Elastografia Supersonic Shear Imaging em músculo esquelético: análise da anisotropia do músculo gastrocnêmio lateral e relação entre a angulação de fibras musculares e sintéticas e o módulo de cisalhamento

Shear wave propagation does not occur completely in the fibers direction in pennate muscles, therefore, anisotropy must be considered when obtained shear modulus (μ) by Supersonic Shear Imaging (SSI) elastography. As the pennation angle (PA) varies between muscles, individuals and dynamic conditions, its relation with the μ is not defined. The aim of this study is to explore the relation between synthetic and muscles fibers, i.e., PA with μ. Additionally, evaluate the lateral gastrocnemius (LG) muscle anisotropy in the x2-x3 plane (parallel to surface). In synthetic and vastus lateralis (VL) muscle fibers, μ values with probe across the fibers were significantly lower than for the parallel (x2-x3 plane). In the oblique plane (x1-x3), the μ values were significantly reduced with the probe angle increase only in the polymer fibers. Considering ten distinct angulations in the x2-x3 plane in LG, there were no significant μ changes. As conclusion, it was confirmed an anisotropic behavior in the synthetic and VL muscle fibers (x2-x3 plane) and a μ reduction with angle increase in the synthetic fibers in x1-x3 plane (approximately 0.90 kPa for each degree of PA).Na obtenção do módulo de cisalhamento (µ) pela elastografia do tipo Supersonic Shear Imaging (SSI) em músculos penados, a anisotropia deve ser considerada, pois a propagação da onda de cisalhamento não ocorre totalmente na direção das fibras. Como o ângulo de penação (AP) varia entre músculos, indivíduos e condições dinâmicas, a sua relação com o µ não está esclarecida. O objetivo do estudo é relacionar o AP de fibras sintéticas e músculos com o µ e avaliar a anisotropia do músculo gastrocnêmio lateral (GL) no plano paralelo à superfície (x2-x3). Nas fibras sintéticas e do músculo vasto lateral (VL), os valores do µ foram maiores significativamente no acoplamento longitudinal que transversal (plano x2-x3) às fibras. No plano oblíquo à superfície (x1- x3), o μ reduziu-se significativamente com o aumento da angulação do probe apenas nas fibras de polímero. Considerando dez angulações distintas no plano x2-x3, não ocorreram mudanças significativas no µ do GL. Como conclusão, confirmou-se o comportamento anisotrópico nas fibras sintéticas e no VL (plano x2-x3) e observou-se uma redução do μ com aumento da angulação das fibras sintéticas no plano x1-x3 (aproximadamente 0,90 kPa para cada grau do AP)

Advanced Photothermal Optical Coherence Tomography (PT-OCT) for Quantification of Tissue Composition

Optical coherence tomography (OCT) is an imaging technique that forms 2D or 3D images of tissue structures with micron-level resolution. Today, OCT systems are widely used in medicine, especially in the fields of ophthalmology, interventional cardiology, oncology, and dermatology. Although OCT images provide insightful structural information of tissues, these images are not specific to the chemical composition of the tissue. Yet, chemical tissue composition is frequently relevant to the stage of a disease (e.g., atherosclerosis), leading to poor diagnostic performance of structural OCT images. Photo-thermal optical coherence tomography (PT-OCT) is a functional extension of OCT with the potential to overcome this shortcoming by overlaying the 3D structural images of OCT with depth-resolved light absorption information. Potentially, signal analysis of the light absorption maps can be used to obtain refined insight into the chemical composition of tissue. Such analysis, however, is complex because the underlying physics of PT-OCT is multifactorial. Aside from tissue chemical composition, the optical, thermal, and mechanical properties of tissue affect PT-OCT signals; system/instrumentation parameters also influence PT-OCT signals. As such, obtaining refined insight into tissue chemical composition requires in-depth research aimed at answering several key unknowns and questions about this technique. The goal of this dissertation is to generate in-depth knowledge on sample and system parameters affecting PT-OCT signals, to develop strategies for optimal detection of a molecule of interest (MOI) and potentially for its quantification, and to improve the imaging rate of the system. The following items are major outcomes of this dissertation: 1- Generated comprehensive theory that discovers relations between sample/tissue properties and experimental conditions and their multifactorial effects on PT-OCT signals. 2- Developed system and experimentation strategies for detection of multiple molecules of interest with high specificity. 3- Generated optimized machine learning-powered model, in light of the above two outcomes, for automated depth-resolved interpretation of tissue composition from PT-OCT images. 4- Increased the imaging rate of PT-OCT by orders of magnitude by introducing a new variant of PT-OCT based on pulsed photothermal excitation. 5- Developed algorithms for signal denoising and improving the quality of received signals and the contrast in images which in return enables faster PT-OCT imaging