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Nico de Jong

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Papers by Nico de Jong

On the Design and Construction of a Transesophageal Scanner

Developments in cardiovascular medicine, 1982

The interest in ultrasound scanning from positions located inside the human body has remained aft... more The interest in ultrasound scanning from positions located inside the human body has remained after the first proposals some 10 years ago (1, 2). The number of workers in this particular field has been, however, rather low. This may be explained by the high success rate of ultrasound in standard non-invasive applications. Still there exists a clinical demand for alternative scanning procedures for some specific applications. The prostate, for instance, is hard to scan successfully from locations outside the patient and therefore intra-rectal scanning has become an accepted procedure.

Comparison of three different transducer concepts for acoustic bladder volume measurements

In a preceding study the importance of noninvasive bladder volume measurements was addressed, and... more In a preceding study the importance of noninvasive bladder volume measurements was addressed, and a new technique to measure the bladder volume on the basis of nonlinear ultrasound wave propagation was validated. It was shown that the harmonic level generated at the posterior bladder wall increases for larger bladder volumes. The objective of this study is to design an optimal transducer to implement this approach. For this purpose, three different transducer concepts, i.e. a multi-layer transducer, a broadband piezo-composite transducer and a multi-element transducer, were mutually compared using calibrated hydrophone measurements in water and pulse-echo measurements on a bladder test phantom. The effects of an additional acoustic lens on the beamwidth and generated peak pressures were also considered.

Quantitative three-dimensional echocardiography using an ultrafast rotating transthoracic scanner for evaluation of ventricular function in humans

Journal of the American College of Cardiology, Mar 1, 2002

Local drug and gene delivery through microbubbles and ultrasound

PubMed, Sep 1, 2004

Although gene therapy has great potential as a treatment for diseases, clinical trials are slowed... more Although gene therapy has great potential as a treatment for diseases, clinical trials are slowed down by the development of a safe and efficient gene delivery system. In this review, we will give an overview of the viral and nonviral vehicles used for drug and gene delivery, and the different nonviral delivery techniques, thereby focusing on delivery through ultrasound contrast agents. The development of ultrasound contrast agents containing encapsulated microbubbles has increased the possibilities not only for diagnostic imaging, but for therapy as well. Microbubbles have been shown to be able to carry drugs and genes, and destruction of the bubbles by ultrasound will result in local release of their contents. Furthermore, ligands can be attached so that they can be targeted to a specific target tissue. The recent advances of microbubbles as vehicles for delivery of drugs and genes will be highlighted.

Harmonic ultrasonic field of medical phased arrays: simulations and measurements

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Jun 1, 2003

With the introduction of harmonic imaging, the design of new array transducers for tissue and con... more With the introduction of harmonic imaging, the design of new array transducers for tissue and contrast imaging became indispensable. Hence, prior knowledge of harmonic beams is essential to attain optimal harmonic performances. For that purpose, a new numerical algorithm that solves the parabolic nonlinear wave equation is developed. The algorithm is based on finite differences and performs exclusively in time domain. Pulsed harmonic fields emitted by a medical transducer were measured and computed at different mechanical indices. Simulations and measurements showed very good agreement for all the harmonic components.

Principles and recent developments in ultrasound contrast agents

Ultrasonics, Jul 1, 1991

The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is revie... more The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications.

Optical imaging of ultrasound contrast bubble motions at 25 million frames per second

Design of a Matrix Transducer for Three-Dimensional Second Harmonic Transesophageal Echocardiography

Springer eBooks, 2012

Three-dimensional (3D) echocardiography visualizes the 3D anatomy and function of the heart. For ... more Three-dimensional (3D) echocardiography visualizes the 3D anatomy and function of the heart. For 3D imaging an ultrasound matrix of several thousands of elements is required. To connect the matrix to an external imaging system, smart signal processing with integrated circuitry in the tip of the TEE probe is required for channel reduction. To separate the low voltage integrated receive circuitry from the high voltages required for transmission, our design features a separate transmit and receive subarray. In this study we focus on the transmit subarray. A 3D model of an individual element was developed using the finite element method (FEM). The model was validated by laser interferometer and acoustic measurements. Measurement and simulations matched well. The maximum transmit transfer was 3 nm/V at 2.4 MHz for both the FEM simulation of an element in air and the laser interferometer measurement. The FEM simulation of an element in water resulted in a maximum transfer of 43 kPa/V at 2.3 MHz and the acoustic measurement in 55 kPa/V at 2.5 MHz. The maximum pressure is ~1 MPa/120Vpp, which is sufficient pressure for second harmonic imaging. The proposed design of the transmit subarray is suitable for its role in a 3D 2H TEE probe.

Acoustic Sizing of an Ultrasound Contrast Agent

Ultrasound in Medicine and Biology, Oct 1, 2010

dBecause the properties of ultrasound contrast agent populations after administration to patients... more dBecause the properties of ultrasound contrast agent populations after administration to patients are largely unknown, methods able to study them noninvasively are required. In this study, we acoustically performed a size distribution measurement of the ultrasound contrast agent Definity Ò. Single lipid-shelled microbubbles were insonified at 25 MHz, which is considerably higher than their resonance frequency, so that their acoustic responses depended on their geometrical cross sections only. We calculated the size of each microbubble from their measured backscattered pressures. The acoustic size measurements were compared with optical reference size measurements to test their accuracy. Our acoustic sizing method was applied to 88 individual Definity Ò bubbles to derive a size distribution of this agent. The size distribution obtained acoustically showed a mean diameter (2.5 mm) and a standard deviation (0.9 mm) in agreement within 8% with the optical reference measurement. At 25 MHz, this method can be applied to bubble sizes larger than 1.2 mm in diameter. It was observed that similar sized bubbles can give different responses (up to a factor 1.5), probably because of shell differences. These limitations should be taken into account when implementing the method in vivo. This acoustic sizing method has potential for estimating the size distribution of an ultrasound contrast agent noninvasively.

Abstract 1070: Targeted Delivery of Macromolecules Using Ultrasound and Microbubbles is Regulated by Induction of Endocytosis and Pore Formation

Circulation

Ultrasound (US) contrast microbubbles are promising vehicles for local drug and gene delivery. Ho... more Ultrasound (US) contrast microbubbles are promising vehicles for local drug and gene delivery. However, the exact mechanisms behind intracellular delivery of therapeutic compounds remain to be resolved. We hypothesized that endocytosis and pore formation are involved during US and microbubble targeted delivery (UMTD) of therapeutic compounds. Primary bovine aortic endothelial cells were subjected to UMTD of fluorescent dextrans (4.4 – 500 kDa) using 1-MHz US during 30s with 0.22 MPa peak-negative pressure. Duty cycle: 6.2%, pulse repetition frequency 20 Hz. Confocal laser microscopy showed the localization of 155 and 500 kDa dextrans in distinct vesicles after UMTD, indicating uptake via endocytosis. Independently inhibiting the main routes of active cellular uptake, i.e. clathrin- and caveolae-mediated endocytosis and macropinocytosis, caused significant decreases of 50 – 70% in intracellular delivery of 4.4 – 500 kDa dextrans (p<0.05). Furthermore, 3D immunofluorescence microsc...

Corrigendum for “Intravital microscopy of localized stem cell delivery using microbubbles and acoustic radiation force” (Vol. 112, Issue 1, pp. 220–227)

Biotechnology and Bioengineering, 2021

Stichting voor de Technische Wetenschappen The authors regret that there was a mistake in calcula... more Stichting voor de Technische Wetenschappen The authors regret that there was a mistake in calculating the mol% of the microbubble coating composition used. For all experiments the unit in mg/ml was utilized and the conversion mistake only came when converting to mol% to define the ratio between the coating formulation

Corrigendum to “Secondary Bjerknes Forces Deform Targeted Microbubbles” (Ultrasound Med Biol 2013;39:490–506)

Ultrasound in Medicine & Biology, 2021

Abstract 15053: Directing Stem Cells to the Infarcted Heart Using StemBells™: Introducing a Novel Technique Using Targeted Microbubbles

Circulation, 2013

Microbubbles for ultrasound imaging and therapy

Ultrasound is the most widely used medical imaging modality. T he majority of ultrasound systems ... more Ultrasound is the most widely used medical imaging modality. T he majority of ultrasound systems operate at frequencies in the I to 5 MHz range and form images using a hand-held transducer that is external to the body. It is capable of provid ing real-time information about tissue structure and blood flow in the heart and larger vessels. Unfortunately, in smaller vessels and capillaries blood detection is not possib le due to the low signal strength of blood, tissue motion effects, and limited resol ution (-0.5-1 mm). It is the blood volume in small capillaries, monitored as a

Opening of endothelial cell–cell contacts due to sonoporation

Journal of Controlled Release, 2020

Ultrasound insonification of microbubbles can locally increase vascular permeability to enhance d... more Ultrasound insonification of microbubbles can locally increase vascular permeability to enhance drug delivery. To control and optimize the therapeutic potential, we need to better understand the underlying biological mechanisms of the drug delivery pathways. The aim of this in vitro study was to elucidate the microbubbleendothelial cell interaction using the Brandaris 128 ultra-high-speed camera (up to 25 Mfps) coupled to a custom-built Nikon confocal microscope, to visualize both microbubble oscillation and the cellular response. Sonoporation and opening of cell-cell contacts by single α V β 3-targeted microbubbles (n = 152) was monitored up to 4 min after ultrasound insonification (2 MHz, 100-400 kPa, 10 cycles). Sonoporation occurred when microbubble excursion amplitudes exceeded 0.7 μm. Quantification of the influx of the fluorescent model drug propidium iodide upon sonoporation showed that the size of the created pore increased for larger microbubble excursion amplitudes. Microbubble-mediated opening of cell-cell contacts occurred as a cellular response upon sonoporation and did not correlate with the microbubble excursion amplitude itself. The initial integrity of the cell-cell contacts affected the susceptibly to drug delivery, since cell-cell contacts opened more often when cells were only partially attached to their neighbors (48%) than when fully attached (14%). The drug delivery outcomes were independent of nonlinear microbubble behavior, microbubble location, and cell size. In conclusion, by studying the microbubble-cell interaction at nanosecond and nanometer resolution the relationship between drug delivery pathways and their underlying mechanisms was further unraveled. These novel insights will aid the development of safe and efficient microbubble-mediated drug delivery.

SPIO labeling of endothelial cells using ultrasound and targeted microbubbles at diagnostic pressures

PLOS ONE, 2018

In vivo cell tracking of therapeutic, tumor, and endothelial cells is an emerging field and a pro... more In vivo cell tracking of therapeutic, tumor, and endothelial cells is an emerging field and a promising technique for imaging cardiovascular disease and cancer development. Site-specific labeling of endothelial cells with the MRI contrast agent superparamagnetic iron oxide (SPIO) in the absence of toxic agents is challenging. Therefore, the aim of this in vitro study was to find optimal parameters for efficient and safe SPIO-labeling of endothelial cells using ultrasound-activated CD31-targeted microbubbles for future MRI tracking. Ultrasound at a frequency of 1 MHz (10,000 cycles, repetition rate of 20 Hz) was used for varying applied peak negative pressures (10-160 kPa, i.e. low mechanical index (MI) of 0.01-0.16), treatment durations (0-30 s), time of SPIO addition (-5 min-15 min with respect to the start of the ultrasound), and incubation time after SPIO addition (5 min-3 h). Iron specific Prussian Blue staining in combination with calcein-AM based cell viability assays were applied to define the most efficient and safe conditions for SPIO-labeling. Optimal SPIO labeling was observed when the ultrasound parameters were 40 kPa peak negative pressure (MI 0.04), applied for 30 s just before SPIO addition (0 min). Compared to the control, this resulted in an approximate 12 times increase of SPIO uptake in endothelial cells in vitro with 85% cell viability. Therefore, ultrasound-activated targeted ultrasound contrast agents show great potential for effective and safe labeling of endothelial cells with SPIO.

On the dynamics of StemBells: Microbubble-conjugated stem cells for ultrasound-controlled delivery

Applied Physics Letters, 2017

The use of stem cells for regenerative tissue repair is promising but hampered by the low number ... more The use of stem cells for regenerative tissue repair is promising but hampered by the low number of cells delivered to the site of injury. To increase the delivery, we propose a technique in which stem cells are linked to functionalized microbubbles, creating echogenic complex dubbed StemBells. StemBells are highly susceptible to acoustic radiation force which can be employed after injection to push the StemBells locally to the treatment site. To optimally benefit from the delivery technique, a thorough characterization of the dynamics of StemBells during ultrasound exposure is needed. Using high-speed optical imaging, we study the dynamics of StemBells as a function of the applied frequency from which resonance curves were constructed. A theoretical model, based on a modified Rayleigh-Plesset type equation, captured the experimental resonance characteristics and radial dynamics in detail.

Microbubble composition and preparation for high-frequency contrast-enhanced ultrasound imaging: in vitro and in vivo evaluation

IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Mar 15, 2016

Although high-frequency ultrasound imaging is gaining attention in various applications, hardly a... more Although high-frequency ultrasound imaging is gaining attention in various applications, hardly any ultrasound contrast agents (UCAs) dedicated to such frequencies (>15 MHz) are available for contrast-enhanced ultrasound imaging (CEUS). Moreover, the composition of the limited commercially available UCAs for high-frequency CEUS (hfCEUS) is largely unknown, while shell properties have been shown to be an important factor for their performance. The aim of our study was to produce UCAs in-house for hfCEUS. Twelve different UCA formulations A-L were made by either sonication or mechanical agitation. The gas core consisted of C4F10 and the main coating lipid was either DSPC (A-F formulation) or DPPC (G-L formulation). Mechanical agitation resulted in UCAs with smaller microbubbles (number weighted mean diameter ~1 μm) than sonication (number weighted mean diameter ~2 μm). UCA formulations with similar size distributions but different main lipid component, showed that the DPPC-based UC...

Development of a new therapeutic technique to direct stem cells to the infarcted heart using targeted microbubbles: StemBells

Stem cell research, Jan 30, 2016

Successful stem cell therapy after acute myocardial infarction (AMI) is hindered by lack of engra... more Successful stem cell therapy after acute myocardial infarction (AMI) is hindered by lack of engraftment of sufficient stem cells at the site of injury. We designed a novel technique to overcome this problem by assembling stem cell-microbubble complexes, named 'StemBells'. StemBells were assembled through binding of dual-targeted microbubbles (~3μm) to adipose-derived stem cells (ASCs) via a CD90 antibody. StemBells were targeted to the infarct area via an ICAM-1 antibody on the microbubbles. StemBells were characterized microscopically and by flow cytometry. The effect of ultrasound on directing StemBells towards the vessel wall was demonstrated in an in vitro flow model. In a rat AMI-reperfusion model, StemBells or ASCs were injected one week post-infarction. A pilot study demonstrated feasibility of intravenous StemBell injection, resulting in localization in ICAM-1-positive infarct area three hours post-injection. In a functional study five weeks after injection of StemBe...

Targeted ultrasound contrast agents for ultrasound molecular imaging and therapy

International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group, Jan 24, 2015

Ultrasound contrast agents (UCAs) are used routinely in the clinic to enhance contrast in ultraso... more Ultrasound contrast agents (UCAs) are used routinely in the clinic to enhance contrast in ultrasonography. More recently, UCAs have been functionalised by conjugating ligands to their surface to target specific biomarkers of a disease or a disease process. These targeted UCAs (tUCAs) are used for a wide range of pre-clinical applications including diagnosis, monitoring of drug treatment, and therapy. In this review, recent achievements with tUCAs in the field of molecular imaging, evaluation of therapy, drug delivery, and therapeutic applications are discussed. We present the different coating materials and aspects that have to be considered when manufacturing tUCAs. Next to tUCA design and the choice of ligands for specific biomarkers, additional techniques are discussed that are applied to improve binding of the tUCAs to their target and to quantify the strength of this bond. As imaging techniques rely on the specific behaviour of tUCAs in an ultrasound field, it is crucial to und...

On the Design and Construction of a Transesophageal Scanner

Developments in cardiovascular medicine, 1982

The interest in ultrasound scanning from positions located inside the human body has remained aft... more The interest in ultrasound scanning from positions located inside the human body has remained after the first proposals some 10 years ago (1, 2). The number of workers in this particular field has been, however, rather low. This may be explained by the high success rate of ultrasound in standard non-invasive applications. Still there exists a clinical demand for alternative scanning procedures for some specific applications. The prostate, for instance, is hard to scan successfully from locations outside the patient and therefore intra-rectal scanning has become an accepted procedure.

Comparison of three different transducer concepts for acoustic bladder volume measurements

In a preceding study the importance of noninvasive bladder volume measurements was addressed, and... more In a preceding study the importance of noninvasive bladder volume measurements was addressed, and a new technique to measure the bladder volume on the basis of nonlinear ultrasound wave propagation was validated. It was shown that the harmonic level generated at the posterior bladder wall increases for larger bladder volumes. The objective of this study is to design an optimal transducer to implement this approach. For this purpose, three different transducer concepts, i.e. a multi-layer transducer, a broadband piezo-composite transducer and a multi-element transducer, were mutually compared using calibrated hydrophone measurements in water and pulse-echo measurements on a bladder test phantom. The effects of an additional acoustic lens on the beamwidth and generated peak pressures were also considered.

Quantitative three-dimensional echocardiography using an ultrafast rotating transthoracic scanner for evaluation of ventricular function in humans

Journal of the American College of Cardiology, Mar 1, 2002

Local drug and gene delivery through microbubbles and ultrasound

PubMed, Sep 1, 2004

Although gene therapy has great potential as a treatment for diseases, clinical trials are slowed... more Although gene therapy has great potential as a treatment for diseases, clinical trials are slowed down by the development of a safe and efficient gene delivery system. In this review, we will give an overview of the viral and nonviral vehicles used for drug and gene delivery, and the different nonviral delivery techniques, thereby focusing on delivery through ultrasound contrast agents. The development of ultrasound contrast agents containing encapsulated microbubbles has increased the possibilities not only for diagnostic imaging, but for therapy as well. Microbubbles have been shown to be able to carry drugs and genes, and destruction of the bubbles by ultrasound will result in local release of their contents. Furthermore, ligands can be attached so that they can be targeted to a specific target tissue. The recent advances of microbubbles as vehicles for delivery of drugs and genes will be highlighted.

Harmonic ultrasonic field of medical phased arrays: simulations and measurements

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Jun 1, 2003

With the introduction of harmonic imaging, the design of new array transducers for tissue and con... more With the introduction of harmonic imaging, the design of new array transducers for tissue and contrast imaging became indispensable. Hence, prior knowledge of harmonic beams is essential to attain optimal harmonic performances. For that purpose, a new numerical algorithm that solves the parabolic nonlinear wave equation is developed. The algorithm is based on finite differences and performs exclusively in time domain. Pulsed harmonic fields emitted by a medical transducer were measured and computed at different mechanical indices. Simulations and measurements showed very good agreement for all the harmonic components.

Principles and recent developments in ultrasound contrast agents

Ultrasonics, Jul 1, 1991

The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is revie... more The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications.

Optical imaging of ultrasound contrast bubble motions at 25 million frames per second

Design of a Matrix Transducer for Three-Dimensional Second Harmonic Transesophageal Echocardiography

Springer eBooks, 2012

Three-dimensional (3D) echocardiography visualizes the 3D anatomy and function of the heart. For ... more Three-dimensional (3D) echocardiography visualizes the 3D anatomy and function of the heart. For 3D imaging an ultrasound matrix of several thousands of elements is required. To connect the matrix to an external imaging system, smart signal processing with integrated circuitry in the tip of the TEE probe is required for channel reduction. To separate the low voltage integrated receive circuitry from the high voltages required for transmission, our design features a separate transmit and receive subarray. In this study we focus on the transmit subarray. A 3D model of an individual element was developed using the finite element method (FEM). The model was validated by laser interferometer and acoustic measurements. Measurement and simulations matched well. The maximum transmit transfer was 3 nm/V at 2.4 MHz for both the FEM simulation of an element in air and the laser interferometer measurement. The FEM simulation of an element in water resulted in a maximum transfer of 43 kPa/V at 2.3 MHz and the acoustic measurement in 55 kPa/V at 2.5 MHz. The maximum pressure is ~1 MPa/120Vpp, which is sufficient pressure for second harmonic imaging. The proposed design of the transmit subarray is suitable for its role in a 3D 2H TEE probe.

Acoustic Sizing of an Ultrasound Contrast Agent

Ultrasound in Medicine and Biology, Oct 1, 2010

dBecause the properties of ultrasound contrast agent populations after administration to patients... more dBecause the properties of ultrasound contrast agent populations after administration to patients are largely unknown, methods able to study them noninvasively are required. In this study, we acoustically performed a size distribution measurement of the ultrasound contrast agent Definity Ò. Single lipid-shelled microbubbles were insonified at 25 MHz, which is considerably higher than their resonance frequency, so that their acoustic responses depended on their geometrical cross sections only. We calculated the size of each microbubble from their measured backscattered pressures. The acoustic size measurements were compared with optical reference size measurements to test their accuracy. Our acoustic sizing method was applied to 88 individual Definity Ò bubbles to derive a size distribution of this agent. The size distribution obtained acoustically showed a mean diameter (2.5 mm) and a standard deviation (0.9 mm) in agreement within 8% with the optical reference measurement. At 25 MHz, this method can be applied to bubble sizes larger than 1.2 mm in diameter. It was observed that similar sized bubbles can give different responses (up to a factor 1.5), probably because of shell differences. These limitations should be taken into account when implementing the method in vivo. This acoustic sizing method has potential for estimating the size distribution of an ultrasound contrast agent noninvasively.

Abstract 1070: Targeted Delivery of Macromolecules Using Ultrasound and Microbubbles is Regulated by Induction of Endocytosis and Pore Formation

Circulation

Ultrasound (US) contrast microbubbles are promising vehicles for local drug and gene delivery. Ho... more Ultrasound (US) contrast microbubbles are promising vehicles for local drug and gene delivery. However, the exact mechanisms behind intracellular delivery of therapeutic compounds remain to be resolved. We hypothesized that endocytosis and pore formation are involved during US and microbubble targeted delivery (UMTD) of therapeutic compounds. Primary bovine aortic endothelial cells were subjected to UMTD of fluorescent dextrans (4.4 – 500 kDa) using 1-MHz US during 30s with 0.22 MPa peak-negative pressure. Duty cycle: 6.2%, pulse repetition frequency 20 Hz. Confocal laser microscopy showed the localization of 155 and 500 kDa dextrans in distinct vesicles after UMTD, indicating uptake via endocytosis. Independently inhibiting the main routes of active cellular uptake, i.e. clathrin- and caveolae-mediated endocytosis and macropinocytosis, caused significant decreases of 50 – 70% in intracellular delivery of 4.4 – 500 kDa dextrans (p<0.05). Furthermore, 3D immunofluorescence microsc...

Corrigendum for “Intravital microscopy of localized stem cell delivery using microbubbles and acoustic radiation force” (Vol. 112, Issue 1, pp. 220–227)

Biotechnology and Bioengineering, 2021

Stichting voor de Technische Wetenschappen The authors regret that there was a mistake in calcula... more Stichting voor de Technische Wetenschappen The authors regret that there was a mistake in calculating the mol% of the microbubble coating composition used. For all experiments the unit in mg/ml was utilized and the conversion mistake only came when converting to mol% to define the ratio between the coating formulation

Corrigendum to “Secondary Bjerknes Forces Deform Targeted Microbubbles” (Ultrasound Med Biol 2013;39:490–506)

Ultrasound in Medicine & Biology, 2021

Abstract 15053: Directing Stem Cells to the Infarcted Heart Using StemBells™: Introducing a Novel Technique Using Targeted Microbubbles

Circulation, 2013

Microbubbles for ultrasound imaging and therapy

Ultrasound is the most widely used medical imaging modality. T he majority of ultrasound systems ... more Ultrasound is the most widely used medical imaging modality. T he majority of ultrasound systems operate at frequencies in the I to 5 MHz range and form images using a hand-held transducer that is external to the body. It is capable of provid ing real-time information about tissue structure and blood flow in the heart and larger vessels. Unfortunately, in smaller vessels and capillaries blood detection is not possib le due to the low signal strength of blood, tissue motion effects, and limited resol ution (-0.5-1 mm). It is the blood volume in small capillaries, monitored as a

Opening of endothelial cell–cell contacts due to sonoporation

Journal of Controlled Release, 2020

Ultrasound insonification of microbubbles can locally increase vascular permeability to enhance d... more Ultrasound insonification of microbubbles can locally increase vascular permeability to enhance drug delivery. To control and optimize the therapeutic potential, we need to better understand the underlying biological mechanisms of the drug delivery pathways. The aim of this in vitro study was to elucidate the microbubbleendothelial cell interaction using the Brandaris 128 ultra-high-speed camera (up to 25 Mfps) coupled to a custom-built Nikon confocal microscope, to visualize both microbubble oscillation and the cellular response. Sonoporation and opening of cell-cell contacts by single α V β 3-targeted microbubbles (n = 152) was monitored up to 4 min after ultrasound insonification (2 MHz, 100-400 kPa, 10 cycles). Sonoporation occurred when microbubble excursion amplitudes exceeded 0.7 μm. Quantification of the influx of the fluorescent model drug propidium iodide upon sonoporation showed that the size of the created pore increased for larger microbubble excursion amplitudes. Microbubble-mediated opening of cell-cell contacts occurred as a cellular response upon sonoporation and did not correlate with the microbubble excursion amplitude itself. The initial integrity of the cell-cell contacts affected the susceptibly to drug delivery, since cell-cell contacts opened more often when cells were only partially attached to their neighbors (48%) than when fully attached (14%). The drug delivery outcomes were independent of nonlinear microbubble behavior, microbubble location, and cell size. In conclusion, by studying the microbubble-cell interaction at nanosecond and nanometer resolution the relationship between drug delivery pathways and their underlying mechanisms was further unraveled. These novel insights will aid the development of safe and efficient microbubble-mediated drug delivery.

SPIO labeling of endothelial cells using ultrasound and targeted microbubbles at diagnostic pressures

PLOS ONE, 2018

In vivo cell tracking of therapeutic, tumor, and endothelial cells is an emerging field and a pro... more In vivo cell tracking of therapeutic, tumor, and endothelial cells is an emerging field and a promising technique for imaging cardiovascular disease and cancer development. Site-specific labeling of endothelial cells with the MRI contrast agent superparamagnetic iron oxide (SPIO) in the absence of toxic agents is challenging. Therefore, the aim of this in vitro study was to find optimal parameters for efficient and safe SPIO-labeling of endothelial cells using ultrasound-activated CD31-targeted microbubbles for future MRI tracking. Ultrasound at a frequency of 1 MHz (10,000 cycles, repetition rate of 20 Hz) was used for varying applied peak negative pressures (10-160 kPa, i.e. low mechanical index (MI) of 0.01-0.16), treatment durations (0-30 s), time of SPIO addition (-5 min-15 min with respect to the start of the ultrasound), and incubation time after SPIO addition (5 min-3 h). Iron specific Prussian Blue staining in combination with calcein-AM based cell viability assays were applied to define the most efficient and safe conditions for SPIO-labeling. Optimal SPIO labeling was observed when the ultrasound parameters were 40 kPa peak negative pressure (MI 0.04), applied for 30 s just before SPIO addition (0 min). Compared to the control, this resulted in an approximate 12 times increase of SPIO uptake in endothelial cells in vitro with 85% cell viability. Therefore, ultrasound-activated targeted ultrasound contrast agents show great potential for effective and safe labeling of endothelial cells with SPIO.

On the dynamics of StemBells: Microbubble-conjugated stem cells for ultrasound-controlled delivery

Applied Physics Letters, 2017

The use of stem cells for regenerative tissue repair is promising but hampered by the low number ... more The use of stem cells for regenerative tissue repair is promising but hampered by the low number of cells delivered to the site of injury. To increase the delivery, we propose a technique in which stem cells are linked to functionalized microbubbles, creating echogenic complex dubbed StemBells. StemBells are highly susceptible to acoustic radiation force which can be employed after injection to push the StemBells locally to the treatment site. To optimally benefit from the delivery technique, a thorough characterization of the dynamics of StemBells during ultrasound exposure is needed. Using high-speed optical imaging, we study the dynamics of StemBells as a function of the applied frequency from which resonance curves were constructed. A theoretical model, based on a modified Rayleigh-Plesset type equation, captured the experimental resonance characteristics and radial dynamics in detail.

Microbubble composition and preparation for high-frequency contrast-enhanced ultrasound imaging: in vitro and in vivo evaluation

IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Mar 15, 2016

Although high-frequency ultrasound imaging is gaining attention in various applications, hardly a... more Although high-frequency ultrasound imaging is gaining attention in various applications, hardly any ultrasound contrast agents (UCAs) dedicated to such frequencies (>15 MHz) are available for contrast-enhanced ultrasound imaging (CEUS). Moreover, the composition of the limited commercially available UCAs for high-frequency CEUS (hfCEUS) is largely unknown, while shell properties have been shown to be an important factor for their performance. The aim of our study was to produce UCAs in-house for hfCEUS. Twelve different UCA formulations A-L were made by either sonication or mechanical agitation. The gas core consisted of C4F10 and the main coating lipid was either DSPC (A-F formulation) or DPPC (G-L formulation). Mechanical agitation resulted in UCAs with smaller microbubbles (number weighted mean diameter ~1 μm) than sonication (number weighted mean diameter ~2 μm). UCA formulations with similar size distributions but different main lipid component, showed that the DPPC-based UC...

Development of a new therapeutic technique to direct stem cells to the infarcted heart using targeted microbubbles: StemBells

Stem cell research, Jan 30, 2016

Successful stem cell therapy after acute myocardial infarction (AMI) is hindered by lack of engra... more Successful stem cell therapy after acute myocardial infarction (AMI) is hindered by lack of engraftment of sufficient stem cells at the site of injury. We designed a novel technique to overcome this problem by assembling stem cell-microbubble complexes, named 'StemBells'. StemBells were assembled through binding of dual-targeted microbubbles (~3μm) to adipose-derived stem cells (ASCs) via a CD90 antibody. StemBells were targeted to the infarct area via an ICAM-1 antibody on the microbubbles. StemBells were characterized microscopically and by flow cytometry. The effect of ultrasound on directing StemBells towards the vessel wall was demonstrated in an in vitro flow model. In a rat AMI-reperfusion model, StemBells or ASCs were injected one week post-infarction. A pilot study demonstrated feasibility of intravenous StemBell injection, resulting in localization in ICAM-1-positive infarct area three hours post-injection. In a functional study five weeks after injection of StemBe...

Targeted ultrasound contrast agents for ultrasound molecular imaging and therapy

International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group, Jan 24, 2015

Ultrasound contrast agents (UCAs) are used routinely in the clinic to enhance contrast in ultraso... more Ultrasound contrast agents (UCAs) are used routinely in the clinic to enhance contrast in ultrasonography. More recently, UCAs have been functionalised by conjugating ligands to their surface to target specific biomarkers of a disease or a disease process. These targeted UCAs (tUCAs) are used for a wide range of pre-clinical applications including diagnosis, monitoring of drug treatment, and therapy. In this review, recent achievements with tUCAs in the field of molecular imaging, evaluation of therapy, drug delivery, and therapeutic applications are discussed. We present the different coating materials and aspects that have to be considered when manufacturing tUCAs. Next to tUCA design and the choice of ligands for specific biomarkers, additional techniques are discussed that are applied to improve binding of the tUCAs to their target and to quantify the strength of this bond. As imaging techniques rely on the specific behaviour of tUCAs in an ultrasound field, it is crucial to und...