Wideband photoacoustic tomography using polymer microringresonators

Photoacoustic tomography is an imaging technique based on the reconstruction of distribution of acoustic pressure, generated by the absorption of short laser pulses in biological tissues. The detected ultrasound signals can be represented by the convolution of the structure of objects, the laser pulse, and the impulse response of the ultrasound detectors. Detector's wideband response is essential for imaging reconstruction of multiscale objects by utilizing a range of characteristic acoustic wavelengths. Optical detection of ultrasound has the advantage of realizing high-frequency wide-bandwidth ultrasound detection. Previously we have demonstrated a polymer microring resonator based ultrasound detector with flat spectral response from dc to high frequency, over 90 MHz at -3-dB. By using a reconstruction algorithm to simulate the photoacoustic tomography of microspheres of different sizes, we compared the imaging performance of the microring resonators and piezoelectric transducers. Due to the broadband response, the former was able to faithfully detect both the boundaries that are characteristics of high spatial frequencies and the inner structure consisting primarily of low spatial frequency components. Piezoelectric transducers can only preserve one of the two aspects, depending on the choice of detector's central frequency. Experimental results demonstrate the benefit of broadband response of polymer microring resonators.