Browsing by Author "Elvira, Luis"

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    Determination of phase jumps in the measurement of phase velocity of samples obeying a frequency power-law attenuation coefficient using Kramers-Kronig relations.
    (2020) Elvira, Luis; Tiago, Marcelo Moreira; Yoza, Suelen Akemi Nakazato; Kitano, Claudio; Higuti, Ricardo Tokio
    Ultrasonic phase velocity spectroscopy is a very sensitive technique used in the measurement of material properties. In phase velocity calculation, ambiguities can arise in the spectral phases, in the form of integer multiples of 2π rad, which, if not corrected, result in large errors. In this work we propose a method for determining these ambiguities, more specifically, the number of 2π rad phase jumps, using KramersKronig relations, for samples exhibiting a frequency power-law attenuation coefficient. The method is based on a first estimate of the phase velocity from group velocity and attenuation coefficient, which are not affected by phase jumps. This estimated phase velocity is used to obtain the number of 2π rad phase jumps, which in turn is used to calculate the corrected phase velocity. The method was tested with samples of liquids with frequency power-law attenuation coefficient (exponent y varying from 1.5 to 2) and a solid (PMMA - polymethyl methacrylate) with y ∼ 1, and velocity dispersions ranging from 0 to 34 (cm/s)/MHz.
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    Development and characterization of medical phantoms for ultrasound imaging based on customizable and mouldable polyvinyl alcohol cryogel–based materials and 3-D printing : application to high-frequency cranial ultrasonography in infants.
    (2019) Elvira, Luis; Durán, Carmen; Higuti, Ricardo Tokio; Tiago, Marcelo Moreira; Ibáñez, Alberto; Parrilla, Montserrat; Valverde, Eva; Jiménez, Javier; Bassat, Quique
    This work presents an affordable and easily customizable methodology for phantom manufacturing, which can be used to mimic different anatomic organs and structures. This methodology is based on the use of polyvinyl alcohol–based cryogels as a physical substitute for biologic soft tissues and of 3-D printed polymers for hard tissues, moulding and supporting elements. Thin and durable soft-tissue mimicking layers and multilayer arrangements can be obtained using these materials. Special attention was paid to the acoustic properties (sound speed, attenuation coefficient and mechanical impedance) of the materials developed to simulate soft tissues. These properties were characterized as a function of the additives concentration (propylene-glycol and alumina particles). The polyvinyl alcohol formulation proposed in this work is stable over several freeze-thaw cycles, allowing the manufacturing of multilayer materials with controlled properties. The manufacturing methodology presented was applied to the development of a phantom for high-frequency cranial ultrasonography in infants. This phantom was able to reproduce the main characteristics of the ultrasound images obtained in neonates through the anterior fontanel, down to 8-mm depth.
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    Versatile ultrasonic spectrometer for liquids with practical sample handling by using standard cuvettes.
    (2019) Tiago, Marcelo Moreira; Higuti, Ricardo Tokio; Oliveira, Samuel L.; Assunção, Edvaldo; Kitano, Claudio; Elvira, Luis
    This work describes the development and tests of a new ultrasonic spectrometer for liquids based on the use of commercial cuvettes for sample handling. The spectrometer operates in the frequency range from 20 to 80 MHz and gathers some important characteristics, which are its high thermal stability (better than 0.01oC), by the use of Peltier cells, and practical sample handling with small volume ( 3 ml) samples placed inside cuvettes which can be easily removed from the spectrometer, cleaned/sterilized or simply discarded. Throughtransmission operation is used to measure propagation velocity and attenuation coefficient, and the spectrometer was tested with mixtures of water and NaCl, which have attenuations smaller than that of distilled water, and higher attenuation samples of silicone and castor oil. Backscattering studies of polystyrene particles of 10 and 15 μm-diameters were also conducted, showing the versatility of the instrument.