Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Magn Reson Med. 2019 Feb;81(2):765-772. doi: 10.1002/mrm.27441. Epub 2018 Sep 14.
Absolute MR temperature measurements are currently difficult because they require precalibration procedures specific for tissue types and conditions. Reference of the lipid-dissolved Xe resonance frequency to temperature-insensitive methylene protons (rLDX) has been proposed to remove the effect of macro- and microscopic susceptibility gradients to obtain absolute temperature information. The scope of this work is to evaluate the rLDX chemical shift (CS) dependence on lipid composition to estimate the precision of absolute temperature measurements in lipids.
Neat triglycerides, vegetable oils, and samples of freshly excised human and rodent adipose tissue (AT) are prepared under Xe atmosphere and studied using high-resolution NMR. The rLDX CS is measured as a function of temperature. H spectra are also acquired and the consistency of methylene-referenced water proton and rLDX CS values are compared in human AT.
Although rLDX CS shows a dependence on lipid composition, in human and rodent AT samples the rLDX shows consistent CS values with a similar temperature dependence (-0.2058 ± 0.0010) ppm/°C × T (°C) + (200.15 ± 0.03) ppm, enabling absolute temperature measurements with an accuracy of 0.3°C. Methylene-referenced water CS values present variations of up to 4°C, even under well-controlled conditions.
The rLDX can be used to obtain accurate absolute temperature measurements in AT, opening new opportunities for hyperpolarized Xe MR to measure tissue absolute temperature.
由于绝对磁共振温度测量需要针对组织类型和条件的特定预校准程序，因此目前难以进行绝对 MR 温度测量。已经提出将溶解的脂质 Xe 共振频率参考到对温度不敏感的亚甲基质子（rLDX），以消除宏观和微观磁化率梯度对获得绝对温度信息的影响。这项工作的范围是评估 rLDX 化学位移（CS）对脂质组成的依赖性，以估计脂质中绝对温度测量的精度。
在 Xe 气氛下制备纯甘油三酯、植物油以及新鲜切除的人和啮齿动物脂肪组织（AT）的样品，并使用高分辨率 NMR 进行研究。测量 rLDX CS 随温度的变化。还获取 H 谱，并比较人 AT 中亚甲基参考水质子和 rLDX CS 值的一致性。
尽管 rLDX CS 显示出对脂质组成的依赖性，但在人和啮齿动物 AT 样品中，rLDX 显示出一致的 CS 值，具有相似的温度依赖性（-0.2058 ± 0.0010）ppm/°C × T（°C）+（200.15 ± 0.03）ppm，能够以 0.3°C 的精度进行绝对温度测量。即使在控制良好的条件下，亚甲基参考水 CS 值也会有高达 4°C 的变化。
rLDX 可用于在 AT 中获得准确的绝对温度测量，为利用超极化 Xe MR 测量组织绝对温度开辟了新的机会。
