Department of Radiology, School of Medicine, Stanford University, Stanford, CA, USA.
Insightec Inc., Dallas, TX, USA.
Int J Hyperthermia. 2021;38(1):22-29. doi: 10.1080/02656736.2020.1867242.
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.
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.
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 = 0.96 °C ± 0.55 °C for the body coil to σ = 0.41 °C ± 0.24 °C for the head coil.
Greater SNR from the dual-channel head coil provides access to better treatment day visualization for treatment planning and higher precision intra-operative thermometry.
经颅磁共振引导聚焦超声（tcMRgFUS）消融靶点距离关键神经结构<5mm，因此需要改进磁共振成像和测温技术。本研究旨在评估专为集成 tcMRgFUS 而设计的双通道射频接收式头线圈的性能。
使用 3T MRI 和 ExAblate Neuro 系统（以色列 INSIGHTEC 公司）进行成像。灵敏度图确定了接收式线圈的均匀性。通过志愿者在换能器头盔中的 1）T2 加权成像和 2）多回波磁共振测温，在丘脑水平对头线圈和容积体线圈进行了比较。在加热体模中采集了 40W、24s 的热声脉冲。构建了热图以评估温度不确定性、焦点加热和温度演化。
归一化信号强度的变化高达 35%。在 T2wFSE 图像上，使用头线圈时轴向平面的 SNR 提高了 4 倍，矢状面和冠状面提高了 3 倍。与体线圈相比，头线圈提供了更好的丘脑和苍白球（轴向）以及前/后连合、脑干/小脑（矢状面）的可视化效果。磁共振测温显示在丘脑处 SNR 提高了 4 倍。测温显示焦点斑点保持不变，温度升高 20°C。体线圈的平均温度不确定性（平均值±标准差）从σ=0.96°C±0.55°C 降低到头线圈的σ=0.41°C±0.24°C。
双通道头线圈的更高 SNR 可实现更好的治疗日可视化，有助于治疗计划和术中更高精度的测温。
