High-frequency ultrasound array-based imaging system for biomedical applications

2015-04-28High frequency ultrasound imaging, capable of achieving superior spatial resolution in real-time, has been shown to be useful for imaging and visualizing blood flow in ophthalmology, dermatology, and small animal research. The utilization of high frequency array-based imaging system can alleviate the limitations of the systems with single element transducers. This dissertation presents an investigation of high frequency array-based imaging system and its potential biomedical applications. The system is capable of B-mode imaging, PW-Doppler, color Doppler imaging, and RF data acquisition. Three different types of high frequency (30 MHz 256-element linear, 20 MHz 192-element convex, and 20 MHz 48-element phased) array transducers were implemented on the array-based imaging system. The system was also utilized for ophthalmic imaging: 30 MHz linear array for anterior segment and 20 MHz convex array for both anterior and posterior segments imaging of the eye. Anatomical structures, such as cornea, iris, ciliary body, lens, and retina, choroid, and sclera layers were identified. The high frequency PW Doppler and micro-ECG were integrated to assess the ventricular diastolic function during heart regeneration of the adult zebrafish. Synchronized PW Doppler with ECG signals confirmed the A-wave in response to atrial contraction (P wave in ECG), E-wave in response to ventricular relaxation (T wave in ECG), and ventricular outflow in response to ventricular contraction (QRS complex in ECG). The E/A ratio is less than 1 in zebrafish at baseline, reflecting a higher active filling (A-wave) than passive filling (E-wave) velocities in the two-chamber heart system. High frequency dual mode pulsed-wave Doppler imaging, which provides both tissue Doppler and Doppler flow in a same cardiac cycle, was implemented on the array-based imaging system for monitoring the functional regeneration of adult zebrafish hearts. In the in vivo study of zebrafish, both tissue Doppler and flow Doppler signals were simultaneously obtained and the synchronized valve motions with the blood flow were identified. In the longitudinal study on the zebrafish heart regeneration, the parameters for diagnosing the diastolic dysfunction were measured, and the type of diastolic dysfunction caused by the amputation was found to be similar to the restrictive filling. The diastolic function was fully recovered within four weeks post-amputation. High frequency color Doppler imaging was implemented on the array-based imaging system and evaluated by the flow phantom and adult zebrafish in vivo studies. In the flow phantom study, constant velocity with opposite flow directions was detected utilizing color Doppler imaging. Also, color Doppler imaging could be used to monitor blood flows inside adult zebrafish heart and flow directions were clearly identified by the color-coded images