Quantification and monitoring of inflammation in murine inflammatory bowel disease with targeted contrast-enhanced US

Aptamer-Functionalized Microbubbles Targeted to P-selectin for Ultrasound Molecular Imaging of Murine Bowel Inflammation

PURPOSE

Our objectives were to develop a targeted microbubble with an anti-P-selectin aptamer and assess its ability to detect bowel inflammation in two murine models of acute colitis.

PROCEDURES

Lipid-shelled microbubbles were prepared using mechanical agitation. A rapid copper-free click chemistry approach (azide-DBCO) was used to conjugate the fluorescent anti-P-selectin aptamer (Fluor-P-Ap) to the microbubble surface. Bowel inflammation was chemically induced using 2,4,6-trinitrobenzenesulfonic acid (TNBS) in both Balb/C and interleukin-10-deficient (IL-10 KO) mice. Mouse bowels were imaged using non-linear contrast mode following an i.v. bolus of 1 × 10⁸ microbubbles. Each mouse received a bolus of aptamer-functionalized and non-targeted microbubbles. Mouse phenotypes and the presence of P-selectin were validated using histology and immunostaining, respectively.

RESULTS

Microbubble labelling of Fluor-P-Ap was complete after 20 min at 37 ̊C. We estimate approximately 300,000 Fluor-P-Ap per microbubble and confirmed fluorescence using confocal microscopy. There was a significant increase in ultrasound molecular imaging signal from both Balb/C (p = 0.003) and IL-10 KO (p = 0.02) mice with inflamed bowels using aptamer-functionalized microbubbles in comparison to non-targeted microbubbles. There was no signal in healthy mice (p = 0.4051) using either microbubble.

CONCLUSIONS

We constructed an aptamer-functionalized microbubble specific for P-selectin using a clinically relevant azide-DBCO click reaction, which could detect bowel inflammation in vivo. Aptamers have potential as a next generation targeting agent for developing cost-efficient and clinically translatable targeted microbubbles.

Acoustic Molecular Imaging Beyond the Diffraction Limit In Vivo

Ultrasound molecular imaging (USMI) is a technique used to noninvasively estimate the distribution of molecular markers in vivo by imaging microbubble contrast agents (MCAs) that have been modified to target receptors of interest on the vascular endothelium. USMI is especially relevant for preclinical and clinical cancer research and has been used to predict tumor malignancy and response to treatment. In the last decade, methods that improve the resolution of contrast-enhanced ultrasound by an order of magnitude and allow researchers to noninvasively image individual capillaries have emerged. However, these approaches do not translate directly to molecular imaging. In this work, we demonstrate super-resolution visualization of biomarker expression in vivo using superharmonic ultrasound imaging (SpHI) with dual-frequency transducers, targeted contrast agents, and localization microscopy processing. We validate and optimize the proposed method in vitro using concurrent optical and ultrasound microscopy and a microvessel phantom. With the same technique, we perform a proof-of-concept experiment in vivo in a rat fibrosarcoma model and create maps of biomarker expression co-registered with images of microvasculature. From these images, we measure a resolution of 23 μm, a nearly fivefold improvement in resolution compared to previous diffraction-limited molecular imaging studies.

Contrast Enhanced Ultrasound Molecular Imaging of Spontaneous Chronic Inflammatory Bowel Disease in an Interleukin-2 Receptor α−/− Transgenic Mouse Model Using Targeted Microbubbles

Inflammatory bowel disease (IBD) is a lifelong inflammatory disorder with relapsing–remission cycles, which is currently diagnosed by clinical symptoms and signs, along with laboratory and imaging findings. However, such clinical findings are not parallel to the disease activity of IBD and are difficult to use in treatment monitoring. Therefore, non-invasive quantitative imaging tools are required for the multiple follow-up exams of IBD patients in order to monitor the disease activity and determine treatment regimens. In this study, we evaluated a dual P- and E-selectin-targeted microbubble (MB_Selectin) in an interleukin-2 receptor α deficient (IL-2Rα^−/−) spontaneous chronic IBD mouse model for assessing long-term anti-inflammatory effects with ultrasound molecular imaging (USMI). We used IL-2Rα^−/− (male and female on a C57BL/6 genetic background; n = 39) and C57BL/6 wild-type (negative control; n = 6) mice for the study. USMI of the proximal, middle, and distal colon was performed with MB_Selectin using a small animal scanner (Vevo 2100) up to six times in each IL-2Rα^−/− mouse between 6–30 weeks of age. USMI signals were compared between IL-2Rα^−/− vs. wild-type mice, and sexes in three colonic locations. Imaged colon segments were analyzed ex vivo for inflammatory changes on H&E-stained sections and for selectin expression by immunofluorescence staining. We successfully detected spontaneous chronic colitis in IL-2Rα^−/− mice between 6–30 weeks (onset at 6–14 weeks) compared to wild-type mice. Both male and female IL-2Rα^−/− mice were equally (p = 0.996) affected with the disease, and there was no significant (p > 0.05) difference in USMI signals of colitis between the proximal, middle, and distal colon. We observed the fluctuating USMI signals in IL-2Rα^−/− mice between 6–30 weeks, which might suggest a resemblance of the remission-flare pattern of human IBD. The ex vivo H&E and immunostaining further confirmed the inflammatory changes, and the high expression of P- and E-selectin in the colon. The results of this study highlight the IL-2Rα^−/− mice as a chronic colitis model and are suitable for the long-term assessment of treatment response using a dual P- and E-selectin-targeted USMI.

Ultrasound-Guided Microbubble-Mediated Locoregional Delivery of Multiple MicroRNAs Improves Chemotherapy in Hepatocellular Carcinoma

Rationale: To assess treatment effects of 4 complementary miRNAs (miRNA-100/miRNA-122/antimiRNA-10b/antimiRNA-21) encapsulated in a biodegradable PLGA-PEG nanoparticle, administered by an ultrasound-guided microbubble-mediated targeted delivery (UGMMTD) approach in mouse models of hepatocellular carcinoma (HCC). Methods:In vitro apoptotic index was measured in HepG2 and Hepa1-6 HCC cells treated with various combinations of the 4 miRNAs with doxorubicin. Three promising combinations were further tested in vivo by using UGMMTD. 63 HepG2 xenografts in mice were randomized into: group 1, miRNA-122/antimiRNA-10b/antimiRNA-21/US/doxorubicin; group 2, miRNA-100/miRNA-122/antimiRNA-10b/antimiRNA-21/US/doxorubicin; group 3, miRNA-100/miRNA-122/antimiRNA-10b/US/doxorubicin; group 4, miRNA-122/anitmiRNA-10b/antimiRNA-21/doxorubicin; group 5, miRNA-100/miRNA-122/antimiRNA-10b/antimiRNA-21/doxorubicin; group 6, miRNA-100/miRNA-122/antimiRNA-10b/doxorubicin; group 7, doxorubicin only treatment; and group 8, without any treatment. Tumor volumes were measured through 18 days. H&E staining, TUNEL assay, and qRT-PCR quantification for delivered miRNAs were performed. Results:In vivo results showed that UGMMTD of miRNAs with doxorubicin in groups 1-3 significantly (P<0.05) delayed tumor growth compared to control without any treatment, and doxorubicin only from day 7 to 18. On qRT-PCR, levels of delivered miRNAs were significantly (P<0.05) higher in groups 1-3 upon UGMMTD treatment compared to controls. TUNEL assay showed that upon UGMMTD, significantly higher levels of apoptotic cell populations were observed in groups 1-3 compared to controls. Toxicity was not observed in various organs of different groups. Conclusions: UGMMTD of miRNA-100/miRNA-122/antimiRNA-10b/antimiRNA-21 combination improved therapeutic outcome of doxorubicin chemotherapy in mouse models of HCC by substantial inhibition of tumor growth and significant increase in apoptotic index.

Intracolic ultrasound molecular imaging: a novel method for assessing colonic tumor necrosis factor-α expression in inflammatory bowel disease

BACKGROUND

While anti-tumor necrosis factor alpha (TNF-α) therapy has been proven effective in inflammatory bowel disease (IBD), approximately 40% of patients lose the response. Transmembrane TNF-α (mTNF-α) expression in the intestinal mucosa is correlated with therapeutic efficacy, and quantification of mTNF-α expression is significant for predicting response. However, conventional intravenous application of microbubbles is unable to assess mTNF-α expression in intestinal mucosa. Herein, we proposed intracolic ultrasound molecular imaging with TNF-α-targeted microbubbles (MBTNF-α) to quantitatively detect mTNF-α expression in the intestinal mucosa.

METHODS

MBTNF-α was synthesized via a biotin-streptavidin bridging method. TNF-α-targeted ultrasound imaging was performed by intracolic application of MBTNF-α to detect mTNF-α expression in surgical specimens from a murine model and patients with IBD. Linear regression analyses were performed to confirm the accuracy of quantitative targeted ultrasound imaging.

RESULTS

On quantitative TNF-α-targeted ultrasound images, a greater signal intensity was observed in the mouse colons with colitis ([1.96 ± 0.45] × 106 a.u.) compared to that of the controls ([0.56 ± 0.21] × 106 a.u., P < 0.001). Targeted US signal intensities and inflammatory lesions were topographically coupled in mouse colons. Linear regression analyses in specimens of mice and patients demonstrated significant correlations between the targeted ultrasound signal intensity and mTNF-α expression (both P < 0.001). Furthermore, TNF-α-targeted ultrasound imaging qualitatively distinguished the varying inflammatory severity in intestinal specimens from IBD patients.

CONCLUSION

Intracolic ultrasound molecular imaging with MBTNF-α enables quantitative assessment of mTNF-α expression. It may be a potential tool for facilitating the implementation of personalized medicine in IBD.

In vivo visualization and characterization of inflamed intestinal wall: the exploration of targeted microbubbles in assessing NF-κB expression

NF‐κB, a critical cytokine of inflammatory bowel diseases (IBD), is a viable marker to reflect the inflammatory activity of the intestine. We aimed to develop NF‐κB‐targeted microbubbles (MBs) and perform molecular contrast‐enhanced ultrasound (CEUS) to quantify NF‐κB expressions on the intestinal wall in IBD mice in vivo. In this study, NF‐κB‐targeted MBs were fabricated by connecting biotin‐loaded NF‐κB antibodies and avidin‐loaded MBs. NF‐κB‐targeted MBs presented as transparent and round bubbles with an average diameter of 1.03/μm±0.01. The specific binding of targeted MBs and inflammatory cells was validated by in vitro experiments, including flow cytometry, Western blot and immunofluorescence, which revealed the specific binding of targeted MBs and inflammatory cells. Subsequently, NF‐κB‐targeted CEUS imaging was performed on mice with chemical‐induced colitis, and the peak intensity (PI) and time‐to‐peak (TTP) were quantified. Pathological and immunohistochemical (IHC) examinations were further implemented. For the target CEUS group, fast enhancement followed by slow subsiding was observed. The PI of target CEUS of the IBD mice was significantly higher than that of non‐target CEUS of the IBD mice, healthy controls and target CEUS of the treated IBD mice (34835%[13379–73492%] VS 437%[236–901%], 130%[79–231%], 528%[274–779%], p<0.0001), in accordance with the IHC results of NF‐κB expressions. The TTP of target CEUS of the treated mice was significantly higher than that of untreated mice (35.7s [18.1–49.5s] VS 8.3s [4.2–12.5s], p<0.0001). Therefore, we suggested that NF‐κB‐targeted CEUS could accurately detect and quantify NF‐κB expressions on the intestinal walls of IBD, enabling the evaluation of intestinal inflammation.

Molecular Ultrasound Imaging

In the last decade, molecular ultrasound imaging has been rapidly progressing. It has proven promising to diagnose angiogenesis, inflammation, and thrombosis, and many intravascular targets, such as VEGFR2, integrins, and selectins, have been successfully visualized in vivo. Furthermore, pre-clinical studies demonstrated that molecular ultrasound increased sensitivity and specificity in disease detection, classification, and therapy response monitoring compared to current clinically applied ultrasound technologies. Several techniques were developed to detect target-bound microbubbles comprising sensitive particle acoustic quantification (SPAQ), destruction-replenishment analysis, and dwelling time assessment. Moreover, some groups tried to assess microbubble binding by a change in their echogenicity after target binding. These techniques can be complemented by radiation force ultrasound improving target binding by pushing microbubbles to vessel walls. Two targeted microbubble formulations are already in clinical trials for tumor detection and liver lesion characterization, and further clinical scale targeted microbubbles are prepared for clinical translation. The recent enormous progress in the field of molecular ultrasound imaging is summarized in this review article by introducing the most relevant detection technologies, concepts for targeted nano- and micro-bubbles, as well as their applications to characterize various diseases. Finally, progress in clinical translation is highlighted, and roadblocks are discussed that currently slow the clinical translation.

Multimodal VEGF-Targeted Contrast-Enhanced Ultrasound and Photoacoustic Imaging of Rats with Inflammatory Arthritis: Using Dye-VEGF-Antibody-Loaded Microbubbles

Owing to the heavy health burdens from rheumatoid arthritis, a sensitive and objective imaging method is needed for early diagnosis and accurate evaluation of the disease. We aimed to fabricate vascular epithelial growth factor (VEGF)-targeted microbubbles (MBs) to evaluate the expression levels of VEGF within the inflammatory lesions of rats with adjuvant-induced arthritis (AIA) using a multimodal photoacoustic (PA)/ultrasound (US) imaging system. Fluorescein isothiocyanate-biotin double-labeled vascular endothelial growth factor receptor 2 antibodies and Cy5.5-biotin double-labeled VEGF2 antibodies were added to the avidin-labeled MBs to synthesize VEGF-targeted MBs. The antibodies could specifically bind to the MBs according to the flow cytometry and fluorescence imaging. In vitro experiments on the cellular uptake of the target MBs also validated the interaction of the VEGF antibodies and the MBs. Multimodal contrast-enhanced US (CEUS)/PA imaging was performed in sequence on the inflamed paws of the AIA rats with a single PA/US imaging system after the injection of the targeted MBs. The CEUS and PA signals were then quantified and verified by the pathologic results. A CEUS pattern of fast wash in and slow washout was observed in the AIA rats after injection of targeted MBs. Compared with AIA rats injected with unconnected VEGF antibodies and naked MBs, AIA rats injected with targeted MBs presented a higher peak intensity (p = 0.0079 and 0.0079 respectively) and a longer time to peak (p = 0.0117 and 0.0117, respectively). The PA signals were also significantly enhanced after injection of targeted MBs (p = 0.0112 and 0.0119, respectively), which was in accordance with the pathologic and immunohistochemical results. In conclusion, VEGF-targeted MBs can be used as agents for multimodal CEUS/PA imaging and to detect VEGF expression in the inflammatory lesions of AIA rats in vivo. This strategy may be useful in imaging evaluation of arthritis by identifying inflammation-related molecules in different imaging modes.

Toward Molecular Imaging of Intestinal Pathology

Inflammatory bowel disease (IBD) is defined by a chronic relapsing and remitting inflammation of the gastrointestinal tract, with intestinal fibrosis being a major complication. The etiology of IBD remains unknown, but it is thought to arise from a dysregulated and excessive immune response to gut luminal microbes triggered by genetic and environmental factors. To date, IBD has no cure, and treatments are currently directed at relieving symptoms and treating inflammation. The current diagnostic of IBD relies on endoscopy, which is invasive and does not provide information on the presence of extraluminal complications and molecular aspect of the disease. Cross-sectional imaging modalities such as computed tomography enterography (CTE), magnetic resonance enterography (MRE), positron emission tomography (PET), single photon emission computed tomography (SPECT), and hybrid modalities have demonstrated high accuracy for the diagnosis of IBD and can provide both functional and morphological information when combined with the use of molecular imaging probes. This review presents the state-of-the-art imaging techniques and molecular imaging approaches in the field of IBD and points out future directions that could help improve our understanding of IBD pathological processes, along with the development of efficient treatments.

Diffuse reflectance spectroscopy to monitor murine colorectal tumor progression and therapeutic response

SIGNIFICANCE

Many studies in colorectal cancer (CRC) use murine ectopic tumor models to determine response to treatment. However, these models do not replicate the tumor microenvironment of CRC. Physiological information of treatment response derived via diffuse reflectance spectroscopy (DRS) from murine primary CRC tumors provide a better understanding for the development of new drugs and dosing strategies in CRC.

AIM

Tumor response to chemotherapy in a primary CRC model was quantified via DRS to extract total hemoglobin content (tHb), oxygen saturation (StO2), oxyhemoglobin, and deoxyhemoglobin in tissue.

APPROACH

A multimodal DRS and imaging probe (0.78 mm outside diameter) was designed and validated to acquire diffuse spectra longitudinally-via endoscopic guidance-in developing colon tumors under 5-fluoruracil (5-FU) maximum-tolerated (MTD) and metronomic regimens. A filtering algorithm was developed to compensate for positional uncertainty in DRS measurements Results: A maximum increase in StO2 was observed in both MTD and metronomic chemotherapy-treated murine primary CRC tumors at week 4 of neoadjuvant chemotherapy, with 21  ±  6  %   and 17  ±  6  %   fold changes, respectively. No significant changes were observed in tHb.

CONCLUSION

Our study demonstrates the feasibility of DRS to quantify response to treatment in primary CRC models.

Current status and recent advances on the use of ultrasonography in pediatric rheumatic diseases

BACKGROUND

Ultrasonography has become a useful tool in the clinical rheumatology settings in the last two decades, but its use has only recently been explored by pediatric rheumatologists. The aim of this article is to review the literature on the current status and recent advances on the use of ultrasound in pediatric rheumatic diseases.

DATA SOURCES

We have retrieved and reviewed the relevant articles from MEDLINE/PubMed databases published so far, on the applications of ultrasound in juvenile idiopathic arthritis (JIA), systemic lupus erythematosus, dermatomyositis, enthesitis, Sjogren's syndrome, and other rheumatic diseases. In addition, articles on novel ultrasound imaging technology of potential use in pediatric rheumatology are also reviewed.

RESULTS

In JIA, ultrasound can be used to detect subclinical synovitis, to improve the classification of patients in JIA subtypes, to capture early articular damage, to monitor treatment response, and to guide intraarticular injections. Ultrasound is also considered useful in other rheumatic disorders for the evaluation of musculoskeletal symptoms, assessment of parotid gland pathology, and measurement of skin thickness and pathology. Novel ultrasound techniques developed to augment the functionality of ultrasonography may also be applicable in pediatric rheumatic disorders.

CONCLUSIONS

Ultrasound shows great promise in the assessment and management of children with rheumatologic disorders. However, standardization and validation of ultrasound in healthy children and in patients with rheumatic diseases are still needed.

Ultrasound/Optical Dual-Modality Imaging for Evaluation of Vulnerable Atherosclerotic Plaques with Osteopontin Targeted Nanoparticles

Because of the high mortality of coronary atherosclerotic heart diseases, it is necessary to develop novel early detection methods for vulnerable atherosclerotic plaques. Phenotype transformation of vascular smooth muscle cells (VSMCs) plays a vital role in progressed atherosclerotic plaques. Osteopontin (OPN) is one of the biomarkers for phenotypic conversion of VSMCs. Significant higher OPN expression is found in foam cells along with the aggravating capacity of macrophage recruitment due to its arginine-glycine-aspartate sequence and interaction with CD44. Herein, a dual-modality imaging probe, OPN targeted nanoparticles (Cy5.5-anti-OPN-PEG-PLA-PFOB, denoted as COP-NPs), is constructed to identify the molecular characteristics of high-risk atherosclerosis by ultrasound and optical imaging. Characterization, biocompatibility, good binding sensibility, and specificity are evaluated in vitro. For in vivo study, apolipoprotein E deficien (ApoE^-/- ) mice fed with high fat diet for 20-24 weeks are used as atherosclerotic model. Ultrasound and optical imaging reveal that the nanoparticles are accumulated in the vulnerable atherosclerotic plaques. OPN targeted nanoparticles are demonstrated to be a good contrast agent in molecular imaging of synthetic VSMCs and foam cells, which can be a promising tool to identify the vulnerable atherosclerotic plaques.

Chronic Model of Inflammatory Bowel Disease in IL-10-/- Transgenic Mice: Evaluation with Ultrasound Molecular Imaging

Objective: Acute mouse models of inflammatory bowel disease (IBD) fail to mirror the chronic nature of IBD in patients. We sought to develop a chronic mouse IBD model for assessing long-term anti-inflammatory effects with ultrasound molecular imaging (USMI) by using dual P- and E-selectin targeted microbubbles (MB_Selectin). Materials and Methods: Interleukin 10 deficient (IL-10^-/- on a C57BL/6 genetic background; n=55) and FVB (n=16) mice were used. In IL-10^-/-mice, various experimental regimens including piroxicam, 2,4,6-trinitrobenzenesulfonic acid (TNBS) or dextran sulfate sodium (DSS), respectively were used for promoting colitis; colitis was induced with DSS in FVB mice. Using clinical and small animal ultrasound scanners, evolution of inflammation in proximal, middle and distal colon, was monitored with USMI by using MB_Selectin at multiple time points. Imaged colon segments were analyzed ex vivo for inflammatory changes on H&E staining and for P-selectin expression on immunofluorescence staining. Results: Sustained colitis was not detected with USMI in IL-10^-/- or FVB mice with various experimental regimens. USMI signals either gradually decreased after the colitis enhancing/inducing drug/agents were discontinued, or the mortality rate of mice was high. Inflammation was observed on H&E staining in IL-10^-/- mice with piroxicam promotion, while stable overexpression of P-selectin was not found on immunofluorescence staining in the same mice. Conclusion: Sustained colitis in IL-10^-/- mice induced with piroxicam, TNBS or DSS, and in FVB mice induced with DSS, was not detected with USMI using MB_Selectin, and this was verified by immunofluorescence staining for inflammation marker P-selectin. Thus, these models may not be appropriate for long-term monitoring of chronic colitis and subsequent treatment response with dual-selectin targeted USMI.

Contrast-Enhanced µCT for Visualizing and Evaluating Murine Intestinal Inflammation

Rationale: To develop a simple and fast protocol for the assessment of acute and chronic experimental intestinal inflammation using contrast-enhanced µCT.

Methods: For the imaging studies, an acute 2% and 3% dextran sodium sulfate (n = 15, female, 8-12 weeks) and a chronic adoptive transfer colitis model (n = 10, female, 8-9 weeks) were established over 9 days or 6 weeks, respectively. Throughout the experiments, longitudinal measurement of murine intestinal wall thickness and time dependent perfusion was performed on a small animal µCT system (90 kV, 160 μA, FOV: 60 mm, scan time: 17 s, image size: 512x512, layer thickness: 118 µm) between 0.5 and 30 min after intravenous bolus injection of an iodine contrast agent. Weight development, small animal endoscopy, and histological ex vivo analysis were compared to contrast-enhanced µCT imaging findings.

Results: Murine intestinal wall thickness was significantly increased in inflamed colons of acute colitis at day 9 in comparison to pre-inflamed state. Perfusion analysis revealed a late contrast enhancement in acute inflamed colons and the renal medulla at day 9 compared to control mice. An increasing intestinal wall thickness was monitored 3, 5 and 6 weeks after on-set of chronic colitis in comparison to controls. A good correlation with endoscopic (r = 0.75, p < 0.0001) and histologic degree of inflammation (r = 0.83, p = 0.04) was found.

Conclusion: Contrast-enhanced µCT is a simple and fast method to assess acute intestinal inflammation and to monitor disease progression in experimental models of chronic colitis. According to our findings, one single contrast-enhanced µCT-scan is a valid non-invasive modality to quantify the degree of inflammation in the entire digestive tract in murine inflammatory models.

Persistent Enhancement on Contrast-Enhanced Ultrasound Studies of Severe Crohn's Disease: Stuck Bubbles?

A small population of patients with severe Crohn's disease (CD) exhibit atypical lack of intensity decline on intestinal contrast-enhanced ultrasound. From a retrospective CD cohort examined with contrast-enhanced ultrasound, 104 patients were identified. Twenty study patients with severe active disease exhibited high peak enhancement (>23 dB) and minimal decline. From the same cohort, 84 control patients also exhibited high peak enhancement >23dB, but with typical intensity decline. Patient outcomes were assessed. Time-intensity curve analysis revealed a significantly higher (p < 0.0001) area under the curve (44.7 ± 1.5 dB·s), washout time and intensities at 60s and 120s in the study population compared with controls (40.0 ± 1.1 dB·s). Study patients had a worse overall outcome with surgery in 30% versus 10% (p = 0.027) during follow-up. Heightened enhancement with lack of decline on contrast-enhanced ultrasound suggests microbubbles are stuck within the inflamed bowel wall for an extended period. This observation occurs in patients with severe disease and a bad outcome.

US Molecular Imaging of Acute Ileitis: Anti-Inflammatory Treatment Response Monitored with Targeted Microbubbles in a Preclinical Model

Purpose To evaluate whether dual-selectin-targeted US molecular imaging allows longitudinal monitoring of anti-inflammatory treatment effects in an acute terminal ileitis model in swine. Materials and Methods The Institutional Animal Care and Use Committee approved all animal studies. Fourteen swine with chemically induced acute terminal ileitis (day 0) were randomized into the following groups: (a) an anti-inflammatory treatment group (n = 8; meloxicam, 0.25 mg per kilogram of body weight; prednisone, 0.5 mg/kg) and (b) a control group (n = 6; saline). US molecular imaging was performed with a clinical US machine after intravenous injection of clinically translatable dual P- and E-selectin-targeted microbubbles (5 × 108/kg). Three inflamed bowel segments per swine were imaged at baseline, as well as on days 1, 3, and 6 after treatment initiation. At day 6, bowel segments were analyzed ex vivo for selectin expression levels by using quantitative immunofluorescence. Results After induction of inflammation, US molecular imaging signal increased at day 1 in both animal groups (P < .001). At day 3, signal in the treatment group decreased (P < .001 vs day 1), while signal in control animals did not significantly change (P = .18 vs day 1) and was higher (P = .001) compared with that in the treatment group. At day 6, signal in the treatment group further decreased and remained lower (P = .02) compared with that in the control group. Immunofluorescence confirmed significant (P ≤ .04) downregulation of both P- and E-selectin expression levels in treated versus control bowel segments. Conclusion Dual-selectin-targeted US molecular imaging allows longitudinal monitoring of anti-inflammatory treatment effects in a large-animal model of acute ileitis. This supports further clinical development of this quantitative and radiation-free technique for monitoring inflammatory bowel disease. © RSNA, 2018 Online supplemental material is available for this article.

Multimodal Molecular Imaging: Current Status and Future Directions

Molecular imaging has emerged at the end of the last century as an interdisciplinary method involving in vivo imaging and molecular biology aiming at identifying living biological processes at a cellular and molecular level in a noninvasive manner. It has a profound role in determining disease changes and facilitating drug research and development, thus creating new medical modalities to monitor human health. At present, a variety of different molecular imaging techniques have their advantages, disadvantages, and limitations. In order to overcome these shortcomings, researchers combine two or more detection techniques to create a new imaging mode, such as multimodal molecular imaging, to obtain a better result and more information regarding monitoring, diagnosis, and treatment. In this review, we first describe the classic molecular imaging technology and its key advantages, and then, we offer some of the latest multimodal molecular imaging modes. Finally, we summarize the great challenges, the future development, and the great potential in this field.

Imaging with ultrasound contrast agents: current status and future

Microbubble ultrasound contrast agents (UCAs) were recently approved by the Food and Drug administration for non-cardiac imaging. The physical principles of UCAs, methods of administration, dosage, adverse effects, and imaging techniques both current and future are described. UCAs consist of microbubbles in suspension which strongly interact with the ultrasound beam and are readily detectable by ultrasound imaging systems. They are confined to the blood pool when administered intravenously, unlike iodinated and gadolinium contrast agents. UCAs have a proven safety record based on over two decades of use, during which they have been used in echocardiography in the U.S. and for non-cardiac imaging in the rest of the world. Adverse effects are less common with UCAs than CT/MR contrast agents. Compared to CT and MR, contrast-enhanced ultrasound has the advantages of real-time imaging, portability, and reduced susceptibility to metal and motion artifact. UCAs are not nephrotoxic and can be used in renal failure. High acoustic amplitudes can cause microbubbles to fragment in a manner that can result in short-term increases in capillary permeability or capillary rupture. These bioeffects can be beneficial and have been used to enhance drug delivery under appropriate conditions. Imaging with a mechanical index of < 0.4 preserves the microbubbles and is not typically associated with substantial bioeffects. Molecularly targeted ultrasound contrast agents are created by conjugating the microbubble shell with a peptide, antibody, or other ligand designed to target an endothelial biomarker associated with tumor angiogenesis or inflammation. These microbubbles then accumulate in the microvasculature at target sites where they can be imaged. Ultrasound contrast agents are a valuable addition to the diagnostic imaging toolkit. They will facilitate cross-sectional abdominal imaging in situations where contrast-enhanced CT and MR are contraindicated or impractical.

Molecular imaging of Toll-like receptor 4 detects ischemia-reperfusion injury during intussusception

We investigated the expression of Toll-like receptor 4 (TLR4) in the acute phase of intestinal I/R injury during intussusception and evaluated whether anti-TLR4 antibody-conjugated lead sulfide quantum dots (TLR4-PbS QDs) could be used to detect and monitor the injury. We first established a mouse model of I/R injury during intussusception. TLR-PbS QDs were then intravenously administered to intestinal I/R injured mice and visualized using whole-body fluorescence imaging in the second near-infrared window (NIR-II). Immunohistochemical analysis of intestinal tissue from the mice revealed that TLR4 expression was higher in the I/R injury group than the control and TAK-242 groups (5.189 ± 2.482, 1.186 ± 1.171, and 2.400 ± 0.857, respectively, P < 0.05). NIR-II fluorescence intensity was also higher in the I/R injury group than in the control and TAK-242 groups (86.415 ± 10.955, 38.975 ± 8.619, and 71.977 ± 3.838, respectively; P < 0.05). Thus, anti-TLR4-PbS QDs bound to TLR4 on the cell membranes of intestinal epithelial cells with high specificity in vitro and in vivo. These results indicate that TLR4 promotes intestinal I/R injury during intussusception and that the injury can be noninvasively imaged using TLR4-PbS QDs.

Targeting of microbubbles: contrast agents for ultrasound molecular imaging

For contrast ultrasound imaging, the most efficient contrast agents comprise highly compressible gas-filled microbubbles. These micrometer-sized particles are typically filled with low-solubility perfluorocarbon gases, and coated with a thin shell, often a lipid monolayer. These particles circulate in the bloodstream for several minutes; they demonstrate good safety and are already in widespread clinical use as blood pool agents with very low dosage necessary (sub-mg per injection). As ultrasound is an ubiquitous medical imaging modality, with tens of millions of exams conducted annually, its use for molecular/targeted imaging of biomarkers of disease may enable wider implementation of personalised medicine applications, precision medicine, non-invasive quantification of biomarkers, targeted guidance of biopsy and therapy in real time. To achieve this capability, microbubbles are decorated with targeting ligands, possessing specific affinity towards vascular biomarkers of disease, such as tumour neovasculature or areas of inflammation, ischaemia-reperfusion injury or ischaemic memory. Once bound to the target, microbubbles can be selectively visualised to delineate disease location by ultrasound imaging. This review discusses the general design trends and approaches for such molecular ultrasound imaging agents, which are currently at the advanced stages of development, and are evolving towards widespread clinical trials.

Contrast-Enhanced Ultrasound for Assessing Renal Perfusion Impairment and Predicting Acute Kidney Injury to Chronic Kidney Disease Progression

AIMS

Acute kidney injury (AKI) is increasingly recognized as a major risk factor leading to progression to chronic kidney disease (CKD). However, the diagnostic tools for predicting AKI to CKD progression are particularly lacking. Here, we tested the utility of contrast-enhanced ultrasound (CEUS) for predicting progression to CKD after AKI by using both mild (20-min) and severe (45-min) bilateral renal ischemia-reperfusion injury mice.

RESULTS

Renal perfusion measured by CEUS reduced to 25% ± 7% and 14% ± 6% of the pre-ischemic levels in mild and severe AKI 1 h after ischemia (p < 0.05). Renal perfusion returned to pre-ischemic levels 1 day after mild AKI followed by restoration of kidney function. However, severe AKI caused persistent renal perfusion impairment (60% ± 9% of baseline levels) accompanied by progressive renal fibrosis and sustained decrease in renal function. Renal perfusion at days 1-21 significantly correlated with tubulointerstitial fibrosis 42 days after AKI. For predicting renal fibrosis at day 42, the area under the receiver operating characteristics curve of renal perfusion impairment at day 1 was 0.84. Similar changes in the renal image of CEUS were observed in patients with AKI-CKD progression.

INNOVATION

This study demonstrates that CEUS enables dynamic and noninvasive detection of renal perfusion impairment after ischemic AKI and the perfusion abnormalities shown by CEUS can early predict the progression to CKD after AKI.

CONCLUSIONS

These results indicate that CEUS enables the evaluation of renal perfusion impairment associated with CKD after ischemic AKI and may serve as a noninvasive technique for assessing AKI-CKD progression. Antioxid. Redox Signal. 27, 1397-1411.

Ultrasound Imaging Based on Molecular Targeting for Quantitative Evaluation of Hepatic Ischemia-Reperfusion Injury

The aim of the present study was to quantitatively diagnose and monitor the therapy response of hepatic ischemia-reperfusion injury (IRI) with the use of targeted ultrasound (US) imaging. Targeted microbubbles (MBs) were fabricated, and the binding of intracellular adhesion molecule 1 (ICAM-1) antibodies to MBs was observed. To establish a quantitative method based on targeted US imaging, contrast-enhanced US was applied for IRI rats. After andrographolide treatment, the IRI rats were subjected to the quantitative targeted US imaging for a therapeutic effect. Effective binding of ICAM-1 antibodies to MBs was observed. According to the quantitative targeted US imaging, the ICAM-1 normalized intensity difference (NID) in the IRI rats (38.74 ± 15.08%) was significantly higher than that in the control rats (10.08 ± 2.52%, p = 0.048). Further, different degrees of IRI (mild IRI, moderate to severe IRI) were distinguished by the use of the NID (37.14 ± 2.14%, 22.34 ± 1.08%, p = 0.002). Analysis of mRNA expression demonstrated the accuracy of analyzing the NID by using quantitative targeted US imaging (R²  = 0.7434, p < 0.001). Andrographolide treatment resulted in an obviously weakened NID of ICAM-1 (17.7 ± 4.8% vs 34.2 ± 6.6%, p < 0.001). The study showed the potential of the quantitative targeted US imaging method for the diagnosis and therapeutic monitoring of IRI.

Anatomical Road Mapping Using CT and MR Enterography for Ultrasound Molecular Imaging of Small Bowel Inflammation in Swine

OBJECTIVES

To evaluate the feasibility and time saving of fusing CT and MR enterography with ultrasound for ultrasound molecular imaging (USMI) of inflammation in an acute small bowel inflammation of swine.

METHODS

Nine swine with ileitis were scanned with either CT (n = 3) or MR (n = 6) enterography. Imaging times to load CT/MR images onto a clinical ultrasound machine, fuse them to ultrasound with an anatomical landmark-based approach, and identify ileitis were compared to the imaging times without anatomical road mapping. Inflammation was then assessed by USMI using dual selectin-targeted (MB_Selectin) and control (MB_Control) contrast agents in diseased and healthy control bowel segments, followed by ex vivo histology.

RESULTS

Cross-sectional image fusion with ultrasound was feasible with an alignment error of 13.9 ± 9.7 mm. Anatomical road mapping significantly reduced (P < 0.001) scanning times by 40%. Localising ileitis was achieved within 1.0 min. Subsequently performed USMI demonstrated significantly (P < 0.001) higher imaging signal using MB_Selectin compared to MB_Control and histology confirmed a significantly higher inflammation score (P = 0.006) and P- and E-selectin expression (P ≤ 0.02) in inflamed vs. healthy bowel.

CONCLUSIONS

Fusion of CT and MR enterography data sets with ultrasound in real time is feasible and allows rapid anatomical localisation of ileitis for subsequent quantification of inflammation using USMI.

KEY POINTS

• Real-time fusion of CT/MRI with ultrasound to localise ileitis is feasible. • Anatomical road mapping using CT/MRI significantly decreases the scanning time for USMI. • USMI allows quantification of inflammation in swine, verified with ex vivo histology.

An Introduction to Contrast-Enhanced Ultrasound for Nephrologists

Contrast-enhanced ultrasound (CEUS) is an emerging technology with no known nephrotoxicity. CEUS has been utilized in cardiac and abdominal imaging for decades in Asia and Europe and has recently received greater attention in the United States with its approval for characterization of indeterminate liver lesions. Emerging data suggest that CEUS has potential as a diagnostic imaging tool among individuals who have contraindications to CT and MRI. Few nephrologists are aware of CEUS and even fewer are aware of its potential applications among individuals with kidney disease. This review introduces CEUS to the nephrology community and provides a basic overview of CEUS technology. Knowledge of the applications, advantages, and disadvantages of CEUS provides the framework for nephrologists to make informed decisions regarding this emerging imaging test in appropriate circumstances. This review focuses on the use of CEUS for the characterization of indeterminate kidney lesions and summarizes the most recent data, some of which specifically includes patients with chronic kidney disease (CKD). The results demonstrate that CEUS has high sensitivity and moderate specificity for detecting malignancy in indeterminate kidney lesions among individuals with and without CKD. In conclusion, CEUS is an emerging imaging technique that may have clinically useful applications for detecting malignant kidney lesions, specifically in patients with CKD. However, most of the current data come from small, single-center studies, and larger, multicenter studies are needed.

Molecular Ultrasound Imaging for the Detection of Neural Inflammation: A Longitudinal Dosing Pilot Study

Molecular ultrasound imaging provides the ability to detect physiologic processes noninvasively by targeting a variety of biomarkers in vivo. The current study was performed by exploiting an inflammatory biomarker, P-selectin, known to be present following spinal cord injury. Using a murine model (n = 6), molecular ultrasound imaging was performed using contrast microbubbles modified to target and adhere to P-selectin, prior to spinal cord injury (0D), acute stage postinjury (7D), and chronic stage (42D). Additionally, two imaging sessions were performed on each subject at specific time points, using doses of 30 μL and 100 μL. Upon analysis, targeted contrast analysis parameters were appreciably increased during the 7D scan compared with the 42D scan, without statistical significance. When examining the dose levels, the 30-μL dose demonstrated greater values than the 100-μL dose but lacked statistical significance. These findings provide additional preclinical evidence for the use of molecular ultrasound imaging for the possible detection of inflammation.

Monitoring inflammation injuries in the progression of atherosclerosis with contrast enhanced ultrasound molecular imaging

Purpose

The upregulation of vascular cell adhesion molecule-1(VCAM-1) on vascular endothelium plays a great role in the progression of atherosclerosis (AS). In this study, ultrasound molecular imaging was performed to monitor the inflammation injuries in the onset and progression of atherosclerosis with microbubbles targeted to VCAM-1.

Methods

Mice deficient for the apolipoprotein E (ApoE^-/-mice) with high-cholesterol diet were studied as an age-dependent model of atherosclerosis. At 8, 16, 24, and 32 weeks of age, contrast enhanced ultrasound (CEU) molecular imaging of proximal ascending aorta was performed with microbubbles targeted to VCAM-1. Plaque size, monocytes infiltration and the expression of VCAM-1 in the proximal ascending aorta were assessed by histology and western blot analysis, separately.

Results

In ApoE^-/- mice, molecular imaging for VCAM-1 detected selective signal enhancement (P<0.01 versus non-targeted microbubbles) at all ages of ApoE^-/- mice. Moreover, signals from targeted microbubbles increased from 8wks to 32wks age (P<0.05 for trend) in ApoE^-/- mice, indicating the upregulation of VCAM-1 with the progression of atherosclerosis. Consistent with CEU imaging results, both western blot analysis and immunohistochemistry revealed the expression of VCAM-1 and monocytes infiltration were age-dependent in ApoE^-/- mice.

Conclusions

CEU molecular imaging can be used to noninvasively detect the VCAM-1 expression on the endothelium in the progression of atherosclerosis. By investigating specific molecular biomarkers, it could help to monitor the inflammation and the progression of AS, which may in some extent contribute to the prediction of vulnerable plaque.

Molecular Ultrasound Imaging of the Spinal Cord for the Detection of Acute Inflammation

Molecular ultrasound imaging provides the ability to detect physiologic processes non-invasively by targeting a wide variety of biological markers in vivo. The current study investigates the novel application of molecular ultrasound imaging for the detection of neural inflammation. Using a murine model with acutely injured spinal cords (n=31), subjects were divided into four groups, each being administered ultrasound contrast microbubbles bearing antibodies against various known inflammatory molecules (P-selectin, vascular cell adhesion protein 1 [VCAM-1], intercellular adhesion molecule 1 [ICAM-1], and isotype control) during molecular ultrasound imaging. Upon administration of the targeted contrast agent, ultrasound imaging of the injured spinal cord was performed at 40MHz for seven minutes, followed by a bursting pulse. We observed significantly enhanced signals from contrast targeted to P-selectin and VCAM-1, using a variety of outcome measures. These findings provide preclinical evidence that molecular ultrasound imaging could be a useful tool in the detection of neural inflammation.

Targeted Contrast-Enhanced Ultrasound for Inflammation Detection

Molecular imaging is a form of nanotechnology that enables the noninvasive examination of biological processes in vivo. Radiopharmaceutical agents are used to target biochemical markers, permitting their detection and evaluation. Early visualization of molecular variations indicative of pathophysiological processes can aid in patient diagnoses and management decisions. Molecular imaging is performed by introducing into the body molecular probes, which are often contrast agents that have been nanoengineered to target and tether to molecules, thus enabling their radiologic identification. Through a nanoengineering process, ultrasound contrast agents can be targeted to specific molecules, extending ultrasound’s capabilities from the tissue to molecular level. Molecular ultrasound, or targeted contrast-enhanced ultrasound (TCEUS), has recently emerged as a popular molecular imaging technique due to its ability to provide real-time anatomic and functional information without ionizing radiation. However, molecular ultrasound represents a novel form of molecular imaging and consequently remains largely preclinical. This review explores the commonalities of TCEUS across several molecular targets and points to the need for standardization of kinetic behavior analysis. The literature underscores evidence gaps and the need for additional research. The application of TCEUS is unlimited but needs further standardization to ensure that future research studies are comparable.

Assessment of murine colorectal cancer by micro-ultrasound using three dimensional reconstruction and non-linear contrast imaging

The relatively low success rates of current colorectal cancer (CRC) therapies have led investigators to search for more specific treatments. Vertebrate models of colorectal cancer are essential tools for the verification of new therapeutic avenues such as gene therapy. The evaluation of colorectal cancer in mouse models has been limited due to the lack of an accurate quantitative and longitudinal noninvasive method. This work introduces a method of three-dimensional micro-ultrasound reconstruction and microbubble administration for the comprehensive and longitudinal evaluation of CRC progression. This approach enabled quantification of both tumor volume and relative vascularity using a well-established inducible murine model of colon carcinogenesis. This inducible model recapitulated the adenocarcinoma sequence that occurs in human CRC allowing systematic in situ evaluation of the ultrasound technique. The administration of intravenous microbubbles facilitated enhancement of colon vascular contrast and quantification of relative vascularity of the mid and distal colon of the mouse in three dimensions. In addition, two-dimensional imaging in the sagittal orientation of the colon using Non-Linear Contrast Mode enabled calculation of relative blood volume and perfusion as the microbubbles entered the colon microvasculature. Quantitative results provided by the outlined protocol represent a noninvasive tool that can more accurately define CRC development and progression. This ultrasound technique will allow the practical and economical longitudinal study of murine CRC in both basic and preclinical studies.

Exploring Targeted Contrast-Enhanced Ultrasound to Detect Neural Inflammation

Targeted contrast-enhanced ultrasound (TCEUS) is an innovative method of molecular imaging used for detection of inflammatory biomarkers in vivo. By targeting ultrasound contrast to cell adhesion molecules (CAMs), which are known inflammatory markers within neural tissue, a more direct evaluation of neural inflammation can be made. Due to the novel nature of TCEUS, standardized methods of image analysis do not yet exist. Time intensity curve (TIC) shape analysis is currently used in magnetic resonance contrast imaging to determine temporal behavior of perfusion. Therefore, the presented research attempts to determine TIC shape analysis utility in TCEUS imaging by applying it to TCEUS scans targeted to CAMs present in neural inflammation. This was done in an animal model that underwent a traumatic spinal cord injury to induce inflammation ( n = 31). Subjects were divided into four groups, each receiving a TCEUS targeted to a different CAM seven days after surgery (P-selectin, intracellular adhesion molecule 1 [ICAM-1], vascular cell adhesion molecule 1 [VCAM-1], and control). TICs were generated using average pixel intensity within the injured region of the spinal cord. TIC shape analysis found similar curves were produced while targeting P-selectin and VCAM-1, both demonstrating rapid and sustained enhancement. Control injections demonstrated no enhancement. ICAM-1 injections demonstrated limited enhancement and a shape similar to the control.

Light and sound - emerging imaging techniques for inflammatory bowel disease

Patients with inflammatory bowel disease are known to have a high demand of recurrent evaluation for therapy and disease activity. Further, the risk of developing cancer during the disease progression is increasing from year to year. New, mostly non-radiant, quick to perform and quantitative methods are challenging, conventional endoscopy with biopsy as gold standard. Especially, new physical imaging approaches utilizing light and sound waves have facilitated the development of advanced functional and molecular modalities. Besides these advantages they hold the promise to predict personalized therapeutic responses and to spare frequent invasive procedures. Within this article we highlight their potential for initial diagnosis, assessment of disease activity and surveillance of cancer development in established techniques and recent advances such as wide-view full-spectrum endoscopy, chromoendoscopy, autofluorescence endoscopy, endocytoscopy, confocal laser endoscopy, multiphoton endoscopy, molecular imaging endoscopy, B-mode and Doppler ultrasound, contrast-enhanced ultrasound, ultrasound molecular imaging, and elastography.

Contrast-Based Real-Time Assessment of Microcirculatory Changes in a Fatty Liver After Ischemia Reperfusion Injury

OBJECTIVES

A fatty liver is known to have impairment of microcirculation, which is worsened after ischemia reperfusion injury (IRI). This makes most fatty grafts unsuitable for transplantation, and in the absence of real time assessment of microcirculation this selection has been at best, random. The aim of this study was to demonstrate the utility of a contrast enhanced ultrasound model in quantitative assessment of the microcirculation of a fatty liver.

METHODS

We subjected fatty mice to IRI, and blood flow dynamics were assessed before and after the injury.

RESULTS

There was a significant increase in the resistive and pulsatility index of the extrahepatic artery and a significant decrease in velocity of the portal vein. There was also a quantifiable decrease in the intrahepatic blood volume, blood flow, time to peak flow, and perfusion index of mice with fatty liver, suggesting that a fatty liver develops hemodynamic abnormalities after IRI, leading to increased hepatocellular injury.

CONCLUSIONS

Hemodynamic abnormalities in liver can be reliably quantified using a contrast, enhanced Doppler ultrasound, which is an inexpensive technique with multiple clinical applications. It can be used to assess the quality of the fatty liver donor graft before organ retrieval; for determining live donor candidacy, for making post-IRI recovery prognosis, and for assessing the effectiveness of therapeutic interventions.

Diagnostic imaging advances in murine models of colitis

Inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis are chronic-remittent inflammatory disorders of the gastrointestinal tract still evoking challenging clinical diagnostic and therapeutic situations. Murine models of experimental colitis are a vital component of research into human IBD concerning questions of its complex pathogenesis or the evaluation of potential new drugs. To monitor the course of colitis, to the present day, classical parameters like histological tissue alterations or analysis of mucosal cytokine/chemokine expression often require euthanasia of animals. Recent advances mean revolutionary non-invasive imaging techniques for in vivo murine colitis diagnostics are increasingly available. These novel and emerging imaging techniques not only allow direct visualization of intestinal inflammation, but also enable molecular imaging and targeting of specific alterations of the inflamed murine mucosa. For the first time, in vivo imaging techniques allow for longitudinal examinations and evaluation of intra-individual therapeutic response. This review discusses the latest developments in the different fields of ultrasound, molecularly targeted contrast agent ultrasound, fluorescence endoscopy, confocal laser endomicroscopy as well as tomographic imaging with magnetic resonance imaging, computed tomography and fluorescence-mediated tomography, discussing their individual limitations and potential future diagnostic applications in the management of human patients with IBD.

Molecular evaluation of thrombosis using X-ray phase contrast imaging with microbubbles targeted to P-selectin in mice

OBJECTIVES

X-ray phase contrast imaging (PCI) provides excellent image contrast by utilizing the phase shift. The introduction of microbubbles into tissues can cause a phase shift to make microbubbles visibly identified on PCI. In this study, we assessed the feasibility of targeted microbubble-based PCI for the detection of thrombosis.

METHODS

The absorption and phase contrast images of P-selectin-targeted microbubbles (MBP) were obtained and compared in vitro. MBP, control IgG-targeted microbubbles (MBC), and unbound microbubbles (MBU) were tested for binding specificity on thrombi expressing P-selectin. MBP were used as molecular PCI probes to evaluate P-selectin expression in a mouse model of arteriovenous shunt thrombosis that was created using PE tubes in the bypass outside of the mouse body.

RESULTS

PCI clearly showed the microbubbles not viewable via absorption contrast imaging (ACI). In vitro attachment of MBP (91.60 ± 11.63) to thrombi was significantly higher than attachment of MBC (17.80 ± 4.02, P < 0.001) or MBU (9.80 ± 2.59, P < 0.001). In the mouse model of arteriovenous shunt thrombosis, the binding affinity of MBP (15.50 ± 6.25) was significantly greater than that of MBC (0.50 ± 0.84, P < 0.001) or MBU (0.33 ± 0.52, P < 0.001).

CONCLUSIONS

Our results indicate that molecular PCI may be considered as a novel and promising imaging modality for the investigation of thrombosis.

KEY POINTS

• Small thrombi are rarely detected by conventional radiography. • Phase contrast imaging (PCI) provides higher contrast and spatial resolution than conventional radiography. • P-selectin targeted microbubbles detected by PCI may suggest early thrombosis.

Assessment of Inflammation in an Acute on Chronic Model of Inflammatory Bowel Disease with Ultrasound Molecular Imaging

BACKGROUND

Ultrasound (US) molecular imaging has shown promise in assessing inflammation in preclinical, murine models of inflammatory bowel disease. These models, however, initiated acute inflammation on previously normal colons, in contrast to patients where acute exacerbations are often in chronically inflamed regions. In this study, we explored the potential of dual P- and E-selectin targeted US imaging for assessing acute inflammation on a murine quiescent chronic inflammatory background.

METHODS

Chronic colitis was induced using three cycles of 4% DSS in male FVB mice. Acute inflammation was initiated 2 weeks after the final DSS cycle through rectal administration of 1% TNBS. Mice at different stages of inflammation were imaged using a small animal ultrasound system following i.v. injection of microbubbles targeted to P- and E-selectin. In vivo imaging results were correlated with ex vivo immunofluorescence and histology.

RESULTS

Induction of acute inflammation resulted in an increase in the targeted US signal from 5.5 ± 5.1 arbitrary units (a.u.) at day 0 to 61.0 ± 45.2 a.u. (P < 0.0001) at day 1, 36.3 ± 33.1 a.u. at day 3, returning to levels similar to control at day 5. Immunofluorescence showed significant increase in the percentage of P- and E-selectin positive vessels at day 1 (P-selectin: 21.0 ± 7.1% of vessels; P < 0.05; E-selectin: 16.4 ±3.7%; P < 0.05) compared to day 0 (P-selectin: 10.3 ± 5.7%; E-selectin: 7.3 ± 7.0%).

CONCLUSIONS

Acute inflammation can be accurately measured in a clinically relevant murine model of chronic IBD using ultrasound molecular imaging with a dual P- and E- selectin-targeted contrast agent.

Effects of anti-inflammatory therapy on bursting pressure of colonic anastomosis in murine dextran sulfate sodium induced colitis

BACKGROUND

The aim of this study was to examine the effect of colitis and anti-inflammatory therapies on the healing of colonic anastomoses in mice.

METHODS

Female C57BL/6 mice were randomized into eight groups; four groups receiving plain tap-water and four groups receiving dextran sulfate sodium. Intra-peritoneal treatment was given therapeutically for 14 days with placebo, prednisolone, azathioprine, or infliximab (IFX). Colonic anastomoses were performed and bursting pressure (BP) measurements were recorded and the inflammation evaluated with histology and zymography.

RESULTS

The mice with colitis had a more active inflammation based on histology and bowel weight compared with the tap water group, 8.3 (7.6-9.5) mg/mm and 5.5 (4.8-6.2) mg/mm respectively (p < 0.0001). Similarly mice with colitis receiving placebo had a more active inflammation, 12.8 (10.6-15.0) mg/mm, which differed significantly from all the other therapy arms among the colitic mice; prednisolone 8.1 (7.5-9.1) mg/mm (p = 0.014), azathioprine 8.2 (7.0-8.5) mg/mm (p = 0.0046), IFX 6.7 (6.4-7.9) mg/mm (p = 0.0055). BP for the placebo group was 90.0 (71.5-102.8) mmHg and did not differ from azathioprine or IFX groups, 84.4 (70.5-112.5) and 92.3 (75.8-122.3) mmHg respectively. In contrast BP for the prednisolone group was significantly decreased compared to placebo, 55.5 (42.8-73.0) mmHg (p = 0.0004).

CONCLUSIONS

All therapies had a beneficial effect on the colitis. An impaired BP of colonic anastomoses was noted after preoperative steroids but not after azathioprine or IFX in this model.

Quantitative Assessment of Inflammation in a Porcine Acute Terminal Ileitis Model: US with a Molecularly Targeted Contrast Agent

PURPOSE

To evaluate the feasibility and reproducibility of ultrasonography (US) performed with dual-selectin-targeted contrast agent microbubbles (MBs) for assessment of inflammation in a porcine acute terminal ileitis model, with histologic findings as a reference standard.

MATERIALS AND METHODS

The study had institutional Animal Care and Use Committee approval. Acute terminal ileitis was established in 19 pigs; four pigs served as control pigs. The ileum was imaged with clinical-grade dual P- and E-selectin-targeted MBs (MBSelectin) at increasing doses (0.5, 1.0, 2.5, 5.0, 10, and 20 × 10(8) MB per kilogram of body weight) and with control nontargeted MBs (MBControl). For reproducibility testing, examinations were repeated twice after the MBSelectin and MBControl injections. After imaging, scanned ileal segments were analyzed ex vivo both for inflammation grade (by using hematoxylin-eosin staining) and for expression of selectins (by using quantitative immunofluorescence analysis). Statistical analysis was performed by using the t test, intraclass correlation coefficients (ICCs), and Spearman correlation analysis.

RESULTS

Imaging signal increased linearly (P < .001) between a dose of 0.5 and a dose of 5.0 × 10(8) MB/kg and plateaued between a dose of 10 and a dose of 20 × 10(8) MB/kg. Imaging signals were reproducible (ICC = 0.70), and administration of MBSelectin in acute ileitis resulted in a significantly higher (P < .001) imaging signal compared with that in control ileum and MBControl. Ex vivo histologic grades of inflammation correlated well with in vivo US signal (ρ = 0.79), and expression levels of both P-selectin (37.4% ± 14.7 [standard deviation] of vessels positive; P < .001) and E-selectin (31.2% ± 25.7) in vessels in the bowel wall of segments with ileitis were higher than in control ileum (5.1% ± 3.7 for P-selectin and 4.8% ± 2.3 for E-selectin).

CONCLUSION

Quantitative measurements of inflammation obtained by using dual-selectin-targeted US are reproducible and correlate well with the extent of inflammation at histologic examination in a porcine acute ileitis model as a next step toward clinical translation.

Noninvasive molecular ultrasound monitoring of vessel healing after intravascular surgical procedures in a preclinical setup

OBJECTIVE

Cardiovascular interventions induce damage to the vessel wall making antithrombotic therapy inevitable until complete endothelial recovery. Without a method to accurately determine the endothelial status, many patients undergo prolonged anticoagulation therapy, denying them any invasive medical procedures, such as surgical operations and dental interventions. Therefore, we aim to introduce molecular ultrasound imaging of the vascular cell adhesion molecule (VCAM)-1 using targeted poly-n-butylcyanoacrylate microbubbles (MB(VCAM-1)) as an easy accessible method to monitor accurately the reendothelialization of vessels.

APPROACH AND RESULTS

ApoE(-/-) mice were fed with an atherogenic diet for 1 and 12 weeks and subsequently, endothelial denudation was performed in the carotid arteries using a guidewire. Molecular ultrasound imaging was performed at different time points after denudation (1, 3, 7, and 14 days). An increased MB(VCAM-1) binding after 1 day, a peak after 3 days, and a decrease after 7 days was found. After 12 weeks of diet, MB(VCAM-1) binding also peaked after 3 days but remained high until 7 days, indicating a delay in endothelial recovery. Two-photon laser scanning microscopy imaging of double fluorescence staining confirmed the exposure of VCAM-1 on the superficial layer after arterial injury only during the healing phase. After complete reendothelialization, VCAM-1 expression persisted in the subendothelial layer but was not reachable for the MBV(CAM-1) anymore.

CONCLUSION

Molecular ultrasound imaging with MB(VCAM-1) is promising to assess vascular damage and to monitor endothelial recovery after arterial interventions. Thus, it may become an important diagnostic tool supporting the development of adequate therapeutic strategies to personalize anticoagulant and anti-inflammatory therapy after cardiovascular intervention.

Ultrasound molecular imaging: Moving toward clinical translation

Ultrasound is a widely available, cost-effective, real-time, non-invasive and safe imaging modality widely used in the clinic for anatomical and functional imaging. With the introduction of novel molecularly-targeted ultrasound contrast agents, another dimension of ultrasound has become a reality: diagnosing and monitoring pathological processes at the molecular level. Most commonly used ultrasound molecular imaging contrast agents are micron sized, gas-containing microbubbles functionalized to recognize and attach to molecules expressed on inflamed or angiogenic vascular endothelial cells. There are several potential clinical applications currently being explored including earlier detection, molecular profiling, and monitoring of cancer, as well as visualization of ischemic memory in transient myocardial ischemia, monitoring of disease activity in inflammatory bowel disease, and assessment of arteriosclerosis. Recently, a first clinical grade ultrasound contrast agent (BR55), targeted at a molecule expressed in neoangiogenesis (vascular endothelial growth factor receptor type 2; VEGFR2) has been introduced and safety and feasibility of VEGFR2-targeted ultrasound imaging is being explored in first inhuman clinical trials in various cancer types. This review describes the design of ultrasound molecular imaging contrast agents, imaging techniques, and potential future clinical applications of ultrasound molecular imaging.

Vascular endothelial growth factor receptor type 2-targeted contrast-enhanced US of pancreatic cancer neovasculature in a genetically engineered mouse model: potential for earlier detection

PURPOSE

To test ultrasonographic (US) imaging with vascular endothelial growth factor receptor type 2 (VEGFR2)-targeted microbubble contrast material for the detection of pancreatic ductal adenocarcinoma (PDAC) in a transgenic mouse model of pancreatic cancer development.

MATERIALS AND METHODS

Experiments involving animals were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. Transgenic mice (n = 44; Pdx1-Cre, KRas(G12D), Ink4a(-/-)) that spontaneously develop PDAC starting at 4 weeks of age were imaged by using a dedicated small-animal US system after intravenous injection of 5 × 10(7) clinical-grade VEGFR2-targeted microbubble contrast material. The pancreata in wild-type (WT) mice (n = 64) were scanned as controls. Pancreatic tissue was analyzed ex vivo by means of histologic examination (with hematoxylin-eosin staining) and immunostaining of vascular endothelial cell marker CD31 and VEGFR2. The Wilcoxon rank sum test and linear mixed-effects model were used for statistical analysis.

RESULTS

VEGFR2-targeted US of PDAC showed significantly higher signal intensities (26.8-fold higher; mean intensity ± standard deviation, 6.7 linear arbitrary units [lau] ± 8.5; P < .001) in transgenic mice compared with normal, control pancreata of WT mice (mean intensity, 0.25 lau ± 0.25). The highest VEGFR2-targeted US signal intensities were observed in smaller tumors, less than 3 mm in diameter (30.8-fold higher than control tissue with mean intensity of 7.7 lau ± 9.3 [P < .001]; and 1.7-fold higher than lesions larger than 3 mm in diameter with mean intensity of 4.6 lau ± 5.8 [P < .024]). Ex vivo quantitative VEGFR2 immunofluorescence demonstrated that VEGFR2 expression was significantly higher in pancreatic tumors (P < .001; mean fluorescent intensity, 499.4 arbitrary units [au] ± 179.1) compared with normal pancreas (mean fluorescent intensity, 232.9 au ± 83.7).

CONCLUSION

US with clinical-grade VEGFR2-targeted microbubbles allows detection of small foci of PDAC in transgenic mice.

Molecular imaging of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a kind of chronic non-specific intestinal inflammatory disease of unknown etiology. Traditional imaging is difficult for early detection of mucosal lesions and is not conducive to early treatment. Colonoscopy is a kind of invasive procedure, and its clinical use is therefore limited. Molecular imaging provides a new approach for early diagnosis of IBD. In this paper, we review recent advances in molecular imaging of IBD.

Ultrasound molecular imaging of E-selectin in tumor vessels using poly n-butyl cyanoacrylate microbubbles covalently coupled to a short targeting peptide

OBJECTIVES

The purposes of this study were the development and preclinical evaluation of clinically translatable E-selectin-specific ultrasound contrast agents based on a peptide ligand with the recognition sequence IELLQAR.

MATERIALS AND METHODS

The E-selectin-specific peptide was synthesized through solid phase peptide synthesis and covalently attached to poly n-butylcyanoacrylate-stabilized microbubbles with an air core. Quantification of the microbubble surface coverage with peptides was performed through flow cytometry. Targeted adhesion of peptide-coated microbubbles was investigated in vitro using parallel plate flow chamber assays on tumor necrosis factor-α-stimulated human umbilical vein endothelial cells. In vivo imaging was performed in nude mice bearing human ovarian carcinoma xenografts (MLS), followed by ex vivo immunohistochemistry validation of E-selectin expression.

RESULTS

Success of peptide synthesis was validated through preparative reverse phase high-pressure liquid chromatography and electronspray ionization-mass spectrometry. Results of the flow cytometry revealed approximately 4000 E-selectin-specific peptides/microbubble surface. Results of the in vitro experiments demonstrated the specificity of peptide-coated microbubbles to E-selectin (1.10 ± 0.48 vs 0.19 ± 0.09 bound microbubbles per cell, before and after competition respectively; P < 0.01). The in vivo imaging enabled specific assessment of E-selectin expression in MLS carcinoma xenografts (5.21 ± 3.41 vs 1.37 ± 0.67 contrast intensity before and after competition, respectively; P < 0.05).

CONCLUSIONS

Clinically translatable microbubbles that were covalently coupled to the short E-selectin-specific peptide (IELLQAR) enabled specific imaging of the E-selectin expression in tumor vessels in vivo.

Recent advances in molecular, multimodal and theranostic ultrasound imaging

Ultrasound (US) imaging is an exquisite tool for the non-invasive and real-time diagnosis of many different diseases. In this context, US contrast agents can improve lesion delineation, characterization and therapy response evaluation. US contrast agents are usually micrometer-sized gas bubbles, stabilized with soft or hard shells. By conjugating antibodies to the microbubble (MB) surface, and by incorporating diagnostic agents, drugs or nucleic acids into or onto the MB shell, molecular, multimodal and theranostic MBs can be generated. We here summarize recent advances in molecular, multimodal and theranostic US imaging, and introduce concepts how such advanced MB can be generated, applied and imaged. Examples are given for their use to image and treat oncological, cardiovascular and neurological diseases. Furthermore, we discuss for which therapeutic entities incorporation into (or conjugation to) MB is meaningful, and how US-mediated MB destruction can increase their extravasation, penetration, internalization and efficacy.

Endoscopic ultrasound of the colon for the differentiation of Crohn's disease and ulcerative colitis in comparison with healthy controls

BACKGROUND

Diagnosis of inflammatory bowel disease (IBD) is based on clinical presentation, colonoscopy and histology. Differentiation of Crohn's disease (CD) and ulcerative colitis (UC) can be difficult in some patients. Endoscopic ultrasound (EUS) provides high resolution images of the gastrointestinal wall (GI) and may be an alternative to differentiate CD/UC.

AIM

EUS of the GI layers in patients with IBD and healthy controls (HC) for the differential diagnosis of UC/CD in a prospective, blinded study.

METHODS

Consecutive patients with CD, UC or HC underwent EUS in the mid sigmoid colon with a forward-viewing radial echoendoscope. Mucosal, submucosal, total wall thickness (TWT) and locoregional lymphnodes (LN) were assessed by EUS in a blinded fashion. TWT was correlated with macroscopic IBD scores and histological inflammation scores.

RESULTS

Total wall thickness of 61 HC was 1.71 ± 0.02 mm, and 3.51 ± 0.15 mm in n = 52 with active IBD. In patients with active UC significant thickening of the mucosa was observed but nearly normal submucosa and m.propria. In active CD significant thickening of the submucosal layer was seen with nearly normal mucosa and m.propria [MucosaUC  = 2.08 ± 0.11 mm, MucosaCD  = 1.32 ± 0.17 mm (P = 0.0001); SubmucosaUC  = 1.01 ± 0.08 mm, SubmucosaCD  = 2.01 ± 0.22 mm (P = 0.0001)]. In 73.7% of patients with active CD, but in none with UC, paracolonic lymph nodes were detected. When mucosal-submucosal and TWT and LNs were combined, the sensitivity was 92.3% for the differentiation of active UC/CD. There was a strong correlation of TWT with histological inflammation scores (UC: r = 0.43; CD: r = 0.69).

CONCLUSIONS

Increased total wall thickness has a high positive predictive value for active IBD. EUS can differentiate active UC from CD and quantify the level of colonic inflammation.