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Biomedical subjects

Dustin E Kruse

Publications and source records attributed to Dustin E Kruse.

9 recordsLinked to original sources
PubMed2006

Acoustic response from adherent targeted contrast agents.

In ultrasonic molecular imaging, encapsulated micron-sized gas bubbles are tethered to a blood vessel wall by targeting ligands. A challenging problem is to detect the echoes from adherent microbubbles and distinguish them from echoes from nonadherent agents and tissue. Echoes from adherent contrast agents are observed to include a high amplitude at the fundamental frequency, and significantly different spectral shape compared with free agents (p <0.0003). Mechanisms for the observed acoustical difference and potential techniques to utilize these differences for molecular imaging are proposed.

Acoustics↗
PubMed2005

Ultrasound radiation force enables targeted deposition of model drug carriers loaded on microbubbles.

A novel drug delivery vehicle that specifically targets using ultrasound radiation force (USRF) and biotin-avidin interactions is presented. Model vehicles consist of avidinated fluorescent nanobeads bound directly to the biotinylated lipid shells of preformed microbubbles. USRF was used to deflect the vehicle from the center of flow to a tube surface in order to facilitate receptor-ligand mediated adhesion. At wall shear stress levels commensurate with venous and arterial flow, USRF was used to direct the vehicles to a biotinylated tube surface. Subsequent high-pressure pulses fragmented the carrier, and molecular interactions induced deposition of the nanobeads on the wall. Targeting of nanobeads to the tube was molecularly specific and dependent on, in order of importance, vehicle concentration, wall shear stress, nanobead size, and insonation time. The observation that portions of the microbubble lipid monolayer shell remain attached to adherent nanobeads is important for future consideration of drug transport mechanisms. This versatile method of delivery is shown to enable targeted deposition of nanoparticles in shear flow and could be modified to carry therapeutic agents for controlled release in targeted delivery applications.

Avidin↗
PubMed2005

A new imaging strategy using wideband transient response of ultrasound contrast agents.

High-resolution clinical systems operating near 15 MHz are becoming more available; however, they lack sensitive harmonic imaging modes for ultrasound contrast agent (UCA) detection, primarily due to limited bandwidth. When an UCA is driven to nonlinear oscillation, a very wideband acoustic transient response is produced that extends beyond 15 MHz. We propose a novel strategy using two separate transducers at widely separated frequencies and arranged confocally to simultaneously excite and receive acoustic transients from UCAs. Experiments were performed to demonstrate that this new mode shows similar resolution, higher echo amplitudes, and greatly reduced attenuation compared to transmission at a higher frequency, and superior resolution compared to transmission and reception at a lower frequency. The proposed method is shown to resolve two 200 microm tubes with centers separated by 400 microm. Strong acoustic transients were detected for rarefaction-first 1-cycle pulses with peak-negative pressures above 300 kPa. The results of this work may lead to uses in flow and/or targeted imaging in applications requiring very high sensitivity to contrast agents.

Algorithms↗
PubMed2005

High-frequency dynamics of ultrasound contrast agents.

Ultrasound contrast agents enhance echoes from the microvasculature and enable the visualization of flow in smaller vessels. Here, we optically and acoustically investigate microbubble oscillation and echoes following insonation with a 10 MHz center frequency pulse. A high-speed camera system with a temporal resolution of 10 ns, which provides two-dimensional (2-D) frame images and streak images, is used in optical experiments. Two confocally aligned transducers, transmitting at 10 MHz and receiving at 5 MHz, are used in acoustical experiments in order to detect subharmonic components. Results of a numerical evaluation of the modified Rayleigh-Plesset equation are used to predict the dynamics of a microbubble and are compared to results of in vitro experiments. From the optical observations of a single microbubble, nonlinear oscillation, destruction, and radiation force are observed. The maximum bubble expansion, resulting from insonation with a 20-cycle, 10-MHz linear chirp with a peak negative pressure of 3.5 MPa, has been evaluated. For an initial diameter ranging from 1.5 to 5 microm, a maximum diameter less than 8 microm is produced during insonation. Optical and acoustical experiments provide insight into the mechanisms of destruction, including fragmentation and active diffusion. High-frequency pulse transmission may provide the opportunity to detect contrast echoes resulting from a single pulse, may be robust in the presence of tissue motion, and may provide the opportunity to incorporate high-frequency ultrasound into destruction-replenishment techniques.

Contrast Media↗
PubMed2005

Influence of lipid shell physicochemical properties on ultrasound-induced microbubble destruction.

We present the first study of the effects of monolayer shell physicochemical properties on the destruction of lipid-coated microbubbles during insonification with single, one-cycle pulses at 2.25 MHz and low-duty cycles. Shell cohesiveness was changed by varying phospholipid and emulsifier composition, and shell microstructure was controlled by postproduction processing. Individual microbubbles with initial resting diameters between 1 and 10 microm were isolated and recorded during pulsing with bright-field and fluorescence video microscopy. Microbubble destruction occurred through two modes: acoustic dissolution at 400 and 600 kPa and fragmentation at 800 kPa peak negative pressure. Lipid composition significantly impacted the acoustic dissolution rate, fragmentation propensity, and mechanism of excess lipid shedding. Less cohesive shells resulted in micron-scale or smaller particles of excess lipid material that shed either spontaneously or on the next pulse. Conversely, more cohesive shells resulted in the buildup of shell-associated lipid strands and globular aggregates of several microns in size; the latter showed a significant increase in total shell surface area and lability. Lipid-coated microbubbles were observed to reach a stable size over many pulses at intermediate acoustic pressures. Observations of shell microstructure between pulses allowed interpretation of the state of the shell during oscillation. We briefly discuss the implications of these results for therapeutic and diagnostic applications involving lipid-coated microbubbles as ultrasound contrast agents and drug/gene delivery vehicles.

Coated Materials, Biocompatible↗
PubMed2004

High-resolution functional vascular assessment with ultrasound.

In order to improve the resolution of contrast-assisted imaging systems, we have created a high-frequency destruction/contrast replenishment imaging system with a spatial resolution of 160 microm x 160 microm. The system utilizes a 1-MHz cylindrically focused transducer for destruction and a 25-MHz spherically focused transducer for pulse/echo imaging. Speckle tracking and a clutter filter are applied across frames to remove the challenging physiologic motion artifacts that are obtained when imaging with a mechanically scanned transducer. Using a new estimation technique, flow constants proportional to absolute flow rate were estimated from B-mode time-intensity curves (TICs). The in vitro results indicate a correlation between the actual flow velocity and the estimated rate constant. In vivo images are presented showing blood perfusion in the ciliary processes and iris of the rabbit eye. The regions of interest (ROIs) from the ciliary processes yielded slower perfusion compared with the iris, as expected from vascular casts of the microcirculation in this region. Potential applications of this system include high-resolution perfusion assessment in small animals.

Algorithms↗
PubMed2003

Effect of coupled oscillations on microbubble behavior.

Ultrasound contrast agents are encapsulated microbubbles whose nonlinear acoustic scattering signatures have been the foundation of their use in diagnostic imaging. The coupled oscillations of microbubbles along their lines of center are investigated theoretically using radial equations in the monopole approximation and an energy balance, which is obtained for the system. Coupled microbubble pairs of different initial radii are investigated numerically relative to the normal modes for the linearized system. For microbubble pairs of different size bubbles driven below the mode of the smaller bubble and above the mode of the larger bubble, it is shown that oscillations of the smaller agent are affected substantially more by the coupling than those of the larger one. For separation distances of 10 and 500 microns, a difference of approximately 10 dB occurs in the second harmonic output of a 1.0-micron radius agent coupled with a 2.2-micron radius agent forced at 2.0 MHz and 0.3 MPa. The subharmonic spectral peak is shown to decrease approximately 19 dB for the coupling of 1.5- and 2.2-micron radius agents at 10- and 500-micron distances under the same acoustic forcing conditions. These coupling effects on the radiated pressure and its spectral power are highlighted for contrast agent imaging applications.

Humans↗
PubMed2002

A new high resolution color flow system using an eigendecomposition-based adaptive filter for clutter rejection.

We present a new signal processing strategy for high frequency color flow mapping in moving tissue environments. A new application of an eigendecomposition-based clutter rejection filter is presented with modifications to deal with high blood-to-clutter ratios (BCR). Additionally, a new method for correcting blood velocity estimates with an estimated tissue motion profile is detailed. The performance of the clutter filter and velocity estimation strategies is quantified using a new swept-scan signal model. In vivo color flow images are presented to illustrate the potential of the system for mapping blood flow in the microcirculation with external tissue motion.

Algorithms↗
PubMed2002

A new high resolution color flow system using an eigendecomposition-based adaptive filter for clutter rejection.

We present a new signal processing strategy for high frequency color flow mapping in moving tissue environments. A new application of an eigendecomposition-based clutter rejection filter is presented with modifications to deal with high blood-to-clutter ratios (BCR). Additionally, a new method for correcting blood velocity estimates with an estimated tissue motion profile is detailed. The performance of the clutter filter and velocity estimation strategies is quantified using a new swept-scan signal model. In vivo color flow images are presented to illustrate the potential of the system for mapping blood flow in the microcirculation with external tissue motion.

Algorithms↗