John A. Hossack

We developed a safe and effective pulsed ultrasound (pUS) protocol targeting the mouse spleen to block inflammation and reduce AKI of multiple etiologies. By using a model of the AKI to CKD transition, we demonstrated the long-term benefits of pUS. The findings of these studies will be used to advance the human translation of spleen-targeted US as a preventative measure for AKI and CKD.

Ultrasound localization microscopy (ULM) enables super-resolution ultrasound (SRUS) imaging of microvasculature, while ultrasound molecular imaging (USMI) characterizes molecular signatures using microbubbles (MBs) targeted to specific biomarkers. Although the co-localization of SRUS and USMI has been demonstrated previously, USMI resolution is limited by ultrasound diffraction-based effects and does not match the super-resolved microvasculature. This study introduces the Incremental Burst Sequence (IBS) method to induce the population of polydisperse targeted MBs to burst progressively, achieving MBs spatial separation and enabling high-resolution USMI (HR-USMI) localization. IBS method employs interleaved imaging and bursting pulses, with transmit voltages of bursting pulses incrementally increased to produce a gradual rise in the acoustic pressure. IBS is first validated optically in vitro using a cellulose tubing phantom, and MB remaining count during IBS is measured. Thereafter, in vivo validation is performed in a murine tumor model, and the intra-tumoral targeted MB signal intensity is measured during IBS. Furthermore, high frame-rate data for SRUS and IBS data for HR-USMI are acquired from a single bolus injection of MBs to generate composite images with high-resolution molecular signatures superimposed on the tumor microvasculature. Both in vitro and in vivo results validate the technical feasibility of the proposed IBS method. In addition, we demonstrate that higher bursting pulse repetitions lead to a faster disruption of the MB population during IBS. Finally, HR-USMI signals localized within a 50 μm × 50 μm grid are aligned with microvessels resolved better than 100 μm, presenting a combination of molecular signatures and anatomical structures at fine resolution.

Objective: Pancreatic adenocarcinoma (PDAC) tumors are often unresectable and do not respond to standard anti-cancer treatments. Boiling histotripsy (BH) is a mechanical focused ultrasound ablation regimen that can target non-operable tumors. BH is a non-invasive procedure that might synergize with immunotherapies being developed for PDAC. We reasoned that BH-mediated release of tumor antigen and damage-associated molecular patterns would augment tumor immunity and cooperate with α-CD40 therapy. Methods: We explored the efficacy of BH ablation either as monotherapy for PDAC or in combination with systemically administered α-CD40 agonistic antibodies in controlling tumor outgrowth. We further assessed the changes in the tumor immune compartment and the ability of BH to release tumor antigens by flow cytometry. Results: A single BH treatment could not control tumor growth and had limited independent immunostimulatory properties. BH effectively liberated tumor antigen into the tumor microenvironment for acquisition by local phagocytes but did not promote its presence in the tumor-draining lymph nodes. BH did not activate either tumor- or lymph node-resident conventional dendritic cells. BH did not impede the ability of α-CD40 immunotherapy to reduce the tumor burden and promote the infiltration of M1-like macrophages and IFN-γ⁺ CD8⁺ T cells to the tumor microenvironment, suggesting that antibody access to the ablated tissue was not obstructed. Conclusion: Our findings indicate that PDAC tumor progression cannot be halted by BH ablation using sub-total ablation, and that the BH treatment regimen utilized in this study has limited immunogenicity. Significance: Our discoveries attest to the need for optimizing BH ablation protocols to unlock its anti-tumor potential.

The past decade has produced a sequence of breakthroughs in imaging that uses both light and sound for signal transmission. Photoacoustic imaging is a prime example with major advances in both the optical and ultrasonic pathways. While the range of possibilities in the optical pathway design is limited by the applicable physics, many innovations are occurring in the ultrasound signal processing pathway. The use of artificial intelligence (AI) in the image reconstruction process is poised to significantly impact photoacoustic imaging. Other innovations, including more versatile system designs, novel transducers, and advanced image reconstruction, are significantly enhancing the capabilities of photoacoustic imaging. The research community has also witnessed a rapid evolution calling upon the new and unique sources of contrast offered by photoacoustic imaging combined with further development of photoacoustic contrast agents. These innovations have provided an approach to monitor the accumulation and distribution of therapeutic agents. Together, innovations contributing to the improved performance of photoacoustic imaging are facilitating pilot studies in both animal models and humans to prepare for the clinical use of photoacoustic imaging in the evaluation of arthritis, skin ulcers, neurovascular and cardiovascular function, and placental vasculature. To highlight these important research activities, the Spotlight Issue on Frontiers in Photoacoustic Imaging has featured 11 articles that cover a broad range of scientific advances on this emerging imaging modality.

Objectives: The objective of this study is to validate the modulated acoustic radiation force (mARF)–based imaging method in the detection of abdominal aortic aneurysm (AAA) in murine models using vascular endothelial growth factor receptor 2 (VEGFR-2)–targeted microbubbles (MBs). Materials and Methods: The mouse AAA model was prepared using the subcutaneous angiotensin II (Ang II) infusion combined with the β-aminopropionitrile monofumarate solution dissolved in drinking water. The ultrasound imaging session was performed at 7 days, 14 days, 21 days, and 28 days after the osmotic pump implantation. For each imaging session, 10 C57BL/6 mice were implanted with Ang II–filled osmotic pumps, and 5 C57BL/6 mice received saline infusion only as the control group. Biotinylated lipid MBs conjugated to either anti–mouse VEGFR-2 antibody (targeted MBs) or isotype control antibody (control MBs) were prepared before each imaging session and were injected into mice via tail vein catheter. Two separate transducers were colocalized to image the AAA and apply ARF to translate MBs simultaneously. After each imaging session, tissue was harvested and the aortas were used for VEGFR-2 immunostaining analysis. From the collected ultrasound image data, the signal magnitude response of the adherent targeted MBs was analyzed, and a parameter, residual-to-saturation ratio (R _{res − sat} ), was defined to measure the enhancement in the adherent targeted MBs signal after the cessation of ARF compared with the initial signal intensity. Statistical analysis was performed with the Welch t test and analysis of variance test. Results: The R _{res − sat} of abdominal aortic segments from Ang II–challenged mice was significantly higher compared with that in the saline-infused control group (P < 0.001) at all 4 time points after osmotic pump implantation (1 week to 4 weeks). In control mice, the R _{res − sat} values were 2.13%, 1.85%, 3.26%, and 4.85% at 1, 2, 3, and 4 weeks postimplantation, respectively. In stark contrast, the R _{res − sat} values for the mice with Ang II–induced AAA lesions were 9.20%, 20.6%, 22.7%, and 31.8%, respectively. It is worth noting that there was a significant difference between the R _{res − sat} for Ang II–infused mice at all 4 time points (P < 0.005), a finding not present in the saline-infused mice. Immunostaining results revealed the VEGFR-2 expression was increased in the abdominal aortic segments of Ang II–infused mice compared with the control group. Conclusions: The mARF-based imaging technique was validated in vivo using a murine model of AAA and VEGFR-2–targeted MBs. Results in this study indicated that the mARF-based imaging technique has the ability to detect and assess AAA growth at early stages based on the signal intensity of adherent targeted MBs, which is correlated with the expression level of the desired molecular biomarker. The results may suggest, in very long term, a pathway toward eventual clinical implementation for an ultrasound molecular imaging–based approach to AAA risk assessment in asymptomatic patients.