Enoch Gutierrez-Herrera

Review of applications of fluorescence excitation spectroscopy to dermatology

Endogenous molecules that exhibit fluorescence hold the potential to serve as reporters of tissue structure, activity and physiology. Fluorescence excitation spectroscopy is one means to measure and express tissues innate fluorescence. This review focuses on the application of endogenous fluorescence ultraviolet excitation spectroscopy to dermatology.

Fluorescence Excitation Photography of Epidermal Cellular Proliferation

Fluorescence excitation provides the ability to interrogate innate molecules whose radiation emission correlates with specific functional states of tissue.

Thermal and elastic response of subcutaneous tissue with different fibrous septa architectures to RF heating: numerical study.

Radiofrequency currents are commonly used in dermatology to treat cutaneous and subcutaneous tissues by heating. The subcutaneous morphology of tissue consists of a fine, collagenous and fibrous septa network enveloping clusters of adipocyte cells. The architecture of this network, namely density and orientation of septa, varies among patients and, furthermore, it correlates with cellulite grading. In this work we study the effect of two clinically relevant fibrous septa architectures on the thermal and elastic response of subcutaneous tissue to the same RF treatment; in particular, we evaluate the thermal damage and thermal stress induced to an intermediate‐ and a high‐density fibrous septa network architecture that correspond to clinical morphologies of 2.5 and 0 cellulite grading, respectively.

Development of a wide-field fluorescence imaging system for evaluation of wound re-epithelialization

Normal skin barrier function depends on having a viable epidermis, an epithelial layer formed by keratinocytes. The transparent epidermis, which is less than a 100 mum thick, is nearly impossible to see. Thus, the clinical evaluation of re-epithelialization is difficult, which hinders selecting appropriate therapy for promoting wound healing. An imaging system was developed to evaluate epithelialization by detecting endogenous fluorescence emissions of cellular proliferation over a wide field of view. A custom-made 295 nm ultraviolet (UV) light source was used for excitation. Detection was done by integrating a near-UV camera with sensitivity down to 300 nm, a 12 mm quartz lens with iris and focus lock for the UV regime, and a fluorescence bandpass filter with 340 nm center wavelength. To demonstrate that changes in fluorescence are related to cellular processes, the epithelialization of a skin substitute was monitored in vitro. The skin substitute or construct was made by embedding microscopic live human skin tissue columns, 1 mm in diameter and spaced 1 mm apart, in acellular porcine dermis. Fluorescence emissions clearly delineate the extent of lateral surface migration of keratinocytes and the total surface covered by the new epithelium. The fluorescence image of new epidermis spatially correlates with the corresponding color image. A simple, user-friendly way of imaging the presence of skin epithelium would improve wound care in civilian burns, ulcers and surgeries.

Quantification of critical alignment parameters for a rotationally-shearing interferometer employing exact ray trace

A rotationally-shearing interferometer (RSI) is sensitive to asymmetries in wave fronts. The rotational system, composed of a Dove prism, provides an adjustable sensitivity to the RSI, which is most desirable for asphericity measurements and extra-solar planet detection. We are interested in determining the magnitude of critical engineering parameters that ensure a performance better than λ/10 for the RSI. Previously, we determined that, when the manufacturing tolerance of the angles of a Dove prism is maintained within ±0.35 arcsec, the maximum wave-front deviation is less than λ/10 (at 633 nm). In this work, we study the angular and the change-induced deviations caused by the positioning of the rotational system. We determine, employing exact ray trace, the positioning tolerances and the resolution of the fine mirror movements needed to satisfy a maximum wave-front deviation of λ/10 in the RSI. This analysis shows that the compensating element of the RSI provides a 0.7 arcsec window, wherein the maximum OPD remains below λ/10. Moreover, the positioning tolerance in the RSI must lie within ±0.33 arcsec. The results suggest the use of piezoelectric actuators to control prism and mirror mounts to ensure the desired performance.

Oxygen saturation in free-diving whales: optical sensor development

Mass stranding of live whales has been explained by proposing many natural or human-related causes. Recent necropsy reports suggest a link between the mass stranding of beaked whales and the use of naval mid-frequency sonar. Surprisingly, whales have experienced symptoms similar to those caused by inert gas bubbles in human divers. Our goal is to develop a compact optical sensor to monitor the consumption of the oxygen stores in the muscle of freely diving whales. To this end we have proposed the use of a near-infrared phase-modulated frequency-domain spectrophotometer, in reflectance mode, to probe tissue oxygenation. Our probe consists of three main components: radiofrequency (RF) modulated light sources, a high-bandwidth avalanche photodiode with transimpedance amplifier, and a RF gain and phase detector. In this work, we concentrate on the design and performance of the light sensor, and its corresponding amplifier unit. We compare three state-of-the-art avalanche photodiodes: one through-hole device and two surface-mount detectors. We demonstrate that the gain due to the avalanche effect differs between sensors. The avalanche gain near maximum bias of the through-hole device exceeds by a factor of 2.5 and 8.3 that of the surface-mount detectors. We present the behavior of our assembled through-hole detector plus high-bandwidth transimpedance amplifier, and compare its performance to that of a commercially available module. The assembled unit enables variable gain, its phase noise is qualitatively lower, and the form factor is significantly smaller. Having a detecting unit that is compact, flexible, and functional is a milestone in the development of our tissue oxygenation tag.

Compensation analysis of a Rotationally-Shearing Interferometer using exact ray trace

We are interested in designing, fabricating and characterizing a Dove prism for interferometric use. In a previous work, we determined the prism tolerance to manufacturing errors. When the manufacturing tolerance of the angles is maintained within ± 0.35 arc sec, the maximum wave-front deviation is better than λ/10 (at 633 nm). Afterward, we studied the optical (angular) and the error-induced misalignments, caused by an interferometric Dove prism. The misalignment analysis showed that to ensure a maximum OPD of λ/10 (at 633 nm) the tolerance to misalignment must be ± 0.33 arc sec. In this work, we analyze the mirror movements in a Rotationally-Shearing Interferometer to reach a performance better than λ/10 (at 633 nm), employing exact ray trace. The compensation study shows the presence of a 0.66 arc sec window needed to ensure such performance. In addition, we demonstrate that it is possible to reduce the wave-front deviation caused by manufacturing errors of the interferometric Dove prism, by implementing fine mirror movements. The analysis illustrates that a piezoelectric might be used to control the mirror mounts, thus ensuring the desired performance.

Misalignment study for a Dove prism employing exact ray trace

We are designing, fabricating and characterizing a Dove prism for interferometric use. In a previous work, we determined the prism tolerance to manufacturing errors. When the manufacturing tolerance of the angles is maintained within ± 0.35 arc sec, the maximum wave-front deviation is better than λ/10 at 633 nm. We evaluated the change in the image quality introduced by this performance deterioration. In this work, we study the optical (angular) and the error-induced misalignments, caused by a real Dove prism, using exact ray trace. A Dove prism is aligned when the interferometer optical axis and the prism axis are collinear. We determine the tolerance to misalignment of the Dove prism for its incorporation in a Rotationally-Shearing Interferometer (RSI). We show that it is possible to reduce the wave-front deviation caused by base-angle errors with a specific optical misalignment. The misalignment analysis of a Dove prism, with an index of refraction of 1.515, shows that to ensure a maximum OPD of λ/10 (at 633 nm) the tolerance to misalignment must be ± 0.33 arc sec.

Preservation media analysis for ex vivo measurements of endogenous UV fluorescence of liver fibrosis in bulk samples

Non-subjective, minimally-invasive, and quantifying techniques may support development and evaluation of a fibrosis regression treatment. The build-up of extracellular matrix in liver fibrosis may result on changes of the endogenous fluorescence of tissue. In this work, we evaluate the fluorescence excitation/emission matrix in the UV range for several bulk samples of murine hepatic tissue preserved in different media. Chemical changes on tissue, caused by formaldehyde preservation, alter the endogenous fluorescence spectra. To avoid these drawbacks, phosphate-buffered saline (PBS) or Iscove’s Modified Dulbecco’s Medium were used. PBS buffer showed to be the less harmful and cost-effective preservation medium to study the endogenous fluorescence in fibrotic tissue.

Design and implementation of a dual-wavelength intrinsic fluorescence camera system

Intrinsic UV fluorescence imaging is a technique that permits the observation of spatial differences in emitted fluorescence. It relies on the fluorescence produced by the innate fluorophores in the sample, and thus can be used for marker-less in-vivo assessment of tissue. It has been studied as a tool for the study of the skin, specifically for the classification of lesions, the delimitation of lesion borders and the study of wound healing, among others. In its most basic setup, a sample is excited with a narrow-band UV light source and the resulting fluorescence is imaged with a UV sensitive camera filtered to the emission wavelength of interest. By carefully selecting the excitation/emission pair, we can observe changes in fluorescence associated with physiological processes. One of the main drawbacks of this simple setup is the inability to observe more than a single excitation/emission pair at the same time, as some phenomena are better studied when two or more different pairs are studied simultaneously. In this work, we describe the design and the hardware and software implementation of a dual wavelength portable UV fluorescence imaging system. Its main components are an UV camera, a dual wavelength UV LED illuminator (295 and 345 nm) and two different emission filters (345 and 390 nm) that can be swapped by a mechanical filter wheel. The system is operated using a laptop computer and custom software that performs basic pre-processing to improve the image. The system was designed to allow us to image fluorescent peaks of tryptophan and collagen cross links in order to study wound healing progression.