Dieckmeyer Michael, Ruschke Stefan, Cordes Christian, Yap Samuel P, Kooijman Hendrik, Hauner Hans, Rummeny Ernst J, Bauer Jan S, Baum Thomas, Karampinos Dimitrios C
Department of Diagnostic and Interventional Radiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
NMR Biomed. 2015 Apr;28(4):432-9. doi: 10.1002/nbm.3267. Epub 2015 Feb 13.
Vertebral bone marrow fat quantification using single-voxel MRS is confounded by overlapping water-fat peaks and the difference in T2 relaxation time between water and fat components. The purposes of the present study were: (i) to determine the proton density fat fraction (PDFF) of vertebral bone marrow using single-voxel multi-TE MRS, addressing these confounding effects; and (ii) to investigate the implications of these corrections with respect to the age dependence of the PDFF. Single-voxel MRS was performed in the L5 vertebral body of 86 subjects (54 women and 32 men). To reliably extract the water peak from the overlying fat peaks, the mean bone marrow fat spectrum was characterized based on the area of measurable fat peaks and an a priori knowledge of the chemical triglyceride structure. MRS measurements were performed at multiple TEs. The T2 -weighted fat fraction was calculated at each TE. In addition, a T2 correction was performed to obtain the PDFF and the T2 value of water (T2w ) was calculated. The implications of the T2 correction were investigated by studying the age dependence of the T2 -weighted fat fractions and the PDFF. Compared with the PDFF, all T2 -weighted fat fractions significantly overestimated the fat fraction. Compared with the age dependence of the PDFF, the age dependence of the T2 -weighted fat fraction showed an increased slope and intercept as TE increased for women and a strongly increased intercept as TE increased for men. For women, a negative association between the T2 value of bone marrow water and PDFF was found. Single-voxel MRS-based vertebral bone marrow fat quantification should be based on a multi-TE MRS measurement to minimize confounding effects on PDFF determination, and also to allow the simultaneous calculation of T2w , which might be considered as an additional parameter sensitive to the composition of the water compartment.
使用单体素磁共振波谱（MRS）对椎体骨髓脂肪进行定量时，水脂峰重叠以及水和脂肪成分之间T2弛豫时间的差异会造成干扰。本研究的目的是：（i）使用单体素多回波时间（multi-TE）MRS测定椎体骨髓的质子密度脂肪分数（PDFF），解决这些干扰因素；（ii）研究这些校正对于PDFF年龄依赖性的影响。对86名受试者（54名女性和32名男性）的L5椎体进行了单体素MRS检查。为了从覆盖的脂肪峰中可靠地提取水峰，基于可测量脂肪峰的面积和化学甘油三酯结构的先验知识对平均骨髓脂肪谱进行了表征。在多个回波时间进行MRS测量。在每个回波时间计算T2加权脂肪分数。此外，进行T2校正以获得PDFF，并计算水的T2值（T2w）。通过研究T2加权脂肪分数和PDFF的年龄依赖性来探讨T2校正的影响。与PDFF相比，所有T2加权脂肪分数均显著高估了脂肪分数。与PDFF的年龄依赖性相比，T2加权脂肪分数的年龄依赖性在女性中随着回波时间增加显示斜率和截距增加，在男性中随着回波时间增加显示截距强烈增加。对于女性，发现骨髓水的T2值与PDFF之间存在负相关。基于单体素MRS的椎体骨髓脂肪定量应基于多回波时间MRS测量，以最小化对PDFF测定的干扰影响，并且还允许同时计算T2w，T2w可被视为对水相组成敏感的另一个参数。
