Developments in angle-independent velocity estimators for blood flow imaging

The frame rate in ultrasonography is significantly better than those in other medical imaging modalities, such as computed tomography and magnetic resonance imaging, even under a traditional imaging scheme, i.e. line-by-line scanning with a focused transmit beam. However, a higher frame rate would provide more possibilities for the measurement of rapidly altering phenomena, such as cardiovascular dynamics. High-frame-rate imaging with unfocused transmit beams, such as plane and diverging transmit beams, enables an extremely high frame rate of over several thousand frames per second and has been shown to be effective for cardiovascular applications, including blood flow imaging. Although an extremely high temporal resolution is achieved by high-frame-rate ultrasound imaging, conventional methods for blood flow imaging are limited because a velocity component only in the direction of ultrasonic propagation is measured. In this paper, recent developments in angle-independent blood flow imaging using high-frame-rate ultrasound are presented.