3T chemical shift‐encoded MRI: Detection of altered proximal femur marrow adipose tissue composition in glucocorticoid users and validation with magnetic resonance spectroscopy

Abstract

Background Osteoporosis (OP) results in weak bone and can ultimately lead to fracture. Drugs such as glucocorticoids can also induce OP (glucocorticoid‐induced osteoporosis [GIO]). Bone marrow adipose tissue composition and quantity may play a role in OP pathophysiology, but has not been thoroughly studied in GIO compared to primary OP. Purpose/Hypothesis Chemical shift‐encoded (CSE) MRI allows detection of subregional differences in bone marrow adipose tissue composition and quantity in the proximal femur of GIO compared to OP subjects and has high agreement with the reference standard of magnetic resonance spectroscopy (MRS). Study Type Prospective. Subjects In all, 18 OP and 13 GIO subjects. Fields Strength 3T. Sequence Multiple gradient‐echo, stimulated echo acquisition mode (STEAM). Assessment Subjects underwent CSE‐MRI in the proximal femurs, and for each parametric map regions of interest (ROIs) were assessed in the femoral head (fHEAD), femoral neck (fNECK), Ward's triangle (fTRIANGLE), and the greater trochanter (GTROCH). In addition, we compared CSE‐MRI against the reference standard of MRS performed in the femoral neck and Ward's triangle. Statistical Tests Differences between OP/GIO were investigated using the Mann–Whitney nonparametric test. Bland–Altman methodology was used to assess measurement agreement between CSE‐MRI and MRS. Results GIO compared with OP subjects demonstrated: decreased monounsaturated fat fraction (MUFA) (–2.1%, P < 0.05) in fHEAD; decreased MUFA (–3.8%, P < 0.05), increased saturated fat fraction (SFA) (5.5%, P < 0.05), and decreased normalT2* (–3.8 msec, P < 0.05) in fNECK; decreased proton density fat fraction (PDFF) (–15.1%, P < 0.05), MUFA (–9.8%, P < 0.05), polyunsaturated fat fraction (PUFA) (–1.8%, P < 0.01), increased SFA (11.6%, P < 0.05), and decreased normalT2* (–5.4 msec, P < 0.05) in fTRIANGLE; and decreased normalT2* (–1.5 msec, P < 0.05) in GTROCH. There was high measurement agreement between MRI and MRS using the Bland–Altman test. Data Conclusion 3T CSE‐MRI may allow reliable assessment of subregional bone marrow adipose tissue (bMAT) quantity and composition in the proximal femur in a clinically reasonable scan time. Glucocorticoids may alter the lipid profile of bMAT and potentially result in reduced bone quality. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:490–496.

Quantitative 1H MRI and MRS of fatty acid composition

“…51 Most recently, Martel et al measured unsaturated and saturated lipid fractions in the proximal femur of osteoporosis patients with MRI and MRS, with a good correlation between the methods (r ~ 0.98) and a small bias (~2 percentage points). 67 Another recent study by Nemeth et al, in which visceral and subcutaneous fat of volunteers were investigated, also found fair agreement between MRS and MRI (ndb: r = 0.82, bias = 0.06, nmidb: r = 0.82, bias = 0.02). 51 However, both methods overestimated ndb and nmidb compared to GC (bias 0.24 and 0.19, respectively), similar to previous in vitro and in vivo validation studies.…”

“…While absolute in vivo quantification of the fatty acid composition is challenging also with MRS, it is nevertheless commonly used as a reference for the MRI-based methods, because of the practical difficulties to use GC as a reference. Promising agreement with MRS results has been found in adipose tissue and bone marrow, 51,66,67 but one group did note a large intra-subject variability and commented on the need for masking of extreme values. 51 Most recently, Martel et al measured unsaturated and saturated lipid fractions in the proximal femur of osteoporosis patients with MRI and MRS, with a good correlation between the methods (r ~ 0.98) and a small bias (~2 percentage points).…”

“…Several publications have investigated the performance of imaging-based FAC estimation using both phantoms 20,22,59,60 and in vivo experiments. 20,51,58,60,66,67 High in vitro reproducibility has been demonstrated, 20 with accuracy comparable to that of MRS. 22 Although the method, in theory, allows for simultaneous estimation of fat content and FAC also in the presence of water signal, the accuracy and robustness of the technique was found to be lower in water/fat mixtures in vitro. 21,22 Example phantom images of a range of vegetable oils are shown as Figure 4.…”

“…21 Nonetheless, both MRI and MRS has been used to investigate an association between the bone marrow FAC and for example, bone quality. The FAC of the bone marrow in the femoral head has also been shown to be heterogeneous, thus, making use of the added possibilities of an imaging approach 66,67 (see Figure 5). Yeung et al studied the vertebral marrow fat of postmenopausal women (mean age 70 y) and found that the UI was lower in osteoporotic (UI = 0.091) and osteopenic (UI = 0.097) subjects, compared with normal subjects (UI = 0.114) and young controls (mean age 28 years, UI = 0.127).…”

“…F I G U R E 5 FAC fractions in the bone marrow of the proximal femur in an osteoporotic patient. Adapted with permission from Martel et al 67 MRS has also been used to monitor FAC changes of the liver in several intervention studies, investigating the effect of exercise or changes in diet and lifestyle. In a study on NAFLD patients with hepatic fat >5%, PRESS MRS was used to investigate whether short-term physical exercise would affect hepatic lipid saturation, insulin resistance, and markers of inflammation and oxidative stress.…”