John A. Hossack

Medical diagnostic ultrasound system and method for mapping surface data for three dimensional imaging

A method and system for mapping surface data onto a geometrical representation of a structure for 3D imaging is provided. A boundary of a structure is determined from one type of data, such as Doppler energy data. Another type of data, such as B-mode data, representing the boundary or an area adjacent the boundary is extracted or identified. The B-mode data is then rendered as a function of the boundary, such as by texture mapping the B-mode data onto or adjacent the boundary. As the user examines the structure representation, the texture mapped data may provide texture details based on an optimally determined representation. The boundary may alternatively be used to select data for volume rendering.

Medical diagnostic ultrasound catheter and method for position determination

A catheter and method for determining a position of the catheter within the cardiovascular system is provided. Local bending and twisting is measured at multiple locations along the catheter. By integrating the measurements, the position and orientation of the catheter is determined. Based on the catheter position information, the location and orientation of an ultrasound transducer array connected with the catheter is known. The imaging array position and orientation information may be used to assist a physician in determining the tissue structure or fluid being scanned and/or assist in the accurate generation of three-dimensional representations.

Intra-operative diagnostic ultrasound multiple-array transducer probe and optional surgical tool

A system, method and probe for diagnostic ultrasound imaging with at least two, and preferably three transducer arrays. The first transducer array provides a primary image. The second transducer array comprises an array of transducer elements positioned near one end of the first transducer array for providing an image in a different plane. An optional third transducer array comprises an array of transducer elements positioned near the other end of the first transducer array for providing an additional image in a different plane. One application of the invention is to collect tissue for medical procedures, wherein at least one surgical tool is attached to the probe near the imaging arrays and moves together with at least one imaging array. As the primary imaging array is drawn across tissue for collection, the operator observes a cross-section of the tissue prior to actually cutting the tissue. Another application of the invention allows an operator to selectively display pseudo 3-D images or 3-D images, using the same probe. Another application of the invention allows an operator to determine the 3-D position of a foreign object in body tissue.

Acoustic radiation force enhances targeted delivery of ultrasound contrast microbubbles: in vitro verification

Recent research has shown that targeted ultrasound contrast microbubbles achieve specific adhesion to regions of intravascular pathology, but not in areas of high flow. It has been suggested that acoustic radiation can be used to force free-stream microbubbles toward the target, but this has not been verified for actual targeted contrast agents. We present evidence that acoustic radiation indeed increases the specific targeted accumulation of microbubbles. Lipid microbubbles bearing an antibody as a targeting ligand were infused through a microcapillary flow chamber coated with P-selectin as the target protein. A 2.0 MHz ultrasonic pulse was applied perpendicular to the flow direction. Microbubble accumulation was observed on the flow chamber surface opposite the transducer. An acoustic pressure of 122 kPa enhanced microbubble adhesion up to 60-fold in a microbubble concentration range of 0.25 /spl times/ 10/sup 6/ to 75 /spl times/ 10/sup 6/ ml/sup -1/. Acoustic pressure mediated the greatest adhesion enhancement at concentrations within the clinical dosing range. Acoustic pressure enhanced targeting nearly 80-fold at a wall shear rate of 1244 s/sup -1/, suggesting that this mechanism is appropriate for achieving targeted microbubble delivery in high-flow vessels. Microbubble adhesion increased with the square of acoustic pressure between 25 and 122 kPa, and decreased substantially at higher pressures.

Unidimensional modeling of 1‐3 composite transducers

Composite transducers, utilizing the complementary properties of a piezoelectric ceramic and a polymer, often possess acoustic matching and electromechanical efficiency that are superior to conventional isotropic materials. The extent of the performance enhancement is a complex function involving composite design in conjunction with external electrical and mechanical loading conditions. This work uses an established modeling technique, supported by finite element analysis and experimental observation, to predict the mechanical, electrical, and piezoelectric properties of 1‐3 composite structures. These parameters are then combined in a modified thickness‐drive model to predict the performance of composite probe assemblies under realistic operating conditions. Accurate correlation between simulation and experimental results is demonstrated over an extensive range of ceramic‐polymer volume fraction. Significantly, the results suggest that composites that possess relatively high‐volume fractions of ceramic a...

Ultrasound Despeckling for Contrast Enhancement

Images produced by ultrasound systems are adversely hampered by a stochastic process known as speckle. A despeckling method based upon removing outlier is proposed. The method is developed to contrast enhance B-mode ultrasound images. The contrast enhancement is with respect to decreasing pixel variations in homogeneous regions while maintaining or improving differences in mean values of distinct regions. A comparison of the proposed despeckling filter is compared with the other well known despeckling filters. The evaluations of despeckling performance are based upon improvements to contrast enhancement, structural similarity, and segmentation results on a Field II simulated image and actual B-mode cardiac ultrasound images captured in vivo.

Improving the characteristics of a transducer using multiple piezoelectric layers

A type of transducer composed of several active piezoelectric layers is described. These layers are independently stimulated electrically to achieve performance, in terms of sensitivity and bandwidth, not available in conventional, single active layer designs. A straightforward modeling technique is employed for predicting the performance of these transducers and for determining the optimal excitation characteristics. The technique is initially developed for transmission, but its extension to reception and pulse-echo conditions is discussed. A selection of experimental results demonstrates the feasibility of the technique.<<ETX>>

Medical diagnostic ultrasound system and method for flow analysis

Medical diagnostic ultrasound methods and systems for automated flow analysis are provided. Multiple cross-sectional areas along a vessel are determined automatically. A processor locates an abnormality as a function of the multiple cross-sectional areas, such as identifying a cross-sectional area that is a threshold amount less than an average cross-sectional area. The abnormal area is highlighted on the display to assist with medical diagnosis. For the carotid artery, the interior and exterior branches are labeled to assist medical diagnosis. The two branches are automatically identified. The branch associated with additional small branches is identified as the exterior carotid.

Targeted gene transfection from microbubbles into vascular smooth muscle cells using focused, ultrasound-mediated delivery

We investigated a method for gene delivery to vascular smooth muscle cells using ultrasound triggered delivery of plasmid DNA from electrostatically coupled cationic microbubbles. Microbubbles carrying reporter plasmid DNA were acoustically ruptured in the vicinity of smooth muscle cells in vitro under a range of acoustic pressures (0 to 950 kPa) and pulse durations (0 to 100 cycles). No effect on gene transfection or viability was observed from application of microbubbles, DNA or ultrasound alone. Microbubbles in combination with ultrasound (500-kPa, 1-MHz, 50-cycle bursts at a pulse repetition frequency [PRF] of 100 Hz) significantly reduced viability both with DNA (53 +/- 27%) and without (19 +/- 8%). Maximal gene transfection ( approximately 1% of cells) occurred using 50-cycle, 1-MHz pulses at 300 kPa, which resulted in 40% viability of cells. We demonstrated that we can locally deliver DNA to vascular smooth muscle cells in vitro using microbubble carriers and focused ultrasound.

Direct sampled I/Q beamforming for compact and very low-cost ultrasound imaging

A wide variety of beamforming approaches are applied in modern ultrasound scanners, ranging from optimal time domain beamforming strategies at one end to rudimentary narrowband schemes at the other. Although significant research has been devoted to improving image quality, usually at the expense of beamformer complexity, we are interested in investigating strategies that sacrifice some image quality in exchange for reduced cost and ease in implementation. This paper describes the direct sampled in-phase/quadrature (DSIQ) beamformer, which is one such low-cost, extremely simple, and compact approach. DSIQ beamforming relies on phase rotation of I/Q data to implement focusing. The I/Q data are generated by directly sampling the received radio frequency (RF) signal, rather than through conventional demodulation. We describe an efficient hardware implementation of the beam-former, which results in significant reductions in beam-former size and cost. We present the results of simulations and experiments that compare the DSIQ beamformer to more conventional approaches, namely, time delay beamforming and traditional complex demodulated I/Q beam-forming. Results that show the effect of an error in the direct sampling process, as well as dependence on signal bandwidth and system f number (f#) are also presented. These results indicate that the image quality and robustness of the DSIQ beamformer are adequate for low end scanners. We also describe implementation of the DSIQ beamformer in an inexpensive hand-held ultrasound system being developed in our laboratory.