Despite advances in cancer immunotherapy, efficacy has been limited to a subset of patients, highlighting the need for continued development of innovative therapeutic approaches. Perfluorocarbon-filled (PFC) particles, due to unique physicochemical properties, biological stability, and quantifiability as 19F-MRI tracers, have been intensely investigated as in vivo macrophage imaging agents. Despite this, little is known about the effect of PFC particle uptake on macrophage behavior. Here, phospholipid-stabilized perfluorohexane (PFH) nanodroplets (NDs) were used to treat bone-marrow-derived macrophages (BMDMs) in vitro and tumor-implanted mice in vivo. Physiological response was assessed by using biochemistry, flow cytometry, fluorescence imaging, and tumor measurements. The incubation of alternatively-activated (M2) BMDMs with PFH NDs led to a dose- and time-dependent increase of iNOS expression but not that of other common M1 or M2 markers. PFH ND-induced iNOS expression was further enhanced when treated M2 BMDMs were co-cultured with MC38 murine colon carcinoma cells, resulting in more effective tumoral cell apoptosis. Similarly, intratumoral injection of PFH NDs in a murine colon carcinoma model led to increased iNOS expression within the tumors and caused a substantial decrease in tumor size. This size reduction was also unexpectedly accompanied by the formation of peritumoral gas pockets, which, when aspirated, abrogated tumoral effects. Conversely, intratumoral injection of emulsions made with high-boiling-point (BP = 142 °C) perfluorooctyl bromide (PFOB) did not produce gas pockets or inhibit tumor growth. Our data collectively show the immunogenic potential of PFH NDs through iNOS expression and promote the potential development of theranostic PFC-based platforms.

Objective: We have previously determined that direct formulation of a phospholipid-based perfluorobutane (PFB) emulsion using high-pressure homogenization produces monodispersed PFB nanodroplets (NDs) with relatively few non-PFB-filled NDs. In this article, we describe a simpler strategy to reproducibly formulate highly concentrated superheated PFB NDs using a probe sonicator, a more widely available tool. Methods: Similar to the homogenization technique, sonicating at low power a solution of phospholipids with condensed PFB at -10 degrees C consistently yields NDs with an encapsulation efficiency close to 100% and very few non-PFB-filled particles. Results: The PFB emulsion is stable with absence of spontaneous vaporization at 37 degrees C and for more than 14 d when frozen or refrigerated and for 3 d at 25 degrees C. Acoustic droplet vaporization (ADV) occurred at a mechanical index >0.5 and continued to increase thereafter. The ADV threshold was similar for freshly made or frozen emulsion after thawing. In contrast to the microbubble (MB) condensation method, in which the ratio of non-PFB-filled to PFB-filled is 2000:1, particularly if MBs are not washed after formulation, nearly 94% of particles produced by direct sonication are PFB filled. Conclusion: PFB NDs can be manufactured with high yield, stability and reproducibility using a probe sonicator that is available in many laboratories. Their ease of manufacture could spark discoveries into highly impactful ND-based diagnostic and therapeutic applications.

Activatable microbubble contrast agents for contrast-enhanced ultrasound have a potential role for measuring physiologic and pathologic states in deep tissues, including tumor acidosis. In this study, we describe a novel observation of increased harmonic oscillation of phosphatidylcholine microbubbles (PC-MBs) in response to lower ambient pH using a clinical ultrasound scanner. MB echogenicity and nonlinear echoes were monitored at neutral and acidic pH using B-mode and Cadence contrast pulse sequencing (CPS), a harmonic imaging technique at 7.0 and 1.5 MHz. A 3-fold increase in harmonic signal intensity was observed when the pH of PC-MB suspensions was decreased from 7.4 to 5.5 to mimic normal and pathophysiological levels that can be encountered in vivo. This pH-mediated activation is tunable based on the chemical structure and length of phospholipids composing the MB shell. It is also reliant on the presence of phosphate groups, as the use of lipids without phosphate instead of phospholipids completely abrogated this phenomenon. The increased harmonic signal likely is the result of increased MB oscillation caused by a decrease of the interfacial tension induced at a lower pH, altering the lipid conformation. While relative signal changes are interpreted clinically as mostly related to blood flow, pH effects could be significant contributors, particularly when imaging tumors. While our observation can be used clinically, it requires further research to isolate the effect of pH from other variables. These findings could pave the way toward for the development of new smart ultrasound contrast agents that expand the clinical utility of contrast-enhanced ultrasound.

Background and Significance: Exercise intolerance and dyspnea on exertion (DOE) are frequent after pulmonary embolism (PE) despite anticoagulation and may impact quality of life. There is little research that fully explains why this occurs, nor are there specific treatments or guidelines for PE complications in children or young adults. The FUVID Program (NCT04583878) will examine the impact of 3 mechanisms underlying exercise intolerance and DOE: cardiac (right ventricular maladaptation and its coupling with the pulmonary circulation) dysfunction, pulmonary limitations secondary to persistent vascular obstruction, and skeletal muscle metabolic abnormalities on exercise intolerance and DOE after PE. Study Design and Methods: This prospective, multi-center, observational study is enrolling previously healthy patients ages 8-21 years with acute, first-episode PE with or without DVT. A positive control group with no PE but with physical activity restrictions mimicking a deconditioning effect as patients with PE (cohort 1) and control group with no prescribed physical activity restrictions and otherwise considered healthy (cohort 2) will be enrolled. Patients will be enrolled within 8 weeks of diagnosis of PE from 13 enrollment and 25 recruitment sites across the US. Due to the complexity of the cutting-edge metabolic and functional tools only available at UTSW (namely, MR spectroscopy at 7 Telsa to study in-vivo muscle metabolic function and perfusion and exercise cardiac MRI), research assessments will occur centrally at 3- and 12-months post-diagnosis. Exercise capacity will be defined as peak oxygen uptake (VO2), expressed as a percent predicted based on ideal body weight during cardiopulmonary exercise testing. The primary comparison will be between participants with and without exercise intolerance. Key secondary subgroup analyses will include: sex (male/female), PE category (low risk/non-low-risk), and thrombolysis (yes/no). Results/Discussion: We have enrolled 67 PE participants (planned=80) from participating enrollment sites and 30 case-controls (planned=30). We propose that 1) the right ventricle will be unable to overcome afterload placed on it during exercise, preventing optimal coupling with pulmonary circulation, 2) arterial desaturation during maximal cycling exercise combined with dysfunctional breathing of deconditioning will provoke greater DOE and intolerance, and 3) depletion and recovery of muscle phosphocreatine in-vivo will predict exercise intolerance. Our results will provide critically informative data to phenotype pediatric post-PE syndrome accurately and allow investigation of cardiac, vascular, and musculoskeletal mechanisms associated with post-PE syndrome assessed during exercise.

This talk will describe a simple and robust method to produce perfluorobutane (PFB) nanodroplets by direct sonication, and will compare the properties of the resultant emulsions with those obtained with the current advocated microbubble condensation method. We found that nearly 100% of particles produced by direct emulsification of PFB liquid at low temperature are liquid PFB-filled, whereas the emulsion produced by microbubble condensation if the microbubbles are not washed, contains 2000 times more non-PFB filled than PFB-filled particles. Consequently, when such suspensions are used to target receptors, the abundance of non-PFB particles will act as competitive inhibitors, and when used to extravasate to reach extravascular targets, the lower count of PFB-filled particles will require larger doses decreasing efficacy and increasing side effects. Adopting this direct formulation could be a game changer for all applications when experimental outcome is dependent on nanodroplet concentration, stability, purity and size. As a result, this method should accelerate the translation of these ultrasound activatable nanodroplets to both image and potentially treat diseased tissues.

Activating patients' immune cells, either by reengineering them or treating them with bioactive molecules, has been a breakthrough in the field of immunotherapy and has revolutionized treatment, especially against cancer. As immune cells naturally home to tumors or injured tissues, labeling such cells holds promise for non-invasive tracking and biologic manipulation. Our study demonstrates that macrophages loaded with extremely low boiling point perfluorocarbon nanodroplets not only survive ultrasound-induced phase change but also maintain their phagocytic function. Unlike observations made when using higher boiling point perfluorocarbon nanodroplets, our results show that phase change occurs intracellularly at a low mechanical index using a clinical scanner operating within the energy limit set by the Food and Drug Administration (FDA). After nanodroplet-loaded macrophages were given intravenously to nude rats, they were invisible in the liver when imaged at a very low mechanical index using a clinical ultrasound scanner. They became visible when power was increased but still within the FDA limits up to 8 h after administration. The acoustic labeling and in vivo detection of macrophages using a clinical ultrasound scanner represent a paradigm shift in the field of cell tracking and pave the way for potential therapeutic strategies in the clinical setting.

Background Contrast-enhanced (CE) US has been studied for use in the detection of residual viable hepatocellular carcinoma (HCC) after locoregional therapy, but multicenter data are lacking. Purpose To compare two-dimensional (2D) and three-dimensional (3D) CE US diagnostic performance with that of CE MRI or CT, the current clinical standard, in the detection of residual viable HCC after transarterial chemoembolization (TACE) in a prospective multicenter trial. Materials and Methods Participants aged at least 21 years with US-visible HCC scheduled for TACE were consecutively enrolled at one of three participating academic medical centers from May 2016 to March 2022. Each underwent baseline 2D and 3D CE US before TACE, 2D and 3D CE US 1-2 weeks and/or 4-6 weeks after TACE, and CE MRI or CT 4-6 weeks after TACE. CE US and CE MRI or CT were evaluated by three fellowship-trained radiologists for the presence or absence of viable tumors and were compared with reference standards of pathology (18%), angiography on re-treatment after identification of residual disease at 1-2-month follow-up imaging (31%), 4-8-month CE MRI or CT (42%), or short-term (approximately 1-2 months) CE MRI or CT if clinically decompensated and estimated viability was greater than 50% at imaging (9%). Diagnostic performance criteria, including sensitivity and specificity, were obtained for each modality and time point with generalized estimating equation analysis. Results A total of 132 participants were included (mean age, 64 years ± 7 [SD], 87 male). Sensitivity of 2D CE US 4-6 weeks after TACE was 91% (95% CI: 84, 95), which was higher than that of CE MRI or CT (68%; 95% CI: 58, 76; P < .001). Sensitivity of 3D CE US 4-6 weeks after TACE was 89% (95% CI: 81, 94), which was higher than that of CE MRI or CT (P < .001), with no evidence of a difference from 2D CE US (P = .22). CE MRI or CT had 85% (95% CI: 76, 91) specificity, higher than that of 4-6-week 2D and 3D CE US (70% [95% CI: 56, 80] and 67% [95% CI: 53, 78], respectively; P = .046 and P = .023, respectively). No evidence of differences in any diagnostic criteria were observed between 1-2-week and 4-6-week 2D CE US (P > .21). Conclusion The 2D and 3D CE US examinations 4-6 weeks after TACE revealed higher sensitivity in the detection of residual HCC than CE MRI or CT, albeit with lower specificity. Importantly, CE US performance was independent of follow-up time. Clinical trial registration no. NCT02764801 © RSNA, 2023 Supplemental material is available for this article.

The cytosolic innate immune sensor cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is crucial for priming adaptive antitumour immunity through antigen-presenting cells (APCs). Natural agonists, such as cyclic dinucleotides (CDNs), activate the cGAS-STING pathway, but their clinical translation is impeded by poor cytosolic entry and serum stability, low specificity and rapid tissue clearance. Here we developed an ultrasound (US)-guided cancer immunotherapy platform using nanocomplexes composed of 2'3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) electrostatically bound to biocompatible branched cationic biopolymers that are conjugated onto APC-targeting microbubbles (MBs). The nanocomplex-conjugated MBs engaged with APCs and efficiently delivered cGAMP into the cytosol via sonoporation, resulting in activation of cGAS-STING and downstream proinflammatory pathways that efficiently prime antigen-specific T cells. This bridging of innate and adaptive immunity inhibited tumour growth in both localized and metastatic murine cancer models. Our findings demonstrate that targeted local activation of STING in APCs under spatiotemporal US stimulation results in systemic antitumour immunity and improves the therapeutic efficacy of checkpoint blockade, thus paving the way towards novel image-guided strategies for targeted immunotherapy of cancer.

Enzymes are biological catalysts that have many potential industrial and biomedical applications. However, the widespread use of enzymes in the industry has been limited by their instability and poor recovery. In biomedical applications, systemic administration of enzymes has faced two main challenges: limited bioactivity mostly due to rapid degradation by proteases and immunogenic activity, since most enzymes are from nonhuman sources. Herein, we propose a robust enzyme-encapsulation strategy to mitigate these limitations. Catalase (CAT) was encapsulated in nanoporous silica nanoparticles (CAT-SiNPs) by first chemically modifying the enzyme surface with a silica precursor, followed by silica growth and finally poly(ethylene glycol) (PEG) conjugation. The formulation was carried out in mild aqueous conditions and yielded nanoparticles (NPs) with a mean diameter of 230 ± 10 nm and a concentration of 1.3 ± 0.8 × 1012 NPs/mL. CAT-SiNPs demonstrated high enzyme activity, optimal protection from proteolysis by proteinase K and trypsin, and excellent stability over time. In addition, a new electrochemical assay was developed to measure CAT activity in a rapid, simple, and accurate manner without interference from chromophore usually present in biological samples. Concentrations of 2.5 × 1010 to 80 × 1010 CAT-SiNPs/mL not only proved to be nontoxic in cell cultures using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay but also conferred cell protection when cells were exposed to 1 mM hydrogen peroxide (H2O2). Finally, the ability of CAT-SiNPs to release oxygen (O2) when exposed to H2O2 was demonstrated in vivo using a rat model. Following the direct injection of CAT-SiNPs in the left kidney, partial pressure of oxygen (pO2) increased by more than 30 mmHg compared to the contralateral control kidney during the systemic infusion of safe levels of H2O2. This pilot study highlights the potential of CAT-SiNPs to generate O2 to relieve hypoxia in tissues and potentially sensitize tumors against radiation therapy.

Breast cancer is the most frequent type of cancer among women. This multi-center study assessed the ability of 3D contrast-enhanced ultrasound to characterize suspicious breast lesions using clinical assessments and quantitative parameters.Women with suspicious breast lesions scheduled for biopsy were enrolled in this prospective, study. Following 2D grayscale ultrasound and power Doppler imaging (PDI), a contrast agent (Definity; Lantheus) was administrated. Contrast-enhanced 3D harmonic imaging (HI; transmitting/receiving at 5.0/10.0 MHz), as well as 3D subharmonic imaging (SHI; transmitting/receiving at 5.8/2.9 MHz), were performed using a modified Logiq 9 scanner (GE Healthcare). Five radiologists independently scored the imaging modes (including standard-of-care imaging) using a 7-point BIRADS scale as well as lesion vascularity and diagnostic confidence. Parametric volumes were constructed from time-intensity curves for vascular heterogeneity, perfusion, and area under the curve. Diagnostic accuracy was determined relative to pathology using receiver operating characteristic (ROC) and reverse, step-wise logistical regression analyses. The κ-statistic was calculated for inter-reader agreement.Data were successfully acquired in 219 cases and biopsies indicated 164 (75%) benign and 55 (25%) malignant lesions. SHI depicted more anastomoses and vascularity than HI (P < .021), but there were no differences by pathology (P > .27). Ultrasound achieved accuracies of 82 to 85%, which was significantly better than standard-of-care imaging (72%; P < .03). SHI increased diagnostic confidence by 3 to 6% (P < .05), but inter-reader agreements were medium to low (κ < 0.52). The best regression model achieved 97% accuracy by combining clinical reads and parametric SHI.Combining quantitative 3D SHI parameters and clinical assessments improves the characterization of suspicious breast lesions.

Contrast-enhanced sonography is a safe, radiation-free, and minimally invasive imaging technique. It takes advantage of the nonlinear behavior of microbubble contrast agents to produce microbubble-only images, which allows for the assessment of the extracranial carotid arteries, with a minuscule total dose of <1 mL. This review highlights the current status of extracranial carotid sonography imaging, including plaque characterization when using standard and contrast-enhanced sonography. Learning Objective: Describe risk factors associated with ischemic stroke and the associated imaging features and how contrast-enhanced sonography can provide direct evaluation for carotid artery stenosis as well as characterization of atherosclerotic plaque.

The innate immune sensor cyclic GMP–AMP synthase–stimulator of interferon genes (cGAS-STING) has recently emerged as a potential therapeutic target to boost antitumor immune responses. However, STING is a cytoplasmic protein, and its natural activator cGAMP is a negatively charged dinucleotide that is difficult to deliver intracellularly. We have developed a new platform called Microbubble-assisted UltraSound (US)-guided Immunotherapy of Cancer (MUSIC) to activate STING with spatio-temporal control to treat cancer. MUSIC showed greater STING activation compared to cGAMP alone in vitro. In murine models,MUSIC showed dramatic tumor growth inhibition and increased survival in both syngeneic breast cancer models. The absence of antitumor immune responses in STING-/- mice shows that MUSIC action is STING-dependent. Furthermore, 6/10 MUSIC-treated mice were tumor-free versus 2/10 cGAMP-treated mice. All the rechallenged MUSIC-treated mice remained tumor-free 30 days after rechallenge. MUSIC also resulted in a 7-fold decrease in metastatic burden when compared to cGAMP alone. In summary, MUSIC showed efficient STING activation invitro. In addition, local MUSIC treatment of primary tumors produced systemic antitumor immune responses in vivo as well as anticancer immune memory preventing tumor growth upon rechallenge. We are now exploring the use of nanobubbles for systemic administration. [Work supported by CPRIT Grants RR150010 and RP190233. R.F.M. is a CPRIT Established Investigator.]

Ultrasound (US) can detect and interact with its contrast agents, allowing perfluorocarbon-based nanodroplets (NDs) or microbubbles (MBs) to detect and treat tumors in deep tissues. Since NDs given IV passively accumulate in tumor macrophages, we aimed to determine whether phagocytosed perfluorobutane (PFB) NDs that boil at -2 °C, can be vaporized in vivo using a clinical scanner. Should that be possible, PFB NDs can then be used to deliver drugs or genes to modulate macrophage function. We formulated stable PFB NDs and validated their internalization into THP-1 macrophages using confocal microscopy. PFB ND loaded macrophages were then infused into nude rats and US imaging (low MI US imaging, 18H6 transducer) of the liver and spleen performed in vivo using a Siemens Sequoia clinical scanner before and after applying MB destruction pulses (at 1.4 MI, 10L4 transducer). PFB ND-loaded macrophages were not visible using low MI imaging, before applying MB destruction pulses. They immediately vaporized into US visible microbubbles when destruction pulses were applied over the liver and remained visible for many minutes after vaporization. Our current focus is to assess ND-loaded macrophage function before and after ND activation to determine the feasibility of modulating immune function. [Study supported by CPRIT RR150010. RFM is a CPRIT Established Investigator. Siemens ACUSON Sequoia Ultrasound System provided as a loan by Siemens Medical Solutions, USA.]

Microbubbles (MBs) are optimal ultrasound contrast agents because their unique acoustic response allows for exquisite sensitivity in vivo. This unique response is derived from MBs' elasticity that allows them to oscillate differently from surrounding tissues. While the main use of MBs in the clinic is for cardiac and perfusion imaging, imparting MBs with bioresponsive properties would expand their use to detect pathophysiologic changes. This can be achieved by damping MBs' oscillations to silence their signal and rescuing it when they encounter the biomarker of interest to improve detection and specificity of diseases such as deep vein thrombosis (DVT). Here, we demonstrate that conjugating perfluorobutane-filled MBs with hyaluronic acid (HA) and cross-linking HA with biodegradable linkers eliminates harmonic signal because of increased MB stiffness and decreased oscillation. In this proof-of-concept study, we used a reversible pH-sensitive cross-linker to establish and validate this targeted and activatable pH-sensitive MB (pH-MB) platform. Conjugation of HA to MBs and targeting of pH-MBs to CD44-positive cells were validated. Harmonic signal loss due to stiffening of pH-MBs' shell was confirmed using a clinical ultrasound scanner equipped with Cadence contrast pulse sequencing. pH-MBs imaged before and after acidification increased harmonic signal fivefold. Because the cleavage of the cross-linker we used is reversible, harmonic signal was silenced again when the acidic suspension was neutralized, confirming that harmonic signal is dependent on the cross-linked HA. The rate of rise and the magnitude of harmonic signal increase could be manipulated by varying the phospholipid composition and the number of HA cross-linkers, indicating that the platform can be tuned to the desired response needed. In this study, we established the feasibility of using targeted and activatable MBs and plan to apply this platform to aid in the diagnosis and management of patients with DVT and potentially other conditions.

Purpose: While mammography has excellent sensitivity for the detection of breast lesions, its specificity is limited. Adjunct screening with ultrasound may partially alleviate this issue but also increases false positives, resulting in unnecessary biopsies. Our study investigated the use of Google AutoML Vision (Mountain View, California), a commercially available machine learning service, to both identify and characterize indeterminate breast lesions on ultrasound. Approach: B-mode images from 253 independent cases of indeterminate breast lesions scheduled for core biopsy were used for model creation and validation. The performances of two sub-models from AutoML Vision, the image classification model and object detection model, were evaluated, while also investigating training strategies to enhance model performances. Pathology from the patient's biopsy was used as a reference standard. Results: The image classification models trained under different conditions demonstrated areas under the precision-recall curve (AUC) ranging from 0.85 to 0.96 during internal validation. Once deployed, the model with highest internal performance demonstrated a sensitivity of 100% [95% confidence interval (CI) of 73.5% to 100%], specificity of 83.3% (CI=51.6% to 97.9%), positive predictive value (PPV) of 85.7% (CI=62.9% to 95.5%), and negative predictive value (NPV) of 100% (CI non-evaluable) in an independent dataset. The object detection model demonstrated lower performance internally during development (AUC=0.67) and during prediction in the independent dataset [sensitivity=75% (CI=42.8 to 94.5), specificity=80% (CI=51.9 to 95.7), PPV=75% (CI=50.8 to 90.0), and NPV=80% (CI=59.3% to 91.7%)], but was able to demonstrate the location of the lesion within the image. Conclusions: Two models appear to be useful tools for identifying and classifying suspicious areas on B-mode images of indeterminate breast lesions.

Phase-change perfluorocarbon microdroplets were introduced over 2 decades ago to occlude downstream vessels in vivo. Interest in perfluorocarbon nanodroplets has recently increased to enable extravascular targeting, to rescue the weak ultrasound signal of perfluorocarbon droplets by converting them to microbubbles and to improve ultrasound-based therapy. Despite great scientific interest and advances, applications of phase-change perfluorocarbon agents have not reached clinical testing because of efficacy and safety concerns, some of which remain unexplained. Here, we report that the coexistence of perfluorocarbon droplets and microbubbles in blood, which is inevitable when droplets spontaneously or intentionally vaporize to form microbubbles, is a major contributor to the observed side effects. We develop the theory to explain why the coexistence of droplets and microbubbles results in microbubble inflation induced by perfluorocarbon transfer from droplets to adjacent microbubbles. We also present the experimental data showing up to 6 orders of magnitude microbubble volume expansion, which occludes a 200 μm tubing in the presence of perfluorocarbon nanodroplets. More importantly, we demonstrate that the rate of microbubble inflation and ultimate size can be controlled by manipulating formulation parameters to tailor the agent's design for the potential theranostic application while minimizing the risk to benefit ratio.

Rationale and Objectives: Breast cancer is the leading type of cancer among women. Visualization and characterization of breast lesions based on vascularity kinetics was evaluated using three-dimensional (3D) contrast-enhanced ultrasound imaging in a clinical study. Materials and Methods: Breast lesions (n = 219) were imaged using power Doppler imaging (PDI), 3D contrast-enhanced harmonic imaging (HI), and 3D contrast-enhanced subharmonic imaging (SHI) with a modified Logiq 9 ultrasound scanner using a 4D10L transducer. Quantitative metrics of vascularity derived from 3D parametric volumes (based on contrast perfusion; PER and area under the curve; AUC) were generated by off-line processing of contrast wash-in and wash-out. Diagnostic accuracy of these quantitative vascular parameters was assessed with biopsy results as the reference standard. Results: Vascularity was observed with PDI in 93 lesions (69 benign and 24 malignant), 3D HI in 8 lesions (5 benign and 3 malignant), and 3D SHI in 83 lesions (58 benign and 25 malignant). Diagnostic accuracy for vascular heterogeneity, PER, and AUC ranged from 0.52 to 0.75, while the best logistical regression model (vascular heterogeneity ratio, central PER, and central AUC) reached 0.90. Conclusion: 3D SHI successfully detects contrast agent flow in breast lesions and characterization of these lesions based on quantitative measures of vascular heterogeneity and 3D parametric volumes is promising. (c) 2019 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.

OBJECTIVE. Hydrogen peroxide (H2O2) plays a key role in neutrophil oxidative defense against infection. Catalase-containing silica nanoshells are nanoparticles that generate O-2 microbubbles imaged with ultrasound in the presence of elevated H2O2. We aimed to determine whether ultrasound-detectable O-2 microbubbles produced by catalase-containing silica nanoshells can determine whether fluid collections drained from patients are infected. SUBJECTS AND METHODS. During this HIPAA-compliant, institutional review board-approved study, 52 human fluid samples were collected from clinically required image-guided percutaneous drainage procedures. Catalase-containing silica nanoshells were added to the fluid samples during imaging in real time using a Sequoia-512 15L8-S linear transducer (Siemens Healthcare). Production of detectable microbubbles was graded subjectively as negative (noninfected) or positive (infected) with low, moderate, or high confidence by a single observer blinded to all clinical data. The truth standard was microbiology laboratory culture results. Performance characteristics including ROC curves were calculated. RESULTS. Microbubble detection to distinguish infected from noninfected fluids was 84% sensitive and 72% specific and offered negative and positive predictive values of 89% and 64%, respectively. The AUC was 0.79. Six of nine false-positive samples were peritoneal fluid collections that were all collected from patients with decompensated cirrhosis. CONCLUSION. The presence of elevated H2O2 indicated by microbubble formation in the presence of catalase-containing silica nanoshells is sensitive in distinguishing infected from noninfected fluids and offers a relatively high negative predictive value. False-positive cases may result from noninfectious oxidative stress. Catalase-containing silica nanoshells may constitute a novel point-of-care test performed at time of percutaneous drainage, potentially obviating placement of drains into otherwise sterile collections and minimizing risk of secondary infection or other complication.