Experimental study of convex coded synthetic transmit aperture imaging

Synthetic transmit aperture imaging is investigated using a convex array transducer. To increase the signal-to-noise ratio, a multi-element subaperture is used to emulate the spherical wave transmission, and the conventional short excitation pulse is replaced by a linear FM signal. The approach is compared to the conventional application of the convex array in commercial scanners. The array used is a commercial 5.5 MHz, 128 element array with 60% bandwidth and λ pitch. For conventional imaging a 64 element transmit aperture is used with a 2 cycle temporally weighted sinusoid as excitation signal. For synthetic aperture imaging an 11 element transmit aperture is used with a 20 μs linear FM signal as excitation. For both methods, 128 elements are used on receive. Measurements are done using our experimental multi-channel ultrasound scanner, RASMUS. Wire phantom measurements show an improvement in lateral resolution of about 30% throughout the image with lower near and far field sidelobe levels. Results from a cyst phantom show big improvements in contrast resolution, and an increase in penetration depth of about 2 cm. In-vivo images of the abdomen of a healthy 27 year old male show slight improvements in image quality, especially in the near field.