JOM thanks the reviewers who served the journal in 2022.

Guest Editors Hongki Yoo, Michalina Gora, and Xingde Li introduce the Special Section on Microendoscopy.

There is a critical need for a technology that can assist doctors in more accurately evaluating lung nodules at the time of biopsy. To address this need, a multispectral fluorescence line-scan confocal endomicroscope was developed that employs a fiber bundle probe to image tissue at the distal tip of the biopsy introducer needle. The multispectral nature of the instrument allows the simultaneous use of multiple FDA-approved dyes that stain different cellular/tissue compartments in different spectral regions to distinguish between lung cancer and benign conditions of the lung. The imaging system has been used to image normal rat lung as well as ex vivo human core-biopsy lung tissue.

Microendoscopes are commonly used in small lumens in the body for which a focus near to the distal tip and ability to operate in an aqueous environment are paramount for navigation and disease detection. Commercially available distal optic systems below 1 mm in diameter are severely limited, and custom micro lenses are generally very expensive. Gradient index of refraction (GRIN) singlets are available in small diameters but have limited optical performance adjustability. Three-dimensional (3D)-printed monolithic optical systems are an emerging option that may be suitable for enabling high performance, close-focus imaging. In this manuscript, we compared the optical performance of three custom distal optic systems; a custom-pitch GRIN singlet, 3D-printed monolithic doublet, and 3D-printed monolithic triplet, with a nominal working distance (WD) of 1.5, 0.5, and 0.4 mm in 0.9% saline. These short WDs are ideal for microendoscopy in collapsed or flushed lumens such as pancreatic duct or fallopian tube. The GRIN singlet had performance limited only by the fiber bundle relay over 0.9- to 1.6-mm depth of field (DOF). The 3D-printed doublet was able to achieve a comparable DOF of 0.71 mm, whereas the 3D-printed triplet suffered the most limited DOF of 0.55 mm. 3D printing enables flexible design of monolithic multielement systems with aspheric surfaces of very short WDs and relative ease of integration.

Endomicroscopy is a technique to visualize microscopic structures of internal tissues through tubular instruments that can be inserted through a small cut or an opening in the body. There has been a growing demand for miniaturizing endoscopic instruments while preserving a high resolution to achieve a real-time histopathologic diagnosis. Meanwhile, there has recently been tremendous progress in the coherent manipulation of light in which an optical wave is deterministically manipulated through a linear, disordered medium for optical focusing and imaging. Here, we review recent research efforts in developing new endomicroscopic imaging schemes based on the coherent formulation and manipulation of optical fibers. In contrast to the conventional schemes using optical fibers as incoherent channels for optical power, these approaches provide a route to fully exploiting useful information transmitted through an ultrathin probe, thereby potentially achieving practical endomicroscopic imaging through a submillimeter thick probe.

We present a preclinical-grade, forward-viewing endomicroscope for in-contact optical coherence tomography (OCT) and optical coherence angiography (OCA) imaging through the working channel of a conventional cystoscope. Beam scanning is achieved with a fiber scanner driven by a tubular piezoelectric actuator. A focusing lens at the fiber tip helps engineering of the operation frequency within a compact probe length to avoid lateral undersampling. Microstructuring of fused silica through selective laser-induced etching was used for manufacturing a self-aligning housing for the probe head. The entire micro-optical system is assembled and encapsulated within a custom-developed sterilizable packaging with 4.5 mm outer diameter. The presented design and fabrication strategy can be used for any forward-viewing probe, independent of its imaging modalities. We demonstrate OCT imaging within a 2.1-mm diameter field of view at a transverse resolution of 19 μm and microvasculature visualization through OCA. The presented probe’s mechanical characteristics and optical performance make it particularly attractive for outpatient care use in the detection of tissue pathology inside the bladder. The presented fabrication methodology provides a reliable strategy for enabling preclinical trials with endoscopic imaging probes.