D-L Donald Liu

Time-delay compensation system and method for adaptive ultrasound imaging

An ultrasound imaging system directs a transmit beam of ultrasound from a plurality of elements in a transducer array into a region of interest (ROI) of a patients body. The receive beam back from the ROI contains a separate waveform for each of the array elements. These waveforms are partitioned into groups, and a control waveform is determined for each group. The control waveform is then jittered, that is, time-shifted, by a trial delay time, and trial delay times for the other waveforms in the group are determined by interpolation. A waveform similarity factor (WSF), which is preferably a function of the r.m.s. value of the sum of the waveforms in the group, is then evaluated. The control waveform is then repeatedly shifted by different trial amounts, with a new WSF being determined for each trial shift. The trial delay for the control waveform is then assumed to be optimum that yielded the greatest group WSF. A global time compensation profile for the entire array is then determined by interpolation, given the locally optimal time delays of the various control waveforms. This global profile is then applied by a beamformer to compensate the receive beamforming and subsequent transmit beamforming to generate the ultrasound image. The array may also be two-dimensional. The user may select, using input devices and visual feedback, a portion of the displayed ultrasound image to identify a region of interest. The optimum time compensation is then calculated based on the waveforms only in this region, but is applied by the beamformer to the entire displayed image.

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 ...

Single transmit imaging

Single transmit imaging, formed by scanning the receive beam around a single transmit beam is used to study the characteristics of fundamental and harmonic beams and to evaluate the performance of time-shift compensation as a means of phase aberration correction. The results indicate that the harmonic beam has a greater depth of field compared to the normal beam, and that time-shift compensation can restore the beam pattern using random scattering data under ideal aberration conditions. Results of time-shift compensation using random scattering data also showed significant improvement in image quality on a special phase aberration phantom that contains an aberration layer of extended thickness.

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.