Photoacoustic radar imaging signal-to-noise ratio, contrast, and resolution enhancement using nonlinear chirp modulation.

Cross-correlation (radar) frequency-domain photoacoustic (PA) imaging parameters [signal-to-noise ratio (SNR), contrast, and spatial resolution] are explored. The application of nonlinear frequency modulation instead of the standard linear frequency chirps is investigated. In addition to the image produced by the amplitude of the cross correlation between input and detected signals, the phase of the correlation signal is used as a filter of the PA amplitude combined with linear or nonlinear frequency chirps to improve SNR, contrast, and spatial resolution. The experimental results with a high-frequency transducer exhibit more than 10 and 8 times contrast enhancement using nonlinear and linear chirps, respectively. Concomitant improvements in SNR and image resolution were also observed.