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Doctoral Thesis
DOI
https://doi.org/10.11606/T.59.2020.tde-31072020-162346
Document
Author
Full name
Guilherme de Araujo Braz
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Ribeirão Preto, 2020
Supervisor
Committee
Carneiro, Antonio Adilton Oliveira (President)
Andrade, José Henrique Araújo Lopes de
Barbosa, Marcello Henrique Nogueira
Rahal, Sheila Canevese
Salmon, Carlos Ernesto Garrido
Shimano, Antonio Carlos
Title in Portuguese
Implementação de uma técnica de caracterização de tecidos biológicos baseada na emissão acústica em baixa frequência (kHz) de alvos excitados em alta frequência (MHz)
Keywords in Portuguese
Caracterização de tecidos
Elastografia
Força de radiação acústica
Osteoporose
Propriedades de tecidos biológicos
Ultrassom
Abstract in Portuguese
As propriedades mecânicas de tecidos moles podem estar relacionadas a diversos processos patológicos. Técnicas ultrassônicas têm sido exploradas como uma alternativa não invasiva para caracterizar tais tecidos. No entanto, as metodologias existentes requerem o uso de sistemas de frequência variável, frequência dupla e alta potência. Aqui, propomos demonstrar o uso de pulsos de radiação acústica de megahertz para observar respostas mecânicas em quilohertz de tecidos biológicos. Ossos fêmures foram retirados de dez camundongos saudáveis e de outros dez camundongos nos quais a osteoporose havia sido induzida. A porosidade do osso, número trabecular, espaçamento trabecular, conectividade e densidade de conectividade foram determinadas usando micro-CT. As amostras foram irradiadas com pulsos curtos de radiação acústica focalizada (f = 3,1 MHz, t = 15 μs) e a resposta acústica de baixa frequência (1 kHz - 80 kHz) foi adquirida usando um hidrofone dedicado. Foi encontrada x uma forte correlação entre os mapas espectrais dos sinais adquiridos e os dados do micro-CT. Em um teste adicional, foram realizadas simulações do mapeamento da rigidez de tecidos moles com um simulador de parafina gel contendo três inclusões esféricas com diferentes densidades, módulos de Young e aproximadamente a mesma ecogenicidade. O ultrassom convencional do modo-B não conseguiu visualizar as inclusões, enquanto a nova técnica aqui proposta mostrou um bom contraste da imagem na identificação das inclusões com diferentes rigidezes.
Title in English
Characterization of biological tissues using low frequency acoustic radiation in response to a high frequency focused ultrasound pulse
Keywords in English
Acoustic radiation force
Elastography
Mechanical properties
Osteoporosis
Tissue characterization
Ultrasound
Abstract in English
The mechanical properties of biological tissues are fingerprints of some pathological processes. Ultrasound systems have been used as a non-invasive technique to both induce kilohertz mechanical vibrations and to detect the resulting waves after interaction with the biological structures. However, existing methodologies to produce kilohertz mechanical vibrations using ultrasound require the use of variable-frequency, dual-frequency and high-power systems. Here, we propose and demonstrate the use of bursts of megahertz acoustic radiation to observe kilohertz mechanical responses of biological tissues. Femoral bones were excised from ten healthy mice and from another ten mice where osteoporosis had been induced. The bone's porosity, trabecular number, trabecular spacing, connectivity, and connectivity density were determined using micro-CT. The samples were irradiated with short, focused acoustic radiation pulses (f = 3.1 MHz, t = 15 μs), and the low-frequency acoustic response (1 kHz - 80 kHz) was acquired using a dedicated hydrophone. A strong correlation between spectral maps of the acquired signals and the micro-CT data was found. In a further test, soft tissue stiffness measurement simulations were performed with a gel wax phantom containing three spherical inclusions of the same type of gel but different densities, different Young moduli, and approximately same echogenicity. Conventional B-mode ultrasound was unable to image the inclusions, while the novel technique here proposed showed good image contrast to identify inclusions with different stiffness.
 
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Publishing Date
2020-11-19
 
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