Modeling of T2* decay in vertebral bone marrow fat quantification

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 T-2* 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 T-2* 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 T-2* effects: (a) single-T-2* correction, (b) dual-T-2* correction, (c) T-2' correction using the a priori-known T-2 from the MRS at each vertebral body and (d) T-2' correction using the a priori-known T-2 equal to previously measured average values. Dual-T-2* correction resulted in noisier imaging fat fraction maps than single-T-2* correction or T-2' correction using a priori-known T-2. Linear regression analysis between imaging and MRS fat fraction showed a slope significantly different from 1 when using single-T-2* correction (R-2=0.96) or dual-T-2* correction (R-2=0.87). T-2' correction using the a priori-known T-2 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 T-2' correction using a priori-known T-2 can remove the fat fraction bias induced by the difference in T-2* between water and fat components without degrading noise performance in fat fraction mapping of vertebral bone marrow. Copyright (c) 2015 John Wiley & Sons, Ltd.