Compensation for Electrical Fatigue in Piezoelectric Transducers

Malfunction of ultrasonic transducers is one of the most common factors affecting the quality of medical ultrasound images. In this work, the effect of electrical fatigue in piezoelectric transducers on the image quality is investigated and subsequently compensated. To this end, through a combination of simulation and controlled experimental and clinical evaluations, the effect of fatigue and its compensation is realized. Initially, the electrical fatigue is simulated by reducing the piezoelectric permittivity and piezoelectric constant parameters based on finite element method (FEM). Next, the transducer's electromechanical impulse response is obtained, and the quality of reconstructed images from the fatigued transducer array elements is evaluated by applying the FEM simulation results to the Field II simulation program. Also, experimental measurements are conducted using a tissue-mimicking phantom and in vivo imaging. To evaluate the image quality, various metrics such as signal to noise ratio (SNR), side lobe level (SLL), full width at half maximum (FWHM) and contrast to noise ratio (CNR) are measured for the simulated and tissue-mimicking phantoms. To compensate for negative effects of electrical fatigue, a method based on the nonblind deconvolution of the ultrasound radio frequency (RF) signals is proposed. This method utilizes the corresponded electromechanical impulse responses to the fatigue level as the known undesired impulse responses. The results show that the image quality metrics which were significantly degraded due to electrical fatigue, are appropriately improved as a result of the proposed restoration method.