Multiperspective Bistatic Ultrasound Imaging and Elastography of the Ex Vivo Abdominal Aorta

Abstract

Knowledge of aneurysm geometry and local mechanical wall parameters using ultrasound (US) can contribute to a better prediction of rupture risk in abdominal aortic aneurysms (AAAs). However, aortic strain imaging using conventional US is limited by the lateral lumen-wall contrast and resolution. In this study, ultrafast multiperspective bistatic (MP BS) imaging is used to improve aortic US, in which two curved array transducers receive simultaneously on each transmit event. The advantage of such bistatic US imaging on both image quality and strain estimations was investigated by comparing it to single-perspective monostatic (SP MS) and MP monostatic (MP MS) imaging, i.e., alternately transmitting and receiving with either transducer. Experimental strain imaging was performed in US simulations and in an experimental study on porcine aortas. Different compounding strategies were tested to retrieve the most useful information from each received US signal. Finally, apart from the conventional sector grid in curved array US imaging, a polar grid with respect to the vessel's local coordinate system is introduced. This new reconstruction method demonstrated improved displacement estimations in aortic US. The US simulations showed increased strain estimation accuracy using MP BS imaging bistatic imaging compared to MP MS imaging, with a decrease in the average relative error between 41% and 84% in vessel wall regions between transducers. In the experimental results, the mean image contrast-to-noise ratio was improved by up to 8 dB in the vessel wall regions between transducers. This resulted in an increased mean elastographic signalto-noise ratio by about 15 dB in radial strain and 6 dB in circumferential strain.

Feasibility of 3-D Coherent Multi-Transducer Ultrasound Imaging with Two Sparse Arrays

“…In addition, large aperture studies with an external tracker showed a gain for deep imaging [44] and it is expected that CoMTUS should only improve on this. Previous studies with two curved array transducers show that multiperspective images calibrated using image registration still can improve the reconstruction of particularly challenging applications such as the aortic wall and provide significant benefits for strain imaging [9]. Bottenus et al [10] quantified the accuracy required to coherently merge information from different probe locations in 2-D imaging.…”

“…These image fusion techniques based on the exploitation of multiple points of view can reduce view-dependent artefacts [7] and improve contrast [5]. Recent studies have demonstrated that the contrast improvements also enhance motion and strain estimations from US image data [8] [9]. However, such approaches do not improve the diffraction-limited resolution and they cannot directly achieve the gains in sensitivity that could be realized if the multiple arrays were coherently combined into a one large effective aperture [10].…”

“…Recently, we have developed coherent-multi transducer ultrasound (CoMTUS) imaging [11], which coherently combines the radio frequency (RF) data received by multiple synchronized transducers that take turns transmitting plane waves (PWs) into a common FOV. In contrast to previous proposed techniques, which rely on external tracking devices [10] or on fixed and known geometries [8], [9], CoMTUS achieves subwavelength localization accuracy, required for coherent compounding, by directly using the backscattered sound field of multiple transducers. CoMTUS estimates the optimal beamforming parameters, which include the relative transducer locations and the local speed of sound, by maximizing the coherence of the received echoes, resulting from different targeted scatterers in the medium, by crosscorrelation.…”

Coherent Bistatic 3-D Ultrasound Imaging Using Two Sparse Matrix Arrays

“…This results in four different combinations of transmit (T) and receive (R). [29] constructed. The term bistatic imaging originates from radar technology [25], where the position between transmitter and receiver is separated, opposed to monostatic imaging where the transmitter and receiver are co-located.…”

Cardiac Strain Imaging Using Multi-Perspective Ultrafast Ultrasound

“…In addition, no separate recording and temporal registration are needed. Improvements of this method in image quality and vascular strain imaging have been demonstrated in a mock circulation setup using a porcine aorta [25][26][27]. However, for cardiac imaging, considering the limited imaging windows, asymmetrical and inhomogeneous deformation pattern, and high strain levels in different regions of LV, a different imaging setup and strain compounding method are required.…”