Ultrasound focusing using magnetic resonance acoustic radiation force imaging: Application to ultrasound transcranial therapy
Ultrasound focusing using magnetic resonance acoustic radiation force imaging: Application to ultrasound transcranial therapy
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DOI：
10.1118/1.3395553
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发表时间：
2010-06-01
期刊：
影响因子：
3.8
通讯作者：
Navon, G.
中科院分区：
文献类型：
--
作者：
Hertzberg, Y.;Volovick, A.;Navon, G.
目的：磁共振引导下的超声治疗是一种有前途的微创技术，临床应用范围不断扩大。高度期望以最佳强度将聚焦超声（FUS）能量递送到目标点;然而，由于组织像差，并不总是实现最佳聚焦强度。特别是在经颅应用中，声波主要通过颅骨移位和扭曲。为了验证磁共振声辐射力成像（MR-ARFI）可以用作经颅治疗中的聚焦工具，通过离体人颅骨在猪脑上体内应用这种成像。方法：采用GE 1.5 T扫描仪，配备InSightec FUS系统Experimate 2000和Experimate 4000，采集MR ARFI图像，并进行分析。成像采用MR-ARFI序列行扫描自旋回波和单次激发梯度回波回波平面回波。两次采集的平面内分辨率均为0.9 x 0.9 mm（2）。MR-ARFI图像的总采集时间行扫描序列为31 s，回波平面序列为1 s。使用FUS换能器进行体内实验，FUS换能器由1024个超声发射压电元件以220 kHz频率构建。将换能器聚焦到猪的大脑中，猪被包裹在人的头骨中，在脱气的水环境中，以类似于人的治疗。猪接受了宽双侧颅骨切除术，以防止超声波束引起的骨加热。两个聚焦实验中进行的幻影使用1 MHz和710 kHz的FUS换能器工作与208和225元素，分别。在第一个实验中，通过将随机相位添加到换能器的相位图来虚拟地将像差添加到装置。一个简单的聚焦校正方案，其中一组元件的校正相位被选择为使得它最大化在焦点处的辐射力。在第二个实验中，由人的头骨的像差进行了校正，使用几何和相位为基础的调整段transducer.Results：一个最大的位移为10 μ m，获得使用1.4千瓦的声功率在生猪的头部，其头骨被删除，并取代了离体人的头骨。使用MR-ARFI的像差校正导致接近最佳焦点，因为辐射力与无像差情况相似。经颅，MR-ARFI为基础的畸变校正比CT为基础的畸变校正，目前使用的技术，在脑FUS treatment.Conclusions：在目前的工作中，作者首次显示了MR-ARFI的结果在活脑通过离体人类颅骨。他们已经证明，可以通过测量焦点处的辐射力，使用MR-ARFI进行像差校正。使用MR-ARFI进行像差校正是一种很有前途的经颅聚焦无创技术，可获得接近最佳的聚焦和更可靠、更安全的脑部FUS治疗。(C)2010年美国医学物理学家协会。[DOI：10.1118/1.3395553]
Purpose: Magnetic resonance guided ultrasonic therapy is a promising minimally invasive technology for constantly growing variety of clinical applications. Delivery of focused ultrasound (FUS) energy to the targeted point with optimal intensity is highly desired; however, due to tissue aberrations, optimal focal intensity is not always achieved. Especially in transcranial applications, the acoustic waves are shifted and distorted mainly by the skull. In order to verify that magnetic resonance acoustic radiation force imaging (MR-ARFI) can be used as a focusing tool in transcranial treatments, such an imaging was applied in vivo on a porcine brain via ex vivo human skull. Then, by the use of MR-ARFI technique, an improved ultrasound focusing algorithm is proposed and demonstrated for both transcranial and none brain applications.Methods: MR-ARFI images were acquired on a GE 1.5 T scanner equipped with InSightec FUS systems ExAblate 2000 and ExAblate 4000. Imaging was performed with MR-ARFI sequences of line-scan spin-echo and single-shot gradient-echo echo-planar. The in-plane resolution of both acquisitions was 0.9 x 0.9 mm(2). The total acquisition time of MR-ARFI image was 31 s by the line-scan sequence and 1 s by the echo-planar sequence. An in vivo experiment was performed using FUS transducer, which is built out of 1024 ultrasound transmitting piezoelectric elements at 220 kHz frequency. The transducer was focused into the brain of a pig, which was wrapped in a human skull, in degassed water environment to resemble human treatments. The pig underwent a wide bilateral craniectomy to prevent a bone heating from the ultrasound beams. Two focusing experiments were performed in phantoms using 1 MHz and 710 kHz FUS transducers working with 208 and 225 elements, respectively. In the first experiment, aberration was added virtually to the apparatus by adding random phases to the phase map of the transducer. A simple focusing correction scheme was used, in which the corrected phase of a group of elements was chosen such that it maximizes the radiation force at the focal point. In the second experiment, aberrations made by a human skull were corrected using geometrical and phase based adjustments on segments of the transducer.Results: A maximum displacement of 10 mu m was obtained using 1.4 kW acoustic power on a live pig's head that its skull was removed and replaced by ex vivo human skull. Aberration correction using MR-ARFI resulted in near optimal focus, as the radiation force was similar to the nonaberration case. Transcranial, MR-ARFI based aberration correction performed better than CT based aberration correction, a technique that is currently used in brain FUS treatments.Conclusions: In the present work, the authors show for the first time a result of MR-ARFI in a live brain through ex vivo human skull. They have demonstrated that aberration correction could be done using MR-ARFI by measuring the radiation force at the focal point. Aberration correction using MR-ARFI is a promising noninvasive technique for transcranial focusing, which may result in near optimal focus and more reliable and safer brain FUS treatments. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3395553]