Department of Biomedical Engineering, University of California, Davis, CA, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2010;57(2):305-16. doi: 10.1109/TUFFC.2010.1411.
The primary goals of ultrasound molecular imaging are the detection and imaging of ultrasound contrast agents (microbubbles), which are bound to specific vascular surface receptors. Imaging methods that can sensitively and selectively detect and distinguish bound microbubbles from freely circulating microbubbles (free microbubbles) and surrounding tissue are critically important for the practical application of ultrasound contrast molecular imaging. Microbubbles excited by low-frequency acoustic pulses emit wide-band echoes with a bandwidth extending beyond 20 MHz; we refer to this technique as transmission at a low frequency and reception at a high frequency (TLRH). Using this wideband, transient echo, we have developed and implemented a targeted imaging technique incorporating a multifrequency colinear array and the Siemens Antares imaging system. The multifrequency colinear array integrates a center 5.4-MHz array, used to receive echoes and produce radiation force, and 2 outer 1.5-MHz arrays used to transmit low-frequency incident pulses. The targeted imaging technique makes use of an acoustic radiation force subsequence to enhance accumulation and a TLRH imaging subsequence to detect bound microbubbles. The radiofrequency (RF) data obtained from the TLRH imaging subsequence are processed to separate echo signatures between tissue, free microbubbles, and bound microbubbles. By imaging biotin-coated microbubbles targeted to avidin-coated cellulose tubes, we demonstrate that the proposed method has a high contrast-to-tissue ratio (up to 34 dB) and a high sensitivity to bound microbubbles (with the ratio of echoes from bound microbubbles versus free microbubbles extending up to 23 dB). The effects of the imaging pulse acoustic pressure, the radiation force subsequence, and the use of various slow-time filters on the targeted imaging quality are studied. The TLRH targeted imaging method is demonstrated in this study to provide sensitive and selective detection of bound microbubbles for ultrasound molecularly targeted imaging.
超声分子成像的主要目标是检测和成像超声造影剂（微泡），这些微泡与特定的血管表面受体结合。能够敏感且选择性地检测和区分结合的微泡与游离循环的微泡（游离微泡）以及周围组织的成像方法对于超声对比分子成像的实际应用至关重要。用低频声脉冲激发的微泡会发出带宽超过 20MHz 的宽带回波；我们将这种技术称为低频发射和高频接收（TLRH）。利用这种宽带瞬态回波，我们开发并实现了一种结合多频共线阵和西门子 Antares 成像系统的靶向成像技术。多频共线阵集成了一个中心 5.4MHz 的阵元，用于接收回波并产生辐射力，以及两个外部的 1.5MHz 阵元，用于发射低频入射脉冲。靶向成像技术利用声辐射力序列来增强聚集，以及 TLRH 成像序列来检测结合的微泡。从 TLRH 成像序列获得的射频（RF）数据被处理以分离组织、游离微泡和结合微泡之间的回波特征。通过对靶向到亲和素涂层纤维素管的生物素涂层微泡进行成像，我们证明了所提出的方法具有高的组织对比比（高达 34dB）和对结合微泡的高灵敏度（结合微泡的回波与游离微泡的回波之比高达 23dB）。研究了成像脉冲声压、辐射力序列以及使用各种慢时滤波器对靶向成像质量的影响。本研究证明了 TLRH 靶向成像方法可用于敏感和选择性地检测超声分子靶向成像中的结合微泡。
