Single-shot hybrid photoacoustic-fluorescent microendoscopy through a multimode fiber with wavefront shaping

Abstract

We present a minimally-invasive endoscope based on a multimode fiber that combines photoacoustic and fluorescence sensing. From the measurement of a transmission matrix during a prior calibration step, a focused spot is produced and raster-scanned over a sample at the distal tip of the fiber by use of a fast spatial light modulator. An ultra-sensitive fiber-optic ultrasound sensor for photoacoustic detection placed next to the fiber is combined with a photodetector to obtain both fluorescence and photoacoustic images with a distal imaging tip no larger than 250 µm. The high signal-to-noise ratio provided by wavefront shaping based focusing and the ultra-sensitive ultrasound sensor enables imaging with a single laser shot per pixel, demonstrating fast two-dimensional hybrid in vitro imaging of red blood cells and fluorescent beads.

Video-rate dual-modal photoacoustic and fluorescence imaging through a multimode fibre towards forward-viewing endomicroscopy

“…Here the frame rate of the DMD was set to be 22.7 kHz, which corresponds to scanning 22.7 k image pixels per second. To our best knowledge, the fastest pixel-scanning rate for MMF-based PAE in literature was 60 Hz and it took 30 s to acquire a 1800-pixel image ( 0.03 fps) [42] . In comparison, our system enabled an imaging frame rate of 20 fps over a similar field-of-view and a similar scanning step size.…”

“…With MMF-based optical endoscopy, a focused light beam is raster-scanned at the distal tip of a MMF via wavefront shaping with the knowledge of the light transmission characteristics of the MMF, which are usually achieved with transmission matrix-based methods [32] , [40] or digital optical phase conjugate [35] , [37] approaches using a liquid-crystal spatial light modulator (LC-SLM). In the past decade, several groups have developed ultrathin endoscopes based on MMFs and wavefront shaping for a wide range of biomedical imaging modalities including wide-field microscopy [30] , confocal [31] , fluorescence [29] , [33] , two-photon [36] , Raman [38] , PA imaging [37] , [41] and multi-modal imaging probes [42] . However, due to the slow rates of LC-SLM ( ) and data acquisition, the fastest MMF-based PAE system reported in literature required 30 s for the acquisition of a single PA image frame comprising 1800 pixels [42] , which hinders its clinical translation.…”

“…In the past decade, several groups have developed ultrathin endoscopes based on MMFs and wavefront shaping for a wide range of biomedical imaging modalities including wide-field microscopy [30] , confocal [31] , fluorescence [29] , [33] , two-photon [36] , Raman [38] , PA imaging [37] , [41] and multi-modal imaging probes [42] . However, due to the slow rates of LC-SLM ( ) and data acquisition, the fastest MMF-based PAE system reported in literature required 30 s for the acquisition of a single PA image frame comprising 1800 pixels [42] , which hinders its clinical translation. In contrast to LC-SLMs, DMDs have a much higher frame rate of 22.7 kHz and consist of large arrays of micromirrors, offering binary amplitude modulations by switching ‘ON’ or ‘OFF’ micromirrors.…”

Multimodal 3D photoacoustic remote sensing and confocal fluorescence microscopy imaging

“… 9 , 10 When combined with fluorescence, micrometastases and cancerous regions labeled with tumor markers have enabled the study of the tumor microenvironment and the assessment of antineoplastic drugs. 11 – 16 However, most current PAM systems are not yet all optical and require ultrasound transducers. These transducers require acoustic coupling and limit strong optical focusing in reflection mode.…”

Video-rate dual-modal forward-viewing photoacoustic and fluorescence endo-microscopy through a multimode fibre

“…In the past decade, several groups have developed ultrathin endoscopes based on MMFs and wavefront shaping for a wide range of biomedical imaging modalities including wide-field microscopy, 22 confocal, 23 fluorescence, 21,25 two-photon, 28 Raman, 30 PA imaging 29 and multi-modal imaging probes. 33 However, due to the slow rates of LC-SLM ( 100 Hz) and data acquisition, the fastest MMF-based PAE system reported in literature required 30 s for the acquisition of a single PA image frame comprising 1800 pixels 33 and hence hinders its clinical translation. In contrast to the LC-SLM, a digital micromirror device (DMD) that consisted of a large array of micromirrors, offers binary amplitude modulations by switching 'ON' or 'OFF' micromirrors at a high frame rate of 23 kHz.…”