An improved transducer for measurement of cardiac dimensions with sonomicrometry

Although pulse-transit sonomicrometry is an accurate and sensitive technique for measuring cardiac dimensions, transducer directionality has been a significant problem in certain applications. Construction of an improved ultrasonic dimension transducer is described for the measurement of global cardiac diameters. The transducer consists of a hemispheric piezoelectric crystal with a quarter-wavelength impedance matched faceplate. The in vitro acoustic characteristics of this transducer reveal a substantially improved beam pattern compared to the flat piezoceramic transducer commonly used. This improvement in transducer design greatly facilitates sonic alignment, enhances tracking throughout the cardiac cycle, and allows the measurement of more complex cardiac dimensions.