Optimization of speed-of-sound estimation from noisy ultrasonic signals

Sound speed estimation using automatic ultrasound image registration

A mismatch between the sound speed assumed for beamforming and scan conversion and the true sound speed in the tissue to be imaged can lead to significant defocusing and some geometric distortions in ultrasound images. A method is presented for estimating the average sound speed based on detection of these distortions using automatic registration of overlapping, electronically steered images. An acrylamide gel phantom containing vaporized dodecafluoropentane droplets as point targets was constructed to evaluate the technique. Good agreement (rms deviation <0.4%) was found between the sound speeds measured in the phantom using a reference pulse-echo technique and the image-based sound speed estimates. A significant improvement in accuracy (rms deviation <0.1%) was achieved by including the simulated sound field of the probe rather than assuming straight acoustic beams and propagation according to ray acoustics.

On the feasibility of pulse-echo speed of sound estimation in small regions: simulation studies

Computer simulations are used to study the feasibility of the estimation of sound speed in small regions with precision better than 1% using the Beam Tracking method. The speed of sound is estimated in a 10-mm by 10-mm region by considering a number of parallel tracks confined to the small region. The transducer focusing and the step sizes for the tracking and tracked transducers required to extract the maximum amount of uncorrelated data from the 10-mm by 10-mm region is evaluated. The results show that the speed of sound can be estimated with error less than 1% in a small region using a typical medical transducer. The statistical comparison of estimates in small areas with different speed of sound is also considered.

Pulse-echo ultrasound speed measurements: progress and prospects

The data on the relationship of sound speed to tissue condition, and the development of methods for measurement of sound speed in vivo, are outlined. The methods developed by the authors are discussed. These include methods which use the spatial shift in images of targets viewed from different directions, time-of-flight measurements along incrementally tracked beams and echo tracking during transaxial compression of tissue. The reported sound-speed values are discussed, discrepancies noted and suggestions made on the potential clinical applications of in vivo sound-speed estimation.