서강대학교

초록/요약

A 3-D automatic breast ultrasound imaging technique is useful to diagnose breast cancer in an accurate and efficient way. To realize this technique, it is necessary to develop an ultrasound transducer with a large aperture and uniform performance of each transducer element, which is a demanding requirement achieved by the current transducer fabrication process. In this paper, the recent development of a 7-MHz, 1024-element ultrasound linear array transducer dedicated to a 3-D automatic breast ultrasound imaging system is reported. This transducer consists of four 512-element linear array transducers to achieve a large aperture (i.e., 25 cm) and uniformity of both acoustic and electric characteristics of each element at the same time. However, this method inevitably has a drawback of degrading image quality because it is practically impossible to combine the sub-arrays without a gap between them. This paper presents the results of theoretical and simulation studies about the effect of the gap on spatial and contrast resolutions of ultrasound images. Based on the results, the linear array transducer was designed, simulated, and fabricated. In particular, the paper proposes a systematic approach to finding the precise mechanical and electrical properties of a piezoelectric material in order to perform accurate structural simulation of a transducer through a finite element method (FEM), i.e., PZFlex in this study. It is demonstrated that piezoelectric parameters in the transverse direction become dominant factors in the case of a slab-shaped material of which shape is suitable for ultrasound imaging array transducers and this fact can be used to find precise piezoelectric parameters. Additionally, it is shown that the proposed method allows FEM simulation to predict the measured one-way waveform of a custom-made 2-2 piezocomposite array with good agreement. Finally, the performance evaluation of the fabricated linear array transducer was conducted in terms of the uniformity of its center frequency and spectral bandwidth, electrical impedance, and the crosstalk between the elements. The measured electrical impedance was used when a PCB (printed circuit board) for the electrical impedance matching between the transducer and imaging system was constructed. Additionally, the imaging performance of the developed linear array was evaluated in phantom test and ex vivo experiments with pig fat tissue. From these experimental results, it was seen that the proposed design and fabrication methods are useful to construct an ultrasound array transducer with large aperture and performance uniformity of each element.