DEEP STRUCTURE ULTRASOUND IMAGING USING FUNDAMENTAL AND THIRD HARMONIC CODED EXCITATION TECHNIQUES BY

ii A novel coded excitation method, combining Golay coding with fundamental and third harmonic 1, 3 chirps with resolution enhancement compression (REC) and frequency compounding, increases the axial resolution, lateral resolution, penetration depth and the contrast-to-noise ratio (CNR) for an ultrasonic imaging system. The thickness mode of piezoelectric transducers produces a signal that is resonant at a fundamental frequency and odd harmonics. This behavior is exploited using coded excitation techniques to increase the usable bandwidth of the source and create compounded images of different bands centered at the first and third harmonics. The images are already registered using a single transducer and the frame rate is not decreased because a single transmit per line is used, rather than transmit at each frequency. With 1, 3 REC compounding, several advantages were demonstrated: 1) the REC technique increased both the fundamental and third harmonic bandwidth which boosted axial resolution, 2) the third harmonic improved lateral resolution of ultrasonic images, and 3