Improved in vivo abdominal image quality using real-time estimation and correction of wavefront arrival time errors

The speed of sound varies with tissue type, yet commercial ultrasound imagers assume it is constant. Sound speed variation in abdominal fat and muscle layers is widely believed to be largely responsible for poor image contrast and resolution in some patients. The simplest model of the abdominal wall assumes that it adds a spatially varying time delay to the ultrasound wavefront. We describe an adaptive imaging system consisting of a GE LOGIQ 700 imager connected to a multi-processor computer. Arrival time errors for each beamforming channel, estimated by correlating each channel signal with the beamsum signal, are used to correct the imager's transmit and receive beamforming time delays at the image frame rate. A multi-row transducer provides two dimensional sampling of wavefront arrival time errors. After beamforming time delay correction, we observe significant improvement in abdominal images of healthy male volunteers, including increased contrast of blood vessels, increased brightness of liver tissue, and improved definition of the renal capsule and splenic boundary.