Field-conjugate adaptive optics enables extended field-of-view microendoscopy for deep brain imaging

Multiphoton microendoscopy using gradient-index (GRIN) lenses enables in vivo imaging of neuronal activity in deep brain regions of mammals. However, the intrinsic spatially varying aberrations and restricted etendue of GRIN lenses severely limit the field of view (FOV). While several methods have been developed to extend the FOV, such as pupil adaptive optics (AO) correction and optical lens designs, they either compromise imaging speed or lack adaptability across different GRIN lens types. Here, we introduce a field-conjugate adaptive optics (FCAO) approach, which positions the wavefront modulator near a plane conjugate to the imaging field, thereby allowing spatially varying aberration correction across the FOV. We demonstrate that FCAO significantly expands the usable FOV for various types of GRIN lenses, effectively restoring image quality in peripheral FOV regions and improving in vivo imaging of deep-brain neural structures without compromising imaging speed. Additionally, we incorporate FCAO and pupil AO modes within a single microscope system, enabling a unified platform for correcting both pupil and field-dependent aberrations.