  Fiber-based confocal endomicroscopy has shown great promise for
minimally-invasive deep-tissue imaging. Despite its advantages, confocal
fiber-bundle endoscopy inherently suffers from undersampling due to the spacing
between fiber cores, and low collection efficiency when the target is not in
proximity to the distal fiber facet. Here, we demonstrate an adaptation of
image-scanning microscopy (ISM) to lensless fiber bundle endoscopy, doubling
the spatial sampling frequency and significantly improving collection
efficiency. Our approach only requires replacing the confocal detector with a
camera. It improves the spatial resolution for targets placed at a distance
from the fiber tip, and addresses the fundamental challenge of
aliasing/pixelization artifacts.
