目的:评估了射频(RF)功率放大器(RFPA)的漂移,并研究了几个影响因素。提出了两种前瞻性校正漂移的方法,并对其有效性进行了评估。
方法:RFPA漂移评估包括脉冲内和脉冲间漂移分析。具有不同翻转角(FA)的扫描协议,射频长度,和脉冲重复时间(TR)用于测量这些参数对漂移的影响。定向耦合器(DICO)监测RFPA输出的正向波形。DICO数据被存储用于评估,允许计算校正因子以调整RFPA传输电压。两种校正方法,预测和运行时,采用:预测校正需要校准扫描,而运行时校正计算正在进行的扫描期间的因素。
结果:RFPA漂移确实受到RF占空比的影响,在最大占空比为66%的情况下,潜在漂移约为41%或15%,取决于特定的RFPA修订版。值得注意的是,在低传输电压情况下,FA对RFPA漂移的影响最小。预测和运行时漂移校正技术的应用有效地将平均漂移从10.0%降低到小于1%,增强MR信号的稳定性。
结论:利用DICO记录和实施反馈机制可以对RFPA漂移进行前瞻性校正。进行校准扫描,预测校正可以以较低的复杂度使用;为了增强性能,可以采用运行时方法。
OBJECTIVE: The
drift in radiofrequency (RF) power amplifiers (RFPAs) is assessed and several contributing factors are investigated. Two approaches for prospective correction of
drift are proposed and their effectiveness is evaluated.
METHODS: RFPA
drift assessment encompasses both intra-pulse and inter-pulse
drift analyses. Scan protocols with varying flip angle (FA), RF length, and pulse repetition time (TR) are used to gauge the influence of these parameters on drift. Directional couplers (DICOs) monitor the forward waveforms of the RFPA outputs. DICOs data is stored for evaluation, allowing calculation of correction factors to adjust RFPAs\' transmit voltage. Two correction methods, predictive and run-time, are employed: predictive correction necessitates a calibration scan, while run-time correction calculates factors during the ongoing scan.
RESULTS: RFPA drift is indeed influenced by the RF duty-cycle, and in the cases examined with a maximum duty-cycle of 66%, the potential drift is approximately 41% or 15%, depending on the specific RFPA revision. Notably, in low transmit voltage scenarios, FA has minimal impact on RFPA
drift. The application of predictive and run-time drift correction techniques effectively reduces the average
drift from 10.0% to less than 1%, resulting in enhanced MR signal stability.
CONCLUSIONS: Utilizing DICO recordings and implementing a feedback mechanism enable the prospective correction of RFPA drift. Having a calibration scan, predictive correction can be utilized with fewer complexity; for enhanced performance, a run-time approach can be employed.