Multimodal ultrasound computer-assisted tomography: An approach to the recognition of breast lesions.

Imaging results of multi-modal ultrasound computerized tomography system designed for breast diagnosis

Structural model of standard ultrasonic transducer array developed for FEM analysis of mechanical crosstalk.

Triclinic materials are categorized as anisotropic elastic materials with no existence of a symmetry plane. To characterize such materials, 21 elastic constants are required. The previous studies have not investigated triclinic materials due to a high number of material constants considered in the modelling. This paper presents a closed-form 3D piezoelectric model to investigate the free vibration of an arbitrary thick triclinic piezoelectric hollow cylinder. The piezoelectric cylinder is assumed to be infinitely long and short circuit boundary conditions are applied at the inner and outer surfaces of the shell. The natural frequencies of the cylinder are calculated using the transfer matrix approach along with the state space method. The effects of different anisotropic piezoelectric properties including orthotropic, monoclinic, and triclinic materials on the dispersion curve of natural frequencies are studied. The numerical results show that if the value of the axial wave number, the circumferential wave number, or natural frequency increase the resonant frequency of triclinic material deviates from other anisotropic materials such as orthotropic. Finally the validity of the proposed model is confirmed by comparing with simplified cases studied in the literature.

Three-dimensional free vibration analysis of triclinic piezoelectric hollow cylinder

Linear arrays of ultrasonic transducers are commonly used as ultrasonic probes in medical diagnostics for imaging the interior of a human body in vivo . The crosstalk phenomenon occurs during the operation of transducers in which electrical voltages and mechanical vibrations are transmitted to adjacent components. As a result of such additional excitation of the transducers in the array, the directivity characteristics of the aperture used changes, and consequently there is interference with proper operation of a given array and the emergence of distortions in the obtained ultrasound image that reduce its quality. This paper studies the manner of propagation of mechanical crosstalk in the designed model of a linear array of ultrasonic transducers on the basis of unwanted signals, which appeared on elementary piezoelectric transducers when power is supplied to the selected transducer in the array. The universal model of linear array of ultrasonic transducers, which has been developed, allowed the simulation of mechanical crosstalk, taking into account the cross-coupling phenomenon in all of its structure with the use of finite elements method (FEM) implemented in COMSOL Multiphysics software. The analysis of crosstalk signals showed that they consist of aggregated pulses propagating with different speeds and frequencies. This signifies the formation of different vibration modes transmitted simultaneously via different paths. The paper is an original approach which enables to identify different vibration modes and estimate their participation in the crosstalk signal and their ways of propagation. Conclusions from the research allow predicting specific design changes which are significant due to the minimization of mechanical crosstalk in linear arrays of ultrasonic transducers.

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Research and Modeling of Mechanical Crosstalk in Linear Arrays of Ultrasonic Transducers

Various types of undesirable crosstalk can occur in ultrasonic arrays consisting of a number of elementary piezoelectric transducers. Crosstalk is a result of deficiency in electrical or mechanical isolation between the array's elements. It is a function of proximity between piezoelectric transducers of the array or between connections. Small piezoceramic transducers tightly located inside of a circle (cylinder or sphere in 3-D systems) are used for in vivo ultrasound tomography imaging of breast tissue. This means that correct switching of transducers makes it possible to quickly acquire tomographic transmission and reflection data. A problem with such arrangements is the occurrence of crosstalk, which introduces specific errors to measurement data. Transmission and reflection tomographic images reconstructed based on ultrasonic measurements with crosstalk are distorted in a characteristic way. This work analyses the effect of crosstalk in a circular transducer array on ultrasound transmission tomography - especially, when used for examination of breast tissue.

The effect of crosstalk in a circular transducer array on ultrasound transmission tomography of breast

The paper presents the preliminary results of examinations of biological structures and healthy breast tissue in vivo obtained with the developed ultrasound tomography model. This device uses an innovative combination of ultrasound transmission tomography (UTT) and ultrasound reflection tomography (URT) which enable to obtain three-dimensional images in the same way as in the classical computer tomography (CT). The huge advantage of these methods is not exposing the patient to ionizing radiation. Compared to conventional breast ultrasonic echography (US), UTT and URT methods enable to acquire a much larger amount of information whose clinical significance has not been well documented yet. Based on the preliminary results, it is anticipated that the ultrasound tomography may contribute to the creation of a new standard of diagnosis and treatment of breast cancer. Currently, a Polish manufacturer of ultrasound scanners aims at getting an ultrasonic tomography device for examining women’s breasts to market.

Wlodzimierz Roguski

Papers

The effect of crosstalk in a circular transducer array on ultrasound transmission tomography of breast

Breast Ultrasound Tomography: Preliminary In Vivo Results