Radial-modulation chirp imaging for high-resolution contrast detection

In this study, we propose a radial-modulation chirp imaging method for contrast detection with high frequency ultrasound. This method detects microbubbles by extracting and then selectively compressing the radial-modulated chirp component of the response. The amplitude of the imaging chirp signal will be radial modulated at the resonance frequency due to the high-amplitude oscillation of the microbubble wall which are insonated simultaneously with a pumping signal; thus forming frequency sum-and-difference chirp terms. The frequency sum or difference chirp component is then extracted by a band-pass filter (BPF). The differences between the band-pass filtered frequency components of tissues and bubbles provide the contrast. Pulse compression of the extracted chirp signal is performed to further improve axial resolution and contrast-to-tissue ratio (CTR). Experiments of flow phantoms with speckle-generating background were performed to demonstrate the efficacy the proposed technique. The attainable SNR improvement and CTR were up to 6 and 20 dB, respectively. Improvement in axial resolution after pulse compression was also verified. These results indicate that our proposed method have potential for providing high resolution contrast detection in the microvasculature.