Gorny Krzysztof R, Hangiandreou Nicholas J, Ward Heidi A, Hesley Gina K, Brown Douglas L, Felmlee Joel P
Department of Radiology, Mayo Clinic, Rochester, MN 55905, USA.
Phys Med Biol. 2009 Apr 7;54(7):N83-91. doi: 10.1088/0031-9155/54/7/N01. Epub 2009 Mar 5.
During MRI-guided focused ultrasound (MRgFUS) treatments of uterine fibroids using ExAblate 2000, tissue ablations are delivered by a FUS transducer while MR imaging is performed with a pelvic receiver coil. The consistency of the pelvic coil performance is crucial for reliable MR temperature measurements as well as detailed anatomic imaging in patients. Test sonications in a gel phantom combined with MR thermometry are used to test the performance of the FUS transducer prior to each treatment. As we show, however, these tests do not adequately evaluate receiver coil performance prior to clinical use. This could become a problem since the posterior part of the coil is frequently moved and can malfunction. The aim of this work is to demonstrate the utility of the signal-to-noise ratio (SNR) as a reliable indicator of pelvic coil performance. Slight modification of the vendor-provided coil support was accomplished to assure reproducible coil positioning. The SNR was measured in a gel phantom using axial acquisitions from the 3D-localizer scan. MR temperature and SNR measurements were obtained using a degraded receiver coil (with posterior element removed) and a known faulty coil, and compared to those obtained with a fully functioning coil. While the MR temperature-based tests were insensitive to change in pelvic coil performance, (degraded, p = 0.24; faulty, p = 0.28), the SNR tests were highly sensitive to coil performance, (degraded, p < 0.001; faulty, p < 0.001). Additional clinical data illustrate the utility of SNR testing of the receiver coil. These tests require minimal (or possibly no) additional scan time and have proven to be effective in our clinical practice.
在使用ExAblate 2000进行磁共振成像引导聚焦超声（MRgFUS）治疗子宫肌瘤的过程中，组织消融由聚焦超声换能器完成，同时使用盆腔接收线圈进行磁共振成像。盆腔线圈性能的一致性对于可靠的磁共振温度测量以及患者详细的解剖成像至关重要。在每次治疗前，会在凝胶体模中进行测试超声并结合磁共振温度测量来测试聚焦超声换能器的性能。然而，正如我们所展示的，这些测试在临床使用前并不能充分评估接收线圈的性能。这可能会成为一个问题，因为线圈的后部经常移动且可能出现故障。这项工作的目的是证明信噪比（SNR）作为盆腔线圈性能可靠指标的实用性。对供应商提供的线圈支架进行了轻微修改，以确保线圈定位可重复。在凝胶体模中使用来自三维定位扫描的轴向采集测量信噪比。使用一个退化的接收线圈（移除了后部元件）和一个已知有故障的线圈获得磁共振温度和信噪比测量值，并与使用功能正常的线圈获得的测量值进行比较。基于磁共振温度的测试对盆腔线圈性能的变化不敏感（退化，p = 0.24；有故障，p = 0.28），而信噪比测试对线圈性能高度敏感（退化，p < 0.001；有故障，p < 0.001）。更多临床数据说明了接收线圈信噪比测试的实用性。这些测试所需的额外扫描时间最少（或可能不需要），并且在我们的临床实践中已被证明是有效的。
