The performance of interventional loopless MRI antennae at higher magnetic field strengths
The performance of interventional loopless MRI antennae at higher magnetic field strengths
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DOI：
10.1118/1.2905027
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发表时间：
2008-05-01
期刊：
影响因子：
3.8
通讯作者：
Bottomley, Paul A.
中科院分区：
文献类型：
--
作者：
El-Sharkawy, AbdEl-Monem M.;Qian, Di;Bottomley, Paul A.
介入性“无环天线”MRI探测器目前仅限于1.5 T。本研究调查了无环天线是否在更高的场提供信噪比（SNR）和视场（FOV）优势，以及器械加热是否可以控制在安全范围内。从0.5到5 T的无环天线的绝对SNR性能的研究分析，使用电磁（EM）偶极天线理论，和数值与EM矩量法，并发现几乎二次变化的场强取决于介质的电性能，噪声主要由直接样品传导损耗。预测证实了绝对SNR的测量低损耗无环天线制造的1.5，3，和4.7 T，浸泡在生理上相当的盐水。与1.5 T相比，在3 T和4.7 T下分别观察到SNR增益为3.8 +/- 0.2倍和9.7 +/- 0.3倍，有用FOV面积增益约为10倍和50倍。使用重新设计的去耦电路制造的3 T生物相容性镍钛合金水循环微波消融针的热测试显示，在高MRI暴露水平下运行的MRI的最大致热接近1 ℃。家兔主动脉实验证实了3 T水循环微波消融针相对于同品种市售1.5 T器械的SNR和FOV优势。这项工作是第一次研究实验性内部MRI探测器在1.5 T以上的性能。实现的大SNR和FOV增益为血管病理学和MRI引导介入的高分辨率成像提供了重要机会。(C)2008年美国医学物理学家协会。
Interventional, "loopless antenna" MRI detectors are currently limited to 1.5 T. This study investigates whether loopless antennae offer signal-to-noise ratio (SNR) and field-of-view (FOV) advantages at higher fields, and whether device heating can be controlled within safe limits. The absolute SNR performance of loopless antennae from 0.5 to 5 T is investigated both analytically, using electromagnetic (EM) dipole antenna theory, and numerically with the EM method of moments, and found to vary almost quadratically with field strength depending on the medium's electrical properties, the noise being dominated by direct sample conduction losses. The prediction is confirmed by measurements of the absolute SNR of low-loss loopless antennae fabricated for 1.5, 3, and 4.7 T, immersed in physiologically comparable saline. Gains of 3.8 +/- 0.2- and 9.7 +/- 0.3-fold in SNR, and approximately 10- and 50-fold gains in the useful FOV area are observed at 3 and 4.7 T, respectively, compared to 1.5 T. Heat testing of a 3 T biocompatible nitinol-antenna fabricated with a redesigned decoupling circuit shows maximum heating of similar to 1 degrees C for MRI operating at high MRI exposure levels. Experiments in the rabbit aorta confirm the SNR and FOV advantages of the 3 T antenna versus an equivalent commercial 1.5 T device in vivo. This work is the first to study the performance of experimental internal MRI detectors above 1.5 T. The large SNR and FOV gains realized present a major opportunity for high-resolution imaging of vascular pathology and MRI-guided intervention. (C) 2008 American Association of Physicists in Medicine.