Looking and listening to light: the evolution of whole-body photonic imaging

Tetramethylbenzidine: An Acoustogenic Photoacoustic Probe for Reactive Oxygen Species Detection

Photoacoustic imaging is attracting a great deal of interest owing to its distinct advantages over other imaging techniques such as fluorescence or magnetic resonance image. The availability of photoacoustic probes for reactive oxygen and nitrogen species (ROS/RNS) could shed light on a plethora of biological processes mediated by these key intermediates. Tetramethylbenzidine (TMB) is a non-toxic and non-mutagenic colorless dye that develops a distinctive blue color upon oxidation. In this work, we have investigated the potential of TMB as an acoustogenic photoacoustic probe for ROS/RNS. Our results indicate that TMB reacts with hypochlorite, hydrogen peroxide, singlet oxygen, and nitrogen dioxide to produce the blue oxidation product, while ROS, such as the superoxide radical anion, sodium peroxide, hydroxyl radical, or peroxynitrite, yield a colorless oxidation product. TMB does not penetrate the Escherichia coli cytoplasm but is capable of detecting singlet oxygen generated in its outer membrane.

Full Color Tunable Aggregation-Induced Emission Luminogen for Bioimaging Based on an Indolizine Molecular Framework

By taking advantage of a unique mechanism of aggregation-induced emission (AIE) phenomena, AIE luminogens (AIEgens) have been provided as a solution to overcome the limitations of conventional fluorophores bearing the feature of aggregation-caused quenching (ACQ) phenomena. Especially, AIEgens paved the way to develop fluorogenic probes ideal for fluorescent imaging in live cell conditions. Despite the high demand for discovery of new AIEgens, it is still challenging to find a versatile molecular platform to generate diverse AIEgens. Herein, we report a new colorful molecular framework, Kaleidolizine (KIz), as a molecular platform for AIEgen generation. The KIz system allows systematic tuning of the emission wavelength from 455 to 564 nm via perturbation of the electron density of substituents on the indolizine core. Increasing the water fraction of the KIz solution in the THF/water mixture induces the fluorescence intensity increase up to 120-fold. Crystal structure analysis, computational calculations, and solvatochromism studies suggest that a synergistic effect between the intramolecular charge transfer and restriction of intramolecular rotation acts as the AIE mechanism in the KIz system. Conjugation of the triphenylphosphonium moiety to KIz allows successful development of triphenylphosphonium (TPP)-KIz for real-time bioimaging of innate mitochondria in live cells, thereby revealing the potential of KIz as a versatile molecular platform to generate fluorogenic probes based on AIE phenomena. We do believe the KIz system could serve as a new, reliable, and generally applicable molecular platform to develop various AIEgens having desired photophysical properties along with an excellent signal-to-noise ratio and with experimental convenience especially for fluorogenic live cell imaging.

Preoperative endoscopic marking of the gastrointestinal tract using fluorescence imaging: submucosal indocyanine green tattooing versus a novel fluorescent over-the-scope clip in a survival experimental study

BACKGROUND

Intraoperative localization of endoluminal lesions is can be difficult during laparoscopy. Preoperative endoscopic marking is therefore necessary. Current methods include submucosal tattooing using visible dyes, which in case of transmural injection can impair surgical dissection. Tattooing using indocyanine green (ICG) coupled to intraoperative near-infrared (NIR) laparoscopy has been described. ICG is only visible under NIR-light, therefore, it doesn't impair the surgical workflow under white light even if there is spillage. However, ICG tattoos have rapid diffusion and short longevity. We propose fluorescent over-the-scope clips (FOSC), using a novel biocompatible fluorescent paint, as durable lesion marking.

METHODS

In six pigs, gastric and colonic endoscopic tattoos using 0.05 mg/mL of ICG and markings using the fluorescent OSC were performed (T0). Simultaneously, NIR laparoscopy was executed. Follow-up laparoscopies were conducted at postoperative day (POD) 4-6 (T1) and POD 11-12 (T2). During laparoscopy, fluorescence intensity was assessed. In one human cadaver, FOSC was used to mark a site on the stomach and on the sigmoid colon, respectively. Intraoperative detection during NIR laparoscopy was assessed.

RESULTS

Gastric and colonic ICG tattooing and OSC markings were easily visible using NIR laparoscopy on T0. All FOSC were visible at T1 and T2 in both stomach and colon, whereas the ICG tattooing at T1 was only visible in the stomach of 2 animals and in the colon of 3 animals. At T2, tattoos were not visible in any animal. FOSC were still visible in both stomach and colon of the human cadaver at 10 days.

CONCLUSION

Endoscopic marking using FOSC can be an efficient and durable alternative to standard methods.

Linear scheme for the direct reconstruction of noncontact time-domain fluorescence molecular lifetime tomography

Direct reconstruction of the noncontact time-domain fluorescence molecular lifetime tomography (TD-FMLT) with current nonlinear algorithms has suffered from complexity and heavy computation loads of the physical model for a large imaging area in TD-FMLT. In this work, we discretize the system matrix along time points and apply a linearized reconstruction algorithm using the fused least absolute shrinkage and selection operator method. The reconstructed yield map and object geometry are used as a priori information to mitigate the ill conditions. This approach is implemented on a fully noncontact TD-FMLT system equipped with a femtosecond pulse laser and a high-speed, time-gated camera. We validate the methodology using both numerical simulations and inhomogeneous phantom experiments. The results exhibit good localization accuracy for fluorescent targets and an efficient computation capability for the reconstruction of fluorescence lifetime in noncontact TD-FMLT. We envision that the proposed linear scheme for the direct reconstruction method in noncontact TD-FMLT has a significant potential for in vivo preclinical studies.

Considerations for using optical clearing techniques for 3D imaging of nanoparticle biodistribution

A key consideration in the clinical translation of nanomedicines is determining their in vivo biodistribution in preclinical studies, which is important for predicting and correlating therapeutic efficacy and safety. There are a number of techniques available for analyzing the in vivo biodistribution of nanoparticles, with each having its own advantages and limitations. However, conventional techniques are limited by their inability to image the three-dimensional (3D) association of nanoparticles with cells, vasculature and other biological structures in whole organs at a subcellular level. Recently, optical clearing techniques have been used to evaluate the biodistribution of nanoparticles by 3D organ imaging. Optical clearing is a procedure that is increasingly being used to improve the imaging of biological tissues, whereby light scattering substances are removed to better match the refractive indices of different tissue layers. The use of optical clearing techniques has the potential to transform the way we evaluate the biodistribution of new and existing nanomedicines, as it allows the visualization of the interaction of nanoparticles with the biological environment in intact tissues. This review will compare the main optical clearing techniques and will address the considerations for the use of these techniques to evaluate nanoparticle biodistribution.

Time delay effect in a microchip pulse laser for the nonlinear photoacoustic signal enhancement

The Grüneisen relaxation effect has been successfully employed to improve the photoacoustic (PA) imaging contrast. However, complex system design and cost hinder the progress from benchside to bedside, since an additional pre-heating laser source needs to be coupled into the original light path and synchronized with other equipment for conducting the nonlinear effect. To overcome the limitation, we propose a time delay heating PA imaging (TDH-PAI) method based on the time delay effect in a passively Q-switched laser. Experimentally, only one single microchip pulse laser is built and utilized for the nonlinear PA signal enhancement without additional components. The 808 nm pump pulse of the laser diode and the excited 1064 nm pulse are respectively used for pre-heating and acquiring PA signals. The heating effect is optimized by adjusting the input parameters and an enhancement of more than 30% in PA signals is achieved. TDH-PAI reduces the cost and complexity of the nonlinear PA system, which provides an efficient way for achieving a high-contrast PA imaging.

Stimuli-responsive Drug Delivery Nanocarriers in the Treatment of Breast Cancer

Stimuli-responsive drug-delivery nanocarriers (DDNs) have been increasingly reported in the literature as an alternative for breast cancer therapy. Stimuli-responsive DDNs are developed with materials that present a drastic change in response to intrinsic/chemical stimuli (pH, redox and enzyme) and extrinsic/physical stimuli (ultrasound, Near-infrared (NIR) light, magnetic field and electric current). In addition, they can be developed using different strategies, such as functionalization with signaling molecules, leading to several advantages, such as (a) improved pharmaceutical properties of liposoluble drugs, (b) selectivity with the tumor tissue decreasing systemic toxic effects, (c) controlled release upon different stimuli, which are all fundamental to improving the therapeutic effectiveness of breast cancer treatment. Therefore, this review summarizes the use of stimuli-responsive DDNs in the treatment of breast cancer. We have divided the discussions into intrinsic and extrinsic stimuli and have separately detailed them regarding their definitions and applications. Finally, we aim to address the ability of these stimuli-responsive DDNs to control the drug release in vitro and the influence on breast cancer therapy, evaluated in vivo in breast cancer models.

Computed tomography for in vivo deep over-1000 nm near-infrared fluorescence imaging

This study aims to develop a novel cross-sectional imaging of fluorescence in over-1000 nm near-infrared (OTN-NIR), which allows in vivo deep imaging, using computed tomography (CT) system. Cylindrical specimens of composite of OTN-NIR fluorophore, NaGdF₄ co-doped with Yb³⁺ and Ho³⁺ (ex: 980 nm, em: 1150 nm), were embedded in cubic agar (10.5-12 mm) or in the peritoneal cavity of mice and placed on a rotatable stage. When the fluorescence from inside of the samples was serially captured from multiple angles, the images were disrupted by the reflection and refraction of emitted light on the sample-air interface. Immersing the sample into water filled in a rectangular bath suppressed the disruption at the interface and successfully reconstructed the position and concentration of OTN-NIR fluorophores on the cross-sectional images using a CT technique. This is promising as a novel three-dimensional imaging technique for OTN-NIR fluorescent image projections of small animals captured from multiple angles.

Detecting hemodynamic changes in the foot vessels of diabetic patients by photoacoustic tomography

Limb perfusion monitoring is critical for diabetes mellitus (DM) patients as they are vulnerable to vascular complications due to prolonged hyperglycemia. However, current clinical approaches are ineffective in vascular imaging and in assessing vascular function in lower limbs. In this work, a concave ultrasound transducer array-based photoacoustic tomography (PAT) system was used to image the foot dorsal section of a subject, and a total of seven DM patients and seven healthy volunteers were enrolled in this study. Hemodynamic changes in foot vessels during vascular occlusion as well as oxygen saturation (SO₂ ) in rest were analyzed for both groups. The results obtained showed that DM patients have a unique peripheral hemodynamic response to occlusion and a lower level SO₂ , compared to that for healthy subjects. This suggests that PAT has the potential to detect vascular dysfunction in DM patients and to measure the effect of treatment.

Simultaneous transrectal ultrasound and photoacoustic human prostate imaging

Imaging technologies that simultaneously provide anatomical, functional, and molecular information are emerging as an attractive choice for disease screening and management. Since the 1980s, transrectal ultrasound (TRUS) has been routinely used to visualize prostatic anatomy and guide needle biopsy, despite limited specificity. Photoacoustic imaging (PAI) provides functional and molecular information at ultrasonic resolution based on optical absorption. Combining the strengths of TRUS and PAI approaches, we report the development and bench-to-bedside translation of an integrated TRUS and photoacoustic (TRUSPA) device. TRUSPA uses a miniaturized capacitive micromachined ultrasonic transducer array for simultaneous imaging of anatomical and molecular optical contrasts [intrinsic: hemoglobin; extrinsic: intravenous indocyanine green (ICG)] of the human prostate. Hemoglobin absorption mapped vascularity of the prostate and surroundings, whereas ICG absorption enhanced the intraprostatic photoacoustic contrast. Future work using the TRUSPA device for biomarker-specific molecular imaging may enable a fundamentally new approach to prostate cancer diagnosis, prognostication, and therapeutic monitoring.

Localization of Fluorescent Targets in Deep Tissue With Expanded Beam Illumination for Studies of Cancer and the Brain

Imaging fluorescence through millimeters or centimeters of tissue has important in vivo applications, such as guiding surgery and studying the brain. Often, the important information is the location of one of more optical reporters, rather than the specifics of the local geometry, motivating the need for a localization method that provides this information. We present an optimization approach based on a diffusion model for the fast localization of fluorescent inhomogeneities in deep tissue with expanded beam illumination that simplifies the experiment and the reconstruction. We show that the position of a fluorescent inhomogeneity can be estimated while assuming homogeneous tissue parameters and without having to model the excitation profile, reducing the computational burden and improving the utility of the method. We perform two experiments as a demonstration. First, a tumor in a mouse is localized using a near infrared folate-targeted fluorescent agent (OTL38). This result shows that localization can quickly provide tumor depth information, which could reduce damage to healthy tissue during fluorescence-guided surgery. Second, another near infrared fluorescent agent (ATTO647N) is injected into the brain of a rat, and localized through the intact skull and surface tissue. This result will enable studies of protein aggregation and neuron signaling.

Spatial and Spectral Mapping and Decomposition of Neural Dynamics and Organization of the Mouse Brain with Multispectral Optoacoustic Tomography

In traditional optical imaging, limited light penetration constrains high-resolution interrogation to tissue surfaces. Optoacoustic imaging combines the superb contrast of optical imaging with deep penetration of ultrasound, enabling a range of new applications. We used multispectral optoacoustic tomography (MSOT) for functional and structural neuroimaging in mice at resolution, depth, and specificity unattainable by other neuroimaging modalities. Based on multispectral readouts, we computed hemoglobin gradient and oxygen saturation changes related to processing of somatosensory signals in different structures along the entire subcortical-cortical axis. Using temporal correlation analysis and seed-based maps, we reveal the connectivity between cortical, thalamic, and sub-thalamic formations. With the same modality, high-resolution structural tomography of intact mouse brain was achieved based on endogenous contrasts, demonstrating near-perfect matches with anatomical features revealed by histology. These results extend the limits of noninvasive observations beyond the reach of standard high-resolution neuroimaging, verifying the suitability of MSOT for small-animal studies.

Photoacoustic imaging of kidney fibrosis for assessing pretransplant organ quality

Roughly 10% of the world's population has chronic kidney disease (CKD). In its advanced stages, CKD greatly increases the risk of hospitalization and death. Although kidney transplantation has revolutionized the care of advanced CKD, clinicians have limited ways of assessing donor kidney quality. Thus, optimal donor kidney-recipient matching cannot be performed, meaning that some patients receive damaged kidneys that function poorly. Fibrosis is a form of chronic damage often present in donor kidneys, and it is an important predictor of future renal function. Currently, no safe, easy-to-perform technique exists that accurately quantifies renal fibrosis. We describe a potentially novel photoacoustic (PA) imaging technique that directly images collagen, the principal component of fibrotic tissue. PA imaging noninvasively quantifies whole kidney fibrotic burden in mice, and cortical fibrosis in pig and human kidneys, with outstanding accuracy and speed. Remarkably, 3-dimensional PA imaging exhibited sufficiently high resolution to capture intrarenal variations in collagen content. We further show that PA imaging can be performed in a setting that mimics human kidney transplantation, suggesting the potential for rapid clinical translation. Taken together, our data suggest that PA collagen imaging is a major advance in fibrosis quantification that could have widespread preclinical and clinical impact.

Tomographic Ultrasound and LED-Based Photoacoustic System for Preclinical Imaging

Small animals are widely used as disease models in medical research. Noninvasive imaging modalities with functional capability play an important role in studying the disease state and treatment progress. Photoacoustics, being a noninvasive and functional modality, has the potential for small-animal imaging. However, the conventional photoacoustic tomographic systems use pulsed lasers, making it expensive, bulky, and require long acquisition time. In this work, we propose the use of photoacoustic and ultrasound tomographic imaging with LEDs as the light source and acoustic detection using a linear transducer array. We have demonstrated full-view tomographic imaging of a euthanized mouse and a potential application in liver fibrosis research.

Recent advances in molecular imaging of atherosclerotic plaques and thrombosis

As the complications of atherosclerosis such as myocardial infarction and stroke are still one of the leading causes of mortality worldwide, the development of new diagnostic tools for the early detection of plaque instability and thrombosis is urgently needed. Advanced molecular imaging probes based on functional nanomaterials in combination with cutting edge imaging techniques are now paving the way for novel and unique approaches to monitor the inflammatory progress in atherosclerosis. This review focuses on the development of various molecular probes for the diagnosis of plaques and thrombosis in atherosclerosis, along with perspectives of their diagnostic applications in cardiovascular diseases. Specifically, we summarize the biological targets that can be used for atherosclerosis and thrombosis imaging. Then we describe the emerging molecular imaging techniques based on the utilization of engineered nanoprobes together with their challenges in clinical translation.

In vivo fluorescence molecular tomography of induced haemarthrosis in haemophilic mice: link between bleeding characteristics and development of bone pathology

Background

Haemophilic arthropathy is a chronic and debilitating joint disease caused by recurrent spontaneous joint bleeds in patients with haemophilia. Understanding how characteristics of individual joint bleeds relate to the subsequent development of arthropathy could improve management and prevention of this joint disease. Here, we aimed to explore relations between joint bleed characteristics and development of bone pathology in a mouse model of haemophilic arthropathy by using novel in vivo imaging methodology.

Methods

We characterised induced knee bleeds in a murine model of haemophilic arthropathy by quantitative in vivo fluorescence molecular tomography (FMT) and by measurements of changes in the diameter of the injured knee. Wild-type mice and non-injured haemophilic mice acted as controls. Development of arthropathy was characterised by post mortem evaluation of bone pathology by micro-CT 14 days after bleed-induction. In an in vitro study, we assessed the effect of blood on the quantification of fluorescent signal with FMT.

Results

In most injured haemophilic mice, we observed significant loss of trabecular bone, and half of the mice developed pathological bone remodelling. Development of pathological bone remodelling was associated with significantly increased fluorescent signal and diameter of the injured knee just 1 day after induction of the bleed. Further, a correlation between the fluorescent signal 1 day after induction of the bleed and loss of trabecular bone reached borderline significance. In the in vitro study, we found that high concentrations of blood significantly decreased the fluorescent signal.

Conclusion

Our results add novel insights on the pathogenesis of haemophilic arthropathy and underline the importance of the acute phase of joint bleeds for the subsequent development of arthropathy.

How Non-invasive in vivo Cell Tracking Supports the Development and Translation of Cancer Immunotherapies

Immunotherapy is a relatively new treatment regimen for cancer, and it is based on the modulation of the immune system to battle cancer. Immunotherapies can be classified as either molecular or cell-based immunotherapies, and both types have demonstrated promising results in a growing number of cancers. Indeed, several immunotherapies representing both classes are already approved for clinical use in oncology. While spectacular treatment successes have been reported, particularly for so-called immune checkpoint inhibitors and certain cell-based immunotherapies, they have also been accompanied by a variety of severe, sometimes life-threatening side effects. Furthermore, not all patients respond to immunotherapy. Hence, there is the need for more research to render these promising therapeutics more efficacious, more widely applicable, and safer to use. Whole-body in vivo imaging technologies that can interrogate cancers and/or immunotherapies are highly beneficial tools for immunotherapy development and translation to the clinic. In this review, we explain how in vivo imaging can aid the development of molecular and cell-based anti-cancer immunotherapies. We describe the principles of imaging host T-cells and adoptively transferred therapeutic T-cells as well as the value of traceable cancer cell models in immunotherapy development. Our emphasis is on in vivo cell tracking methodology, including important aspects and caveats specific to immunotherapies. We discuss a variety of associated experimental design aspects including parameters such as cell type, observation times/intervals, and detection sensitivity. The focus is on non-invasive 3D cell tracking on the whole-body level including aspects relevant for both preclinical experimentation and clinical translatability of the underlying methodologies.

Photoacoustic Imaging-Trackable Magnetic Microswimmers for Pathogenic Bacterial Infection Treatment

Micro/nanorobots have been extensively explored as a tetherless small-scale robotic biodevice to perform minimally invasive interventions in hard-to-reach regions. Despite the emergence of versatile micro/nanorobots in recent years, matched in vivo development remains challenging, limited by unsatisfactory integration of core functions. Herein, we report a polydopamine (PDA)-coated magnetic microswimmer consisting of a magnetized Spirulina (MSP) matrix and PDA surface. Apart from the properties of the existing MSP (e.g., robust propulsion, natural fluorescence, tailored biodegradation, and selective cytotoxicity), the introduced PDA coating enhances the photoacoustic (PA) signal and photothermal effect of the MSP, thus making PA image tracking and photothermal therapy possible. Meanwhile, the PDA's innate fluorescence quenching and diverse surface reactivity allows an off-on fluorescence diagnosis with fluorescence probes (e.g., coumarin 7). As a proof of concept, real-time image tracking (by PA imaging) and desired theranostic capabilities of PDA-MSP microswimmer swarms are demonstrated for the treatment of pathogenic bacterial infection. Our study suggests a feasible antibacterial microrobot for in vivo development and a facile yet versatile functionalization strategy of micro/nanorobots.

Light-Activatable Transfection System Using Hybrid Vectors Composed of Thermosensitive Dendron Lipids and Gold Nanorods

BACKGROUND

Gene delivery to target cells is crucially important to establish gene therapy and regenerative medicine. Although various virus-based and synthetic molecule-based gene vectors have been developed to date, selective transfection in a site or a cell level is still challenging. For this study, both light-responsive and temperature-responsive synthetic gene vectors were designed for spatiotemporal control of a transfection system.

METHODS

11-Mercaptoundecanoic acid-coated gold nanorods were mixed with polyamidoamine dendron-bearing lipids of two types having amino-terminus or ethoxydiethylene glycol-terminus to obtain hybrid vectors. Hybrid vectors were mixed further with pDNA. Then we investigated their physicochemical properties and transfection efficacy with or without near infrared laser irradiation.

RESULTS

Hybrid vectors formed complexes with pDNA and exhibited enhanced photothermal property under near infrared laser irradiation compared with parent gold nanorods. Transfection efficacy of complexes was promoted considerably by brief laser irradiation soon after complex application to the cells. Analysis of intracellular distribution revealed that laser irradiation promoted the adsorption of complexes to the cells and cytosolic release of pDNA, which is derived from the change in surface hydrophobicity of complexes through dehydration of temperature-responsive groups.

CONCLUSIONS

Hybrid vector is promising as a light-activatable transfection system.

Visualizing cortical response to optogenetic stimulation and sensory inputs using multispectral handheld optoacoustic imaging

To date, the vast majority of intra-vital neuroimaging systems applied in clinic and diagnostics is stationary with a rigid scanning element, requires specialized facilities and costly infrastructure. Here, we describe a simple yet radical approach for optoacoustic (photoacoustic) brain imaging in vivo using a light-weight handheld probe. It enables multispectral video-rate visualization of hemoglobin gradient changes in the cortex of adult rats induced by whisker and forelimb sensory inputs, as well as by optogenetic stimulation of intra-cortical connections. With superb penetration and molecular specificity, described here in method holds major promises for future applications in research, routine ambulatory neuroimaging, and diagnostics.

Small-animal 360-deg fluorescence diffuse optical tomography using structural prior information from ultrasound imaging

We demonstrate dual modality of free-space fluorescence diffuse optical tomography (FDOT) and handheld ultrasound (US) imaging to reveal both functional and structural information in small animals. FDOT is a noninvasive method for examining the fluorophore inside an object from the light distribution of the surface. In FDOT, a 660-nm continuous wave diode laser was used as an excitation source and an electron-multiplying charge-coupled device (EMCCD) was used for fluorescence data acquisition. Both the laser and EMCCD were mounted on a 360-deg rotation gantry for the transmission optical data collection. The structural information is obtained from a 6- to 17-MHz handheld US linear transducer by single-side access and conducts in the reconstruction as soft priors. The rotation ranges from 0 deg to 360 deg; different rotation degrees, object positions, and parameters were determined for comparison. Both phantom and tissue phantom results demonstrate that fluorophore distribution can be recovered accurately and quantitatively using this imaging system. Finally, an animal study confirms that the system can extract a dual-modality image, validating its feasibility for further in vivo experiments. In all experiments, the error and standard deviation decrease as the rotation degree is increased and the error was reduced to 10% when the rotation degree was increased over 135 deg.

Indocyanine green-loaded injectable alginate hydrogel as a marker for precision cancer surgery

Background

Accurate identification of tumor sites and boundaries is of paramount importance during minimally invasive surgery. Although laparoscopic resection is being increasingly and widely performed for early gastric and colorectal cancers, the detection of tumors located inside the stomach and intestine is difficult owing to the lack of tactile sensation. Here, we propose the application of an indocyanine green (ICG)-loaded alginate hydrogel system as a fluorescence surgical marker for precise laparoscopic operations.

Methods

A physical complex of ICG and human serum albumin (HSA) was mixed with sodium alginate to form an injectable hydrogel system. Calcium carbonate and D-gluconic acid (GA) were added to the gel to control its strength and gelation time, respectively. The optimal conditions for the preparation of injectable hydrogels were determined by analyzing the fluorescence spectra and sol-gel transition time of the prepared samples at various concentrations and compositions. Next, the aqueous solutions of ICG, ICG-HSA, and ICG-HSA-loaded alginate were subcutaneously injected into nude mice (three mice per group), and near-infrared (NIR) fluorescence images of the mice (λ_ex. =780 nm, λ_em. =845 nm) were obtained at different points in time for 8 days. Then, fluorescence intensities at the injection sites, target-to-background ratio, and areas of ICG fluorescence were analyzed. Finally, the potential utility of ICG-HSA-loaded alginate hydrogel as a surgical marker was evaluated in a porcine model. The ICG-HSA-loaded alginate solution was injected into three sites in the submucosal space of the porcine stomach via a catheter. A fluorescent laparoscopic system was installed on the abdomen of the pig 3 days post-injection, and the fluorescence signal generated from the fluorescence surgical marker located inside the stomach was evaluated using the fluorescence laparoscope system (λ_ex. =785 nm, λ_em. =805 nm).

Results

The optimal concentration of ICG-HSA complex was determined to be 30 µM, and maximum fluorescence intensity of the complex was obtained at a 1:1 mole ratio of HSA to ICG. The subcutaneous injection of ICG or ICG-HSA solution in mice resulted in the rapid spread of the fluorescence signal around the injection site in 3 h, and a weak fluorescence was detected at the injection site 24 h post-injection. In contrast, the fluorescence detection time was effectively prolonged up to 96 h post-injection in the case of ICG-HSA-loaded alginate gel, while diffusion of the injected ICG from the injection site was effectively prevented. In the laparoscopic operation, injection sites of the hydrogel in porcine stomach could be accurately detected in real time even after 3 days.

Conclusions

This alginate hydrogel system may be potentially useful as an effective surgical marker in terms of accuracy and persistence for laparoscopic operation.

An innovative approach for the synthesis of dual modality peptide imaging probes based on the native chemical ligation approach

Peptide-targeting probes tagged with optical imaging and PET reporters may find applications in innovative diagnostic procedures and image-guided surgeries. The reported synthesis procedure is of general applicability to obtain dual imaging probes using fully unprotected moieties with a selective and rapid chemistry based on native chemical ligation.

Beyond the Green Fluorescent Protein: Biomolecular Reporters for Anaerobic and Deep-Tissue Imaging

Fluorescence imaging represents cornerstone technology for studying biological function at the cellular and molecular levels. The technology's centerpiece is a prolific collection of genetic reporters based on the green fluorescent protein (GFP) and related analogs. More than two decades of protein engineering have endowed the GFP repertoire with an incredible assortment of fluorescent proteins, allowing scientists immense latitude in choosing reporters tailored to various cellular and environmental contexts. Nevertheless, GFP and derivative reporters have specific limitations that hinder their unrestricted use for molecular imaging. These challenges have inspired the development of new reporter proteins and imaging mechanisms. Here, we review how these developments are expanding the frontiers of reporter gene techniques to enable nondestructive studies of cell function in anaerobic environments and deep inside intact animals-two important biological contexts that are fundamentally incompatible with the use of GFP-based reporters.

Semiconducting Polymer Nanoreporters for Near-Infrared Chemiluminescence Imaging of Immunoactivation

Real-time in vivo imaging of immunoactivation is critical for longitudinal evaluation of cancer immunotherapy, which, however, is rarely demonstrated. This study reports semiconducting polymer nanoreporters (SPNRs) with superoxide anion (O₂ ^•- )-activatable chemiluminescence signals for in vivo imaging of immunoactivation during cancer immunotherapy. SPNRs are designed to comprise an SP and a caged chemiluminescence phenoxy-dioxetane substrate, which respectively serve as the chemiluminescence acceptor and donor to enable intraparticle chemiluminescence resonance energy transfer. SPNRs are intrinsically fluorescent but only become chemiluminescent upon activation by O₂ ^•- . Representing the first O₂ ^•- -activatable near-infrared chemiluminescent reporter, SPNR3 sensitively differentiates higher O₂ ^•- levels in immune cells from other cells including cancer and normal cells. Following systemic administration, SPNR3 passively accumulates into tumors in living mice and activates the chemiluminescence signals responding to the concentration of O₂ ^•- in the tumor microenvironment. Moreover, the enhancement of in vivo chemiluminescence signal after cancer immunotherapy is correlated with increased population of T cells in the tumor, proving its feasibility in tracking of T cell activation. Thus, SPNRs represent the first kind of chemiluminescent reporters competent for in vivo imaging of immunoactivation.

Snapshot hyperspectral light field imaging using image mapping spectrometry

In this Letter, we present a snapshot hyperspectral light field imaging system using a single camera. By integrating an unfocused light field camera with a snapshot hyperspectral imager, the image mapping spectrometer, we captured a five-dimensional (5D) ($x,y,u,v,\lambda $x,y,u,v,λ) ($x,y,$x,y, spatial coordinates; $u,v,$u,v, emittance angles; $\lambda ,$λ, wavelength) datacube in a single camera exposure. The corresponding volumetric image ($x,y,z$x,y,z) at each wavelength is then computed through a scale-depth space transform. We demonstrated the snapshot advantage of our system by imaging the spectral-volumetric scenes in real time.

Fast and robust reconstruction algorithm for fluorescence diffuse optical tomography assuming a cuboid target

A fast algorithm for fluorescence diffuse optical tomography is proposed. The algorithm is robust against the choice of initial guesses. We estimate the position of a fluorescent target by assuming a cuboid (rectangular parallelepiped) for the fluorophore target. The proposed numerical algorithm is verified by a numerical experiment and an experiment with a meat phantom. The target position is reconstructed with a cuboid from measurements in the time domain. Moreover, the long-time behavior of the emission light is investigated making use of the analytical solution to the diffusion equation.

In vivo antitumour activity of Britanin against gastric cancer through nuclear factor-κB-mediated immune response

OBJECTIVES

Britanin was explored for the antitumour effect on gastric cancer, which is a sesquiterpene lactone (SL) extracted from Inula japonica.

METHODS

In the present study, cell viability assays were performed to evaluate the antiproliferation effect of Britanin on gastric cancer cells. Tumour development in BGC-823 cell-bearing nude mice was monitored in real-time after Britanin treatment via a bioluminescent imaging method. Western blotting analysis and enzyme-linked immunosorbent assays detected proteins associated with the nuclear factor (NF)-κB signalling pathway.

KEY FINDINGS

Britanin can suppress the proliferation of gastric cancer cells in vitro and the growth of tumours in vivo. In the treatment group, decreased levels of p65 and phosphorylated (p)-p65 were observed. This indicated that NF-κB plays an important role in the antitumour effect of Britanin. Furthermore, considering the additional role of NF-κB in the immune system, the levels of the downstream molecules interleukin (IL)-2 and the cytokine IL-10 were subsequently determined in vivo. An increase in the IL-2 level and a decrease in the IL-10 level indicated that Britanin elicited an enhanced immune response.

CONCLUSIONS

Britanin may be a promising candidate for gastric cancer chemotherapy, and its anticancer effect likely depends on an NF-κB-mediated immune response.

Glutathione-responsive disassembly of disulfide dicyanine for tumor imaging with reduction in background signal intensity

Near-infrared (NIR) fluorescence imaging has been proved as an effective modality in identifying the tumor border and distinguishing the tumor cells from healthy tissue during the oncological surgery. Developing NIR fluorescent probes with high tumor to background (T/B) signal is essential for the complete debulking of the tumor, which will prolong the survival rate of tumor patients. However, the nonspecific binding and "always-on" properties of the conventional fluorescent probes leads to high background signals and poor specificity. Method: To address this problem, glutathione (GSH)-responsive, two disulfide-bonded dicyanine dyes (ss-diCy5 and ss-diNH800CW) were synthesized. As synthesized dyes are quenched under normal physiological conditions, however, once reached to the tumor site, these dyes are capable of emitting strong fluorescence signals primarily because of the cleavage of the disulfide bond in the tumor microenvironment with high GSH concentration. Besides, the GSH-responsive behavior of these dyes was monitored using the UV-vis and fluorescence spectroscopy. The diagnostic accuracy of the aforementioned dyes was also tested both in tumor cells and 4T1-bearing mice. Results: The fluorescence signal intensity of disulfide dicyanine dyes was quenched up to 89% compared to the mono cyanine dyes, thus providing a very low fluorescence background. However, when the disulfide dicyanine dye reaches the tumor site, the dicyanine is cleaved by GSH into two mono-dyes with high fluorescence strength, thus producing strong fluorescent signals upon excitation. The fluorescent signal of the dicyanine was enhanced by up to 27-fold after interacting with the GSH solution. In vivo xenografts tumor studies further revealed that the fluorescence signals of aforementioned dyes can be quickly recovered in the solid tumor. Conclusion: In summary, the disulfide dicyanines dyes can provide a promising platform for specific tumor-activatable fluorescence imaging with improved T/B value.

Reconstruction for Fluorescence Molecular Tomography via Adaptive Group Orthogonal Matching Pursuit

OBJECTIVE

Fluorescence molecular tomography (FMT) is a promising medical imaging technology aimed at the non-invasive, specific, and sensitive detection of the distribution of fluorophore. Conventional sparsity prior-based methods of FMT commonly face problems such as over-sparseness, spatial discontinuity, and poor robustness, due to the neglect of the interrelation within the local subspace. To address this, we propose an adaptive group orthogonal matching pursuit (AGOMP) method.

METHODS

AGOMP is based on a novel local spatial-structured sparse regularization, which leverages local spatial interrelations as group sparsity without the hard prior of the tumor region. The adaptive grouped subspace matching pursuit method was adopted to enhance the interrelatedness of elements within a group, which alleviates the over-sparsity problem to some extent and improves the accuracy, robustness, and morphological similarity of FMT reconstruction. A series of numerical simulation experiments, based on digital mouse with both one and several tumors, were conducted, as well as in vivo mouse experiments.

RESULTS

The results demonstrated that the proposed AGOMP method achieved better location accuracy, fluorescent yield reconstruction, relative sparsity, and morphology than state-of-the-art methods under complex conditions for levels of Gaussian noise ranging from 5-25%. Furthermore, the in vivo mouse experiments demonstrated the practical application of FMT with AGOMP.

CONCLUSION

The proposed AGOMP can improve the accuracy and robustness for FMT reconstruction in biomedical application.

Spatial heterogeneity of nanomedicine investigated by multiscale imaging of the drug, the nanoparticle and the tumour environment

Genetic and phenotypic tumour heterogeneity is an important cause of therapy resistance. Moreover, non-uniform spatial drug distribution in cancer treatment may cause pseudo-resistance, meaning that a treatment is ineffective because the drug does not reach its target at sufficient concentrations. Together with tumour heterogeneity, non-uniform drug distribution causes “therapy heterogeneity”: a spatially heterogeneous treatment effect. Spatial heterogeneity in drug distribution occurs on all scales ranging from interpatient differences to intratumour differences on tissue or cellular scale. Nanomedicine aims to improve the balance between efficacy and safety of drugs by targeting drug-loaded nanoparticles specifically to tumours. Spatial heterogeneity in nanoparticle and payload distribution could be an important factor that limits their efficacy in patients. Therefore, imaging spatial nanoparticle distribution and imaging the tumour environment giving rise to this distribution could help understand (lack of) clinical success of nanomedicine. Imaging the nanoparticle, drug and tumour environment can lead to improvements of new nanotherapies, increase understanding of underlying mechanisms of heterogeneous distribution, facilitate patient selection for nanotherapies and help assess the effect of treatments that aim to reduce heterogeneity in nanoparticle distribution.

In this review, we discuss three groups of imaging modalities applied in nanomedicine research: non-invasive clinical imaging methods (nuclear imaging, MRI, CT, ultrasound), optical imaging and mass spectrometry imaging. Because each imaging modality provides information at a different scale and has its own strengths and weaknesses, choosing wisely and combining modalities will lead to a wealth of information that will help bring nanomedicine forward.

Optical and Optoacoustic Imaging

The spatiotemporal determination of molecular events and cells is important for understanding disease processes, especially in oncology, and thus for the development of novel treatments. Equally important is the knowledge of the biodistribution, localization, and targeted accumulation of novel therapies as well as monitoring of tumor growth and therapeutic response. Optical imaging provides an ideal versatile platform for imaging of all these problems and questions.

Barbituric Acid Based Fluorogens: Synthesis, Aggregation-Induced Emission, and Protein Fibril Detection

Fluorescent dyes, especially those emitting in the long wavelength region, are excellent candidates in the area of bioassay and bioimaging. In this work, we report a series of simple organic fluorescent dyes consisting of electron-donating aniline groups and electron-withdrawing barbituric acid groups. These dyes are very easy to construct while emitting strongly in the red region in their solid state. The photophysical properties of these dyes, such as solvatochromism and aggregation-induced emission, are systematically characterized. Afterward, the structure-property relationships of these barbituric acid based fluorogens are discussed. Finally, we demonstrate their potential applications for protein amyloid fibril detection.

Principal Component Analysis Based Dynamic Cone Beam X-Ray Luminescence Computed Tomography: A Feasibility Study

Cone beam X-ray luminescence computed tomography (CB-XLCT) is a promising imaging technique in studying the physiological and pathological processes in small animals. However, the dynamic bio-distributions of probes in small animal, especially in adjacent targets are still hard to be captured directly from dynamic CB-XLCT. In this paper, a 4D temporal-spatial reconstruction method based on principal component analysis (PCA) in the projection space is proposed for dynamic CB-XLCT. First, projections of angles in each 3D frame are compressed to reduce the noises initially. Then a temporal PCA is performed on the projection data to decorrelate the 4D problem into separate 3D problems in the PCA domain. In the PCA domain, the difference between dynamic behaviors of multiple targets can be reflected by the first several principal components which can be further used for fast and improved reconstruction by a restarted Tikhonov regularization method. At last, by discarding the principal components mainly reflecting noise, the concentration series of targets are recovered from the first few reconstruction results with a mask as the constraint. The numerical simulation and phantom experiment demonstrate that the proposed method can resolve multiple targets and recover the dynamic distributions with high computation efficiency. The proposed method provides new feasibility for imaging dynamic bio-distributions of probes in vivo.

Minimally invasive photoacoustic imaging: Current status and future perspectives

Photoacoustic imaging (PAI) is an emerging biomedical imaging modality that is based on optical absorption contrast, capable of revealing distinct spectroscopic signatures of tissue at high spatial resolution and large imaging depths. However, clinical applications of conventional non-invasive PAI systems have been restricted to examinations of tissues at depths less than a few cm due to strong light attenuation. Minimally invasive photoacoustic imaging (miPAI) has greatly extended the landscape of PAI by delivering excitation light within tissue through miniature fibre-optic probes. In the past decade, various miPAI systems have been developed with demonstrated applicability in several clinical fields. In this article, we present an overview of the current status of miPAI and our thoughts on future perspectives.

Adaptive Gaussian Weighted Laplace Prior Regularization Enables Accurate Morphological Reconstruction in Fluorescence Molecular Tomography

Fluorescence molecular tomography (FMT), as a powerful imaging technique in preclinical research, can offer the three-dimensional distribution of biomarkers by detecting the fluorescently labelled probe noninvasively. However, because of the light scattering effect and the ill-pose of inverse problem, it is challenging to develop an efficient reconstruction method, which can provide accurate location and morphology of the fluorescence distribution. In this research, we proposed a novel adaptive Gaussian weighted Laplace prior (AGWLP) regularization method, which assumed the variance of fluorescence intensity between any two voxels had a non-linear correlation with their Gaussian distance. It utilized an adaptive Gaussian kernel parameter strategy to achieve accurate morphological reconstructions in FMT. To evaluate the performance of the AGWLP method, we conducted numerical simulation and in vivo experiments. The results were compared with fast iterative shrinkage (FIS) thresholding method, split Bregman-resolved TV (SBRTV) regularization method, and Gaussian weighted Laplace prior (GWLP) regularization method. We validated in vivo imaging results against planar fluorescence images of frozen sections. The results demonstrated that the AGWLP method achieved superior performance in both location and shape recovery of fluorescence distribution. This enabled FMT more suitable and practical for in vivo visualization of biomarkers.

Harnessing the Power of Optical Microscopic and Macroscopic Imaging for Natural Products as Cancer Therapeutics

Natural products (NPs) are an important source for new drug discovery over the past decades, which have been demonstrated to be effectively used in cancer prevention, treatment, and adjuvant therapy. Many methods, such as the genomic and metabolomic approaches, immunochemistry, mass spectrometry, and chromatography, have been used to study the effects of NPs on cancer as well as themselves. Because of the advantages in specificity, sensitivity, high throughput, and cost-effectiveness, optical imaging (OI) approaches, including optical microscopic imaging and macroscopic imaging techniques have also been applied in the studies of NPs. Optical microscopic imaging can observe NPs as cancer therapeutics at the cellular level and analyze its cytotoxicity and mechanism of action. Optical macroscopic imaging observes the distribution, metabolic pathway, and target lesions of NPs in vivo, and evaluates NPs as cancer therapeutics at the whole-body level in small living animals. This review focuses on the recent advances in NPs as cancer therapeutics, with particular emphasis on the powerful use of optical microscopic and macroscopic imaging techniques, including the studies of observation of ingestion by cells, anticancer mechanism, and in vivo delivery. Finally, we prospect the wider application and future potential of OI approaches in NPs as cancer therapeutics.

Activatable molecular agents for cancer theranostics

Theranostics that integrates diagnosis and treatment modalities has attracted great attention due to its abilities of personalized therapy and real-time monitoring of therapeutic outcome. Such a theranostic paradigm requires agents to simultaneously possess the capabilities of targeting, imaging, and treatment. Activatable molecular agents (AMAs) are promising for cancer theranostics, as they show a higher signal-to-noise ratio (SNR), real-time detection of cancer-associated biomarkers, lower normal tissue toxicity, and a higher therapeutic effect. This perspective summarizes the recent advancements of AMAs, which include imaging-guided chemotherapy, imaging-guided photodynamic therapy, and imaging-guided photothermal therapy. The molecular design principles, theranostic mechanisms, and biomedical applications of AMAs are described, followed by a discussion of potential challenges of AMAs in cancer theranostics.

Improved Block Sparse Bayesian Learning Method Using K-Nearest Neighbor Strategy for Accurate Tumor Morphology Reconstruction in Bioluminescence Tomography

OBJECTIVE

Bioluminescence tomography (BLT) is a non-invasive technique designed to enable three-dimensional (3D) visualization and quantification of viable tumor cells in living organisms. However, despite the excellent sensitivity and specificity of bioluminescence imaging (BLI), BLT is limited by the photon scattering effect and ill-posed inverse problem. If the complete structural information of a light source is considered when solving the inverse problem, reconstruction accuracy will be improved.

METHODS

This article proposed a block sparse Bayesian learning method based on K-nearest neighbor strategy (KNN-BSBL), which incorporated several types of a priori information including sparsity, spatial correlations among neighboring points, and anatomical information to balance over-sparsity and morphology preservation in BLT. Furthermore, we considered the Gaussian weighted distance prior in a light source and proposed a KNN-GBSBL method to further improve the performance of KNN-BSBL.

RESULTS

The results of numerical simulations and in vivo glioma-bearing mouse experiments demonstrated that KNN-BSBL and KNN-GBSBL achieved superior accuracy for tumor spatial positioning and morphology reconstruction.

CONCLUSION

The proposed method KNN-BSBL incorporated several types of a priori information is an efficient and robust reconstruction method for BLT.

In vivo three-dimensional evaluation of tumour hypoxia in nasopharyngeal carcinomas using FMT-CT and MSOT

Purpose

Accurate evaluation of hypoxia is particularly important in patients with nasopharyngeal carcinoma (NPC) undergoing radiotherapy. The aim of this study was to propose a novel imaging strategy for quantitative three-dimensional (3D) evaluation of hypoxia in a small animal model of NPC.

Methods

A carbonic anhydrase IX (CAIX)-specific molecular probe (CAIX-800) was developed for imaging of hypoxia. Mouse models of subcutaneous, orthotopic, and spontaneous lymph node metastasis from NPC (5 mice per group) were established to assess the imaging strategy. A multi-modality imaging method that consisted of a hybrid combination of fluorescence molecular tomography-computed tomography (FMT-CT) and multispectral optoacoustic tomography (MSOT) was used for 3D quantitative evaluation of tumour hypoxia. Magnetic resonance imaging, histological examination, and immunohistochemical analysis were used as references for comparison and validation.

Results

In the early stage of NPC (2 weeks after implantation), FMT-CT enabled precise 3D localisation of the hypoxia biomarker with high sensitivity. At the advanced stage (6 weeks after implantation), MSOT allowed multispectral analysis of the biomarker and haemoglobin molecules with high resolution. The combination of high sensitivity and high resolution from FMT-CT and MSOT could not only detect hypoxia in small-sized NPCs but also visualise the heterogeneity of hypoxia in 3D.

Conclusions

Integration of FMT-CT and MSOT could allow comprehensive and quantifiable evaluation of hypoxia in NPC. These findings may potentially benefit patients with NPC undergoing radiotherapy in the future.

Graphical abstract