@article{cambria_coughlin_floryan_offeddu_shelton_kamm_2024, title={Linking cell mechanical memory and cancer metastasis}, url={https://doi.org/10.1038/s41568-023-00656-5}, DOI={10.1038/s41568-023-00656-5}, journal={Nature Reviews Cancer}, author={Cambria, Elena and Coughlin, Mark F. and Floryan, Marie A. and Offeddu, Giovanni S. and Shelton, Sarah E. and Kamm, Roger D.}, year={2024}, month={Mar} }
 @article{chen_blazeski_zhang_shelton_offeddu_kamm_2023, title={Development of a perfusable, hierarchical microvasculature-on-a-chip model}, volume={9}, ISSN={["1473-0189"]}, DOI={10.1039/d3lc00512}, journal={LAB ON A CHIP}, author={Chen, Sophia W. and Blazeski, Adriana and Zhang, Shun and Shelton, Sarah E. and Offeddu, Giovanni S. and Kamm, Roger D.}, year={2023}, month={Sep} }
 @article{chen_blazeski_zhang_shelton_offeddu_kamm_2023, title={Development of a perfusable, hierarchical microvasculature-on-a-chip model}, volume={23}, ISSN={["1473-0189"]}, url={https://doi.org/10.1039/D3LC00512G}, DOI={10.1039/d3lc00512g}, abstractNote={Several methods have been developed for generating 3D, in vitro, organ-on-chip models of human vasculature to study vascular function, transport, and tissue engineering. However, many of these existing models lack the hierarchical nature of the arterial-to-capillary-to-venous architecture that is key to capturing a more comprehensive view of the human microvasculature. Here, we present a perfusable, multi-compartmental model that recapitulates the three microvascular compartments to assess various physiological properties such as vessel permeability, vasoconstriction dynamics, and circulating cell arrest and extravasation. Viscous finger patterning and passive pumping create the larger arterial and venular lumens, while the smaller diameter capillary bed vessels are generated through self-assembly. These compartments anastomose and form a perfusable, hierarchical system that portrays the directionality of blood flow through the microvasculature. The addition of collagen channels reduces the apparent permeability of the central capillary region, likely by reducing leakage from the side channels, enabling more accurate measurements of vascular permeability—an important motivation for this study. Furthermore, the model permits modulation of fluid flow and shear stress conditions throughout the system by using hydrostatic pressure heads to apply pressure differentials across either the arteriole or the capillary. This is a pertinent system for modeling circulating tumor or T cell dissemination and extravasation. Circulating cells were found to arrest in areas conducive to physical trapping or areas with the least amount of shear stress, consistent with hemodynamic or mechanical theories of metastasis. Overall, this model captures more features of human microvascular beds and is capable of testing a broad variety of hypotheses.}, number={20}, journal={LAB ON A CHIP}, author={Chen, Sophia W. and Blazeski, Adriana and Zhang, Shun and Shelton, Sarah E. and Offeddu, Giovanni S. and Kamm, Roger D.}, year={2023}, month={Oct}, pages={4552–4564} }
 @article{angelidakis_chen_zhang_wan_kamm_shelton_2023, title={Impact of Fibrinogen, Fibrin Thrombi, and Thrombin on Cancer Cell Extravasation Using In Vitro Microvascular Networks}, url={https://doi.org/10.1002/adhm.202202984}, DOI={10.1002/adhm.202202984}, abstractNote={A bidirectional association exists between metastatic dissemination and the hypercoagulable state associated with many types of cancer. As such, clinical studies have provided evidence that markers associated with elevated levels of coagulation and fibrinolysis correlate with decreased patient survival. However, elucidating the mechanisms underpinning the effects of different components of the coagulation system on metastasis formation is challenging both in animal models and 2D models lacking the complex cellular interactions necessary to model both thrombosis and metastasis. Here, an in vitro, 3D, microvascular model for observing the formation of fibrin thrombi is described, which is in turn used to study how different aspects of the hypercoagulable state associated with cancer affect the endothelium. Using this platform, cancer cells expressing ICAM‐1 are shown to form a fibrinogen‐dependent bridge and transmigrate through the endothelium more effectively. Cancer cells are also demonstrated to interact with fibrin thrombi, using them to adhere, spread, and enhance their extravasation efficiency. Finally, thrombin is also shown to enhance cancer cell extravasation. This system presents a physiologically relevant model of fibrin clot formation in the human microvasculature, enabling in‐depth investigation of the cellular interactions between cancer cells and the coagulation system affecting cancer cell extravasation.}, journal={Advanced Healthcare Materials}, author={Angelidakis, Emmanouil and Chen, Sophia and Zhang, Shun and Wan, Zhengpeng and Kamm, Roger D. and Shelton, Sarah E.}, year={2023}, month={Jul} }
 @article{kim_anandh_null_przanowski_bhatnagar_kumar_shelton_grundy_chiappinelli_kamm_et al._2023, title={Priming a vascular-selective cytokine response permits CD8+ T-cell entry into tumors}, volume={14}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-023-37807-z}, DOI={10.1038/s41467-023-37807-z}, abstractNote={Targeting DNA methyltransferase 1 (DNMT1) has immunomodulatory and anti-neoplastic activity, especially when paired with cancer immunotherapies. Here we explore the immunoregulatory functions of DNMT1 in the tumor vasculature of female mice. Dnmt1 deletion in endothelial cells (ECs) impairs tumor growth while priming expression of cytokine-driven cell adhesion molecules and chemokines important for CD8+ T-cell trafficking across the vasculature; consequently, the efficacy of immune checkpoint blockade (ICB) is enhanced. We find that the proangiogenic factor FGF2 promotes ERK-mediated DNMT1 phosphorylation and nuclear translocation to repress transcription of the chemokines Cxcl9/Cxcl10 in ECs. Targeting Dnmt1 in ECs reduces proliferation but augments Th1 chemokine production and extravasation of CD8+ T-cells, suggesting DNMT1 programs immunologically anergic tumor vasculature. Our study is in good accord with preclinical observations that pharmacologically disrupting DNMT1 enhances the activity of ICB but suggests an epigenetic pathway presumed to be targeted in cancer cells is also operative in the tumor vasculature.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Kim, Dae Joong and Anandh, Swetha and Null, Jamie L. and Przanowski, Piotr and Bhatnagar, Sanchita and Kumar, Pankaj and Shelton, Sarah E. and Grundy, Erin E. and Chiappinelli, Katherine B. and Kamm, Roger D. and et al.}, year={2023}, month={Apr} }
 @article{wan_zhong_zhang_pavlou_coughlin_shelton_nguyen_lorch_barbie_kamm_2022, title={A Robust Method for Perfusable Microvascular Network Formation In Vitro}, volume={6}, ISSN={2366-9608 2366-9608}, url={http://dx.doi.org/10.1002/smtd.202200143}, DOI={10.1002/smtd.202200143}, abstractNote={Micropost‐based microfluidic devices are widely used for microvascular network (MVN) formation in diverse research fields. However, consistently generating perfusable MVNs of physiological morphology and dimension has proven to be challenging. Here, how initial seeding parameters determine key characteristics of MVN formation is investigated and a robust two‐step seeding strategy to generate perfusable physiological MVNs in microfluidic devices is established.}, number={6}, journal={Small Methods}, publisher={Wiley}, author={Wan, Zhengpeng and Zhong, Amy X. and Zhang, Shun and Pavlou, Georgios and Coughlin, Mark F. and Shelton, Sarah E. and Nguyen, Huu Tuan and Lorch, Jochen H. and Barbie, David A. and Kamm, Roger D.}, year={2022}, month={Apr} }
 @article{campisi_shelton_chen_kamm_barbie_knelson_2022, title={Engineered Microphysiological Systems for Testing Effectiveness of Cell-Based Cancer Immunotherapies}, volume={14}, ISSN={2072-6694}, url={http://dx.doi.org/10.3390/cancers14153561}, DOI={10.3390/cancers14153561}, abstractNote={Simple Summary Cell therapy has transformed oncology and drug development, yet better model systems are needed to recapitulate the tumor immune microenvironment (TIME). Microphysiological systems (MPS) can comprehensively model the human TIME, including immune cells, endothelial cells, fibroblasts, matrix, and cytokines. This review discusses current barriers to developing cell therapies for solid tumors from the perspective of MPS model design approaches. Overcoming current limitations in model systems and advancing MPS engineering will facilitate oncology drug development. Abstract Cell therapies, including adoptive immune cell therapies and genetically engineered chimeric antigen receptor (CAR) T or NK cells, have shown promise in treating hematologic malignancies. Yet, immune cell infiltration and expansion has proven challenging in solid tumors due to immune cell exclusion and exhaustion and the presence of vascular barriers. Testing next-generation immune therapies remains challenging in animals, motivating sophisticated ex vivo models of human tumor biology and prognostic assays to predict treatment response in real-time while comprehensively recapitulating the human tumor immune microenvironment (TIME). This review examines current strategies for testing cell-based cancer immunotherapies using ex vivo microphysiological systems and microfluidic technologies. Insights into the multicellular interactions of the TIME will identify novel therapeutic strategies to help patients whose tumors are refractory or resistant to current immunotherapies. Altogether, these microphysiological systems (MPS) have the capability to predict therapeutic vulnerabilities and biological barriers while studying immune cell infiltration and killing in a more physiologically relevant context, thereby providing important insights into fundamental biologic mechanisms to expand our understanding of and treatments for currently incurable malignancies.}, number={15}, journal={Cancers}, publisher={MDPI AG}, author={Campisi, Marco and Shelton, Sarah E. and Chen, Minyue and Kamm, Roger D. and Barbie, David A. and Knelson, Erik H.}, year={2022}, month={Jul}, pages={3561} }
 @article{wan_floryan_coughlin_zhang_zhong_shelton_wang_xu_barbie_kamm_2022, title={New Strategy for Promoting Vascularization in Tumor Spheroids in a Microfluidic Assay}, volume={12}, ISSN={2192-2640 2192-2659}, url={http://dx.doi.org/10.1002/adhm.202201784}, DOI={10.1002/adhm.202201784}, abstractNote={Abstract Previous studies have developed vascularized tumor spheroid models to demonstrate the impact of intravascular flow on tumor progression and treatment. However, these models have not been widely adopted so the vascularization of tumor spheroids in vitro is generally lower than vascularized tumor tissues in vivo. To improve the tumor vascularization level, a new strategy is introduced to form tumor spheroids by adding fibroblasts (FBs) sequentially to a pre‐formed tumor spheroid and demonstrate this method with tumor cell lines from kidney, lung, and ovary cancer. Tumor spheroids made with the new strategy have higher FB densities on the periphery of the tumor spheroid, which tend to enhance vascularization. The vessels close to the tumor spheroid made with this new strategy are more perfusable than the ones made with other methods. Finally, chimeric antigen receptor (CAR) T cells are perfused under continuous flow into vascularized tumor spheroids to demonstrate immunotherapy evaluation using vascularized tumor‐on‐a‐chip model. This new strategy for establishing tumor spheroids leads to increased vascularization in vitro, allowing for the examination of immune, endothelial, stromal, and tumor cell responses under static or flow conditions.}, number={14}, journal={Advanced Healthcare Materials}, publisher={Wiley}, author={Wan, Zhengpeng and Floryan, Marie A. and Coughlin, Mark F. and Zhang, Shun and Zhong, Amy X. and Shelton, Sarah E. and Wang, Xun and Xu, Chenguang and Barbie, David A. and Kamm, Roger D.}, year={2022}, month={Nov} }
 @article{wang_shelton_kastrunes_barbie_freeman_marasco_2022, title={Preclinical models for development of immune–oncology therapies}, volume={03}, ISSN={2634-5099 2634-5099}, url={http://dx.doi.org/10.18609/ioi.2022.41}, DOI={10.18609/ioi.2022.41}, abstractNote={Immunotherapy has demonstrated great success in clinical treatment, especially for cancer care. Here we review preclinical models, including cell lines, three dimensional (3D) cultures, and mouse models to support the need for tools enabling the development of novel immune-oncology (I-O) therapies. While in vitro studies have the advantage of being relatively simpler, faster, and higher throughput than in vivo models, they must be designed carefully to recapitulate the biological conditions that influence drug efficacy. The growing prevalence of 3D in vitro and ex vivo models has enabled screening and mechanistic studies in more complex, tissue-like environments containing multiple interacting cell types. On the other hand, syngeneic mouse models have been instrumental in the historical development of immunotherapies and remain an important tool in drug development, despite lacking fidelity to certain aspects of human physiology and pathology. Xenograft and humanized mouse models address some of these challenges, yet present limitations of their own. Successful development and translation of new I-O therapies will likely require thoughtful combination of several of these preclinical models, and we aim to help research and development scientists utilize the appropriate tools and technologies to facilitate rapid transition from preclinical evaluation to clinical trials.}, number={08}, journal={Immuno Oncology Insights}, publisher={BioInsights Publishing, Ltd.}, author={Wang, Yufei and Shelton, Sarah E and Kastrunes, Gabriella and Barbie, David A and Freeman, Gordon J and Marasco, Wayne A}, year={2022}, month={Oct}, pages={396–398} }
 @article{wan_zhang_zhong_shelton_campisi_sundararaman_offeddu_ko_ibrahim_coughlin_et al._2021, title={A robust vasculogenic microfluidic model using human immortalized endothelial cells and Thy1 positive fibroblasts}, volume={276}, ISSN={0142-9612}, url={http://dx.doi.org/10.1016/j.biomaterials.2021.121032}, DOI={10.1016/j.biomaterials.2021.121032}, abstractNote={Human umbilical vein endothelial cells (HUVECs) and stromal cells, such as human lung fibroblasts (FBs), have been widely used to generate functional microvascular networks (μVNs) in vitro. However, primary cells derived from different donors have batch-to-batch variations and limited lifespans when cultured in vitro, which hampers the reproducibility of μVN formation. Here, we immortalize HUVECs and FBs by exogenously expressing human telomerase reverse transcriptase (hTERT) to obtain stable endothelial cell and FB sources for μVN formation in vitro. Interestingly, we find that immortalized HUVECs can only form functional μVNs with immortalized FBs from earlier passages but not from later passages. Mechanistically, we show that Thy1 expression decreases in FBs from later passages. Compared to Thy1 negative FBs, Thy1 positive FBs express higher IGFBP2, IGFBP7, and SPARC, which are important for angiogenesis and lumen formation during vasculogenesis in 3D. Moreover, Thy1 negative FBs physically block microvessel openings, reducing the perfusability of μVNs. Finally, by culturing immortalized FBs on gelatin-coated surfaces in serum-free medium, we are able to maintain the majority of Thy1 positive immortalized FBs to support perfusable μVN formation. Overall, we establish stable cell sources for μVN formation and characterize the functions of Thy1 positive and negative FBs in vasculogenesis in vitro.}, journal={Biomaterials}, publisher={Elsevier BV}, author={Wan, Zhengpeng and Zhang, Shun and Zhong, Amy X. and Shelton, Sarah E. and Campisi, Marco and Sundararaman, Shriram K. and Offeddu, Giovanni S. and Ko, Eunkyung and Ibrahim, Lina and Coughlin, Mark F. and et al.}, year={2021}, month={Sep}, pages={121032} }
 @article{shelton_nguyen_barbie_kamm_2021, title={Engineering approaches for studying immune-tumor cell interactions and immunotherapy}, volume={24}, ISSN={2589-0042}, url={http://dx.doi.org/10.1016/j.isci.2020.101985}, DOI={10.1016/j.isci.2020.101985}, abstractNote={This review describes recent research that has advanced our understanding of the role of immune cells in the tumor microenvironment (TME) using advanced 3D in vitro models and engineering approaches. The TME can hinder effective eradication of tumor cells by the immune system, but immunotherapy has been able to reverse this effect in some cases. However, patient-to-patient variability in response suggests that we require deeper understanding of the mechanistic interactions between immune and tumor cells to improve response and develop novel therapeutics. Reconstruction of the TME using engineered 3D models allows high-resolution observation of cell interactions while allowing control of conditions such as hypoxia, matrix stiffness, and flow. Moreover, patient-derived organotypic models are an emerging tool for prediction of drug efficacy. This review highlights the importance of modeling and understanding the immune TME and describes new tools for identifying new biological targets, drug testing, and strategies for personalized medicine.}, number={1}, journal={iScience}, publisher={Elsevier BV}, author={Shelton, Sarah E. and Nguyen, Huu Tuan and Barbie, David A. and Kamm, Roger D.}, year={2021}, month={Jan}, pages={101985} }
 @inbook{shelton_kamm_2021, title={In vitro, primarily microfluidic models for atherosclerosis}, url={http://dx.doi.org/10.1016/b978-0-12-817195-0.00013-5}, DOI={10.1016/b978-0-12-817195-0.00013-5}, abstractNote={Atherosclerosis develops over many years, so in vivo and in vitro models are necessary to understand each step in the progression of the disease and to test interventions meant to prevent, halt, or reverse it. While animal models are immensely useful, they do not fully recapitulate the biochemistry or pathology of human disease. Therefore, in vitro models fill an important role, and sophisticated systems for incorporating fluid flow to mimic arterial hemodynamics have developed over the last 40 years. The earliest designs gradually became more complex to include more cell types, stenosis geometry, and disturbed flow regimes. These custom, in vitro flow devices culminated in microfluidic designs in the 2000s once investigators could mold arbitrary geometry at the microscale to finely control cellular exposure to flow. This chapter explores the evolution of in vitro models of atherosclerosis and the variety of hypotheses and results that have emerged from these efforts.}, booktitle={Biomechanics of Coronary Atherosclerotic Plaque}, publisher={Elsevier}, author={Shelton, Sarah E. and Kamm, Roger D.}, year={2021}, pages={299–313} }
 @article{offeddu_serrano_chen_shelton_shin_floryan_kamm_2021, title={Microheart: A microfluidic pump for functional vascular culture in microphysiological systems}, volume={119}, ISSN={0021-9290}, url={http://dx.doi.org/10.1016/j.jbiomech.2021.110330}, DOI={10.1016/j.jbiomech.2021.110330}, abstractNote={Advances in microphysiological systems have prompted the need for long-term cell culture under physiological flow conditions. Conventional laboratory pumps typically lack the ability to deliver cell culture media at the low flow rates required to meet the physiological ranges of fluid flow, and are often pulsatile or require flow reversal. Here, a microfluidic-based pump is presented, which allows for the controlled delivery of media for vascular microphysiological applications. The performance of the pump was characterized in a range of microfluidic systems, including straight channels of varying dimensions and self-assembled microvascular networks. A theoretical framework was developed based on lumped element analysis to predict the performance of the pump for different fluidic configurations and a finite element model of the included check-valves. The use of the pump for microvascular physiological studies demonstrated the utility of this system to recapitulate vascular fluid transport phenomena in microphysiological systems, which may find applications in disease models and drug screening.}, journal={Journal of Biomechanics}, publisher={Elsevier BV}, author={Offeddu, Giovanni S. and Serrano, Jean Carlos and Chen, Sophia W. and Shelton, Sarah E. and Shin, Yoojin and Floryan, Marie and Kamm, Roger D.}, year={2021}, month={Apr}, pages={110330} }
 @article{shelton_stone_gao_zeng_dayton_2020, title={Microvascular Ultrasonic Imaging of Angiogenesis Identifies Tumors in a Murine Spontaneous Breast Cancer Model}, volume={2020}, ISSN={1687-4188 1687-4196}, url={http://dx.doi.org/10.1155/2020/7862089}, DOI={10.1155/2020/7862089}, abstractNote={The purpose of this study is to determine if microvascular tortuosity can be used as an imaging biomarker for the presence of tumor-associated angiogenesis and if imaging this biomarker can be used as a specific and sensitive method of locating solid tumors. Acoustic angiography, an ultrasound-based microvascular imaging technology, was used to visualize angiogenesis development of a spontaneous mouse model of breast cancer (n = 48). A reader study was used to assess visual discrimination between image types, and quantitative methods utilized metrics of tortuosity and spatial clustering for tumor detection. The reader study resulted in an area under the curve of 0.8, while the clustering approach resulted in the best classification with an area under the curve of 0.95. Both the qualitative and quantitative methods produced a correlation between sensitivity and tumor diameter. Imaging of vascular geometry with acoustic angiography provides a robust method for discriminating between tumor and healthy tissue in a mouse model of breast cancer. Multiple methods of analysis have been presented for a wide range of tumor sizes. Application of these techniques to clinical imaging could improve breast cancer diagnosis, as well as improve specificity in assessing cancer in other tissues. The clustering approach may be beneficial for other types of morphological analysis beyond vascular ultrasound images.}, journal={International Journal of Biomedical Imaging}, publisher={Hindawi Limited}, author={Shelton, Sarah E. and Stone, Jodi and Gao, Fei and Zeng, Donglin and Dayton, Paul A.}, year={2020}, month={Feb}, pages={1–10} }
 @article{campisi_sundararaman_shelton_knelson_mahadevan_yoshida_tani_ivanova_cañadas_osaki_et al._2020, title={Tumor-Derived cGAMP Regulates Activation of the Vasculature}, volume={11}, ISSN={1664-3224}, url={http://dx.doi.org/10.3389/fimmu.2020.02090}, DOI={10.3389/fimmu.2020.02090}, abstractNote={Intratumoral recruitment of immune cells following innate immune activation is critical for anti-tumor immunity and involves cytosolic dsDNA sensing by the cGAS/STING pathway. We have previously shown that KRAS-LKB1 (KL) mutant lung cancer, which is resistant to PD-1 blockade, exhibits silencing of STING, impaired tumor cell production of immune chemoattractants, and T cell exclusion. Since the vasculature is also a critical gatekeeper of immune cell infiltration into tumors, we developed a novel microfluidic model to study KL tumor-vascular interactions. Notably, dsDNA priming of LKB1-reconstituted tumor cells activates the microvasculature, even when tumor cell STING is deleted. cGAS-driven extracellular export of 2′3′ cGAMP by cancer cells activates STING signaling in endothelial cells and cooperates with type 1 interferon to increase vascular permeability and expression of E selectin, VCAM-1, and ICAM-1 and T cell adhesion to the endothelium. Thus, tumor cell cGAS-STING signaling not only produces T cell chemoattractants, but also primes tumor vasculature for immune cell escape.}, journal={Frontiers in Immunology}, publisher={Frontiers Media SA}, author={Campisi, Marco and Sundararaman, Shriram K. and Shelton, Sarah E. and Knelson, Erik H. and Mahadevan, Navin R. and Yoshida, Ryohei and Tani, Tetsuo and Ivanova, Elena and Cañadas, Israel and Osaki, Tatsuya and et al.}, year={2020}, month={Sep} }
 @article{panfilova_shelton_caresio_sloun_molinari_wijkstra_dayton_mischi_2019, title={ON THE RELATIONSHIP BETWEEN DYNAMIC CONTRAST-ENHANCED ULTRASOUND PARAMETERS AND THE UNDERLYING VASCULAR ARCHITECTURE EXTRACTED FROM ACOUSTIC ANGIOGRAPHY}, volume={45}, ISSN={["1879-291X"]}, url={https://europepmc.org/articles/PMC6352898}, DOI={10.1016/j.ultrasmedbio.2018.08.018}, abstractNote={Dynamic contrast-enhanced ultrasound (DCE-US) has been proposed as a powerful tool for cancer diagnosis by estimation of perfusion and dispersion parameters reflecting angiogenic vascular changes. This work was aimed at identifying which vascular features are reflected by the estimated perfusion and dispersion parameters through comparison with acoustic angiography (AA). AA is a high-resolution technique that allows quantification of vascular morphology. Three-dimensional AA and 2-D DCE-US bolus acquisitions were used to monitor the growth of fibrosarcoma tumors in nine rats. AA-derived vascular properties were analyzed along with DCE-US perfusion and dispersion to investigate the differences between tumor and control and their evolution in time. AA-derived microvascular density and DCE-US perfusion exhibited good agreement, confirmed by their spatial distributions. No vascular feature was correlated with dispersion. Yet, dispersion provided better cancer classification than perfusion. We therefore hypothesize that dispersion characterizes vessels that are smaller than those visible with AA.}, number={2}, journal={ULTRASOUND IN MEDICINE AND BIOLOGY}, author={Panfilova, Anastasiia and Shelton, Sarah E. and Caresio, Cristina and Sloun, Ruud J. G. and Molinari, Filippo and Wijkstra, Hessel and Dayton, Paul A. and Mischi, Massimo}, year={2019}, month={Feb}, pages={539–548} }
 @article{mohanty_papadopoulou_newsome_shelton_dayton_muller_2019, title={Ultrasound multiple scattering with microbubbles can differentiate between tumor and healthy tissue in vivo}, volume={64}, ISSN={["1361-6560"]}, url={https://europepmc.org/articles/PMC6876296}, DOI={10.1088/1361-6560/ab1a44}, abstractNote={Most solid tumors are characterized by highly dense, isotropic vessel networks. Characterization of such features has shown promise for early cancer diagnosis. Ultrasound diffusion has been used to characterize the micro-architecture of complex media, such as bone and the lungs. In this work, we examine a non-invasive diffusion-based ultrasound technique to assess neo-vascularization. Because the diffusion constant reflects the density of scatterers in heterogeneous media, we hypothesize that by injecting microbubbles into the vasculature, ultrasound diffusivity can reflect vascular density (VD), thus differentiating the microvascular patterns between tumors and healthy tissue. The diffusion constant and its anisotropy are shown to be significantly different between fibrosarcoma tumors (n  =  16) and control tissue (n  =  18) in a rat animal model in vivo. The diffusion constant values for control and tumor were found to be 1.38  ±  0.51 mm2 µs−1 and 0.65  ±  0.27 mm2 µs−1, respectively. These results are corroborated with VD from acoustic angiography (AA) data, confirming increased vessel density in tumors compared to controls. The diffusion constant offers a promising way to quantitatively assess vascular networks when combined with contrast agents, which may allow early tumor detection and characterization.}, number={11}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, author={Mohanty, Kaustav and Papadopoulou, Virginie and Newsome, Isabel G. and Shelton, Sarah and Dayton, Paul A. and Muller, Marie}, year={2019}, month={Jun} }
 @article{lin_shelton_espíndola_rojas_pinton_dayton_2017, title={3-D Ultrasound Localization Microscopy for Identifying Microvascular Morphology Features of Tumor Angiogenesis at a Resolution Beyond the Diffraction Limit of Conventional Ultrasound}, volume={7}, ISSN={1838-7640}, url={http://dx.doi.org/10.7150/thno.16899}, DOI={10.7150/thno.16899}, abstractNote={Angiogenesis has been known as a hallmark of solid tumor cancers for decades, yet ultrasound has been limited in its ability to detect the microvascular changes associated with malignancy. Here, we demonstrate the potential of 'ultrasound localization microscopy' applied volumetrically in combination with quantitative analysis of microvascular morphology, as an approach to overcome this limitation. This pilot study demonstrates our ability to image complex microvascular patterns associated with tumor angiogenesis in-vivo at a resolution of tens of microns - substantially better than the diffraction limit of traditional clinical ultrasound, yet using an 8 MHz clinical ultrasound probe. Furthermore, it is observed that data from healthy and tumor-bearing tissue exhibit significant differences in microvascular pattern and density. Results suggests that with continued development of these novel technologies, ultrasound has the potential to detect biomarkers of cancer based on the microvascular 'fingerprint' of malignant angiogenesis rather than through imaging of blood flow dynamics or the tumor mass itself.}, number={1}, journal={Theranostics}, publisher={Ivyspring International Publisher}, author={Lin, Fanglue and Shelton, Sarah E. and Espíndola, David and Rojas, Juan D. and Pinton, Gianmarco and Dayton, Paul A.}, year={2017}, pages={196–204} }
 @article{lindsey_shelton_foster_dayton_2017, title={Assessment of Molecular Acoustic Angiography for Combined Microvascular and Molecular Imaging in Preclinical Tumor Models}, volume={19}, ISSN={1536-1632 1860-2002}, url={http://dx.doi.org/10.1007/s11307-016-0991-4}, DOI={10.1007/s11307-016-0991-4}, abstractNote={The purposes of the present study is to evaluate a new ultrasound molecular imaging approach in its ability to image a preclinical tumor model and to investigate the capacity to visualize and quantify co-registered microvascular and molecular imaging volumes.Molecular imaging using the new technique was compared with a conventional ultrasound molecular imaging technique (multi-pulse imaging) by varying the injected microbubble dose and scanning each animal using both techniques. Each of the 14 animals was randomly assigned one of three doses; bolus dose was varied, and the animals were imaged for three consecutive days so that each animal received every dose. A microvascular scan was also acquired for each animal by administering an infusion of nontargeted microbubbles. These scans were paired with co-registered molecular images (VEGFR2-targeted microbubbles), the vessels were segmented, and the spatial relationships between vessels and VEGFR2 targeting locations were analyzed. In five animals, an additional scan was performed in which the animal received a bolus of microbubbles targeted to E- and P-selectins. Vessel tortuosity as a function of distance from VEGF and selectin targeting was analyzed in these animals.Although resulting differences in image intensity due to varying microbubble dose were not significant between the two lowest doses, superharmonic imaging had significantly higher contrast-to-tissue ratio (CTR) than multi-pulse imaging (mean across all doses 13.98 dB for molecular acoustic angiography vs. 0.53 dB for multi-pulse imaging; p = 4.9 × 10-10). Analysis of registered microvascular and molecular imaging volumes indicated that vessel tortuosity decreases with increasing distance from both VEGFR2- and selectin-targeting sites.Molecular acoustic angiography (superharmonic molecular imaging) exhibited a significant increase in CTR at all doses tested due to superior rejection of tissue artifact signals. Due to the high resolution of acoustic angiography molecular imaging, it is possible to analyze spatial relationships in aligned microvascular and molecular superharmonic imaging volumes. Future studies are required to separate the effects of biomarker expression and blood flow kinetics in comparing local tortuosity differences between different endothelial markers such as VEGFR2, E-selectin, and P-selectin.}, number={2}, journal={Molecular Imaging and Biology}, publisher={Springer Science and Business Media LLC}, author={Lindsey, Brooks D. and Shelton, Sarah E. and Foster, F. Stuart and Dayton, Paul A.}, year={2017}, pages={194–202} }
 @inproceedings{newsome_lindsey_shelton_cherin_yin_foster_dayton_2017, title={Characterization of a prototype transmit 2 MHz receive 21 MHz array for superharmonic imaging}, url={http://dx.doi.org/10.1109/ultsym.2017.8092707}, DOI={10.1109/ultsym.2017.8092707}, abstractNote={The role of angiogenesis in cancer has spurred the development of new methods for imaging vasculature. One such method is acoustic angiography, a dual-frequency superharmonic contrast imaging technique. Custom transducers are necessary for the ultra-wide bandwidth required for this technique, but the current single-element designs present several limitations for translation to clinical use, such as a fixed focus and limited frame rates. In this work, we present initial tests of a dual-frequency array for superharmonic contrast-enhanced microvascular imaging. The array was characterized by in vitro measurements, including imaging of microcellulose tubes in water and phantom material.}, booktitle={2017 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Newsome, Isabel G. and Lindsey, Brooks D. and Shelton, Sarah E. and Cherin, Emmanuel and Yin, Jianhua and Foster, F. Stuart and Dayton, Paul A.}, year={2017}, month={Sep} }
 @article{shelton_lindsey_dayton_lee_2017, title={First-in-Human Study of Acoustic Angiography in the Breast and Peripheral Vasculature}, volume={43}, ISSN={0301-5629}, url={http://dx.doi.org/10.1016/j.ultrasmedbio.2017.08.1881}, DOI={10.1016/j.ultrasmedbio.2017.08.1881}, abstractNote={Screening with mammography has been found to increase breast cancer survival rates by about 20%. However, the current system in which mammography is used to direct patients toward biopsy or surgical excision also results in relatively high rates of unnecessary biopsy, as 66.8% of biopsies are benign. A non-ionizing radiation imaging approach with increased specificity might reduce the rate of unnecessary biopsies. Quantifying the vascular characteristics within and surrounding lesions represents one potential target for assessing likelihood of malignancy via imaging. In this clinical note, we describe the translation of a contrast-enhanced ultrasound technique, acoustic angiography, to human imaging. We illustrate the feasibility of this technique with initial studies in imaging the hand, wrist and breast using Definity microbubble contrast agent and a mechanically steered prototype dual-frequency transducer in healthy volunteers. Finally, this approach was used to image pre-biopsy Breast Imaging Reporting and Data System (BI-RADS) 4 and 5 lesions <2 cm in depth in 11 patients. Results indicate that sensitivity and spatial resolution are sufficient to image vessels as small as 0.2 mm in diameter at depths of ~15 mm in the human breast. Challenges observed include motion artifacts, as well as limited depth of field and sensitivity, which could be improved by correction algorithms and improved transducer technologies.}, number={12}, journal={Ultrasound in Medicine & Biology}, publisher={Elsevier BV}, author={Shelton, Sarah E. and Lindsey, Brooks D. and Dayton, Paul A. and Lee, Yueh Z.}, year={2017}, month={Dec}, pages={2939–2946} }
 @article{lindsey_shelton_martin_ozgun_rojas_foster_dayton_2017, title={High Resolution Ultrasound Superharmonic Perfusion Imaging: In Vivo Feasibility and Quantification of Dynamic Contrast-Enhanced Acoustic Angiography}, volume={45}, ISSN={["1573-9686"]}, url={https://europepmc.org/articles/PMC5682933}, DOI={10.1007/s10439-016-1753-9}, abstractNote={Mapping blood perfusion quantitatively allows localization of abnormal physiology and can improve understanding of disease progression. Dynamic contrast-enhanced ultrasound is a low-cost, real-time technique for imaging perfusion dynamics with microbubble contrast agents. Previously, we have demonstrated another contrast agent-specific ultrasound imaging technique, acoustic angiography, which forms static anatomical images of the superharmonic signal produced by microbubbles. In this work, we seek to determine whether acoustic angiography can be utilized for high resolution perfusion imaging in vivo by examining the effect of acquisition rate on superharmonic imaging at low flow rates and demonstrating the feasibility of dynamic contrast-enhanced superharmonic perfusion imaging for the first time. Results in the chorioallantoic membrane model indicate that frame rate and frame averaging do not affect the measured diameter of individual vessels observed, but that frame rate does influence the detection of vessels near and below the resolution limit. The highest number of resolvable vessels was observed at an intermediate frame rate of 3 Hz using a mechanically-steered prototype transducer. We also demonstrate the feasibility of quantitatively mapping perfusion rate in 2D in a mouse model with spatial resolution of ~100 μm. This type of imaging could provide non-invasive, high resolution quantification of microvascular function at penetration depths of several centimeters.}, number={4}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Lindsey, Brooks D. and Shelton, Sarah E. and Martin, K. Heath and Ozgun, Kathryn A. and Rojas, Juan D. and Foster, F. Stuart and Dayton, Paul A.}, year={2017}, month={Apr}, pages={939–948} }
 @inproceedings{panfilova_shelton_van sloun_caresio_wijkstra_dayton_mischi_2017, title={Which properties of the vascular architecture are reflected by dynamic contrast-enhanced ultrasound imaging of dispersion and wash-in rate? A comparison with acoustic angiography}, url={http://dx.doi.org/10.1109/ultsym.2017.8092873}, DOI={10.1109/ultsym.2017.8092873}, abstractNote={Tumor growth requires angiogenesis and neovascularization, resulting in the formation of microvessels which differ in their morphology from those of healthy tissue. These vascular abnormalities result in altered blood flow dynamics, which can be assessed by dynamic contrast-enhanced ultrasound (DCE-US). Two distinct approaches are typically employed in DCE-US: the assessment of either perfusion or dispersion parameters from the measured time intensity curves. In this paper, we look at longitudinal trends of wash-in-rate (WIR), a perfusion parameter, and correlation coefficient, a dispersion parameter, in 3 fibrosarcoma xenograft models. We compare them to the microvascular density (MVD) extracted from acoustic angiography (AA), a high resolution technique enabling the delineation of microvessels. We also compare spatial parameter distributions acquired with both imaging modalities. The performed analysis indicates that WIR reflects MVD, while no microvascular parameter that reflects the correlation coefficient has been identified. We hypothesize that the correlation coefficient reflects properties of smaller vessels than those visible with AA.}, booktitle={2017 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Panfilova, Anastasiia and Shelton, Sarah and van Sloun, Ruud J G and Caresio, Cristina and Wijkstra, Hessel and Dayton, Paul and Mischi, Massimo}, year={2017}, month={Sep} }
 @article{shelton_lindsey_gessner_lee_aylward_lee_cherin_foster_dayton_2016, title={Acoustic angiography: A new high frequency contrast ultrasound technique for biomedical imaging}, volume={9871}, ISSN={["1996-756X"]}, DOI={10.1117/12.2229179}, abstractNote={Acoustic Angiography is a new approach to high-resolution contrast enhanced ultrasound imaging enabled by ultra-broadband transducer designs. The high frequency imaging technique provides signal separation from tissue which does not produce significant harmonics in the same frequency range, as well as high resolution. This approach enables imaging of microvasculature in-vivo with high resolution and signal to noise, producing images that resemble x-ray angiography. Data shows that acoustic angiography can provide important information about the presence of disease based on vascular patterns, and may enable a new paradigm in medical imaging.}, journal={SENSING AND ANALYSIS TECHNOLOGIES FOR BIOMEDICAL AND COGNITIVE APPLICATIONS 2016}, author={Shelton, Sarah E. and Lindsey, Brooks D. and Gessner, Ryan and Lee, Yueh and Aylward, Stephen and Lee, Hyunggyun and Cherin, Emmanuel and Foster, F. Stuart and Dayton, Paul A.}, year={2016} }
 @inproceedings{panfilova_shelton_van sloun_demi_wijkstra_dayton_mischi_2016, title={Does contrast ultrasound dispersion imaging reveal changes in tortuosity? A comparison with acoustic angiography}, booktitle={IEEE International Ultrasound Symposium}, author={Panfilova, A. and Shelton, S.E. and van Sloun, R.J.G. and Demi, L. and Wijkstra, H. and Dayton, P. and Mischi, M.}, year={2016}, month={Sep} }
 @article{joshi_shelton_papadopoulou_lindsey_dayton_muller_2016, title={In-vivo</i> quantitative analysis of the angiogenic microvasculature in tumor-bearing rats using multiple scattering: A preliminary study}, volume={140}, ISSN={0001-4966 1520-8524}, url={http://dx.doi.org/10.1121/1.4970022}, DOI={10.1121/1.4970022}, abstractNote={We propose a method to quantify the vascular density in vascular networks using contrast-enhanced multiple scattering. We measured the diffusion constant D and transport mean free path L* from the time evolution of the incoherent intensity in a rat model of cancer. An 8 MHz linear transducer array was used to record the backscattered signals from subcutaneous fibrosarcoma tumors and control tissue. The coherent and incoherent contributions to the backscattered intensity were separated, and the growth rate of the incoherent contribution was measured, giving the D and L*, knowing the effective speed of sound. By translating the linear array along the tumor, mapping of L* was achieved. Tumors were implanted in the right flank of four rats, and the contralateral side served as control. Acoustic angiography and measurements of the incoherent intensity were performed. The mean L* values in control and tumor tissue were significantly different (105.27 + /- 30.96 micron and 41.28+ /- 14.23 micron, respectively, p = 8.4033 × 10-49). The mean distance between vessels was estimated from acoustic angiography images using Monte-Carlo simulations, and was in agreement with the experimentally calculated values of L* (r = 0.9507, p = 1.4957 × 10-9).}, number={4_Supplement}, journal={Journal of the Acoustical Society of America}, publisher={Acoustical Society of America (ASA)}, author={Joshi, Aditya and Shelton, Sarah and Papadopoulou, Virginie and Lindsey, Brooks and Dayton, Paul and Muller, Marie}, year={2016}, month={Oct}, pages={3187–3187} }
 @article{shelton_lindsey_tsuruta_foster_dayton_2016, title={MOLECULAR ACOUSTIC ANGIOGRAPHY: A NEW TECHNIQUE FOR HIGH-RESOLUTION SUPERHARMONIC ULTRASOUND MOLECULAR IMAGING}, volume={42}, ISSN={["1879-291X"]}, url={https://europepmc.org/articles/PMC5653972}, DOI={10.1016/j.ultrasmedbio.2015.10.015}, abstractNote={Ultrasound molecular imaging utilizes targeted microbubbles to bind to vascular targets such as integrins, selectins and other extracellular binding domains. After binding, these microbubbles are typically imaged using low pressures and multi-pulse imaging sequences. In this article, we present an alternative approach for molecular imaging using ultrasound that relies on superharmonic signals produced by microbubble contrast agents. Bound bubbles were insonified near resonance using a low frequency (4 MHz) element and superharmonic echoes were received at high frequencies (25-30 MHz). Although this approach was observed to produce declining image intensity during repeated imaging in both in vitro and in vivo experiments because of bubble destruction, the feasibility of superharmonic molecular imaging was demonstrated for transmit pressures, which are sufficiently high to induce shell disruption in bound microbubbles. This approach was validated using microbubbles targeted to the αvβ3 integrin in a rat fibrosarcoma model (n = 5) and combined with superharmonic images of free microbubbles to produce high-contrast, high-resolution 3-D volumes of both microvascular anatomy and molecular targeting. Image intensity over repeated scans and the effect of microbubble diameter were also assessed in vivo, indicating that larger microbubbles yield increased persistence in image intensity. Using ultrasound-based acoustic angiography images rather than conventional B-mode ultrasound to provide the underlying anatomic information facilitates anatomic localization of molecular markers. Quantitative analysis of relationships between microvasculature and targeting information indicated that most targeting occurred within 50 μm of a resolvable vessel (>100 μm diameter). The combined information provided by these scans may present new opportunities for analyzing relationships between microvascular anatomy and vascular targets, subject only to limitations of the current mechanically scanned system and microbubble persistence to repeated imaging at moderate mechanical indices.}, number={3}, journal={ULTRASOUND IN MEDICINE AND BIOLOGY}, author={Shelton, Sarah E. and Lindsey, Brooks D. and Tsuruta, James K. and Foster, F. Stuart and Dayton, Paul A.}, year={2016}, month={Mar}, pages={769–781} }
 @inproceedings{shelton_lindsey_dayton_foster_2016, title={Molecular acoustic angiography: Comparison of contrast-to-tissue ratio with multi-pulse techniques and imaging multiple targeted microbubbles}, url={http://dx.doi.org/10.1109/ultsym.2016.7728703}, DOI={10.1109/ultsym.2016.7728703}, abstractNote={Acoustic angiography is a high resolution (~100 μm) approach that utilizes the superharmonic signal produced by microbubbles, which we have recently extended for molecular imaging. These molecular images can also be overlaid onto images of microvascular anatomy in order to assess relationships between vascular morphology and targeting distribution. In this work we compare the contrast-to-tissue ratio (CTR) between superharmonic and multi-pulse molecular imaging and present images of microbubbles targeted to different biomarkers expressed by the vascular endothelial cells. Combing molecular and microvascular information about developing tumors could provide vital information for treatment planning, monitoring, and for ensuring clean margins in surgical resection.}, booktitle={2016 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Shelton, Sarah E. and Lindsey, Brooks D. and Dayton, Paul A. and Foster, F. Stuart}, year={2016}, month={Sep} }
 @article{rao_shelton_dayton_2016, title={The "Fingerprint" of Cancer Extends Beyond Solid Tumor Boundaries: Assessment With a Novel Ultrasound Imaging Approach}, volume={63}, ISSN={["1558-2531"]}, url={https://europepmc.org/articles/PMC5070672}, DOI={10.1109/tbme.2015.2479590}, abstractNote={Goal: Abnormalities of microvascular morphology have been associated with tumor angiogenesis for more than a decade, and are believed to be intimately related to both tumor malignancy and response to treatment. However, the study of these vascular changes in-vivo has been challenged due to the lack of imaging approaches which can assess the microvasculature in 3-D volumes noninvasively. Here, we use contrast-enhanced “acoustic angiography” ultrasound imaging to observe and quantify heterogeneity in vascular morphology around solid tumors. Methods: Acoustic angiography, a recent advance in contrast-enhanced ultrasound imaging, generates high-resolution microvascular images unlike anything possible with standard ultrasound imaging techniques. Acoustic angiography images of a genetically engineered mouse breast cancer model were acquired to develop an image acquisition and processing routine that isolated radially expanding regions of a 3-D image from the tumor boundary to the edge of the imaging field for assessment of vascular morphology of tumor and surrounding vessels. Results: Quantitative analysis of vessel tortuosity for the tissue surrounding tumors 3 to 7 mm in diameter revealed that tortuosity decreased in a region 6 to 10 mm from the tumor boundary, but was still significantly elevated when compared to control vasculature. Conclusion: Our analysis of angiogenesis-induced changes in the vasculature outside the tumor margin reveals that the extent of abnormal tortuosity extends significantly beyond the primary tumor mass. Significance: Visualization of abnormal vascular tortuosity may make acoustic angiography an invaluable tool for early tumor detection based on quantifying the vascular footprint of small tumors and a sensitive method for understanding changes in the vascular microenvironment during tumor progression.}, number={5}, journal={IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING}, author={Rao, Sneha R. and Shelton, Sarah E. and Dayton, Paul A.}, year={2016}, month={May}, pages={1082–1086} }
 @inproceedings{shelton_dayton_aylward_foster_2016, title={The application of acoustic angiography to assess the progression of angiogenesis in a spontaneous mouse model of breast cancer}, url={http://dx.doi.org/10.1109/ultsym.2016.7728697}, DOI={10.1109/ultsym.2016.7728697}, abstractNote={Acoustic angiography is a method for contrast enhanced ultrasound imaging that provides sufficient contrast and resolution to visualize microvasculature non-invasively. A dual-frequency transducer is used to transmit at low frequency and receive high frequency (superharmonic) echoes originating from intravascular microbubbles. Analysis of these images in healthy and tumor-bearing mice revealed that tumors possess quantifiably different vascular structure than healthy control animals, through measurements of vascular density and 2 metrics of tortuosity. Furthermore, tortuosity is correlated to proximity to the tumor margin, and distal tissue surrounding tumor regions has an intermediate level of tortuosity between that of tumor and control tissue. Overall, these results indicate that acoustic angiography images can reveal microvasculature in sufficient detail for vascular morphology to be used as a biomarker for cancer imaging.}, booktitle={2016 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Shelton, Sarah E. and Dayton, Paul A. and Aylward, Stephen R. and Foster, F. Stuart}, year={2016}, month={Sep} }
 @inproceedings{lindsey_shelton_tsuruta_dayton_foster_2015, title={Molecular acoustic angiography: Demonstration of in vivo feasibility for high resolution superharmonic ultrasound molecular imaging}, url={http://dx.doi.org/10.1109/ultsym.2015.0007}, DOI={10.1109/ultsym.2015.0007}, abstractNote={Ultrasound molecular imaging utilizes targeted microbubbles to image molecular targets such as integrins, selectins, and other extracellular binding domains. Targeted microbubbles have typically been imaged using contrast-specific multi-pulse imaging sequences. Here we present an alternative strategy for ultrasound molecular imaging based on superharmonic signals produced by microbubbles. Bound bubbles were insonified near resonance using a low frequency (4 MHz) and superharmonic echoes were received at high frequencies (30 MHz). The feasibility of superharmonic molecular imaging was shown using microbubbles targeted to the αvβ3 integrin in a rat fibrosarcoma model (n=5) and combined with superharmonic images of free microbubbles to produce high contrast, high resolution 3D volumes of both microvascular anatomy and molecular targeting. Anatomical localization of molecular markers may prove easier using ultrasound-based acoustic angiography images as a reference rather than conventional B-mode images.}, booktitle={2015 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Lindsey, Brooks D. and Shelton, Sarah E. and Tsuruta, James K. and Dayton, Paul A. and Foster, F. Stuart}, year={2015}, month={Oct} }
 @article{lindsey_shelton_dayton_2015, title={Optimization of Contrast-to-Tissue Ratio Through Pulse Windowing in Dual-Frequency “Acoustic Angiography” Imaging}, volume={41}, ISSN={0301-5629}, url={http://dx.doi.org/10.1016/j.ultrasmedbio.2015.02.011}, DOI={10.1016/j.ultrasmedbio.2015.02.011}, abstractNote={Early-stage tumors in many cancers are characterized by vascular remodeling, indicative of transformations in cell function. We have previously presented a high-resolution ultrasound imaging approach to detecting these changes that is based on microbubble contrast agents. In this technique, images are formed from only the higher harmonics of microbubble contrast agents, producing images of vasculature alone with 100- to 200-μm resolution. In this study, shaped transmit pulses were used to image the higher broadband harmonic echoes of microbubble contrast agents, and the effects of varying pulse window and phasing on microbubble and tissue harmonic echoes were evaluated using a dual-frequency transducer in vitro and in vivo. An increase in the contrast-to-tissue ratio of 6.8 ± 2.3 dB was observed in vitro using an inverted pulse with a cosine window relative to a non-inverted pulse with a rectangular window. The increase in mean image intensity resulting from contrast enhancement in vivo in five rodents was 13.9 ± 3.0 dB greater for an inverted cosine-windowed pulse and 17.8 ± 3.6 dB greater for a non-inverted Gaussian-windowed pulse relative to a non-inverted pulse with a rectangular window. Implications for pre-clinical and diagnostic imaging are discussed.}, number={7}, journal={Ultrasound in Medicine & Biology}, publisher={Elsevier BV}, author={Lindsey, Brooks D. and Shelton, Sarah E. and Dayton, Paul A.}, year={2015}, month={Jul}, pages={1884–1895} }
 @article{shelton_lee_lee_cherin_foster_aylward_dayton_2015, title={QUANTIFICATION OF MICROVASCULAR TORTUOSITY DURING TUMOR EVOLUTION USING ACOUSTIC ANGIOGRAPHY}, volume={41}, ISSN={["1879-291X"]}, url={https://europepmc.org/articles/PMC4778417}, DOI={10.1016/j.ultrasmedbio.2015.02.012}, abstractNote={The recent design of ultra-broadband, multifrequency ultrasound transducers has enabled high-sensitivity, high-resolution contrast imaging, with very efficient suppression of tissue background using a technique called acoustic angiography. Here we perform the first application of acoustic angiography to evolving tumors in mice predisposed to develop mammary carcinoma, with the intent of visualizing and quantifying angiogenesis progression associated with tumor growth. Metrics compared include vascular density and two measures of vessel tortuosity quantified from segmentations of vessels traversing and surrounding 24 tumors and abdominal vessels from control mice. Quantitative morphologic analysis of tumor vessels revealed significantly increased vascular tortuosity abnormalities associated with tumor growth, with the distance metric elevated approximately 14% and the sum of angles metric increased 60% in tumor vessels versus controls. Future applications of this imaging approach may provide clinicians with a new tool in tumor detection, differentiation or evaluation, though with limited depth of penetration using the current configuration.}, number={7}, journal={ULTRASOUND IN MEDICINE AND BIOLOGY}, author={Shelton, Sarah E. and Lee, Yueh Z. and Lee, Mike and Cherin, Emmanuel and Foster, F. Stuart and Aylward, Stephen R. and Dayton, Paul A.}, year={2015}, month={Jul}, pages={1896–1904} }
 @article{lindsey_rojas_martin_shelton_dayton_2014, title={Acoustic Characterization of Contrast-to-issue Ratio and Axial Resolution for Dual-Frequency Contrast-Specific Acoustic Angiography Imaging}, volume={61}, ISSN={["1525-8955"]}, url={https://europepmc.org/articles/PMC8375273}, DOI={10.1109/tuffc.2014.006466}, abstractNote={Recently, dual-frequency transducers have enabled high-spatial-resolution and high-contrast imaging of vasculature with minimal tissue artifacts by transmitting at a low frequency and receiving broadband superharmonic echoes scattered by microbubble contrast agents. In this work, we examine the imaging parameters for optimizing contrast-totissue ratio (CTR) for dual-frequency imaging and the relationship with spatial resolution. Confocal piston transducers are used in a water bath setup to measure the SNR, CTR, and axial resolution for ultrasound imaging of nonlinear scattering of microbubble contrast agents when transmitting at a lower frequency (1.5 to 8 MHz) and receiving at a higher frequency (7.5 to 25 MHz). Parameters varied include the frequency and peak negative pressure of transmitted waves, center frequency of the receiving transducer, microbubble concentration, and microbubble size. CTR is maximized at the lowest transmission frequencies but would be acceptable for imaging in the 1.5 to 3.5 MHz range. At these frequencies, CTR is optimized when a receiving transducer with a center frequency of 10 MHz is used, with the maximum CTR of 25.5 dB occurring when transmitting at 1.5 MHz with a peak negative pressure of 1600 kPa and receiving with a center frequency of 10 MHz. Axial resolution is influenced more heavily by the receiving center frequency, with a weak decrease in measured pulse lengths associated with increasing transmit frequency. A microbubble population containing predominately 4-μm-diameter bubbles yielded the greatest CTR, followed by 1- and then 2-μm bubbles. Varying concentration showed little effect over the tested parameters. CTR dependence on transmit frequency and peak pressure were confirmed through in vivo imaging in two rodents. These findings may lead to improved imaging of vascular remodeling in superficial or luminal cancers such as those of the breast, prostate, and colon.}, number={10}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Lindsey, Brooks D. and Rojas, Juan D. and Martin, K. Heath and Shelton, Sarah E. and Dayton, Paul A.}, year={2014}, month={Oct}, pages={1668–1687} }
 @article{lindsey_rojas_martin_shelton_dayton_2014, title={Optimization of Contrast-to-tissue Ratio and Role of Bubble Destruction in Dual-Frequency Contrast-Specific "Acoustic Angiography" Imaging}, ISSN={["1948-5719"]}, DOI={10.1109/ultsym.2014.0440}, abstractNote={Recently, dual-frequency transducers have enabled high-spatial resolution, high-contrast imaging of microvasculature by transmitting at a low frequency and receiving broadband superharmonic echoes from microbubble contrast agents at a higher frequency. In this work, we examine the imaging parameters for optimizing contrast-to-tissue ratio (CTR) for dual-frequency imaging and the relationship between bubble destruction and broadband harmonic signal production. CTR was assessed in vitro by acquiring scattered echoes by bubbles and beef muscle for transmit pressures up to 2 MPa, transmit frequencies from 1.5-8 MHz, and receive frequencies from 7.5 to 25 MHz. Optimum CTR (25.5 dB) was found to occur at the lowest transmit frequencies, though a broad peak exists within the 1.5-3.5 MHz range. At these frequencies, CTR is optimized when receiving at a center frequency of 10 - 15 MHz. A 4 μm-diameter microbubble population yielded ~5 dB higher CTR than a 1 μm population. Single bubble behavior was assessed with simultaneous acoustic and optical recordings. For n=250 single bubbles subjected to five consecutive single-cycle pulses (100-500 kPa), three primary categories of bubble behavior were observed optically: 1) no change in bubble diameter, 2) bubble shrinking (deflation), and 3) immediate bubble destruction (fragmentation). Matched acoustic data indicate that superharmonic signals having the broadest bandwidth and highest energy are associated with shell fragmentation. In the deflation case, a weaker superharmonic signal is produced with an amplitude approximately 25% of the signal in the shell fragmentation case. Similar regimes were observed in vivo, suggesting that bubble diameter, transmit frequency, peak negative pressure, and frame rate must be selected in light of the intended application, accounting for attenuation and local perfusion rate in the region of interest.}, journal={2014 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS)}, author={Lindsey, Brooks D. and Rojas, Juan D. and Martin, K. Heath and Shelton, Sarah E. and Dayton, Paul A.}, year={2014}, pages={1774–1777} }
 @inproceedings{dayton_gessner_phillips_shelton_martin_lee_foster_2014, title={The implementation of acoustic angiography for microvascular and angiogenesis imaging}, url={http://dx.doi.org/10.1109/embc.2014.6944571}, DOI={10.1109/embc.2014.6944571}, abstractNote={Recently, it has been demonstrated that through the use of contrast agents and multi-frequency transducer technology, high resolution and high signal to noise ultrasound images can be obtained which illustrate microvascular structure in unprecedented detail for an ultrasound modality. The enabling technology is ultrasound transducers which are fabricated with elements which can excite microbubble contrast agents near resonance and detect their broadband harmonics at a much higher bandwidth (several times the fundamental frequency). The resulting images contain very little background from tissue scattering and thus provide high contrast, and can have a resolution on the order of 130 microns with an appropriate high frequency receiving element. Because microbubbles are strictly an intravascular agent, this approach enables visualization of microvascular morphology with unique clarity, providing insight into angiogenesis associated with tumor development.}, booktitle={2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society}, publisher={IEEE}, author={Dayton, Paul A. and Gessner, Ryan C. and Phillips, Linsey and Shelton, Sarah E. and Martin, K.H. and Lee, Mike and Foster, F. Stuart}, year={2014}, month={Aug} }
 @article{dunleavey_xiao_thompson_kim_shields_shelton_irvin_brings_ollila_brekken_et al._2014, title={Vascular channels formed by subpopulations of PECAM1+ melanoma cells}, volume={5}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/ncomms6200}, DOI={10.1038/ncomms6200}, abstractNote={Targeting the vasculature remains a promising approach for treating solid tumours; however, the mechanisms of tumour neovascularization are diverse and complex. Here we uncover a new subpopulation of melanoma cells that express the vascular cell adhesion molecule PECAM1, but not VEGFR-2, and participate in a PECAM1-dependent form of vasculogenic mimicry (VM). Clonally derived PECAM1+ tumour cells coalesce to form PECAM1-dependent networks in vitro and they generate well-perfused, vascular endothelial growth factor (VEGF)-independent channels in mice. The neural crest specifier AP-2α is diminished in PECAM1+ melanoma cells and is a transcriptional repressor of PECAM1. Re-introduction of AP-2α into PECAM1+ tumour cells represses PECAM1 and abolishes tube-forming ability, whereas AP-2α knockdown in PECAM1− tumour cells upregulates PECAM1 expression and promotes tube formation. Thus, VM-competent subpopulations, rather than all cells within a tumour, may instigate VM, supplant host-derived endothelium, and form PECAM1-dependent conduits that are not diminished by neutralizing VEGF. Tumours acquire new vasculature through angiogenesis or through alternative pathways including the less understood vasculogenesis mimicry. Here the authors identify a vasculogenic mimicry-competent subpopulation of melanoma cells that expresses the vascular cell adhesion molecule PECAM1, but not VEGFR-2.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Dunleavey, James M. and Xiao, Lin and Thompson, Joshua and Kim, Mi Mi and Shields, Janiel M. and Shelton, Sarah E. and Irvin, David M. and Brings, Victoria E. and Ollila, David W. and Brekken, Rolf A. and et al.}, year={2014}, month={Oct} }
 @article{sciumè_shelton_gray_miller_hussain_ferrari_decuzzi_schrefler_2013, title={A multiphase model for three-dimensional tumor growth}, volume={15}, ISSN={1367-2630}, url={http://dx.doi.org/10.1088/1367-2630/15/1/015005}, DOI={10.1088/1367-2630/15/1/015005}, abstractNote={Several mathematical formulations have analyzed the time-dependent behavior of a tumor mass. However, most of these propose simplifications that compromise the physical soundness of the model. Here, multiphase porous media mechanics is extended to model tumor evolution, using governing equations obtained via the thermodynamically constrained averaging theory. A tumor mass is treated as a multiphase medium composed of an extracellular matrix (ECM); tumor cells (TCs), which may become necrotic depending on the nutrient concentration and tumor phase pressure; healthy cells (HCs); and an interstitial fluid for the transport of nutrients. The equations are solved by a finite element method to predict the growth rate of the tumor mass as a function of the initial tumor-to-healthy cell density ratio, nutrient concentration, mechanical strain, cell adhesion and geometry. Results are shown for three cases of practical biological interest such as multicellular tumor spheroids (MTSs) and tumor cords. First, the model is validated by experimental data for time-dependent growth of an MTS in a culture medium. The tumor growth pattern follows a biphasic behavior: initially, the rapidly growing TCs tend to saturate the volume available without any significant increase in overall tumor size; then, a classical Gompertzian pattern is observed for the MTS radius variation with time. A core with necrotic cells appears for tumor sizes larger than 150 μm, surrounded by a shell of viable TCs whose thickness stays almost constant with time. A formula to estimate the size of the necrotic core is proposed. In the second case, the MTS is confined within a healthy tissue. The growth rate is reduced, as compared to the first case—mostly due to the relative adhesion of the TCs and HCs to the ECM, and the less favorable transport of nutrients. In particular, for HCs adhering less avidly to the ECM, the healthy tissue is progressively displaced as the malignant mass grows, whereas TC infiltration is predicted for the opposite condition. Interestingly, the infiltration potential of the tumor mass is mostly driven by the relative cell adhesion to the ECM. In the third case, a tumor cord model is analyzed where the malignant cells grow around microvessels in a three-dimensional geometry. It is shown that TCs tend to migrate among adjacent vessels seeking new oxygen and nutrients. This model can predict and optimize the efficacy of anticancer therapeutic strategies. It can be further developed to answer questions on tumor biophysics, related to the effects of ECM stiffness and cell adhesion on TC proliferation.}, number={1}, journal={New Journal of Physics}, publisher={IOP Publishing}, author={Sciumè, G and Shelton, S and Gray, W G and Miller, C T and Hussain, F and Ferrari, M and Decuzzi, P and Schrefler, B A}, year={2013}, month={Jan}, pages={015005} }
 @article{tumor growth modeling from the perspective of multiphase porous media mechanics._2012, url={https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/23285734/?tool=EBI}, journal={Molecular & cellular biomechanics : MCB}, year={2012}, month={Sep} }