DMAS Beamforming with Complementary Subset Transmit for Ultrasound Coherence-Based Power Doppler Detection in Multi-Angle Plane-Wave Imaging.

Conventional ultrasonic coherent plane-wave (PW) compounding corresponds to Delay-and-Sum (DAS) beamforming of low-resolution images from distinct PW transmit angles. Nonetheless, the trade-off between the level of clutter artifacts and the number of PW transmit angle may compromise the image quality in ultrafast acquisition. Delay-Multiply-and-Sum (DMAS) beamforming in the dimension of PW transmit angle is capable of suppressing clutter interference and is readily compatible with the conventional method. In DMAS, a tunable p value is used to modulate the signal coherence estimated from the low-resolution images to produce the final high-resolution output and does not require huge memory allocation to record all the received channel data in multi-angle PW imaging. In this study, DMAS beamforming is used to construct a novel coherence-based power Doppler detection together with the complementary subset transmit (CST) technique to further reduce the noise level. For p = 2.0 as an example, simulation results indicate that the DMAS beamforming alone can improve the Doppler SNR by 8.2 dB compared to DAS counterpart. Another 6-dB increase in Doppler SNR can be further obtained when the CST technique is combined with DMAS beamforming with sufficient ensemble averaging. The CST technique can also be performed with DAS beamforming, though the improvement in Doppler SNR and CNR is relatively minor. Experimental results also agree with the simulations. Nonetheless, since the DMAS beamforming involves multiplicative operation, clutter filtering in the ensemble direction has to be performed on the low-resolution images before DMAS to remove the stationary tissue without coupling from the flow signal.

[2,2](5,8)Picenophanedienes: Syntheses, Structural Analyses, Molecular Dynamics, and Reversible Intramolecular Structure Conversion.

This study presents an important and efficient synthetic approach to 5,8-dibromo-2,11-di-tert-butylpicene (3), with multigram scale, which was then converted to a new series of picenophanes (6-10). The tub-shaped [2,2](5,8)picenophanediene 8 with two cis-ethylene linkers was explored using X-ray crystallography. The tub-to-tub inversion proceed through the successive bending of the linkers and the barrier for isopropyl-substituted derivative 10 was experimentally estimated to be 18.7 kcal/mol. Picenophanes with a large π-system and semi-rigid structure exhibited anomalous photophysical properties. The ethano-bridged picenophane shows the weak exciton delocalization while the cis-ethylene-bridged picenophane exhibits dual emission rendered by the weakly delocalized exciton and excimer. With the aid of the ultrafast time-resolved emission spectroscopy, the mechanism of the excimer formation is resolved, showing a unique behavior of two-state reversible reaction with fast structural deformation whose lifetime is around 20 ps at 298 K. This work demonstrates that the slight difference in the bridge of tub-shaped picenophanes renders distinct photophysical behavior, revealing the potential of harnessing inter-moiety reaction in the picenophane systems.