Contrast imaging with chirped excitation

With a contrast agent, wideband signals have been hypothesized to increase the contrast-to-tissue ratio (CTR). However, nonlinear properties of contrast agents make decoding difficult when applying coded excitation to contrast imaging. Here, we propose two frequency modulated excitation methods to image contrast agents, with a mechanical index (MI) from 0.05 to 0.34. In a single chirp method, one chirp is transmitted, followed by a clutter filter to reject tissue echoes and a matched filter to recover range resolution. In a chirp sequence method, an increasing and decreasing chirp sequence is transmitted followed by subtraction of the compressed echoes to reject tissue echoes (assuming tissue is a linear scatterer at low MI). Ten independent acoustic experiments were performed to evaluate the CTR for chirp and tone burst insonation, with same spatial peak temporal averaged intensity (I _SPTA- A significant increase in CTR, ranging from 4 dB to 8 dB, is observed for chirped excitation as compared with tone burst insonation, at an I_SPTA of 0.1 and 0.3 mW/cm² (P < 5×10 ^-3). Deconvolution of the linear microbubble response from the received echoes is proposed as a method to recover spatial resolution. The difference in the axial resolution between chirp and 3-cycle tone burst insonation is approximately 220 μm. The difference in the mainlobe width between experimental and predicted compressed echoes is less than 20%. The sidelobe amplitude is 9 dB to 16 dB below the mainlobe with a transmitted I _SPTA from 0.1 to 6.6 mW/cm².