Novell Anthony, Arena Christopher B, Kasoji Sandeep, Dayton Paul A
Joint Department of Biomedical Engineering, The University of North Carolina and North Carolina State University, Chapel Hill, NC 27599, USA.
Phys Med Biol. 2015 Apr 21;60(8):3111-27. doi: 10.1088/0031-9155/60/8/3111. Epub 2015 Mar 24.
Capacitive micromachined ultrasonic transducer (cMUT) technology provides advantages such as wide frequency bandwidth, which can be exploited for contrast agent imaging. Nevertheless, the efficiency of traditional multi-pulse imaging schemes, such as pulse inversion (PI), remains limited because of the intrinsic nonlinear character of cMUTs. Recently, a new contrast imaging sequence, called bias voltage modulation sequence (BVM), has been specifically developed for cMUTs to suppress their unwanted nonlinear behavior. In this study, we propose to optimize contrast agent detection by combining the BVM sequence with PI and/or chirp reversal (CR). An aqueous dispersion of lipid encapsulated microbubbles was exposed to several combinations of multi-pulse imaging sequences. Approaches were evaluated in vitro using 9 inter-connected elements of a cMUT linear array (excitation frequency of 4 MHz; peak negative pressure of 100 kPa). For sequences using chirp excitations, a specific compression filter was designed to compress and extract several nonlinear components from the received microbubble responses. A satisfactory cancellation of the nonlinear signal from the source is achieved when BVM is combined with PI and CR. In comparison with PI and CR imaging modes alone, using sequences incorporating BVM increases the contrast-to-tissue ratio by 10.0 dB and 4.6 dB, respectively. Furthermore, the combination of BVM with CR and PI results in a significant increase of the contrast-to-noise ratio (+29 dB). This enhancement is attributed to the use of chirps as excitation signals and the improved preservation of several nonlinear components contained within the contrast agent response.
电容式微机械超声换能器（cMUT）技术具有诸如宽频率带宽等优点，可用于造影剂成像。然而，由于cMUT的固有非线性特性，传统的多脉冲成像方案（如脉冲反转（PI））的效率仍然有限。最近，一种名为偏置电压调制序列（BVM）的新型造影成像序列专门为cMUT开发，以抑制其不需要的非线性行为。在本研究中，我们建议通过将BVM序列与PI和/或啁啾反转（CR）相结合来优化造影剂检测。脂质包裹微泡的水分散体暴露于多脉冲成像序列的几种组合中。使用cMUT线性阵列的9个互连元件（激发频率为4 MHz；峰值负压为100 kPa）在体外评估这些方法。对于使用啁啾激发的序列，设计了一种特定的压缩滤波器，以压缩并从接收到的微泡响应中提取几个非线性分量。当BVM与PI和CR相结合时，可实现对来自源的非线性信号的满意消除。与单独的PI和CR成像模式相比，使用包含BVM的序列分别将对比组织比提高了10.0 dB和4.6 dB。此外，BVM与CR和PI的组合导致对比噪声比显著增加（+29 dB）。这种增强归因于使用啁啾作为激发信号以及对造影剂响应中包含的几个非线性分量的更好保留。
