Treatment envelope evaluation in transcranial magnetic resonance-guided focused ultrasound utilizing 3D MR thermometry.
Treatment envelope evaluation in transcranial magnetic resonance-guided focused ultrasound utilizing 3D MR thermometry.
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DOI：
10.1186/2050-5736-2-19
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Parker DL
中科院分区：
文献类型：
--
作者：
Odéen H;de Bever J;Almquist S;Farrer A;Todd N;Payne A;Snell JW;Christensen DA;Parker DL
目前的经颅磁共振引导聚焦超声(TcMRgFUS)的临床靶点都位于颅骨凸起的几何中心附近，这最大限度地减少了通过颅骨聚焦超声的挑战。必须达到非中枢靶点才能治疗更广泛的神经疾病和实体肿瘤。以前已经利用二维(2D)磁共振(MR)测温进行了治疗包络研究，以确定目前可以提供治疗水平的FUS的区域。由于使用了2D磁共振测温技术，因此可以推断的关于近场组织/骨界面意外加热的信息非常有限。在这篇文章中，我们提出了一项概念验证治疗包络研究，使用三维(3D)磁共振测温技术监测在体模和羔羊模型中进行的FUS加热。虽然所使用的中等尺寸换能器不是为经颅几何形状而设计的，但3D温度图能够监控整个超声视野，包括焦点和近场组织/骨界面，以全面描述可能发生的所有加热。三维磁共振测温是通过k空间子采样和前面描述的时间约束重建方法的组合来实现的。我们提出了两种不同类型的治疗信封。第一种方法仅基于焦点加热--这种类型可以从2D磁共振测温中得出。第二类是基于相对近场加热，计算为焦斑加热与近场加热之比。这利用了在这项研究中获得的完整的3D磁共振测温数据。结果表明，三维磁共振测温技术可用于改善治疗包络评价中的安全性评价。使用非最佳换能器，它表明，如第一类包络所建议的那样，可以提供治疗水平的FUS的某些区域，由于发生了意想不到的近场加热量，不一定得到安全治疗。这项研究的结果强调了在tcMRgFUS中进行3D MR测温的必要性。
Current clinical targets for transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) are all located close to the geometric center of the skull convexity, which minimizes challenges related to focusing the ultrasound through the skull bone. Non-central targets will have to be reached to treat a wider variety of neurological disorders and solid tumors. Treatment envelope studies utilizing two-dimensional (2D) magnetic resonance (MR) thermometry have previously been performed to determine the regions in which therapeutic levels of FUS can currently be delivered. Since 2D MR thermometry was used, very limited information about unintended heating in near-field tissue/bone interfaces could be deduced. In this paper, we present a proof-of-concept treatment envelope study with three-dimensional (3D) MR thermometry monitoring of FUS heatings performed in a phantom and a lamb model. While the moderate-sized transducer used was not designed for transcranial geometries, the 3D temperature maps enable monitoring of the entire sonication field of view, including both the focal spot and near-field tissue/bone interfaces, for full characterization of all heating that may occur. 3D MR thermometry is achieved by a combination of k-space subsampling and a previously described temporally constrained reconstruction method. We present two different types of treatment envelopes. The first is based only on the focal spot heating—the type that can be derived from 2D MR thermometry. The second type is based on the relative near-field heating and is calculated as the ratio between the focal spot heating and the near-field heating. This utilizes the full 3D MR thermometry data achieved in this study. It is shown that 3D MR thermometry can be used to improve the safety assessment in treatment envelope evaluations. Using a non-optimal transducer, it is shown that some regions where therapeutic levels of FUS can be delivered, as suggested by the first type of envelope, are not necessarily safely treated due to the amount of unintended near-field heating occurring. The results presented in this study highlight the need for 3D MR thermometry in tcMRgFUS.