Synthesis of ultrasound contrast agents: characteristics and size distribution analysis (secondary publication)

Tailoring biomaterials for monitoring and evoking tertiary lymphoid structures

Despite the remarkable clinical success of immune checkpoint blockade (ICB) in the treatment of cancer, the response rate to ICB therapy remains suboptimal. Recent studies have strongly demonstrated that intratumoral tertiary lymphoid structures (TLSs) are associated with a good prognosis and a successful clinical response to immunotherapy. However, there is still a shortage of efficient and wieldy approaches to image and induce intratumoral TLSs in vivo. Biomaterials have made great strides in overcoming the deficiencies of conventional diagnosis and therapies for cancer, and antitumor therapy has also benefited from biomaterial-based drug delivery models. In this review, we summarize the reported methods for TLS imaging and induction based on biomaterials and provide potential strategies that can further enhance the effectiveness of imaging and stimulating intratumoral TLSs to predict and promote the response rates of ICB therapies for patients. STATEMENT OF SIGNIFICANCE: In this review, we focused on the promising of biomaterials for imaging and induction of TLSs. We reviewed the applications of biomaterials in molecular imaging and immunotherapy, identified the biomaterials that may be suitable for TLS imaging and induction, and provided outlooks for further research. Accurate imaging and effective induction of TLSs are of great significance for understanding the mechanism and clinical application. We highlighted the need for multidisciplinary coordination and cooperation in this field, and proposed the possible future direction of noninvasive imaging and artificial induction of TLSs based on biomaterials. We believe that it can facilitate collaboration and galvanize a broader effort.

Contrast-enhanced ultrasound-based ultrasomics score: a potential biomarker for predicting early recurrence of hepatocellular carcinoma after resection or ablation

OBJECTIVES

This study aimed to construct a prediction model based on contrast-enhanced ultrasound (CEUS) ultrasomics features and investigate its efficacy in predicting early recurrence (ER) of primary hepatocellular carcinoma (HCC) after resection or ablation.

METHODS

This study retrospectively included 215 patients with primary HCC, who were divided into a developmental cohort (n = 139) and a test cohort (n = 76). Four representative images-grayscale ultrasound, arterial phase, portal venous phase and delayed phase-were extracted from each CEUS video. Ultrasomics features were extracted from tumoral and peritumoral area inside the region of interest. Logistic regression was used to establish models, including a tumoral model, a peritumoral model and a combined model with additional clinical risk factors. The performance of the three models in predicting recurrence within 2 years was verified.

RESULTS

The combined model performed best in predicting recurrence within 2 years, with an area under the curve (AUC) of 0.845, while the tumoral model had an AUC of 0.810 and the peritumoral model one of 0.808. For prediction of recurrence-free survival, the 2-year cumulative recurrence rate was significant higher in the high-risk group (76.5%) than in the low-risk group (9.5%; p < 0.0001).

CONCLUSION

These CEUS ultrasomics models, especially the combined model, had good efficacy in predicting early recurrence of HCC. The combined model has potential for individual survival assessment for HCC patients undergoing resection or ablation.

ADVANCES IN KNOWLEDGE

CEUS ultrasomics had high sensitivity, specificity and PPV in diagnosing early recurrence of HCC, and high efficacy in predicting early recurrence of HCC (AUC > 0.8). The combined model performed better than the tumoral ultrasomics model and peritumoral ultrasomics model in predicting recurrence within 2 years. Recurrence was more likely to occur in the high-risk group than in the low-risk group, with 2-year cumulative recurrence rates, respectively, 76.5% and 9.5% (p < 0.0001).

Biological Utility of Fluorinated Compounds: from Materials Design to Molecular Imaging, Therapeutics and Environmental Remediation

The applications of fluorinated molecules in bioengineering and nanotechnology are expanding rapidly with the controlled introduction of fluorine being broadly studied due to the unique properties of C-F bonds. This review will focus on the design and utility of C-F containing materials in imaging, therapeutics, and environmental applications with a central theme being the importance of controlling fluorine-fluorine interactions and understanding how such interactions impact biological behavior. Low natural abundance of fluorine is shown to provide sensitivity and background advantages for imaging and detection of a variety of diseases with ¹⁹F magnetic resonance imaging, ¹⁸F positron emission tomography and ultrasound discussed as illustrative examples. The presence of C-F bonds can also be used to tailor membrane permeability and pharmacokinetic properties of drugs and delivery agents for enhanced cell uptake and therapeutics. A key message of this review is that while the promise of C-F containing materials is significant, a subset of highly fluorinated compounds such as per- and polyfluoroalkyl substances (PFAS), have been identified as posing a potential risk to human health. The unique properties of the C-F bond and the significant potential for fluorine-fluorine interactions in PFAS structures necessitate the development of new strategies for facile and efficient environmental removal and remediation. Recent progress in the development of fluorine-containing compounds as molecular imaging and therapeutic agents will be reviewed and their design features contrasted with environmental and health risks for PFAS systems. Finally, present challenges and future directions in the exploitation of the biological aspects of fluorinated systems will be described.

19 F MRI Probes for Multimodal Imaging*

Magnetic resonance imaging (MRI) is one of the most powerful imaging tools today, capable of displaying superior soft-tissue contrast. This review discusses developments in the field of ¹⁹ F MRI multimodal probes in combination with optical fluorescence imaging (OFI), ¹ H MRI, chemical exchange saturation transfer (CEST) MRI, ultrasonography (USG), X-ray computed tomography (CT), single photon emission tomography (SPECT), positron emission tomography (PET), and photoacoustic imaging (PAI). In each case, multimodal ¹⁹ F MRI probes compensate for the deficiency of individual techniques and offer improved sensitivity or accuracy of detection over unimodal counterparts. Strategies for designing ¹⁹ F MRI multimodal probes are described with respect to their structure, physicochemical properties, biocompatibility, and the quality of images.

Human microvascular reactivity: a review of vasomodulating stimuli and non-invasive imaging assessment

The microvasculature serves an imperative function in regulating perfusion and nutrient exchange throughout the body, adaptively altering blood flow to preserve hemodynamic and metabolic homeostasis. Its normal functioning is vital to tissue health, whereas its dysfunction is present in many chronic conditions, including diabetes, heart disease, and cognitive decline. As microvascular dysfunction often appears early in disease progression, its detection can offer early diagnostic information. To detect microvascular dysfunction, one uses imaging to probe the microvasculature's ability to react to a stimulus, also known as microvascular reactivity (MVR). An assessment of MVR requires an integrated understanding of vascular physiology, techniques for stimulating reactivity, and available imaging methods to capture the dynamic response. Practical considerations, including compatibility between the selected stimulus and imaging approach, likewise require attention. In this review, we provide a comprehensive foundation necessary for informed imaging of MVR, with a particular focus on the challenging endeavor of assessing microvascular function in deep tissues.

The Impact of Lipid Handling and Phase Distribution on the Acoustic Behavior of Microbubbles

Phospholipid-coated microbubbles are ultrasound contrast agents that can be employed for ultrasound molecular imaging and drug delivery. For safe and effective implementation, microbubbles must respond uniformly and predictably to ultrasound. Therefore, we investigated how lipid handling and phase distribution affected the variability in the acoustic behavior of microbubbles. Cholesterol was used to modify the lateral molecular packing of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-based microbubbles. To assess the effect of lipid handling, microbubbles were produced by a direct method, i.e., lipids directly dispersed in an aqueous medium or indirect method, i.e., lipids first dissolved in an organic solvent. The lipid phase and ligand distribution in the microbubble coating were investigated using confocal microscopy, and the acoustic response was recorded with the Brandaris 128 ultra-high-speed camera. In microbubbles with 12 mol% cholesterol, the lipids were miscible and all in the same phase, which resulted in more buckle formation, lower shell elasticity and higher shell viscosity. Indirect DSPC microbubbles had a more uniform response to ultrasound than direct DSPC and indirect DSPC-cholesterol microbubbles. The difference in lipid handling between direct and indirect DSPC microbubbles significantly affected the acoustic behavior. Indirect DSPC microbubbles are the most promising candidate for ultrasound molecular imaging and drug delivery applications.

Assessment of the Superharmonic Response of Microbubble Contrast Agents for Acoustic Angiography as a Function of Microbubble Parameters

Acoustic angiography is a superharmonic contrast-enhanced ultrasound imaging technique that enables 3-D high-resolution microvascular visualization. This technique utilizes a dual-frequency imaging strategy, transmitting at a low frequency and receiving at a higher frequency, to detect high-frequency contrast agent signatures and separate them from tissue background. Prior studies have illustrated differences in microbubble scatter dependent on microbubble size and composition; however, most previously reported data have utilized a relatively narrow frequency bandwidth centered around the excitation frequency. To date, a comprehensive study of isolated microbubble superharmonic responses with a broadband dual-frequency system has not been performed. Here, the superharmonic signal production of 14 contrast agents with various gas cores, shell compositions, and bubble diameters at mechanical indices of 0.2 to 1.2 was evaluated using a transmit 4 MHz, receive 25 MHz configuration. Results indicate that perfluorocarbon cores or lipid shells with 18- or 20-carbon acyl chains produce more superharmonic signal than sulfur hexafluoride cores or lipid shells with 16-carbon acyl chains, respectively. As microbubble diameter increases from 1 to 4 µm, superharmonic generation decreases. In a comparison of two clinical agents, Definity and Optison, and one preclinical agent, Micromarker, Optison produced the least superharmonic signal. Overall, this work suggests that microbubbles around 1 μm in diameter with perfluorocarbon cores and longer-chained lipid shells perform best for superharmonic imaging at 4 MHz. Studies have found that microbubble superharmonic response follows trends different from those described in prior studies using a narrower frequency bandwidth centered around the excitation frequency. Future work will apply these results in vivo to optimize the sensitivity of acoustic angiography.

Phase Change Ultrasound Contrast Agents with a Photopolymerized Diacetylene Shell

Phase change contrast agents for ultrasound (US) imaging consist of nanodroplets (NDs) with a perfluorocarbon (PFC) liquid core stabilized with a lipid or a polymer shell. Liquid ↔ gas transition, occurring in the core, can be triggered by US to produce acoustically active microbubbles (MBs) in a process named acoustic droplet vaporization (ADV). MB shells containing polymerized diacetylene moiety were considered as a good trade off between the lipid MBs, showing optimal attenuation, and the polymeric ones, displaying enhanced stability. This work reports on novel perfluoropentane and perfluorobutane NDs stabilized with a monolayer of an amphiphilic fatty acid, i.e. 10,12-pentacosadiynoic acid (PCDA), cured with ultraviolet (UV) irradiation. The photopolymerization of the diacetylene groups, evidenced by the appearance of a blue color due to the conjugation of ene-yne sequences, exhibits a chromatic transition from the nonfluorescent blue color to a fluorescent red color when the NDs are heated or the pH of the suspension is basic. An estimate of the molecular weights reached by the polymerized PCDA in the shell, poly(PCDA), has been obtained using gel permeation chromatography and MALDI-TOF mass spectrometry. The poly(PCDA)/PFC NDs show good biocompatibility with fibroblast cells. ADV efficiency and acoustic properties before and after the transition were tested using a 1 MHz probe, revealing a resonance frequency between 1 and 2 MHz similar to other lipidic MBs. The surface of PCDA shelled NDs can be easily modified without influencing the stability and the acoustic performances of droplets. As a proof of concept we report on the conjugation of cyclic RGD and PEG chains of the particles to support targeting ability toward endothelial cells.

Multicore Liquid Perfluorocarbon-Loaded Multimodal Nanoparticles for Stable Ultrasound and 19F MRI Applied to In Vivo Cell Tracking

Ultrasound is the most commonly used clinical imaging modality. However, in applications requiring cell-labeling, the large size and short active lifetime of ultrasound contrast agents limit their longitudinal use. Here, 100 nm radius, clinically applicable, polymeric nanoparticles containing a liquid perfluorocarbon, which enhance ultrasound contrast during repeated ultrasound imaging over the course of at least 48 h, are described. The perfluorocarbon enables monitoring the nanoparticles with quantitative 19F magnetic resonance imaging, making these particles effective multimodal imaging agents. Unlike typical core-shell perfluorocarbon-based ultrasound contrast agents, these nanoparticles have an atypical fractal internal structure. The nonvaporizing highly hydrophobic perfluorocarbon forms multiple cores within the polymeric matrix and is, surprisingly, hydrated with water, as determined from small-angle neutron scattering and nuclear magnetic resonance spectroscopy. Finally, the nanoparticles are used to image therapeutic dendritic cells with ultrasound in vivo, as well as with 19F MRI and fluorescence imaging, demonstrating their potential for long-term in vivo multimodal imaging.