1Karmanos Cancer Institute, Wayne State University, Detroit, MI, USA
Imaging with acoustic waves has made great advances in recent decades. In opposing limits of wavelength, acoustics have played a major role in geophysical applications on the one hand and in medical ultrasound imaging on the other. However, unlike seismic imaging, for example, medical ultrasound has been slow to evolve into the tomographic domain where X-ray imaging still plays a dominant role. In contrast to X-rays, acoustic waves interact strongly with materials through which they propagate, through processes such as refraction, reflection and diffraction. The interactions can be very strong in heterogeneous media such as human tissue. Tomographic reconstructions of ultrasound data therefore require much more sophisticated modeling of acoustic wave propagation often involving highly non-linear inversions. These factors have impeded progress in this otherwise promising methodology. The advancement of computing power and the rise of high-throughput data acquisition hardware have made ultrasound tomography (UST) feasible in recent years. The objective of this presentation is to relate these developments to practical applications of UST, particularly in the area of medical imaging. The major techniques that will be covered include (i) the development of physics-based forward modeling, (ii) the application of new inversion techniques, (iii) the capabilities of modern data acquisition systems and (iv) the current capabilities for signal and data processing in the context of multi-CPU and GPU computing. Today, a number of laboratory groups are collecting data with UST prototypes and some projects have become commercial ventures. This presentation will review the status of UST imaging, particularly in the area of breast cancer detection, where some of the most recent advances have taken place. Results from these groups will be presented and compared. It is shown that the parallel developments in the four methodologies, noted above, have given rise to exciting new possibilities for UST and for acoustic tomography, at all wavelengths, with potential applications in areas as diverse as seismic exploration, nondestructive testing and cancer detection.