High frequency, high frame rate pulse inversion chirp coded tissue harmonic imaging

The pulse inversion method, which alternatively transmits a burst and a subsequent one with its amplitude inversed, has been utilized to cancel out fundamental signal by summing up the pulse pair for second harmonic imaging. The approach was implemented with chirp coded excitation for a high frame rate mechanical sector scanner or an ultrasound biomicroscope (UBM), to suppress range side lobe level (RSLL) and to enhance spatial resolution and echo signal to noise ratio (eSNR). For this purpose, beam sequences and transmission timing strategy were optimized to reduce moving artifacts caused by the motor movement. The system was evaluated by scanning wire targets at a scanning speed of 68 Hz employing a 40 MHz lithium niobate (LiNbO₃) single element light weight transducer. The wire phantom results showed that pulse inversion chirp coded tissue harmonic imaging (PI-CTHI) achieved a 4 dB higher eSNR than conventional pulse inversion tissue harmonic imaging (PI-THI), while maintaining the spatial resolution. RSLL of PI-CTHI was improved by 4 dB compared to band-pass filtered (F-CTHI).