3D contrast harmonic echocardiography

Fast acquisition and reconstruction is required for 3D-echocardiography to be applicable and accepted as a clinical tool. We developed a fast rotating phased array transducer for 3D-imaging of the heart with harmonic capabilities making it highly suitable for contrast imaging. In this study the feasibility of 3D harmonic contrast imaging was evaluated in-vitro and in-vivo. This goal is pursued because improved endocardial border delineation with the application of contrast agents should allow for less complex and faster quantification algorithms. A commercially available tissue mimicking flow phantom was used in combination with Optison micro bubbles. Backscatter power spectra from a tissue and contrast regions of interest were calculated from recorded radio frequency data. The spectra and the extracted contrast to tissue ratio from these spectra were used to optimize the excitation frequency, the pulse length and the receive filter settings for the transducer. Frequencies ranging from 1.6 to 2.5 MHz and pulse lengths of 1.5 and 2.5 cycles were explored. An increase of 8 dB in the contrast to tissue ratio was found at the second harmonic compared to the fundamental frequency. This was found for an optimal transmit frequency of 1.74 MHz and an optimal pulse length of 2.5 cycles. For these optimal transmit settings the receive filter was configured with a center frequency of 3.6 MHz and a bandwidth of 1.3 MHz giving the maximum harmonic amplitude. Using the optimized settings, clinical harmonic contrast recordings were made. The results presented in this paper show the feasibility of 3D contrast imaging and improved endocardial border delineation when used in combination with harmonic imaging.