BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Madison-Physics-Events BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-9326 DTSTART:20250715T150000Z DTEND:20250715T050000Z DTSTAMP:20260413T133109Z LAST-MODIFIED:20250701T161655Z LOCATION:Engineering Centers Building 1045 SUMMARY:A combined theoretical and computational analysis of collagen structure in biological tissues by 3D second harmonic generation excit ation and emission tomography\, Thesis Defense\, Emily Shelton\, Physi cs PhD Graduate Student DESCRIPTION:Second harmonic generation (SHG) has been used to great ex tent as an imaging modality that selectively targets fibrillar collage n without the need for exogenous dyes to investigate the collagen arch itecture in biological tissues\, as this structure is frequently alter ed in many diseases including cancers and fibroses. While SHG metrics have been developed to characterize the fiber\, fibril and supramolecu lar aspects of collagen\, there remains a need to better understand th e underlying non ideal phase-matching that governs the contrast and th e emission directionality\, where these arise from the sub-resolution intermediary fibril size\, packing\, and polarity. This dissertation p resents a new combined theoretical and computational treatment based o n quasi-phase-matching of the how the three-dimensional SHG spatial em ission pattern is determined by the fibril organization. This is used to place bounds on the fibril size and packing parameters as well as e xplore the effects of heterogeneity in both fibril size and polarity c lustering on the emission pattern. This work is then expanded to inclu de fibril organization into fibers and simulate the fibrils in a more realistic fashion in order to explore the effects of fiber rotation on the emission pattern and more accurately model individual tissue type s\, specifically focusing on normal and cancerous ovarian tissue. This treatment not only provides a more rigorous physical basis for unders tanding SHG in the non-ideal phase-matching regime\, but also as an ad ditional characterization tool of collagen alterations in diseased sta tes.
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\nAlthough SHG microscopy has intrinsic optical sectioni ng\, it is not a true 3D modality as fibers with axes that lie along t he direction of laser propagation are transparent to SHG as the intera ction is electric dipole forbidden. As such\, current SHG microscopy c ould miss important information and does not provide a full tomographi c image of the collagen structure in biological tissue. Previously a s tage-insertable platform was developed that rotates the sample to allo w for multiview SHG imaging such that any fibers missing in any single view would be visualized in another. While the initial reconstruction method resulted in a reasonable tomographic view of rat tail tendon\, it did not perform as well on other\, less aligned tissues. However\, evaluating reconstruction methods on experimental data is inherently difficult due to the lack of a ground truth. In this dissertation\, a toy model of tomographic SHG imaging was developed through the derivat ion of the dependence of SHG intensity on the angle between the fiber and laser axes\, which is then used to better examine the limitations of our current reconstruction methods. This model could be used to dev elop and evaluate new reconstruction methods leading to improved tomog raphic SHG imaging. URL:https://www.physics.wisc.edu/events/?id=9326 END:VEVENT END:VCALENDAR