Application of the frequency domain acoustic wave equation on data acquired from ultrasound tomography scans is shown to yield high resolution sound speed images on the order of the wavelength of the highest reconstructed frequency. Using a signal bandwidth of 0.4–1 MHz and an average sound speed of 1500 m/s, the resolution is approximately 1.5 mm. The quantitative sound speed values and morphology provided by these images have the potential to inform diagnosis and classification of breast disease. In this study, we present the formalism, practical application, and in vivo results of waveform tomography applied to breast data gathered by two different ultrasound tomography scanners that utilize ring transducers. The formalism includes a review of frequency domain modeling of the wave equation using finite difference operators as well as a review of the gradient descent method for the iterative reconstruction scheme. It is shown that the practical application of waveform tomography requires an accurate starting model, careful data processing, and a method to gradually incorporate higher frequency information into the sound speed reconstruction. Following these steps resulted in high resolution quantitative sound speed images of the breast. These images show marked improvement relative to commonly used ray tomography reconstruction methods. The robustness of the method is demonstrated by obtaining similar results from two different ultrasound tomography devices. We also compare our method to MRI to demonstrate concordant findings. The clinical data used in this work was obtained from a HIPAA compliant clinical study (IRB 040912M1F).

Flux pumping provides a method of inductively magnetizing superconducting coils and can provide thermal, electrical and mechanical isolation between cryogenic environment and power supply. This offers the possibility of lower cryogenic loading and more flexible arrangements for superconducting magnet systems. This paper reports on the performance and analysis of an HTS half-bridge transformer-rectifier type flux pump using two switching elements formed by applying AC magnetic field to sections of HTS. Theory of operation is presented followed by results from an experimental prototype which are compared with SPICE simulation. There is good qualitative agreement between simulation and experiment and all current, voltage and power waveforms from experiment are presented. This work represents a step forward in the understanding of the operation of HTS transformer-rectifier flux pumps and shows that SPICE simulation can provide designers of future HTS flux pumping systems with a useful tool for making design decisions.