Test bench for development of imaging reconstruction algorithms for ultrasound tomography.

• Ano de defesa: 2020
• Autor(a) principal: Rosa Júnior, Nilton Barbosa da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Imageamento (Bioengenharia); Lung monitoring; Mechanical ventilation; Pulmão (Monitoramento); PZT transducer; Respiradores mecânicos; Tomografia; Ultrasound tomography; Ultrassonografia
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/3/3152/tde-14122020-112727/

Imaging exams are important to monitor patients under mechanical ventilation in the Intensive Care Unit (ICU). A common exam for anatomical imaging is the Computed Tomography. However, this imaging method has its drawbacks, such as the need to remove the patient from the ICU, which increases the risk for complications; use of ionizing radiation, which is harmful if used continuously. For functional imaging, Electrical Impedance Tomography (EIT) is a recent imaging technique to continuously monitor pulmonary functions at the bedside in ICUs. Nevertheless, EIT still presents low spatial resolution and low location accuracy. The Ultrasound Tomography (UST) has the potential to provide better pulmonary functional imaging. However, it has never been used before. The aim of this work is to develop an experimental test bench, to simulate an UST system, and to evaluate its feasibility for pulmonary functional imaging. 9 single-element transducers were manufactured by using 500 kHz piezoelectric ceramic and were characterized by measuring its electrical impedance, pulse-echo response, transmitted acoustic pressure and sensitivity, through the transmission and reflection techniques. 8 of the manufactured transducers were selected to be assembled on a wooden cylinder that was placed inside a tank filled with water. One transducer was used as emitter and four others as receptors, with a phantom placed in several positions inside. The electrical impedance and the pulse-echo results showed frequencies below 200 kHz with amplitudes between 20 and 300 mV (peak-to-peak). Moreover, the acoustic pressure and sensitivity measurements showed that the manufactured transducers have central frequencies around 170 kHz with transmitted acoustic pressure between 8.9 kPa and 148 kPa, and sensitivity responses from 15.24 V/MPa to 59 V/MPa. The evaluation of the test bench also showed signals compatible to expected, showing the feasibility of this UST test bench for the development of reconstruction imaging algorithms.