Unwarping the Pulse Echo Wavetrain for High Resolution Imaging

Normal pulse echo ultrasound images are a straight line, constant wavespeed mapping of the echo wavetrain on to an image plane. However, the path the ultrasound beam actually traverses is curved because of refraction in the imaged volume [I]. Additionally, the speed-of-sound in this volume is usually spatially variant. The procedure for unwarping the pulse echo image begins with determining the spatial variations in speed-of-sound in the imaged volume. The speed distribution may be known or can be measured using high resolution ultrasonic computed tomography (UCT). Next, rays are traced from the pulse echo transducer position through the volume under investigation. Finally, the measured echo wavetrain is mapped along the curved ray with corrections being made for the wavespeed along the ray path. The result is an image with the echoes placed at their correct origin.