High-contrast ultrafast imaging of the heart

Abstract

Non-invasive ultrafast imaging for human cardiac applications is a big challenge to image intrinsic waves such as electromechanical waves or remotely induced shear waves in elastography imaging techniques. In this paper we propose to perform ultrafast imaging of the heart with adapted sector size by using diverging waves emitted from a classical transthoracic cardiac phased array probe. As in ultrafast imaging with plane wave coherent compounding, diverging waves can be summed coherently to obtain high-quality images of the entire heart at high frame rate in a full field-ofview. To image shear waves propagation at high SNR, the field-of-view can be adapted by changing the angular aperture of the transmitted wave. Backscattered echoes from successive circular wave acquisitions are coherently summed at every location in the image to improve the image quality while maintaining very high frame rates. The transmitted diverging waves, angular apertures and subapertures size are tested in simulation and ultrafast coherent compounding is implemented on a commercial scanner. The improvement of the imaging quality is quantified in phantom and in vivo on human heart. Imaging shear wave propagation at 2500 frame/s using 5 diverging waves provides a strong increase of the Signal to noise ratio of the tissue velocity estimates while maintaining a high frame rate. Finally, ultrafast imaging with a 1 to 5 diverging waves is used to image the human heart at a frame rate of 900 frames/s over an entire cardiac cycle. Thanks to spatial coherent compounding, a strong improvement of imaging quality is obtained with a small number of transmitted diverging waves and a high frame rate, which allows imaging the propagation of electromechanical and shear waves with good image quality.

Extension of Fourier-Based Techniques for Ultrafast Imaging in Ultrasound With Diverging Waves

“…Thus, by reproducing the scheme proposed in [26], i.e. emitting several diverging waves with virtual sources positioned at z v = −D/(2 tan(α)) and for different x v values, our formalism can be used to reconstruct wide field of view ultrasound images with efficient compounding scheme.…”

“…2) Transmission scheme: for comparison purposes and because of its efficiency, we used the same transmission scheme as the one proposed in [26]. Each DW involved in transmission was emitted from a virtual source point with an angular aperture of 90…”

“…In particular, the authors proposed to use several diverging beams with different directions to cover the entire medium. Contrary to this approach, Papadacci et al proposed to use several DWs which individually insonify the entire field of view along with a compound strategy in order to improve the image quality [26]. Recently, Porée et al developed an original coherent compounding approach with Doppler-based motioncompensation to generate high-quality cardiac images by DW imaging [27].…”

“…The above mentioned ultrafast imaging methods can be classified into two groups: the Fourier-based techniques where the received raw-data are used to reconstruct the Fourier spectrum of the object of interest [5], [8], [9] and the spatialbased approaches where the images are directly computed from the space domain [10], [25], [26]. The main advantage of the Fourier-based approaches concerns the computational complexity, this aspect having been investigated in several studies in the context of planar acquisition from SPW [8], [28].…”

Effect of Ultrafast Imaging on Shear Wave Visualization and Characterization: An Experimental and Computational Study in a Pediatric Ventricular Model

“…In this manner, the image quality is improved compared to single plane wave imaging while still maintaining sufficiently high frame rates [10]. The concept of compounding has been applied to different ultrasound modalities [11][12][13][14], and has become a key feature of ultrafast ultrasound imaging.…”