@article{rojas_joiner_velasco_bautista_aji_moore_beaumont_pylayeva-gupta_dayton_gessner_et al._2022, title={Validation of a combined ultrasound and bioluminescence imaging system with magnetic resonance imaging in orthotopic pancreatic murine tumors}, volume={12}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-021-03684-z}, abstractNote={AbstractPreclinical mouse solid tumor models are widely used to evaluate efficacy of novel cancer therapeutics. Recent reports have highlighted the need for utilizing orthotopic implantation to represent clinical disease more accurately, however the deep tissue location of these tumors makes longitudinal assessment challenging without the use of imaging techniques. The purpose of this study was to evaluate the performance of a new multi-modality high-throughput in vivo imaging system that combines bioluminescence imaging (BLI) with robotic, hands-free ultrasound (US) for evaluating orthotopic mouse models. Long utilized in cancer research as independent modalities, we hypothesized that the combination of BLI and US would offer complementary advantages of detection sensitivity and quantification accuracy, while mitigating individual technological weaknesses. Bioluminescent pancreatic tumor cells were injected into the pancreas tail of C57BL/6 mice and imaged weekly with the combination system and magnetic resonance imaging (MRI) to serve as a gold standard. BLI photon flux was quantified to assess tumor activity and distribution, and US and MRI datasets were manually segmented for gross tumor volume. Robotic US and MRI demonstrated a strong agreement (R2 = 0.94) for tumor volume measurement. BLI showed a weak overall agreement with MRI (R2 = 0.21), however, it offered the greatest sensitivity to detecting the presence of tumors. We conclude that combining BLI with robotic US offers an efficient screening tool for orthotopic tumor models.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Rojas, Juan D. and Joiner, Jordan B. and Velasco, Brian and Bautista, Kathlyne Jayne B. and Aji, Adam M. and Moore, Christopher J. and Beaumont, Nathan J. and Pylayeva-Gupta, Yuliya and Dayton, Paul A. and Gessner, Ryan C. and et al.}, year={2022}, month={Jan} }
 @article{czernuszewicz_papadopoulou_rojas_rajamahendiran_perdomo_butler_harlacher_o'connell_zukic_dayton_et al._2019, title={A preclinical ultrasound platform for widefield 3D imaging of rodent tumors}, volume={79}, ISSN={["1538-7445"]}, DOI={10.1158/1538-7445.AM2019-1955}, abstractNote={Abstract
               Background: Preclinical ultrasound (US) and contrast-enhanced ultrasound (CEUS) imaging have long been used in oncology to noninvasively measure tumor volume and vascularity. While the value of preclinical US has been repeatedly demonstrated, these modalities are not without several key limitations that make them unattractive to cancer researchers, including: high user-variability, low throughput, and limited imaging field-of-view (FOV). Herein, we present a novel robotic preclinical US/CEUS system that addresses these limitations and demonstrates its use in evaluating tumors in 3D in a rodent model.
               Methods: The imaging system was designed to allow seamless whole-body 3D imaging, which requires rodents to be imaged without physical contact between the US transducer and the animal. To achieve this, a custom dual-element transducer was mounted on a robotic carriage, submerged in a hydrocarbon fluid, and the reservoir sealed with an acoustically transmissive top platform. Eight NOD/scid/gamma (NSG) female mice were injected subcutaneously in the flank with 8×109 786-O human clear-cell renal cell carcinoma (ccRCC) cells. Weekly imaging commenced after tumors reached a size of 150 mm3 and continued until tumors reached a maximum size of 1 cm3 (∼4-5 weeks). An additional six nude athymic female mice were injected subcutaneously in the flank with 7 × 105 SVR angiosarcoma cells to perform an inter-operator variability study. Imaging consisted of 3D B-mode (conventional ultrasound) of the whole abdomen (< 1 min), as well as contrast-enhanced acoustic angiography (< 10 min) to measure blood vessel density (BVD). Tumors were manually segmented in 3D (< 2 min) and inter-operator and inter-reader reliability was assessed with Krippendorff’s alpha.
               Results: Wide-field US images reconstructed from 3D volumetric data showed superior FOV over conventional US. Several anatomical landmarks could be identified within each image surrounding the tumor, including the liver, small intestines, bladder, and inguinal lymph nodes. Tumor boundaries were clearly delineated in both B-mode and BVD images, with BVD images showing heterogeneous microvessel density at later timepoints suggesting tumor necrosis. Excellent agreement was measured for both inter-reader and inter-operator experiments, with alpha coefficients of 0.914 (95% CI: 0.824-0.948) and 0.959 (0.911-0.981), respectively.
               Conclusion: We have demonstrated a novel preclinical US imaging system that can accurately and consistently evaluate tumors in rodent models. The system leverages cost-effective robotic technology, and a new scanning paradigm that allows for easy and reproducible data acquisition to enable wide-field, 3D, multi-parametric ultrasound imaging.
               Note: This abstract was not presented at the meeting.
               Citation Format: Tomasz Czernuszewicz, Virginie Papadopoulou, Juan D. Rojas, Rajalekha Rajamahendiran, Jonathan Perdomo, James Butler, Max Harlacher, Graeme O'Connell, Dzenan Zukic, Paul A. Dayton, Stephen Aylward, Ryan C. Gessner. A preclinical ultrasound platform for widefield 3D imaging of rodent tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1955.}, number={13}, journal={CANCER RESEARCH}, author={Czernuszewicz, Tomasz and Papadopoulou, Virginie and Rojas, Juan D. and Rajamahendiran, Rajalekha and Perdomo, Jonathan and Butler, James and Harlacher, Max and O'Connell, Graeme and Zukic, Dzenan and Dayton, Paul A. and et al.}, year={2019}, month={Jul} }
 @article{rojas_papadopoulou_czernuszewicz_rajamahendiran_chytil_chiang_chong_bautch_rathmell_aylward_et al._2019, title={Early treatment response detected in a murine clear cell renal cell carcinoma model in response to combination therapy with antiangiogenic and notch inhibition therapy using a non-invasive imaging tool}, volume={79}, ISSN={["1538-7445"]}, DOI={10.1158/1538-7445.AM2019-1958}, abstractNote={Abstract
               Background: Functional and molecular changes often precede gross anatomical changes in cancer, so early assessment of a tumor’s functional and molecular response to therapy can help reduce a patient’s exposure to the side effects of ineffective chemotherapeutics or other treatment strategies. Clear-cell renal cell carcinoma (ccRCC) is an aggressive and hyper-vascular form of renal cancer that is often treated with anti-angiogenic and Notch Inhibition therapies, which target the vasculature feeding the disease. The purpose of this work is to show that ultrasound microvascular imaging can provide indications of response to antiangiogenic and Notch Inhibition therapies prior to measurable changes in tumor size.
               Methods: Mice bearing 786-O ccRCC xenograft tumors were treated with SU (Sunitnib malate, Selleckchem, TX), an antiangiogenic drug, and a combination of SU and the Notch inhibitor GSI (Gamma secretase inhibitor, PF-03084014, Pfizer, New York, NY) therapies (n=8). A 3D ultrasound system (SonoVol Inc., Research Triangle Park, NC), in addition to microbubble ultrasound contrast agents, was used to obtain a measurement of microvascular density over time and assess the response of the tumors to the therapies. CD31 immunohistochemistry was performed to serve as a gold standard for comparison against imaging results. Statistical tests included: Spearman correlation to compare imaging and histology; Kruskal-Wallis analysis with Tukey multiple comparison post-test to determine if the vessel density or tumor volume were significantly different between the treatment groups; and receiver operating characteristic (ROC) curve analysis to determine sensitivity/specificity for separating treated/untreated groups.
               Results: Data indicated that ultrasound-derived microvascular density can detect response to antiangiogenic and Notch inhibition therapies a week prior to changes in tumor volume. Furthermore, the imaging measurements of vasculature are strongly correlated with physiological characteristics of the tumors as measured by histology (p=0.75). Moreover, data demonstrated that ultrasound measurements of vascular density can determine response to therapy and classify between-treatment groups 1 week after the start of treatment with a high sensitivity and specificity of 94% and 86%, respectively.
               Conclusion: This work shows vascular density measurements that are strongly correlated with histology can be obtained using ultrasound, and that imaging-derived vessel density metrics may be a better tool for assessing the response of ccRCC to antiangiogenic and Notch inhibition therapies than anatomical size measurements.
               Note: This abstract was not presented at the meeting.
               Citation Format: Juan D. Rojas, Virginie Papadopoulou, Tomasz Czernuszewicz, Rajalekha Rajamahendiran, Anna Chytil, Yun-Chen Chiang, Diana Chong, Victoria L. Bautch, Wendy K. Rathmell, Stephen Aylward, Ryan Gessner, Paul Dayton. Early treatment response detected in a murine clear cell renal cell carcinoma model in response to combination therapy with antiangiogenic and notch inhibition therapy using a non-invasive imaging tool [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1958.}, number={13}, journal={CANCER RESEARCH}, author={Rojas, Juan D. and Papadopoulou, Virginie and Czernuszewicz, Tomasz and Rajamahendiran, Rajalekha and Chytil, Anna and Chiang, Yun-Chen and Chong, Diana and Bautch, Victoria L. and Rathmell, Wendy K. and Aylward, Stephen and et al.}, year={2019}, month={Jul} }
 @article{rojas_rajamahendiran_czernuszewicz_velasco_perdomo_harlacher_o'connell_butler_damania_dayton_et al._2019, title={Tracking angiogenesis induced microvascular changes in a lymphoma model via a new high throughput non-invasive dual modality imaging platform}, volume={79}, ISSN={["1538-7445"]}, DOI={10.1158/1538-7445.AM2019-1935}, abstractNote={Abstract
               This study presents a novel dual-modality imaging system for assessing cancer progression in rodents. The system incorporates bioluminescence imaging (BLI), used to assess tumor growth, and contrast-enhanced ultrasound (CEUS), used to assess anatomical information and map microvasculature. The combination of the two modalities has previously been shown to reduce inter-user variability of BLI quantification, and in this work, we demonstrate that a dual BLI/US system can provide a more holistic assessment of disease.
               NSG (NOD/scid/gamma) female mice were implanted with luc-tagged lymphoma cells (BCBL-1, RRID: CVCL_0165, 1x105 cells, intraperitoneal (IP) injection, N = 8 mice) and imaged using the US and BLI hybrid modality system (SonoVol, Inc.), and a BLI-alone system (Perkin Elmer, Inc.) for comparison to a widely available commercial BLI system. BLI sensitivity was evaluated using a weakly luminescent tritium phantom to find the shortest exposure required to detect signal. In vivo studies consisted of an IP injection of D-luciferin (250 µL at 15 mg/mL) and serial captures of images with exposure times of 60 s every 3 min. Acoustic Angiography (AA), a high-resolution CEUS technique, was used to acquire 3D volumes in the abdomen surrounding the tumor site to assess angiogenesis-induced vascular remodeling associated with tumor growth.
               In vitro BLI sensitivity experiments showed that the dual-modality system required an exposure of 3 sec to detect signal (p < 0.05) and the BLI-alone system required an exposure of 1 sec (p< 0.05). For in vivo studies, the change in luminescence occurring between week 2 and 3 post-cell implantation was calculated (a surrogate measurement for tumor growth), and the difference in signal was 17.15 ± 10.1 photons/sec and 16.04 ± 7.6 for the dual-modality and BLI-alone systems, respectively. Images of the vascular remodeling arising during the first two weeks of tumor growth were captured with AA and demonstrated an increase in perfusion in the vicinity of BLI signal by a factor of 1.4 ± 0.38, with vascular remodeling being evident even at the periphery of BLI signal.
               This work demonstrates that non-invasive measurements of in vivo microvascular remodeling can be precisely mapped to changes in tumor growth with a hybrid modality system. The system has comparable sensitivity to a BLI-alone system and provides similar assessments of longitudinal tumor growth. Adding quantitative metrics for vascular remodeling to the widely used luminescent imaging could provide a more comprehensive assessment for tumor functional status than either modality could individually. This should prove valuable when using antiangiogenic therapies because changes in vasculature will precede cell death, and the ability to monitor both the cells and their blood supply might help to elucidate underlying biological processes.
               Citation Format: Juan D. Rojas, Rajalekha Rajamahendiran, Tomasz J. Czernuszewicz, Brian Velasco, Jonathan Perdomo, Max Harlacher, Graeme O'Connell, James Butler, Blossom Damania, Paul A. Dayton, Ryan C. Gessner. Tracking angiogenesis induced microvascular changes in a lymphoma model via a new high throughput non-invasive dual modality imaging platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1935.}, number={13}, journal={CANCER RESEARCH}, author={Rojas, Juan D. and Rajamahendiran, Rajalekha and Czernuszewicz, Tomasz J. and Velasco, Brian and Perdomo, Jonathan and Harlacher, Max and O'Connell, Graeme and Butler, James and Damania, Blossom and Dayton, Paul A. and et al.}, year={2019}, month={Jul} }
 @article{rojas_papadopoulou_czernuszewicz_rajamahendiran_chytil_chiang_chong_bautch_rathmell_aylward_et al._2019, title={Ultrasound Measurement of Vascular Density to Evaluate Response to Anti-Angiogenic Therapy in Renal Cell Carcinoma}, volume={66}, ISSN={["1558-2531"]}, DOI={10.1109/TBME.2018.2860932}, abstractNote={<italic>Background:</italic> Functional and molecular changes often precede gross anatomical changes, so early assessment of a tumor's functional and molecular response to therapy can help reduce a patient's exposure to the side effects of ineffective chemotherapeutics or other treatment strategies. <italic>Objective:</italic> Our intent was to test the hypothesis that an ultrasound microvascular imaging approach might provide indications of response to therapy prior to assessment of tumor size. <italic>Methods:</italic> Mice bearing clear-cell renal cell carcinoma xenograft tumors were treated with antiangiogenic and Notch inhibition therapies. An ultrasound measurement of microvascular density was used to serially track the tumor response to therapy. <italic>Results:</italic> Data indicated that ultrasound-derived microvascular density can indicate response to therapy a week prior to changes in tumor volume and is strongly correlated with physiological characteristics of the tumors as measured by histology (<inline-formula><tex-math notation="LaTeX">$\rho = {\text{0.75}}$</tex-math></inline-formula>). Furthermore, data demonstrated that ultrasound measurements of vascular density can determine response to therapy and classify between-treatment groups with high sensitivity and specificity. <italic>Conclusion/Significance:</italic> Results suggests that future applications utilizing ultrasound imaging to monitor tumor response to therapy may be able to provide earlier insight into tumor behavior from metrics of microvascular density rather than anatomical tumor size measurements.}, number={3}, journal={IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING}, author={Rojas, Juan D. and Papadopoulou, Virginie and Czernuszewicz, Tomasz J. and Rajamahendiran, Rajalekha M. and Chytil, Anna and Chiang, Yun-Chen and Chong, Diana C. and Bautch, Victoria L. and Rathmell, W. Kimryn and Aylward, Stephen and et al.}, year={2019}, month={Mar}, pages={873–880} }
 @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} }
 @article{gessner_streeter_kothadia_feingold_dayton_2012, title={AN IN VIVO VALIDATION OF THE APPLICATION OF ACOUSTIC RADIATION FORCE TO ENHANCE THE DIAGNOSTIC UTILITY OF MOLECULAR IMAGING USING 3-D ULTRASOUND}, volume={38}, ISSN={["1879-291X"]}, DOI={10.1016/j.ultrasmedbio.2011.12.005}, abstractNote={For more than a decade, the application of acoustic radiation force (ARF) has been proposed as a mechanism to increase ultrasonic molecular imaging (MI) sensitivity in vivo. Presented herein is the first noninvasive in vivo validation of ARF-enhanced MI with an unmodified clinical system. First, an in vitro optical-acoustical setup was used to optimize system parameters and ensure sufficient microbubble translation when exposed to ARF. 3-D ARF-enhanced MI was then performed on 7 rat fibrosarcoma tumors using microbubbles targeted to αvβ3 and nontargeted microbubbles. Low-amplitude (<25 kPa) 3-D ARF pulse sequences were tested and compared with passive targeting studies in the same animal. Our results demonstrate that a 78% increase in image intensity from targeted microbubbles can be achieved when using ARF relative to the passive targeting studies. Furthermore, ARF did not significantly increase image contrast when applied to nontargeted agents, suggesting that ARF did not increase nonspecific adhesion.}, number={4}, journal={ULTRASOUND IN MEDICINE AND BIOLOGY}, author={Gessner, Ryan C. and Streeter, Jason E. and Kothadia, Roshni and Feingold, Steven and Dayton, Paul A.}, year={2012}, month={Apr}, pages={651–660} }
 @article{gessner_aylward_dayton_2012, title={Mapping Microvasculature with Acoustic Angiography Yields Quantifiable Differences between Healthy and Tumor-bearing Tissue Volumes in a Rodent Model}, volume={264}, ISSN={["0033-8419"]}, DOI={10.1148/radiol.12112000}, abstractNote={PURPOSE
To determine if the morphologies of microvessels could be extracted from contrast material-enhanced acoustic angiographic ultrasonographic (US) images and used as a quantitative basis for distinguishing healthy from diseased tissue.


MATERIALS AND METHODS
All studies were institutional animal care and use committee approved. Three-dimensional contrast-enhanced acoustic angiographic images were acquired in both healthy (n = 7) and tumor-bearing (n = 10) rats. High-spatial-resolution and high signal-to-noise acquisition was enabled by using a prototype dual-frequency US transducer (transmit at 4 MHz, receive at 30 MHz). A segmentation algorithm was utilized to extract microvessel structure from image data, and the distance metric (DM) and the sum of angles metric (SOAM), designed to distinguish different types of tortuosity, were applied to image data. The vessel populations extracted from tumor-bearing tissue volumes were compared against vessels extracted from tissue volumes in the same anatomic location within healthy control animals by using the two-sided Student t test.


RESULTS
Metrics of microvascular tortuosity were significantly higher in the tumor population. The average DM of the tumor population (1.34 ± 0.40 [standard deviation]) was 23.76% higher than that of the control population (1.08 ± 0.08) (P < .0001), while the average SOAM (22.53 ± 7.82) was 50.73% higher than that of the control population (14.95 ± 4.83) (P < .0001). The DM and SOAM metrics for the control and tumor populations were significantly different when all vessels were pooled between the two animal populations. In addition, each animal in the tumor population had significantly different DM and SOAM metrics relative to the control population (P < .05 for all; P value ranges for DM, 3.89 × 10(-)(7) to 5.63 × 10(-)(3); and those for SOAM, 2.42 × 10(-)(12) to 1.57 × 10(-)(3)).


CONCLUSION
Vascular network quantification by using high-spatial-resolution acoustic angiographic images is feasible. Data suggest that the angiogenic processes associated with tumor development in the models studied result in higher instances of vessel tortuosity near the tumor site.}, number={3}, journal={RADIOLOGY}, author={Gessner, Ryan C. and Aylward, Stephen R. and Dayton, Paul A.}, year={2012}, month={Sep}, pages={733–740} }
 @article{gessner_kothadia_feingold_dayton_2011, title={3-D MICROVESSEL-MIMICKING ULTRASOUND PHANTOMS PRODUCED WITH A SCANNING MOTION SYSTEM}, volume={37}, ISSN={["1879-291X"]}, DOI={10.1016/j.ultrasmedbio.2010.12.013}, abstractNote={Ultrasound techniques are currently being developed that can assess the vascularization of tissue as a marker for therapeutic response. Some of these ultrasound imaging techniques seek to extract quantitative features about vessel networks, whereas high-frequency imaging also allows individual vessels to be resolved. The development of these new techniques, and subsequent imaging analysis strategies, necessitates an understanding of their sensitivities to vessel and vessel network structural abnormalities. Constructing in-vitro flow phantoms for this purpose can be prohibitively challenging, because simulating precise flow environments with nontrivial structures is often impossible using conventional methods of construction for flow phantoms. Presented in this manuscript is a method to create predefined structures with <10 μm precision using a three-axis motion system. The application of this technique is demonstrated for the creation of individual vessel and vessel networks, which can easily be made to simulate the development of structural abnormalities typical of diseased vasculature in vivo. In addition, beyond facilitating the creation of phantoms that would otherwise be very challenging to construct, the method presented herein enables one to precisely simulate very slow blood flow and respiration artifacts, and to measure imaging resolution. (E-mail: [email protected])}, number={5}, journal={ULTRASOUND IN MEDICINE AND BIOLOGY}, author={Gessner, Ryan C. and Kothadia, Roshni and Feingold, Steven and Dayton, Paul A.}, year={2011}, month={May}, pages={827–833} }
 @article{mullin_gessner_kwan_kaya_borden_dayton_2011, title={Effect of anesthesia carrier gas on in vivo circulation times of ultrasound microbubble contrast agents in rats}, volume={6}, ISSN={["1555-4317"]}, DOI={10.1002/cmmi.414}, abstractNote={Purpose:Microbubble contrast agents are currently implemented in a variety of both clinical and preclinical ultrasound imaging studies. The therapeutic and diagnostic capabilities of these contrast agents are limited by their short in‐vivo lifetimes, and research to lengthen their circulation times is on going. In this manuscript, observations are presented from a controlled experiment performed to evaluate differences in circulation times for lipid shelled perfluorocarbon‐filled contrast agents circulating within rodents as a function of inhaled anesthesia carrier gas.Methods:The effects of two common anesthesia carrier gas selections ‐ pure oxygen and medical air were observed within five rats. Contrast agent persistence within the kidney was measured and compared for oxygen and air anesthesia carrier gas for six bolus contrast injections in each animal. Simulations were performed to examine microbubble behavior with changes in external environment gases.Results:A statistically significant extension of contrast circulation time was observed for animals breathing medical air compared to breathing pure oxygen. Simulations support experimental observations and indicate that enhanced contrast persistence may be explained by reduced ventilation/perfusion mismatch and classical diffusion, in which nitrogen plays a key role by contributing to the volume and diluting other gas species in the microbubble gas core.Conclusion:Using medical air in place of oxygen as the carrier gas for isoflurane anesthesia can increase the circulation lifetime of ultrasound microbubble contrast agents. Copyright © 2011 John Wiley & Sons, Ltd.}, number={3}, journal={CONTRAST MEDIA & MOLECULAR IMAGING}, author={Mullin, Lee and Gessner, Ryan and Kwan, James and Kaya, Mehmet and Borden, Mark A. and Dayton, Paul A.}, year={2011}, pages={126–131} }
 @misc{gessner_dayton_2010, title={Advances in molecular imaging with ultrasound}, volume={9}, number={3}, journal={Molecular Imaging}, author={Gessner, R. and Dayton, P. A.}, year={2010}, pages={117–127} }
 @article{gessner_lukacs_lee_cherin_foster_dayton_2010, title={High-Resolution, High-Contrast Ultrasound Imaging Using a Prototype Dual-Frequency Transducer: In Vitro and In Vivo Studies}, volume={57}, ISSN={["1525-8955"]}, DOI={10.1109/tuffc.2010.1615}, abstractNote={With recent advances in animal models of disease, there has been great interest in capabilities for highresolution contrast-enhanced ultrasound imaging. Microbubble contrast agents are unique in that they scatter broadband ultrasound energy because of their nonlinear behavior. For optimal response, it is desirable to excite the microbubbles near their resonant frequency. To date, this has been challenging with high-frequency imaging systems because most contrast agents are resonant at frequencies in the order of several megahertz. Our team has developed a unique dual-frequency confocal transducer which enables low-frequency excitation of bubbles near their resonance with one element, and detection of their emitted high-frequency content with the second element. Using this imaging approach, we have attained an average 12.3 dB improvement in contrast-to-tissue ratios over fundamental mode imaging, with spatial resolution near that of the high-frequency element. Because this detection method does not rely on signal decorrelation, it is not susceptible to corruption by tissue motion. This probe demonstrates contrast imaging capability with significant tissue suppression, enabling high-resolution contrast-enhanced images of microvascular blood flow. Additionally, this probe can readily produce radiation force on flowing contrast agents, which may be beneficial for targeted imaging or therapy.}, number={8}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Gessner, Ryan and Lukacs, Marc and Lee, Mike and Cherin, Emmanuel and Foster, F. Stuart and Dayton, Paul A.}, year={2010}, month={Aug}, pages={1772–1781} }
 @article{streeter_gessner_miles_dayton_2010, title={Improving sensitivity in ultrasound molecular imaging by tailoring contrast agent size distribution: In vivo studies}, volume={9}, number={2}, journal={Molecular Imaging}, author={Streeter, J. E. and Gessner, R. and Miles, I. and Dayton, P. A.}, year={2010}, pages={87–95} }
 @article{feingold_gessner_guracar_dayton_2010, title={Quantitative Volumetric Perfusion Mapping of the Microvasculature Using Contrast Ultrasound}, volume={45}, ISSN={["1536-0210"]}, DOI={10.1097/rli.0b013e3181ef0a78}, abstractNote={Objectives:Contrast-enhanced ultrasound imaging has demonstrated significant potential as a noninvasive technology for monitoring blood flow in the microvasculature. With the application of nondestructive contrast imaging pulse sequences combined with a clearance-refill approach, it is possible to create quantitative time-to-refill maps of tissue correlating to blood perfusion rate. One limitation to standard two-dimensional (2D) perfusion imaging is that the narrow elevational beamwidth of 1- or 1.5-D ultrasound transducers provides information in only a single slice of tissue, and thus it is difficult to image exactly the same plane from study to study. We hypothesize that inhomogeneity in vascularization, such as that common in many types of tumors, makes serial perfusion estimates inconsistent unless the same region can be imaged repeatedly. Our objective was to evaluate error in 2D quantitative perfusion estimation in an in vivo sample volume because of differences in transducer positioning. To mitigate observed errors due to imaging plane misalignment, we propose and demonstrate the application of quantitative 3-dimensional (3D) perfusion imaging. We also evaluate the effect of contrast agent concentration and infusion rate on perfusion estimates. Materials and Methods:Contrast-enhanced destruction-reperfusion imaging was performed using parametric mapping of refill times and custom software for image alignment to compensate for tissue motion. Imaging was performed in rats using a Siemens Sequoia 512 imaging system with a 15L8 transducer. A custom 3D perfusion mapping system was designed by incorporating a computer-controlled positioning system to move the transducer in the elevational direction, and the Sequoia was interfaced to the motion system for timing of the destruction-reperfusion sequence and data acquisition. Perfusion estimates were acquired from rat kidneys as a function of imaging plane and in response to the vasoactive drug dopamine. Results:Our results indicate that perfusion estimates generated by 2D imaging in the rat kidney have mean standard deviations on the order of 10%, and as high as 22%, because of differences in initial transducer position. This difference was larger than changes in kidney perfusion induced by dopamine. With application of 3D perfusion mapping, repeatability in perfusion estimated in the kidney is reduced to a standard deviation of less than 3%, despite random initial transducer positioning. Varying contrast agent administration rate was also observed to bias measured perfusion time, especially at low concentrations; however, we observed that contrast administration rates between 2.7 × 108 and 3.9 × 108 bubbles/min provided results that were consistent within 3% for the contrast agent type evaluated. Conclusions:Three-dimensional perfusion imaging allows a significant reduction in the error caused by transducer positioning, and significantly improves the reliability of quantitative perfusion time estimates in a rat kidney model. When performing perfusion imaging, it is important to use appropriate and consistent contrast agent infusion rates to avoid bias.}, number={10}, journal={INVESTIGATIVE RADIOLOGY}, author={Feingold, Steven and Gessner, Ryan and Guracar, Ismayil M. and Dayton, Paul A.}, year={2010}, month={Oct}, pages={669–674} }
 @article{streeter_gessner_tsuruta_feingold_dayton, title={Assessment of molecular imaging of angiogenesis with three-dimensional ultrasonography}, volume={10}, number={6}, journal={Molecular Imaging}, author={Streeter, J. E. and Gessner, R. C. and Tsuruta, J. and Feingold, S. and Dayton, P. A.}, pages={460–468} }