Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
J Magn Reson Imaging. 2019 Jan;49(1):141-151. doi: 10.1002/jmri.26219. Epub 2018 Oct 4.
Susceptibility differences between fat and water can cause changes in the water-fat frequency separation that can negatively affect the accuracy of fat fraction techniques. This may be especially relevant for brown adipose tissue, as MRI fat fraction techniques have been proposed for its detection.
To assess the effect of microscopic magnetic susceptibility gradients on the water-fat frequency separation and its impact on chemical-shift-based fat fraction quantification techniques in the supraclavicular fat, where brown adipose tissue is commonly found in humans.
Prospective.
POPULATION/SUBJECTS/PHANTOM/SPECIMEN/ANIMAL MODEL: Subjects: 11 healthy volunteers, mean age of 26 and mean BMI of 23, three overweight volunteers, mean age of 38 and mean BMI of 33. Phantoms: bovine phantom and intralipid fat emulsion. Simulations: various water-fat distributions.
FIELD STRENGTH/SEQUENCE: Six-echo gradient echo chemical-shift-encoded sequence at 3T.
Fat fraction values as obtained from a water-fat spectral model accounting for susceptibility-induced water-fat frequency variations were directly compared to traditional spectral models that assume constant water-fat frequency separation.
Two-tail t-tests were used for significance testing (p < 0.05.) A Bayesian Information Criterion difference of 6 between fits was taken as strong evidence of an improved model.
Phantom experiments and simulation results showed variations of the water-fat frequency separation up to 0.4 ppm and 0.6 ppm, respectively. In the supraclavicular area, the water-fat frequency separation produced by magnetic susceptibility gradients varied by as much as ±0.4 ppm, with a mean of 0.08 ± 0.14 ppm, producing a mean difference in fat fraction of -1.26 ± 5.26%.
In the supraclavicular fat depot, microscopic susceptibility gradients that exist within a voxel between water and fat compartments can produce variations in the water-fat frequency separation. These variations may produce fat fraction quantification errors of 5% when a spectral model with a fixed water-fat frequency separation is applied, which could impact MR brown fat techniques.
1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:141-151.
脂肪和水之间的磁化率差异会导致水-脂频率分离发生变化，从而对脂肪分数技术的准确性产生负面影响。这对于棕色脂肪组织尤其重要，因为 MRI 脂肪分数技术已被提议用于其检测。
评估微观磁化率梯度对水-脂频率分离的影响及其对锁骨上脂肪中化学位移脂肪分数定量技术的影响，因为在人体中常见棕色脂肪组织。
前瞻性。
人群/受试者/体模/标本/动物模型：受试者：11 名健康志愿者，平均年龄 26 岁，平均 BMI 为 23；3 名超重志愿者，平均年龄 38 岁，平均 BMI 为 33。体模：牛体模和 Intralipid 脂肪乳剂。模拟：各种水-脂分布。
磁场强度/序列：3T 六回波梯度回波化学位移编码序列。
直接比较从考虑磁化率诱导的水-脂频率变化的水-脂谱模型获得的脂肪分数值与传统的谱模型，该传统谱模型假设水-脂频率分离恒定。
使用双尾 t 检验进行显著性检验（p<0.05）。拟合之间相差 6 的贝叶斯信息准则被认为是改进模型的有力证据。
体模实验和模拟结果显示，水-脂频率分离的变化高达 0.4ppm 和 0.6ppm。在锁骨区，由磁化率梯度引起的水-脂频率分离变化高达±0.4ppm，平均值为 0.08±0.14ppm，导致脂肪分数的平均差异为-1.26±5.26%。
在锁骨脂肪库中，水和脂肪之间的体素内存在微观磁化率梯度会导致水-脂频率分离发生变化。当应用具有固定水-脂频率分离的谱模型时，这些变化可能会导致 5%的脂肪分数定量误差，这可能会影响磁共振棕色脂肪技术。
1 技术功效：阶段 1 J. Magn. Reson. Imaging 2019;49:141-151。
