Hybrid modality photoacoustic/fluorescence microscopy through a multimode fiber using speckle illumination (Conference Presentation)

We present an ultra-thin endoscope that combines a multimode optical fiber (MMF) attached to an optical hydrophone for simultaneous optical-resolution photoacoustic microscopy and fluorescence imaging. The MMF is used for light delivery and fluorescence collection and the hydrophone for acoustic detection; a digital micro-mirror device (DMD) modulates the amplitude of the optical wavefront of a pulsed laser coupled into the MMF, controlling the illumination at the distal tip. The DMD allows for fast calibration approaches to reach calibration and measurement times of a few seconds. We obtain optical-diffraction-limited images with full field illumination recording the intensity of a series of various calibrated speckle patterns produced by different configurations of the DMD at the input, with no wavefront shaping. The intensity fluctuations from speckle pattern to speckle pattern encodes for the position at which the signal is emitted. The fluorescence signal from the sample is collected with the MMF and detected with a PMT at the proximal side. For the acoustic detection, embedding the ultrasound detection within the device avoids the absorption of high-frequency ultrasound by the tissue and therefore removes any limitation on the insertion depth. The footprint of the probe is 250 um x 125 um making it thinner than common GRIN lenses used for endoscopy. To best of our knowledge, our approach provides the thinnest endoscope head capable of obtaining optical-resolution photoacoustic and fluorescence images simultaneously.