Signal-to-noise ratio and absorbed power as functions of main magnetic field strength, and definition of "90°" RF pulse for the head in the birdcage coil
Signal-to-noise ratio and absorbed power as functions of main magnetic field strength, and definition of "90°" RF pulse for the head in the birdcage coil
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DOI：
10.1002/mrm.1091
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发表时间：
2001-04-01
影响因子：
3.3
通讯作者：
Smith, MB
中科院分区：
文献类型：
--
作者：
Collins, CM;Smith, MB
针对理想化鸟笼线圈中的头部模型，计算了RF磁场（B-1）随64 MHz和345 MHz之间频率的变化。使用定义激励脉冲振幅的三种不同方法计算每个频率下的吸收功率（P-abs）和SNR：在线圈中心保持90度翻转角（中心α = pi /2），最大化FID振幅（Max，A（FID）），以及最大化重建图像中的总信号振幅（Max，A（图像））。对于中心alpha = pi /2和Max. A（图像），SNR随着场强的增加而线性增加，直到260 MHz，在那里它开始以更大的速率增加。对于这两种方法，P-abs持续增加，但在较高的场强下以较低的速率增加。在215 MHz以上的人头部MRI中，使用FID幅度来设置B-1激励脉冲可能导致SNR和功率要求随着静态场强的增加而明显降低。Magn Reson Med 45：684-691，2001. (C)2001 Wiley-Liss，Inc.
Calculations of the RF magnetic (B-1) field as a function of frequency between 64 and 345 MHz were performed for a head model in an idealized birdcage coil. Absorbed power (P-abs) and SNR were calculated at each frequency with three different methods of defining excitation pulse amplitude: maintaining 90 degrees flip angle at the coil center (center alpha = pi /2), maximizing FID amplitude (Max, A(FID)), and maximizing total signal amplitude in a reconstructed image (Max, A(image)). For center alpha = pi /2 and Max. A(image), SNR increases linearly with increasing field strength until 260 MHz, where it begins to increase at a greater rate. For these two methods, P-abs increases continually, but at a lower rate at higher field strengths. Above 215 MHz in MRI of the human head, the use of FID amplitude to set B-1 excitation pulses may result in apparent decreases in SNR and power requirements with increasing static field strength. Magn Reson Med 45:684-691, 2001. (C) 2001 Wiley-Liss, Inc.