John C. Lazenby

Ultrasound imaging system employing phase inversion subtraction to enhance the image

A method for generating an ultrasound image that enhances regions occupied by non linear scattering media. The method utilizes first and second ultrasound pulses that are alternatively transmitted into the specimen being imaged. The first and second ultrasound pulses are amplitude modulated harmonic signals, the first ultrasound pulse differing from the second ultrasound pulse by the phase of the harmonic signal. The echo signals generated by these pulses are measured and combined. In one embodiment of the present invention, the first and second ultrasound signals differ by 180 degrees and the echo signals are combined by adding the echo signals generated by each of the ultrasound pulses.

Wideband harmonic imaging: A novel contrast ultrasound imaging technique

Abstract. A novel ultrasonic imaging method, wideband harmonic imaging, for nonlinear imaging of microbubble contrast agents is evaluated. In wideband harmonic mode, two pulses of alternate phase are send out. The image is then processed from the sum of both pulses, resulting in an image of nonlinear scatterers such as microbubbles. A prototype ultrasound system, Siemens Elegra, was evaluated with in vitro investigations and animal trials, using conventional, harmonic and wideband harmonic settings with the galactose based ultrasound contrast agent Levovist. Wideband harmonic imaging offers superior sensitivity for ultrasound contrast agents compared to conventional imaging and harmonic imaging. At low transmit power settings (MI 0.1–0.5) the nonlinear response is already sufficient to generate a image of the blood pool distribution of Levovist in the rabbit kidney including the microvasculature, with clear delineation of vessels and perfused parenchyma. At high transmit amplitudes, nonlinear tissue response reduced the apparent image contrast between contrast agent and tissue. The results suggest that wideband harmonic imaging is currently the most sensitive contrast imaging technique, maintaining highest spatial resolution. This may add to image quality and offer new clinical potential for the use of ultrasound contrast agents such as Levovist.

A new tissue harmonic imaging scheme with better fundamental frequency cancellation and higher signal-to-noise ratio

Tissue Harmonic Imaging (THI) is a new ultrasound imaging technique, which uses the harmonic components generated by nonlinear acoustic propagation through human tissues to form an image. Several factors affect THI image quality. First, strong suppression of the fundamental signals is necessary to allow the full dynamic range of the harmonic signals to be seen. This will allow the full benefits of harmonic imaging to be seen. Second, since the harmonic components are much weaker (15-20 dB lower) than the fundamental, they must be enhanced as much as possible relative to noise. This will allow the maximum possible image penetration. This paper will compare the phase inversion technique with another data acquisition and processing scheme from the literature in terms of suppression of fundamental frequencies, and signal-to-noise ratio (SNR) improvement. The comparison will be both theoretical, using a very simple model, and experimental, using data acquired in vitro. The phase inversion technique appears to be a better choice to realize THI in an ultrasound imaging system. This technique gives better cancellation of the fundamental frequencies while simultaneously improving SNR.

Optimized receive filters and phase-coded pulse sequences for contrast agent and nonlinear imaging

Phase- or amplitude-coded pulse sequences are commonly used to discriminate linear form nonlinear scatterers or to enhance image quality by imaging spectral components that are due to nonlinear sound propagation. The transmit pulse sequences are designed so that a coherent, weighted summation of the resultant echoes followed by a demodulation enhances the image contrast between nonlinear and linear scatters or the separation of higher harmonics from the fundamental. Because of limitations in the signal generation in ultrasound scanners and unknown effects of the sound propagation, experimental results do not agree with those of simulations. Separate receive filters for each of the echoes can compensate for the above-mentioned shortcomings and unknown factors. In this paper, an algorithm for the design of FIR filters based on training data is presented and experimental results are discussed.

Adaptive ultrasonic imaging using SONOLINE Elegra

Adaptive correction of the effects of propagation through inhomogeneous tissue is critical to the improvement of current ultrasonic imaging systems. Currently, estimation and correction of time‐delay errors is more feasible than other more sophisticated approaches. Data acquisition, time‐delay estimation and compensation have been implemented on the SONOLINE Elegra system using the system CPU, the Crescendo image processor, and the existing front‐end electronics. Experimental results with this implementation will be reported. The effects of compensating the transmit beam is studied using the waveform similarity factor and single transmit imaging. On an RMI404 phantom plus a 1‐D aberration layer with a rms time fluctuation of 40 ns and correlation length of 5 mm, the waveform similarity factor of randomly scattered waveforms improved from 0.362 to 0.477 by iteration. Correspondingly, the −20 dB lateral resolution improved from 1.62 to 0.77 mm, and the image contrast improved by 8.5 dB (speckle region is 6 ...

Direct velocity estimator for ultrasound blood flow imaging

A method and apparatus for estimating blood flow velocities with an ultrasound imaging system. The method includes radiating a plurality of ultrasound beams having a fixed phase relationship with a reference frequency; receiving a plurality of successive echoes from the successive beams from the same volume of blood; and estimating the blood flow velocity from the phase shift changes, relative to the reference frequency, between a plurality of successive echo pairs by multiplying each phase shift change by coefficients stored in a RAM and accumulating the results. Desirably, the phase shift changes between the multiple pairs of successive echoes are weight averaged during the multiplication and accumulation process to arrive at the velocity estimate. A method of improving the blood flow velocity estimate at a given volume by obtaining velocity estimates at a plurality of contiguous volumes and multiplying each velocity estimate by coefficients stored in a RAM and accumulating the products to arrive at a substitute velocity estimate at the given volume.

Adaptive ultrasonic imaging using SONOLINE Elegra/sup TM/

Data acquisition, time delay estimation and correction for adaptive imaging are implemented on the SONOLINE Elegra/sup TM/ system using the system CPU, the Crescendo(TM) processor, and the existing front-end electronics, with no hardware modifications. With the current implementation, phase aberration correction takes about 2 seconds from activation to completion. The effects of compensating the transmit beam are studied using the waveform similarity factor and single transmit imaging. On a scattering phantom plus a 1-D aberration layer with an rms time fluctuation of 40 ns and correlation length of 5 mm, the waveform similarity factor of randomly scattered waveforms improved from 0.362 to 0.477 by iteration. Correspondingly, the -20 dB lateral resolution improved from 1.62 mm to 0.77 mm, and the image contrast improved by 8.5 dB (the speckle region is 6 dB brighter while the echo-free region is 2.5 dB darker). Experiments with a 2-D aberration layer and with a special phase aberration phantom showed less image improvements. Preliminary body scan trials with adaptive imaging showed improved image contrast and details in some cases but the results are mixed and influenced by such factors as isoplanatic patch size and complex scattering structures.

A method for detecting echoes from microbubble contrast agents based on time-variance

Most ultrasound contrast agents, which are injected into the blood stream, use encapsulated microbubbles as acoustical scatterers in order to increase the reflectivity of the blood. The fact that the acoustic properties of microbubbles and those of scatterers in tissue differ significantly offers various possibilities to develop contrast agent specific imaging techniques. These new imaging modes may overcome the limitations of Doppler modes concerning their axial resolution and their sensitivity to motion artifacts and, therefore, improve the visualization of small vessels and the assessment of perfusion. Insonification can change the acoustic properties of bubbles, e.g., by breaking the shells and thus accelerating shrinkage and diffusion processes. Time-Variance Imaging (TVI), the new imaging mode the authors propose, detects these alterations by processing the echo signals resulting from sequences of broadband transmit pulses. TVI provides high resolution images which show the distribution of microbubbles.

Method for scalable manufacturing of medical diagnostic ultrasound imaging systems

A plurality of application specific integrated circuit (ASIC) chips with different functions is provided. Each of the ASICs performs one or more functions along an ultrasound data path. The chips include communications protocols or processes for allowing scaling. For example, ASICs for backend processing include data exchange ports for communicating between other ASICs of the same type. As another example, receive beamformer ASICs cascade for beamformation. By providing ASICs implementing many or most of the ultrasound data path functions, with scalability, the same ASICs may be used for different system designs. A family of systems from high end to low-end using the same types of ASICs, but in different configurations, is provided.

Cross correlation phase aberration estimates with sparse arrays and parallel beamforming

2D arrays and parallel beamforming are useful technologies for 3D scanning. 2D arrays are also considered to be valuable for phase aberration correction. However, many researchers have investigated sparse 2D arrays to limit the number of needed beamforming channels. Therefore, the authors investigate whether sparse 2D arrays and parallel beamforming are compatible with cross correlation based phase aberration estimates. The van Cittert-Zernike theorem is applied to some models of transmit apertures for random and periodic sparse arrays and parallel beamforming. The theoretical results show that these approaches all degrade the performance of the cross correlation phase aberration estimator. The theoretical results are compared to experimental data from sparse 1D arrays, as well as measurements from a broad transmit beam suitable for parallel beam formation. The experimental measurements confirm the theoretical predictions.