Contrast harmonic TEE: A feasibility study

Ultrasound (US) contrast agents serve as tracers for the noninvasive quantification of blood flow, and many of them are now approved for left ventricular opacification and for enhanced endocardial border delineation. The availability of more stable contrast bubbles has stimulated many new classes of imaging methods, such as harmonic imaging, which is already employed in commercial systems for transthoracic imaging. However, transesophageal echocardiography (TEE) still lacks appropriate technology, mainly transducer technology, to be able to take advantage of contrast harmonic benefits. We investigate, in this study, a new TEE transducer that has a frequency bandwidth wide enough to be able transmit at a lower fundamental frequency and to receive the second harmonic frequency. The transducer characteristics are measured, as well as the optimal transmit settings that allow the achievement of a high contrast-to-tissue ratio. The transducer has a center frequency of 3.5 MHz with a bandwidth ranging from 2.3 MHz to 3.9 MHz. For optimal harmonic imaging, transmit settings consisted of a transmit pulse at 2.5 MHz containing two periods. The transducer, using these settings, was then evaluated in patients to investigate myocardial contrast perfusion imaging using TEE in the operating theater.