Shen Sheng, Koonjoo Neha, Ogier Stephen E, Boele Thomas, Saksena Mansi A, Keenan Kathryn E, Rosen Matthew S
A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, USA.
Harvard Medical School, Boston, Massachusetts, USA.
Magn Reson Med. 2025 Jun 16. doi: 10.1002/mrm.30602.
This study aims to develop an efficient T mapping approach that is free from systematic bias caused by B inhomogeneity in ultralow-field (ULF) MRI and to determine the T values (without fat suppression) of breast tissues at 6.5 mT.
We describe here a method for ULF T mapping using a variable flip angle approach for both mapping T and B. The B mapping is used to correct the T maps-and, unique to operation in the ULF regime, a B map acquired in a phantom can be applied to the in vivo T mapping data, reducing in vivo scan time. The T mapping method was validated in vitro with copper sulphate phantoms at seven different concentrations. A breast phantom was scanned to test the T mapping protocol. Four healthy volunteers were recruited for T mapping to obtain in vivo T values of breast tissues. No fat suppression was implemented in this preliminary study.
The copper sulphate phantom T map measurements have less than 13% deviation from the reference T values, and less than 6% deviation when the reference T was greater than 50 ms. Four healthy volunteers were scanned for T mapping. In these in vivo breast T maps, the 25th to 75th percentiles ranged from 79 to 243 ms at 6.5 mT.
Variable flip angle method can be used for both B and T mapping at ULFs, which enables efficient in vivo T mapping for ULF MRI.
本研究旨在开发一种高效的T映射方法，该方法可消除超低场（ULF）MRI中由B不均匀性引起的系统偏差，并确定6.5 mT下乳腺组织的T值（不进行脂肪抑制）。
我们在此描述一种用于ULF T映射的方法，该方法使用可变翻转角方法同时映射T和B。B映射用于校正T映射，并且在ULF模式下操作特有的是，在体模中获取的B映射可应用于体内T映射数据，从而减少体内扫描时间。T映射方法在体外使用七种不同浓度的硫酸铜体模进行了验证。扫描了一个乳腺体模以测试T映射方案。招募了四名健康志愿者进行T映射，以获得乳腺组织的体内T值。在这项初步研究中未实施脂肪抑制。
硫酸铜体模T映射测量值与参考T值的偏差小于13%，当参考T大于50 ms时偏差小于6%。对四名健康志愿者进行了T映射扫描。在这些体内乳腺T映射中，6.5 mT下第25至75百分位数范围为79至243 ms。
可变翻转角方法可用于ULF下的B和T映射，这使得ULF MRI能够高效地进行体内T映射。
