Molecular optical imaging with radioactive probes

Construction of a high-sensitivity Cherenkov luminescence endoscopy system for the detection of gastrointestinal cancers

BACKGROUND

The diagnostic yield of conventional gastrointestinal (GI) endoscopy for early cancers is low because it is mainly based on morphological changes of tumors. Molecular functional changes in tumors precede morphological changes. Cherenkov luminescence endoscopy (CLE) system can perform molecular imaging of GI cancers, achieving early diagnosis of cancers. However, previous CLE systems had only been able to detect Cherenkov luminescence (CL) from about one μCi nuclide at a minimum (in vivo), but the nuclide probe absorbed by the tumor of a patient was often much less than one μCi at a routinely administered dose. This study aims to construct a clinically usable high-sensitivity CLE for molecular imaging of GI cancers.

RESULTS

The minimum resolvable radioactivity of the CLE reached 0.020 μCi within 300 s (in vivo), with a sensitivity at the nanocurie for the first time. The detection sensitivity of the CLE increased by up to nearly twenty-two times over the previous system. In tumor-bearing nude mice, CLE could effectively identify all tumors with 100% concordance with both histopathology and PET/CT, and the CL signals of tumors were much stronger than those of the surrounding normal tissues (P < 0.05). The quality of CLE imaging at 60 s was comparable to that at 300 s (signal-to-background ratio, 2.70 ± 0.48 versus 2.98 ± 0.69, P = 0.56).

CONCLUSIONS

We constructed a high-sensitivity CLE that could detect radionuclides at the nanocurie radioactivity. The CLE could detect cancers accurately through rapid molecular imaging and had the potential for early diagnosis of GI cancers in clinical practice.

Nanoscale Radiotheranostics for Cancer Treatment: From Bench to Bedside

In recent years, the application of radionuclides-containing nanomaterials in cancer treatment has garnered widespread attention. The diversity of nanomaterials allows researchers to selectively combine them with appropriate radionuclides for biomedical purposes, addressing challenges faced by peptides, small molecules, or antibodies used for radionuclide labeling. However, with advantages come challenges, and nanoradionuclides still encounter significant issues during clinical translation. This review summarized the recent progress of nanosized radionuclides for cancer treatment or diagnosis. The discussion began with representative radionuclides and the methods of incorporating them into nanomaterial structures. Subsequently, new combinations of nanomaterials and radionuclides, along with their applications, were introduced to demonstrate their future trends. The benefits of nanoradionuclides included optimized pharmacokinetic properties, enhanced disease-targeting efficacy, and synergistic application with other treatment techniques. Besides, the basic rule of this section was to summarize how these nanoradionuclides can truly impact the diagnosis and therapy of various cancer types. In the last part, the focus was devoted to the nanoradionuclides currently applicable in clinics and how to address the existing issues and problems based on our knowledge.

Self-Illuminating In Situ Hydrogel with Immune-Adjuvant Amplify Cerenkov Radiation-Induced Photodynamic Therapy

Cerenkov radiation-induced photodynamic therapy (CR-induced PDT) has shown the potential to overcome the light penetration limitation in conventional PDT. In addition, the tumor-associated antigens (TAAs) produced by PDT can initiate an antitumor immune process but only show a limited immunotherapeutic effect without the use of immunotherapeutic agents. Herein, a CR-induced PDT hydrogel (R837/89Zr-HG-PpIX) has been developed by in situ formation of a hyaluronic acid (HA)-based hydrogel integrated with internal light source 89Zr, photosensitizer protoporphyrin IX (PpIX), and immune adjuvant imiquimod (R837). The obtained R837/89Zr-HG-PpIX hydrogel with long-term tumor retention and low radiation leakage can provide long-lasting photodynamic therapy without phototoxicity in normal tissues. In addition, the loaded R837 improves the immunogenicity of TAAs released after PDT, resulting in considerably enhanced immune responses. At relatively low radioactivity, R837/89Zr-HG-PpIX shows significant inhibition in subcutaneous H22 tumor-bearing BALB/c mice and orthotopic VX2 liver tumor-bearing rabbits. Furthermore, the combination of such a CR-induced PDT hydrogel with anti-PD-L1 exhibits the abscopal effect to inhibit the growth of distant tumors. Therefore, the proposed in situ formed CR-induced PDT hydrogel with long-term photodynamic-immunotherapy provides an effective strategy for deep tumor therapy.

Molecularly generated light and its biomedical applications

Molecularly generated light, referred to here as "molecular light", mainly includes bioluminescence, chemiluminescence, and Cerenkov luminescence. Molecular light possesses unique dual features of being both a molecule and a source of light. Its molecular nature enables it to be delivered as molecules to regions deep within the body, overcoming the limitations of natural sunlight and physically generated light sources like lasers and LEDs. Simultaneously, its light properties make it valuable for applications such as imaging, photodynamic therapy, photo-oxidative therapy, and photobiomodulation. In this review article, we provide an updated overview of the diverse applications of molecular light and discuss the strengths and weaknesses of molecular light across various domains. Lastly, we present forward-looking perspectives on the potential of molecular light in the realms of molecular imaging, photobiological mechanisms, therapeutic applications, and photobiomodulation. While some of these perspectives may be considered bold and contentious, our intent is to inspire further innovations in the field of molecular light applications.

Cherenkov Radiation induced photodynamic therapy - repurposing older photosensitizers, and radionuclides

CONTEXT

Old-generation photosensitizers are minimally used in current photodynamic therapy (PDT) because they absorb in the UV/blue/green region of the spectrum where biological tissues are generally highly absorbing. The UV/blue light of Cherenkov Radiation (CR) from nuclear disintegration of beta-emitter radionuclides shows promise as an internal light source to activate these photosensitizers within tissue. Outline of the study: 1) radionuclide choice and Cherenkov Radiation, 2) Photosensitizer choice, synthesis and radiolabeling, 3) CR-induced fluorescence, 4) Verification of ROS formation, 5) CR-induced PDT with either free eosine and free CR emitter, or with radiolabelled eosin.

RESULTS

Cherenkov Radiation Energy Transfer (CRET) from therapeutic radionuclides (90Y) and PET imaging radionuclides (18F, 68Ga) to eosin was shown by spectrofluorimetry and in vitro, and was shown to result in a PDT process. The feasibility of CR-induced PDT (CR-PDT) was demonstrated in vitro on B16F10 murine melanoma cells mixing free eosin (λabs = 524 nm, ΦΔ 0.67) with free CR-emitter [18F]-FDG under their respective intrinsic toxicity levels (0.5 mM/8 MBq) and by trapping singlet oxygen with diphenylisobenzofuran (DPBF). An eosin-DOTAGA-chelate conjugate 1 was synthesized and radiometallated with CR-emitter [68Ga] allowed to reach 25 % cell toxicity at 0.125 mM/2 MBq, i.e. below the toxicity threshold of each component measured on controls. Incubation time was carefully examined, especially for CR emitters, in light of its toxicity, and its CR-emitting yield expected to be 3 times as much for 68Ga than 18F (considering their β particle energy) per radionuclide decay, while its half-life is about twice as small.

PERSPECTIVE

This study showed that in complete darkness, as it is at depth in tissues, PDT could proceed relying on CR emission from radionuclides only. Interestingly, this study also repurposed PET imaging radionuclides, such as 68Ga, to trigger a therapeutic event (PDT), albeit in a modest extent. Moreover, although it remains modest, such a PDT approach may be used to achieve additional tumoricidal effect to RIT treatment, where radionuclides, such as 90Y, are strong CR emitters, i.e. very potent light source for photosensitizer activation.

Cerenkov radiation-mediated in situ activation of silicon nanocrystals for NIR optical imaging

Cerenkov radiation from radiopharmaceuticals (18F-FDG) serves as an internal light source to excite UV-responsive silicon nanocrystals for near-infrared luminescence imaging that offers deeper tissue penetration and high signal-to-noise ratio.

Practical Guidance for Developing Small-Molecule Optical Probes for In Vivo Imaging

The WMIS Education Committee (2019-2022) reached a consensus that white papers on molecular imaging could be beneficial for practitioners of molecular imaging at their early career stages and other scientists who are interested in molecular imaging. With this consensus, the committee plans to publish a series of white papers on topics related to the daily practice of molecular imaging. In this white paper, we aim to provide practical guidance that could be helpful for optical molecular imaging, particularly for small molecule probe development and validation in vitro and in vivo. The focus of this paper is preclinical animal studies with small-molecule optical probes. Near-infrared fluorescence imaging, bioluminescence imaging, chemiluminescence imaging, image-guided surgery, and Cerenkov luminescence imaging are discussed in this white paper.

Cherenkov Luminescence in Tumor Diagnosis and Treatment: A Review

Malignant tumors rank as a leading cause of death worldwide. Accurate diagnosis and advanced treatment options are crucial to win battle against tumors. In recent years, Cherenkov luminescence (CL) has shown its technical advantages and clinical transformation potential in many important fields, particularly in tumor diagnosis and treatment, such as tumor detection in vivo, surgical navigation, radiotherapy, photodynamic therapy, and the evaluation of therapeutic effect. In this review, we summarize the advances in CL for tumor diagnosis and treatment. We first describe the physical principles of CL and discuss the imaging techniques used in tumor diagnosis, including CL imaging, CL endoscope, and CL tomography. Then we present a broad overview of the current status of surgical resection, radiotherapy, photodynamic therapy, and tumor microenvironment monitoring using CL. Finally, we shed light on the challenges and possible solutions for tumor diagnosis and therapy using CL.

Smart 131 I-Labeled Self-Illuminating Photosensitizers for Deep Tumor Therapy

Stimulating photosensitizers (PS) by Cerenkov radiation (CR) can overcome the light penetration limitation in traditional photodynamic therapy. However, separate injection of radiopharmaceuticals and PS cannot guarantee their efficient interaction in tumor areas, while co-delivery of radionuclides and PS face the problem of nonnegligible phototoxicity in normal tissues. Here, we describe a ¹³¹ I-labeled smart photosensitizer, composed of pyropheophorbide-a (photosensitizer), a diisopropylamino group (pH-sensitive group), an ¹³¹ I-labeled tyrosine group (CR donor), and polyethylene glycol, which can self-assemble into nanoparticles (¹³¹ I-sPS NPs). The ¹³¹ I-sPS NPs showed low phototoxicity in normal tissues due to aggregation-caused quenching effect, but could self-produce reactive oxygen species in tumor sites upon disassembly. Upon intravenous injection, ¹³¹ I-sPS NPs showed great tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice and orthotopic VX2 liver tumor bearing rabbits. We believed ¹³¹ I-sPS NPs could expand the application of CR and provide an effective strategy for deep tumor theranostics.

Radiopharmaceutical and Eu3+ doped gadolinium oxide nanoparticles mediated triple-excited fluorescence imaging and image-guided surgery

Cerenkov luminescence imaging (CLI) is a novel optical imaging technique that has been applied in clinic using various radionuclides and radiopharmaceuticals. However, clinical application of CLI has been limited by weak optical signal and restricted tissue penetration depth. Various fluorescent probes have been combined with radiopharmaceuticals for improved imaging performances. However, as most of these probes only interact with Cerenkov luminescence (CL), the low photon fluence of CL greatly restricted it's interaction with fluorescent probes for in vivo imaging. Therefore, it is important to develop probes that can effectively convert energy beyond CL such as β and γ to the low energy optical signals. In this study, a Eu3+ doped gadolinium oxide (Gd2O3:Eu) was synthesized and combined with radiopharmaceuticals to achieve a red-shifted optical spectrum with less tissue scattering and enhanced optical signal intensity in this study. The interaction between Gd2O3:Eu and radiopharmaceutical were investigated using 18F-fluorodeoxyglucose (18F-FDG). The ex vivo optical signal intensity of the mixture of Gd2O3:Eu and 18F-FDG reached 369 times as high as that of CLI using 18F-FDG alone. To achieve improved biocompatibility, the Gd2O3:Eu nanoparticles were then modified with polyvinyl alcohol (PVA), and the resulted nanoprobe PVA modified Gd2O3:Eu (Gd2O3:Eu@PVA) was applied in intraoperative tumor imaging. Compared with 18F-FDG alone, intraoperative administration of Gd2O3:Eu@PVA and 18F-FDG combination achieved a much higher tumor-to-normal tissue ratio (TNR, 10.24 ± 2.24 vs. 1.87 ± 0.73, P = 0.0030). The use of Gd2O3:Eu@PVA and 18F-FDG also assisted intraoperative detection of tumors that were omitted by preoperative positron emission tomography (PET) imaging. Further experiment of image-guided surgery demonstrated feasibility of image-guided tumor resection using Gd2O3:Eu@PVA and 18F-FDG. In summary, Gd2O3:Eu can achieve significantly optimized imaging property when combined with 18F-FDG in intraoperative tumor imaging and image-guided tumor resection surgery. It is expected that the development of the Gd2O3:Eu nanoparticle will promote investigation and application of novel nanoparticles that can interact with radiopharmaceuticals for improved imaging properties. This work highlighted the impact of the nanoprobe that can be excited by radiopharmaceuticals emitting CL, β, and γ radiation for precisely imaging of tumor and intraoperatively guide tumor resection.

Surgical Advances in Osteosarcoma

Simple Summary

Osteosarcoma (OS) is the most common bone cancer in children. OS most commonly arises in the legs, but can arise in any bone, including the spine, head or neck. Along with chemotherapy, surgery is a mainstay of OS treatment and in the 1990s, surgeons began to shift from amputation to limb-preserving surgery. Since then, improvements in imaging, surgical techniques and implant design have led to improvements in functional outcomes without compromising on the cancer outcomes for these patients. This paper summarises these advances, along with a brief discussion of future technologies currently in development.

Abstract

Osteosarcoma (OS) is the most common primary bone cancer in children and, unfortunately, is associated with poor survival rates. OS most commonly arises around the knee joint, and was traditionally treated with amputation until surgeons began to favour limb-preserving surgery in the 1990s. Whilst improving functional outcomes, this was not without problems, such as implant failure and limb length discrepancies. OS can also arise in areas such as the pelvis, spine, head, and neck, which creates additional technical difficulty given the anatomical complexity of the areas. We reviewed the literature and summarised the recent advances in OS surgery. Improvements have been made in many areas; developments in pre-operative imaging technology have allowed improved planning, whilst the ongoing development of intraoperative imaging techniques, such as fluorescent dyes, offer the possibility of improved surgical margins. Technological developments, such as computer navigation, patient specific instruments, and improved implant design similarly provide the opportunity to improve patient outcomes. Going forward, there are a number of promising avenues currently being pursued, such as targeted fluorescent dyes, robotics, and augmented reality, which bring the prospect of improving these outcomes further.

Discovery of the luminescence of water during irradiation of radiation at a lower energy than the Cherenkov light threshold

It is widely believed that light is not emitted in water during irradiation of radiation at energies lower than the Cherenkov light threshold. Contrary to this consensus, we discovered that light (luminescence) is emitted in water during irradiation of radiation, and imaging of this luminescence was possible. In this review, the author describes the optical images obtained for various types of radiation, their characteristics and origins, and potential applications of the luminescence of water during irradiation at a lower energy than the Cherenkov light threshold. The author also describes the luminescence of other transparent materials and future prospects of the discovered luminescence.

Nanoparticles for Cerenkov and Radioluminescent Light Enhancement for Imaging and Radiotherapy

Cerenkov luminescence imaging and Cerenkov photodynamic therapy have been developed in recent years to exploit the Cerenkov radiation (CR) generated by radioisotopes, frequently used in Nuclear Medicine, to diagnose and fight cancer lesions. For in vivo detection, the endpoint energy of the radioisotope and, thus, the total number of the emitted Cerenkov photons, represents a very important variable and explains why, for example, ⁶⁸Ga is better than ¹⁸F. However, it was also found that the scintillation process is an important mechanism for light production. Nanotechnology represents the most important field, providing nanosctructures which are able to shift the UV-blue emission into a more suitable wavelength, with reduced absorption, which is useful especially for in vivo imaging and therapy applications. Nanoparticles can be made, loaded or linked to fluorescent dyes to modify the optical properties of CR radiation. They also represent a useful platform for therapeutic agents, such as photosensitizer drugs for the production of reactive oxygen species (ROS). Generally, NPs can be spaced by CR sources; however, for in vivo imaging applications, NPs bound to or incorporating radioisotopes are the most interesting nanocomplexes thanks to their high degree of mutual colocalization and the reduced problem of false uptake detection. Moreover, the distance between the NPs and CR source is crucial for energy conversion. Here, we review the principal NPs proposed in the literature, discussing their properties and the main results obtained by the proponent experimental groups.

Dual Cherenkov Radiation-Induced Near-Infrared Luminescence Imaging and Photodynamic Therapy toward Tumor Resection

Cherenkov radiation (CR), the blue light seen in nuclear reactors, is emitted by some radiopharmaceuticals. This study showed that (1) a portion of CR could be transferred in the region of the optical spectrum, where biological tissues are most transparent: as a result, upon radiance amplification in the near-infrared window, the detection of light could occur twice deeper in tissues than during classical Cherenkov luminescence imaging and (2) Cherenkov-photodynamic therapy (CR-PDT) on cells could be achieved under conditions mimicking unlimited depth using the CR-embarked light source, which is unlike standard PDT, where light penetration depth is limited in biological tissues. Both results are of utmost importance for simultaneous applications in tumor resection and post-resection treatment of remaining unresected margins, thanks to a molecular construct designed to raise its light collection efficiency (i.e., CR energy transfer) by conjugation with multiple CR-absorbing (water-soluble) antenna followed by intramolecular-FRET/TBET energy transfers.

A novel in vivo Cerenkov luminescence image-guided surgery on primary and metastatic colorectal cancer

Intraoperative Cerenkov luminescence imaging (CLI) can effectively improve the performance of tumor surgery. Nevertheless, the existing approaches are still unsatisfying to the clinical demands of open surgery. This study develops a novel intraoperative in vivo CLI approach to investigate the potential and value of Cerenkov luminescence (CL) image-guided surgery. A system characterized with high sensitivity (19.61 kBq mL^{-1 18} F-FDG) and desirable spatial resolution (88.34 μm) is developed. CL image-guided surgery is performed on colorectal cancer (CRC) models of mice and swine. Tumor surgery is guided by the static CL images, and the resection quality is evaluated quantitatively and contrasted with other imaging modalities exemplified by bioluminescence imaging (BLI). The in vivo results demonstrated the effectiveness of the proposed intraoperative CLI approach for removing primary and metastatic CRC. Safety of performing in vivo CL image-guided surgery is verified as well through radiation measurements of related staffs. Overall, the developed intraoperative in vivo CLI approach can efficiently improve the cancer treatment.

Radionuclide-Activated Nanomaterials and Their Biomedical Applications

Radio-nanomedicine, or the use of radiolabeled nanoparticles in nuclear medicine, has attracted much attention in the last few decades. Since the discovery of Cerenkov radiation and its employment in Cerenkov luminescence imaging, the combination of nanomaterials and Cerenkov radiation emitters has been revolutionizing the way nanomaterials are perceived in the field: from simple inert carriers of radioactivity to activatable nanomaterials for both diagnostic and therapeutic applications. Herein, we provide a comprehensive review on the types of nanomaterials that have been used to interact with Cerenkov radiation and the gamma and beta scintillation of radionuclides, as well as on their biological applications.

Radiometals for imaging and theranostics, current production, and future perspectives

The aim of this review is to make the reader familiar with currently available radiometals, their production modes, capacities, and quality concerns related to their medical use, as well as new emerging radiometals and irradiation technologies from the perspective of their diagnostic and theranostic applications. Production methods of ¹⁷⁷ Lu serve as an example of various issues related to the production yield, specific activity, radionuclidic and chemical purity, and production economy. Other radiometals that are currently used or explored for potential medical applications, with particular focus on their theranostic value, are discussed. Using radiometals for diagnostic imaging and therapy is on the rise. The high demand for radiometals for medical use prompts investigations towards using alternative irradiation reactions, while using existing nuclear reactors and accelerator facilities. This review discusses these production capacities and what is necessary to cover the growing demand for theranostic nuclides.

Theoretical and experimental characterization of emission and transmission spectra of Cerenkov radiation generated by 177Lu in tissue

Cerenkov radiation (CR) is the emission of UV-vis light generated by the de-excitation of the molecules in the medium, after being polarized by an excited particle traveling faster than the speed of light. When β particles travel through tissue with energies greater than 219 keV, CR occurs. Tissues possess a spectral optical window of 600 to 1100 nm. The CR within this range can be useful for quantitative preclinical studies using optical imaging and for the in-vivo evaluation of Lu177-radiopharmaceuticals (β-particle emitters). The objective of our research was to determine the experimental emission light spectrum of Lu177-CR and evaluate its transmission properties in tissue as well as the feasibility to applying CR imaging in the preclinical studies of Lu177-radiopharmaceuticals. The theoretical and experimental characterizations of the emission and transmission spectra of Lu177-CR in tissue, in the vis-NIR region (350 to 900 nm), were performed using Monte Carlo simulation and UV-vis spectroscopy. Mice Lu177-CR images were acquired using a charge-coupled detector camera and were quantitatively analyzed. The results demonstrated good agreement between the theoretical and the experimental Lu177-CR emission spectra. Preclinical CR imaging demonstrated that the biokinetics of Lu177-radiopharmaceuticals in the main organs of mice can be acquired.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

A Monte Carlo study of pinhole collimated Cerenkov luminescence imaging integrated with radionuclide treatment

Cerenkov luminescence imaging (CLI) is an emerging optical imaging technique, which has been widely investigated for biological imaging. In this study, we proposed to integrate the CLI technique with the radionuclide treatment as a "see-and-treat" approach, and evaluated the performance of the pinhole collimator-based CLI technique. The detection of Cerenkov luminescence during radionuclide therapy was simulated using the Monte Carlo technique for breast cancer treatment as an example. Our results show that with the pinhole collimator-based configuration, the location, size and shape of the tumors can be clearly visualized on the Cerenkov luminescence images of the breast phantom. In addition, the CLI of multiple tumors can reflect the relative density of radioactivity among tumors, indicating that the intensity of Cerenkov luminescence is independent of the size and shape of a tumor. The current study has demonstrated the high-quality performance of the pinhole collimator-based CLI in breast tumor imaging for the "see-and-treat" multi-modality treatment.

Radioluminescence in biomedicine: physics, applications, and models

The electromagnetic spectrum contains different frequency bands useful for medical imaging and therapy. Short wavelengths (ionizing radiation) are commonly used for radiological and radionuclide imaging and for cancer radiation therapy. Intermediate wavelengths (optical radiation) are useful for more localized imaging and for photodynamic therapy (PDT). Finally, longer wavelengths are the basis for magnetic resonance imaging and for hyperthermia treatments. Recently, there has been a surge of interest for new biomedical methods that synergize optical and ionizing radiation by exploiting the ability of ionizing radiation to stimulate optical emissions. These physical phenomena, together known as radioluminescence, are being used for applications as diverse as radionuclide imaging, radiation therapy monitoring, phototherapy, and nanoparticle-based molecular imaging. This review provides a comprehensive treatment of the physics of radioluminescence and includes simple analytical models to estimate the luminescence yield of scintillators and nanoscintillators, Cherenkov radiation, air fluorescence, and biologically endogenous radioluminescence. Examples of methods that use radioluminescence for diagnostic or therapeutic applications are reviewed and analyzed in light of these quantitative physical models of radioluminescence.

Cherenkov luminescence imaging of shallow sources in semitransparent media

We experimentally investigated the Cherenkov luminescence imaging (CLI) of the isotopes with different beta particles energies (Cu64, F18, Au198, P32, and Br76) in semitransparent biological equivalent media. The main focus of this work is to characterize the CLI when the sources are at the depth comparable with the range of beta particles. The experimental results were compared with Monte Carlo (MC) simulation results to fine tune the simulation parameters to better model the phantom materials. This approach can be applied to estimate the CLI performance for different phantom materials and isotopes. This work also demonstrates some unique properties of high energy beta particles that can be beneficial for CLI, including the possibility to utilize the betas escaped from the object for imaging purposes.

Quantification of Cerenkov Luminescence Imaging (CLI) Comparable With 3-D PET Standard Measurements

Cerenkov luminescence imaging (CLI) is commonly performed using two-dimensional (2-D) conventional optical imaging systems for its cost-effective solution. However, quantification of CLI comparable to conventional three-dimensional positron emission tomography (PET) is challenging using these systems due to both the high attenuation of Cerenkov radiation (CR) on mouse tissue and nonexisting depth resolution of CLI using 2-D imaging systems (2-D CLI). In this study, we developed a model that estimates effective tissue attenuation coefficient and corrects the tissue attenuation of CLI signal intensity independent of tissue depth and size. To evaluate this model, we used several thin slices of ham as a phantom and placed a radionuclide (⁸⁹Zr and ⁶⁴Cu) inside the phantom at different tissue depths and sizes (2, 7, and 12 mm). We performed 2-D CLI and MicroPET/CT (Combined small animal PET and Computed Tomography (CT)) imaging of the phantom and in vivo mouse model after administration of ⁸⁹Zr tracer. Estimates of the effective tissue attenuation coefficient (μ_eff) for ⁸⁹Zr and ⁶⁴Cu were ∼2.4 and ∼2.6 cm⁻¹, respectively. The computed unit conversion factor to %ID/g from 2-D CLI signal was 2.74 × 10⁻³ μCi/radiance estimated from phantom study. After applying tissue attenuation correction and unit conversion to the in vivo animal study, an average quantification difference of 10% for spleen and 35% for liver was obtained compared to PET measurements. The proposed model provides comparable quantification accuracy to standard PET system independent of deep tissue CLI signal attenuation.

Visualization and Quantification of Radiochemical Purity by Cerenkov Luminescence Imaging

Determination of radiochemical purity is essential for characterization of all radioactive compounds, including clinical radiopharmaceuticals. Radio-thin layer chromatography (radio-TLC) has been used as the gold standard for measurement of radiochemical purity; however, this method has several limitations in terms of sensitivity, spatial resolution, two-dimensional scanning, and quantification accuracy. Here, we report a new analytical technique for determination of radiochemical purity based on Cerenkov luminescence imaging (CLI), whereby entire TLC plates are visualized by detection of Cerenkov radiation. Sixteen routinely used TLC plates were tested in combination with three different radioisotopes (¹³¹I, ¹²⁴I, and ³²P). All TLC plates doped with a fluorescent indicator showed excellent detection sensitivity with scanning times of less than 1 min. The new CLI method was superior to the traditional radio-TLC scanning method in terms of sensitivity, scanning time, spatial resolution, and two-dimensional scanning. The CLI method also showed better quantification features across a wider range of radioactivity values compared with radio-TLC and classical zonal analysis, especially for β^--emitters such as ¹³¹I and ³²P.

Performance evaluation of the LightPath imaging system for intra-operative Cerenkov luminescence imaging

The performances of an intra-operative optical imaging system for Cerenkov luminescence imaging of resected tumor specimens were evaluated with phantom studies. The spatial resolution, the linearity of the measured signal with the activity concentration and the minimum detectable activity concentration were considered. A high linearity was observed over a broad range of activity concentration (R²⩾0.99 down to ∼40 kBq/ml of ¹⁸F-FDG). For ¹⁸F-FDG activity distributions 2 mm deep in biological tissue, the measured detection limit was 8 kBq/ml and a spatial resolution of 2.5 mm was obtained. The detection limit of the imaging system is comparable with clinical activity concentrations in tumor specimens, and the spatial resolution is compatible with clinical requirements.

Innovations in Nuclear Imaging Instrumentation: Cerenkov Imaging

Cerenkov luminescence (CL) is blue glow light produced by charged subatomic particles travelling faster than the phase velocity of light in a dielectric medium such as water or tissue. CL was first discovered in 1934, but for biomedical research it was recognized only in 2009 after advances in optical camera sensors brought the required high sensitivity. Recently, applications of CL from clinical radionuclides have been rapidly expanding to include not only preclinical and clinical biomedical imaging but also an approach to therapy. Cerenkov Luminescence Imaging (CLI) utilizes CL generated from clinically relevant radionuclides alongside optical imaging instrumentation. CLI is advantageous over traditional nuclear imaging methods in terms of infrastructure cost, resolution, and imaging time. Furthermore, CLI is a truly multimodal imaging method where the same agent can be detected by two independent modalities, with optical (CL) imaging and with positron emission tomography (PET) imaging. CL has been combined with small molecules, biomolecules and nanoparticles to improve diagnosis and therapy in cancer research. Here, we cover the fundamental breakthroughs and recent advances in reagents and instrumentation methods for CLI as well as therapeutic application of CL.

Gamma rays excited radioluminescence tomographic imaging

Background

Radionuclide-excited luminescence imaging is an optical radionuclide imaging strategy to reveal the distributions of radioluminescent nanophosphors (RLNPs) inside small animals, which uses radioluminescence emitted from RLNPs when excited by high energy rays such as gamma rays generated during the decay of radiotracers used in clinical nuclear medicine imaging. Currently, there is no report of tomographic imaging based on radioluminescence.

Methods

In this paper, we proposed a gamma rays excited radioluminescence tomography (GRLT) to reveal three-dimensional distributions of RLNPs inside a small animal using radioluminescence through image reconstruction from surface measurements of radioluminescent photons using an inverse algorithm. The diffusion equation was employed to model propagations of radioluminescent photons in biological tissues with highly scattering and low absorption characteristics.

Results

Phantom and artificial source-implanted mouse model experiments were employed to test the feasibility of GRLT, and the results demonstrated that the ability of GRLT to reveal the distribution of RLNPs such as Gd₂O₂S:Tb using the radioluminescent signals when excited by gamma rays produced from ^99mTc.

Conclusions

With the emerging of targeted RLNPs, GRLT can provide new possibilities for in vivo and noninvasive examination of biological processes at cellular levels. Especially, combining with Cerenkov luminescence imaging, GRLT can achieve dual molecular information of RLNPs and nuclides using single optical imaging technology.

Lens implementation on the GATE Monte Carlo toolkit for optical imaging simulation

Optical imaging techniques are widely used for in vivo preclinical studies, and it is well known that the Geant4 Application for Emission Tomography (GATE) can be employed for the Monte Carlo (MC) modeling of light transport inside heterogeneous tissues. However, the GATE MC toolkit is limited in that it does not yet include optical lens implementation, even though this is required for a more realistic optical imaging simulation. We describe our implementation of a biconvex lens into the GATE MC toolkit to improve both the sensitivity and spatial resolution for optical imaging simulation. The lens implemented into the GATE was validated against the ZEMAX optical simulation using an US air force 1951 resolution target. The ray diagrams and the charge-coupled device images of the GATE optical simulation agreed with the ZEMAX optical simulation results. In conclusion, the use of a lens on the GATE optical simulation could improve the image quality of bioluminescence and fluorescence significantly as compared with pinhole optics.

Influence of DOTA Chelators on Radiochemical Purity and Biodistribution of 177Lu- and 90Y-Rituximab in Xenografted Mice

This work presents a comparative biological evaluation of ⁹⁰Y- and ¹⁷⁷Lu- labelled DOTA-SCN and DOTA-NHS conjugated to Rituximab in tumour-bearing mice. Two DOTA derivatives, p-SCN-Bn-DOTA and DOTA-NHS-ester were conjugated to Rituximab and then freeze-dried kit formulations were prepared, as previously described (1). Tissue distribution was investigated in tumour-bearing (Raji s.c.) male Rj: NMRI-Foxn1^nu/Foxn1^nu mice at different time points after administration of ¹⁷⁷Lu-DOTA-Rituximab or ⁹⁰Y-DOTA-Rituximab (6 MBq/10 μg per mouse). In addition, tumour images were acquired with a PhotonIMAGER^TM after injection of ⁹⁰Y-DOTA (SCN)-Rituximab. All radioimmunoconjugates were obtained with high radiolabelling yield (RCP > 98%) and specific activity of ca. 0.6 GBq/mg. The conjugates were stable in human serum and in 0.9% NaCl; however, progressive aggregation was observed with time, in particular for DOTA -(SCN) conjugates. Both ¹⁷⁷Lu- and ⁹⁰Y-DOTA -(SCN)-Rituximab revealed slow blood clearance. The maximum tumour uptake was found 72 h after injection of ¹⁷⁷Lu-DOTA -(SCN)-Rituximab (9.3 ID/g). A high radioactivity uptake was observed in liver and spleen, confirming the hepatobiliary excretion route. The results obtained by the radioactive optical imaging harmonize with those from the biodistribution study.

Hybrid Light Imaging Using Cerenkov Luminescence and Liquid Scintillation for Preclinical Optical Imaging In Vivo

PURPOSE

Cerenkov luminescence imaging (CLI) has recently emerged as a molecular imaging modality for radionuclides emitting β-particles. The aim of this study was to develop a hybrid light imaging (HLI) technique using a liquid scintillator to assist CLI by increasing the optical signal intensity from both β-particle and γ-ray emitting radionuclides located at deep regions in vivo.

PROCEDURES

A commercial optical imaging system was employed to collect all images by HLI and CLI. To investigate the performance characteristics of HLI with a commercially available liquid scintillator (Emulsifier-safe), phantom experiments were conducted for two typical β-particle and γ-ray emitters, sodium iodide (Na[(131)I]I) and 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG), respectively. To evaluate the feasibility of HLI for in vivo imaging, HLI was applied to a Na[(131)I]I injected nu/nu mouse and an [(18)F]FDG injected Balb-c mouse and compared with CLI alone.

RESULTS

Measured HLI wavelength spectra with Emulsifier-safe showed higher signal intensities than for CLI at 500-600 nm. For material preventing light transmission of 12-mm thickness, CLI imaging provided quite low intensity and obscure signals of the source. However, despite degraded spatial resolution, HLI imaging provided sustained visualization of the source shape, with signal intensities 10-14 times higher than for CLI at 10-mm thickness. Furthermore, at 0, 4, and 8-mm material thicknesses, HLI showed a strong correlation between Na[(131)I]I or [(18)F]FDG radioactivity and signal intensity, as for CLI. In vivo studies also demonstrated that HLI could successfully visualize Na[(131)I]I uptake in the mouse thyroid gland in the prone position and [(18)F]FDG accumulation in the heart in the supine position, which were not observed with CLI.

CONCLUSION

Our preliminary studies suggest that HLI can provide enhanced imaging of a β-particle probe emitting together with γ-rays at deep tissue locations. HLI may be a promising imaging technique to assist with preclinical in vivo imaging using CLI.

Quantitative Measurement of the Thyroid Uptake Function of Mouse by Cerenkov Luminescence Imaging

Cerenkov luminescence imaging (CLI) has been an evolutional and alternative approach of nuclear imaging in basic research. This study aimed to measure the ¹³¹I thyroid uptake of mouse using CLI for assessment of thyroid function. Quantification of ¹³¹I thyroid uptake of mice in euthyroid, hypothyroid and hyperthyroid status was performed by CLI and γ-scintigraphy at 24 hours after injection of ¹³¹I. The ¹³¹I thyroid uptake was calculated using the equation: (thyroid counts − background counts)/(counts of injected dose of ¹³¹I) × 100%. Serum T4 concentration was determined to evaluate the thyroid function. The radioactivity of ¹³¹I was linearly correlated with the CL signals in both in vitro and in vivo measurements. CLI showed a significant decrease and increase of ¹³¹I thyroid uptake in the mice in hypo- and hyperfunctioning status, respectively, and highly correlated with that measured by γ-scintigraphy. However, the percent thyroid uptake measured by CLI were one-fifth of those measured by γ-scintigraphy due to insufficient tissue penetration of CL. These results indicate that CLI, in addition to nuclear imaging, is able to image and evaluate the ¹³¹I thyroid uptake function in mice in preclinical and research settings.

Cerenkov Radiation-Induced Photoimmunotherapy with 18F-FDG

Near-infrared photoimmunotherapy (NIR-PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with toxicity induced by photoabsorbers after irradiation with NIR light. A limitation of NIR-PIT is the inability to deliver NIR light to a tumor located deep inside the body. Cerenkov radiation (CR) is the ultraviolet and blue light that is produced by a charged particle traveling through a dielectric medium faster than the speed of light in that medium and is commonly produced during radioactive decay. Here, we demonstrate the feasibility of using CR generated by ¹⁸F-FDG accumulated in tumors to induce photoimmunotherapy. Methods: Using A431-luc cells, we evaluated the therapeutic effects of CR-PIT in vitro and in vivo using bioluminescence imaging. Results: CR-PIT showed significant suppression of tumor size, but the decrease of bioluminescence after CR-PIT was not observed consistently over the entire time course. Conclusion: Although CR-PIT can induce tumor killing deep within body, it is less effective than NIR-PIT, possibly related to the relatively lower efficiency of short wavelength light than NIR.

Redshifted Cherenkov Radiation for in vivo Imaging: Coupling Cherenkov Radiation Energy Transfer to multiple Förster Resonance Energy Transfers

Cherenkov Radiation (CR), this blue glow seen in nuclear reactors, is an optical light originating from energetic β-emitter radionuclides. CR emitter ⁹⁰Y triggers a cascade of energy transfers in the presence of a mixed population of fluorophores (which each other match their respective absorption and emission maxima): Cherenkov Radiation Energy Transfer (CRET) first, followed by multiple Förster Resonance Energy transfers (FRET): CRET ratios were calculated to give a rough estimate of the transfer efficiency. While CR is blue-weighted (300–500 nm), such cascades of Energy Transfers allowed to get a) fluorescence emission up to 710 nm, which is beyond the main CR window and within the near-infrared (NIR) window where biological tissues are most transparent, b) to amplify this emission and boost the radiance on that window: EMT6-tumor bearing mice injected with both a radionuclide and a mixture of fluorophores having a good spectral overlap, were shown to have nearly a two-fold radiance boost (measured on a NIR window centered on the emission wavelength of the last fluorophore in the Energy Transfer cascade) compared to a tumor injected with the radionuclide only. Some CR embarked light source could be converted into a near-infrared radiation, where biological tissues are most transparent.

Flexible radioluminescence imaging for FDG-guided surgery

PURPOSE

Flexible radioluminescence imaging (Flex-RLI) is an optical method for imaging ¹⁸F-fluorodeoxyglucose (FDG)-avid tumors. The authors hypothesize that a gadolinium oxysulfide: terbium (GOS:Tb) flexible scintillator, which loosely conforms to the body contour, can enhance tumor signal-to-background ratio (SBR) compared with RLI, which utilizes a flat scintillator. The purpose of this paper is to characterize flex-RLI with respect to alternative modalities including RLI, beta-RLI (RLI with gamma rejection), and Cerenkov luminescence imaging (CLI).

METHODS

The photon sensitivity, spatial resolution, and signal linearity of flex-RLI were characterized with in vitro phantoms. In vivo experiments utilizing 13 nude mice inoculated with the head and neck (UMSCC1-Luc) cell line were then conducted in accordance with the institutional Administrative Panel on Laboratory Animal Care. After intravenous injection of ¹⁸F-FDG, the tumor SBR values for flex-RLI were compared to those for RLI, beta-RLI, and CLI using the Wilcoxon signed rank test.

RESULTS

With respect to photon sensitivity, RLI, beta-RLI, and flex-RLI produced 1216.2, 407.0, and 98.6 times more radiance per second than CLI. Respective full-width half maximum values across a 0.5 mm capillary tube were 6.9, 6.4, 2.2, and 1.5 mm, respectively. Flex-RLI demonstrated a near perfect correlation with ¹⁸F activity (r = 0.99). Signal uniformity for flex-RLI improved after more aggressive homogenization of the GOS powder with the silicone elastomer during formulation. In vivo, the SBR value for flex-RLI (median 1.29; interquartile range 1.18-1.36) was statistically greater than that for RLI (1.08; 1.02-1.14; p < 0.01) by 26%. However, there was no statistically significant difference in SBR values between flex-RLI and beta-RLI (p = 0.92). Furthermore, there was no statistically significant difference in SBR values between flex-RLI and CLI (p = 0.11) in a more limited dataset.

CONCLUSIONS

Flex-RLI provides high quality images with SBRs comparable to those from CLI and beta-RLI in a single 10 s acquisition.

Nuclear medicine for photodynamic therapy in cancer: Planning, monitoring and nuclear PDT

Photodynamic therapy (PDT) is a modality with promising results for the treatment of various cancers. PDT is increasingly included in the standard of care for different pathologies. This therapy relies on the effects of light delivered to photosensitized cells. At different stages of delivery, PDT requires imaging to plan, evaluate and monitor treatment. The contribution of molecular imaging in this context is important and continues to increase. In this article, we review the contribution of nuclear medicine imaging in oncology to PDT for planning and therapeutic monitoring purposes. Several solutions have been proposed to plan PDT from nuclear medicine imaging. For instance, photosensitizer biodistribution has been evaluated with a radiolabeled photosensitizer or with conventional radiopharmaceuticals on positron emission tomography. The effects of PDT delivery have also been explored with specific SPECT or PET radiopharmaceuticals to evaluate the effects on cells (apoptosis, necrosis, proliferation, metabolism) or vascular damage. Finally, the synergy between photosensitizers and radiopharmaceuticals has been studied considering the Cerenkov effect to activate photosensitized cells.

Cerenkov luminescence imaging: physics principles and potential applications in biomedical sciences

Cerenkov luminescence imaging (CLI) is a novel imaging modality to study charged particles with optical methods by detecting the Cerenkov luminescence produced in tissue. This paper first describes the physical processes that govern the production and transport in tissue of Cerenkov luminescence. The detectors used for CLI and their most relevant specifications to optimize the acquisition of the Cerenkov signal are then presented, and CLI is compared with the other optical imaging modalities sharing the same data acquisition and processing methods. Finally, the scientific work related to CLI and the applications for which CLI has been proposed are reviewed. The paper ends with some considerations about further perspectives for this novel imaging modality.

Radiolabeled inorganic nanoparticles for positron emission tomography imaging of cancer: an overview

Over the last few years, a plethora of radiolabeled inorganic nanoparticles have been developed and evaluated for their potential use as probes in positron emission tomography (PET) imaging of a wide variety of cancers. Inorganic nanoparticles represent an emerging paradigm in molecular imaging probe design, allowing the incorporation of various imaging modalities, targeting ligands, and therapeutic payloads into a single vector. A major challenge in this endeavor is to develop disease-specific nanoparticles with facile and robust radiolabeling strategies. Also, the radiolabeled nanoparticles should demonstrate adequate in vitro and in vivo stability, enhanced sensitivity for detection of disease at an early stage, optimized in vivo pharmacokinetics for reduced non-specific organ uptake, and improved targeting for achieving high efficacy. Owing to these challenges and other technological and regulatory issues, only a single radiolabeled nanoparticle formulation, namely "C-dots" (Cornell dots), has found its way into clinical trials thus far. This review describes the available options for radiolabeling of nanoparticles and summarizes the recent developments in PET imaging of cancer in preclinical and clinical settings using radiolabeled nanoparticles as probes. The key considerations toward clinical translation of these novel PET imaging probes are discussed, which will be beneficial for advancement of the field.

Advancing Precision Nuclear Medicine and Molecular Imaging for Lymphoma

PET with fluorodeoxyglucose F 18 (¹⁸F FDG-PET) is a meaningful biomarker for the detection, targeted biopsy, and treatment of lymphoma. This article reviews the evolution of ¹⁸F FDG-PET as a putative biomarker for lymphoma and addresses the current capabilities, challenges, and opportunities to enable precision medicine practices for lymphoma. Precision nuclear medicine is driven by new imaging technologies and methodologies to more accurately detect malignant disease. Although quantitative assessment of response is limited, such technologies will enable a more precise metabolic mapping with much higher definition image detail and thus may make it a robust and valid quantitative response assessment methodology.

Removing Noises Induced by Gamma Radiation in Cerenkov Luminescence Imaging Using a Temporal Median Filter

Cerenkov luminescence imaging (CLI) can provide information of medical radionuclides used in nuclear imaging based on Cerenkov radiation, which makes it possible for optical means to image clinical radionuclide labeled probes. However, the exceptionally weak Cerenkov luminescence (CL) from Cerenkov radiation is susceptible to lots of impulse noises introduced by high energy gamma rays generating from the decays of radionuclides. In this work, a temporal median filter is proposed to remove this kind of impulse noises. Unlike traditional CLI collecting a single CL image with long exposure time and smoothing it using median filter, the proposed method captures a temporal sequence of CL images with shorter exposure time and employs a temporal median filter to smooth a temporal sequence of pixels. Results of in vivo experiments demonstrated that the proposed temporal median method can effectively remove random pulse noises induced by gamma radiation and achieve a robust CLI image.

Advancing theranostics with tumor-targeting peptides for precision otolaryngology

Worldwide, about 600,000 head and neck squamous cell carcinoma (HNSCC) are detected annually, many of which involve high risk human papilloma virus (HPV). Surgery is the primary and desired first treatment option. Following surgery, the existence of cancer cells at the surgical margin is strongly associated with eventual recurrence of cancer and a poor outcome. Despite improved surgical methods (robotics, microsurgery, endoscopic/laparoscopic, and external imaging), surgeons rely only on their vision and touch to locate tumors during surgery. Diagnostic imaging systems like computed tomography (CT), magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT) and positron-emission tomography (PET) are too large, slow and costly to use efficiently during most surgeries and, ultrasound imaging, while fast and portable, is not cancer specific. This purpose of this article is to review the fundamental technologies that will radically advance Precision Otolaryngology practices to the benefit of patients with HNSCC. In particular, this article will address the potential for tumor-targeting peptides to enable more precise diagnostic imaging while simultaneously advancing new therapeutic paradigms for next generation image-guided surgery, tumor-specific chemotherapeutic delivery and tumor-selective targeted radiotherapy (i.e., theranostic).

Cerenkov luminescence imaging (CLI) for image-guided cancer surgery

Cerenkov luminescence imaging (CLI) is a novel molecular optical imaging technique based on the detection of optical Cerenkov photons emitted by positron emission tomography (PET) imaging agents. The ability to use clinically approved tumour-targeted tracers in combination with small-sized imaging equipment makes CLI a particularly interesting technique for image-guided cancer surgery. The past few years have witnessed a rapid increase in proof-of-concept preclinical studies in this field, and several clinical trials are currently underway. This article provides an overview of the basic principles of Cerenkov radiation and outlines the challenges of CLI-guided surgery for clinical use. The preclinical and clinical trial literature is examined including applications focussed on image-guided lymph node detection and Cerenkov luminescence endoscopy, and the ongoing clinical studies and technological developments are highlighted. By intraoperatively guiding the oncosurgeon towards more accurate and complete resections, CLI has the potential to transform current surgical practice, and improve oncological and cosmetic outcomes for patients.

Iodine-131 imaging using 284 keV photons with a small animal CZT-SPECT system dedicated to low-medium-energy photon detection

OBJECTIVE

Iodine-131 is widely used for radionuclide therapy because of its β-particle and for diagnostic imaging employing its principal gamma ray. Since that principal gamma ray has the relatively high energy of 364 keV, small animal single-photon emission computed tomography (SPECT) imaging systems may be required to possess the ability to image such higher energy photons. The aim of this study was to investigate the possibility of imaging I-131 using its 284 keV photons instead of its 364 keV photons in a small animal SPECT imaging system dedicated to the detection of low-medium-energy photons (below 300 keV).

METHODS

The imaging system used was a commercially available preclinical SPECT instrument with CZT detectors that was equipped with multi-pinhole collimators and was accompanied by a CT imager. An energy window for I-131 imaging was set to a photopeak of 284 keV with a low abundance compared with 364 keV photons. Small line sources and two mice, one of each of two types, that were injected with NaI-131 were scanned.

RESULTS

Although higher counts occurred at the peripheral region of the reconstructed images due to the collimator penetration by the 364 keV photons, the shape of the small line sources could be well visualized. The measured spatial resolution was relatively poor (~1.9 mm for full width at half maximum and ~3.9 mm for full width at tenth maximum). However, a good linear correlation between SPECT values and the level of I-131 radioactivity was observed. Furthermore, the uptake of NaI-131 to the thyroid gland for the two mice was clearly identified in the 3D-SPECT image fused with the X-ray CT image.

CONCLUSION

We conclude that the use of an energy window set on the photopeak of 284 keV and the multi-pinhole collimator may permit I-131 imaging for a preclinical CZT-SPECT system that does not have the ability to acquire images using the 364 keV photons.

In vivo near-infrared and Cerenkov luminescence imaging of amyloid-β deposits in the brain: a fluorinated small molecule used for dual-modality imaging

Three fluorinated (¹⁹F or ¹⁸F) small molecules were evaluated as fluorescent or radiolabeled probes for Aβ deposits in the brain.