Duan Yunsuo, Peterson Bradley S, Liu Feng, Brown Truman R, Ibrahim Tamer S, Kangarlu Alayar
Department of Psychiatry, Columbia University, New York, New York, USA.
J Magn Reson Imaging. 2009 Jan;29(1):13-22. doi: 10.1002/jmri.21509.
To optimize the homogeneity and efficiency of the B(1) magnetic field of a four-ring birdcage head coil that is double-tuned at the Larmor frequencies of both (31)P and (1)H and optimized to acquire magnetic resonance spectroscopy (MRS) data at 3T for the study of infants.
We developed a finite difference time domain (FDTD) tool in-house to iteratively compute and seek the range of geometric and electromagnetic parameters of a dual-tuned, four-ring birdcage coil that would produce the desired resonance patterns, optimize homogeneity of the B(1)-field, and maximize efficiency of the coil. To demonstrate the validity of our computational results, we constructed three RF coils: one dual-tuned coil that was based on the calculated optimized parameters and two single-tuned coils that had dimensions similar to those of the dual-tuned coil, but tuned at the Larmor frequencies of both (31)P and (1)H, respectively. We then tested and compared the performances of the dual-tuned coil and single-tuned coils at both of these frequencies.
We found that a dual-tuned, four-ring birdcage coil with a diameter of 180 mm, an inner birdcage length of 100-300 mm, and an outer birdcage length of 25-100 mm produces the desired resonance patterns. For the use of this coil with human infants, optimization of the homogeneity of the B(1) field, combined with improved coil efficiency, yielded a dual-tuned birdcage coil with diameter of 180mm, an inner birdcage length of 150 mm, an outer birdcage length of 25 mm, and corresponding inner and outer capacitances of 17.2 pF and 7.6 pF, respectively. The experimental results from a constructed coil having the same parameters with the modeled coil agreed well with the computational results from the modeled coil. This optimized design overcame the deficiencies of existing dual-tuned, four-ring birdcage coils.
The homogeneity and efficiency of the B(1) field for (31)P/(1)H dual-tuned, four-ring birdcage coils can be optimized well using our FDTD tool, especially at high static magnetic fields (B(0)).
优化一种四环鸟笼式头部线圈的B(1)磁场的均匀性和效率，该线圈在(31)P和(1)H的拉莫尔频率下进行双调谐，并进行了优化，以在3T磁场下采集磁共振波谱（MRS）数据用于婴儿研究。
我们自行开发了一种时域有限差分（FDTD）工具，用于迭代计算并寻找双调谐四环鸟笼式线圈的几何和电磁参数范围，该范围应能产生所需的共振模式、优化B(1)场的均匀性并使线圈效率最大化。为了证明我们计算结果的有效性，我们构建了三个射频线圈：一个基于计算出的优化参数的双调谐线圈，以及两个单调谐线圈，其尺寸与双调谐线圈相似，但分别在(31)P和(1)H的拉莫尔频率下进行调谐。然后我们在这两个频率下测试并比较了双调谐线圈和单调谐线圈的性能。
我们发现，直径为180mm、内鸟笼长度为100 - 300mm、外鸟笼长度为25 - 100mm的双调谐四环鸟笼式线圈能产生所需的共振模式。对于该线圈在人类婴儿中的应用，B(1)场均匀性的优化与线圈效率的提高相结合，得到了一个直径为180mm、内鸟笼长度为150mm、外鸟笼长度为25mm、相应的内电容和外电容分别为17.2pF和7.6pF的双调谐鸟笼式线圈。构建的与模型线圈具有相同参数的线圈的实验结果与模型线圈的计算结果吻合良好。这种优化设计克服了现有双调谐四环鸟笼式线圈的缺陷。
使用我们的FDTD工具可以很好地优化(31)P/(1)H双调谐四环鸟笼式线圈的B(1)场的均匀性和效率，尤其是在高静磁场（B(0)）下。
