Rot Samuel, Oliver-Taylor Aaron, Baker Rebecca R, Steeden Jennifer A, Golay Xavier, Solanky Bhavana S, Gandini Wheeler-Kingshott Claudia A M
NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Queen Square Institute of Neurology, Faculty of Brain Sciences, UCL, London, UK.
Department of Medical Physics and Biomedical Engineering, UCL, London, UK.
NMR Biomed. 2025 Jun;38(6):e70056. doi: 10.1002/nbm.70056.
Quantitative sodium (Na) MRI utilises a signal calibration approach to derive maps of total sodium concentration (TSC). Agarose gel vials are often used as calibration phantoms, but as a naturally occurring substance, agarose may exhibit unfavourable qualities relating to instabilities, inconsistencies and heterogeneity. To contribute towards standardisation and methods harmonisation of quantitative Na MRI, the objective of this study was to develop and test a novel, standardisable synthetic polymer calibration phantom for in vivo quantitative Na MRI. Seven crosslinked polyacrylamide gel (PAG) samples were prepared, doped with sodium chloride (NaCl) at nominal concentrations of 10-150 mM. The sodium concentrations of all samples were estimated by volumetrics using high-precision mass measurements. Relaxation time constants ( ) of all samples were measured at 3 T with a non-localised pulse-acquire sequence. was measured longitudinally over 14 months to assess stability. Finally, in vivo TSC quantification with PAG phantoms was demonstrated in the human brain and calf muscle on different systems, with different imaging sequences. The measured sodium concentrations of phantoms were on average 5% lower than nominal ones, owing to the unknown volumetric contribution of the solid fraction. Hence, they were reported as apparent sodium concentrations, and the apparent TSC (aTSC) was quantified in vivo. Mean relaxation time constants of Na in PAG were in the following ranges: = 27-39 ms, = 4.8-7.1 ms, = 16.8-18.8 ms, short fraction = 0.64-0.77. Over 14 months, relaxation time constants were stable within 10% (above sodium concentrations of 25 mM). In vivo aTSC measurements were in the expected ranges. PAG phantoms are well suited for quantification and standardisation in Na MRI, offering tissue-matched relaxation time constants and the intrinsic benefits of a synthetic material.
定量钠（Na）磁共振成像（MRI）采用信号校准方法来获取总钠浓度（TSC）图谱。琼脂糖凝胶小瓶常被用作校准体模，但作为一种天然存在的物质，琼脂糖可能会表现出与不稳定性、不一致性和异质性相关的不利特性。为推动定量Na MRI的标准化和方法协调，本研究的目的是开发并测试一种用于体内定量Na MRI的新型、可标准化的合成聚合物校准体模。制备了7个交联聚丙烯酰胺凝胶（PAG）样品，以10 - 150 mM的标称浓度掺杂氯化钠（NaCl）。使用高精度质量测量通过容量法估算所有样品的钠浓度。在3 T下用非定位脉冲采集序列测量所有样品的弛豫时间常数（ ）。纵向测量 超过14个月以评估稳定性。最后，在不同系统上使用不同成像序列，在人脑和小腿肌肉中展示了使用PAG体模进行体内TSC定量。由于固体部分的体积贡献未知，所测体模的钠浓度平均比标称浓度低5%。因此，将其报告为表观钠浓度，并在体内对表观TSC（aTSC）进行了定量。PAG中Na的平均弛豫时间常数在以下范围内： = 27 - 39 ms， = 4.8 - 7.1 ms， = 16.8 - 18.8 ms，短弛豫部分 = 0.64 - 0.77。在14个月内，弛豫时间常数在10%以内稳定（钠浓度高于25 mM）。体内aTSC测量值在预期范围内。PAG体模非常适合Na MRI中的定量和标准化，提供了与组织匹配的弛豫时间常数以及合成材料的固有优势。
