Department of Biomedical Engineering, NIH Resource Center for Medical Ultrasonic Transducer Technology, University of Southern California, Los Angeles, CA, USA.
Phys Med Biol. 2010 Apr 7;55(7):1889-902. doi: 10.1088/0031-9155/55/7/007. Epub 2010 Mar 12.
It was previously demonstrated that it is feasible to simultaneously perform ultrasound therapy and imaging of a coagulated lesion during treatment with an integrated transducer that is capable of high intensity focused ultrasound (HIFU) and B-mode ultrasound imaging. It was found that coded excitation and fixed notch filtering upon reception could significantly reduce interference caused by the therapeutic transducer. During HIFU sonication, the imaging signal generated with coded excitation and fixed notch filtering had a range side-lobe level of less than -40 dB, while traditional short-pulse excitation and fixed notch filtering produced a range side-lobe level of -20 dB. The shortcoming is, however, that relatively complicated electronics may be needed to utilize coded excitation in an array imaging system. It is for this reason that in this paper an adaptive noise canceling technique is proposed to improve image quality by minimizing not only the therapeutic interference, but also the remnant side-lobe 'ripples' when using the traditional short-pulse excitation. The performance of this technique was verified through simulation and experiments using a prototype integrated HIFU/imaging transducer. Although it is known that the remnant ripples are related to the notch attenuation value of the fixed notch filter, in reality, it is difficult to find the optimal notch attenuation value due to the change in targets or the media resulted from motion or different acoustic properties even during one sonication pulse. In contrast, the proposed adaptive noise canceling technique is capable of optimally minimizing both the therapeutic interference and residual ripples without such constraints. The prototype integrated HIFU/imaging transducer is composed of three rectangular elements. The 6 MHz center element is used for imaging and the outer two identical 4 MHz elements work together to transmit the HIFU beam. Two HIFU elements of 14.4 mm x 20.0 mm dimensions could increase the temperature of the soft biological tissue from 55 degrees C to 71 degrees C within 60 s. Two types of experiments for simultaneous therapy and imaging were conducted to acquire a single scan-line and B-mode image with an aluminum plate and a slice of porcine muscle, respectively. The B-mode image was obtained using the single element imaging system during HIFU beam transmission. The experimental results proved that the combination of the traditional short-pulse excitation and the adaptive noise canceling method could significantly reduce therapeutic interference and remnant ripples and thus may be a better way to implement real-time simultaneous therapy and imaging.
先前已经证明，使用能够进行高强度聚焦超声（HIFU）和 B 模式超声成像的集成换能器，同时进行超声治疗和对凝固病变的成像在技术上是可行的。研究发现，在接收时采用编码激励和固定陷波滤波可以显著减少治疗换能器引起的干扰。在 HIFU 超声处理期间，使用编码激励和固定陷波滤波生成的成像信号的旁瓣电平小于-40dB，而传统的短脉冲激励和固定陷波滤波产生的旁瓣电平为-20dB。然而，缺点是，在阵列成像系统中使用编码激励可能需要相对复杂的电子设备。正是出于这个原因，在本文中，提出了一种自适应噪声消除技术，通过不仅最小化治疗干扰，而且最小化使用传统短脉冲激励时残余旁瓣“波纹”，来提高图像质量。通过使用原型集成 HIFU/成像换能器进行仿真和实验验证了该技术的性能。尽管已知残余波纹与固定陷波滤波器的衰减值有关，但实际上，由于目标或介质的变化，或者由于运动或不同的声特性，即使在一次超声脉冲期间，也很难找到最佳的陷波衰减值。相比之下，所提出的自适应噪声消除技术能够在没有这些约束的情况下，最佳地最小化治疗干扰和残余波纹。原型集成 HIFU/成像换能器由三个矩形元件组成。6MHz 中心元件用于成像，外部两个相同的 4MHz 元件共同发射 HIFU 波束。两个 14.4mm x 20.0mm 尺寸的 HIFU 元件可以在 60s 内将软生物组织的温度从 55°C 升高到 71°C。进行了两种类型的同时治疗和成像实验，分别使用铝板和猪肌肉切片获取单扫描线和 B 模式图像。在 HIFU 波束传输期间，使用单个元件成像系统获得 B 模式图像。实验结果证明，传统短脉冲激励和自适应噪声消除方法的结合可以显著降低治疗干扰和残余波纹，因此可能是实现实时同时治疗和成像的更好方法。
