A new apodization technique to enhance the contrast resolution of medical ultrasonic imaging systems is presented. It can easily be implemented on any commercial transducer array. The array aperture windowing in the transmitting mode is performed without modifying the driver voltage over the whole array, but only varying the driving pulse length from an element to another. A design curve has been determined which transforms any conventional amplitude apodization into a `time apodization'. Experimental and numerical results are given for a 3.5 MHz convex array and for a 2.5 MHz phased array. They demonstrate the effectiveness of this method in reducing the off-axis energy in the radiated pattern. Moreover, they point out that `time apodization' improves also the range resolution, since the overall length of the ultrasonic pulse transmitted by the probe is reduced.
Acoustic bullet waves are a class of solutions of the scalar wave equation which have the property of maintaining their shape upon propagation, without spreading in space and in time. This is a very interesting issue that suggests the use of acoustic bullets in many fields, among which there is acoustical imaging. In this work, a necessary and sufficient condition for the generation of acoustic bullets is presented and an impulse response for the case of axial symmetry is obtained. These aspects shed light onto the peculiarities of acoustic bullets and give also hints for the practical realization of this kind of fields. Numerical simulations are also presented in order to analyze the departures from the ideal case when using a finite- dimensional aperture. In particular, the performances of 2D transducer arrays, sparse and not, are considered in the simulations.
Many deconvolution techniques have been proposed in literature based on the knowledge of the Point Spread Function or on its estimation from the observed image. In this paper, we propose an alternative approach, which performs a local inversion through an iterative technique. The proposed iterative deconvolution combines accuracy with fast execution and it is well suited for fast hardware implementation. A discussion on the convergence of the algorithm is also presented in the paper. A novel approach to the deconvolution in medical imaging is proposed. Although its efficiency has been demonstrated in the work only for improving lateral resolution, it can easily be applied to full 2-dimensional deconvolution. The proposed technique has local characteristics and can operate on a limited number of data at a time with great advantage for memory storage requirements; further, it is well suited for a fast hardware implementation because only multiplications and summations are used in the algorithm. The feasibility of an alternative technique for the medical image deconvolution is analyzed theoretically; experimental results are also presented. The results are compared with those obtained by a conventional Fourier-based method.
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