IEEE Trans Med Imaging. 2018 Jan;37(1):241-250. doi: 10.1109/TMI.2017.2774814.
Ultrasound molecular imaging (USMI) is accomplished by detecting microbubble (MB) contrast agents that have bound to specific biomarkers, and can be used for a variety of imaging applications, such as the early detection of cancer. USMI has been widely utilized in preclinical imaging in mice; however, USMI in humans can be challenging because of the low concentration of bound MBs and the signal degradation caused by the presence of heterogenous soft tissue between the transducer and the lesion. Short-lag spatial coherence (SLSC) beamforming has been proposed as a robust technique that is less affected by poor signal quality than standard delay-and-sum (DAS) beamforming. In this paper, USMI performance was assessed using contrast-enhanced ultrasound imaging combined with DAS (conventional CEUS) and with SLSC (SLSC-CEUS). Each method was characterized by flow channel phantom experiments. In a USMI-mimicking phantom, SLSC-CEUS was found to be more robust to high levels of additive thermal noise than DAS, with a 6dB SNR improvement when the thermal noise level was +6dB or higher. However, SLSC-CEUS was also found to be insensitive to increases in MB concentration, making it a poor choice for perfusion imaging. USMI performance was also measured in vivo using VEGFR2-targeted MBs in mice with subcutaneous human hepatocellular carcinoma tumors, with clinical imaging conditions mimicked using a porcine tissue layer between the tumor and the transducer. SLSC-CEUS improved the SNR in each of ten tumors by an average of 41%, corresponding to 3.0dB SNR. These results indicate that the SLSC beamformer is well-suited for USMI applications because of its high sensitivity and robust properties under challenging imaging conditions.
超声分子成像（USMI）通过检测与特定生物标志物结合的微泡（MB）造影剂来实现，可用于各种成像应用，如癌症的早期检测。USMI 已广泛应用于小鼠的临床前成像；然而，由于结合的 MB 浓度低，以及换能器与病变之间异质软组织的存在导致信号衰减，USMI 在人体中的应用具有挑战性。短延迟时间空间相干（SLSC）波束形成已被提出为一种稳健的技术，它比标准延迟和求和（DAS）波束形成受信号质量差的影响更小。在本文中，使用对比增强超声成像结合 DAS（常规 CEUS）和 SLSC（SLSC-CEUS）评估了 USMI 的性能。每种方法都通过流动通道体模实验进行了表征。在 USMI 模拟体模中，发现 SLSC-CEUS 比 DAS 对高电平附加热噪声更稳健，当热噪声水平为+6dB 或更高时，SNR 提高了 6dB。然而，SLSC-CEUS 对 MB 浓度的增加也不敏感，使其成为灌注成像的不佳选择。还使用带有皮下人肝癌肿瘤的 VEGFR2 靶向 MB 在体内测量了 USMI 的性能，使用猪组织层模拟肿瘤和换能器之间的临床成像条件。SLSC-CEUS 使十个肿瘤中的每个肿瘤的 SNR 平均提高了 41%，对应于 3.0dB SNR。这些结果表明，由于 SLSC 波束形成器在具有挑战性的成像条件下具有高灵敏度和稳健的特性，因此非常适合 USMI 应用。
