Design and implementation of fiber-based multiphoton endoscopy with microelectromechanical systems scanning

Abstract

Multiphoton microscopy (MPM) is an important tool for high-resolution, noninvasive imaging of thick biological tissues.^{1, 2, 3, 4, 5} MPM utilizes femtosecond lasers to excite nonlinear contrast signals that include two-photon excited fluorescence (TPEF) and second-harmonic generation (SHG). TPEF can be detected from intrinsic sources (e.g., cofactors, proteins) and exogenous fluorophores, while strong SHG signals can be obtained from noncentrosymmetric molecules such as collagen, a common extracellular matrix protein. Thus, MPM can image and distinguish cellular and extracellular matrix structures simultaneously. MPM systems have been mostly developed using free-space optics and microscope platforms. However, for in vivo imaging and clinical applications, a fiber-optic MPM endoscope is desirable where light can be delivered through a flexible fiber and images can be acquired using a miniature probe.^{6, 7, 8, 9} Delivering femtosecond pulses through fibers and designing miniature scanning probes are two challenges in MPM endoscopy.