Yeung Kylie, Ng Kher Lik, McGing Jordan J, Axford Aaron, Birkhoelzer Sarah, Shinozaki Ayaka, Ricchi Mattia, Sgambelluri Noemi, Zaccagna Fulvio, Mills Rebecca, Lewis Andrew J M, Rayner Jennifer J, Ravetz Zack, Berner Lise, Jacob Kenneth, McIntyre Anthony, Durrant Marianne, Rider Oliver J, Schulte Rolf F, Gleeson Fergus V, Tyler Damian J, Grist James T
Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, UK.
Department of Oncology, University of Oxford, Oxford, UK.
Magn Reson Med. 2025 Apr;93(4):1615-1628. doi: 10.1002/mrm.30378. Epub 2024 Nov 17.
The purpose of this work is to validate a simple and versatile integrated variable flip angle (VFA) method for mapping B in hyperpolarized MRI, which can be used to correct signal variations due to coil inhomogeneity.
Simulations were run to assess performance of the VFA B mapping method compared to the currently used constant flip angle (CFA) approach. Simulation results were used to inform the design of VFA sequences, validated in four volunteers for hyperpolarized xenon-129 imaging of the lungs and another four volunteers for hyperpolarized carbon-13 imaging of the human brain. B maps obtained were used to correct transmit and receive inhomogeneity in the images.
Simulations showed improved performance of the VFA approach over the CFA approach with reduced sensitivity to T. For xenon-129, the B maps accurately reflected the variation of signal depolarization, but in some cases could not be used to correct for coil receive inhomogeneity due to a lack of transmit-receive reciprocity resulting from suboptimal coil positioning. For carbon-13, the B maps showed good agreement with a separately acquired B map of a phantom and were effectively used to correct coil-induced signal inhomogeneity.
A simple, versatile, and effective VFA B mapping method was implemented and evaluated. Inclusion of the B mapping method in hyperpolarized imaging studies can enable more robust signal quantification.
本研究旨在验证一种简单且通用的集成可变翻转角（VFA）方法，用于在超极化磁共振成像中绘制B值，该方法可用于校正由于线圈不均匀性导致的信号变化。
进行模拟以评估VFA B值映射方法与当前使用的恒定翻转角（CFA）方法相比的性能。模拟结果用于指导VFA序列的设计，并在四名志愿者中进行了验证，用于肺部超极化氙-129成像，另外四名志愿者用于人脑超极化碳-13成像。获得的B值图用于校正图像中的发射和接收不均匀性。
模拟显示VFA方法相对于CFA方法具有更好的性能，对T的敏感性降低。对于氙-129，B值图准确反映了信号去极化的变化，但在某些情况下，由于线圈定位欠佳导致缺乏发射-接收互易性，无法用于校正线圈接收不均匀性。对于碳-13，B值图与单独获取的模体B值图显示出良好的一致性，并有效地用于校正线圈引起的信号不均匀性。
实施并评估了一种简单、通用且有效的VFA B值映射方法。在超极化成像研究中纳入B值映射方法可以实现更可靠的信号量化。
