Karampinos Dimitrios C, Ruschke Stefan, Dieckmeyer Michael, Eggers Holger, Kooijman Hendrik, Rummeny Ernst J, Bauer Jan S, Baum Thomas
Department of Diagnostic and Interventional Radiology, Technische Universität München, Munich, Germany.
Philips Research Laboratory, Hamburg, Germany.
NMR Biomed. 2015 Nov;28(11):1535-42. doi: 10.1002/nbm.3420. Epub 2015 Oct 1.
Bone marrow fat fraction mapping using chemical shift encoding-based water-fat separation is becoming a useful tool in investigating the association between bone marrow adiposity and bone health and in assessing cancer treatment-induced bone marrow damage. Vertebral bone marrow is characterized by short T2* relaxation times, which are in general different for the water and fat components and can confound fat quantification. The purpose of the present study is to compare different approaches to T2* correction in chemical shift encoding-based water-fat imaging of vertebral bone marrow using single-voxel MRS as reference. Eight-echo gradient-echo imaging and single-voxel MRS measurements were made on the spine (L3-L5) of 25 healthy volunteers. Different approaches were evaluated for correction of T2* effects: (a) single-T2* correction, (b) dual-T2* correction, (c) T2' correction using the a priori-known T2 from the MRS at each vertebral body and (d) T2' correction using the a priori-known T2 equal to previously measured average values. Dual-T2* correction resulted in noisier imaging fat fraction maps than single-T2* correction or T2' correction using a priori-known T2. Linear regression analysis between imaging and MRS fat fraction showed a slope significantly different from 1 when using single-T2* correction (R(2) = 0.96) or dual-T2* correction (R(2) = 0.87). T2' correction using the a priori-known T2 resulted in a slope not significantly different from 1, an intercept significantly different from 0 (between 2.4% and 3%) and R(2) = 0.96. Therefore, a T2' correction using a priori-known T2 can remove the fat fraction bias induced by the difference in T2* between water and fat components without degrading noise performance in fat fraction mapping of vertebral bone marrow.
使用基于化学位移编码的水脂分离技术进行骨髓脂肪分数映射，正成为研究骨髓脂肪与骨骼健康之间关联以及评估癌症治疗引起的骨髓损伤的一种有用工具。椎体骨髓的特征是T2弛豫时间较短，水和脂肪成分的T2弛豫时间通常不同，这可能会混淆脂肪定量。本研究的目的是以单体素磁共振波谱（MRS）为参考，比较基于化学位移编码的椎体骨髓水脂成像中不同的T2校正方法。对25名健康志愿者的脊柱（L3-L5）进行了八回波梯度回波成像和单体素MRS测量。评估了不同的T2效应校正方法：（a）单T2校正，（b）双T2校正，（c）使用每个椎体MRS中先验已知的T2进行T2'校正，以及（d）使用等于先前测量平均值的先验已知T2进行T2'校正。与单T2校正或使用先验已知T2的T2'校正相比，双T2校正导致成像脂肪分数图的噪声更大。当使用单T2校正（R(2) = 0.96）或双T2校正（R(2) = 0.87）时，成像与MRS脂肪分数之间的线性回归分析显示斜率显著不同于1。使用先验已知T2的T2'校正导致斜率与1无显著差异，截距与0有显著差异（在2.4%和3%之间），R(2) = 0.96。因此，使用先验已知T2的T2'校正可以消除水和脂肪成分之间T2*差异引起的脂肪分数偏差，而不会降低椎体骨髓脂肪分数映射中的噪声性能。
