Design of digital apodization technique for medical ultrasound imaging

Ultrasound imaging is one of the important noninvasive techniques used in medical diagnosis. Unfortunately, the far field beam pattern in ultrasound is a sinc function, which has a better main lobe (the resolution of ultrasound imaging) and high side-lobe about -13dB down from the maximum on axis value (the contrast of ultrasound imaging). The result for that is one of a famous artifact in medical ultrasound that the anatomy of the organ outside the main beam to be mapped into the main beam. In this work we used different types of FIR filter to round edges of the aperture that taper towards zero at the ends of the aperture to create low side-lobe levels and reduce the false echo. We used the windowing function (Blackman, Kaiser (β=10), Parzen and Bohman) as apodization function to the reconstructed image to reduce the effect of the side-lobes. We computed the SNR for each image as well as for the main lobe and the side-lobe. The results showed that there is trade-off in selecting these functions: the main lobe of the beam broadens as the side-lobes lower. However, Kaiser (β =10) gave the best SNR (188.75 db) and best compensation between the contrast and resolution (main lobe=1.10 db and the side-lobe= -71.7 db). We found that if we use the Kaiser filter (β =10) this would reduce the side-lobe and improve the false echo in the ultrasound imaging.