Imaging Heart Dynamics With Ultrafast Cascaded-Wave Ultrasound

Abstract

The heart is an organ with highly dynamic complexity, including cyclic fast electrical activation, muscle kinematics, and blood dynamics. Although ultrafast cardiac imaging techniques based on pulsed-wave ultrasound (PUS) have rapidly emerged to permit mapping of heart dynamics, they suffer from limited sonographic signal-to-noise ratio (SNR) and penetration due to insufficient energy delivery and inevitable attenuation through the chest wall. We hereby propose ultrafast cascadedwave ultrasound (uCUS) imaging to depict heart dynamics in higher SNR and larger penetration than conventional ultrafast PUS. To solve the known tradeoff between the length of transmitted ultrasound signals and spatial resolution while achieving ultrafast frame rates (>1000 Hz), we develop a cascaded synthetic aperture (CaSA) imaging method. In CaSA, an array probe is divided into subapertures; each subaperture transmits a train of diverging waves. These diverging waves are weighted in both the aperture (i.e., spatial) and range (i.e., temporal) directions with a coding matrix containing only +1 and −1 polarity coefficients. A corresponding spatiotemporal decoding matrix is designed to recover backscattered signals. The decoded signals are thereafter beamformed and coherently compounded to obtain one high-SNR beamformed image frame. For CaSA with M subapertures and N cascaded diverging waves, sonographic SNR is increased by 10 × log 10 (N × M) (dB) compared with conventional synthetic aperture (SA) imaging. The proposed uCUS with CaSA was evaluated with conventional SA and Hadamard-encoded SA (H-SA) methods in a calibration phantom for B-mode image quality and an in vivo human heart in a transthoracic setting for the quality assessment of anatomical, myocardial motion, and chamber blood power Doppler images. Our results demonstrated that the proposed uCUS with CaSA (4 subapertures, 32 cascaded waves) improved SNR (+20.46 dB versus SA, + 14.83 dB versus H-SA) and contrast ratio (+8.44 dB versus SA, +7.81 dB versus H-SA) with comparable spatial resolutions to and at the same frame rates as benchmarks.

Cascaded Plane Wave Ultrasound for Blood Velocity Vector Imaging in the Carotid Artery

“…Decoding is performed offline, summing the different transmit-receive events, which overcomes the need of a pulse compression filter [15,17,18,19]. Zhang et al introduced a Cascaded Dual-polarity Waves (CDW) imaging scheme, where two trains of pulses are transmitted both with a different polarity order [15,20]. After transmitting and receiving both trains, they can be decoded by rather simple summation, subtraction, and delaying operations.…”

“…The spatiotemporal resolution is not compromised by the use of CDW. The application of CDW has already been shown for tissue motion imaging and power Doppler imaging [20]. However, its application in VVI, where high blood velocities, strong gradients and complex patterns can result in fast moving and changing (i.e.…”

Ultrasound Ultrafast Power Doppler Imaging with High Signal-to-Noise Ratio by Temporal Multiply-and-Sum (TMAS) Autocorrelation

“…Assuming that 10 LRI are combined for CPWC at a pulse-repetition-frequency (PRF) of 10 kHz, the resultant HRI in the CPWC imaging will be produced at a frame rate of 1 kHz. Due to this high frame rate, CPWC imaging generally refers to ultrafast imaging, and it has been applied for detecting the motion of imaged objects in transient elastography [ 4 , 5 ] and Doppler flow imaging [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. For example, compared to conventional line-by-line imaging with fixed transmit focusing, the high frame rate of CPWC imaging enables a much larger number of frames to be produced (i.e., Doppler ensembles) during the same amount of observation time such that the estimation of the Doppler parameters becomes more reliable.…”

Signal-to-noise ratio of diverging waves in multiscattering media: Effects of signal duration and divergence angle

“…In addition to the coding sequences, another approach to obtain coding is to use matrix-based coding techniques. Hadamard coding, 38,39 its extended versions, [40][41][42] and Ssequence coding 43 techniques benefit from the matrix-based coding. The experimental results show that encoding with matrices also improves the SNR and penetration depth.…”