In the realm of medical diagnostics, the evolution of endoscopic imaging techniques has been pivotal in enabling minimally invasive procedures while ensuring high-quality visualization of internal structures. A recent publication in Opto-Electronic Science (DOI: 10.29026/oes.2024.230041) delves into the advancements in optical scanning endoscopes, particularly via a single multimode optical fiber (MMF), offering promising prospects for biomedical applications.
Endoscopes serve as indispensable tools in modern medicine, facilitating detailed imaging of inaccessible regions within the body with minimal discomfort to patients. The continual demand for miniaturization, enhanced resolution, and superior imaging quality has spurred innovations in endoscopic technologies, with optical fiber-based systems emerging as frontrunners.
Traditional fiber bundle endoscopes and single-mode fiber scanning endoscopes have been effective for imaging relatively large anatomical structures. However, challenges persist in scenarios requiring high-resolution imaging of intricate regions, such as deep brain areas. These challenges have sparked significant interest in MMF-based endoscopes due to their potential to reduce footprint and enhance imaging capabilities.
The focal point of this review lies in MMF scanning endoscopes employing the wavefront shaping technique. By mitigating the disorderly nature of MMF output caused by intermodal dispersion and mode coupling effects, these endoscopes achieve focused light spots for scanning imaging. The review outlines techniques such as transmission matrix measurement, digital phase conjugation, and phase optimization algorithms, elucidating their physical principles and experimental implementations.
Furthermore, the article analyzes key performance metrics of MMF scanning endoscopes, including resolution, contrast, speed, working distance, field-of-view, and system stability. Notably, recent advancements have yielded impressive results, with resolutions as fine as 250 nm, contrast levels reaching 96%, and imaging speeds of 3.5 frames per second for 7-kilopixel images.
Despite these achievements, challenges persist, particularly regarding the susceptibility of MMF scanning endoscopes to external disturbances. Strategies to mitigate these challenges involve shielding MMFs from external disruptions and real-time recalibration of transmission matrices.
Moreover, the integration of MMF scanning endoscopes with advanced imaging modalities such as confocal imaging, two-photon imaging, Raman imaging, and photoacoustic imaging holds promise for further enhancing imaging performance and expanding application scenarios.
While significant progress has been made, the practical implementation of MMF scanning endoscopes remains a work in progress. Addressing issues related to external disturbances and enhancing imaging speed are crucial steps towards their widespread adoption in biomedical and other fields. Nevertheless, the trajectory of advancements suggests a promising future for MMF scanning endoscopes, poised to revolutionize medical diagnostics and drive progress in related fields.
