New approaches to aberration correction in medical ultrasound imaging

Medical ultrasound imaging is in widespread use today due to its low cost, portability, lack of side e®ects, and unique ability to probe the mechanical properties of tissue. As transducer apertures and operating frequencies grow, however, ultrasound's resolving power continues to be limited by variations in the speed of sound within tissue. Concepts borrowed from other imaging disciplines can provide new insights into the aberration problem in medical ultrasound; in particular, some of the same issues have been studied for many years to improve acoustic imaging of the nonhomogeneous Earth. The seismic imaging community has understood for some time that layered media may be approximated by constant-sound-speed media for beamforming purposes, leading to so-called time-migration algorithms. This raises the possibility of medical ultrasound applications|for example, brain imaging through the adult human skull. While our simulation results have been encouraging, experiments with animal skulls have been inconclusive due to the high attenuation of ultrasound in skull bone. Further research may validate the time-migration concept for brain imaging