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Feng K, Li X, Huang A, Wan M, Zong Y. Effect of tissue viscoelasticity and adjacent phase-changed microbubbles on vaporization process and direct growth threshold of nanodroplet in an ultrasonic field. ULTRASONICS SONOCHEMISTRY 2023; 101:106665. [PMID: 37922720 PMCID: PMC10643523 DOI: 10.1016/j.ultsonch.2023.106665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 10/13/2023] [Accepted: 10/26/2023] [Indexed: 11/07/2023]
Abstract
Understanding the behavior of nanodroplets converted into microbubbles with applied ultrasound is an important problem in tumor therapeutical and diagnostic applications. In this study, a comprehensive model is proposed to investigate the vaporization process and the direct growth threshold of the nanodroplet by following the vapor bubble growth, especially attention devoted to the effect of tissue viscoelasticity and adjacent phase-changed microbubbles (PCMBs). It is shown that the ultrasonic energy must be sufficiently strong to counterbalance the natural condensation of the vapor bubble and the tissue stiffness-inhibitory effect. The softer tissue with a lower shear modulus favors the vaporization process, and the nanodroplet has a lower direct growth threshold in the softer tissue. Moreover, the adjacent PCMBs show a suppression effect on the vaporization process due to the negative value of the secondary Bjerknes force, implying an attractive force, preventing the nanodroplet from escaping from the constraint of the adjacent PCMBs. However, according to the linear scattering theory, the attractive force signifies that the constraint is weak, causing the direct growth threshold to increase in the range of 0.09-0.24 MPa. The weak increase in threshold demonstrates that the direct growth threshold is relatively unaffected by the adjacent PCMBs. The prediction results of our model are in good agreement with the experiment results obtained by the echo enhancement method, in which the threshold is relatively independent of the intermediate concentration. The findings presented here provide physical insight that will be further helpful in understanding the complex behavior of the nanodroplet responses to ultrasound in practical medical applications.
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Affiliation(s)
- Kangyi Feng
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
| | - Xinyue Li
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
| | - Anqi Huang
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
| | - Mingxi Wan
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
| | - Yujin Zong
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
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Zhang W, Metzger H, Vlatakis S, Claxton A, Carbajal MA, Fung LF, Mason J, Chan KLA, Pouliopoulos AN, Fleck RA, Prentice P, Thanou M. Characterising the chemical and physical properties of phase-change nanodroplets. ULTRASONICS SONOCHEMISTRY 2023; 97:106445. [PMID: 37257208 PMCID: PMC10241977 DOI: 10.1016/j.ultsonch.2023.106445] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 05/04/2023] [Accepted: 05/15/2023] [Indexed: 06/02/2023]
Abstract
Phase-change nanodroplets have attracted increasing interest in recent years as ultrasound theranostic nanoparticles. They are smaller compared to microbubbles and they may distribute better in tissues (e.g. in tumours). They are composed of a stabilising shell and a perfluorocarbon core. Nanodroplets can vaporise into echogenic microbubbles forming cavitation nuclei when exposed to ultrasound. Their perfluorocarbon core phase-change is responsible for the acoustic droplet vaporisation. However, methods to quantify the perfluorocarbon core in nanodroplets are lacking. This is an important feature that can help explain nanodroplet phase change characteristics. In this study, we fabricated nanodroplets using lipids shell and perfluorocarbons. To assess the amount of perfluorocarbon in the core we used two methods, 19F NMR and FTIR. To assess the cavitation after vaporisation we used an ultrasound transducer (1.1 MHz) and a high-speed camera. The 19F NMR based method showed that the fluorine signal correlated accurately with the perfluorocarbon concentration. Using this correlation, we were able to quantify the perfluorocarbon core of nanodroplets. This method was used to assess the content of the perfluorocarbon of the nanodroplets in solutions over time. It was found that perfluoropentane nanodroplets lost their content faster and at higher ratio compared to perfluorohexane nanodroplets. The high-speed imaging indicates that the nanodroplets generate cavitation comparable to that from commercial contrast agent microbubbles. Nanodroplet characterisation should include perfluorocarbon concentration assessment as critical information for their development.
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Affiliation(s)
- Weiqi Zhang
- Institute of Cancer & Pharmaceutical Sciences, King's College London, United Kingdom
| | - Hilde Metzger
- School of Engineering, University of Glasgow, United Kingdom
| | - Stavros Vlatakis
- Institute of Cancer & Pharmaceutical Sciences, King's College London, United Kingdom
| | - Amelia Claxton
- Institute of Cancer & Pharmaceutical Sciences, King's College London, United Kingdom
| | | | - Leong Fan Fung
- Department of Surgical & Interventional Engineering, King's College London, United Kingdom
| | - James Mason
- Institute of Cancer & Pharmaceutical Sciences, King's College London, United Kingdom
| | - K L Andrew Chan
- Institute of Cancer & Pharmaceutical Sciences, King's College London, United Kingdom
| | | | - Roland A Fleck
- Centre for Ultrastructural Imaging, King's College London, United Kingdom
| | - Paul Prentice
- School of Engineering, University of Glasgow, United Kingdom
| | - Maya Thanou
- Institute of Cancer & Pharmaceutical Sciences, King's College London, United Kingdom.
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3
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Zhang Q, Yang Y, Xue H, Zhang H, Yuan Z, Shen Y, Guo X, Fan Z, Wu X, Zhang D, Tu J. Intensified and controllable vaporization of phase-changeable nanodroplets induced by simultaneous exposure of laser and ultrasound. ULTRASONICS SONOCHEMISTRY 2023; 94:106312. [PMID: 36731283 PMCID: PMC9926226 DOI: 10.1016/j.ultsonch.2023.106312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/20/2023] [Accepted: 01/22/2023] [Indexed: 06/18/2023]
Abstract
Phase-changeable contrast agents have been proposed as a next-generation ultrasound contrast agent over conventional microbubbles given its stability, longer circulation time and ability to extravasate. Safe vaporization of nanodroplets (NDs) plays an essential role in the practical translation of ND applications in industry and medical therapy. In particular, the exposure parameters for initializing phase change as well as the site of phase change are concerned to be controlled. Compared to the traditional optical vaporization or acoustic droplet vaporization, this study exhibited the potential of using simultaneous, single burst laser and ultrasound incidence as a means of activating phase change of NDs to generate cavitation nuclei with reduced fluence and sound pressure. A theoretical model considering the laser heating, vapor cavity nucleation and growth was established, where qualitative agreement with experiment findings were found in terms of the trend of combined exposure parameters in order to achieve the same level of vaporization outcome. The results indicate that using single burst laser pulse and 10-cycle ultrasound might be sufficient to lower the exposure levels under FDA limit for laser skin exposure and ultrasound imaging. The combination of laser and ultrasound also provides temporal and spatial control of ND vaporization and cavitation nucleation without altering the sound field, which is beneficial for further safe and effective applications of phase-changeable NDs in medical, environmental, food processing and other industrial areas.
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Affiliation(s)
- Qi Zhang
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Yanye Yang
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Honghui Xue
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China; Wuxi Vocational Institute of Commerce, Wuxi 214153, Jiangsu, China
| | - Haijun Zhang
- Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai 200092, China; National United Engineering Laboratory for Biomedical Material Modification, Branden Industrial Park, Dezhou 251100, Shandong, China
| | - Ziyan Yuan
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Yuchen Shen
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Xiasheng Guo
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Zheng Fan
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Xiaoge Wu
- Environment Science and Engineering College, Yangzhou University, Yangzhou 225009, Jiangsu, China.
| | - Dong Zhang
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China.
| | - Juan Tu
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China.
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Benton RP, Al Rifai N, Stone K, Clark A, Zhang B, Haworth KJ. Impact of Perfluoropentane Microdroplets Diameter and Concentration on Acoustic Droplet Vaporization Transition Efficiency and Oxygen Scavenging. Pharmaceutics 2022; 14:pharmaceutics14112392. [PMID: 36365210 PMCID: PMC9694497 DOI: 10.3390/pharmaceutics14112392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/25/2022] [Accepted: 11/02/2022] [Indexed: 11/09/2022] Open
Abstract
Acoustic droplet vaporization is the ultrasound-mediated phase change of liquid droplets into gas microbubbles. Following the phase change, oxygen diffuses from the surrounding fluid into the microbubble. An in vitro model was used to study the effects of droplet diameter, the presence of an ultrasound contrast agent, ultrasound duty cycle, and droplet concentration on the magnitude of oxygen scavenging in oxygenated deionized water. Perfluoropentane droplets were manufactured through a microfluidic approach at nominal diameters of 1, 3, 5, 7, 9, and 12 µm and studied at concentrations varying from 5.1 × 10-5 to 6.3 × 10-3 mL/mL. Droplets were exposed to an ultrasound transduced by an EkoSonicTM catheter (2.35 MHz, 47 W, and duty cycles of 1.70%, 2.34%, or 3.79%). Oxygen scavenging and the total volume of perfluoropentane that phase-transitioned increased with droplet concentration. The ADV transition efficiency decreased with increasing droplet concentration. The increasing duty cycle resulted in statistically significant increases in oxygen scavenging for 1, 3, 5, and 7 µm droplets, although the increase was smaller than when the droplet diameter or concentration were increased. Under the ultrasound conditions tested, droplet diameter and concentration had the greatest impact on the amount of ADV and subsequent oxygen scavenging occurred, which should be considered when using ADV-mediated oxygen scavenging in therapeutic ultrasounds.
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Affiliation(s)
- Rachel P. Benton
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Nour Al Rifai
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Kateryna Stone
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Abigail Clark
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Bin Zhang
- Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
- Department of Pediatrics, University of Cincinnati, Cincinnati, OH 45229, USA
| | - Kevin J. Haworth
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati, Cincinnati, OH 45267, USA
- Department of Pediatrics, University of Cincinnati, Cincinnati, OH 45229, USA
- Correspondence: ; Tel.: +1-513-558-3536
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Zeng P, Chen C, Lof J, Stolze E, Li S, Chen X, Pacella J, Villanueva FS, Matsunaga T, Everbach EC, Fei H, Xie F, Porter T. Acoustic Detection of Retained Perfluoropropane Droplets Within the Developing Myocardial Infarct Zone. ULTRASOUND IN MEDICINE & BIOLOGY 2022; 48:2322-2334. [PMID: 36050231 PMCID: PMC9547398 DOI: 10.1016/j.ultrasmedbio.2022.07.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 07/11/2022] [Accepted: 07/12/2022] [Indexed: 06/15/2023]
Abstract
Perfluoropropane droplets (PDs) cross endothelial barriers and can be acoustically activated for selective myocardial extravascular enhancement following intravenous injection (IVI). Our objective was to determine how to optimally activate extravascular PDs for transthoracic ultrasound-enhanced delineation of a developing scar zone (DSZ). Ultrafast-frame-rate microscopy was conducted to determine the effect of pulse sequence on the threshold of bubble formation from PDs. In vitro studies were subsequently performed at different flow rates to determine acoustic activation and inertial cavitation thresholds for a PD infusion using multipulse fundamental non-linear or single-pulse harmonic imaging. IVIs of PDs were given in 9 rats and 10 pigs following prolonged left anterior descending ischemia to detect and quantify PD kinetics within the DSZ. A multipulse sequence had a lower myocardial index threshold for acoustic activation by ultrafast-frame-rate microscopy. Acoustic activation was observed at a myocardial index ≥0.4 below the inertial cavitation threshold for both pulse sequences. In rats, confocal microscopy and serial acoustic activation imaging detected higher droplet presence (relative to remote regions) within the DSZ at 3 min post-IVI. Transthoracic high-mechanical-index impulses with fundamental non-linear imaging in pigs at this time post-IVI resulted in selective contrast enhancement within the DSZ.
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Affiliation(s)
- Ping Zeng
- Department of Cardiology, Guangdong Cardiovascular Institute, Guangdong Provincial People's Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China; Division of Cardiovascular Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Cheng Chen
- Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - John Lof
- Division of Cardiovascular Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Elizabeth Stolze
- Division of Cardiovascular Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Shouqiang Li
- Division of Cardiovascular Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA; Department of Ultrasound, Second Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Xucai Chen
- Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - John Pacella
- Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Flordeliza S Villanueva
- Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Terry Matsunaga
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA; Department of Medical Imaging, University of Arizona, Tucson, Arizona, USA
| | | | - Hongwen Fei
- Department of Cardiology, Guangdong Cardiovascular Institute, Guangdong Provincial People's Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China
| | - Feng Xie
- Division of Cardiovascular Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Thomas Porter
- Division of Cardiovascular Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA.
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Tu J, Yu ACH. Ultrasound-Mediated Drug Delivery: Sonoporation Mechanisms, Biophysics, and Critical Factors. BME FRONTIERS 2022; 2022:9807347. [PMID: 37850169 PMCID: PMC10521752 DOI: 10.34133/2022/9807347] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2021] [Accepted: 12/31/2021] [Indexed: 10/19/2023] Open
Abstract
Sonoporation, or the use of ultrasound in the presence of cavitation nuclei to induce plasma membrane perforation, is well considered as an emerging physical approach to facilitate the delivery of drugs and genes to living cells. Nevertheless, this emerging drug delivery paradigm has not yet reached widespread clinical use, because the efficiency of sonoporation is often deemed to be mediocre due to the lack of detailed understanding of the pertinent scientific mechanisms. Here, we summarize the current observational evidence available on the notion of sonoporation, and we discuss the prevailing understanding of the physical and biological processes related to sonoporation. To facilitate systematic understanding, we also present how the extent of sonoporation is dependent on a multitude of factors related to acoustic excitation parameters (ultrasound frequency, pressure, cavitation dose, exposure time), microbubble parameters (size, concentration, bubble-to-cell distance, shell composition), and cellular properties (cell type, cell cycle, biochemical contents). By adopting a science-backed approach to the realization of sonoporation, ultrasound-mediated drug delivery can be more controllably achieved to viably enhance drug uptake into living cells with high sonoporation efficiency. This drug delivery approach, when coupled with concurrent advances in ultrasound imaging, has potential to become an effective therapeutic paradigm.
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Affiliation(s)
- Juan Tu
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing, China
| | - Alfred C. H. Yu
- Schlegel Research Institute for Aging, University of Waterloo, Waterloo, ON, Canada
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Song R, Zhang C, Teng F, Tu J, Guo X, Fan Z, Zheng Y, Zhang D. Cavitation-facilitated transmembrane permeability enhancement induced by acoustically vaporized nanodroplets. ULTRASONICS SONOCHEMISTRY 2021; 79:105790. [PMID: 34662804 PMCID: PMC8526759 DOI: 10.1016/j.ultsonch.2021.105790] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/09/2021] [Accepted: 10/12/2021] [Indexed: 05/05/2023]
Abstract
Ultrasound-facilitated transmembrane permeability enhancement has attracted broad attention in the treatment of central nervous system (CNS) diseases, by delivering gene/drugs into the deep site of brain tissues with a safer and more effective way. Although the feasibility of using acoustically vaporized nanodroplets to open the blood-brain-barrier (BBB) has previously been reported, the relevant physical mechanisms and impact factors are not well known. In the current study, a nitrocellulose (NC) membrane was used to mimic the multi-layered pore structure of BBB. The cavitation activity and the penetration ability of phase-changed nanodroplets were systemically evaluated at different concentration levels, and compared with the results obtained for SonoVue microbubbles. Passive cavitation detection showed that less intensified but more sustained inertial cavitation (IC) activity would be generated by vaporized nanodroplets than microbubbles. As the results, with a sufficiently high concentration (∼5 × 108/mL), phase-changed nanodroplets were more effective than microbubbles in enabling a fluorescent tracer agent (FITC, 150 kDa) to penetrate deeper and more homogeneously through the NC membrane, and a positive correlation was observed between accumulated IC dose and the amount of penetrated FITC. In vivo studies further confirmed acoustically vaporized nanodroplets performed better than microbubbles by opening the BBB in rats' brains. These results indicated that phase-changed nanodroplets can be used as a safe, efficient and durable agent to achieve satisfactory cavitation-mediated permeability enhancement effect in biomedical applications.
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Affiliation(s)
- Renjie Song
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Chunbing Zhang
- Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210023, China
| | - Fengmeng Teng
- Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210023, China
| | - Juan Tu
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China; The State Key Laboratory of Acoustics, Chinese Academy of Science, Beijing 10080, China.
| | - Xiasheng Guo
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China
| | - Zheng Fan
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Yinfei Zheng
- Research Center for Intelligent Sensing, Zhejiang Lab, Hangzhou 311100, China.
| | - Dong Zhang
- Key Laboratory of Modern Acoustics (MOE), Department of Physics, Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing 210093, China; The State Key Laboratory of Acoustics, Chinese Academy of Science, Beijing 10080, China.
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Delayed Echo Enhancement Imaging to Quantify Myocardial Infarct Size. J Am Soc Echocardiogr 2021; 34:898-909. [PMID: 33711458 DOI: 10.1016/j.echo.2021.02.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 01/07/2021] [Accepted: 02/28/2021] [Indexed: 12/12/2022]
Abstract
BACKGROUND Perfluoropropane droplets formulated from commercial microbubbles exhibit different acoustic characteristics than their parent microbubbles, most likely from enhanced endothelial permeability. This enhanced permeability may permit delayed echo-enhancement imaging (DEEI) similar to delayed enhancement magnetic resonance imaging (DE-MRI). We hypothesized this would allow detection and quantification of myocardial scar. METHODS In 15 pigs undergoing 90 minutes of left anterior descending ischemia by either balloon (n = 13) or thrombotic occlusion (n = 2), DE-MRI was performed at 2-24 days postocclusion. Delayed echo-enhancement imaging was performed at 2-4 minutes following an intravenous injection of 1 mL of 50% Definity (Lantheus Medical) compressed into 180 nm droplets; DEEI was attempted in all pigs with single-pulse harmonic imaging at 1.7 transmit/3.4 MHz receive. Myocardial defects observed with DEEI were quantified (percentage of infarct area) and compared with DE-MRI as well as postmortem staining. In six pigs, multipulse low-mechanical index (MI) fundamental nonlinear imaging (FNLI) with intermittent high-MI impulses was performed to determine whether droplet activation within the infarct zone was achievable with a longer pulse duration. RESULTS The range of infarct size area by DE-MRI ranged from 0% to 46% of total left ventricular area. Single-pulse harmonic imaging detected a contrast defect that correlated closely with infarct area by DE-MRI (r = 0.81, P = .0001). The FNLI high-MI impulses resulted in droplet activation in both the infarct and normal zones. Harmonic subtraction of the FNLI images resulted in infarct zone enhancement that also correlated closely with infarct size (r = 0.83; P = .04). Droplets were observed on postmortem transmission electron microscopy within myocytes of the infarct and remote normal zone. CONCLUSION Intravenously Definity nanodroplets can be utilized to detect and quantify infarct zone at the bedside using DEEI techniques.
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