Electrodynamics and ultimate SNR in parallel MR imaging
Electrodynamics and ultimate SNR in parallel MR imaging
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DOI：
10.1002/mrm.20183
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发表时间：
2004-08-01
影响因子：
3.3
通讯作者：
Pruessmann, KP
中科院分区：
文献类型：
--
作者：
Wiesinger, F;Boesiger, P;Pruessmann, KP
本文的目的是阐明并行MRI性能的固有局限性。研究的重点是极限信噪比（SNR），它是指信号检测过程的电动力学所允许的最大信噪比。利用球形模型对象，结果表明，在平行成像中，最终信噪比的行为对加速度有明显的限制。对于低加速和中等加速，最终的信噪比性能几乎是最佳的，几何因子接近1。然而，对于超过临界值的高压缩因子，最终性能迅速恶化，对应于几何因子的指数增长。从最佳性能到恶化性能的转变取决于被检测射频场的电动力学特性。在近场条件下，即对于低B-o和小物体尺寸，球体内一维加速度的临界折减因子是恒定的，近似等于4。在远场波域中，临界折减系数较大，且随B-o和物体尺寸的增大而增大。因此，平行成像技术在人体高场核磁共振成像中具有特殊的应用前景。
The purpose of this article is to elucidate inherent limitations to the performance of parallel MRI. The study focuses on the ultimate signal-to-noise ratio (SNR), which refers to the maximum SNR permitted by the electrodynamics of the signal detection process. Using a spherical model object, it is shown that the behavior of the ultimate SNR imposes distinct limits on the acceleration rate in parallel imaging. For low and moderate acceleration, the ultimate SNR performance is nearly optimal, with geometry factors close to 1. However, for high reduction factors beyond a critical value, the ultimate performance deteriorates rapidly, corresponding to exponential growth of the geometry factor. The transition from optimal to deteriorating performance depends on the electrodynamic characteristics of the detected RF fields. In the near-field regime, i.e., for low B-o and small object size, the critical reduction factor is constant and approximately equal to four for 1D acceleration in the sphere. In the far-field wave regime the critical reduction factor is larger and increases both with B-o and object size. Therefore, it is concluded that parallel techniques hold particular promise for human MR imaging at very high field.