Conventional ultrasound imaging probes typically comprise finite-sized arrays of periodically spaced transducer elements which, in the case of phased arrays, can result in severe grating and sidelobe artifacts. Whereas side lobes can be effectively suppressed through amplitude apodization ("AmpA"), grating lobes arising from periodicity in transducer placement can only be suppressed by decreasing the element pitch, which is technologically challenging and costly. In this work, we present source density apodization ("SDA") as an alternative apodization scheme, where the spatial source density (and, hence, the element pitch) is varied across the imaging aperture. Using an all-optical ultrasound imaging setup capable of video-rate 2-D imaging as well as dynamic and arbitrary reconfiguration of the source array geometry, we show both numerically and experimentally how SDA and AmpA are equivalent for large numbers of sources. For low numbers of sources, SDA is shown to yield superior image quality as both side and grating lobes are effectively suppressed. In addition, we demonstrate how asymmetric SDA schemes can be used to locally and dynamically improve the image quality. Finally, we demonstrate how a nonsmoothly varying spatial source density (such as that obtained for randomized arrays or in the presence of source positioning uncertainty or inaccuracy) can yield severe image artifacts. The application of SDA can, thus, yield high image quality even for low channel counts, which can ultimately result in higher imaging frame rates using acquisition systems of reduced complexity.

中文翻译：

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源密度变迹：通过源间距不均匀性抑制图像伪影。


传统的超声成像探头通常包括周期性间隔开的换能器元件的有限尺寸阵列，在相控阵的情况下，可能会导致严重的光栅和旁瓣伪影。虽然旁瓣可以通过振幅变迹（“AmpA”）来有效抑制，但由于换能器放置的周期性而产生的栅瓣只能通过减小元件间距来抑制，这在技术上具有挑战性并且成本高昂。在这项工作中，我们提出源密度变迹（“SDA”）作为替代变迹方案，其中空间源密度（以及元件间距）在整个成像孔径上变化。使用能够进行视频速率二维成像以及源阵列几何结构的动态和任意重新配置的全光学超声成像装置，我们通过数值和实验方式展示了 SDA 和 AmpA 对于大量源而言是如何等效的。对于少量光源，SDA 可以产生卓越的图像质量，因为旁瓣和栅瓣均得到有效抑制。此外，我们还演示了如何使用非对称 SDA 方案来局部动态地提高图像质量。最后，我们演示了非平滑变化的空间源密度（例如随机阵列获得的空间源密度或存在源定位不确定性或不准确的情况）如何产生严重的图像伪影。因此，即使通道数较少，SDA 的应用也可以产生高图像质量，这最终可以使用复杂性降低的采集系统获得更高的成像帧速率。