Felder Jörg, Zimmermann Markus, Shah N Jon
Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Jülich, Germany.
Faculty of Medicine, RWTH Aachen University, Aachen, Germany.
Magn Reson Med. 2025 Mar;93(3):1298-1305. doi: 10.1002/mrm.30349. Epub 2024 Oct 27.
Demonstration of a high dynamic-range and high SNR method for acquiring absolute maps from a combination of gradient echo and actual-flip-angle measurements that is especially useful during the construction of parallel-transmit arrays.
Low flip angle gradient echo images, acquired when transmitting with each channel individually, are used to compute relative maps. Instead of computing these in a conventional manner, the equivalence of the problem to the ESPIRiT parallel image reconstruction method is used to compute maps with a higher SNR. Absolute maps are generated by calibration against a single actual flip-angle acquisition when transmitting on all channels simultaneously.
Depending on the number of receiver channels and the location of the receive elements with respect to the subject being investigated, moderate to high gains in the SNR of the acquired maps can be achieved.
The proposed method is especially suited for the acquisition of maps during the construction of transceiver arrays. Compared to the original method, maps with higher SNR can be computed without the need for additional measurements, and maps can also be generated using previously acquired data. Furthermore, easy adoption and fast estimation of receiver channels is possible because of existing highly optimized open-source implementations of ESPIRiT, such as in the BART toolbox.
演示一种高动态范围和高信噪比的方法，用于从梯度回波和实际翻转角测量的组合中获取绝对图谱，该方法在并行发射阵列构建过程中特别有用。
在单独使用每个通道进行发射时采集的低翻转角梯度回波图像，用于计算相对图谱。不是以传统方式计算这些图谱，而是利用该问题与ESPIRiT并行图像重建方法的等效性来计算具有更高信噪比的图谱。通过在所有通道同时发射时针对单个实际翻转角采集进行校准来生成绝对图谱。
根据接收通道的数量以及接收元件相对于被研究对象的位置，可以在采集的图谱信噪比方面实现中等至高增益。
所提出的方法特别适用于收发器阵列构建过程中的图谱采集。与原始方法相比，无需额外测量即可计算出具有更高信噪比的图谱，并且还可以使用先前采集的数据生成图谱。此外，由于ESPIRiT现有高度优化的开源实现，如在BART工具箱中，因此可以轻松采用并快速估计接收通道。
