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| Author(s): |
João Henrique Uliana
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Ribeirão Preto. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC) |
| Defense date: | 2021-03-09 |
| Examining board members: |
Théo Zeferino Pavan;
Rinaldo Roberto de Jesus Guirro;
Joaquim Miguel Maia;
Denise Maria Zezell
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| Advisor: | Théo Zeferino Pavan |
| Abstract | |
Photoacoustic images are based on the photoacoustic effect which consists in the emission of acoustic waves due to the light absorption by a material. The magnitude of the emitted acoustic waves is proportional to the thermal and mechanical characteristics of the medium, the optical absorption coefficient and the local light fluence. Thus, photoacoustic images are able to encode the optical absorption of material into acoustic waves, combining the contrast of purely optical imaging technique with the spatial resolution of ultrasound. This combination results in an imaging technique with huge potential for biomedical applications, for example, tumor diagnosis, blood oxygen measurement, lipid detection in organs, tissue thermometry and biomarker tracking. In this Ph.D. work, systems were developed for the acquisition of unidimensional photoacoustic signals and multispectral photoacoustic images. The acquisition of unidimensional photoacoustic signals provided the optical characterization of inorganic chromophores. The relative values of the optical absorption spectrum obtained by the amplitude of the photoacoustic signal were compared with data provided by a spectrophotometer, resulting in substantial Lin\"s concordance values (ρc > 0.95). The limitations and possibilities for improving the technique for optical absorption absolute measurement by fitting the initial compressive part of the photoacoustic signal were studied by means of simulations and experiments. The results showed improved procedures capable of estimating the absolute optical absorption coefficient with substantial Lin\" concordance values when compared with the tabulated values from the literature. For the acquisition of photoacoustic images, the development of a new illumination scheme, multiangular by the long-axis of the linear ultrasound transducer, allowed an improved light delivery to targets smaller than the transducer\"s width, generating photoacoustic images with sufficient quality for the application in preclinical and clinical research. For example, photoacoustic images of a volunteer\'s index finger and mouse tumors, with a high signal-to-noise ratio, are reported. Finally, the multispectral evaluation of the new illumination scheme for the measurement of blood oxygenation in humans, mice and mouse xenograft models was performed. In a normoxic condition, the estimated blood oxygen saturation in humans and in healthy mice showed values close to 95% in blood vessels and arteries. For the xenograft models, the combination of conventional ultrasound images, single-wavelength photoacoustic images and multispectral photoacoustic images provided anatomical and functional information for the characterization of the tumor mass. The results showed the presence of oxygenated blood in well-structured blood vessels around the tumor mass and a heterogeneous distribution of oxygenated blood with the presence of hypoxic regions within the tumor. (AU) | |
| FAPESP's process: | 16/22374-8 - Blood oxygenation analysis in tumors using photoacoustic imaging |
| Grantee: | João Henrique Uliana |
| Support Opportunities: | Scholarships in Brazil - Doctorate |