Jing Bowen, Lindsey Brooks D
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA.
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA; School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA.
Ultrasound Med Biol. 2022 Mar;48(3):530-545. doi: 10.1016/j.ultrasmedbio.2021.11.010. Epub 2021 Dec 28.
Contrast-enhanced ultrasound imaging allows vascular imaging in a variety of diseases. Radial modulation imaging is a contrast agent-specific imaging approach for improving microbubble detection at high imaging frequencies (≥7.5 MHz), with imaging depth limited to a few centimeters. To provide high-sensitivity contrast-enhanced ultrasound imaging at high penetration depths, a new radial modulation imaging strategy using a very low frequency (100 kHz) ultrasound modulation wave in combination with imaging pulses ≤5 MHz is proposed. Microbubbles driven at 100 kHz were imaged in 10 successive oscillation states by manipulating the pulse repetition frequency to unlock the frame rate from the number of oscillation states. Tissue background was suppressed using frequency domain radial modulation imaging (F-RMI) and singular value decomposition-based radial modulation imaging (S-RMI). One hundred-kilohertz modulation resulted in significantly higher microbubble signal magnitude (63-88 dB) at the modulation frequency relative to that without 100-kHz modulation (51-59 dB). F-RMI produced images with high contrast-to-tissue ratios (CTRs) of 15 to 22 dB in a stationary tissue phantom, while S-RMI further improved the CTR (19-26 dB). These CTR values were significantly higher than that of amplitude modulation pulse inversion images (11.9 dB). In the presence of tissue motion (1 and 10 mm/s), S-RMI produced high-contrast images with CTR up to 18 dB; however, F-RMI resulted in minimal contrast enhancement in the presence of tissue motion. Finally, in transcranial ultrasound imaging studies through a highly attenuating ex vivo cranial bone, CTR values with S-RMI were as high as 23 dB. The proposed technique demonstrates successful modulation of microbubble response at 100 kHz for the first time. The presented S-RMI low-frequency radial modulation imaging strategy represents the first demonstration of real-time (20 frames/s), high-penetration-depth radial modulation imaging for contrast-enhanced ultrasound imaging.
超声造影成像可实现多种疾病的血管成像。径向调制成像是一种针对造影剂的成像方法，用于在高成像频率（≥7.5 MHz）下改善微泡检测，但其成像深度限制在几厘米。为了在高穿透深度下提供高灵敏度的超声造影成像，本文提出了一种新的径向调制成像策略，该策略使用非常低频率（100 kHz）的超声调制波与≤5 MHz的成像脉冲相结合。通过操纵脉冲重复频率，使以100 kHz驱动的微泡在10个连续振荡状态下成像，从而将帧率从振荡状态数中解放出来。使用频域径向调制成像（F-RMI）和基于奇异值分解的径向调制成像（S-RMI）抑制组织背景。100 kHz调制相对于无100 kHz调制时（51 - 59 dB），在调制频率处产生的微泡信号幅度显著更高（63 - 88 dB）。在静态组织模型中，F-RMI产生的图像具有15至22 dB的高对比组织比（CTR），而S-RMI进一步提高了CTR（19 - 26 dB）。这些CTR值显著高于幅度调制脉冲反转图像的CTR值（11.9 dB）。在存在组织运动（1和10 mm/s）的情况下，S-RMI产生了CTR高达18 dB的高对比度图像；然而，在存在组织运动的情况下，F-RMI导致的对比度增强最小。最后，在通过高度衰减的离体颅骨进行的经颅超声成像研究中，S-RMI的CTR值高达23 dB。所提出的技术首次证明了在100 kHz时成功调制微泡响应。所展示的S-RMI低频径向调制成像策略代表了超声造影成像中实时（20帧/秒）、高穿透深度径向调制成像的首次证明。
