| This thesis describes the development of noninvasive high frequency (30-100MHz) imaging devices, ultrasound backscatter microscope (UBMs), for testing the transducers built at NIH transducer resource center at Penn State University and for clinical applications primarily in ophthalmology and dermatology.; The single channel UBM system, consisting of three components including a mechanical position control, imaging electronics, and data acquisition/display units was designed and built.; A time domain simulation model for pulse transmission was developed in the PSpice electronic simulation program. The model consisted of the Mason model for the transducer, a simplified pulser/receiver circuit, and impedance matching components including a transmission line and series inductor. The length of the transmission line, values of series inductor, and receive resistance were evaluated for optimization of the pulse echo performance. The performance was quantified by pulse-echo amplitude, echo pulse length, and center frequency, which affected the image sensitivity, axial and lateral image resolution. The simulation model was tested by comparing it to experimental results obtained from a 50MHz focused transducer. The results showed that the transmission efficiency can be optimizated by the matching condition with a 100nH series inductance and 300Ω receive resistance without the cable. If the cable is included, a 50cm cable length, which compensates for the transducer reactance, has the best performance.; The 3-D imaging was achieved with a 3-D motor system which can step the transducer through 2-D scan planes.; A major disadvantage of using highly focused single element transducers in a high frequency imaging system is the limited focus in the field of view, resulting in poor resolution outside of focus. A 30MHz annular array imaging system and beamforming methods were developed as an intermediate step to improve focusing throughout the image field and, therefore, image resolution via dynamic focusing in 2-D. The simulated and experimental results showed that improved resolution can be reduced with a cross-fade method. The preliminary images of an excised eye have been acquired with the imaging system in vitro. (Abstract shortened by UMI.)... |
