Comparison of spatial resolutions of parallel beamforming and diffraction tomography in high frame rate echocardiography

Echocardiography is a predominant modality for diagnosis of the heart by noninvasive and real-time observation of its cross-sectional images. In addition, it has been recently shown that measurement of the rapid transition of myocardial contraction/relaxation and propagation of heart-wall vibration would be useful for assessment of myocardial function and viscoelasticity. However, such measurements require a higher frame rate of several hundred hertz. Therefore, we realized high-frame-rate echocardiography using parallel beamforming with unfocused transmit beams. On the other hand, there is another imaging method, namely, diffraction tomography. It has been reported that diffraction tomography realizes high spatial resolution. One of the problems of parallel beamforming with unfocused transmit beams is the degradation of spatial resolution; diffraction tomography may alleviate this problem. In the present study, diffraction tomography was applied to high-frame-rate echocardiography with unfocused transmit beams, and spatial resolutions realized by diffraction tomography and parallel beamforming were compared. Diffraction tomography showed a spatial resolution (1.16mm) similar to that (1.18 mm) of parallel beamforming in a relatively near region (44mm in range distance). In a deeper region (84mm), diffraction tomography realized better spatial resolution (1.90 mm) than that (2.27 mm) of parallel beamforming. However, still better spatial resolution (1.57mm) was realized by parallel beamforming when it was used with a phase coherence factor. The use of the phase coherence factor is not computationally intensive, and parallel beamforming with a phase coherence factor was shown to be feasible in high-frame-rate echocardiography for the improvement of spatial resolution.