Characterization of contrast agent for low-field MRI

• Autor(a) principal: Augusto, Ana Margarida Rocha
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/39679
• topic: Magnetic resonance imaging; Contrast agents; Nanoparticles; Magnetic memory

Diagnostic techniques in oncology play a key role in reducing cancer-related mortality. In addition to determining the status and size, they determine the location of the tumor, critical for a correct treatment. Magnetic resonance imaging is one of the most widely used diagnostic techniques in healthcare systems; it has excellent contrast and uses contrast agents to support the visualization of specific locations. Among MRI systems, lowfield MRI systems stand out for their practical usability and low costs. The use of nanoparticles with high coercivity in a low-field MRI system opens new possibilities, explored in this work. This work aimed to study a contrast agent that when used in low-field MRI systems, has contrast dependent on the direction of the external field. In this context, nanoparticles were placed in hydrogels and exposed to a high magnetic field in order to orient their magnetic moments in the direction of the external field. With the MRI system, the relaxation constants of the samples were obtained as a function of the angle between the direction of the nanoparticles and the field of the magnetic resonance system, demonstrating their dependence. By varying the angle, images with different contrast are obtained. In this way, through image subtraction, it is possible to visualize only the contrast agent, a system that can allow the identification of its exact location in respect to the body. Later, through the same method, the application of an external magnetic field, it was possible to record a new direction in the magnetic moments previously recorded, of the nanoparticles present in the hydrogel. Through this system it is also possible to identify in which direction a magnetic field was applied, and also if rotation has occurred since that moment. Having determined that the nanoparticles were capable of having a magnetic memory and that this information could be read by the magnetic resonance system, the elimination of this magnetic information was tested. It was observed that changing the state of the hydrogels to a solution eliminates the orientation of the nanoparticles, making it another possible tool to identify the viscosity state of a particular tissue in the body.