A novel side lobe estimation method in medical ultrasound imaging systems

We propose a new method of estimating side lobes from received ultrasound channel data. Ultrasound signals impinging on an array transducer manifest themselves as sinusoids whose spatial frequency varies as a function of the incident angle. The channel data received from the main lobe direction have a spatial frequency of zero because the individual channel data have the same phase, while those from the side lobe directions have a spatial frequency that is not zero and varies with the incident direction of an ultrasound beam. The side lobe waveforms in the received channel data are modeled as a sum of sinusoids having a spatial frequency of an integer plus a half. The window length is adaptively varied in the estimation of those side lobe waveforms. The effect of side lobes on ultrasound image can be reduced in receive focusing by subtracting the estimated side lobe waveforms. To confirm the efficacy of the proposed method, ultrasound field simulations were carried out. By estimating and subtracting the waveforms of the 1st to 20th spatial frequency side lobes, we were able to reduce the side lobe levels by up to 14 dB when imaging point targets.