the conclusion that inorganic nanomedicine applied to spectral CT will be a powerful collaboration both in basic research and in clinics. In this review, the underlying principles and types of spectral CT techniques are discussed, and some evolving clinical diagnosis applications of spectral CT techniques are introduced. In particular, recent developments in inorganic CAs used for spectral CT are summarized. Finally, the challenges and future developments of inorganic nanomedicine in spectral CT are briefly discussed.

Significance of Capping Agents of Colloidal Nanoparticles from the Perspective of Drug and Gene Delivery, Bioimaging, and Biosensing: An Insight

The over-growth and coagulation of nanoparticles is prevented using capping agents by the production of stearic effect that plays a pivotal role in stabilizing the interface. This strategy of coating the nanoparticles’ surface with capping agents is an emerging trend in assembling multipurpose nanoparticles that is beneficial for improving their physicochemical and biological behavior. The enhancement of reactivity and negligible toxicity is the outcome. In this review article, an attempt has been made to introduce the significance of different capping agents in the preparation of nanoparticles. Most importantly, we have highlighted the recent progress, existing roadblocks, and upcoming opportunities of using surface modified nanoparticles in nanomedicine from the drug and gene delivery, bioimaging, and biosensing perspectives.

Size characterization of nanomaterials in environmental and biological matrices through non-electron microscopic techniques

Engineered nanomaterials (ENs) can enter the environment, and accumulate in food chains, thereby causing environmental and health problems. Size characterization of ENs is critical for further evaluating the interactions among ENs in biological and ecological systems. Although electron microscope is a powerful tool in obtaining the size information, it has limitations when studying nanomaterials in complex matrices. In this review, we summarized non-electron microscope-based techniques, including chromatography-based, mass spectrometry-based, synchrotron radiation- and neutron-based techniques for detecting the size of ENs in environmental and biological matrices. The advantages and disadvantages of these techniques were highlighted. The perspectives on size characterization of ENs in complex matrices were also presented.

Polymer-coated BiOCl nanosheets for safe and regioselective gastrointestinal X-ray imaging

Bismuth-based compounds are considered to be the best candidates for computed tomography (CT) imaging of gastrointestinal (GI) tract due to high X-ray absorption. Here, we report the introduction of polymer-coated bismuth oxychloride (BiOCl) nanosheets for highly efficient CT imaging in healthy mice and animal with colitis. We demonstrate simple, low cost and fast aqueous synthesis protocol which provides gram-quantity yield of chemically stable BiOCl nanosheets. The developed contrast gives 2.55-fold better CT enhancement compared to conventional contrast with negligible in vivo toxicity. As a major finding we report a regioselective CT imaging of GI tract by using nanoparticles coated with differentially charged polymers. Coating of nanoparticles with a positively charged polymer leads to their fast accumulation in small intestine, while the coating with negatively charged polymers stimulates prolonged stomach retention. We propose that this effect may be explained by a pH-controlled aggregation of nanoparticles in stomach. This feature may become the basis for advancement in clinical diagnosis of entire GI tract.

Prospecting Cellular Gold Nanoparticle Biomineralization as a Viable Alternative to Prefabricated Gold Nanoparticles

Gold nanoparticles (GNPs) have shown considerable potential in a vast number of biomedical applications. However, currently there are no clinically approved injectable GNP formulations. Conversely, gold salts have been used in the clinic for nearly a century. Further, there is evidence of GNP formation in patients treated with gold salts (i.e., chrysiasis). Recent reports evaluating this phenomenon in human cells and in murine models indicate that the use of gold ions for in situ formation of theranostic GNPs could greatly improve the delivery within dense biological tissues, increase efficiency of intracellular gold uptake, and specificity of GNP formation within cancer cells. These attributes in combination with safe clinical application of gold salts make this process a viable strategy for clinical translation. Here, the first summary of the current knowledge related to GNP biomineralization in mammalian cells is provided along with critical assessment of potential biomedical applications of this newly emergent field.

Fabrication of gelatin Bi2S3 capsules as a highly sensitive X-ray contrast agent for gastrointestinal motility assessment in vivo

Tiny BaSO₄ rod-based X-ray imaging is the most frequently-used method for clinical diagnosis of gastrointestinal motility disorders. The BaSO₄ rods usually have a small size to pass through the gastrointestinal tract smoothly, but suffer from unavoidably low sensitivity. Herein, we developed Bi₂S₃ capsules as a high-performance X-ray contrast agent for gastrointestinal motility assessment for the first time. The Bi₂S₃ capsules were synthesized by the encapsulation of commercial Bi₂S₃ powder into commercial gelatin capsules and subsequent coating of ultraviolet-curable resin. The prepared Bi₂S₃ capsules showed excellent biocompatibility in vitro and in vivo and superior X-ray attenuation ability due to the large atomic number and high K-edge value of Bi. The developed Bi₂S₃ capsules can serve as a small but highly sensitive X-ray contrast agent to quantitatively assess gastrointestinal motility in a vincristine-induced gastrointestinal motility disorder model in vivo by X-ray, CT and spectral CT imaging successfully, solving the intrinsic drawbacks of clinically used BaSO₄.

Hitchhiking probiotic vectors to deliver ultra-small hafnia nanoparticles for 'Color' gastrointestinal tract photon counting X-ray imaging

Gastrointestinal (GI) tract is one of the hard-to-reach target tissues for the delivery of contrast agents and drugs mediated by nanoparticles due to its harsh environment. Herein, we overcame this barrier by designing orally ingestible probiotic vectors for 'hitchhiking' ultrasmall hafnia (HfO2) (∼1-2 nm) nanoparticles. The minute-made synthesis of these nanoparticles is accomplished through a simple reduction reaction. These nanoparticles were incubated with probiotic bacteria with potential health benefits and were non-specifically taken up due to their small size. Subsequently, the bacteria were lyophilized and packed into a capsule to be administered orally as the radiopaque contrast agents for delineating the GI features. These nano-bio-hybrid entities could successfully be utilized as contrast agents in vivo in the conventional and multispectral computed tomography (CT). We demonstrated in 'color' the accumulated nanoparticles using advanced detectors of the photon counting CT. The enhanced nano-bio-interfacing capability achieved here can circumvent traditional nanoparticle solubility and delivery problems while offering a patient friendly approach for GI imaging to replace the currently practiced barium meal.

Small-Molecule Bi-DOTA Complex for High-Performance CT and Spectral CT Bioimaging

Objectives

It is necessary to develop a high-performance and biocompatible contrast agent to accurately diagnose various diseases via in vivo computed tomography (CT) imaging. Here, we synthesized a small molecular Bi-DOTA complex as a high-performance contrast agent for in vitro and in vivo CT bioimaging.

Materials and Methods

In our study, Bi-DOTA was fabricated through a facile and one-pot synthesis strategy. The formed Bi-DOTA complex was characterized via different techniques. Furthermore, Bi-DOTA was used for in vitro and in vivo CT bioimaging to verify its X-ray attenuation ability, especially in vivo kidney imaging, gastrointestinal tract CT imaging, and spectral CT imaging.

Results

A small molecular Bi-DOTA complex with a molecular mass of 0.61 kDa was synthesized successfully, which exhibited outstanding dispersion, good biocompatibility, and superior X-ray attenuation ability. Meanwhile, we showed that the obtained contrast agent was quite biocompatible and safe in the given concentration range as confirmed by in vitro and in vivo cytotoxicity assay. Also, the proposed contrast agent can be rapidly excreted from the body via the urinary system, avoiding the potential side effects caused by long-term retention in vivo. Importantly, Bi-DOTA was successfully used in high-quality in vitro CT imaging, in vivo kidney imaging, gastrointestinal tract CT imaging, and spectral CT imaging.

Conclusions

These superiorities allowed Bi-DOTA to be used as an efficient CT contrast agent and laid down a new way of designing high-performance CT contrast agents with great clinical transformation potential.

One-pot synthesis of flower-like Bi2S3 nanoparticles for spectral CT imaging and photothermal therapy in vivo

A facile and green strategy was developed for fabricating Bi2S3 nanoparticles for spectral CT imaging and photothermal therapy in vivo.

Gram-scale synthesis of a neodymium chelate as a spectral CT and second near-infrared window imaging agent for visualizing the gastrointestinal tract in vivo

The diagnosis of gastrointestinal (GI) tract diseases is frequently performed in the clinic, so it is crucial to develop high-performance contrast agents for real-time and non-invasive imaging examination of the GI tract. Herein, we show a novel method to synthesize a neodymium (Nd) chelate, Nd-diethylenetriaminepentaacetic acid (Nd-DTPA), on a large scale without byproducts for spectral computed tomography (CT) and second near-infrared window imaging of the GI tract in vivo. The Nd-DTPA was simply generated by heating the mixture of Nd2O3 and DTPA in water at 85 °C for 2 h. This dual-modal imaging agent has the advantages of a simple and green synthesis route, no need of purification process, high yield (86.24%), large-scale production capability (>10 g in lab synthesis), good chemical stability and excellent water solubility (≈2 g mL-1). Moreover, the Nd-DTPA emitted strong near-infrared fluorescence at 1308 nm, and exhibited superior X-ray attenuation ability compared to clinical iohexol. The proposed Nd-DTPA can integrate the complementary merits of dual-modal imaging to realize spatial-temporal and highly sensitive imaging of the GI tract in vivo, and accurate diagnosis of the location of intestinal obstruction and monitor its recovery after surgery. The developed highly efficient method for the gram-scale synthesis of Nd-DTPA and the proposed spectral CT and second near-infrared window dual-modal imaging strategy provide a promising route for accurate visualization of the GI tract in vivo.

Unlocking the power of optical imaging in the second biological window: Structuring near-infrared II materials from organic molecules to nanoparticles

Biomedical imaging techniques play a crucial role in clinical diagnosis, surgical intervention, and prognosis. Fluorescence imaging in the second biological window (second near-infrared [NIR-II]; 1000-1700 nm) has attracted attention recently. NIR-II fluorescence imaging offers unique advantages in terms of reduced photon scattering, deep tissue penetration, high sensitivity, and many others. A host of materials, including small organic molecules, single-walled carbon nanotubes, polymeric and rare-earth-doped nanoparticles, have been explored as NIR-II emitting fluorescent probes. Efficient and viable approaches to design and develop fluorescence probes with tunable photophysical properties without compromising other key features are of paramount importance. Various chemical strategies are explored to increase the quantum yield of these imaging agents without compromising their spatiotemporal resolution, specificity, and tissue penetration capabilities. This review summarizes the strategies implemented to design and synthesize NIR-II emitting nanoparticles and small organic molecule-based fluorescent probes for applications in the biomedical field. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

A one-pot synthesis of multifunctional Bi2S3 nanoparticles and the construction of core-shell Bi2S3@Ce6-CeO2 nanocomposites for NIR-triggered phototherapy

As a direct thin band gap n-type semiconductor, bismuth sulfide (Bi2S3) nanomaterials possess great near-infrared (NIR)-triggered photothermal effects, photoacoustic (PA) and computed tomography (CT) imaging properties. Hence, Bi2S3 nanomaterials have become a research focal point in multiple domains, such as the construction of NIR-triggered nanosystems for cancer therapy. In this study, through a simple one-pot synthesis with the assistance of EDTA-2Na, we first obtained monodispersed spherical Bi2S3 of uniform particle sizes with fascinating photothermal and PA/CT imaging properties. Based on this, we introduced the photosensitizer Ce6 with photodynamic property and CeO2 with the O2-evolving characteristic, and thus designed a core-shell structure of the Bi2S3@Ce6-CeO2 nanocomposites (Bi2S3@Ce6-CeO2 NCs). The as-received Bi2S3@Ce6-CeO2 NCs exhibited a remarkable synergetic photothermal and photodynamic therapeutic effect both in vitro and in vivo, demonstrating its promising potential for cancer treatments. In the long term, the multifunctional PA/CT properties of both Bi2S3 NPs and Bi2S3@Ce6-CeO2 NCs in this study also supply a novel Bi2S3-based platform for constructing integrated diagnosis and treatment platforms.

X-ray-Based Techniques to Study the Nano-Bio Interface

X-ray-based analytics are routinely applied in many fields, including physics, chemistry, materials science, and engineering. The full potential of such techniques in the life sciences and medicine, however, has not yet been fully exploited. We highlight current and upcoming advances in this direction. We describe different X-ray-based methodologies (including those performed at synchrotron light sources and X-ray free-electron lasers) and their potentials for application to investigate the nano-bio interface. The discussion is predominantly guided by asking how such methods could better help to understand and to improve nanoparticle-based drug delivery, though the concepts also apply to nano-bio interactions in general. We discuss current limitations and how they might be overcome, particularly for future use in vivo.

Pnictogen Semimetal (Sb, Bi)-Based Nanomaterials for Cancer Imaging and Therapy: A Materials Perspective

Innovative multifunctional nanomaterials have attracted tremendous interest in current research by facilitating simultaneous cancer imaging and therapy. Among them, antimony (Sb)- and bismuth (Bi)-based nanoparticles are important species with multifunction to boost cancer theranostic efficacy. Despite the rapid development, the extensive previous work treated Sb- and Bi-based nanoparticles as mutually independent species, and therefore a thorough understanding of their relationship in cancer theranostics was lacking. We propose here that the identical chemical nature of Sb and Bi, being semimetals, provides their derived nanoparticles with inherent multifunction for near-infrared laser-driven and/or X-ray-based cancer imaging and therapy as well as some other imparted functions. An overview of recent progress on Sb- and Bi-based nanoparticles for cancer theranostics is provided to highlight the relationship between chemical nature and multifunction. The understanding of Sb- and Bi-based nanoparticles in this way might shed light on the further design of smart multifunctional nanoparticles for cancer theranostics.

Cardiac Computed Tomography Perfusion: Contrast Agents, Challenges and Emerging Methodologies from Preclinical Research to the Clinics

Computed Tomography (CT) has long been regarded as a purely anatomical imaging modality. Recent advances on CT technology and Contrast Agents (CA) in both clinical and preclinical cardiac imaging offer opportunities for the use of CT in functional imaging. Combined with modern ECG-gating techniques, functional CT has now become a reality allowing a comprehensive evaluation of myocardial global and regional function, perfusion and coronary angiography. This article aims at reviewing the current status of cardiac CT perfusion and micro-CT perfusion with established and experimental scanners and contrast agents, from clinical practice to the experimental domain of investigations based on animal models of heart diseases.

Current trends in pyrrole and porphyrin-derived nanoscale materials for biomedical applications

This article is written to provide an up-to-date review of pyrrole-based biomedical materials. Porphyrins and other tetrapyrrolic molecules possess unique magnetic, optical and other photophysical properties that make them useful for bioimaging and therapy. This review touches briefly on some of the synthetic strategies to obtain porphyrin- and tetrapyrrole-based nanoparticles, as well as the variety of applications in which crosslinked, self-assembled, porphyrin-coated and other nanoparticles are utilized. We explore examples of these nanoparticles' applications in photothermal therapy, drug delivery, photodynamic therapy, stimuli response, fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, computed tomography and positron emission tomography. We anticipate that this review will provide a comprehensive summary of pyrrole-derived nanoparticles and provide a guideline for their further development.

Assessment of Multienergy Interpixel Coincidence Counters (MEICC) for Charge Sharing Correction or Compensation for Photon Counting Detectors With Boxcar Signals

Recently, multi-energy inter-pixel coincidence counter (MEICC) has been proposed for charge sharing correction and compensation for photon counting detectors (PCDs), which uses energy-dependent coincidence counters to record coincident events between multiple energy windows of a pixel-of-interest and those of neighboring pixels. A Monte Carlo (MC) simulation study was performed to assess the performance of MEICC; however, the performance might have been overestimated in a previous study. The charge sharing increases the number of photons recorded at a PCD pixel at the expense of the spatial resolution, and therefore, when spatially uniform flat-field x-ray signals are used, it gives PCDs with charge sharing more signals than a PCD without charge sharing. In this paper, we propose to use spatially modulated boxcar signals for evaluating the performances for high spatial frequency tasks because they provide consistent signals regardless of the presence of absence of charge sharing. The flat-field signals must be used for low spatial frequency tasks. We assessed the performances of MEICC and other PCDs with both flat-field signals and boxcar signals, with optimal threshold energies, and with two different pixel sizes. As it is expected, normalized Cramér-Rao lower bounds (nCRLBs) measured with the boxcar signals were worse than those with flat-field signals in general. The nCRLBs of MEICC with 225-μm pixel were close to the current 450-μm PCD. We studied a combination of flat-field signals and N×N super-pixels, where the output of N×N pixels were added, using an MC simulation and a simple charge sharing counting model. The study showed that charge sharing had two opposing impacts on the conventional CT imaging-a negative impact with double-counting among N×N pixels and a positive impact with single-counting spill-in and spill-out across the super-pixel boundary-and the positive impact diminished with increasing N. A use of large N×N super-pixels such as N≥25 was suggested to approximate the zero-frequency detection quantum efficiency of PCD with charge sharing.

Multi-energy inter-pixel coincidence counters for charge sharing correction and compensation in photon counting detectors

PURPOSE

Smaller pixel sizes of x-ray photon counting detectors (PCDs) are advantageous for count rate capabilities but disadvantageous for charge sharing. With charge sharing, the energy of an x-ray photon may be split and one photon may produce two or more counts at adjacent pixels, both at lower energies than the incident energy. This "double-counting" increases noise variance and degrades the spectral response. Overall, it has a significantly negative impact on the performance of PCD-based computed tomography (CT). Charge sharing is induced by the detection physics and occurs regardless of count rates; thus, it is impossible to avoid. We propose in this paper a method that has a potential to address both noise and bias added by charge sharing.

METHODS

We propose applying a multi-energy inter-pixel coincidence counter (MEICC) technique, which uses energy-dependent coincidence counters, keeps the book of charge sharing events during data acquisition, and provides the exact number of charge sharing occurrences, which can be used to either correct or compensate for them after the acquisition is completed. MEICC does not interfere with the primary counting process; therefore, PCDs with MEICC will remain as fast as those without MEICC. MEICC can be implemented using current electronics technology because its inter-pixel coincidence counters used to handle digital data are rather simple. We evaluated Cramér-Rao lower bound (CRLB) of PCDs with and without MEICC using a Monte Carlo simulation.

RESULTS

When the number of energy windows was four or larger and eight neighboring pixels were used, the CRLBs of 225-µm PCD with MEICC normalized by those of the current PCD with the same number of windows were 0.361-0.383 for water density images of two basis functions, which was only 5.7-16.4% worse than those of a PCD without charge sharing (which were at 0.329-0.358). In contrast, the normalized CRLBs of the PCD with one coincidence counter were 0.466-0.499, which were 37.3-45.6% worse than the PCD without charge sharing. The use of eight neighboring pixels provided ~10% better CRLB values than four neighboring pixels for MEICC. With four energy windows, decreasing the number of coincidence counters from 16 to 9 only slightly increased the CRLB from 0.255 to 0.269 (which corresponded to as little as a 5.5% change). The normalized CRLBs of MEICC for K-edge imaging (gold) were 0.295-0.426, while those of the one coincidence counter were 0.926-0.959 and the ideal PCDs were 0.126-0.146.

CONCLUSIONS

The proposed MEICC provides spectral information that can be used to address charge sharing problems in PCDs and is expected to satisfy the requirements for clinical x-ray CT. MEICC is very effective, especially for K-edge imaging, which requires accurate spectral information.

Nanoparticle contrast agents for X-ray imaging applications

X-ray imaging is the most widely used diagnostic imaging method in modern medicine and several advanced forms of this technology have recently emerged. Iodinated molecules and barium sulfate suspensions are clinically approved X-ray contrast agents and are widely used. However, these existing contrast agents provide limited information, are suboptimal for new X-ray imaging techniques and are developing safety concerns. Thus, over the past 15 years, there has been a rapid growth in the development of nanoparticles as X-ray contrast agents. Nanoparticles have several desirable features such as high contrast payloads, the potential for long circulation times, and tunable physicochemical properties. Nanoparticles have also been used in a range of biomedical applications such as disease treatment, targeted imaging, and cell tracking. In this review, we discuss the principles behind X-ray contrast generation and introduce new types of X-ray imaging modalities, as well as potential elements and chemical compositions that are suitable for novel contrast agent development. We focus on the progress in nanoparticle X-ray contrast agents developed to be renally clearable, long circulating, theranostic, targeted, or for cell tracking. We feature agents that are used in conjunction with the newly developed multi-energy computed tomography and mammographic imaging technologies. Finally, we offer perspectives on current limitations and emerging research topics as well as expectations for the future development of the field. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

A novel bi-modal probe based on BaHoF5 and Cu-doped QDs with enhanced CT contrast efficiency and fluorescent brightness for tumor-targeting imaging

In this work, a novel bi-modal imaging probe with enhanced CT contrast efficiency and FL brightness was constructed, in which the combination of a binary CT contrast agent BaHoF₅ and Cu-doped QDs served as a vehicle; hyaluronic acid (HA) was employed as a tumor-targeting ligand. With its CT contrast efficiency about 2.1- and 3.9-fold higher than PEG-BaHoF₅ and Iohexol, the CT contrast efficiency and the fluorescent brightness of the bi-modal probe were both enhanced. Likewise, its fluorescent brightness is almost 6-fold brighter after Cu-doped QDs loading. The most important contribution of this work lies on the proposed strategy. The inherent contradiction of the imaging sensitivity of CT and FL imaging is well balanced and a great CT/FL bi-modal imaging performance is simultaneously obtained even at low concentration (400 μg/mL) of the probe, which was superior to the previous CT/FL bi-modal probes. Moreover, since BaHoF₅ as a binary CT contrast agent was introduced instead of conventional Au and Bi₂S₃, the CT/FL bi-modal probe would be more suitable for different patients under different operation voltages. In addition, the in vitro tumor cell imaging also demonstrated a good photo-stability, FL brightness, and tumor-targeting capability of the probe, indicating its great potential in practical bi-modal imaging for further tumor diagnosis and therapy. Graphical abstract A novel bi-modal imaging probe with enhanced CT contrast efficiency and FL brightness was fabricated, in which its CT contrast efficiency was about 2.1- and 3.9-fold higher than PEG-BaHoF₅ and Iohexol, respectively, and its fluorescent brightness almost 6-fold brighter after Cu-doped QDs loading.

Radioprotective garment-inspired biodegradable polymetal nanoparticles for enhanced CT contrast production

Numerous formulations of nanoparticle-based X-ray computed tomography (CT) contrast agents made of heavy metal elements are under investigation for their ability to provide improved CT imaging. Thus far, most experimental nanoparticle-based CT contrast agents have been developed with atoms of a single element. However, inspired by the composites formed from multiple elements used in radioprotective garments, we hypothesized that contrast agents made of several elements whose K-edge energies are spaced out in the high photon flux region could achieve high, broadband X-ray attenuation across the energies used in X-ray source spectra. Herein, we synthesized sub-5 nm core inorganic nanoparticles containing gold, tantalum, and cerium, and encapsulated them in polymeric nanoparticles to form polymetal nanoparticles (PMNP). We found that PMNP with multiple payload elements generate higher and more stable CT contrast than contrast agents made from a single contrast generating material, demonstrating the potential benefits of incorporating multiple suitable elements as CT contrast payloads.

Iodinated polymer nanoparticles as contrast agent for spectral photon counting computed tomography

Suspensions of iodinated polymer nanoparticles are evaluated as contrast agent for Computed Tomography (CT) and Spectral Photon Counting Computed Tomography (SPCCT).

Rhenium Sulfide Nanoparticles as a Biosafe Spectral CT Contrast Agent for Gastrointestinal Tract Imaging and Tumor Theranostics in Vivo

Spectral computed tomography (CT) imaging as a novel imaging technique shows promising prospects in the accurate diagnosis of various diseases. However, clinically iodinated contrast agents suffer from poor signal-to-noise ratio, and emerging heavy-metal-based CT contrast agents arouse great biosafety concern. Herein, we show the fabrication of rhenium sulfide (ReS₂) nanoparticles, a clinic radiotherapy sensitizer, as a biosafe spectral CT contrast agent for the gastrointestinal tract imaging and tumor theranostics in vivo by teaching old drugs new tricks. The ReS₂ nanoparticles were fabricated in a one-pot facile method at room temperature, and exhibited sub-10 nm size, favorable monodispersity, admirable aqueous solubility, and strong X-ray attenuation capability. More importantly, the proposed nanoparticles possess an outstanding spectral CT imaging ability and undoubted biosafety as a clinic therapeutic agent. Besides, the ReS₂ nanoparticles possess appealing photothermal performance due to their intense near-infrared absorption. The proposed nano-agent not only guarantees obvious contrast enhancement in gastrointestinal tract spectral CT imaging in vivo, but also allows effective CT imaging-guided tumor photothermal therapy. The proposed "teaching old drugs new tricks" strategy shortens the time and cuts the cost required for clinical application of nano-agents based on existing clinical toxicology testing and trial results, and lays down a low-cost, time-saving, and energy-saving method for the development of multifunctional nano-agents toward clinical applications.

An unmet clinical need: The history of thrombus imaging

Robust thrombus imaging is an unresolved clinical unmet need dating back to the mid 1970s. While early molecular imaging approaches began with nuclear SPECT imaging, contrast agents for virtually all biomedical imaging modalities have been demonstrated in vivo with unique strengths and common weaknesses. Two primary molecular imaging targets have been pursued for thrombus imaging: platelets and fibrin. Some common issues noted over 40 years ago persist today. Acute thrombus is readily imaged with all probes and modalities, but aged thrombus remains a challenge. Similarly, anti-coagulation continues to interfere with and often negate thrombus imaging efficacy, but heparin is clinically required in patients suspected of pulmonary embolism, deep venous thrombosis or coronary ruptured plaque prior to confirmatory diagnostic studies have been executed and interpreted. These fundamental issues can be overcome, but an innovative departure from the prior approaches will be needed.

Recent Research Trends on Bismuth Compounds in Cancer Chemoand Radiotherapy

Background:

Application of coordination chemistry in nanotechnology is a rapidly developing research field in medicine. Bismuth complexes have been widely used in biomedicine with satisfactory therapeutic effects, mostly in Helicobacter pylori eradication, but also as potential antimicrobial and anti-leishmanial agents. Additionally, in recent years, application of bismuth-based compounds as potent anticancer drugs has been studied extensively.

Methods:

Search for data connected with recent trends on bismuth compounds in cancer chemo- and radiotherapy was carried out using web-based literature searching tools such as ScienceDirect, Springer, Royal Society of Chemistry, American Chemical Society and Wiley. Pertinent literature is covered up to 2016.

Results:

In this review, based on 213 papers, we highlighted a number of current problems connected with: (i) characterization of bismuth complexes with selected thiosemicarbazone, hydrazone, and dithiocarbamate classes of ligands as potential chemotherapeutics. Literature results derived from 50 papers show that almost all bismuth compounds inhibit growth and proliferation of breast, colon, ovarian, lung, and other tumours; (ii) pioneering research on application of bismuth-based nanoparticles and nanodots for radiosensitization. Results show great promise for improvement in therapeutic efficacy of ionizing radiation in advanced radiotherapy (described in 36 papers); and (iii) research challenges in using bismuth radionuclides in targeted radioimmunotherapy, connected with choice of adequate radionuclide, targeting vector, proper bifunctional ligand and problems with 213Bi recoil daughters toxicity (derived from 92 papers).

Conclusion:

This review presents recent research trends on bismuth compounds in cancer chemo- and radiotherapy, suggesting directions for future research.

Bi-DTPA as a high-performance CT contrast agent for in vivo imaging

Clinically used iodinated computer tomography (CT) contrast agents suffer from low sensitivity, and the emerging lanthanide-chelates and CT imaging nanoagents raise great safety concerns. The fusion of high sensitivity and good biocompatibility is highly desired for the development of CT contrast agents. Herein, we propose a facile and green one-pot synthesis strategy for the fabrication of a small molecular CT contrast agent, Bi-diethylene triamine pentaacetate acid (DTPA) complex, for high-performance CT and spectral CT imaging. The Bi-DTPA exhibits yield of near 100%, outstanding water solubility, favorable biocompatibility, large-scale production capability, and superior X-ray attenuation ability, and is successfully applied in high-quality in vivo kidney imaging and gastrointestinal tract CT imaging and appealing spectral CT imaging. The proposed contrast agent can be rapidly excreted from body, avoiding the potential side effects caused by the long-term retention in vivo. Furthermore, our design shows great potential in developing diverse multifunctional contrast agents via chemical modification. The proposed Bi-DTPA with unique superiorities shows a bright prospect in clinic CT imaging, especially spectral CT imaging, and lays down a new way for the design of high-performance CT contrast agents with great clinical transformation potential.

Evaluation of X-ray tomography contrast agents: A review of production, protocols, and biological applications

X-ray computed tomography is a strong tool that finds many applications both in medical applications and in the investigation of biological and nonbiological samples. In the clinics, X-ray tomography is widely used for diagnostic purposes whose three-dimensional imaging in high resolution helps physicians to obtain detailed image of investigated regions. Researchers in biological sciences and engineering use X-ray tomography because it is a nondestructive method to assess the structure of their samples. In both medical and biological applications, visualization of soft tissues and structures requires special treatment, in which special contrast agents are used. In this detailed report, molecule-based and nanoparticle-based contrast agents used in biological applications to enhance the image quality were compiled and reported. Special contrast agent applications and protocols to enhance the contrast for the biological applications and works to develop nanoparticle contrast agents to enhance the contrast for targeted drug delivery and general imaging applications were also assessed and listed.

Quantification of multiple mixed contrast and tissue compositions using photon-counting spectral computed tomography

Quantitative material decomposition of multiple mixed, or spatially coincident, contrast agent (gadolinium and iodine) and tissue (calcium and water) compositions is demonstrated using photon-counting spectral computed tomography (CT). Material decomposition is performed using constrained maximum likelihood estimation (MLE) in the image domain. MLE is calibrated by multiple linear regression of all pure material compositions, which exhibits a strong correlation ( R 2 > 0.91 ) between the measured x-ray attenuation in each photon energy bin and known concentrations in the calibration phantom. Material decomposition of mixed compositions in the sample phantom provides color material concentration maps that clearly identify and differentiate each material. The measured area under the receiver operating characteristic curve is > 0.95 , indicating highly accurate material identification. Material decomposition also provides accurate quantitative estimates of material concentrations in mixed compositions with a root-mean-squared error < 12 % of the maximum concentration for each material. Thus, photon-counting spectral CT enables quantitative molecular imaging of multiple spatially coincident contrast agent (gadolinium and iodine) and tissue (calcium and water) compositions, which is not possible with current clinical molecular imaging modalities, such as nuclear imaging and magnetic resonance imaging.

Water-Dispersible Bismuth-Organic Materials with Computed Tomography Contrast Properties

Two bismuth-organic network polymers were synthesized by means of a one-step polycondensation reaction between an aromatic dithiol/trithiol and triphenylbismuth. The materials were characterized by solid-state UV-vis spectroscopy, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, elemental microanalysis, and thermogravimetric analysis. Uniform dispersion of the hydrophobic and water-insoluble bismuth-containing polymers in aqueous media was achieved by the addition of 2 kDa poly(ethylene glycol) methyl ether thiol. This enabled quantitative phantom imaging experiments on a clinical computed tomography (CT) scanner, which showed that the coordination polymers possessed strong CT contrast properties. The observed X-ray attenuation properties of each coordination polymer were correlated with its bismuth payload. The X-ray opacity, thermal and chemical stabilities, and aqueous dispersibility of this novel class of bismuth-organic materials make them potentially useful as biomedical CT contrast agents and radiopaque materials.

Multicolour imaging with spectral photon-counting CT: a phantom study

Background

To evaluate the feasibility of multicolour quantitative imaging with spectral photon-counting computed tomography (SPCCT) of different mixed contrast agents.

Methods

Phantoms containing eleven tubes with mixtures of varying proportions of two contrast agents (i.e. two selected from gadolinium, iodine or gold nanoparticles) were prepared so that the attenuation of each tube was about 280 HU. Scans were acquired at 120 kVp and 100 mAs using a five-bin preclinical SPCCT prototype, generating conventional, water, iodine, gadolinium and gold images. The correlation between prepared and measured concentrations was assessed using linear regression. The cross-contamination was measured for each material as the root mean square error (RMSE) of its concentration in the other material images, where no signal was expected. The contrast-to-noise ratio (CNR) relative to a phosphate buffered saline tube was calculated for each contrast agent.

Results

The solutions had similar attenuations (279 ± 10 HU, mean ± standard deviation) and could not be differentiated on conventional images. However, a distinction was observed in the material images within the same samples, and the measured and prepared concentrations were strongly correlated (R² ≥ 0.97, 0.81 ≤ slope ≤ 0.95, -0.68 ≤ offset ≤ 0.89 mg/mL). Cross-contamination in the iodine images for the mixture of gold and gadolinium contrast agents (RMSE = 0.34 mg/mL) was observed. CNR for 1 mg/mL of contrast agent was better for the mixture of iodine and gadolinium (CNR_iodine = 3.20, CNR_gadolinium = 2.80) than gold and gadolinium (CNR_gadolinium = 1.67, CNR_gold = 1.37).

Conclusions

SPCCT enables multicolour quantitative imaging. As a result, it should be possible to perform imaging of multiple uptake phases of a given tissue/organ within a single scan by injecting different contrast agents sequentially.

X-ray based virtual histology allows guided sectioning of heavy ion stained murine lungs for histological analysis

Examination of histological or immunohistochemically stained 2D sections of embedded tissue is one of the most frequently used tools in biomedical research and clinical routine. Since to date, targeted sectioning of specific regions of interest (ROI) in the sample is not possible, we aimed at developing a guided sectioning approach based on x-ray 3D virtual histology for heavy ion stained murine lung samples. For this purpose, we increased the contrast to noise ratio of a standard benchtop microCT by 5–10-fold using free-propagation phase contrast imaging and thus substantially improved image quality. We then show that microCT 3D datasets deliver more precise anatomical information and quantification of the sample than traditional histological sections, which display deformations of the tissue. To quantify these deformations caused by sectioning we developed the “Displacement Index (DI)”, which combines block-matching with the calculation of the local mutual information. We show that the DI substantially decreases when a femtosecond laser microtome is used for sections as opposed to a traditional microtome. In conclusion, our microCT based virtual histology approach can be used as a supplement and a guidance tool for traditional histology, providing 3D measurement capabilities and offering the ability to perform sectioning directly at an ROI.

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.

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).

Evaluation of spectral photon counting computed tomography K-edge imaging for determination of gold nanoparticle biodistribution in vivo

Spectral photon counting computed tomography (SPCCT) is an emerging medical imaging technology. SPCCT scanners record the energy of incident photons, which allows specific detection of contrast agents due to measurement of their characteristic X-ray attenuation profiles. This approach is known as K-edge imaging. Nanoparticles formed from elements such as gold, bismuth or ytterbium have been reported as potential contrast agents for SPCCT imaging. Furthermore, gold nanoparticles have many applications in medicine, such as adjuvants for radiotherapy and photothermal ablation. In particular, longitudinal imaging of the biodistribution of nanoparticles would be highly attractive for their clinical translation. We therefore studied the capabilities of a novel SPCCT scanner to quantify the biodistribution of gold nanoparticles in vivo. PEGylated gold nanoparticles were used. Phantom imaging showed that concentrations measured on gold images correlated well with known concentrations (slope = 0.94, intercept = 0.18, RMSE = 0.18, R² = 0.99). The SPCCT system allowed repetitive and quick acquisitions in vivo, and follow-up of changes in the AuNP biodistribution over time. Measurements performed on gold images correlated with the inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements in the organs of interest (slope = 0.77, intercept = 0.47, RMSE = 0.72, R² = 0.93). TEM results were in agreement with the imaging and ICP-OES in that much higher concentrations of AuNPs were observed in the liver, spleen, bone marrow and lymph nodes (mainly in macrophages). In conclusion, we found that SPCCT can be used for repetitive and non-invasive determination of the biodistribution of gold nanoparticles in vivo.

Integrating nanomedicine and imaging

Biomedical engineering and its associated disciplines play a pivotal role in improving our understanding and management of disease. Motivated by past accomplishments, such as the clinical implementation of coronary stents, pacemakers or recent developments in antibody therapies, disease management now enters a new era in which precision imaging and nanotechnology-enabled therapeutics are maturing to clinical translation. Preclinical molecular imaging increasingly focuses on specific components of the immune system that drive disease progression and complications, allowing the in vivo study of potential therapeutic targets. The first multicentre trials highlight the potential of clinical multimodality imaging for more efficient drug development. In this perspective, the role of integrating engineering, nanotechnology, molecular imaging and immunology to yield precision medicine is discussed.This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.

Human Imaging With Photon Counting-Based Computed Tomography at Clinical Dose Levels: Contrast-to-Noise Ratio and Cadaver Studies

OBJECTIVES

The purpose of this work was to measure and compare the iodine contrast-to-noise ratio (CNR) between a commercial energy-integrating detector (EID) computed tomography (CT) system and a photon-counting detector (PCD) CT scanner capable of human imaging at clinical dose rates, as well as to determine clinical feasibility using human cadavers.

MATERIALS AND METHODS

A research dual-source PCD-CT scanner was used, where the "A" tube/detector subsystem used an EID and the "B" tube/detector subsystem used a PCD. Iodine CNR was measured in 4 anthropomorphic phantoms, simulating 4 patient sizes, at 4 tube potential settings. After biospecimen committee approval, PCD scans were performed on a fresh-frozen human head and a whole-body cadaver using clinical dose rates. Scans were repeated using the EID and identical parameters, and qualitative side-by-side comparisons were performed.

RESULTS

For the same photon fluence, phantom measurements demonstrated a mean increase in CNR of 11%, 23%, 31%, 38% for the PCD system, relative to the EID system, at 80, 100, 120, and 140 kV, respectively. Photon-counting detector CT additionally provided energy-selective imaging, where low- and high-energy images reflected the energy dependence of the iodine signal. Photon-counting detector images of cadaveric anatomy demonstrated decreased beam hardening and calcium blooming in the high-energy bin images and increased contrast in the low-energy bins images relative to the EID images. Threshold-based PCD images were qualitatively deemed equivalent in other aspects.

CONCLUSIONS

The evaluated research PCD-CT system was capable of clinical levels of image quality at clinical dose rates. It further provided improved CNR relative to state-of-the-art EID-CT. The energy-selective bin images provide further opportunity for dual-energy and multienergy analyses.

Thrombin-activatable fluorescent peptide incorporated gold nanoparticles for dual optical/computed tomography thrombus imaging

Thrombosis is an important pathophysiologic phenomenon in various cardiovascular diseases, which can lead to oxygen deprivation and infarction of tissues by generation of a thrombus. Thus, direct thrombus imaging can provide beneficial in diagnosis and therapy of thrombosis. Herein, we developed thrombin-activatable fluorescent peptide (TAP) incorporated silica-coated gold nanoparticles (TAP-SiO₂@AuNPs) for direct imaging of thrombus by dual near-infrared fluorescence (NIRF) and micro-computed tomography (micro-CT) imaging, wherein TAP molecules were used as targeted thrombin-activatable peptide probes for thrombin-specific NIRF imaging. The freshly prepared TAP-SiO₂@AuNPs had an average diameter of 39.8 ± 2.55 nm and they showed the quenched NIRF signal in aqueous condition, due to the excellent quenching effect of TAP molecules on the silica-gold nanoparticle surface. However, 30.31-fold higher NIRF intensity was rapidly recovered in the presence of thrombin in vitro, due to the thrombin-specific cleavage of quenched TAP molecules on the gold particle surface. Furthermore, TAP-SiO₂@AuNPs were successfully accumulated in thrombus by their particle size-dependent capturing property, and they presented a potential X-ray absorption property in a dose-dependent manner. Finally, thrombotic lesion was clearly distinguished from peripheral tissues by dual NIRF/micro-CT imaging after intravenous injection of TAP-SiO₂@AuNPs in the in situ thrombotic mouse model, simultaneously. This study showed that thrombin-activatable fluorescent peptide incorporated silica-coated gold nanoparticles can be potentially used as a dual imaging probe for direct thrombus imaging and therapy in clinical applications.