Laser and X-Ray induced photoacoustic imaging

Author(s)

Diego Ronaldo Thomaz Sampaio

• 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: 2020-03-26

Examining board members

Théo Zeferino Pavan; Luciano Bachmann; Alexandre Colello Bruno; Pablo José Gonçalves; Homero Schiabel; Silvio Leão Vieira

• Advisor: Théo Zeferino Pavan; Juliana Fernandes Pavoni

Abstract

In biomedical applications, Laser-based photoacoustic imaging (PAI) has been used for physical and chemical characterization of biological tissues, providing for studies at anatomical, microscopic and molecular scales; because of providing an image with optical contrast and ultrasonic resolution. Recently, the X-ray-based PAI has been proposed as a dosimetric technique for external beam radiotherapy, providing information on the spatial dose distribution at the same time that it is delivered by X-ray beams. Both PAI induced by laser or X-rays have great potential for applied science, medical physics and biomedicine. In this thesis, we first investigated the formation of X-ray-based PAI by using diagnostic ultrasound (US) imaging equipment to obtain dose estimates for radiotherapy. We developed simulations and experimental arrangements to evaluate the feasibility of forming images as a function of dose in materials such as metals and bone at different irradiation configurations (e.g., water depth, X-ray field size and dose rate). We found that the diagnostic US imaging equipment is capable of forming images with dose sensitivity, but with low SNR; therefore, to solve this limitation, we proposed a method of noise reduction by means of wavelets. The results obtained are important to assess the potential use of X-ray-based PAI in the radiotherapy. Also, confirmed the feasibility of obtaining dose of metals (aluminum, brass and lead) and bone through X-ray-based PAI, however US imaging equipment did not make it possible to form images of the water dose gradient, which occurs at the edge of the X-ray field. In the second part of this thesis, we investigated multi-wavelength PAI noise in order to provide methods of reducing errors in the estimation of oxygen saturation (SO2). Also, the use of contrast agents and their influence in the estimation of SO2 is investigated. First, we proposed to observe the influence of electronic noise in PAI. We performed an experiment with a post-mortem rodent in which tubes with animal blood with known SO2 at a depth of the order of one centimeter, and then, we developed two methods of characterization of noise by means of statistic calculation of SNR and another one considering noise as a chromophore, which bias the SO2 estimates. We reduced the bias in the SO2 estimates by applying noise removal masks. Moreover, we studied the use of contrast agents for PAI. We carried out experiments in phantoms, simulating conditions of administration of contrast agent in a region of interest that mimics vascularized tumors and healthy tissues in its surroundings. In these conditions, we showed that Lipo-JICG, a new contrast agent, which was built with substances approved by the FDA for clinical use, does not create a bias in the estimation of SO2 as evident as ICG, which has been approved by FDA already. Also, we obtained PAI of Lipo-JICG at clinically relevant depths in the order of one centimeter. The results obtained are important for assessing the potential use of Lipo-JICG in cancer studies by using PAI at clinically relevant depth. (AU)

• FAPESP's process: 15/05684-0 - Laser and X-ray induced photoacoustic imaging
• Grantee: Diego Ronaldo Thomaz Sampaio
• Support Opportunities: Scholarships in Brazil - Doctorate