Browsing by Author "Jeon, Hamin"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Development of Miniature Objectives for Clinical Applications
    (2021-04-30) Jeon, Hamin; Tkaczyk, Tomasz S.
    Over the years, the most significant challenges for designing endomicroscopic objectives involved balancing between practical operational parameters. These parameters have included numerical aperture/resolution, field of view, working distance, and outer diameter of an objective. In addition, many applications nowadays use laser as a light source, for which, materials considered in the systems need to be carefully chosen. This dissertation focuses on addressing two specific issues to expand the capabilities of miniature microscopic objectives: (a) maximizing field (critical in clinical applications) while imaging at high resolution and (b) analyzing material properties that are critical in non-linear imaging and developing technologies specific to such materials. Two example system designs were developed to address these challenges. This dissertation describes spectrally encoded detection with a miniature objective to maximize data content and sampling. The objective works in tandem with a coherent imaging bundle, but can be also used with scanning systems. I also present on the development of a crystal based miniature objective for non-linear microsurgery applications. Ultrafast laser microsurgery requires a miniature objective that can non-invasively deliver high power laser pulses with high precision and, to this end, an objective with high NA (0.5 NA) as well as CaF2 and ZnS lenses was developed. CaF2 has a low nonlinear absorption coefficient, which enables the objective to better withstand the high power laser pulses. The high refractive index of ZnS is beneficial for the design of an objective with challenging requirements such as high NA or small outer diameter. As part of the prototyping process for the crystal-based objective, I developed a fabrication protocol for CaF2 and ZnS materials using the single point diamond turning method, which can yield surfaces with optical quality. This aspect has a broader impact since both CaF2 and ZnS materials transmit light from the visible range to long-wave infrared spectral range and can be applied to a number of other imaging applications. As a finishing step, both prototyped systems’ performance was assessed; against an USAF resolution target and ex vivo tissue samples (spectrally encoded system), and by measuring the focal spot size (miniature objective for laser microsurgery). As a result of the assessment, both systems demonstrated results that met the expected performance.
  • Thumbnail Image
    Item
    High-resolution endomicroscopy with a spectrally encoded miniature objective
    (Optical Society of America, 2019) Jeon, Hamin; Pawlowski, Michal E.; Tkaczyk, Tomasz S.
    Fiber bundle endomicroscopy techniques have been used for numerous minimally invasive imaging applications. However, these techniques may provide limited spatial sampling due to the limited number of imaging cores inside the fiber bundle. Here, we present a custom-fabricated miniature objective that can be coupled to a fiber bundle and can overcome the fiber bundle’s sampling threshold by utilizing the spectral encoding concept. The objective has an NA of 0.3 and an outer diameter of 2.4 mm, and can yield a maximum spatial resolution of 2 μm. The objective has been validated against a USAF resolution target and ex vivo tissue samples, and as a result yielded images with higher resolution and more details after the spectral encoding concept was employed.
  • Thumbnail Image
    Item
    Ultrafast laser surgery probe for sub-surface ablation to enable biomaterial injection in vocal folds
    (Springer Nature, 2022) Andrus, Liam; Jeon, Hamin; Pawlowski, Michal; Debord, Benoit; Gerome, Frederic; Benabid, Fetah; Mau, Ted; Tkaczyk, Tomasz; Ben-Yakar, Adela
    Creation of sub-epithelial voids within scarred vocal folds via ultrafast laser ablation may help in localization of injectable therapeutic biomaterials towards an improved treatment for vocal fold scarring. Several ultrafast laser surgery probes have been developed for precise ablation of surface tissues; however, these probes lack the tight beam focusing required for sub-surface ablation in highly scattering tissues such as vocal folds. Here, we present a miniaturized ultrafast laser surgery probe designed to perform sub-epithelial ablation in vocal folds. The requirement of high numerical aperture for sub-surface ablation, in addition to the small form factor and side-firing architecture required for clinical use, made for a challenging optical design. An Inhibited Coupling guiding Kagome hollow core photonic crystal fiber delivered micro-Joule level ultrashort pulses from a high repetition rate fiber laser towards a custom-built miniaturized objective, producing a 1/e2 focal beam radius of 1.12 ± 0.10 μm and covering a 46 × 46 μm2 scan area. The probe could deliver up to 3.8 μJ pulses to the tissue surface at 40% transmission efficiency through the entire system, providing significantly higher fluences at the focal plane than were required for sub-epithelial ablation. To assess surgical performance, we performed ablation studies on freshly excised porcine hemi-larynges and found that large area sub-epithelial voids could be created within vocal folds by mechanically translating the probe tip across the tissue surface using external stages. Finally, injection of a model biomaterial into a 1 × 2 mm2 void created 114 ± 30 μm beneath the vocal fold epithelium surface indicated improved localization when compared to direct injection into the tissue without a void, suggesting that our probe may be useful for pre-clinical evaluation of injectable therapeutic biomaterials for vocal fold scarring therapy. With future developments, the surgical system presented here may enable treatment of vocal fold scarring in a clinical setting.