ULTRASONIC INSTRUMENTATION FOR CARDIOVASCULAR STUDIES

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The high frequency cardiac Doppler system developed at Baylor has been used for many years for studying small animals and patients. However, the performance of the transducers is relatively poor and can be further improved by including driver and receiver characteristics into the design process. The KLM model was employed to model the RF components of the Baylor Doppler system as an ABCD parameter network, include source and receiver impedances, cable lengths and transducer active and passive components. Two active materials were studied as transducer components, a PZT 5A (Motorola 3195) and a modified lead titanate (Edo EC-97). Active areas and cable lengths were varied, and modifications were made to the RF electronics to provide an optimum operation point for the Doppler transducers. Optimization of the two active materials lead to area versus sensitivity curves with an overall optimum achieved in the lead titanate; however because of the low dielectric constant, the optimal area was too large to be practical for cardiac Doppler measurements on mice. The optimum design using the Baylor configured system was found to be a 1.6mm diameter PZT5A transducer. A 330pF capacitor was inserted in series with the transducer on the RF board replacing an existing jumper, tuning the source and receive impedances to nearly real values and the designs were re-optimized. Using these modified source and receiver impedances, the overall optimum transducer design which remained practical for fine Doppler measurements was determined to be a 2.6mm diameter PZT5A transducer with a simple epoxy matching layer and a light, but structurally rigid backing of conductive micro-balloons. Future work on this project include a similar procedure with the Baylor 20 MHz system as well as application of Resource PZFlex code to analyze lens effects on transducer behavior and beam profiles.