E. Moreno

Laboratory characterization of electromechanical behaviour of Bessel array-transducer annuli for detection & imaging in biological media

X wave annular arrays, properly driven, could be extensively applied for medical imaging and detection. The main utility of such a device is to permit the achieving of good collimation in the ultrasonic beam maintained along certain depth. In order to generate these kinds of waves, it is necessary to precisely excite a radiating aperture in a Bessel-transducer way. The work aim is the characterization of the behavior of array annuli in a 2 MHz piezoelectric Bessel transducer. The analysis, in function of the frequency, of a basic electrical characterization, measuring the electrical complex admittance and the cross-coupling of the array elements, as well as the evaluation of the annuli emission impulse responses, are performed by employing an installation of own design (Videus-CSIC lab), reciently developed for: pulsed acoustic signals acquisition, efficient array driving and advanced processing. Knowing the response of each one of elements in this type of array, it is already possible the achieving of a correct design of the especial multichannel pulsed electrical driving needed to generate limited diffraction X-waves applicable in medicine.

Some perturbations on the ultrasonic measurements in phantoms using transit-time flow-metering systems

The use of test and calibration systems has great importance during the design & development of medical ultrasonic devices. In the particular case of analyzing in a laboratory new transit-time designs (for flow estimation in cardiac vessels) using phantoms (artificial tissues), it is necessary to confirm the existence of a certain linearity in the measurements, and also to achieve accurate calibrations of those in absolute value. However, the distinct acoustic and elastic properties encountered in the walls of the artificial blood vessels, commonly used in laboratory (based on plastic o silicone materials), during the design and development phases, can significantly alter these results, leading en many cases to wrong conclusions in laboratory evaluations. This work is devoted to study the influence that the characteristics of artificial vessels, respect to the real blood vessels, can exert in the measures acquired by an electronic broadband Transit-Time system, which is due to the distinct propagation times through the walls of the phantom devices.

Mathematical model for an accurate measurement of flow in blood vessels, considering their cyclic deformation in the time

The mathematical models, used for the electronic implementation of the method for measuring flow in a blood vessel, based in transit time estimation, not take into account the mechanical changes suffered by vessels during the cardiac cycle. In the paper, a mathematical model proposed for the characterization of this method of flow measurement, with a major precision, is presented. In this physical approach, it is assumed that both, the vessel radius and the wall thickness, change following the cyclic sequence of the cardiac function, as happens in reality. This could be useful as a support during the electronic design and implementations of new TTFM flow measuring technique, and also to quantify its real accuracy.

Some remarks about the acoustic field collimations generated by 0-order X-wave excitations of annular arrays and their possible use for medical imaging

Some consideration are made about the properties of the different acoustic fields that can be produced by a 0-order X wave in terms of velocity potential field, and of the possible use of those for medical imaging applications in annular arrays. First, the way to obtain 0-order X waves in velocity potential is shown, and later the acoustics fields generated by an annular array of Bessel type are commented. The specific properties of such a type of fields, mainly the beam collimation capability along large depths, becomes this radiating option in a possible alternative tool to be used for some special problems of diagnostic imaging. In addition, a good 2D spatial resolution for echographic purposes can be achieved with simple annular radiators specially driven with finite-time signals related to distinct X-waves time-solutions.

Semi-analytical finite elements methods for dispersion curves using higher order elements for long range ultrasonic testing

Guided waves have great potential as a NDE method. For this purposes it is very important to obtain the dispersion curves which depend on the cross-section of the structures in the guide waves. For the case of an arbitrary cross-section semi analytical finite element methods are developed. This paper describes the use of different node elements in the performance of the SAFEM algorithm using high order elements.