長谷川 英之^{1, 2}, 金井 浩^{1, 2}

Hideyuki HASEGAWA^{1, 2}, Hiroshi KANAI^{1, 2}

¹東北大学大学院医工学研究科, ²東北大学大学院工学研究科

¹Graduate School of Biomedical Engineering, Tohoku University, ²Graduate School of Engineering, Tohoku University

キーワード :

1. Background
High-frame-rate echocardiography using unfocused transmit beams and parallel receive beamforming is a promising method for evaluation of cardiac function. In this technique, high temporal resolution is realized at the expense of spatial resolution and contrast. In the present study, a method was proposed for improvement of the spatial resolution in high frame rate echocardiography.
2. Principle
Phase coherence factor （PCF）［1］ improves spatial resolution by evaluating phase variance of echoes received by individual transducer elements. However, phase variance of an echo from a weak scatterer in diffuse scattering medium cannot be evaluated correctly due to interference of echoes. By sub-aperture beamforming （SABF） before evaluating phase variance, an echo from a weak scatterer at a focal point can be enhanced, and estimation of phase variance can be improved.
3. Experimental Results
Effect of SABF was evaluated by basic experiments using a phantom （model 54GS, CIRS, USA）. Figure 1 shows ultrasonic images obtained by diverging transmit beams （position of virtual point source: -100 mm） and parallel receive beamforming［2］. Figures 1（a）, 1（b）, and 1（c） were obtained without PCF, with PCF without SABF, and with PCF with SABF. Using PCF, lateral spatial resolutions （at range distance of 42 mm） were improved to be 0.78 mm （without SABF） and 0.75 mm （with SABF） from 1.06 mm （without PCF）. However, as can be seen in Fig. 1（b）, speckle echoes from diffuse scattering medium are significantly suppressed when PCF is used without SABF. On the other hand, using PCF with SABF, improvement of spatial resolution can be realized with preserving speckle echoes, as shown in Fig. 1（c）.
4. Conclusion
In the present study, improved spatial resolution and visualization of speckle echoes were realized at the same time by PCF with SABF.
References
［1］Camacho, et al., IEEE Trans UFFC, 2009.
［2］Hasegawa and Kanai, J Med Ultrason, 2011.