Application of Zernike polynomials towards accelerated adaptive focusing of transcranial high intensity focused ultrasound
Application of Zernike polynomials towards accelerated adaptive focusing of transcranial high intensity focused ultrasound
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DOI：
10.1118/1.4752085
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发表时间：
2012-10-01
期刊：
影响因子：
3.8
通讯作者：
Pauly, Kim Butts
中科院分区：
文献类型：
--
作者：
Kaye, Elena A.;Hertzberg, Yoni;Pauly, Kim Butts
目的：研究经颅磁共振引导聚焦超声手术(MRgFUS)中人体头骨产生的位相像差，论证Zernike多项式(ZPs)加速自适应聚焦过程的潜力，并探讨利用先前研究中获得的位相校正为新数据集的校正提供初始猜测的益处。方法：根据临床原型半球换能器进行经颅MRgFUS治疗时获得的头部CT图像，计算所分析的五个位相像差数据集。非迭代自适应聚焦算法[Larrat等人，“MR引导的超声自适应聚焦”，IEEE Trans.超音波。铁电。弗雷克。Control 57(8)，1734-1747(2010)]被修改，将Hadamard编码替换为Zernike编码。该算法在仿真中进行了测试，以校正患者的相位像差。利用磁共振声辐射力成像(MR-ARFI)技术研究了位相像差校正对半球形换能器聚焦的影响。此外，还研究了两种基于先前患者数据构造初始相位校正估计的方法。通过测量Zernike算法中初始估计值对焦点处的超声强度以及达到无像差情况下90%的强度所需的ZP模数的影响，分析了初始估计值的益处。结果：多对相位像差数据集的协方差显示了几个患者的像差数据之间的高度相关性，并建议可以基于相关程度来划分子组。对基于Zernike算法的仿真结果表明，ZPS的低阶模式具有更好的整体校正效果。使用不到170个模式的ZPS，焦点强度达到了90%的无像差强度。通过对不同亚组受试者的位相像差数据进行平均，初步估计出5个受试者的焦点处的强度都有所增加。结论：ZPS用于位相像差校正有利于经颅超声的自适应聚焦。基于颅骨的相位像差被发现很好地近似于ZP模式的数量，仅代表半球换能器中元件数量的一小部分。将初始相位像差估计与基于Zernike的算法一起实施可用于提高稳健性，并潜在地极大地提高用于临床经颅MRgFUS治疗的基于MR-ARFI的聚焦的可行性。(C)2012年美国医学物理学家协会。[http://dx.doi.org/10.1118/1.4752085]
Purpose: To study the phase aberrations produced by human skulls during transcranial magnetic resonance imaging guided focused ultrasound surgery (MRgFUS), to demonstrate the potential of Zernike polynomials (ZPs) to accelerate the adaptive focusing process, and to investigate the benefits of using phase corrections obtained in previous studies to provide the initial guess for correction of a new data set.Methods: The five phase aberration data sets, analyzed here, were calculated based on preoperative computerized tomography (CT) images of the head obtained during previous transcranial MRgFUS treatments performed using a clinical prototype hemispherical transducer. The noniterative adaptive focusing algorithm [Larrat et al., "MR-guided adaptive focusing of ultrasound," IEEE Trans. Ultrason. Ferroelectr. Freq. Control 57(8), 1734-1747 (2010)] was modified by replacing Hadamard encoding with Zernike encoding. The algorithm was tested in simulations to correct the patients' phase aberrations. MR acoustic radiation force imaging (MR-ARFI) was used to visualize the effect of the phase aberration correction on the focusing of a hemispherical transducer. In addition, two methods for constructing initial phase correction estimate based on previous patient's data were investigated. The benefits of the initial estimates in the Zernike-based algorithm were analyzed by measuring their effect on the ultrasound intensity at the focus and on the number of ZP modes necessary to achieve 90% of the intensity of the nonaberrated case.Results: Covariance of the pairs of the phase aberrations data sets showed high correlation between aberration data of several patients and suggested that subgroups can be based on level of correlation. Simulation of the Zernike-based algorithm demonstrated the overall greater correction effectiveness of the low modes of ZPs. The focal intensity achieves 90% of nonaberrated intensity using fewer than 170 modes of ZPs. The initial estimates based on using the average of the phase aberration data from the individual subgroups of subjects was shown to increase the intensity at the focal spot for the five subjects.Conclusions: The application of ZPs to phase aberration correction was shown to be beneficial for adaptive focusing of transcranial ultrasound. The skull-based phase aberrations were found to be well approximated by the number of ZP modes representing only a fraction of the number of elements in the hemispherical transducer. Implementing the initial phase aberration estimate together with Zernike-based algorithm can be used to improve the robustness and can potentially greatly increase the viability of MR-ARFI-based focusing for a clinical transcranial MRgFUS therapy. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4752085]