Abstract

Background

Trans-cranial MR guided focused ultrasound (tcMRgFUS) ablation targets are <5mm from critical neurological structures, creating a need for improved MR imaging and thermometry. The purpose of this study was to evaluate the performance of a dual-channel radiofrequency receive-only head coil designed specifically for integrated use in tcMRgFUS.

Methods

Imaging used a 3 T MRI and the ExAblate Neuro System (INSIGHTEC Inc., Israel). Sensitivity maps determined receive-only coil uniformity. The head coil was compared to the volume body coil at the level of the thalamus using 1) T2-weighted imaging and 2) multi-echo MR thermometry of volunteers in the transducer helmet. Thermal sonications (40 W, 24s) were acquired in a heating phantom. Thermal maps in were constructed to evaluate temperature uncertainty, focal heating, and temperature evolution.

Results

The normalized signal intensity showed up to a 35% variation. On T2wFSE images the SNR with the head coil is improved by 4x in the axial plane, and 3x in sagittal and coronal planes. The head coil provided better visualization of the thalamus and globus pallidus (axial), and of the anterior/posterior commissure, and brain stem/cerebellum (sagittal) compared to the body coil. MR thermometry showed a 4x gain in SNR in the thalamus. Thermometry showed a preserved focal spot with 20 °C temperature rise. The average temperature uncertainty (mean ± std) was reduced from σ _T = 0.96 °C ± 0.55 °C for the body coil to σ _T = 0.41 °C ± 0.24 °C for the head coil.

Conclusions

Greater SNR from the dual-channel head coil provides access to better treatment day visualization for treatment planning and higher precision intra-operative thermometry.

中文翻译：

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对用于功能性神经外科的经颅MR引导聚焦超声的MRI接收头线圈的评估

摘要

背景

经颅MR引导的聚焦超声（tcMRgFUS）消融目标距离关键的神经结构不到5毫米，因此需要改进MR成像和测温。这项研究的目的是评估专门为集成在tcMRgFUS中使用而设计的双通道射频仅接收磁头线圈的性能。

方法

成像使用3 T MRI和ExAblate神经系统（以色列INSIGHTEC Inc.）。灵敏度图确定了仅接收线圈的均匀性。使用1）T2加权成像和2）换能器头盔中志愿者的多回波MR测温，将头线圈与丘脑水平的体线圈进行比较。在加热体模中获得热超声（40 W，24s）。构建了热图以评估温度不确定性，焦点加热和温度变化。

结果

归一化的信号强度显示高达35％的变化。在T2wFSE图像上，头部线圈的SNR在轴向平面中提高了4倍，在矢状和冠状平面中提高了3倍。与身体线圈相比，头线圈可更好地显示丘脑和苍白球（轴向），前/后连合以及脑干/小脑（矢状）。MR测温显示丘脑的SNR增长了4倍。测温显示温度上升20°C时保留的焦点。的平均温度的不确定性（平均值±标准）从σ减小_Ť = 0.96℃，±0.55℃，体线圈到σ _Ť = 0.41℃，±0.24℃，头部线圈。

结论

双通道头线圈的信噪比更高，可以更好地观察治疗日，以制定治疗计划和更高精度的术中体温计。